JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III DYNAMICS OF MACHINERY Previous Question Paper (July/August - 2023 - R16)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
Part A
What is the gyroscopic effect during pitching of the naval ship.
Answer
During the pitching of a naval ship, the axis of spin of the rotor (propeller) oscillates in a vertical plane. This motion causes the gyroscopic couple to act in a horizontal plane, which results in the ship tending to turn or yaw to the left or right, depending on the direction of rotation of the propeller and the direction of the pitch.
Explain D’Alemberts principle.
Answer
D'Alembert's principle states that a system of rigid bodies in motion can be considered to be in a state of dynamic equilibrium if an inertia force is applied to each body in addition to the external forces acting on it. Mathematically, it is expressed as the sum of all external forces and the inertia force acting on a body is equal to zero.
Where ΣF represents the resultant of all external forces and Fi is the inertia force, defined as the product of the mass of the body and its acceleration acting in the opposite direction of acceleration (Fi = -ma). This principle effectively transforms a dynamic problem into an equivalent static problem, allowing the use of equations of static equilibrium to solve for unknown forces or accelerations in machinery.
Define fluctuation of energy.
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Sketch the turning moment diagram four stroke cycle IC Engine.
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Define Greasy friction.
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State the laws of friction.
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Differentiate porter and proell governors.
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What is hammer blow?
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Describe the basic features of vibrating system.
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Explain the Rayleigh’s method to employ vibrating system.
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Part B
A trolley can with a total mass of 2700 kg runs on rail 1m apart with a speed of 30-km/hr. The track is curved with a radius of 40m towards the rigid of the driver. The car has four wheels each of diameter 70 cm and the total moment of inertia of each pair of wheels and the axle is 15 kg-m2. The car is driven by a motor running in the direction opposite to that of the wheels at a speed five times the speed of rotation of the wheels. The motor and the gear pinion have a moment of inertia 10 kg- m2. The rails are at the same level and the height of the center of gravity of the car is 1m above the rail level. Determine the vertical force exerted by each wheel on the rails.
Answer
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Determine the torque required to be applied to link OA for the static equilibrium of the mechanism as shown in Figure 1.
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During forward stroke of the piston of the double acting steam engine, the turning moment has the maximum value of 2000 Nm when the crank makes an angle of 80 degrees with the inner dead centre. During the backward stroke, the maximum turning moment is 1500 Nm when the crank makes an angle of 80 degrees with the outer dead centre. The turning moment diagram for the engine may be assumed for simplicity to be represented by two triangles. If the crank makes 100 r.p.m and the radius of gyration of the flywheel is 1.75 m, find the coefficient of fluctuation of energy and the mass of the flywheel to keep the speed within +/- 0.75% of the mean speed. Also determine the crank angle at which the speed has its minimum and maximum values.
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A certain machine required a torque of (2000 + 300 sin θ) N-m to drive it, where θ is the angle of rotation of its shaft measured from some datum. The machine is directly coupled to an electric motor developing uniform torque. The mean speed of the machine is 200 r.p.m. Find the power of the driving electric motor and the moment of inertia of the flywheel required to be used if the fluctuation of the speed is limited to ±2%.
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Sketch the turning moment diagram for the multicylinder engine.
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The engine of an automobile is rated to give 80 kW at 1800 rpm with a maximum torque of 550 Nm. Design a dry single plate clutch assuming the outer radius of the friction plate to be 1.2 times the inner radius. The coefficient of friction is 0.25 and the intensity of pressure between the plates is not to exceed 80 kN/m2. Six springs are used to provide axial force necessary to engage the clutch and each spring has a stiffness of 50 N/mm. find the initial compression in the springs and dimensions of the friction plate.
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Explain the film friction concept for a journal rotating in a bearing.
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Explain the working principle of belt transmission dynamometer.
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The following data refer to a laboratory experiment with rope brake: Diameter of the flywheel – 1m, Diameter of the rope – 10mm, Dead Weight on the brake – 50 kg, Speed of the engine – 180 rpm, Spring balance reading – 120 N, Find the power of the engine.
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Each arm of a porter governor is 300 mm long and is pivoted on the axis of rotation. Each ball has a mass of 6 kg and the sleeve weights 18 kg. The radius of rotation of the ball is 200 mm when the governor begins to lift and 250 mm when the speed is maximum. Determine the maximum and the minimum speeds and the range of speed of the governor.
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Determine the bearing reaction at A & B for the system shown in figure 2 if the speed is 300 rev/min. determine the magnitude and the angular orientation of the balancing mass if it is located at a radius of 50 mm.
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A shaft 1.5 m long, supported in flexible bearings at the ends carries two wheels each of 50 kg mass. One wheel is situated at the centre of the shaft and the other at a distance of 375 mm from the centre towards left. The shaft is hollow of external diameter 75 mm and internal diameter 40 mm. the density of the shaft material is 7700 kg/m3 and its modulus of elasticity is 200 GN/m2. Find the lowest whirling speed of the shaft, taking into account the mass of the shaft.
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Derive the resisting torque of the Bifilar suspension under torsional vibrations.
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Discuss about the free torsional vibrations of three rotor system.
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