MECHANICAL VIBRATIONS

mechanical vibration Exam questions And answers

Free and Forced Vibration of Single Degree of Freedom Systems:

In mechanical engineering, the concept of single degree of freedom (SDOF) systems is often used to simplify the analysis of vibrating systems. SDOF systems consist of a mass, a spring, and a damper connected in series.

Free Vibration:

Free vibration occurs when an SDOF system is initially displaced or set into motion without any external force acting on it. The system oscillates back and forth at its natural frequency, which is determined by the stiffness of the spring and the mass of the system. The amplitude and frequency of free vibrations depend on the initial conditions and the system’s properties.

Forced Vibration:

Forced vibration occurs when an external force or excitation is applied to an SDOF system. The external force can be either periodic, which repeats at regular intervals, or non-periodic, which does not follow a predictable pattern. When a periodic force is applied, the system responds with forced vibrations at the frequency of the excitation force. The response can be steady-state or transient, depending on the time duration and magnitude of the excitation.

Questions on Free and Forced Vibration of Single Degree of Freedom (SDOF) Systems :

1. What type of motion occurs in free vibration? (Answer: Oscillation)
2. What determines the natural frequency of an SDOF system? (Answer: Stiffness and mass)
3. What reduces the amplitude of vibrations in free vibration? (Answer: Damping)
4. What causes forced vibration in an SDOF system? (Answer: External force)
5. What happens during resonance in forced vibration? (Answer: Amplification)
6. What is the steady-state response in forced vibration characterized by? (Answer: Frequency)
7. What decreases the amplitude of vibrations in forced vibration? (Answer: Damping)
8. What is the frequency at which resonance occurs called? (Answer: Resonant frequency)
9. What is used to control forced vibrations in SDOF systems? (Answer: Active control)
10. What is the purpose of vibration isolators in SDOF systems? (Answer: Reduction)

Mechanical Vibration Exam…

Effect of Damping:

Damping is a characteristic of vibrating systems that causes the dissipation of energy. It affects the behavior of vibrations in several ways:

Damping Ratio:

Damping ratio, represented by the symbol ζ (zeta), is a parameter that defines the ratio of the actual damping in a system to the critical damping. It influences the rate at which vibrations decay over time. Higher damping ratios lead to faster decay of vibrations.

Effect of Damping on Natural Frequency:

Damping also affects the natural frequency of a system. Increased damping reduces the natural frequency, resulting in a shift in the system’s response.

Questions on the Effect of Damping in Vibrations :

1. What does damping do to vibrations? (Answer: Reduces)
2. How does damping affect the amplitude of vibrations? (Answer: Decreases)
3. What is the opposite of damping? (Answer: Amplification)
4. What is the function of damping in regulating vibrations? (Answer: Mitigation)
5. Does higher damping lead to faster or slower decay of vibrations? (Answer: Faster)
6. What is the parameter that quantifies damping in a system? (Answer: Damping ratio)
7. Does damping have an impact on the natural frequency of a system? (Answer: Yes)
8. What type of energy does damping dissipate? (Answer: Vibrational)
9. Is damping always desirable in mechanical systems? (Answer: Yes)
10. What is the purpose of adding damping to vibrating systems? (Answer: Control)

Mechanical Vibration Exam Questions…

Vibration Isolation:

Vibration isolation is the process of reducing the transmission of vibrations from one system to another. It is crucial in applications where vibrations can negatively impact the performance, accuracy, or comfort of nearby components or structures. Various techniques such as using vibration isolators (e.g., rubber mounts, springs) or implementing vibration-absorbing materials are employed to minimize the transfer of vibrations.

Questions on Vibration Isolation in vibrations:

1. What does vibration isolation reduce? (Answer: Transmission)
2. What is used to isolate vibrations in mechanical systems? (Answer: Isolators)
3. Does vibration isolation increase or decrease the transmission of vibrations? (Answer: Decrease)
4. What does vibration isolation aim to minimize? (Answer: Transfer)
5. What is the purpose of using vibration isolators? (Answer: Attenuation)
6. Does vibration isolation prevent or eliminate vibrations? (Answer: Prevent)
7. What is the opposite of vibration isolation? (Answer: Transmission)
8. What type of materials are commonly used for vibration isolation? (Answer: Rubber, elastomers)
9. What is the goal of vibration isolation in mechanical systems? (Answer: Reduction)
10. Is vibration isolation important for the performance of sensitive equipment? (Answer: Yes)

Mechanical Vibration Exam Questions…

Resonance:

Resonance is a remarkable phenomenon that arises when the frequency of an external force precisely aligns with the natural frequency of a system, resulting in a significant amplification of vibrations.”. When resonance occurs, the amplitude of vibrations can become significantly amplified. This can lead to excessive vibrations, potential structural damage, or even failure. Engineers need to consider resonance effects and implement measures to avoid or mitigate resonance conditions in mechanical systems.

questions on Resonance in vibrations:

1. What is the result of resonance? (Answer: Amplification)
2. Does resonance increase or decrease vibrations? (Answer: Increase)
3. What happens when the frequency of an external force matches the natural frequency of a system? (Answer: Resonance)
4. Is resonance desirable in most mechanical systems? (Answer: No)
5. What is the primary concern with resonance? (Answer: Damage)
6. Does resonance occur at the natural frequency or forced frequency? (Answer: Natural frequency)
7. What is the primary cause of resonance? (Answer: Frequency match)
8. What can resonance lead to in vibrating systems? (Answer: Vibration problems)
9. Can resonance be mitigated or eliminated? (Answer: Yes)
10. What is the primary objective in dealing with resonance? (Answer: Prevention)

Mechanical Vibration Exam Questions…

Critical Speeds of Shafts:

Critical speeds of shafts refer to the rotational speeds at which resonant vibrations occur in rotating systems. These critical speeds can cause significant vibrations, leading to issues such as excessive wear, fatigue, and even catastrophic failure. Understanding critical speeds is crucial for the design and operation of rotating machinery, and engineers take measures to avoid operating at or near these critical speeds.

questions on Critical Speeds of Shafts in vibrations:

1. What do critical speeds of shafts represent? (Answer: Instability)
2. Are critical speeds associated with high or low vibration amplitudes? (Answer: High)
3. At critical speeds, do vibrations decrease or increase? (Answer: Increase)
4. What causes critical speeds in rotating shafts? (Answer: Resonance)
5. Do critical speeds occur when the rotational frequency matches the natural frequency? (Answer: Yes)
6. What type of failures can result from operating at critical speeds? (Answer: Fatigue, fracture)
7. Can critical speeds be adjusted or controlled? (Answer: Yes)
8. Is it desirable to operate at or near critical speeds? (Answer: No)
9. What can be done to avoid critical speeds in shafts? (Answer: Design modifications)
10. Are critical speeds specific to each shaft design? (Answer: Yes)

Mechanical Vibration Exam Questions…

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