Class 4 (4th Engineer) SC&S 📅 May 2023

Exam Question

(a) Explain what is meant by synchronous or resonant vibration. (6)

(b) A ship's speed is increased by 20% above normal for hours, reduced by 10% below normal for 10 hours and for the remaining 6 hours of the day the speed is normal.

Calculate the percentage variation in fuel consumption in that day from normal. (10)

Reference Answer

(a) **Synchronous or Resonant Vibration**
### 1. Definition
Synchronous or resonant vibration is a critical dynamic phenomenon that occurs when the frequency of an external periodic force (forcing frequency) acting on a system coincides with one of the system's natural frequencies of vibration. At this point of resonance, the energy input by the forcing function is not effectively dissipated, leading to a rapid and significant amplification of the vibrational amplitude, which can result in excessive stresses, noise, and potential catastrophic failure.
### 2. Mechanism

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