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Something About the Mechanical Moment of Inertia American Journal of Applied Sciences Original Research Paper Something about the Mechanical Moment of Inertia 1Florian Ion T. Petrescu, 2Antonio Apicella, 2Aversa Raffaella, 3Relly Victoria Petrescu, 4John Kaiser Calautit and 5Aniello Riccio 1Department of Theory of Mechanisms and Robots, Bucharest Polytechnic University, Bucharest, Romania 2Advanced Material Lab, Department of Architecture and Industrial Design, Second University of Naples, Aversa (CE) Italy 3Department of Transport, Traffic and Logistics, Bucharest Polytechnic University, Bucharest, Romania 4Department of Mechanical Engineering, University of Sheffield, Sheffield, United Kingdom 5Second University of Naples, Naples, Italy Article history Abstract: In this study , the relations to determining mass moments of Received: 10-10-2016 inertia (mechanical) for different mass and mechanical inertia Revised: 28-10-2016 corresponding to geometric shapes, objects and profiles are explored. The Accepted: 03-11-2016 formulas for calculating the mass moments of inertia (mechanical) for various bodies (various geometrical forms), to certain major axis indicated Corresponding Author: Florian Ion T. Petrescu (as the axis of calculation) are presented. The total mass M of the body is Department of Theory of used to determine the mass moment of inertia (mechanical). In the first part Mechanisms and Robots, of the paper, an original method for determining the mass moment of Bucharest Polytechnic inertia (mechanical) of the flywheel is presented. Mass moment of inertia University, Bucharest, Romania (the whole mechanism) reduced at the crank (reduced to the element leader) Email: [email protected] consists in a constant mass inertia moment and one variable, to which we may include an additional mass moment of inertia flywheel, which aims to reduce the degree of unevenness of the mechanism and the default machine. The more the mass moment of inertia of the flywheel is increased the more the unevenness decreased and dynamic functioning of the mechanism is improved. Engineering optimization of these values can be realized through new relationships presented on the second paragraph of the article. Determining of the mass moment of inertia of the flywheel with the new method proposed is also based on the total kinetic energy conservation. Keywords: Mass Moment of Inertia, Compute Axis, Unevenness, Flywheel Moment of Inertia, Energy Conservation Introduction This is extremely useful for rotor dynamics that have high speed (Heat engines with internal and external Determination of mechanical moments of inertia combustion, electric motors, turbines, jet). (mass) is becoming increasingly important in modern industrial design and mechanical systems. The exact calculation of mechanical inertial moments no longer Determining the Mechanical Moments of easily found today (only in older textbooks mechanics Inertia or mechanisms). The mechanical mass moments of inertia (Antonescu, In this paper the authors aim initial to reminder the 2000; Pelecudi, 1985; Petrescu, 2012), of kinematic relations to determining mass moments of inertia elements represent the mass to the rotational movement of (mechanical) for different mass and mechanical inertia these elements. Such as the known mechanical mass of a corresponding to geometric shapes, objects and profiles. kinematic element that characterizes the translational The second part of this paper provides an overview of movement of the respectively cinematic element. the equations for determining the mechanical mass For the kinetic energy of a system to be complete it is moments of inertia. essential that the dynamic calculations to be taken into The first part of the paper presents, an original method account and the rotation kinetic energy. This is due to for determining the degree of irregularity of a machine (car) movements of rotation of each kinematic element and a minimum mass moment of inertia the flywheel. belonging to the mechanism or to the assembly. © 2016 Florian Ion T. Petrescu, Antonio Apicella, Aversa Raffaella, Relly Victoria Petrescu, John Kaiser Calautit and Aniello Riccio. This open access article is distributed under a Creative Commons Attribution (CC-BY) 3.0 license. Florian Ion T. Petrescu et al . / American Journal of Applied Sciences 2016, 13 (11): 1085.1090 DOI: 10.3844/ajassp.2016.1085.1090 Dynamics is the only one that can simulate theoretical an additional mass inertia moment, of a flywheel Jv, the real movement of a machine. In general, in the which aims to reduce the degree of unevenness of the works of mechanics or mechanisms, motors, dynamics, mechanism (machine) (see relation 5). When Jv is etc., (scientific articles, books) there is no an emphasis increased, the more the δ drops (Pelecudi, 1985). It is on the determination of mass moments of inertia necessary