Covenant Journal of Engineering Technology (CJET) Vol.3 No.1, June 2019
ISSN: p. 2682-5317 e. 2682-5325
An Open Access Journal Available Online
Covenant Journal of Engineering Technology (CJET)
Vol. 3 No. 1, June 2019
Publication of the College of Engineering, Covenant University, Canaanland.
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Managing Editor: Edwin O. Agbaike [email protected]
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Achebe C. H., et al CJET (2019) 3(1) 1-19
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ISSN: p. 2682-5317 e. 2682-5325
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Achebe C. H., et al CJET (2019) 3(1) 1-19
Articles
Evaluation of Frictional Heat and Oil Cooling Rate in Mechanical Contact Due to Debris Formation. Achebe C. H., Nwagu I. A., Chukwuneke J. L. & Sinebe J. E. 1
Mismatch Between Anthropometry Characteristics of Nigerian Occupational Bus Drivers and the In-Vehicle Measurement. Fajobi, Moses O. Onawumi, Ayodele S., Mfon Udoh, M. O. & Awoyemi, Elijah A. 20
A Review of Voice-Base Person Identification: State-of-the-Art. Folorunso C.O., Asaolu O.S. & Popoola O.P. 38
Community-Based LDPE Wastes Recycling Machine. I. D. Okeke, T. M. Ibezim, O. T. Ndusorouwa, U. C. Okonkwo & I. P. Okokpujie 61
Ship Propeller Performance Prediction under Cavitation. Thaddeus C. Nwaoha & Sidum Adumene 76
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Achebe C. H., et al CJET (2019) 3(1) 1-19
Covenant Journal of Engineering Technology (CJET) Vol.3 No.1, June 2019 ISSN: p 2682-5317 e 2682-5325 DOI: 10.20370/ha8r-p563
An Open Access Journal Available Online
Evaluation of Frictional Heat and Oil Cooling Rate in Mechanical Contact Due to Debris Formation
Achebe C. H1., Nwagu I. A1, Chukwuneke J. L1* & Sinebe J. E2
1Department of Mechanical Engineering, Nnamdi Azikiwe University, Awka, Nigeria 2Department of Mechanical Engineering, Delta State University, Abraka, Nigeria *[email protected]
Received: 12.05.2019 Accepted: 26.06.2019 Date of Publication: June, 2019
Abstract- This paper evaluated experimentally, the amount of frictional heat generated in a Mitsubishi main journal bearing and the cooling performance of the lubricating oils A, B and C. The test rig used in this experiment is a mechanical apparatus that consists of mechanical drive, metal support, bevel gear, a rotating shaft and a bearing attached at its lower end. When the shaft was rotated by the mechanical drive of power 0.75kw and speed 1440rpm, the frictional force in journal bearing helped to convert the mechanical energy of the drive into frictional heat. The amount of heat absorbed from the surface of the journal bearing by the oil cooled the surface. The cooling rate of the oil was obtained at each time interval. The vibrating movement of the molecules helped to transfer the frictional heat to the lubricant and the calorimeter. This effect caused the temperature of the system to rise. The frictional heat generated at the contact increased linearly with the change in temperature in the mechanical contact which was absorbed differently in the three lubes, depending on their heat capacity and molecular movement. When there was no debris in the contact, the temperature changed within the range of 1.2-1.80C at interval of 3minutes in oil B, 10C in oil C and 0.8-1.20C in oil A. When there was sand debris in the contact, the temperature changed within the range of 2-2.50C at interval of 3minutes in oil B, 1.5-20C in oil C and 20C in oil A. Oil B has the best cooling performance based on the three local lubes used and was equally the most expensive. Mechanical failures like galling, fatigue and surface indentation occurred when the vibrational force (energy) of the molecules were greater than the binding force or energy of the atomic lattice of the bearing. Keywords: Cooling rate, Debris, Frictional heat, Journal bearing, Lubricant, Mechanical contact, Temperature 1. Introduction relative to each other. If two metal Friction has a stick-slip effect at the surfaces are moved relative to each interaction of two surfaces moving other, one or both surfaces will
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1 Achebe C. H., et al CJET (2019) 3(1) 1-19 gradually be eroded. The process of bearing points and to cool the sliding erosion depends on the nature of the surfaces. surfaces but, in general, tiny Related works were thermo- fragments (debris) are torn out of the mechanical analysis of dry clutches surfaces as the welded junctions shear under different boundary conditions at the areas of contact. The use of a [4], synthesis versus mineral fluids, lubricant such as oil or grease evaluation of engine parts using nano between the surfaces reduces the lubricant in agricultural tractors [5], frictional force but does not entirely experimental analysis of lubricant for eliminate it. So, it seems that friction the prediction of contact surface is undesirable, wasteful of energy behaviour of metals [6], experimental (frictional heat) and costly in terms of evaluation of ball bearings diagnosis the wear it creates and the power by contamination [7], diesel engine expended in machines to overcome it. lubricant contamination and wear. Microscopic particles are the most Estimation of temperature and effects harmful form of contamination in of oxidation in thermal elasto- lubricants. They can irreversibly hydrodynamic lubrication [8], the use damage gear and bearing surfaces, of textured surfaces to mitigate sliding shorten the service life of the friction and wear of lubricated and equipment, and cause unexpected non-lubricated contacts, the effects of breakdown [1]. The entry of lubricant different cooling and lubrication borne solid particles into machine Techniques on material machinability element contacts is important, both for in machining [9], kinetic model and prediction of the body abrasive wear reaction kinetics to analyze the debris and for an understanding of the in plain bearing [10], and the thermal behaviour of solid lubricant additives behaviour of engine oil, they were [2]. Mechanical devices do fail due to carried out using experimental the wear of the rubbing surfaces of methods and modeling. their bearings and journals. Debris is A bearing is one of the fundamental characterized into ferrous and non- elements in the machine; even the ferrous particles in which sand, simplest machine, the lever, must atmospheric contaminants and eroded have a bearing or fulcrum [11]. All particles from the bearing belong [3]. movements in mechanisms and The wear of the surfaces can machines require some sort of bearing theoretically be eliminated by to locate and guide the moving parts. introducing a material weak in shear A machine designer will try to convert (i.e. lubricant) between them. If the energy put into a machine into useful film of lubricant is deep enough, the output work and will, therefore, surfaces will be sufficiently far apart attempt to reduce the energy losses to prevent the formation of any that arise through friction at the welded junctions directly between bearings. Mechanical devices stop them. Lubricant helps to reduce forces working after some time due to the necessary to make the surfaces slide failures of mechanical contacts when thereby reducing the energy loss at the there are insufficient lube supply and
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2 Achebe C. H., et al CJET (2019) 3(1) 1-19 rapid degradation of the quality of the (mass: 200g; specific heat capacity: lubricating oils. Mechanical failures 400J/kgK), thermometer (mercury-in- that occur in mechanical contact are glass: 00C to 3600C), stop clock fatigue, galling, indentation, erosion (unicon-1), digital weighing machine and fretting. These failures release (SF-400: 1g to 7000g), electric motor debris in the contact. Most of the (model no. 5000/99; 0.75kW), analysis to determine oil film lubricating oils (SAE 20W 50), thickness in machine element assumes frictional heat and cooling rate a clean lubricant. In this paper, the evaluation apparatus. The lubricants experimental evaluation of heat used are oil A, oil B and oil C. The released in a Mitsubishi main journal test rig has adjustable journal bearing bearing due to different types of fixed at its lower end (see Figure 1). debris in it was carried out. Cooling 2.2. Debris Characterization rates of different lubricating oils were Two kinds of debris were used in the evaluated experimentally while experiment; Silicon IV oxide debris considering no debris and when and Iron filings debris. Silicon IV infused with different types of debris oxide debris consists of sand of fine in the mechanical contact. particles of diameter 0.012mm. While 2. Materials and Methods iron filings debris consists of iron 2.1. Materials powder of diameter 0.013mm. The The materials used are Mitsubishi method of debris characterization is main journal bearing (size: 0.25 from mechanical characterization (see Mitsubishi engine of model number Table 1). 4G32N24232), copper calorimeter
Table 1: Mechanical characterization of the debris Properties Sand Iron filings
Brittleness Very brittle Ductile Tensile strength ( N/m2) No value (180-210) Chemical constituents Fragments of coral, Iron limestone, shell and silicon iv oxide. Young’s modulus 130-185 210 Thermal conductivity (W/mK) 0.71 79.5 Specific heat capacity (J/gK) 0.73 0.42 Thermal diffusivity (m2/s) 1.4 2.3
2.3. Methods releases the frictional heat energy An experimental method was used for while trying to overcome the friction the evaluation of the amount of heat in the contact. The experiment was generated in the mechanical contact performed with three lubricating oils like that of rotating journal bearing. using different types of debris in the The rotating mechanical element contact. Seven experiments were
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3 Achebe C. H., et al CJET (2019) 3(1) 1-19 carried out to evaluate the amount of time and the final temperatures, were heat generated in the mechanical read and recorded at an interval of contact and the cooling rates of the 3minutes respectively. The quality of lubricating oils under different heat energy released cannot be conditions. The first set of measured with an instrument directly experiments was carried out with the but can be calculated with the lubricants under debris-free condition elementary formula [12], [13], were while the second was done with M = mass, C = specific heat capacity lubricants containing silicon debris. of the substance, change in The third experiment considered the temperature. The components that same lubricants containing ferrous absorb the heat are the journal materials like Iron filings. To evaluate bearing, the oil and the copper the amount of heat energy released in calorimeter. The same procedures the lubricated mechanical contact were repeated in the second and third using a clean lubricant, the following experiments with Silicon IV oxide apparatus was used; digital weighing debris and Iron fillings debris machine, thermometer, stop watch, introduced in the mechanical contact lubricants (oils ‘A’, ‘B’ and ‘C’), respectively. The above procedures lagging material (cotton wool) etc. were replicated for oil ‘B’ and oil ‘C’. The mass of the bearing (M1) and the Calculating the quantity of heat, the mass of the empty calorimeter (M2) amount of heat supplied is equal to were measured and recorded. A the amount of heat absorbed by the known volume (V) of the lubricating lubricant, copper calorimeter and the oil ‘A’ was poured into the bearing at a particular temperature. calorimeter. The mass of the calorimeter and its content (M3) was (1) equally taken. The initial temperature Where: Q1 = quantity of heat absorbed of the calorimeter and its content was by the bearing. recorded. The oil and the calorimeter will have the same initial and final temperatures according to the Zeroth (2) law of thermodynamics [12], [13]. Where: M1 = mass of the bearing (g); The temperature of the bearing is C1 = specific heat capacity of steel approximately mid-way between the (bearing); = final temperature at temperature of the oil film [14]. The the end of each 3min which will be calorimeter and its content were the same for the three materials placed under the frictional heat mentioned above; i = Initial evaluation apparatus as shown in the temperature; Q2 = quantity of heat figure 1, so that the rotating journal absorbed by the calorimeter. bearing and its housing were (3) completely immersed in the oil ‘A’, Where: M2 = mass of the copper that is, electro-hydrodynamic calorimeter (kg); C2 = Specific heat lubrication EHL. The motor and the capacity of copper calorimeter stop watch were started at the same (J/kgK); M3 = mass of oil +
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4 Achebe C. H., et al CJET (2019) 3(1) 1-19 calorimeter; M2 = mass of the empty capacity of the lubricating oil = calorimeter; C3 = specific heat 2.09J/kgK.
Metal Frame work
Pulley
Bevel gear
Shaft
Metal stand
Thermometer
Journal Bearing
Lubricating oil Calorimeter
Figure 1: Schematic of the Frictional Heat and Cooling Rate Evaluation Apparatus
3. Results and Discussion bearing when there was no debris in The results of the change in the contact in the three oils are shown temperature in a Mitsubishi journal in Figure 2.
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Figure 2: Comparison of change in temperature with time in the three debris-free oils From Figure 2, oil ‘B’ showed the other oils was too high, so the highest temperature change than the molecules could not move very fast. other oils. This was because the hot The change in the temperature-time molecules of oil ‘B’ have higher curve of oil ‘B’ was similar to the one kinetic energy than those of other oils. proposed by [16]. The temperature- Since temperature is the measure of time curves of the oils showed that the the average kinetic energy of the molecules of the oils did not absorb molecules of fluid [15]. The entropy frictional heat at the same time. The of the hot molecules of oil ‘B’ was shear stress of oil ‘B’ was the least higher than that of oil A and oil C. and its molecules move faster than Entropy is directly proportional to the those of oils ‘C’ and ‘A’. This quantity of heat absorbed [15]. The movement helped to transfer the increased molecular movement helped frictional heat and increase the to maintain a uniform temperature in temperature of the oil ‘B’. the mechanical contact. The velocity The results of the change in of the hot molecules of oil ‘B’ was temperature of a Mitsubishi journal highest because of its low molecular bearing generated in oil ‘A’ when the mass and weak intermolecular bond. three debris conditions were The inertia of the molecules of the considered are shown in figure 3.
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6 Achebe C. H., et al CJET (2019) 3(1) 1-19
Figure 3: Comparison of temperature change in oil ‘A’ for the three debris conditions
It could be seen from Figure 3 that the and that of iron filings started to temperature increased when there was increase above that of sand debris debris in the contact. The velocity of immediately after 4.6minutes. Until the molecules and the average kinetic after 15minutes, the increase in energy increased gradually. The change in temperature became equal mobile free electrons on the outermost due to the fact that the quantity of iron shell of iron helped to transfer the particles present in the contact has an frictional heat and this affected the equivalent effect with the available temperature change when iron sand debris in the contact. The iron particles were present. The average particles have free mobile electrons in increase in temperature when there their outermost shell, so it helped to was debris in the contact was 2.5 transfer the heat. The charge while it was 1.0 when there was no distribution on the surface of the molecules of oil ‘A’ was very small debris in the contact. The increase in thus facilitating heat transfer. temperature was due to the fact that The results of the change in more kinetic energy was needed to temperature in a Mitsubishi journal overcome friction caused by the bearing generated in oil ‘B’ for the presence of debris in the contact. The three debris conditions are shown in change in temperature due to the Figure 4. presence of sand debris was reduced
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Figure 4: Comparison of temperature change in oil ‘B’ for the three debris conditions From Figure 4, the change in particles were present in the oil was temperature when Iron debris was the highest. The intermolecular bond present was higher than others. The strength of oil ‘B’ was the smallest same explanations that were adduced when compared with the other two in the analysis of the frictional heat in oils thus, its molecules moved faster oil ‘B’ are applicable in temperature than the molecules of the other two change and so both have the same oils. The mass of a molecule of oil ‘B’ temperature-time curves. The degree was smaller than those of the other of disorderliness of the hot molecules two. The mobile free electrons of the of oil ‘B’ was the highest. The iron particles helped to transfer temperature changes when there were uniform temperature coupled with the iron particles in the mechanical charge distribution on the surface of contact was greater than those of sand the molecules of the oil ‘B’. It could debris condition and debris-free be deduced from this experiment that condition. Hot iron debris moved the hot molecules of the oil ‘B’ have easily in the oil ‘B’ because of its low the highest charge distribution. Also, viscosity and shear stress such that the the heat capacity of the oil ‘B’ was hot iron particles transferred frictional higher than the other two oils. The heat uniformly and easily in the oil. viscosity of oil ‘B’ was the smallest This made the temperature-time curve among the three oils and so it allowed of oil ‘B’ to be a smooth curve when the debris to move faster in it such there were iron particles in the that the hot particles transferred the contact. The change in temperature frictional heat uniformly in the oil. generated in oil ‘B’ when Iron
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8 Achebe C. H., et al CJET (2019) 3(1) 1-19
The results of the change in change in temperature of the oil. temperature in a Mitsubishi journal Oxygen is an electronegative element main bearing generated in oil ‘C’ for and it has a high polarizing ability. It the three debris conditions are shown made the oil ‘C’ to become slightly in Table 5. The temperature changes polar and possess more distributed of oil ‘C’ is presented in Figure 5. The charges on its molecules. This effect change in temperature increased when was initially great but it was reduced there was debris in the oil. It shows after 6minutes due to the reduction in that the oxygen in Silicon IV oxide the concentration of sand particles reacted with the oil and so it reduced present in the contact. The presence the molecular movement of the oil of debris increased the amount of while increasing its heat capacity. The friction in the contact and it had to be presence of oxygen bond and silicon overcome before the rotating shaft carbide formed helped to increase the maintained its motion. heat content, thus increasing the
Figure 5: Comparison of the change in temperature of oil ‘C’ due to the three debris conditions From Figure 5, the change in kinetic energy of the rotating shaft temperature when Silicon IV oxide was converted into heat. The debris was present in the oil is greater temperature of the oil was found to than that of the debris-free condition increase after the energy but less than that of iron-particle transformation. The movement of hot contaminated oil after 6minutes. The particles in the oil also helped to
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9 Achebe C. H., et al CJET (2019) 3(1) 1-19
transfer the frictional heat in the oil. temperature of the oil. This change in The mobile free electrons of the Iron temperature was the highest. particles and the oil’s charge The results of variations in viscosity distribution helped to increase the with temperature in the three oils are shown in Tables 2 – 4.
