A Study On The Prediction Of Vibration And Noise Of Diesel Engine Considering The Influence Of Joint Characteristics Of Component Joints

For the vibration and noise prediction research of diesel engine,in general,the vibration prediction is firstly performed by finite element method(FEM),and the predicted results are used as the boundary condition,and then the noise prediction is performed by boundary element method(BEM).The joint surfaces play an important role in transmitting forces and vibrations,and will produce different degrees of mutual compression and slippage under the loading of external forces.And they make the joint surfaces characterized of stiffness and damping,which has a greater impact on the accuracy of prediction.Therefore,establishing a reasonable equivalent model of the joint surface is key to improving the accuracy of vibration and noise prediction of diesel engine.In this paper,an equivalent model of transversely isotropic virtual material is proposed to establish the combined structure finite element model of diesel engine.At the same time,the modal test is introduced to acquire the natural frequency and damping ratio for identifying the unknown parameters of the virtual material layer,by using the BP neural network algorithm.The main excitation forces,such as cylinder gas pressures,piston slap forces,main bearing forces and valve train forces,are calculated and their loading method are given,and the vibration and noise prediction model of diesel engine is established.And then the vibration and noise prediction are performed in time domain,under the loading of each excitation force alone and together.In time and frequency domain,the vibration acceleration level of engine feet,the vibration severity of engine block and the sound pressure level of radiated noise are adopted to analyze the characteristics of the structure vibration and radiated noise of diesel engine,under the loading of each excitation force alone and together.Furthermore,the contribution of each excitation force to structural vibration and radiated noise is analyzed as well.The predicted results of the vibration acceleration level of engine feet,the vibration severity of engine block and the sound pressure level of radiated noise are 146.40 d B,27.09mm/s and92.57 d BA,respectively.The maximum contribution of the them are the main bearing forces,the cylinder gas pressures and the main bearing forces,reaching 50.91%,74.86% and 48.70%,respectively.A test bench of the structural vibration and radiated noise of diesel engine is designed and built for measuring the acceleration of engine feet,the velocity of engine block and the sound pressure of radiated noise.The measured results of the vibration acceleration level of engine feet,the vibration severity of engine block and the sound pressure level of radiated noise are 146.31 d B,23.75mm/s and 96.51 d BA,respectively.Compared with the predicted results,the measured results are analyzed to verify the accuracy of the vibration and noise prediction model of diesel engine in time domain and frequency domain,which is based on transversely isotropic virtual material modeling method of joint surfaces.