Model Reduction Method And Its Application In The Dynamic Analysis Of A Commercial Vehicle Body

Precise body dynamics model is important in optimizing vehicle vibration and noise(NVH) performance and fatigue properties. However, the dynamic response calculation need to consume enormous computing resource s because of the large number of degrees of freedom(DOF) of precise finite element model of body, resulting in inefficiency, and real-time property cannot be guaranteed. Model reduction could reduce the number of degrees of freedom of model and improve calculation accuracy, thus efficient computation could be completed.With the support of a large-scale automobile company project "The establishment and application of vehicle vibration dynamic model based on reduction technology”, a commercial vehicle body is taken as the subject of its research, model reduction theory and method are used and the research of model reduction method and its application in the dynamic analysis of a commercial vehicle body is carried out. The main contests and results are as follow s:1. Introduce the model reduction theory, compare various reduction methods, and then choose Guyan and IRS method to reduce the finite element model of body.2. Establish the finite element model of body, then modify the model according the preliminary results of the modal analysis, in order to suppress the local modes and highlighting the overall modes. Modal analysis is then again carried out, In order to compare the reduced model in the following chapter.3. Based on the Guyan and IRS model reduction methods, the body dynamics model is established respectively. The modeling process includes: extracting the stiffness and mass matrix, selection of master degree s of freedom, establishment and optimization of reduction program; The accuracy of reduction model is verified by comparing the modal properties and dynamic characteristics respectively; Results show that the IRS model has higher accuracy, and could be used to conduct long-time analysis of dynamic response instead of the original model.4. The paper presents a dual-reduction method: performing model reduction furtherly for the primary reduced model to get a compact and accurate equivalent model. The result shows that the dual-reduction model gives better effect than the ordinary reduction model when the two condensation ratios(the ratio between the numbers of DOFs of the full model and the condensation one) are comparable.Reduce the finite model of the body by reduction method, finally, an equivalent reduction model is obtained, which improved the calculation efficiency, and the model accuracy is verified by comparing model properties and dynamic characteristics. The research work of this thesis is an important part of the vehicle vibration modelling, and provides a theoretical reference and engineering guidance for vehicle design and development.