Table 2: Variations of Absolute viscosity of oil Table 3: Variation of Absolute Viscosity of Oil ‘A’ with Temperature ‘B’ with Temperature Absolute viscosity Temperature (0C) Absolute viscosity Temperature (0C) (kg/m-s) (kg/m-s) 0.422 29.2 0.309 34.0 0.363 31.0 0.274 35.8 0.352 32.0 0.254 37.0 0.321 33.4 0.231 38.5 0.305 34.2 0.211 39.8 0.282 35.4 0.196 41.0
Table 4: Variation of Absolute viscosity of oil ‘C’ with Temperature Absolute viscosity Temperature (0C) Absolute viscosity Temperature (0C) (kg/m-s) (kg/m-s) 0.330 33.0 0.238 38.0 0.289 35.0 0.223 39.0 0.271 36.0 0.209 40.0
From Table 2, absolute viscosity of when compared with results in table lubricating oil decreased with an 2. The same explanations proffered increase in temperature. As the above are applicable in the case of oil temperature of the oil increased, hot ‘B’ and oil ‘C’. The table of values of molecules of oil ‘A’ gained kinetic absolute viscosity of oil ‘C’ with energy and velocity. Their temperature is shown in table 4. The intermolecular bonds were broken as values in the tables 3 & 4 are slightly the temperature increased. When the different because their intermolecular molecules were very far apart from covalent bond and their molecular one another, its absolute viscosity velocity are slightly different. As the decreased. The absolute viscosity of temperature of oil ‘C’ was increased, oil ‘A’ was higher than those of oil the degree of its molecular ‘B’ and oil ‘C’ but its performance disorderliness increased also. The was not better than those of oil ‘B’ covalent bonds of the molecules were and oil ‘C’. From table 3, the absolute broken and so its viscosity reduced as viscosity of oil ‘B’ decreased with an shown in Table 4. increase in temperature. The absolute The results of the heat generated in a viscosity of oil ‘B’ was smaller than Mitsubishi journal bearing when there that of oil ‘A’ at a given temperature was no debris in the contact in the
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10 Achebe C. H., et al CJET (2019) 3(1) 1-19 three local oils are shown in Figure 6. vibrate about their mean positions. During the experiment, heat energy This molecular vibration helped to was generated as the journal rotated transfer the frictional heat energy on the surface of the bearing as through the bearing to the lubricant, powered by an electric motor of its housing and the calorimeter. The 0.75kW. This was due to the vibrational movement of the conversion of mechanical energy of molecules increased as the frictional the motor into frictional heat which heat increased. This heat was was absorbed by the lubricants. It absorbed by the bearing, it's housing, made the molecules of the bearing to lubricant and the calorimeter.
Figure 6: Comparison of the frictional heat generated in the three oils From Figure 6, oil ‘B’ absorbed the this reason that the hot molecules of highest frictional heat because its oil ‘B’ moved faster than those of molecular movement was the highest molecules of oil ‘A’ and oil ‘C’. hence the generated frictional heat Also, the specific heat capacity of the was easily transferred uniformly in it. oil ‘B’ was greater than those of oil It is noteworthy that the molecules of ‘C’ and oil ‘A’. Figure 6 shows that oil ‘B’ were not strongly bonded frictional heat in the three oils (‘B’, together and so its molecules moved ‘A’ and ‘C’) increased as the time of faster than others. The mass of a heat generation increased. molecule of oil ‘B’ and its The results of the heat generated in a intermolecular bond was smaller than Mitsubishi journal bearing when it those of oil ‘A’ and oil ‘C’ because was immersed in oil ‘A’ while the average speed of the hot considering the three debris molecules of oil ‘B’ was greater than conditions are shown in Figure 7. It those of oil ‘A’ and oil ‘C’. It is for could be asserted that as the journal
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11 Achebe C. H., et al CJET (2019) 3(1) 1-19 rotated on the bearing, the molecules The amount of frictional heat of oil ‘A’ gradually gained kinetic generated in oil ‘A’ when there were energy due to the heat generated in sand and Iron debris in the oil was the contact. The viscosity of oil ‘A’ greater than that of debris-free was the highest among the three oils condition. Owing to the high shear and so it restricted the movement of stress of the molecules of oil ‘A’, the the hot debris in it. This was due to hot Iron particles could not move the high shear stress of the oil. The easily in the oil so the amount of frictional heat distribution in it was frictional heat transferred in the oil not uniform. The entropy of the was not all that high when compared molecules of oil ‘A’ was the lowest. with that of oil ‘B’.
Figure 7: Comparison of frictional heat generated in oil ‘A’ due to the three debris conditions From Figure 7, the hot molecules Iron filings of the same mass since the increased translational, rotational and density of sand is less than that of vibrational movements due to the fact iron. The initial frictional heat that the frictional heat increased generated in the contact by the Silicon gradually. These molecular IV oxide debris was slightly higher movements increased when there than that of iron. Surprisingly, the were debris particles present in the sand debris was crushed into tiny journal bearing. The number of sand particles by the rotating shaft and particles in the contact with the some escaped through the clearance journal bearing was larger than that of of the bearing as such, its frictional
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12 Achebe C. H., et al CJET (2019) 3(1) 1-19 heat was reduced and that of iron oil ‘B’ was higher than those of the filings started to increase above that other two oils. The frictional heat- of sand debris immediately after time curve when iron particles were 4.6minutes. However, after present was relatively a smooth curve. 15minutes, the increase in the The entropy of the molecules of oil generated frictional heat became equal ‘B’ was the highest. The degree of due to the fact that the amount of iron disorderliness of the molecules of oil particles present in the contact has ‘B’ helped to transfer the frictional equivalent effect with the available heat in the oil. The shear stress of oil sand debris in the contact. The iron ‘B’ was the least and so it allowed the particles have free mobile electrons in hot debris (sand and iron particles) to their outermost shell, so it helped to move easily in it, thereby increasing transfer the heat. The charge the temperature and the amount of distribution on the surface of the frictional heat absorbed by the oil ‘B’. molecules of oil ‘A’ was very small The shear stress of the molecules of thus helping in heat transfer. oil ‘C’ was slightly higher than that of The results of heat evaluation in a oil ‘B’ and so it slightly reduced the Mitsubishi journal bearing generated movement of hot debris in it. Owing in oil ‘B’ for the three debris to this effect, the amount of friction conditions are shown in Figure 8. The absorbed in oil ‘C’ was smaller than amount of frictional heat generated in that of oil ‘B’
Figure 8: Comparison of frictional heat generated in oil ‘B’ for the three debris conditions From Figure 8, the frictional heat strength of oil ‘B’ was the smallest generated in oil ‘B’ when iron when compared with the other two particles were present in the oil was oils thus its hot molecules moved the highest. The intermolecular bond faster than the molecules of the other
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13 Achebe C. H., et al CJET (2019) 3(1) 1-19 two oils. The mass of a molecule of powder and its concentration was oil ‘B’ was smaller than those of the reduced in the bearing. Iron particles other two oils so, it had little inertia to are not brittle like the sand particles, move and transfer the frictional heat. so the iron particles were not easily The mobile free electrons of the iron crushed into a fine powder. The iron particles helped to transfer heat in debris curve intercepted the sand conjunction with the charge debris curve after 6minutes. This was distribution on the surface of the because the same amount of frictional molecules of oil ‘B’. The molecules heat was generated in the journal of oil ‘B’ have the highest charge bearing. The amount of sand particles distribution also the heat capacity of present in the bearing has an oil ‘B’ was higher than those of the equivalent effect with the iron other two oils. particles present at that time. The results of heat evaluation in a The results of the cooling rates of oil Mitsubishi journal bearing generated ‘A’ due to the three debris conditions in oil ‘C’ for the three debris are shown in Figure 10. The cooling conditions are shown in figure 9. The rates decreased non-uniformly with frictional heat increased when there the time taken. This was because the was debris in the journal bearing. The intermolecular force and the covalent molecules of oil ‘C’ gained kinetic bond between the molecules of oil A energy and moved with high velocity. were very high such that the The velocity and kinetic energy of the molecular movement of oil ‘A’ was hot molecules of oil ’C’ was highest reduced. This reduction affected the when iron debris was present in the transfer of frictional heat extracted oil. This was illustrated in Figure 9. from the surface of the bearing to the These explanations are based on the other molecules of the oil. The charge distribution on the surface of amount of heat absorbed by the oil oil ‘C’ molecules and the mobile free ‘A’ when there was debris in the electrons of iron particles were also contact was higher than that of no applicable in this oil. The entropy of debris condition. This was because the molecules of oil ‘C’ was higher more frictional heat was generated in than that of oil ‘A’ but it was lower the contact. In the same vein, more than that of oil ‘B’. The shear stress of kinetic energy was needed to the oil ‘C’ was slightly higher than overcome friction in the contact. The that of oil ‘B’ but it was less than that amount of frictional heat absorbed by of oil ‘A’ thus hot particles could not the oil from the surface of the bearing move easily in the oil to transfer the when there was debris in the contact frictional heat uniformly. would increase also. From Figure 9, the particles of silicon IV oxide was crushed into a fine
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14 Achebe C. H., et al CJET (2019) 3(1) 1-19
Figure 9: Comparison of frictional heat in oil ‘C’ for the three debris conditions
Figure 10: Comparison of cooling rates of oil ‘A’ due to different debris conditions heat very fast. The cooling rate of oil It could be derived from Figure 10 ‘A’ decreased non-uniformly as the that the amount of heat absorbed by temperature increased. This was the oil when iron particles were because the heat generated was present initially decreased and then absorbed into the intermolecular subsequently increased. This was domain which was used to break the because iron is a metal and it conducts covalent bonds of the oil. Also, all the
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15 Achebe C. H., et al CJET (2019) 3(1) 1-19 molecules of the oil did not absorb the time. According to the values, in oil frictional heat at the same time. This ‘B’, it showed that the amount of affected the viscosity and heat frictional heat absorbed from the capacity of the oil. In sand particle surface of the bearing was higher than contamination, there was an increase that of oil ‘A’ so the heat capacity of in the amount of heat generated and oil ‘B’ is higher than the heat capacity so its cooling rate was higher than that of oil ‘A’. The hot iron particles of debris free condition. The amount moved freely in oil ‘B’ while carrying of sand debris in the contact was a large amount of frictional heat higher than that of iron particles of the through the oil owing to its low shear same mass since the density of iron is stress. The heat carried by the hot iron greater than the density of sand. But, particles was absorbed by the oil so in each case, the cooling rate the amount of heat absorbed by the oil decreased with time. The mobile free ‘B’ when there was iron debris in it electrons on the surface of iron was the greatest. The degree of particles helped to generate more disorderliness of the molecules of oil frictional heat. ‘B’ was increased when it absorbed The results of the cooling rates of oil more frictional heat. This ‘B’ when considering the three debris disorderliness promoted the breaking conditions are shown in Figure 11. down of the covalent bonds of its The cooling rate of oil ‘B’ due to the molecules and so it decreased the three debris conditions decreased with cooling rate of the oil.
Figure 11: Comparison of cooling rates of oil ‘B’ due to three debris conditions
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16 In Figure 11, Silicon IV oxide reacted mechanical contact than when there with the oil ‘B’ and it formed larger was debris in the contact. Silicon IV molecules which reduced their oxide is not a good conductor of heat molecular velocities. This affected the and so it acted as an insulator. This amount of heat transferred by the oil. phenomenon could not allow much As the temperature increased, the heat to be extracted from the surface molecular bond broke down. The of the journal bearing. breaking apart of the intermolecular The results of the cooling rates of oil bond due to the amount of heat ‘C’ when considering the three debris absorbed prompted the reduction of conditions are shown in Figure 12. the cooling rate. The molecules The cooling rates decreased with time became far apart from one another. because the intermolecular bonds of The amount of heat carried by each oil ‘C’ molecules were broken. The molecule was smaller compared with hot molecules moved away from one when they clustered together. The another such that the heat absorbed charge distributions on the surface of when they clustered together was the molecules of oil ‘B’ were higher higher than when they were scattered than that of oil ‘A’. Mechanical apart. When there was debris in the failure of the surface of the bearing contact, the frictional heat absorbed occurred when the vibrational kinetic by the oil increased. At some points, energy of its molecules was greater the cooling rate remained constant than the binding energy of the bearing because the frictional heat absorbed lattice. This made the atomic particles was used to break the inter-molecular to break out from the surface of the bond and such could not be detected bearing. It took a long time to occur by the thermometer. when there was no debris in the
Figure 12: Cooling curves of oil ‘C’ due to different debris contamination 17 From Figure 12, when the molecules investigated differ and this affects of oil ‘C’ were far apart, the conduction and convection of molecules could not conduct much frictional heat in Mitsubishi main heat away from the surface of the journal bearing. The cost of bearing. As the hot molecules moved lubricating oil depends on quality and away from one another when their performance of the oils and the bonds were broken, their cooling rates performance of lubricating oil does decreased with time. The cooling rates not depend on how viscous the oil in debris-free condition were smaller appears to be but it depends on how than the other two conditions. There its viscosity decreases over a range of was an increase in frictional heat temperature. The presence of debris in generated in the journal bearing due to a mechanical contact reduces the the debris contamination. There were bearing life cycle and thus causes the constant cooling rates because the failure of the machine element. Apart heat absorbed by the oil was used to from frictional heat generated in the break some intermolecular bonds, this bearing, other effects of debris are is in line with Nasiri-khuzani et al., galling, abrasion, adhesion, erosion [17]. The shapes of some curves and indentation of the mechanical resembled that of Newton’s cooling contact. The temperature of the oil curve. film varied linearly with the surface
4. Conclusion temperature of the bearing. The The amount of frictional heat performance of lubricating oil also generated in a Mitsubishi journal depends on the charge distributions on bearing depends on the nature of the the surface of the molecules of the debris in the contact and the amount oils. The frictional heat will be evenly of frictional heat absorbed depends on distributed on the surface of the the chemical compositions of molecules due to the presence of lubricants. The molecular movement charge distribution. The viscosity of and the heat capacity of the lubricants lubricating oils decreases with time play a vital role in the cooling ability due to the fact that the molecules of the oils. The covalent move far apart from one another after intermolecular bonds of the three oils bond breaking.
Reference cylinder lawn mower. Journal of [1] Moon, M. (2007). Gear solution, Engineering and Applied Journal of Tribology, (18): 574 – Sciences, 1254-1260. 588. [4] Abdullah O.I., Schlattmann J., [2] Dwyer-Joyce R.S., Heymer J. Al-shabibi, A.M. (2014). (1996). The entrainment of solid Thermomechanical Analysis of particles into rolling the Dry Clutches under Different elastohydrodynamic contact, Boundary Conditions. Tribology ASME Journal of Tribology, in Industry, 36(2): 172 – 180. 3(124): 420. [5] Madhuri M., Tiwari S., Ganai P. [3] Okokpujie, I. P., Okokpujie, K. (2014). Analysis of lubricant for O., Ajayi, O. O., Azeta, J., & Prediction of Contact Surface Obinna, N. N. (2017). Design, Behaviour of Metals, construction and evaluation of a International Journal of
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Innovative Technology and Engineering Science Project, (3): Research, 2(3): 933 – 939. 20–25. [6] Okonkwo, U. C., Okokpujie, I. [12] Odume, P.N. (2011). Basic P., Sinebe, J. E., & Ezugwu, C. Physics, First Edition, Published A. (2015). Comparative analysis by Nukak Publishers, Enugu, of aluminium surface roughness Nigeria, 239 – 255. in end-milling under dry and [13] Achebe C.H., Nwagu A.I. minimum quantity lubrication Anosike B.N. (2016). Evaluation (MQL) conditions. of Frictional Heat Generated in a Manufacturing Review, 2(30), 1- Mechanical Contact due to 11. Debris Formation and the [7] Ghanbari A., Khanmohamadi S. Cooling Rates of (2016). Experimental Evaluation some Lubricating Oils. SCIREA of Ball Bearing Diagnostics by Journal of Mechanical Contamination, Proceedings of Engineering, 1(1): 12 – 32. the 10th WSEAS International [14] Khurmi R.S., Gupta J.K. (2012). Conference on Systems, 10(12): Machine Design, Fourteenth 80 – 85. Edition, Published by Eurasia [8] Raj S., Jesse K. (2016). Publishing House (p) Ltd, 7361, Estimation of temperature and Ram Nagar, New Delhi (8): 978– Effects of Oxidation in Thermal 980. Elastohydrodynamic Lubrication, [15] Osei Y.A., Akpanisi L.E.S., Igwe Lubrication Fundamental III, H. (2011), New School 2(11): 1 – 12. Chemistry, Sixth Edition, [9] Sredanovic B., Gordana G. L., Published by African First Cica D. (2013). Effects of Publishers plc, Africana First Different Cooling and Drive, Onitsha, Nigeria, (8): 436 Lubrication Techniques on – 439. Material Machinability, Journal [16] Macek J., Emrich M. (2011). A of Mechanical Engineering, simple physical model of ICT 59(12): 748 – 754. mechanical losses, Journal of [10] Shojace, Maryam (2015). Tribology,(12): 1– 25. Modelling for the Thermal Nasiri-khuzani Gh., Asooder Behaviour of Engine Oil in M.A., Rahnama M. Sharifnasab Diesel Engine, Journal of H. (2012). Evaluation of Engine Tribology, 14(15):1 – 15. parts wears Using Nano lubricant [11] Carter, G. (1993). Tribology, Oil in agricultural Tractors Nano Published by Macmillan lubricant, Global Journal of Education, Loughborough Science Frontier Research University of Technology, Agricultural and Veterinary Science, 12(8): 1 – 10.
