| As an important part of the ship power system,the engine is also the major noise source.The cylinder head cover accounts for about 20%of the radiated noise on the engine surface.On the one hand,the vibration noise of the engine affects the stealth performance of the ship.On the other hand,it also affects the comfortableness of the working environment of crew.Therefore,it is of great significance to study the acoustic radiation characteristics of engine cylinder head cover.In this thesis,the modal characteristics of a diesel engine cylinder head cover are analyzed and verified through experiments.Then,based on acoustic-vibration coupling method,the acoustic radiation characteristics of diesel engine cylinder head cover structure are studied.Finally,the vibration characteristics of diesel engine cylinder head cover are studied,and the structural optimization analysis of diesel engine cylinder head cover is carried out based on morphological topology optimization.The main contents and conclusions are as follows:(1)Structural modeling and modal characteristics analysis of diesel engine cylinder head cover.The three-dimensional model of a diesel engine cylinder head cover is established by ProE,and the finite element model of the diesel engine cylinder head cover is established by using Hyper Mesh to divide the grid.The free mode and constrained mode of the cylinder head cover are analyzed by Optistruct module.The results show that the first six orders of free modes of the diesel engine cylinder head cover are distributed in the 200 Hz～610 Hz frequency band,and the constrained modes are distributed in the 440 Hz～940 Hz frequency band,and the vibration modes are concentrated in the side plate position of the cylinder head cover.Modal characteristics analysis lays a foundation for the acoustic radiation characteristics analysis and structural optimization of the diesel engine cylinder head cover.(2)Research on vibration response characteristics of diesel engine cylinder head cover.The free modal test and vibration response characteristics test of diesel engine cylinder head cover are carried out.The measured vibration response of cylinder head cover surface is used as the input excitation to solve the acoustic radiation of cylinder head cover,and the vibration transmission characteristics are analyzed.The results show that in the free state,the modal test results of the cylinder head cover are consistent with the simulation results.Through the experiment,the frequency response curves of the vibration velocity of the cylinder head cover in the X,Y and Z directions at each measuring point in the 100 Hz～4000 Hz frequency band are obtained.The vibration in the Y direction of the side plate position of the diesel engine cylinder head cover is the most severe,and the maximum vibration acceleration in the Y direction is 6.0 m/s~2.Research on vibration response characteristics provides a basis for the subsequent acoustic radiation analysis of the cylinder head cover.(3)Analysis of acoustic radiation characteristics of diesel engine cylinder head cover.In the Virtual.Lab,the boundary element method is used to study the acoustic radiation generated by the coupling of the shell structure and the internal acoustic cavity under the surface acceleration excitation of the simulated cylinder head cover,the sound pressure frequency response diagram on the field point and the sound pressure cloud diagram on the surface of the sound field are obtained.The results show that the maximum sound power level of the cylinder head cover is 89.1 d B at 1140 Hz,and the total sound power level is 99.4 d B in the range of 100 Hz～4000 Hz.From the modal participation factor diagram,it can be seen that in the 100 Hz～400 Hz frequency band,the first and second modal modes of the cylinder head cover involve more frequently,especially at 400 Hz,where reaches the maximum peak value.Therefore,the structural parameters should be optimized according to the first two modes of the cylinder head cover structure.(4)Structural optimization analysis of diesel engine cylinder head cover.Based on morphology optimization and topology optimization,the acoustic radiation characteristics of diesel engine cylinder head cover structure are optimized.Opti Struct is used to optimize the structure of the cylinder head cover.In order to improve the low-order modal frequency,the surface acoustic radiation characteristics of the optimized cylinder head cover structure are calculated.The results show that the first two modal frequencies of the cylinder head cover structure are increased by 20.4%and 31.6%respectively after the shape optimization.After topology optimization,the first and second modal frequencies of the cylinder head cover are increased by 54.1%and 54.2%respectively.According to the final optimization scheme,the maximum radiated sound power level of the cylinder head cover structure surface is reduced by 2.5 d B,and the total sound power level is reduced by 1.0 d B.The research results of this thesis can provide reference for the vibration and noise control of diesel engine cylinder head cover. |
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