JNTU
JNTU B.Tech IV MECHANICAL VIBRATIONS Previous Question Paper (July/August - 2022 - R18)
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What do you understand by free vibrations, forced vibration and damped vibration. Explain the significance and importance of each of these?
Answer
Free vibration occurs when a system oscillates under the action of forces inherent in the system itself, such as restoring forces (springs) or inertia, without any external excitation. It is significant for determining the natural frequency of a structure, which is critical for avoiding resonance.
Forced vibration occurs when a system is subjected to an external periodic force or motion. It is essential in engineering design to analyze the response of machines (like engines or compressors) to operating loads and to ensure that the excitation frequency does not coincide with the natural frequency.
Damped vibration involves the dissipation of energy over time due to friction or other resistance, causing the amplitude of oscillation to decay. It is vital for controlling vibrations, preventing structural failure, and ensuring stability in mechanical systems, as it limits the amplitude of motion at resonance.
Explain the rotating and reciprocating unbalance with sketches?
Answer
Rotating unbalance occurs when the center of mass of a rotating component does not coincide with its axis of rotation. This creates a centrifugal force
Reciprocating unbalance is caused by the inertia forces of parts moving in a straight line, such as a piston in an engine. The primary inertia force is
Explain the concept of over damped ,critical damped and under damped system?
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In a spring mass vibrating system, the natural frequency of vibration is 3.56 Hz. When the amount of suspended mass is increased by 5 kg, the natural frequency is lowered to 2.9 Hz. Determine the original unknown mass and spring constant.
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Explain the responses to non-Periodic Excitations.
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Plot the frequency response curve of a linear undamped single degree of freedom system to an alternating square wave excitation.
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A mass weighing 85 Kgf is supported on springs which deflects 1.8 cm under the weight of the mass. The vibration of mass are constrained to be linear and vertical and are damped by a dashpot which reduces the amplitude to one –quarter of its initial value in two complete oscillations, find a) the magnitude of the damping force at unit speed and b) periodic time of damped vibration.
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Explain the analysis of a combined rectilinear and angular mode system.
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Explain the working principle of a undamped vibration absorber.
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Determine the natural frequencies and mode shapes associated with the system shown in Figure for m1 = 10 kg, m2 = 20 kg, k1 = 100 N/m, k2 = 100 N/m, and k3 = 50 N/m.
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What do you mean by whirling motion? Does it involve transverse or torsional vibrations? Explain.
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A shaft of length 0.8 m supported freely at the ends, carries a load of mass 100 kg at 0.3m from one end. Find the natural frequency of transverse vibration, Assume E = 200 G/N/m2 and shaft diameter is 50 mm.
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What are the different sound measuring instruments, Explain any of it.
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Illustrate the relationship between sound intensity level and sound pressure level.
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