URL: http://journals.covenantuniversity.edu.ng/index.php/cjet 19 Fajobi Moses O., et al CJET (2019) 3(1) 20-37
Covenant Journal of Engineering Technology (CJET) Vol.3 No.1, June 2019 ISSN: p 2682-5317 e 2682-5325 DOI: 10.20370/5y5f-7733
An Open Access Journal Available Online
Mismatch between Anthropometry Characteristics of Nigerian Occupational Bus Drivers and the In- Vehicle Measurement
Fajobi Moses O1*, Onawumi Ayodele S.1.2, Mfon Udoh M. O2 & Awoyemi Elijah A3
1,2Department of Mechanical Engineering, Ladoke Akintola University of Technology, P.M.B. 4000, Ogbomoso. Oyo State. Nigeria. 2Department of Mechanical Engineering, Covenant University, P.M.B. 1023, Ota, Ogun State, Nigeria. 3Department of Works and Maintenance, Osun State University, Osogbo, Osun State, Nigeria. [email protected]
Received: 26.04.2019 Accepted: 20.05.2019 Date of Publication: June, 2019
Abstract- The characterization of interfacing elements of in-vehicle and driver’s anthropometric variables of a randomly selected operators with sample size of 161 subjects of commercial buses in the study area were considered in this work. Participatory ergonomic intervention approach was employed in data mining, opinion gathering and subsequent analysis. Related variables between the two systems were compared to establish fitness as well as the level to which human operator were accommodated in the vehicle dimension. A few cases of misfit were recorded based on drivers’ opinion and the measurements taken. Work related musculoskeletal disorder experienced by the users under study were traceable to inappropriate design variable of the in-vehicle elements. Keywords: Anthropometry, Workstation, Bus Driver, Ergonomics, Musculoskeletal Disorders
1. Introduction whose capabilities and limitation are The movement of goods and services rarely considered at the development plays significant role in everyday life stage of the means of transportation bustle with varying means of especially in the face of international transportation resulting from vivid trading of automobile industry. Work research and development activities. related musculoskeletal disorder Common technological systems in use reported by drivers of automobile are usually operated by human being continue to create design challenges
URL: http://journals.covenantuniversity.edu.ng/index.php/cjet 20 Fajobi Moses O., et al CJET (2019) 3(1) 20-37 receiving attention of ergonomists and with the scientific study of human automobile in-vehicle developers [1] subjects for the development of [2]. Although the risk exposure of standards and evolving of specific both driver and passengers of demands associated particularly with automobiles are seemingly of the manufactured goods and services to same level, the vigilance level enhance product usability and required for save control of the system ergonomics suitability for the user place higher demand on the driver [3]. population [12] [13]. Anthropometric Some of the occupational risks data bank for citizen of varying age experienced by the users includes group have been developed in most fatigue, health damages by noise, developed countries and used in area vibration, toxic and irritable effects by of product design and manufacture. atmospheric pollution, injury or death However, anthropometric dimensions in case of fatal accidents. Significant and other various factors such as mismatch of in-vehicle design gender, age, race, nutritional status, variables and the anthropometric physiological build and nature of characteristics demand of taxi cab work were found to vary widely drivers in Nigeria was found to be across every region, state and country responsible for reported disorder and [14]. This suggests significance other uncomfortable conditions [4] [5] differences in anthropometric data of [6]. Much of the challenges, trauma, populace/subject from among and disorders complained by operator countries and the misfit of products of automobiles in Nigeria were more imported from place with organised of absence of effective legislation and database (UK, USA, Japan. Germany. absence of enforcement of existing China etc.) into developing countries rules and regulations in automotive like Nigeria, Ghana, Cameroon etc. industry. Ongoing efforts to mitigate where required body dimensions were persistence musculoskeletal and not considered in product psychological trauma imposed by development [4]. In the case of imported technological systems are automobile industry, a number of yet to yield reasonable result due to drivers’ workstation were reported to technically missing link [7]. The cause discomforts due poor design combined work design and and inadequate adjustability as well as ergonomics approach, especially for lack of application of ergonomic the redesign of faulty physical principles in the design of some in- environment do not only increase the vehicle components. Reliable production output but also the user’s anthropometric data for a targeted safety and comfort for effective and population becomes necessary when efficient performance [8]. designing for that population Anthropometry: is the art and otherwise the product may not be science of measurement the physical suitable for the users [15]. geometry, mass properties, and The challenges associated with the strength capabilities of the human applications ergonomic principles body [9] [10] [11]. It is concerned become obvious due to significance of
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21 Fajobi Moses O., et al CJET (2019) 3(1) 20-37 the variations in human capabilities researches have it that sitting position and the unavailability of updated enhances the comfort and user’s anthropometric database. These effectiveness of bus drivers. The have posed enormous task for posture is however limited to 30 ergonomists and designers of products minutes in constrained location and/or and components peculiar [16] [17] fixed position.
[18]. 2. Materials and Methods Anthropometric data application in Sampling Technique man-machine system and similar Two commonly used model of facilities design can be stressful due to passenger vehicles namely Toyota number of design parameters involved Hiace and Mazda identified through [19] [20], this problem has recently preliminary survey at the study area been made much easier giving some were considered for further study. developed design principles like With the use of participatory design for adjustable range, design for ergonomic intervention approach, average sizes (50th percentile) and opinion of 161 randomly selected bus design for extremities (5th/95th operators from six prominent motor percentiles). park units were used for ergonomic This study seeks to identify research evaluation and anthropometric and development gaps and areas of characterization study. Three trained mismatch between driver and enumerators were involved in the technological systems characteristics. procedure for collection of fifteen Driver’s posture is also important to relevant anthropometric vehicle design process, man-machine measurements for each of the subjects system as well as the static and who volunteered to the rigour of the dynamic anthropometric demands of procedure adopted by [26]. the operator [21] [22]. Other variables Bus Operators Anthropometric that could be used to determine Characterization Procedures: The ergonomic suitability of driver in the procedure for taking subject’s workstation are; seating comfort, anthropometric measurement used by postural composition and body [4] was adopted in this study with the flexibility. These can also be used to assistance of three trained estimate the driver’s resilience and enumerators. Body variables endurance level at work [23] [24]. considered were Shoulder-Height- To have a better understanding of the Sitting, Shoulder-Elbow-Length, causal factors of musculoskeletal Shoulder-Breadth, Sitting-Height- disorder and discomfort to the driver Normal, Sitting-Height-Erect, while at workstation, the relationship Buttock-Knee-Length, Buttock- between the operator’s seat, steering Popliteal-Length, Thigh-Clearance- column and wheel and pedals in the Height, Popliteal-Height-Sitting, workstation must be clearly Thumb-Tip-Reach-Sitting, Anterior- understood [25]. Arm-Reach, Stature, Hip-Breadth and These have a great influence on Maximum-Body-Breadth. posture of the operator. Previous
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The instrument employed in the depth, Backrest seat plane height, measurement include Stadiometer, Backrest height, Distance from edge Vernier-Callipers, measuring Tape, of seat to application of force point, Anthropometric-Seat, and Bathroom- Lumber support height, Lumber Weighing-Scale, clipboard, Data support depth Lumber support collection form pencil with cleaner extension, Rounded front edge width, and digital camera. The average Armrest clearance, Backrest width values of the triplicated measurements (Lumber level), Backrest width were calculated and considered for (Thoracic level), Horizontal lumber further analysis. concavity (Radius), Horizontal A 2D model of each of the Thoracic concavity(Radius), Headrest anthropometric dimension of a seated length, Headrest width, Armrest operator were divided into three surface length, Armrest surface groups for easy identification as breadth, Backrest angle and Seat follows: plane angle. Data collected were i. Sagittal Plane (Vertical processed in Microsoft Excel Dimensions) Spreadsheet 2010 version and ii. Sagittal Plane (Horizontal imported into SPSS 17.0 for further Dimensions) and analysis. Descriptive statistics which iii. Frontal Plane. included; mean, standard deviation, Driver’s Seat and Workstation range and percentiles (5th, 50th and Characteristics: Twenty-three 95th percentiles) were determined. physical characteristics of driver seat Results obtained from both and other workstation parameters characterizations were compared with were considered for the study. The each other and these formed the bases considered physical dimensions of the upon which bus design specifications driver and the workstation were were developed and the characterised with measurements anthropometric database created. which include: Seat height, Seat
Table 1: Anthropometric Description of Seated Vehicle Operator from Vertical View of the Sagittal Plane Model Description In-vehicle applications Shoulder Height (Sitting) Backrest height, Door Height, (SHS): Headrest adjustable range, Seat The vertical distance from the belt design sitting surface to the uppermost point on the lateral edge of the shoulder (acromiale).
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23 Fajobi Moses O., et al CJET (2019) 3(1) 20-37
Shoulder – Elbow Length Armrest height (SL): The vertical distance Armrest depth from the uppermost point on Armrest clearance, the lateral edge of the shoulder Side gear control knob. (acromiale) to the bottom of the Door opening lever location elbow (alecranon). Side door armrest buttons
Sitting Height Normal: The Vehicle roof-seat plane vertical distance from the distance, sitting surface to the uppermost Seat plane vatical adjustment point of the head (subject sits range, relaxed)
Sitting Height Erect: The Backrest-seat plane height, vertical distance from the Headrest height, sitting surface to the uppermost Vehicle roof-seat plane point of the head (subject sits distance, erect) Seat plane vatical adjustment range,
Popliteal Height Sitting Seat plane height (PHS): The vertical distance Seat plane vatical adjustment between the floor and to the range, thigh immediately behind the Seat depth knee.
Thigh Clearance Height Seat plane-steering wheel (TCH): The vertical distance distance from the sitting surface to the Seat depth adjustment range top of thigh at its intersection with the abdomen.
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Stature/Standing Height: The Seat stretch and pedal room vertical distance between the design centre of the head and the sole of the feet was measured.
Table 2: Anthropometric Description of Seated Vehicle Operator from Horizontal View of the Sagittal Plane Model Description In-vehicle Applications Buttock – Knee Length (BNL): The Seat plane depth horizontal distance from the most Backrest-dashboard distance posterior point on the buttocks to the Pedal room design most anterior point on the knee. Knee-dashboard clearance
Buttock – Popliteal Length: The Seat depth horizontal distance from the most Seat plane contour posterior point on the buttocks to the most interior point on the knee (i.e., back of the kneel)
Anterior Arm Reach, Sitting Seat Backrest- windscreen (AAR): The horizontal distance from distance, the back of the shoulder (greatest In-vehicle work space evilop. bulge of trapezium) to the tip of the extended middle finger.
Thumb – Tip Reach, Sitting (TRS): Dashboard buttons-driver The horizontal distance from the back distance, of the shoulder (greatest bulge of Seat Backrest- windscreen trapezium) to the tip of the extended distance, thumb. In-vehicle work space evilop. Door opening lever location Side door buttons Armrest surface length
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25 Fajobi Moses O., et al CJET (2019) 3(1) 20-37
Table 3: Anthropometric Description of Seated Vehicle Operator from Front View of the Sagittal Plane Model Description In-vehicle Application Shoulder Breadth (SB): Backrest width (Thoracic level) The maximum horizontal Backrest contour design distance across the deltoid (triangular muscle on the human shoulder) muscles.
Hip Breadth (Sitting) Backrest width (Lumber level) (HB): The maximum Pedal room width horizontal distance across the hips.
Maximum Body Breadth (MBB): The maximum horizontal distance between the lateral surfaces of the elbows.
3. Results and Discussion drivers. The suggests a redesign In-Vehicle’s Variable and using design recommendation Anthropometric Characteristics: dimension of average door height and Age group of the studied subjects width of 140.0cm by 99.5cm ranges between 18 to 60 years. Table respectively for the extreme 95th 4 shows the summary of the percentile. descriptive and percentiles statistics of Ground-to-driver’s door height: the anthropometric characteristics. Interactions and personal observations Table 5 shows the results of the in- revealed that the existing ground-to- vehicle geometrical characterization. driver’s door height might not be Table 6 shows individual adequate as it is too high (70.4cm) characteristics of the in-vehicle especially for the short drivers. This geometry against the pertinent makes the drivers uncomfortable anthropometric dimension(s). while ingress and egress his Driver’s door (Height and Width): workstation. Therefore, as suggested Data obtained from the design reveals by Brooks, 1979, ground-to-driver’s that existing door variables (door door height be lowered to an average height) of the buses (135.7cm by of 34.8cm and stair steps would be 99.5cm) does not adequately meet the necessary. The existing handrail operators’ requirements as indicated should be designed to ergonomically in the percentile statistics of the conform to the driver’s fingers shape
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26 Fajobi Moses O., et al CJET (2019) 3(1) 20-37 in order to generally reduce the reduced to about 17.8% of the present problems (like sliding of the hand dimension i.e., 45.7cm, so as to against the handrail) faced by the comfortably accommodate at least 5th drivers while entering as well as percentile range, i.e., 95% of the exiting through the driver’s doors. drivers. Seat: As defined by SAE 2013 Seat adjustments: Upper, middle and (Motor Vehicle Seating System), lower; back pains, knee joints pain, motor vehicle seat system is a elbows pains, chest pain, neck pain structure engineered to seat the driver amongst others were identified as and/or passengers, including all pads, major musculoskeletal disorders upholstery, decorative metal trim experienced by drivers [4]. parts and seat adjusters or supporting Consequently, these forms of components. For better performance disorders can be reduced to the barest of the drivers at workstations, the seat minimal if all the necessary should be designed putting into adjustments ranges and devices are in consideration, the following design place and functional. These specifications for each of the adjustments include; seat fore/aft variables; adjustment, seat height adjustment Seat widths: From Table 3 the seat and seat back angle adjustment width is seen to be satisfactory for the (tilting). 95th percentile of the drivers as Seat heights: Although through compared with the hip breadth as an interview, none of the drivers said the anthropometric dimension. Since it is seat height were too high but many suitable for the 5th percentile of the agreed that the seat height was too drivers, it is therefore recommended low, therefore, it is suggested that the that the average seat width for the bus average seat height should remain as should be maintained as existing 45.1 and seat adjustment be included 49.8cm. to accommodate users in the extreme Seat length: Over 50% of the studied percentiles. Therefore, the seat height drivers might find the average seat adjustments should be 7.2cm for total length in the existing design as upward and downward adjustment. measured (55.6cm) uncomfortable. So This will enable drivers in the 5th it is suggested that the average seat percentile to adjust the seat to their length in the existing design should be comfort.
