Vibration and Forces - Primary and secondary forces and couple

Page 5

Index

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1. Engine vibration and critical speed
2. Force and Moments in slow speed diesel engine
3. Vibration damper and detuner
4. Static and dynamic loading and balancing in engine
5. Primary and secondary forces and couple
6. Torsional vibration
7. Axial vibration details
8. Purifier vibration reasons
9. Important element in ship vibration

10. Engine Dynamics

Primary and secondary forces and couple

Primary and Secondary Forces and Couples
The disturbances set up by the reciprocating masses are divisible into primary and secondary unbalanced forces and couples created by them.
Within an engine system the following forces and couples are to be considered. The shaft system is also excited to vibration.

In Engine System:

a) Forces - Revolving, Primary reciprocating, Secondary reciprocating
b) Couples - Revolving, Primary reciprocating, Secondary reciprocating, Guide force moment

In Shaft System - Axial Vibration, Torsional Vibration

The inertia forces originating from the unbalanced rotating and reciprocating masses of the engine create unbalanced external moments although the external forces are zero.

Out of these moments only the first and second order moments need to be considered. The first and second order moments are vertical but the former is produced in one cycle per revolution of the crank and the latter two cycles per revolution.

Again, the engines with low number of cylinders require careful examination of balancing by external balancers to avoid resonance hull vibration.