Conference Year

2014

Keywords

reciprocating compressors, crankshaft torsional vibration, natural frequency, ADAMS, flexible multibody dynamics theory

Abstract

Abstract:The crankshaft accidents due to vibration become severe with increasing number of rows of reciprocating compressors.The crankshaft vibration needs to be studied thoroughly to promote development of the reciprocating compressor.Early calculations of crankshaft torsional vibration was mainly with discretization method, the crankshaft is discretized into a series of lumped inertia and lumped stiffness,then calculate the swing angle of crankshaft in the gas force and inertia force,but because of the simplified calculation,which has low precision.The currently calculation method of crankshaft torsional vibration is simplified into an equivalent system model,the model is composed of a lumped mass disc,massless elastic shaft and a damping.In calculation the torsional natural frequency and forced vibration usually adopt the Holzer method and transfer matrix method,due to this method only calculation the crankshaft torsional direction, so it can only obtained the crankshaft natural frequency and vibration characteristics in the direction.To make the crankshaft torsional vibration calculation more accurately,we proposed a new calculation model based on the flexible multibody dynamics theory.The process of the model establishment and solving by ADAMS was introduced.The torsional vibration of a crankshaft, which often suffers from the crankpin fracture,was calculated before and after the structure change.Results show that before the structure change,the crankshaft natural frequency was closed to the excitation frequency,so that the tortional vibration amplitude of the crankshaft is very large.The stress of piston pins in the first and second row increase so rapidly along the directionof the cylinder center line that the impact factor ofthe crank pin bearing reache the upper limit,thus the oil film of it is damaged.After the structure change,the natural frequency of crankshaft is away from the excitation frequency,the vibration amplitude of the crankshaft torsional vibration decrease substantially,and the crankpin fracture does not happen anymore.This is a successful validation of the proposed calculation method.

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Simulation of Crankshaft Torsional Vibration by Flexible-body Dynamics

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