Table 4: Anthropometric Data of Ogbomoso Bus Operators (n = 161) Anthropometric Variables Mean Std. Dev Range Percentile 5th 50th 95th Shoulder Height Sitting 57.54 2.55 9.7 53.9 57.3 61.5 Shoulder-Elbow Length 37.26 2.26 7.7 34.0 37.0 40.8 Shoulder Breadth 45.42 3.25 10.6 40.4 45.1 50.1 Sitting height normal 79.32 4.31 16.8 72.7 79.3 85.0 Sitting height erect 83.36 6.65 27.4 75.0 83.2 93.6 Buttock-Knee Length 58.89 2.88 13.6 55.0 59.0 63.1 Buttock-Popliteal Length 48.97 2.57 10.5 45.7 48.6 53.2 Thigh Clearance Height 14.06 1.38 4.49 12.1 13.9 16.1 Popliteal Height Sitting 49.39 2.02 6.79 46.3 49.3 52.3
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27 Fajobi Moses O., et al CJET (2019) 3(1) 20-37
Thumb-Tip Reach Sitting 81.44 3.53 12.7 76.7 80.9 87.2 Anterior-Arm Reach 89.19 3.99 15.3 83.7 89.2 95.4 Stature 176.12 6.17 21.8 167.6 175.6 185.9 Hip Breadth 37.95 3.62 15.7 32.8 37.9 42.7 Maximum Body Breadth 46.1 3.2 11.2 41.0 46.2 50.8 Weight 74.05 6.70 31.5 61.7 73.6 85.1 All dimensions were measured in centimetres (cm) except weight which is in kilogram (kg)
Table 5: In- Vehicle Design Data Design Parameters Mean Dimension Toyota Mazda Hiace Seat height 45.1 45.4 Seat width 49.8 50.2 Seat length 55.6 55.6 Back-rest length 53.3 53.5 Back-rest width 47.7 48.1 Dashboard-backrest length 75.1 75.3 Steering-wheel external diameter 44.7 44.7 Steering-wheel thickness Minimum 38.1 38.1 Steering-wheel thickness Maximum 44.7 44.7 Thigh clearance (steering wheel-seat height) 22.6 22.7
Driver’s door height 135.7 135.9 Driver’s door width 99.5 99.6 Ground-to-driver’s door height 70.4 70.3 Elbow clearance N/A N/A Seat-pedal length 34.4 34.4 Rounded front edge width 8.7 8.7 Headrest length 23.8 23.7 Headrest width 12.7 12.6 Headrest breadth 27.8 27.9 Armrest surface length N/A N/A Armrest surface breadth N/A N/A Seat Adjustment Minimum 87.7 88.3 Seat Adjustment Maximum 101.6 101.6
All variables were measured in centimetres (cm)
Seat fore/aft adjustment: Buses with noted by critical look at the seats that, fixed adjustments give drivers most of the seats had fore/aft seat problems as the level of adjusters, but just few were inconvenience and discomfort functional. In fact most seats were increases. During the study, it was found permanently welded to the
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28 Fajobi Moses O., et al CJET (2019) 3(1) 20-37 driver’s workstation thereby not by looking closely at the seats, it was giving room for maneuvering to suit revealed that most of the seats had driver’s postural comfort. It was also damaged backrest adjusters. It is gathered at one of the motor park therefore suggested that the driver’s units visited that over 70% of the seat backrest should adjust backward buses used by the motorists were (Tilt) to 35 degrees from the vertical brought into the country right handed, to accommodate user to who may lean possibly due to less cost of against the backrest as suggested by procurement. To comply with the use [25]. of road act of Nigerian government Other design considerations include these buses were converted into a left the inclusion of armrests that is handed drive. But with this they could adjustable in height and width, to only to convert the steering column accommodate various body and dash boards alone and not the dimensions on the seats as desired by seats. Hence they manipulate the drivers, to reduce some workstation thereby making the seat musculoskeletal problems, relating to not adjustable for the driver but the hand and back pains. In addition, passenger who sits at the front. It is of introduction of removable seat paramount importance to note that cushions will go a long way in with these findings, discrepancies in reducing soiling, odour retention and the design variables and that of the wear; the seats are subjected to, due to anthropometric dimensions of the the fact that diverse drivers use the drivers becomes intensified. Hence it same workstation. Also to increase becomes more pronounced that the driver’s satisfaction and comfort in buses were not pre-designed for his workstation, seats should be Nigerians i.e., anthropometric data of designed to have a perfect seat depth Nigerians were not incorporated into and well comfortable seat to fit the the existing bus design. In general, the user. seat adjustments of the buses across Backrest width: To ensure that the the studied motor park units were not backrest width covers the shoulder adequate even those that seem to be breadth, the average backrest width functional could not be adjusted in should be increased by 5.87% of the their full length of 13.5cm. Therefore, present dimension, thereby making it as it is suggested by [27], that a 50.5cm so as to accommodate 95% of driver’s seat should have a seat the drivers. adjuster to be maintained at an Backrest length: For the backrest average of 18.4cm for total fore/aft length at least to be at the shoulder adjustment for Molue buses, also height for comfort of 95% of the 13.5cm for Toyota Hiace and Mazda drivers, the average backrest length buses. should be increased to about 5.87% of Backrest adjustments: Observations the present dimension (47.7cm) to from the buses measured showed that make it 50.5cm. Seats with air a very limited number among the actuated lumbar and back side bolster buses had adjustable backrest, though support backrest will be desirable by
URL: http://journals.covenantuniversity.edu.ng/index.php/cjet 29 Fajobi Moses O., et al CJET (2019) 3(1) 20-37 the bus drivers and as suggested by The comparison of major [28] for bus operators, to reduce some anthropometric dimensions of musculoskeletal disorders, relating to Ogbomoso bus operators with those back pains. Also adjustable headrest of Lagos Molue bus drivers and (up/down and forward/backward Ibadan taxicab drivers of the same adjustments) will be necessary as region, south western urban centres suggested [28] and desired by the of Nigeria, reveals that there are surveyed drivers. Although there are variations in most of the dimensions headrests in the existing design yet for; Shoulder Breadth, hip breadth, most were found to be designed Thumb-Tip Reach Sitting/Anterior alongside (merged) with the backrest Arm Reach and Stature which stands and not separately. Incorporation of at (166.8, 173.3, 179.7) for Lagos this in the future design would help in drivers, (161.3, 172.0, 182.76) for curtailing some musculoskeletal Ibadan drivers and (167.6, 175.6, problems, relating to neck and back 185.9) for Ogbomoso drivers for 5th, pains while it enhances the comfort of 50th and 95th percentiles respectively, the drivers. Table 5. It may be due to nutrition and Dashboard-backrest length: Driving body build. This shows the distinct task is an activity that requires nature of the anthropometry of the maximum concentration by the driver urban centres and the dynamism. as various judgments need to be made Although the anthropometric data of at every point in time. However, while Ibadan were not obtained from bus he does these, there is need for the operators but it is stipulated that driver to interact with various in- driving is a free for all kind of work in vehicle components. For ease of Ibadan, it is possible that majority of reach for various controls on the these drivers also at one-time drive dashboard, control lever/knobs and buses. Therefore, buses to be designed side/rear mirrors, it is necessary the for the Ogbomoso bus drivers at south design for control reach is within the western Nigeria, need to be modified maximum arm reach so as not to pose with suitable adjustment in body discomfort on the driver. On this note, dimensions affected. it is suggested that the dashboard- The mean values of some major backrest length is increased by anthropometric data (body 11.45% of the present dimension to dimensions) of Ogbomoso in south become 83.7cm. This will allow the western Nigeria were also compared workstation to accommodate 95% of with mean values of passengers in the drivers. The proposed design buses as indicated in Table 6. specification for bus is shown in Analysis of variance (ANOVA) Table 4. performed on the mean values
Anthropometric Comparison of revealed at 95% confidence level that Ogbomoso Bus Drivers with Lagos there was no significant difference (p Molue Bus and Ibadan Taxicab > 0.01). The comparison reveals that Drivers the Ogbomoso bus operators are variably smaller than the passengers
URL: http://journals.covenantuniversity.edu.ng/index.php/cjet 30 Fajobi Moses O., et al CJET (2019) 3(1) 20-37 in bus of Ogun south western Nigeria comparison shows almost similar ratio in all structural body dimensions of sitting height to stature among where data were available except in different ethnic groups which is in stature where they have 176.12 as line with survey carried out on against 174.8. The variation may be anthropometric data of Indian workers attributed to the discrepancies in [29]. Consequently, this comparison is physiological factors and body build in accordance with [30-34] who also up. The lower body dimensions may stipulated that there is a high lead to uncomfortable postures probability that whatever the mean adopted while driving buses posing stature of a sample, any given body fatigue on drivers and possibly dimension of length will be very inefficiency. nearly a constant proportion of the Table 7 presents the comparison of stature. Therefore, if the stature is sitting height to stature ratio of known, any dimension that is not Ogbomoso (south west) bus operator available in the sample can be in Nigeria with different ethnic groups obtained by proportion [35]. across Nigeria. Result from this
Table 6: Driver’s workstation design variables fitted with related anthropometric variables
Design Mean Anthropometric Variable Mean SD 5th 50th 95th Variables Dimension Seat height 45.1 Popliteal height sitting 49.39 2.02 46.3 49.3 52.3
Seat width 49.8 Hip breadth sitting 37.95 3.62 32.8 37.9 42.7 Seat length 55.6 Buttock-popliteal length 48.97 2.57 45.7 48.6 53.2
Back-rest length 53.3 Shoulder height, sitting 57.54 2.55 53.9 57.3 61.5
Back-rest width 47.7 Shoulder breadth 45.42 3.25 40.4 45.1 50.1 Dashboard- 75.1 a. Anterior arm reach 89.19 3.99 83.7 89.2 95.4 backrest length sitting 81.44 3.53 76.7 80.9 87.2 b. Thumb –tip reach sitting 58.89 2.88 55.0 59.0 63.1 c. Buttock-Knee length
Steering-wheel 44.7 Anterior arm reach sitting 89.19 3.99 83.7 89.2 95.4 external diameter Steering-wheel 6.6 Na na na na na na thickness
Thigh clearance 22.6 Thigh height sitting 14.06 1.38 12.1 13.9 16.1 (steering wheel- seat height)
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Driver’s door 135.7 Stature 176.12 6.17 167.6 175.6 185.9 height
Driver’s door 99.5 Max. body breadth 46.1 3.2 41.0 46.2 50.8 width
Ground-to- 70.4 Stature 176.12 6.17 167.6 175.6 185.9 driver’s door height Elbow clearance Na Na na na na na na Seat-pedal 34.4 Popliteal height sitting 49.39 2.02 46.3 49.3 52.3 length
Rounded front 8.7 Popliteal height sitting 49.39 2.02 46.3 49.3 52.3 edge seat width
Headrest length 23.8 Sitting height Normal 79.32 4.31 72.7 79.3 85.0 Sitting height Erect 83.36 6.65 75.0 83.2 93.6
Headrest width 12.7 Sitting height Normal 79.32 4.31 72.7 79.3 85.0 Sitting height Erect 83.36 6.65 75.0 83.2 93.6 Headrest breadth 27.8 Sitting height Normal 79.32 4.31 72.7 79.3 85.0 Sitting height Erect 83.36 6.65 75.0 83.2 93.6
Armrest surface Na Na na na na na na length
Armrest surface Na Na na na na na na breadth
Seat Adjustment 13.1 Buttock-Knee length 58.89 2.88 55.0 59.0 63.1
All variables were measured in centimetres (cm), SD denotes Standard Deviation
Table 7: Proposed In-vehicle design specifications Design variable Proposed design variable (cm) A. Seat height 45.1 B. Seat width 49.8 C. Seat length 45.7* D. Back-rest length 50.5* E. Back-rest width 50.5* F. Dashboard-backrest 83.7* length G. Steering-wheel 44.7 external radius H. Steering-wheel 6.6 (with padding) thickness I. Thigh clearance 22.6 (steering wheel-seat height)
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32 Fajobi Moses O., et al CJET (2019) 3(1) 20-37
J. Driver’s door height 140* K. Driver’s door width 99.5 L. Ground-to-driver’s 34.8* door height M. Elbow clearance Suggested N. Seat-pedal length 34.4 O. Seat fore/aft 13.5 adjustment (Forward and Backward) P. Seat adjustment 7.2* (Upward and Downward)
* Not Present
Table 8: Comparison of Mean Sitting Height to Mean Stature Ratio with other studies on anthropometry
Study Mean Ratio Source Ogbomoso (South 0.4733 Present study (2015) Western Nigeria) Ibadan (South Western 0.4839 Onawumi 2008 Nigeria) Igbo (South Eastern 0.5122 Onuoha 2012 Nigeria) Doko (North Central 0.4661 Jonathan and Shehu 2012 Nigeria) Kutigi (North Central 0.4926 Jonathan and Shehu 2012 Nigeria)
All variables were measured in centimetres (cm)
4. Conclusions and becomes an inevitable tool to define Recommendation the population of the potential users. Stakeholders in the automotive Mainly because the human body industry has yet relent in search for a occupies a central position in the system that meet up with the recent design of man machine interface and challenges of user’s population the system at large. Also, this study requirements, established technical has opened up the need to conduct a standards, and other basic national anthropometry survey for specifications for research uses. The user population in Nigeria. Such data basis for achieving these has been can be used to configure the vehicle, found to be through a comprehensive driver’s workstation layout and in- Participatory Ergonomic Intervention vehicle interface for the purpose of (PEI) approach. enhancing functional effectiveness, However, in ensuring an human comfort and ergonomic ergonomically suitable products and suitability. Consequently, integrating physical equipment, anthropometry the limitations of the potential users in
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33 Fajobi Moses O., et al CJET (2019) 3(1) 20-37 relation to such’s demographics and for overall assessment of driver’s other physical characteristics workplace, the extent to which the enhances the driver’s comfort. existing bus design is found to be Although as a matter of research and ergonomically suitable and its user development a number of studies have friendliness are inevitable, hence the been carried out on driver fatigue and conception of this work. low back disorders however the needs
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STUDY OF A ROAD TRAFFIC [35] Omoruyi, O. N., Omoruyi, M. G., CONFLICT AT THE T- Okokpujie, K. O., & Okokpujie, JUNCTION OF UNIVERSITY I. P. (2018). Electronic Fare OF BENIN MAIN GATE. Collection Systems in Public International Journal of Civil Transits: Issues, Challenges and Engineering and Technology Way-Forward. Covenant Journal (IJCIET), 9(8), 1048-1061. of Engineering Technology, 2(1)
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Covenant Journal of Engineering Technology (CJET) Vol.3 No.1, June 2019 ISSN: p 2682-5317 e 2682-5325 DOI: 10.20370/2cdk-7y54
An Open Access Journal Available Online
A Review of Voice-Base Person Identification: State-of-the-Art
Folorunso C. O.*1, Asaolu O. S.2 & Popoola O. P.3
1, 2, 3Department of Systems Engineering, University of Lagos, Akoka, Lagos. *[email protected], [email protected], [email protected]
Received: 22.10.2018 Accepted: 11.04.2019 Date of Publication: June, 2019
Abstract - Automated person identification and authentication systems are useful for national security, integrity of electoral processes, prevention of cybercrimes and many access control applications. This is a critical component of information and communication technology which is central to national development. The use of biometrics systems in identification is fast replacing traditional methods such as use of names, personal identification numbers codes, password, etc., since nature bestow individuals with distinct personal imprints and signatures. Different measures have been put in place for person identification, ranging from face, to fingerprint and so on. This paper highlights the key approaches and schemes developed in the last five decades for voice-based person identification systems. Voice-base recognition system has gained interest due to its non-intrusive technique of data acquisition and its increasing method of continually studying and adapting to the person’s changes. Information on the benefits and challenges of various biometric systems are also presented in this paper. The present and prominent voice-based recognition methods are discussed. It was observed that these systems application areas have covered intelligent monitoring, surveillance, population management, election forensics, immigration and border control. Keywords: Person-identification, biometrics, information and communication technology, authentication, voice-base person identification.
1. Introduction of distinguishing between persons. Person identification is the process of Conventional person identification recognizing an individual based on technologies are developed based on specific characteristics. Identification “something we know” (password and by name is the most common method personal identification number (PIN)),
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“something we have” (Token, an individual since no two persons share Identity Card, an Access Control Card entirely the same biometric traits [3]. or a Radio Frequency Identity (RFID) With numerous developments in card), unlike something we are (i.e. technology, the security sector has bodily features like fingerprint, encountered some significant finger-vein, voice, gait). These advancement. We can safely say that identification schemes have their technology has transformed security. limitations. For instance, a password The challenge was how to make or a PIN can easily be forgotten or computers identify or recognise an even guessed by an impersonator individual. Biometric being based on while a token or an identity card can measuring physical characteristics be lost, stolen or even cloned. As uses features which are common and such, the conventional forms of readily available to all class of people. identification may not really These features are distinct, easily distinguish between an authorized collected and tested, and have high user and an impersonator [1]. variability to carter for repetition of
The need to verify the identity of an data class. Some of the biometric individual before such individual can features currently used include: Facial have access to some restricted places thermogram, hand vein, gait, is very important as so many means of keystroke, odour, ear, hand geometry, breaking into one’s privacy is being fingerprint, face, retina, iris, palm- developed every day by hackers. The print, voice, signature and DNA. use of the state-of-the-art person In voice-based recognition system, the identification technology which uses features of an individual’s voice are biometrics technology cannot be over- based on the physical characteristics emphasized, due to so many of their vocal tract, nasal cavities and advantages this type of recognition the articulators (which include mouth, system proffers. Biometrics is the lips, teeth and so on) which are used science and technology of measuring, in generating sound. These features analysing and comparing some human are unchanging for an individual physiological and sociological related though the behavioural features may data [2]. Many biometrics-based change over time due to age, location, identification systems have been medical conditions and/or emotional employed both for domestic and state [4]. Voice-based recognition commercial applications. The use of methods are classified into two ways: biometrics has shown increasing Automatic Speaker Verification significance in our daily life and as (ASV) and Automatic Speaker such, many books, journals and Identification (ASI) system [4]. The conference proceedings have limitations of the conventional person enumerated advances in theory and identification system have always application of this technology. In all, been challenging, hence the need to the use of biometrics has emerged as research into the state-of-the-art the best way of identifying an biometric technologies novel
URL: http://journals.covenantuniversity.edu.ng/index.php/cjet 39 Folorunso C.O., et al CJET (2019) 3(1) 38-60 biometric features that can be body (fingerprints, face, finger proposed. geometry, iris scans, retina scans, 2. Review of related works hand geometry, finger-vein among So much research has been done on others) as shown in Figure 1. The person identification using biometrics second category, which is the technology. Biometrics traits or behavioural characteristics are based characteristics are divided into two on what one does (a person’s action), major categories. The first category is it uses data that are derived from physiological characteristics, which indirect measurement of a person’s are based on how one is, using data action (voice recognition, keystroke (features) that are derived from direct scans, signature, gait and so on as measurements of parts of the human shown in Figure 2 [1], [5].
