Simplified model for longitudinal vibration calculation
China Classification Society requires that for the propulsion shafting of large low-speed diesel engines and turbines, the longitudinal vibration characteristics of the propulsion shafting must be submitted and approved by the classification society. In the calculation of longitudinal vibration, the model of longitudinal vibration can be simplified as follows:
(1) The mass of the crank unit of each cylinder of the diesel engine is equally divided at the center of the two main journals of the crank.
(2) Transmission gears, sprockets, flywheels, thrust disks, propellers, etc. are placed as lumped masses in the center of gravity or geometric center of each component, and the propeller should also be included in the additional hydraulic effect.
(3) The intermediate shaft, the tail shaft, and the propeller shaft are dispersed into several lumped masses according to natural segmentation or other methods, and the distribution of mass at each discrete point should keep the position of the center of mass unchanged. Generally, a lumped mass should be placed at the bearing support position, and the shaft segment can also be processed as a distributed system according to natural segmentation.