Optimization Design On The Radiated Noise Of Timing Gear Cover For The Diesel Engine

Each component of the engine is a kind of structure. It is always vibrating because of the exciting force, causing the vibration and radiated noise around the air, therefore, the structure vibration noise is also called the surface radiated noise. The radiated noise of the timing gear cover is a part of structure vibration noise, because the timing gear cover has characteristics that the wall is thin and the surface area is wide, it is the important surface radiated noise. Therefore, through the reasonable design, the development and research of the low radiated component structure is provided with the very high practical value.First, it had conducted the experimental study with the complete engine and its components .On the one hand, according to the Pulse noise test system of B&K Corporation, the recognition of noise source for the engine was finished, and the acoustic intensity and the acoustic power test of the timing gear cover were also carried out. On the other hand, the modal analysis of the timing gear cover was carried out. According to the Test.lab test system of LMS Corporation, The modal experimental analysis of the timing gear cover was completed, the experimental modal parameter was obtained. Compared with the computational results, the accuracy of computational model provided the foundation for later dynamic analysis.Secondly, it was carried on the dynamic response analysis of the timing gear cover. The dynamic response analysis of structure was done by the finite element analysis software, it separated the complex elastic structure vibration problem into the vibration problem of the approximate limited multi-DOF system, then carried out the dynamic analysis. When the structure was vibrating intensely, the surface can produce the radiated noise. And then, the structure had to carry out the vibration analysis, it was namely the structure dynamic response analysis. The experiment obtained the excitation acceleration frequency spectrum of the timing gear cover. It was taken as the excitation of the dynamic response analysis, and obtained the dynamic response distribution of the timing gear cover by FEM.The dynamic response analysis result of the timing gear cover is the boundary condition of BEM, it can carry out the outside radiated sound field analysis, mainly based on boundary element theory. This boundary element analysis method is similar with the finite element method, and is also a numerical method. The difference is that the integral equation is taken as the foundation of the establishment equation. Boundary element analysis method is based on thegreen theorem, transforming the differential equation into the boundary integral equation. Through the boundary integral equation, the dimension of question is reduced according to boundary element method, it can deal with the infinite domain problem, and the sound field analysis is carried out. First, establishing a boundary element model of the timing gear cover, then, using the dynamic response analysis result of the timing gear cover, it is carried out the radiated noise analysis, last, the radiated sound pressure, frequency spectrum of acoustic power is obtained, the peak frequencies are discovered. The noise contribution of the various parts of timing gear cover is obtained, and the optimization area is discovered, it is provided the important basis for the optimization analysis of the timing gear cover in the next step.Through the radiated sound field analysis of the timing gear cover, optimization areas of the finite element model were found. In virtue of Hyperworks optimization analysis software of Altair Corporation, the optimized analysis model of the timing gear cover was established, the parameter variables were needed in the optimization analysis process, and the optimization areas of the timing gear cover were optimized. The optimized model was tested by the computing modal analysis results. it was inspected whether the optimization goal was reached. In this paper, the definition of optimized parameter is as follows: the design variable was the region of the optimization design, the response variables were modal natural frequency and volume ratio, the constraint condition was the modal natural frequency, the objective function was volume ratio. If the result could not be satisfying, then the structure must be optimized again, ultimately it achieved the best optimized effect.The types of the structure optimization include the topology optimization, the topography optimization, the shape optimization and the size optimization, all the types of structure optimization may be combined. In this paper, the topology optimization has been mainly used. The topology optimization is essentially in the design space assigned, and achieves the best material distribution of structural element; The topography optimization is a kind method in the structure assigned, the distribution of ribs are determined, it is mainly applied on the shell elements, its difference with the topology optimization is that, it does not remove the material, and creates ribs in the design region based on the moved nodes in order to make the structure strengthen, and enhances the rigidity and the frequency of the structure; The shape and size optimizations enable the structural partial region to achieve the best shape and the size. The goal of the structure optimization is reducing the radiated noise capacity of the structure surface, and achieving the best acoustics effect.The structural design process may be regarded as a kind of optimization process, the process is that the people try to reduce the cost, and to enhance the performance and the outward appearance for the structure. In a general way, the design process includes the conceptual design, design, verification and optimization. The conceptual design stage is the base of the entire process. The topology optimization is a kind of important design tool in the conceptual design stage. It is based on the result of the optimization, but not depending on the estimation. Using the topology optimization, it can make the calculating result as the foundation of the design, then the concept model can be obtained in the reference design stage, and the change of the conceptual design model can be avoided in the experimental design stage. On the foundation of the conceptual design, the finite element model of the conceptual model can be obtained, then analysis is done by the FEA software, the result usually determines the direction of structure improvement, and then optimizing the details of the structure, until the best structural design is achieved. This is a good process.