Figure 1: Selected physiological biometrics in use [3]
Figure 2: Selected behavioural biometrics in use [3]
A biometric authentication system can fingerprint or face from a Forensic be further classified either as database. Verification on the other identification or a verification system. hand, is a one-to-one system of Identification system is a one-to-many identification where biometrics is system where biometrics is used to used to confirm a person’s identity for determine a person’s identity from a access control [6], [7]. number of some people’s data stored Kaur and Kaur [8], presented a brief in a database. For example, the police survey of different voice biometric for may try to identify an individual’s speaker verification in an attendance
URL: http://journals.covenantuniversity.edu.ng/index.php/cjet 40 Folorunso C.O., et al CJET (2019) 3(1) 38-60 system. They proposed the use of well as environmental conditions. The voice, having considered different voice-based biometric system is methods that have been employed for classified into automatic speaker automatic attendance for students and verification (ASV) and automatic as such the use of voice for this speaker identifications (ASI). The purpose is a very important and highly former uses voice as validation welcome phenomenon. They used characteristic in a one to one Gammatone filter bank instead of Mel verification scenario. While the latter filter bank, after which the discrete uses voice to recognise who a person cosine transform was applied to truly is. A particular voice feature of separate overlaying signals. The use an individual is matched against a of Gammatone frequency cepstral stored pattern in a database. A typical coefficient (GFCC) with the Gaussian voice feature can be formants or any Mixture Model as well as Artificial other sound characteristics which are Neural Networks was incorporated for unique to each individual’s vocal training and matching task tract. respectively. Belin et al [11] working from a Tran et al [9] introduces neuro-cognitive point of view looked normalization technique which at neural association of voice depends on fuzzy set theory to perception. Having considered the improve the performance of voice- ability to evaluate a person’s gender based verification system. In order to and age bracket from listening to their authenticate a claimed personality, a voices was a very strong motivation likeliness value was evaluated with a behind this work. They tried to look at threshold in order to allow or reject the voice as an auditory face in the person. The use of noise comparison with the face recognition clustering as well as the c-means system. They then proposed the use of clustering membership function was Bruce and Young’s model of face introduced to eradicate the problem of perception as a structure for ratio-type scores which affects the understanding the perceptual as well false acceptance rate. Result however, as the cognitive processed contained showed great reduction in the false in voice perception. This purpose acceptance and false rejection rate. model predicts functional detachment
Delac and Grgic [4], and Dugelay et similar to those perceived for faces. In al [10] presented a concise summary future, the use of face archetype to of different biometric methods which test the prediction of the proposed include single as well as multiple model was suggested. Similarly, more biometric systems. Voice-based research is needed in order to biometric system uses some of the ascertain some of the following; - features of human-speech that are not - Are voices more noticeable than changing for a particular individual. any other sound around Though the behavioural features of irrespective of the fact that such the same human speech varies over sound contains speech or not. time due to age medical, emotional as
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- To what degree does the voice security as well as reliability of the perception system permit us to system. excerpt identity and emotional Korshunov and Marcel [13] information from the expression of considered the fact that most other species such as cats, dog and biometric technology systems are so on. vulnerable to spoofing which reduces - What is the perceptual emergent of their wide use sometimes hence they voices? presented the need to develop anti- Aronowitz [12] considering the rapid spoofing detection methods also development of smart phones and referred to as presentation attack mobile internet banking, there is no detection (PAD) systems. They doubt the imperative need of a very presented an integration of PAD and strong authentication system. While Automatic Speaker Verification the current use of password or pattern (ASV) systems using i-vector and to unlock phones is not sufficient for local binary pattern histograms based the smart phones having considered ASV-PAD hybrid system. The the high threat of the device getting to AVspoof database which contains the custody of an un-authorized user. practical presentation attack was used Current developments in voice-based to validate this method and result biometric system present a huge obtained show a significantly potential for a robust authentication of enhanced resistance of this hybrid a mobile smart phone using voice. system to attacks at the detriment of This aspect is very crucial for the trivial degraded implementation for financial and banking industry, where scenarios without spoofing attacks. 40 financial organizations are The use of cascading scheme for score considering a flexible mobile synthesis and evaluating it with the customer services and easy joint ASV-PAD system was suggested authentication and at the same time for future research. In addition, the maintaining security and most state of the art spoofing database can importantly, reducing fraudulent be employed to explore multi-model usage. system considering ASV and PAD They presented the use of the current systems of different modalities for technology text-independent as well instance speech and image may be as text-dependent speaker combined to enhance the performance authentication skills for user in both ‘licit’ and ‘spoof’ scenarios. verification speaker specific digit Krawczyk and Jain [14] considering strings, global digit strings, prompted the large evolution from paper-based digit strings as well as text medical records towards electronic independent were evaluated adapting medical records, guaranteeing the the Joint Factor Analysis (JFA), security of such private and highly Gaussian mixture models with sensitive data cannot be over- nuisance attribute projection (GMM- emphasized since the health care giver NAP) and Hidden Markov Model only need to edit and update patient’s (HMM) with NAP to improve record on the tablet, personal
URL: http://journals.covenantuniversity.edu.ng/index.php/cjet 42 Folorunso C.O., et al CJET (2019) 3(1) 38-60 computers (PC) or even smart phones, factors (GDEB). The GDEB factors hence the need to protect the patient’s classify features extracted from voice privacy as required by all source and tract factors and other governmental regulations. A safe pertinent features such as format data, authentication system must be put in having in mind that male and female place anytime such records are to be voices show both acoustic-phonetic accessed, hence the need for variations as well as physiological biometric-based access cannot be differences. The main idea was to disputed. Research showed that on- improve classification rate in speaker line signature integrated with voice recognition using few parameters. modalities is the most appropriate Scheffer et al [16] worked on two of means for the users in such the challenges facing voice biometrics verification system since tablet PC is technology. These challenges include built with the associated devices. non-ideal recording conditions (these Evaluation of hybrid system of online are often operational situation signature and voice-based biometrics problems such as noise, echoes, voice was carried out in this work. Dynamic channels and so on) and audio programming method of string compression. Adapting the SRI matching was incorporated for the International’s innovations which signature verification while off-the- arise from the Intelligence Advances shelf commercial software Research Project Activity (IARPA) development kit was used for voice Biometric Exploration Science and verification. Fusion of these two Technology (BEST) and the Defence methods were carried out at the Advances Research Projects Agency matching score level after (DARPA) Robust Automatic normalization of the data. The Transcription of speech (RATS) prototype of these hybrid systems was projects. The SRI’s approach uses tested using a small truly multi-modal various features excerpted from database of fifty users and an EER of speech which are demonstrated using 0.86% was reported. latest machine learning algorithm. Mazaira-Fernandez et al [15] came They recommended a general audio from the view of looking at the classification system that excerpts environment which has been so much metadata facts using i-vector. The improved by technology of social logistic regression and the cross media whereby some other people entropy was used to combine the uses these social media as a form of various features that are automatically terrorism to transmit their message. In extracted from the audio signal at the such a situation a typical biometrics i-vector level. recognition method such as face or Bhogal et al [17] research showed that fingerprints have been substituted by voice is a more natural means of another biometric traits such as voice communication and verbal as this may be readily available in communication is quicker and more such scenario. They proposed a efficient than textual communication. gender-dependent extended biometry Considering a virtual environment,
URL: http://journals.covenantuniversity.edu.ng/index.php/cjet 43 Folorunso C.O., et al CJET (2019) 3(1) 38-60 they evaluated the use of virtual out-perform one of the best face universe (VU) residents also known recognizer (Deep face) as Avatars in online service Khitrov [19] at the speech technology employing audio biometrics. The centre reviewed the use of voice- method for example can include, based biometrics for data access and spurring consumer applications with a security. He identified some demand for an utterance, managing challenges and advantages of the the response to the demand and system. developing a voiceprint or voice However, voice can be used with any summary of the speaker or participant. other biometric technology system in This voiceprint can be connected to an order to achieve 100% accurate avatar and when an utterance is recognition and verification. Voice- obtained, the avatar can be recognized based person identification system can by evaluating the utterance with the be used in the following areas to voiceprint. Such evaluation can be safeguard security and expedient user used to recognise avatars as they go verification. These areas include:- from one online service to another and 1. Call centres and interactive voice as such, voice biometrics can be used response systems (IVRs) such as to to verify an avatar for a particular get account balance, medical result activity. The main idea of their etc. which are private and highly research was that they used voiceprint sensitive information in order to to approve an operation limited to an save time while delivering these authorized user. In other word, they services to the rightful owners demonstrated the possibility of using once the system can recognize biometric in internet based activities. their voices. Zhang et al [18] came from the view 2. Mobile voiced based verification of the inability of a system to system helps in securing our recognize an individual from a non- sensitive and private information frontal view. They presented the stored on the smart devices. people in photo Albums (PIPA) 3. For cloud computing and Bring corpus with very high differences in Your Own devices (BYOD) pose, clothing, image resolution, applications, employees prefer the illumination and camera viewpoint. use of their personal smart devices They proposed the pose-invariant to access organization resources. Person Recognition (PIPER) There is a dire need to secure the algorithm to tackle the problem organizational information of these identified earlier. PIPER combines the smart devices. Hence the use of signals of pose-let level individual voice signature presents a natural, identifiers trained by Deep appropriate and legally binding Convolution Neural Network option to hand-written signatures. (DCNN) to reduce the differences in 4. Voice-based authentication system pose and then combine with a global can be employed to secure and recognizer and face recognizer. Result enhance security of our social obtained showed that this algorithm
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44 Folorunso C.O., et al CJET (2019) 3(1) 38-60
networking platforms such as unknown individual. The system will Facebooks, LinkedIn and so on. be successful in identifying the Vatsa et al [20] having researched into individual if the comparison of a various biometric technology, they biometric sample to a template in the identified some serious problems database falls within a previously set affecting this technology and they threshold. This mode can be used for categorise them into accuracy, positive recognition (so that the user computational speed, security, cost, does not have to provide any real-time attacks and scalability. They information about the template to be also identified the various possible used) or for negative recognition of attacks on biometric technology and the person "where the system these include impersonation, coercive, establishes whether the person is who replay attack, as well as the attack on he or she (implicitly or explicitly) feature extractor, template database, denies to be". The latter function can matcher and matching results to only be achieved through biometrics mention a few. In improving the since other methods of personal performance of biometric technology recognition such as passwords, PINs they identified two major ways one or cards are ineffective [6]. can protect the biometric information When an individual uses a biometric from such attack. These include system for the first time, it is referred encryption as well as watermarking. to as enrolment. During this process, They introduced a three level biometric data from the individual is Redundant Discrete Wavelet captured and saved. In subsequent Transform (RDWT) biometric uses, biometric data is sensed and watermarking algorithm to implant matched up to data saved at the time the voice biometric MFCC in a colour of enrolment. The storing and face image of the same person for recovery of such systems must be enhanced robustness, security and critically protected if the biometric accuracy. In biometric watermarking, system is to be robust. In Figure 3, the a particular quantity of information data acquisition phase is made up of also known as watermark is implanted some sensors, which act as link into the initial cover image using a between the real world and the private key such that the constituents system; it has to obtain the entire of the cover image are not altered. required data e.g. image or The result obtained was over 90% fingerprint. All necessary pre- verification accuracy. processing of the raw audio signal in
2.1 Biometric system architecture order to remove sensor noise and Biometrics system for identification unwanted sections are carried out in encompasses different stages as this phase using some kind of shown in Figure 3. standardization. The second stage is In recognition mode, the system the feature extraction phase, where executes a one-to-many comparison highly descriptive and discriminative against a biometric database in an features are extracted and represented. attempt to establish the identity of an This stage is a very important stage of
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45 Folorunso C.O., et al CJET (2019) 3(1) 38-60 a biometric system architecture. At Hamming distance). Decision is based the third stage, a vector of numbers or on the outcome of their evaluation an image with specific characteristic such as granting access or denial from is used to build a template. A template a restricted area [6]. is a representation of most descriptive The use of biometrics as a verification features. It is often created and then system consists of three phases. In the stored in a database for future use. first phase, a sample of a biometric During the enrolment phase, the feature is captured, processed and template is either stored on a card, stored in the database as a reference within a database or both. At the model for future use. In the second matching stage, the obtained input phase, some samples are compared features are passed to a matcher that with a reference model in order to see evaluates it with other current if the newly presented biometrics templates and estimate the distance matches or between them using a metric (e.g.
Figure 3: Biometrics system architecture, for identification process
Figure 4: Biometrics System Architecture, for Verification Process not, after which a threshold is or access is denied if the features do computed. During the third phase, not match. Positive recognition is a access is given if the feature matches common use of the verification mode,
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"where the aim is to stop many people biometric data each time they enrol" from registering into the system by [21]. using similar identity but separate
Figure 5: Word cloud of popular biometric signatures
Figure 5 shows the popularity of vi. Reducibility means the various biometrics used to develop extracted data should be person identification technologies. reduce-able to a file, The popularity is determined by these vii. Circumvention requires that key factors: universality, permanence, the property should not be collectability, uniqueness, masked or manipulated or acceptability, reducibility, even fooled, circumvention, privacy, performance viii. Privacy, demands that and inimitability. Brief explanations capturing process should not of these factors are presented as defy the privacy of the follows: individual, i. Universality implies that ix. Performance requires that the every person must possess identification accuracy should this characteristic, be very high, and ii. Permanence implies that the x. Inimitability means the attributes should not change attribute should be with time, irreproducible by other iii. Collectability requires that the means. properties must be suitable for 2.2 Commonly used algorithm in capture and measured biometrics technology quantitatively without delay, i. Artificial Neural Networks iv. Uniqueness means no two (ANN): ANN are people should have the same computational tools used for characteristics, analysing many complex real v. Acceptability implies that the world problems by using the system must be accepted by biological neuronal networks the majority, based on the structure and functions of neurons. It is made up of layers of computing
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neurons that are interconnected linear decision surfaces. Its uses by some weighted lines that are ranges from handwritten digit capable of performing very recognition to face recognition large parallel computations for to medicine [25], [27]. data processing. ANN has been iv. Hidden Markov Model used in various areas ranging (HMM): HMM is a statistical from speech recognition to tool used for demonstrating prediction as well as in generative sequences described medicine [22]–[24]. by a set of observable ii. Gaussian Mixture Model sequences. HMM is made up of (GMM): The GMM is a two stochastic processes which parameter based probability include the invisible process of density function, which is hidden states and a visible represented as a weighted sum process of observable symbols. of Gaussian element densities. The hidden state makes up the It is majorly used for measuring Markov chain and the continuous distribution features probability distribution of the in biometrics as well as vocal observed symbol depend on the tract associated spectral fundamental state. It is used for features in speaker recognition modelling time-varying spectral system. It can also be used in vector sequences [28]–[30]. automatic laughter recognition v. Deep Neural Network (DNN): system as well as hand Deep learning is a machine geometry detection [25], [26]. learning algorithm that is being iii. Support Vector Machine introduced to the area of large (SVM): SVM is an algorithm vocabulary speech recognition for solving a binary system. It has many hidden classification and regression layers as compared to the analysis problem. This artificial neural network (ANN) algorithm maximize margin by and it incorporates new method defining an optimal hyper- for training its data [30], [31]. plane. It is used for non-linearly The discussion on these algorithms separable problems. It also pros and cons are presented in Table maps data to higher component 1. area where it easily classifies
Table 1: Selected person identification algorithms pros and cons Algorithm Pros Cons i. ANN It has been used to train very It requires more data for training complex models. Choosing the right parameters may It is easy to conceptualize. be very complex. It has lots of libraries for Final model may use up a lot of easy implementations. memory. It can be used extensively Multi-layered neural networks are
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for academic research work. usually harder to train and require tuning of lots of parameter [32].
ii. GMM It is a lot more flexible with Learning may be a little difficult regards to cluster Few libraries for implementation covariance. [33]. GMM allows mixed membership of points to cluster. iii. SVM It reduces overfitting in the It can be time consuming to train. course of training. It manages high dimensional It may not be explanatory enough as problems. it does not return a probabilistic It is used for linearly and confidence value. non-linearly separable data. It does not support structured Its optimality is guaranteed representations of text which gives due to its convex high performance in Natural optimization. Language Processing (NLP) [34]. It can be implemented in various programming languages (Python, Matlab), and its libraries are easily accessible. iv. HMM It is highly flexible. It has a huge numbers of unstructured It is suitable for better data parameters. fitting. It can only represent a small fraction It is highly statistical in of the entire distributions. nature. Dependencies between layers may It can learn from raw data. not be explicitly represented [35], [36].
v. DNN It continuously grows data to It requires very large amount of improve its training. unlabeled data for training. It creates its new features. It requires very high performance hardware for its implementation. It requires more time to train [37].