to obtain an optimal value for Jv: (mechanical) considering themselves too popular. In this article, different mechanical inertia corresponding * J= J0 + Jv + J (5) to different geometric shapes, objects and profiles are presented. The formulas for the calculation of the From the total energy conservation, the entire moments by mass or mechanical inertia for various mechanism (as long as it does not take into account elastic bodies (various shapes) are detailed. deformations and considering only the basic mechanics of It is noted with M, the total mass of the element to rigid body, the potential energy it does not affect the which must be determined the inertia mechanical operation and one uses just the kinematic energy) the moment. Calculation formulas are displayed in the relationship can be written as (6) (Petrescu, 2012): respective Fig. 1-13 (Petrescu, 2012). 1*2 1 * 2 Determining the Mass of Inertia of the ⋅⋅Jmω m ⋅ J max ⋅ ω min = 2 2 Flywheel (J v) 1*2 1 *2 =⋅Jmin ⋅ω max =⋅⋅ J ω (6) The uniformity work of a machine is characterized by 2 2 *2* 2 *2 *2 the degree of irregularity ( δ), defined by equation (1) JJm⋅=ω m max ⋅ ω min = J min ⋅ ω max =⋅ J ω (Antonescu, 2000; Pelecudi, 1985; Petrescu, 2012): ω− ω From Equation 6, only relation (7) is retained and is δ = max min (1) ωmed developed according to expression (5) (Petrescu, 2012). The equation is then written in the form of (8): Average angular velocity is expressed by the * 2 * 2 relation (2): Jmax⋅ω min = J min ⋅ ω max (7) ω+ ω JJJ++ ⋅ω2 =++ JJJ ⋅ ω 2 (8) ω = max min (2) ( 0v max) min( 0 v min) max med 2 where, (Jmax and Jmin ), are the maximum and minimum From Equations 1 and 2, the maximum and minimum of J, from the expression (5). It explains Jv from relation angular velocities are calculated using Equation 3 (8) and one obtains the expression (9) (Petrescu, 2012): (Pelecudi, 1985; Petrescu, 2012): 22 2 2 J0⋅(ωω min − max) +⋅−⋅ J max ω min J min ω max J = δ v 2 2 (9) ωmax = ω med ⋅1 + ω− ω 2 ()max min (3) δ ωmin = ω med ⋅1 + Using the relations from the system (4) the 2 expression (9) takes the form (10) (Petrescu, 2012): Equations 3 are squared to obtain a relational system as 2 2 δ δ shown in Equations 4 (Pelecudi, 1985; Petrescu, 2012): Jmax⋅−1 − J min ⋅+ 1 2 2 Jv = − J 0 + 2 2 (10) δ δ 2 2 1+ − 1 − 2 2δ 2 δ 2 2 ωωmax =med ⋅+1 =⋅++ ω m 1 δ 2 4 (4) 2 δ δ 2 Relation (10) is reduced to the form (11) by ωω2= 2 ⋅+1 ω 2 ⋅+− 1 δ min med m processing the denominator and to the form (12), if 2 4 processing and the fraction numerator (Petrescu, 2012): The mass moment of inertia of the whole mechanism 2 2 which is reduced to the crank (reduced to the leader δ δ * Jmax⋅−1 − J min ⋅+ 1 element) J , usually consists of a constant mass inertia 2 2 Jv = − J 0 + (11) moment J0 and one variable J, to which one may include 2⋅δ 1086 Florian Ion T. Petrescu et al . / American Journal of Applied Sciences 2016, 13 (11): 1085.1090 DOI: 10.3844/ajassp.2016.1085.1090 Jmax− J min 1 δ Jv=−−+ J0 J m ⋅+ (12) 2δ 4 where, Jm = (Jmax + Jmin )/2 and the maximum and minimum are found by would come close to zero of the derivation of J (from expression 5) in relation of variable ϕ. Knowing the maximum allowable δ one calculates with the relation (12) the minimum required (optimal value) of mass moment of inertia of the flywheel, Jv. Results and Discussion Fig. 1. Mass moment of inertia of a ring fixed (calculated) around the longitudinal axis of the ring In this paper the authors aim initial to reminder the relations to determining mass moments of inertia (mechanical) for different mass and mechanical inertia corresponding to geometric shapes, objects and profiles. The second part of this paper provides an overview of the equations for determining the mechanical mass moments of inertia. In the first part of the paper, an original method for determining the degree of irregularity of a machine (car) and a minimum mass moment of inertia to the flywheel was presented. For the kinetic energy of a system to be complete it is essential that the dynamic calculations to be taken into account and the rotation kinetic energy. This is due to movements of rotation of each kinematic element belonging to the mechanism or to the Fig. 2. Mass moment of inertia of a ring fixed around a radial (diametrical) axis of the ring assembly. Dynamics is the only one that can simulate theoretical the real movement of a machine. In general, in the works of mechanics or mechanisms, motors, dynamics, etc., (scientific articles, books) there is no an emphasis on the determination of mass moments of inertia (mechanical) considering themselves too popular. In this article, different mechanical inertia corresponding to different geometric shapes, objects and profiles are presented. The formulas for the calculation of the moments by mass or mechanical inertia for various bodies (various shapes) are detailed.
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