Research On Prediction And Optimization Of Structural Noise Of Main Parts Of IC Engine

The research of structural noise control is an important aspect of noise and vibration control domains. The YC6108 diesel engine made by the Yuchai Machine Stock Company as the research object, the prediction and optimization of the structural noise has been studied detailedly. The work includes these aspects: research of Boundary Element (BE) Method for noise prediction; the construction of entity model and Finite Element (FE) model of the main parts of the engine; the construction of FE model and BE model of the assembly parts; the FE and experimental modal analysis of the parts and their assemblies; the harmonic response analysis and radiated noise prediction of the assembly parts; the study on acoustic sensitivity analysis method; the sensitivity analysis of the natural frequencies and radiated noise of the parts; the research of Parallel Hybrid Genetic Algorithm (PHGA), which suitable for the vibroacoustic optimization; the acoustic optimization of the position and length of the strengthened plate on the sump of the engine.The achievements of former researcher in noise and vibration control of engine are reviewed firstly, which make the key problems clearer.To shorten the time of the noise prediction and solve the difficulties on the acoustic optimization, the speed of the BE method has been improved by adopting the lumped parameter model of the Helmholtz equation. The new formulas for the noise prediction have been derived, which could shorten the calculation time in evidence, with the calculation precision assured.The entity models and FE models of the block, cylinder heads and sump of the 6108 engine are constructed, and then the FE and experimental modal analysis has been implemented. The analysis results indicate that these models are reasonably precise, so they could be the basic models for the following researches. By the modal analysis of the block, cylinder head and sump, the vibration characters have been understood, which could guide to reduce the noise and vibration. The result indicates that the skirt part of the engine, especially the side of the air inlet, is the weakest area in the whole block. So the particular consideration about the area may have better result. By calculating the natural frequencies of the block in different mesh densities, a suitable mesh density has been determined. The FE models of three assemblies are created, which are the assembly of block- cylinder head, block-sump, and block-cylinder head-sump. The difference of the mode shapes of the assemblies in different displacement couple patterns has been compared. In the three parts, the stiffness of the cylinder head is biggest, the block bigger and the sump smallest. The mode shapes of the weakest part dominate the low-stage shapes of an assembly. After analyzing the excitation on the engine, the positions, magnitudes, phase angles and the exerted patterns of three kinds of loads have been determined. Harmonic response analysis has been done with these loads. Then the radiated noise is predicted after the nodes' velocities transferred from the FE model to BE model. The results of the noise prediction are close to the experiment data, which indicate that these algorithms including BE method are precise.The formulas to analyze the acoustic sensitivity with the lumped parameter BEM have been derived. The study reveals that the re-calculation method for the noise sensitivity is suitable for lumped parameter BEM. The natural frequencies sensitivity to five parameters of the block and to four parameters of the sump has been analyzed. The natural frequencies sensitivity and noise sensitivity of the block-cylinder head-sump assembly also has been analyzed. The sensitivity analysis guides the structural modification. The plate thicknesses of the skirt part on the air inlet side of the block, transverse plate in the crankcase, whole sump, flake part of the sump are the effective parameter to the noise character of the assembly.The acoustic optimization of a practical part has been initiated in this dissertation. A par...