3. Timeline of Biometrics technology The advancement of biometric recognition is still in progress, hence the need for continuous improvements in performance and usability.
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Figure 6: Biometrics timeline over the past one and a half centuries
3.1 Importance and application of as authentication. They also biometrics technology timeline employed palm and footprints to The importance of biometrics differentiate one child from technology cannot be over another [39], [40]. emphasized. There are various areas - 1800, Thomas Bewick, an English of applications of this technology naturalist, used the printing of his around the world. Among the various fingerprint to identify his applications are: published books [41]. - As far back as 1792-1750BC, the - 1856, Sir William Herschel, a kings of Babylon used the imprint British officer who worked for the of their right hand for Indian civil service, commenced authenticating the written codes of the use of thumbprint on law printed on clay and also for documents as alternative for business transactions [38], [39]. written signature mostly for - 618-907 Chinese use both illiterate and other people [39]. fingerprint and handprint on clay
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- 1892, Juan Vucetich, an intensifies, different biometric Argentinean police researcher used traits were used to verify fingerprint to identify a mother in electorates during election. the murder of her children, hence, Somaliland was the first to use the Argentina was the first Country to iris biometrics voting system in the substitute anthropometry with world [47]. Also some other fingerprint [42], [43] . countries throughout the world - 1920s, fingerprint identification also implement biometrics was employed by the law technology for election purpose, enforcement all over the world among them are Kenya, Nigeria, including the US military and the Ghana, Angola which implements Federal Bureau of Investigation the fingerprint biometrics system (FBI) as a form of identification to identify registered voters. So [39]. many other biometric technology - 1974, first commercial hand have been used over the years all geometry system for access over the world[48]. control, time, attendance and - 2001, Face Recognition was used personal identification became at the Super Bowl in Tampa available [40]. Florida [49]. Also, Malaysia was - 1975, FBI sponsors the one of the first countries to development of devices and implement thumbprint on her minutiae extracting expertise [44]. national Identity card. Australia - 1996, Iris scanning was included chips for biometric implemented in prison in USA identification on the international [45]. More so, the hand geometry passports. In addition, Canada recognition system was used biometric for anti-terrorism implemented at the Olympic measure [39]. games where over 65,000 people - 2002, the enhanced Border were successfully enrolled [46]. security and Visa Reform Act was - 1998, Nationwide Building put into law. This act include Society in Britain introduced iris biometric data in the passports of recognition within its cash VISA waiver program travelers dispensing machine in substitute of like Belgium and other Union the Personal Identity Number Member States [39]. (PIN)[45]. - 2003, US Government National - 1999, National Bank United in Science and Technology Council, USA introduces the iris inaugurated a subcommittee on recognition technology to three biometrics to coordinate ATM outlets in Houston, Dallas biometrics research and and Ft Worth [45]. development, policy, outreach and - Late 1990s and early 2000s international collaboration [50]. biometrics was introduced for Also, in December 2003, the verification of electorates during United Linkers Company was born election. As research in this area in India. This company offers
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biometric solutions in car security consist of fingerprint, iris, facial implementing various biometrics images and DNA samples [39]. system ranges from voice to - 2010, US national security fingerprint [51]. apparatus employs biometrics for - 2004, US implemented biometrics terrorist identification [40]. In into immigration services and it addition, SBTel and devices was tagged- US-Visit. Also, US commenced the selling of government called for compulsory biometrics devices for attendance government-wide personal and access control solutions in identification card for all federal Nigeria [50]. workers and contractors [50]. In - 2011, Biometrics identification addition, Europe adopted the use was employed in the identification of biometric system for passports of Osama Bin Laden. Also. SBTel, and travel documents using both a biometric device vendor, facial images and fingerprints [39]. launched web based biometrics - 2005, OMRON Corporation show attendance for a cloud-based case the world’s first face attendance system [50]. recognition technology at the - 2013, Apple included fingerprint security show tagged Japan 2005. scanner into smartphones [40]. This technology can be deployed - In January 2017, Australia’s on Personal Digital Assistants Department of Immigration and (PDAs), mobile phones and other Border Protection announced mobile devices with camera strategy to execute a novel system function [52]. Moreso, seven at the country’s international countries in Europe consisting of airport by 2020. This biometric Austria, Belgium, The system makes use of face, iris Netherlands, France, Germany, and/or fingerprint recognition Luxembourg and Spain signed an system. The biometric system is agreement on the improvement of intended to replace the existing cross border information exchange paper identity card passports [54]. and data comparison using DNA In addition, in January of the same profiles, fingerprints and vehicle year, President Donald Trump registration data [39]. ordered that all non-citizens be - 2008, US Government commenced subjected to biometric checks the organization of the use of while entering or leaving the biometric database [40]. Also [53] United States [54]. Moreover, in presented an experimental result August 2017, First-Biometrics on fusion of iris and palm print for announces the use of next multi-biometric system. The result biometrics flexible fingerprint obtained showed a very great sensor for smart payment and improvement on a single biometric identity card [54].
system. In addition, FBI set up a 1- billion dollar database which
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3.2 Evolution of voice-based constructed a phoneme recognition system recognizer which identifies four The initial objective of speech (4) vowels and nine (9) recognition was to develop a system consonants [55]. which imitate a person’s speech - 1960s – Atal and Itakura communication ability. invented the basic theory of - 1773 – The Russian scientist Linear Predictive Coding (LPD) Christian Kratzenstein, a which abridged the professor of physiology in approximation of the vocal tract Copenhagen created vowel reponse from speech waveform sound with the use of resonance [55]. tubes which was attached to the - 1962 – IBM shoebox was organ pipes [55]. developed and it can understand - 1791 – Wolfgang Von Kempelen 16 English words [56]. in Vienna developed the acoustic - 1971 – Alexander Waibel, mechanical speech machine [55]. developed the Harpy machine at - Mid 1800s – Charles Wheatstone Carnegie Mellon University. constructed Von Kempelen’s This machine can understand speaking machine employing 1,011 words with some phrases resonators from leather such that [56]. different speech-like sounds - 1970s – Tom Martins started the could be produced by using hand leading speech recognition to change the configurations company named Threshold [55]. Technology incorporation - 1879 – Thomas Edison building the first Automatic discovered the first dictation Speech Recognition (ASR) machine [56]. product known as VIP-100 - 1930s – Homer Dudley system. Also, Lenny Baum of developed a speech synthesizer Princeton University discovered called Voice Operating a mathematical speech Demonstrator (VODER) which recognizer called the Hidden was an electrical prototype of Markov Model (HMM). In Wheatstone’s work [55]. addition, the use of pattern - 1952 – Davis, Biddulph and recognition technology to speech Balashek of Bell laboratories identification system using LPC developed Audrey a system for was introduced [55]. segregated digit recognition for a - 1980s – The use of Artificial particular talker [55]. Neural Network was introduced - 1950s – Oslon and Belar of RCA for speech hence; speech laboratories constructed a ten recognition tends towards (10) syllable recognizer for a prediction. particular talker[55]. - 1986 – IBM Targora was - 1959 – Fry and Denes of developed employing the HMM University College in England to predict the next phonemes in
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speech. This system was the Although, there are many challenges world’s fastest typist at the time that are needed to be addressed in as it was able to recognize up to order for these systems to be robust 20,000 English words and a and more accurate (Table 2). A major number of sentences [56]. challenge of these systems is spoofing - 1990s – The emergence of attack. It is a condition whereby a Automatic Speech Recognition person effectively impersonates (ASR) [55]. another person. This is often done in - 1997 – The world’s leading order to gain an illegal access to a uninterrupted speech recognizer facility or system.
was announced as a Dragon’s 3.4 Areas of implementation of naturally speaking software. This Voice-based recognition system software was able to understand 1. For attendance system 100 words per minute without 2. In mobile phone for auto texting any break in between the words 3. Forensic [55]. 4. Banking and financial - 2006 – The National Security institutions Agency (NSA) commenced the 5. Using one’s indigenous language use of speech recognition to for recognition purpose. identify key terms in recorded 6. In medicine. speech [56]. 7. Assisting the aged in text - 2008 – Google introduces a composition, bank transaction voice exploration app on mobile and many more devices [56]. 8. According to Boyd [56], “cloud- - 2011 – Apple launches Siri, for based computers have entered voice based digital assistant [56]. millions of homes and can be 3.3 Benefits and challenges of controlled by voice, even biometrics systems offering conversational responses Despite this progress, a number of to a wide range of queries”. challenges continue to restrain the full 9. Voice activated home speakers. potential of biometrics to 10. Purchases can be made over the automatically recognize humans. internet using voice enabled Some specific challenges, in terms of machines. biometrics groups, are presented in According to Akhtar et al [57], the US Table 2 [6]. National Institute of Standards and The need for a reliable system for Technology enumerate the person identification cannot be over- susceptibility of biometrics to emphasized, while the state-of-the-art spoofing in their national vulnerability biometric identification systems are database. Most of the existing taking over access control and many biometrics systems are susceptible to security establishments. These this attack. For instance, the iris, systems have been in existence for finger print and face images taken over five decades, though it started from impersonators were identical gaining attention in recent time. with that of the real users. In order to
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54 Folorunso C.O., et al CJET (2019) 3(1) 38-60 cub this attack, there is a need to to reduce this attack [58-60]. Thus, introduce a liveness detection into more studies are required in this biometrics systems. This is an area of direction. Finally, biometric trait and future research. In addition, the use of databases are needed in order to different biometric systems validate new biometric systems such combination that is a multi-modal as the use of tongue, ear, sneeze, biometric technology has the potential cough, laughter and so on.
Table 2: Benefits and challenges of Biometrics systems
4. Conclusions multiple biometric features in order to Even though there are some ensure very high reliability is challenges facing biometrics essential. Investigating new biometric technology, it has tremendous usage features for identification is an area in this information technology age. where more research is needed to be Choice of biometric type depends on carried out. characteristics measurement and user Having considered the advancement requirement. Other factors which in technology, moving from the use of affect the choice of a biometric based paper to electronics and online base are sensor and device availability, medical records to banking and computational time and reliability, financial industry as well as social cost, sensor size and power media. The huge and sensitive data consumption. In addition, cultural involved must be adequately protected disposition is also a factor that affects from being hacked into. Voice-based biometric technology selection. recognition system has however, been Currently, due to divers’ nature of considered as a very appropriate biometric applications, no single biometrics for this task having biometric trait is likely to be ideal and considered the speed, efficiency and satisfy all the requirements of all customer relation characteristics it applications, hence the need to use possesses.
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According to [56], “Voice is the Acknowledgements future. The world’s technology giants The authors wish to acknowledge are clamouring for vital market share, Ighravwe D. E. for taking his time to with ComScore agitating that 50% of peer review this work. all searches will be voice searches come 2020.”
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Covenant Journal of Engineering Technology (CJET) Vol.3 No.1, June 2019 ISSN: p 2682-5317 e 2682-5325 DOI: 10.20370/1v2e-pd60
An Open Access Journal Available Online
Community-Based LDPE Wastes Recycling Machine
I. D. Okeke 1, T. M. Ibezim 1, O. T. Ndusorouwa 1, U. C. Okonkwo1 & I. P. Okokpujie 2
1Mechanical Engineering Department, Nnamdi Azikiwe University, Awka 2Department of Mechanical Engineering, Covenant University, Ota, Ogun state, Nigeria
Received: 21.04.2019 Accepted: 26.06.2019 Date of Publication: June, 2019
Abstract: Several efforts have been made to proffer solution to the burden placed by plastic wastes on man’s environment. However, the conspicuous presence of these solid waste pollutants in the communities suggests that the efforts made so far only yielded little result. In this study, a small scale hot extrusion process machine which recycles low density polyethylene was designed and constructed. The machine is powered by a 2 Horse power, 3- phase electric motor which transmits a torque of 200N.m at a speed of 37 rpm through a gearbox with the velocity ratio of 20:1 to a 34 diameter single screw. Low density polyethylene materials were fed in through the hopper. The heat from the heater bands and friction and pressure generated along the transition zone of the screw provided the energy needed for the transformation of the materials conveyed to a well-blended molten state. The extradites were channelled to the cooling tank for heat extraction and then collected as raw materials for the plastic industries. It is recommended that providing this machine in our communities will contribute greatly to achieving a greener environment and creating entrepreneurial opportunities in the society, thus contributing to the achievement of the sustainable development goals. Keywords: Low density polyethylene, recycling, sustainable development, entrepreneurship
1. Introduction disposal of plastic wastes has attracted The setting of the sustainable serious attention globally. The united development goals by the United nation’s world environmental day Nations stirred up global concerns 2018 had the theme “beating plastic about the impact of man’s activities pollution” [1-2], capturing the on the environment and the future concern of the international generation. The indiscriminate community to bring to an end the
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61 I. D. Okeke, et al CJET (2019) 3(1) 61-75 menace of plastic pollution, knowing chopper from where it moves to the that it is fundamental to achieving a barrel. A screw inside the barrel is green, sustainable environment. It is rotated by the geared electric motor. estimated that about eight metric As the screw rotates, it conveys the tonnes of plastic are thrown into the polyethylene material to the heated ocean annually [3]. zone of the barrel. From there it The non-degradable polythene moves form the orifices provided at plastics used as commodity goods the end of the barrel. The machine storage and packaging purposes takes time to heat up and after melting accounts for over 60 million tons of of the polyethylene there is always a annual wastes generation worldwide remnant molten polyethylene that gets [4]. It was also reported that 30 % of stuck inside the barrel and this the domestic waste in a typical prevents the screw from rotating. This Nigerian city comprises of the is a major challenge that is facing this polythene and plastic products in very model of polyethylene recycling large quantities; whose disposal has machine. continued to constitute the great Odior [7] developed a polyethylene environmental pollution challenge and recycling machine from locally concern in big and small cities [5]. sourced materials that uses rotary and Since the majority of these wastes are forced blades for slitting the loaded generated at the grass root, it is wastes. Knife penetration first causes logically sound to think of a solution compaction accompanied by frictional that would engage and empower heat. It produces a cutting and heating individuals at this level to action which partially melts the competently manage these pollutants, compacted waste producing thick hence the need for a locally made shreds. The machine uses rotary machine which can be easily operated blades which are rotated by a single with little skill. phase, high speed electric motor. The
2. Review of Locally Made rotary blades helped to improve the Polyethylene Recycling Machine machine performance. The machine Gbasouzor [6] designed a model produces an average of 35kg of small polyethylene recycling machine with flakes of recycled wastes per hour at a economic development and pollution machine speed of 2880 rpm. control in view for the Country, Ugoamadi [8] optimized the Nigeria. The machine was designed to development of a plastic recycling operate at a temperature of 200 – machine that minimizes the 2200C and requires 1hr 45mins for limitations of the already existing heating up before melting the ones to a great extent and at the same polyethylene. This machine makes time ensuring effective waste use of thermostat, a heating element, management. The machine is powered electric motor, gears, screw conveyor, by a 3Hp and 900rpm electric motor, coupling and keys. Polyethylene that while the conveyor shaft runs at has been cut and dried is feed into the 268rpm. It has a capacity of 265kg/hr waste recycling rate and an efficiency
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62 I. D. Okeke, et al CJET (2019) 3(1) 61-75 of 97 percent. The results presented levels of noise and friction, which are show that for every plastic fed into the undesirable. hopper, at 2000C the plastic was 3. Materials and methods converted into a molten state. The 3.1 Extruder Screw machine employs the principle of 3.1.1 Screw diameter selection conveying and heating to effect The choice of 34 mm screw was shredding and melting of the materials primarily arrived at considering the fed through the hopper, and requires overall size of the extruder desired only two persons to operate. The use since other parts of the machine of chain drive in this model from the directly or indirectly relates to it as electric motor could lead to high shown in Fig. 1.
Fig. 1: CAD design of the extruder screw
3.1.2 Length of screw; This is determined from the length to diameter (L/D) ratio of the screw. Feed section depth (Fd) = 0.2D= This is the ratio of the flight length of 6.8mm (2) the screw to the original diameter of the screw. Transition section length A ratio of 10:1 was selected for portability.
