Types of vibration in main engine: 1. linear vibration 2. torsional vibration(most damaging) 3. resonant(with combination to above)
Node: Point where deflection of a shaft is 0 and amplitude changes sign( more node higher the value of natural frequency of vibration).
Forcing frequency: firing impulses super impose and appear as a compex wave form represented as by harmonics(1st order, 2nd order, 3rd order..)
Balancing of vibrations: controlling vibration by arranging out of balance forces and couples so that they cancels out or reduced.
Vibrations in two stroke engine:
1.external unbalanced moments(1st order and 2nd order moments)
2. guide force moments(transverse reaction force acting on the cross-head due to con rod and crankshaft mechanism,they excite engine vibration in athwart ship direction causing rocking( excited by h moment) or twisting (excited by z moment) can be reduced by adding engine bracing)
3. axial vibration in shaft( during gas loading , the arms of crank throw deflect the crankshaft exciting axial vibration, reduced by using axial vibration dampers)
4. torsional vibration in shaft (varying gas pressure causes varying torque in crankshaft along with propeller action on non uniform wake field can reduced by using torsional vibration dampers
Node: Point where deflection of a shaft is 0 and amplitude changes sign( more node higher the value of natural frequency of vibration).
Forcing frequency: firing impulses super impose and appear as a compex wave form represented as by harmonics(1st order, 2nd order, 3rd order..)
Balancing of vibrations: controlling vibration by arranging out of balance forces and couples so that they cancels out or reduced.
Vibrations in two stroke engine:
1.external unbalanced moments(1st order and 2nd order moments)
2. guide force moments(transverse reaction force acting on the cross-head due to con rod and crankshaft mechanism,they excite engine vibration in athwart ship direction causing rocking( excited by h moment) or twisting (excited by z moment) can be reduced by adding engine bracing)
3. axial vibration in shaft( during gas loading , the arms of crank throw deflect the crankshaft exciting axial vibration, reduced by using axial vibration dampers)
4. torsional vibration in shaft (varying gas pressure causes varying torque in crankshaft along with propeller action on non uniform wake field can reduced by using torsional vibration dampers
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