Examination of Marine Engineer Officer s6

78AM-1 Sr. No. 7 EXAMINATION OF MARINE ENGINEER OFFICER

APPLIED MECHANICS

CLASS -I (Time allowed - 3 hours)

INDIA (2001) Morning Paper Total Marks 100

N.B. - (1) Attempt SIX questions only . (2) All questions carry equal marks. (3) Neatness in handwriting and clarity in expression carries weightage

1. (a) Explain briefly what you understand by primary and secondary unbalanced forces with respect to a reciprocating engine. (b) A single cylinder reciprocating engine has stroke 300 mm and speed 500 r.p.m. The mass, of reciprocating parts is 50 kg and the equivalent mass of revolving parts at crank radius is 60 kg. Two revolving balance weights of equal mass are attached to the crankwebs at effective radius of 250 mm to balance whole of the revolving parts and two-third of' the primary unbalanced forces due to reciprocating parts. Find-- (i) The mass of each balance weight. (ii) The residual unbalanced force when the crank has rotated 60' from top dead centre.

2. Three wires joined by two shakles to form one length are rigged athwartship across the engine room of a twin-screw vessel, the free ends of the complete wire being secured to the ships structure at the same level. One shakle is arranged to fall over the port engine and from it is slung an engine part of mass 200 kg; the other shakle is vertically above the starboard engine and is also loaded. The port wire, making an angle of 30' degrees to the vertical, has a tension of 2. 5 KN and the starboard wire is inclined at 45' degrees to the vertical. Calculate- (a) The tension in the middle wire, (b) The angle the middle wire makes with the horizontal, (c) The load on the starboard shakle, (d) The tension in the starboard wire.

3. In a plate clutch, the torque T is transmitted by friction between one or more pairs of co-axial annular faces having r1, r2 as outer and inner radii, maintained in contact by an axial thrust W. The uniform intensity of pressure between surfaces is p. The coefficient of friction is  and number of faces in contact is n. Prove that- Torque transmitted T = 2 / 3  Wn 13 - 23 / r12 – r22 A multi-plate clutch is to transmit 12 KW at 1500 rev/min. The inner and outer radii for the plates are to be 50 mm and 100 mm respectively. The miximum axial spring force is restricted to 1 KN. Calculate the necessary number of pairs of surfaces if  = 0.35 assuming constant wear. What will be the necessary axial force?

4. The stiffness of a closed coil helical spring is such that it deflects 36 mm when an axial force, of 10 N is applied on the end of the hook. Calculate the mass to be hung on the hook so that, when set vibrating, it will make one complete oscillation per second. The mass of the spring is 0.6 kg and the effect of this when vibrating is to be taken as equivalent to a mass on the end hook equal to one-third of the mass of the spring. 5. A steel bar of 20 mm diameter and 400 mm long is placed concentrically inside a gun-metal tube. The tube has inside diameter 22 mm and thickness 4 mm. The length of the tube exceeds the length of the steel bar by 0.12 mm. Rigid plates are placed on the ends of the tube and an axial compressive load applied to the compound assembly. Find- (a) The load which will just make tube and bar of the same length. (b) The stress in the steel and gun ametal when a load of 50 kN is applied. E for steel = 210 GM/m2 E for gun metal = 100 GN/m2.

6. A hydraulic steering gear has 4 rams each 300,mm diameter, the distance between centre line of rams and centre of rudder stock is 750 mm, the miximum rudder angle is 350, and the by-pass valves lift when the pressure in the cylinders is 75,bar (= 75  105 N/m2). (a) If the stress in the rudder stock is not to exceed 70 MN/m2, .,find the diameter of the rudder stock. (b) if the stress in the tiller arms at 600 mm from the centre of the rudder stock is not to exceed 100 MN/m2,. find the diameter of the tiller arms at this section.

7. A short hollow cast iron column has an external diameter of 30 cm and an internal diameter of 25 cm. The bore is eccentric, the thickness of the metal varying from a minimum of 1cm at one extremity of a diameter to a maximum of 4 cm at the other extremity. If the column carries a load of 100 KN along the axis of the bore, calculate the maximum and minimum stresses induced in the section.

8. Derive the following expression for the efficiency of a jet-propelled vessel in which the water is drawn in at the side and expelled at the stern :-  = 2s (v – s) / v2 s = Speed of the ship v = Velocity of the jet relative to the ship. A small ship is fitted with jets of total area 0. 65 m2. The velocity through the jets is 9 m/sec and the ship's speed is 18.5 km/h. Determine the propelling force. Density of water 1025,kg/m3.

9. The speed of a centrifugal pump is 1600 r.p.m. At impeller inlet, diameter is 150 mm, width is 40 mm and blade angle is 25 degrees. At impeller outlet, diameter1is 400 mm, width is 20 mm and blade angle is 15 degrees. Velocity of whirl at inlet is zero. Calculate- (a) Flow rate (b) Work done per kilogram mass of water (c) Power required and (d) Absolute velocity at outlet.

------X------78AM-1 Sr. No. 7 EXAMINATION OF MARINE ENGINEER OFFICER

APPLIED MECHANICS

CLASS -I (Time allowed - 3 hours)

INDIA (2001) Morning Paper Total Marks 100

N.B. - (1) Attempt SIX questions only . (2) All questions carry equal marks. (3) Neatness in handwriting and clarity in expression carries weightage Answers Answer for Question No. 1

28 kg 12.368

Answer for Question No. 2

1266.38 N 9 13.6’ 1767.75 N 148.126 kg

3 pairs 985.4N

7.036 kg 6.836 kg

9.801 kN 70.7518 MN/m2

441.8mm 275mm

Max = 9.96 MN/m2 Min = 1.27 MN/m2 Answer for Question No. 8

23.1572 KN

110.46 liters/sec 970.46 J/kg 107.197 kw 29.29 m/sec