This also implies that the flight length Metering section length of the screw is equal to 10D or 340mm. The feed section, transition section and metering sections of the screw are Metering section depth in the ratios of 3D:3D:4D respectively.
3.1.3 Design Calculations For standard screw profiles, the angle Feed section length that the flight makes with a line
URL: http://journals.covenantuniversity.edu.ng/index.php/cjet 63 I. D. Okeke, et al CJET (2019) 3(1) 61-75 perpendicular to the shaft (flight Selected speed= 38rpm angle) is 17.6568o [9] Bulk density of LPDE (( 0) Pitch of the screw (Lead) =590kg/m3 [11] Throughput rate
Where φ = the flight angle Flight width (screw thickness) Substituting values for this gives
Screw channel width 3.1.5 Screw Power Requirement To achieve this, the total power required for the entire extrusion
Screw (in a smooth barrel) process would first be calculated. The energy required to raise a standard conveying efficiency kilogram of the material by 10C is [10] referred to as the specific heat Screw-barrel clearance ( FLT) = capacity (CP). Its value for LDPE is 0.0017D= 0.17 ×34 = 0.0578 mm 2300 J/kg.k [12] Distance between screw root and Initial temperature LDPE T1=250C or barrel internal wall (H) = S+ FLT 298k (8) Final temperature of LDPE (melting point) T = 1150C or 388k 2 The power required to just melt the Internal diameter of barrel screw
Allowance for energy losses 3.1.4 Screw throughput rate and Power is lost the cooling section, speed The speed and through put rate of the gear reducers and the surrounding recycling machine are interdependent. environment. This accounts for Therefore, either of the two has to be about 30% of Pactual [13] fixed so as to allow the calculation of the other. Speed or throughput of the Therefore, the total power required machine is a factor that the designer for the extrusion process, has to choose based on what work the machine is expected to do. An overview of speed specifications for standard screws in their This power would be enough to manufacturers’ datasheet reveals that drive the screw at full load similar screws run on speeds between neglecting the weight of the screw 20rpm and 130rpm. This depends on and frictional losses. To prevent the material to be extruded and the extrusion process to be adopted. hitting this limit during operation,
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64 I. D. Okeke, et al CJET (2019) 3(1) 61-75 some additional 15% of the actual This is the difference between the power requirement would need to volume of the barrel and the volume be added to serve as reserve power of the screw. and reduce the load of the screw. Volume of barrel (Vm) The volume of the barrel,
The rotation of the screw contributes the greatest percentage of the total power requirement of Where r = internal radius of barrel the extrusion process [14]. L = total length of the barrel occupied Therefore, screw power by the material requirement L = 473.645mm + 30mm = 503.645mm Therefore,
Screw power requirement
Volume of Screw 3.2 Barrel design The screw has an irregular geometry; The barrel is a thick walled cylinder therefore, the volume was evaluated that houses the screw and part of the using the CAD model of the screw material housing. Its primary function with Inventor software presented in is to provide a chamber for pressure Fig. 2. It is noteworthy that only the build up. It has flanges at both ends to flight length of the screw was used, as provide coupling surfaces for the die that was the only portion of the screw head and the bearing housing. immersed in the material in the barrel. Theoretical Volume of the Material in the barrel (Vm)
Fig. 2: Analysis of the flight length of the screw
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65 3.3 The Heater bands Resistance of each heater is given From the CAD analysis: Mass of the by: screw flight length = 1.854 kg, Area of the screw flight length = 46139.508mm2 Volume of the screw flight length= Where: 3 229,486.505mm Pr= resistivity of the heating Total Volume of material in the element at 20oC which is equal to barrel, Vm = Volume of barrel – 1.1 x 104 cm Volume of screw L = average length (circumference) of the heating
element = 2.408m
62 3.3 The Heater bands Quantity of heat required to melt There are three band heaters on the the mass of the material: extruder made up of aluminum and From earlier calculations, total power nichrome alloys, the energy required to drive the system is given contribution of one of the heater was as 2001, the shear force from the computed and multiplied by three to screw rotation contributes 70 to 80% get the total contribution of the of the total power requirement to melt heating system. the material, while the rest is supplied Heater type: aluminum band heater by the heater bands, taking a ratio of heating element nickel chrome: 60% to 40%, the energy requirement (nickel and chromium alloys) heater from the heater band (quantity of heat band diameter is 76.67mm, heater required to melt the material) is given width is 96.67mm (for the die head as shown in equation (19); heater band). 40% of 2001.125W = 0.4 x 2001.125 maximum lead amperes are = 800.45 watts (joules/sec) approximately 13.5A, voltage supply was 220V. 3.4 Temperature at which to set the controller The watt density for this heater From Fourier’s law type is rated at (50W/ in2) which are approximately (7W/cm2)
Surface area of each heater is T1 = set temperature for the given by equation (16) - (18): controller T = temperature at which the low 2 density polythene melts which is 1150 C K = thermal conductivity for high carbon steel = 43 W/m 0 C
66 I. D. Okeke, et al CJET (2019) 3(1) 61-75
A = area normal to the direction of Angular velocity of the electric heat flow, equivalent to the surface motor, area the heater Heater bands 1 & 2 = 2 (70 x 100) = 14000mm2 Heater band 3 = 70 X 150 = 10,500mm2 Heater band 4 = 150 X 30 = Power of the electric motor = torque × 4,500mm2 angular velocity Total Area = 29,000mm2 = 0.0029m2 Where r = radius of the small pulley = 80/2 mm = 0.04m Therefore, power transmitted by the electric motor pulley to the gearbox, = 150.82 ×.04 = 0.90kW
Torque of the electric motor,
3.5 Electric Motor Selection The power of the electric motor 63 is Where P = Power of the electric usually expressed in horsepower (Hp) motor in Watts as presented in equation (21) [15]. N = Number of revolutions Hp (3-phase motor) of the electric motor shaft = The electric motor selected has the following parameters, P = 1.5 kW, N = 1440 rpm Therefore, the torque of the electric Where V = voltage of the required motor, electric motor, I = current required by the electric motor 3.6 Gear Box Selection P.F = power factor of the electric With a speed of 37 rpm of the shaft, motor the selected motor has a speed of V= 220v I= 4A, P. F= 1.1 (gotten 1440rpm from chart for a light medium screw) Note: Input speed of the gear box is Efficiency = 95%. approximately half the electric Substituting the above gives Hp = motor’s velocity ratio 1.94hp. = . A 2 horse power electric motor was selected. The selected electric motor has a speed of 1440rpm (from the name plate).
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The closest velocity reduction gear in Where the market was 20, thus a 1:20 gear box was selected. The torque of the gearbox is a product Length of the chosen belt, L = of the electric motor torque and the 850mm, D = 150mm, d = 80mm gearbox velocity ratio [25].
Therefore, the torque of the gearbox,
3.1 Belt Selection Therefore, From Fenner catalogue for belt drives 1997 the equation (26) is applied [16]
Belt length, 3. Results and Discussions 3.1 Throughput Efficiency Evaluation of the actual throughput Where L = required length of the belt of the machine: in mm C = approximate centre This was calculated by obtaining the distance in mm mass of materials extruded in five D = diameter of the gear box pulley in different intervals, finding their mm average and converting to mass per d = diameter of the electric motor second. pulley in mm The Table 1, shows the results of the findings
Where, D = 150mm d = 80mm Table 1: Mass of Extruder and Time S/N Time Mass of extruder (mins.) (kg) From equation (26) 1 1 400.54 x 10-3
2 2 400.30x10-3
From the above calculation the 3 3 400.12x10-3 maximum length of the belt will be 4 4 400.0 x 10-3 908.4mm but because of slipping a lower standard belt will be selected. 5 5 399.92 x10-3 The standard v-belt available within this range is A32 (850mm) according From the Table 1, to belt catalogue available [17]. Mass of the extrude per minute For accurate Centre distance (CA)
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4.3 Volumetric Efficiency The volumetric efficiency is the ratio of the actual volume of material the machine can process to the total Mass of extrudate per minute = volume of material contained in the 400.176 x 10-3kg barrel. Actual Mass flow rate From our design calculation the theoretical volume of material the machine can process has been calculated as
Throughput efficiency 4.3.1 Actual Capacity of Barrel = The feed section of the screw only conveys materials to the transition η 3.2 e = zone where the actual melting and Thermal efficiency pressurization operation begins, thus The heat energy in the extradite is is an idle part of the screw in respect calculated using to useful work done on the material. Feed section length = 129 where Barrel feed section volume mactual= actual mass flow rate T = measured temperature of the 2 extrudate = 1000C = 373K
T = ambient temperature = 250C 1 Therefore, the actual volumetric =298K capacity of the barrel is the volume Heat energy possessed by the occupied from the transition zone to extrudate the die head [18]. = 6.669 x 10-3 x 2300 x (373 – 298) 4.3.2 Screw feed section volume = 1150.40W (Sfsv) Heat input = 1500W (obtained earlier) This was easily evaluated using the Thermal efficiency = x 100 physical properties of the feed section 65 = 76.69% from the CAD design as shown in Fig.
3
69 I. D. Okeke, et al CJET (2019) 3(1) 61-75
Fig. 3: Analysis of the Screw Volume
Fig. 3: Analysis of the Screw Volume
3 Sfsv = 45,173.099mm Feed section material volume,
= 68.414 % From the calculations above, the Volumetric efficiency, efficiency of the machine is obtained to be about 83.16%
4.4 Evaluation of the relationship between machine variables 4.4.1 Die swell variation with temperature procedure is presented in Table 2.
Table 2: Die swell variation with temperature Procedures Machine set 1 156 171 186 201 216 231 temperature 4 1 Length of die 2. 2.5 2.3 2.2 2.1 1.5 0.9 swell (mm) 7
The machine was operated at a rate of extrudate were obtained at constant speed of 37rpm and a feed varied temperature ranges and the
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70 I. D. Okeke, et al CJET (2019) 3(1) 61-75 maximum die swell effect length The plot obtained is shown Fig. 4 obtained for each of the temperatures.
Fig 4: Effect of Temperature on Die Swell size graph
4.4.2 Feed rate/Throughput versus each set contained feed batches of screw speed relationship equivalent weights the machine was The aim of this is to investigate the fed continuously with each batch for a effect of increasing feed rate on screw duration of two minutes before speed and throughput and obtain the moving over to the next set of feed rate at which optimum batches. The machine was set at a throughput is obtained. fixed temperature of 150oc. The result Procedure of LDPE materials were so obtained is shown in Table 3 and divided into sets of varying weights from Fig. 5 to 9:
Table 3: Feed Rate and Time Time (mins) 0-2 2-4 4-6 6-8 8-10 10-12 12- 14- 14 16 Feed rate (g/s) 2.47 4.94 7.41 9.88 12.35 14.82 17.29 19.76 Screw 37.0 36.8 36.6 36.5 36.0 35.4 35.4 34.3 speed(rpm) Throughput 2.30 4.0 7.40 9.33 11.0 10.40 10.05 9.30 (g/s)
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71 I. D. Okeke, et al CJET (2019) 3(1) 61-75
Fig 5: Feed rate versus screw speed relationship graph
Fig 6: Feed rate versus throughput rate relationship graph
Fig 7: Determination of optimal feed rate graph
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Fig 8: Exploded view of the LDPE recycling machine LDPE recycling machine
Fig. 9: Isometric of the LDPE recycling machine
5. Discussion of results increase in temperature on die swell From Fig. 4, the length of die swell could not be evaluated as the material decreased with increase in could no longer be handled temperature. At a set temperature of It was also observed that the feed rate- 200oc which translates to an internal throughput graph (Fig. 6) reveals a barrel temperature of 175oc, the die linear increment at the initial phase of swell length decreased sharply. This feeding, but a point is reached at was not as a result of elimination of which the increase in feed rate does the die swell but rather a significant not increase output. The feed rate transition of the material from molten above12g/s would be detrimental to to almost liquid state. The effect of the machine’s effective operation.
