Simulation Analysis And Structural Optimization Of Radiated Noise Of Off-road Diesel Engine

The types and possessions of off-road machinery continue to rise.National relevant policies and regulations are becoming increasingly strict.The NVH performance of off-road machinery is also receiving more and more attention.As a power source and noise source,the vibration noise level of off-road engines directly affects the performance of the machine.Controlling its vibration and noise has important practical significance.At present,the research on vibration and noise reduction of diesel engine mainly focuses on road diesel engines,and less attention is paid to off-road diesel engines.In this thesis,the off-road diesel engine in a design and development stage is taken as the research object,and the vibration response analysis and radiation noise prediction are carried out,which provides a reference for the research of vibration and noise reduction of off-road diesel engines.Through theoretical calculation and numerical simulation,the multi-body dynamics method,finite element method and boundary element method are used to complete the vibration response analysis,radiation noise prediction and structural optimization design of off-road diesel engine.(1)The finite element model of off-road diesel engine is established.The whole structure of diesel engine is discretized by grid.The influence of different grid sizes on the modal analysis results of cylinder head is analyzed.The optimal grid sizes of key components are determined by synthesizing the calculation accuracy and model scale.The modal analysis of the whole structure of diesel engine is carried out to obtain its vibration characteristics.(2)A multi-body dynamic model for rigid-flexible mixing of off-road diesel engine is established.The flexibility of crankshaft is treated by modal synthesis method.A multi-body dynamic model of off-road diesel engine with rigid-flexible mixing is established.The calculation shows that the motion state of the piston is consistent with the theoretical derivation.Based on this model,the time and frequency domain data of main exciting forces such as bearing force,piston side thrust force and gas force are calculated.(3)Vibration response of off-road diesel engine is analyzed.Based on the incentive data that has been obtained,the actual loading position of each excitation force is determined.Complete the structural vibration response analysis of diesel engine working process.The time domain and frequency domain data of diesel engine surface vibration velocity are obtained.The results show that the cylinder head cover and bearing are the parts with the greatest vibration speed,followed by the skirt of the body and the bottom of the oil pan.(4)The radiated noise of off-road diesel engine is predicted.A suitable subregional boundary element mesh model is established.The surface vibration velocity data of off-road diesel engine are mapped to the boundary element model,and the radiated noise is calculated by the indirect boundary element method.The results show that the contribution of radiated noise of the diesel engine is large in the frequency range of 300-1500 Hz,and the cylinder head cover is the main noise contribution panel.(5)The radiated noise of the off-road diesel engine is controlled based on structural optimization.The radiated noise of off-road diesel engine based on structural optimization is controlled.According to the vibration response analysis of diesel engine structure and the calculation results of radiated noise.Structural optimization design of cylinder head cover and oil pan is carried out.The results show that the optimized model noise is reduced by 1.17 dB.