Modal ANalysis And Structure Optimization Of Car Frame

With the rapid development of modern economy, auto industry competition becomes increasingly fierce, in order to save costs, improve product r&d efficiency and shorten the development cycle, all the car company around the world using some advanced design means. With the constant perfecting ansys technique and the continuous development of computer, the proportion of the ansys method applicate in research on automobile products become larger and larger, got more extensive application.For most cars, general are adopted load bearing body, rarely exists frame, but because of some special needs, few cars through the frame to bear external load still. The frame act as the main bearing parts of the car, in addition to bear most quality of the car, also suffered other external excitation shock, such as engine incentive and pavement incentive etc. so a reasonable frame structure becomes more important. Frame should have enough stiffness, strength, service life, the safety and reliability, all of these aspects should be considered in reasearch the frame.This paper first introduce the ansys method and software Hyperworks, made theoretical foil for the follow-up modal analysis and structural optimization of frame structure. Secondly, make reasonably local structure simplified for existed car frame three-dimensional geometrical models of shanghai, simplified to omit the little impact on parts of the frame structure, make circular bead as right angle ect. And using the software of Hypermesh for frame modeling, analyzed and studied the modeling process. Through Radioss module analysis the free modal of frame., to get first six order natural frequency and vibration mode of frame. Finally, based on the model, added quality load on the frame, and simulated the constraint of spring, Through Radioss module analysis constraint modal, and obtain first six order modal of frame.After established the model of frame, in order to assure the accuracy of this model, analysis the tested modal of frame. Through testing software LMS to measurements 56 position of frame, measured related test data, And through the follow-up tests data processing, proceed modal parameter identification, obtained six modes of frame last. Compared the results of constraint modal analysis and the results of experimental modal analysis, and the relative error in allowing range, illustrated accurate of the established model. Using the OPTISTRUCT module optimized analysis of frame, Because frame first-order the perpendicular bending frequency(27.3Hz) and engine idling process incentive frequency(26.9Hz) very close, In order to avoid frame produce resonance, affecting service life and safety, need to carries on reasonable optimization of the frame. This article taking frame first-order vertical bending frequency as target function, optimizated the frame beams and longitudinal thickness of design variables size, and discussed four optimization scheme, eventually make the first-order perpendicular bending frequency increased to 28.7Hz, has effective avoided the frame resonate frequency.This paper analysis to the frame modal, and through experiment to amend the model, the process of "Modal analysis-test-model modification-structure optimization" can used in other vehicle research, also for frame structure optimization provides a reference method.