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73 I. D. Okeke, et al CJET (2019) 3(1) 61-75
The effect of screw speed on both the from the result analysis, increase of feed rate and throughput rate was the feed rate will affect the examined by plotting them on the performance of the die swell of the same graph in Fig. 7. It was observed LDPE waste recycling machine. that at a speed of 36.6rpm, the 7. Recommendations throughput and feed rate coincided. A - Although the machine does not need further increase in feed rate slightly much technical knowhow, it is increased throughput and then yielded important to give the operators an no further increase in throughput, introductory training to enhance rather it decreased the speed and efficiency and safety. efficiency of the machine. Therefore, - Low density polyethylene wastes feed rates of 7g/s should be the should be properly sorted and optimal feed rate to run the machine processed to avoid introducing at optimal efficiency. impurities that would make the 6. Conclusion resulting pellets unfit for use as raw Community-based LDPE wastes material in plastic industries. recycling machine had been design - Members of the community should and tested. The result shows that the device lucrative means of gathering efficiency of the machine is 83.16%, waste LDPE materials so as to Thermal efficiency 76.69% and ensure effectiveness of materials Volumetric efficiency 68.414 % collection during operation. Therefore, the - Community policy makers should machine performed better at the enact regulations that discourage optimized parameters of feed rate of 7 collective disposal of plastic wastes g/s, temperature between 150oC and with biodegradables. at screw speed of 36.6 rpm. However,
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bins, University of Ilorin, June, output-should-you-expect. Ph. D (Civil) seminar, Faculty of Retrieved on September, 2015. Engineering &Technology, [13] Nana L. Njobet. Energy Analysis Unpublished, 21pp. in the Extrusion of [6] Gbasouzor A. I., Ekwuozor S.C. plastics.Degree thesis on Plastics and Owuama K.C.(2013). Design Technology Engineering 2012. and Characterization of a Model [14] Electric motor Polythene Recycling Machine for www.engineeringtoolbox.com. Economic Development and Retrieved on May2018 Pollution Control in [15] Igbinigie, O., Okokpujie, I. P., Nigeria.Proceedings of the World Dirisu, J. O., Igbinowmahia, D. Congress On Engineering, July I., & Okokpujie, K. O. (2018). 3-5, 2013 London U.K. Development and Performance [7] Odior A. O., Oyawale Festus A. Analysis of Horizontal Waste and Odusote Joe K (2012). Paper Baling Machine. Development of a Polythene International Journal of Recycling Machine from Locally Mechanical Engineering and Sourced Materials Vol 2, No.6, Technology (IJMET), 9(10), 84- 2012. 101. [8] Ugoamadi C. C., Ihesiulor O. K. [16] Okokpujie, I. P., Okokpujie, K. (2011) Optimization of the O., Ajayi, O. O., Azeta, J., & development of a plastic Obinna, N. N. (2017). Design, recycling machine. Nigerian construction and evaluation of a Journal of Technology Vol. 30, cylinder lawn mower. Journal of No. 3. Engineering and Applied [9] Flight angle. www.slideshare.net Sciences, 1254-1260. Retrieved on May, 2018. [17] Okokpujie, I. P., Okokpujie, K. [10] Understanding plastic O., Nwoke, O. N., & Azeta, J. engineering calculation, screw (2018). Design and profile, screw zone of a single Implementation of 0.5 kw screw extruder. Horizontal Axis Wind Turbine [11] Polyethylene Bulk density for Domestic Use. In www.sabie.com/enrope/a/product Proceedings of the World s/polymer retrieved on Congress on Engineering (Vol. 21/09/2015. Specific heat of 2). LPDE [18] Okokpujie, I. P., Okokpujie, K. www.makeitfrom.com/compare/ O., Salawu, E. Y., & Ismail, A. highdensitypolyethylene. O. (2017). Design, Production Retrieved on22 June 2018 and Testing of a Single Stage [12] Screw Power requirement Centrifugal Pump. International www.ptonline.com/volume/what- Journal of Applied En
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Covenant Journal of Engineering Technology (CJET) Vol.3 No.1, June 2019 ISSN: p 2682-5317 e 2682-5325 DOI: 10.20370/mhb5-vm51
An Open Access Journal Available Online
Ship Propeller Performance Prediction under Cavitation
Thaddeus C. Nwaoha1* & Sidum Adumene2
1Marine Engineering Department, Federal University of Petroleum Resources, Delta State, Nigeria 2Marine Engineering Department, River State University of Science and Technology, Rivers State, Nigeria
Received: 21.11.2018 Accepted: 06.3.2019 Date of Publication: June, 2019
Abstract: In this study, numerically prediction of the screw propeller design that can overcome cavitation is conducted. The research presents a simplified regression model for the analysis of the geometric area ratio, pitch ratio and open water efficiency of propeller, with the aim of revealing quantitatively the effect of cavitation on propeller open water efficiency. The case study takes into consideration factors that can enhance the performance of a propeller. Area of the propeller disc, propeller pitch ratio, diameter of the propeller, delivered power, thrust coefficient, torque is used as inputs into the model, in prediction of performance for cavitated and non-cavitated propellers. Sensitive analysis is carried out by percentage increase and reduction of the blade area ratio, so as to know the effects on the propeller performance. It is revealed that for every 1% increase in the expanded blade areas, the open water efficiency decreases at 0.12% and 0.15% for the non- cavitated and cavitated propellers respectively. This indicates a performance reduction by a cavitation factor of 0.03. The study further shows that at 7.5% reduction in the expanded blade area ratio, the propeller performance in terms of open water efficiency, increases by 1.85%. The analysis exposed an appropriate and accurate operating envelope for optimal screw propeller performance, thus revealing a way of minimizing cavitation effect. Keywords: Propeller; Cavitation; Regression model; Efficiency; Ship
1. Introduction space at equal angle about the axis. As Screw propeller of a ship is regarded the propeller rotates, the face of the as a helical surface which on rotation blade increases pressure on the water screws its way through the water. It with the aim of propulsion of a ship. consists of a hub and blades that are The design and analysis of modern, URL: http://journals.covenantuniversity.edu.ng/index.php/cjet 76 Thaddeus C. Nwaoha & Sidum Adumene CJET (2019) 3(1) 76-90 loaded and highly screw propeller is when there is displacement of the important in the marine field [1]. The water by the propeller blade profile; growing demand of heavily loaded, pressure difference between the highly efficient propeller that is suction and pressure surfaces of the associated with low level noise and propeller during rotation; and the vibration onboard, makes the design periodic fluctuation of the cavity of marine propeller more complicated. volumes caused by the operation of The propeller converts precious power the vessel behind. Three-bladed into forward motion, and if it is propellers have generally proven to be mismatched or damaged, optimal ship the best compromise between blade performance is hindered [2]. area and efficiency [5]. Four or five Therefore, it is mandatory to choose bladed propellers are useful for two the correct propeller type and size to reasons. First their extra blades create prevent cavitation from occurring, more total blade area with the same or which can pose threat to ship less diameter and vibration is reduced propeller optimal operations. to great extent as compared to three However, design of propeller and its blades [6]. efficiency also depends on other 1.1. Screw Propeller Performance several factors [3]. A propeller blade shape will affect its The choice of the number of blades performance [7]. Some propellers are plays a significant role in marine progressively pitched. Cavitation does propeller performance. Marine screw not really affect progressive pitched propeller usually has two, three, four propeller because the leading edge is a or five blades. Four blades are the lower pitch, thus water is moved most common, but [4] revealed that under less pressure differential. The most efficient number of blades is the water then flows along the blade one blade type. This is because the surface, increasing the pitch toward single blade can handle effectively the the trailing edge and this gives higher water flow ahead of it. However, there efficiency. Performance of a propeller has been doubt in this conception, depends on speed of rotation, pitch of because a single blade would be the blades, diameters and surface of impossible to provide balance loading blades [7]. A combination of these in operation. The next most efficient factors creates a thrust which is is two blades, but this can be transmitted to the thrust bearing by impracticable because a propeller with the transmission shaft and propels the a very large diameter that can hull through the water. Before the accommodate large blade area will be propulsion system moves the hull, it is needed for generation of large amount mandatory to match the engine and of thrust. In view of this, most propeller. This entails matching unto propellers have three, four or five the engine on a diagram known as blades [2]. Propeller blade normally engine/propeller matching curve [8]. experience problems such as 1.2. Cavitation Phenomenon vibration, noise, cavitation etc. The advancement in the development According to [5], noise is experienced of high-speed hydraulic machinery URL: http://journals.covenantuniversity.edu.ng/index.php/cjet
77 Thaddeus C. Nwaoha & Sidum Adumene CJET (2019) 3(1) 76-90 and marine propellers has been metal can long withstand this erosive accompanied by appearance of effect and after a period as short as a cavitation [9]. It is a phenomenon that hundred hours, steel plate that was occurs in highly loaded propellers in previously smooth was found to which beyond certain revolutions visibly roughen [13]. results to a progressive breakdown in The avoidance of cavitation and the flow and consequent loss of thrust erosion has therefore become an [10]. It was first thought to be an important requirement in the design of oxidation of the metal by free oxygen, nearly all propellers [12]. Detailed liberated from the water at points of predictions of cavitation performance low pressure, but investigation has are now possible using high level shown it to be a mechanical action. mathematical models, but such Cavitation do not only cause noise methods are hardly appropriate at the and vibration but pitting in the regions early design stage. Normally, the where cavitation bubbles collapse blade surface area is selected using takes place, forming the sponge-lie empirically derived cavitation criteria, surface that is characteristics of which is a function of the propeller cavitation erosion [10, 11]. dimensions, the operating conditions These pits are thought to be caused by and of the immersion of the propeller the repetition of mechanical stress [13]. from the impact wave or the micro-jet The problems related to propeller produced in the liquid as the performance in most cases be traced cavitation bubbles collapses. The to a lack of knowledge during the erosive effects of these collapsing design process of the wake field in bubbles mostly affect the propeller which the propeller is operating [13]. blades, struts and rudders [9]. When a ship had the benefit of model Cavitation damage can also be testing prior to construction, a model dominated by the corrosive action of nominal wake field is very likely to the liquid. Essentially, when have been measured. This then allows cavitation is severe, the cavitation the designer to understand in a erosion which occurs is due to the qualitative sense the characteristics of surface fatigue created by the the wake field in which the propeller alternative mechanical stresses rather is to operate. The designer needs to than the corrosive action of the liquid transform the model nominal wake [12]. Similarly, when the cavitation field into a ship effective velocity intensity is minor, the damage from distribution before it can be used for the cavitation becomes considerably quantitative design purposes [14]. augmented by the corrosive action of Although computational fluid the liquid called the “corrosion dynamics is beginning to address this erosion” effect [10]. At lower levels problem, this transformation is far of cavitation intensity, the damage can from clearly defined within the be characterized as “flow-corrosion. current state of knowledge, and so Experiments at the Massachusetts errors may develop in the definition of institute of technology indicate that no the effective wake field [15,16]. URL: http://journals.covenantuniversity.edu.ng/index.php/cjet
78 Thaddeus C. Nwaoha & Sidum Adumene CJET (2019) 3(1) 76-90
In the case where the ship has not development of these methods started been model tested, the designer has in late nineteenth century. Perhaps, less information to work with, and the most notable of these early works must rely on knowledge of experts was that of Rankine, with his from similar ships. In this way, momentum theory, which was closely predictions are made empirically followed by the blade element based on estimation. Clearly, not all theories of Froude [5]. The modern performance problems are traceable to theories of propeller action, however, lack of knowledge about the wake had to wait for more fundamental field. Other causes, such as poor works in aerodynamics behavior tolerance specification, poor analysis of propeller [2]. A simple specification of design criteria and performance analysis flow chart of incorrect design and manufacture are screw propeller under cavitation is common causes of poor performance illustrated in Figure 1. The of ship propeller [12, 14]. Modeling momentum theory, blade element the common causes and effects on the theory, regression method and propeller performance using numerical methods are described as Computational Fluid Dynamics follows: (CFD) presents computational 1.3.1 Momentum Theory complexity, time and cost. Therefore, The momentum theory of propeller this work seeks to present a simplified action is based on the axial motion of regression model analysis for the water passing through the propeller performance prediction propeller disc. Hence, this theory did under cavitation to overcome the not concern itself with the geometry challenges of computational time and of the propeller, which was producing cost associated with propeller the thrust, and consequently, this hydrodynamic characteristics CFD method is not very useful for blade models and the unavailability of design purposes. It does, however, Model Test facilities. The models lead to some general conclusions were developed from previous about propeller action which have predicted test model and analysis, and subsequently been validated by more it show capacity for accurate recent propeller theoretical methods predictive analysis. [11]. 1.3 Methods of Propeller 1.3.2 Blade Element Theory Performance Prediction and The blade element theory is quite Analysis different model of propeller action, Propeller performance prediction and which took account of the geometry analysis can be conducted using any of the propeller blade. In its original of the four basic methods. The form, the theory did not take account methods are momentum theory, blade of the acceleration of the inflowing element theory, numerical methods water from its far upstream value and regression model. These relative to the propeller disc. This is theoretical methods are used to somewhat surprising, since this could predict the action of propellers. The have been deduced from the earlier URL: http://journals.covenantuniversity.edu.ng/index.php/cjet 79 Thaddeus C. Nwaoha & Sidum Adumene CJET (2019) 3(1) 76-90 work of Rankine. Nevertheless, this 1.3.4 Numerical Method omission was rectified in subsequent Numerical methods are used to developments of the [15]. Blade predict the performance of ship element theory is based on dividing propeller under cavitation effect. The the blade up into many elementary simulation is based on the viscid-flow strips, as seen in Figure 2 & 3. Each theory such as the Reynolds-Averaged of these elementary strips can then be Navier-Strokes (RANS) solver [14]. It regarded as an aero foil subject to a was used in the performance resultant incident Velocity w. The evaluation of a podded propulsion resultant incident velocity was system to model the unsteady thrust considered to comprise an axial and torque of the pod. The blade velocity V together with a rotational boundary parameter and zero pressure velocity r, which clearly varies conditions are applied for the blade linearly up the blade. In the normal profile modeling using CFD [11, 14]. working condition, the advance angle The performance of a propeller β is less than the blade pitch angle θ at hydrodynamic characteristic can be the section, and hence gives rise to the enhanced using numerical models section having an angle of incidence α [14], to improve the live cycle of the [15, 1]. propeller for sustainable development 1.3.3 Regression Method [18-20]. However, [14] observed that Regression methodology is a form of in most cases, the numerical predictive modeling techniques which prediction of propeller under sheet investigate the inter and intra cavitation are not consistent with the relationship between variables in form generic experimental results. They of target and predictor. It is applicable further used the turbulence model to in forecasting, time series modeling examine a 3-D cavitation flow and used for the causal effect propeller to validate the measured relationship between parameters 17]. observations. This method also This method has demonstrated presents high computational time and strength for impact analysis in cost in performance based analysis. multiple independency system 2 Research Methodology performance. This technique provides In this research, the regression model a simplified model that can be used listed as one of the methods for for ship propeller performance propeller performance prediction and prediction. The models can be analysis in sub-section 1.3 is used. expressed in the form of linear The regression model is developed for regression, logistic regression, the modeling of the area ratios and polynomial regression, stepwise open water efficiencies of propeller at regression, ridge regression, lasso different conditions. The developed regression and Elastic Net regression. regression models were modified from the work of [9, 11] as follows:
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Start
Input Blade series, blade number, engine power, blade areas
Estimate blade area ratios, propeller efficiencies & cavitation
Is estimated efficiencies lower under cavitation Yes
No
Define propeller characteristic & performance
Stop
Figure 1: Performance analysis flow chart of screw propeller under cavitation
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81 Thaddeus C. Nwaoha & Sidum Adumene CJET (2019) 3(1) 76-90
Figure 2: Ideal propeller efficiency from general momentum theory [5]
Figure 3: Blade element theory [1]
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is the pressure differential on the blade surface.
3. Application of Regression Model vessel under various assumptions. The in Propeller Performance prediction is hypothetically evaluated Prediction and Analysis at different blade diameters and The study uses regression model to geometric blade areas ratio. The analyse and predict the performance results of the analysis at the given of a screw propeller for a marine URL: http://journals.covenantuniversity.edu.ng/index.php/cjet 83 Thaddeus C. Nwaoha & Sidum Adumene CJET (2019) 3(1) 76-90 range of blade profile and blade area decreases at 0.12% and 0.15% for the ratios are shown in Figures 4-9. non-cavitated and cavitated propellers The result of the analysis in Figure 4 respectively. This indicate a &5 show the trend of the open water performance reduction factor of 0.03. efficiency for the selected blade area This factor, though minimal, over ratio. As the ratio increases, the open time can results to performance water efficiency decreases at a steep deterioration, especially when the rate with blade diameter of 7.00m. propeller is fully loaded. The This further revealed that for every consequences may result to 1% increase in the expanded blade catastrophic failures. areas, the open water efficiency
0.65 0.645 0.64 0.635 0.63
0.625
0.62 0.615 Open Water Efficiency 0.61 0.605 0.6 0.595 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 Blade Area Ratio
Figure 4: Effect of blade area ratio on open water efficiency
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84 Thaddeus C. Nwaoha & Sidum Adumene CJET (2019) 3(1) 76-90
0.65 non- caviated 0.64 propeller 0.63 efficency curve 0.62 Cavitated 0.61 propeller efficiency 0.6 curve
Open Water Efficiency 0.59 0.58 0.4 0.6 0.8 1 1.2 Expanded Blade Area Ratio
Figure 5: Comparative prediction of open water efficiency for non-cavitated and cavitated propeller
Figure 6 describes the effect of cavitation effects decrease as blade expanded area ratio reduction on the area ratio increases. Beyond certain performance of the propeller. Selected allowable pressure fluctuation, this percentage reduction ranges from 2% increment may result to the overall to 10%, where used to evaluate the propeller performance deterioration optimal percentage incremental effect over time. It is therefore of concern on the open water efficiency. The that selection and prediction should be result show that at 7.5% reduction in done within the optimum performance the expanded blade area, the open envelope for safer operation in fully water efficiency has the optimal loaded propeller. From the result percentage increment. That is at 7.5% analysis of this study, the predicted increase in the expanded blade area, propeller performance optimizing the propeller performance increase by range is and 1.85%. This is an indication that the blade area ratio is a factor to be . considered in propeller choices and performance criteria. Although, the
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2 2.5% blade 1.5 area reduction 1 5% blade area reduction
Efficiency 0.5
0 7.5%
% % Increase in Open Water blade 1.978 1.98 1.982 1.984 1.986 1.988 1.99 1.992 area -0.5 reduction Blade Area Ratio
Figure 6: Effect of percentage reduction in blade area ratio on the open water efficiency
1.12 1.1 1.08 1.06 1.04 1.02 1 Pitch Ratio 0.98 0.96 0.94 0.92 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 Blade Area Ratio
Figure 7: Effect of blade area ratio on pitch ratio of a screw propeller
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Figure 8: Comparative effects of blade area ratio on pitch ratio and open water efficiency
The result of the study as shown in propeller at the given normal pitch. Figures 7 and 8, show the effect of There is an even distribution of the blade area ratio on the propeller pitch pitch at the right and left sides of the ratio. This described theoretically the nominal value as shown in Figure 8. advances during the complete cycle So critical decision making is needed and how pitch ratio may lead to an to operate within the acceptable increase in the propulsive efficiency. criteria considering the decline in the It also shows that the propeller open water efficiency. propulsive efficiency is dependent on Figure 9 indicate that the open water propeller pitch ratio. It is therefore efficiency increases as the blade important for propeller performance diameter reduction ratio decrease analysis to predict the pitch ratio towards the zero axis. The result show during propeller design. For the that between the ratio of 0.55 and proper performance of a screw 0.40, the efficiency has a peak value, propeller, the propeller pitch ratio which gradually decline as we move prediction should be holistic for an toward the zero axis. It also means optimum output. that the propeller disc area will also Cavitation also affect the propeller affect the propeller efficiency in pitch ratio as shown in this analysis. operation. The propeller disc area is It revealed that as there is an increase also a major factor of consideration in in the cavitation number, the propeller screw propeller performance due to its pitch ratio decreases. Also, the result significant on propeller efficiency shows that for a nominal pitch ratio of prediction. So, to enhance propeller 0.944 at the blade area ratio of 0.748, efficiency during propeller design, the the corresponding open water area of the disc should be accurate efficiency is 0.635. This further predicted to avoid errors that can limit explain the mean performance of the performance. Furthermore, a URL: http://journals.covenantuniversity.edu.ng/index.php/cjet
87 Thaddeus C. Nwaoha & Sidum Adumene CJET (2019) 3(1) 76-90 predictive profile for operational acceptable limit under cavitation can decision making and proactive prolong the life of the propeller and planning can be deduced from the minimize the maintenance downtime curves shown in Figure 9. It was in operation. observed that operating within the
Figure 9: Effect of percentage reduction in blade diameter on open water efficiency
4. Conclusion consequences of the effect of In this research, the regression model cavitation when the propeller is fully was utilized in propeller performance loaded. prediction, when cavitation is Furthermore, for operational safety experienced. The model shows and design consideration, cavitation accurate predictive result with reduction or monitoring should be minimum associated error. It was integrated into the design for safety of identified that the cavitation reduces ships. Increasing propeller immersion, the performance by a factor of 0.03 in introduction of ventilation, increase of the open water efficiency. This factor clearances from the hull and overtime enhances reduction in the application of skewed bladed propeller effective power and causes propeller can serves as cavitation performance deterioration and reduction measures that can minimize frequent breakdown. Therefore, an propeller failure in operation and effective operating envelope of optimize the performance. and Acknowledgement The authors acknowledged the was proposed contributions of Onyeozu, Daniel for the operation, considering the Chigozim in this research work.
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