Exam Question
(a) Explain why large slow speed, diesel engines may have a barred speed range and why the engine must not be operated continuously within that range. (10)
(b) Explain how the barred speed range is avoided when on bridge control. (6)
Class 4 (4th Engineer)
MEKM
📅 Oct 2022
Reference Answer
### Part (a): Barred Speed Range - Existence and Dangers (10 Marks)
A barred speed range, also known as a critical speed range, is a specific range of engine revolutions per minute (RPM) at which continuous operation is prohibited. This prohibition is due to the phenomenon of **Resonance**.
**1. The Concept of Resonance:**
* **Natural Frequency:** Every mechanical system, including the entire propulsion train (engine crankshaft, intermediate shaft, propeller shaft, and propeller), possesses one or more natural frequencies of vibration. The ship's hull structure also has its own natural frequencies.
A barred speed range, also known as a critical speed range, is a specific range of engine revolutions per minute (RPM) at which continuous operation is prohibited. This prohibition is due to the phenomenon of **Resonance**.
**1. The Concept of Resonance:**
* **Natural Frequency:** Every mechanical system, including the entire propulsion train (engine crankshaft, intermediate shaft, propeller shaft, and propeller), possesses one or more natural frequencies of vibration. The ship's hull structure also has its own natural frequencies.
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