Research On Structure Vibration Characteristic In Thermal Environment

With the development of the technology of hypersonic vehicle, aircraft aerodynamic heating environment is becoming increasingly harsh, the thermal modal research for the safety of the aircraft is getting more and more important.In this thesis, cantilever and clamped-clamped beams in thermal environment are set as research objects. The variation of nature frequency and damping ratio of beam is summarized via simulation and thermal modal test. This offers research reference to complex structure’s thermal modal. Sever aspects of work have been done.(1) Initial stress stiffness matrix of beam element is deducted and verified on the basis of theory of statics. It turns out that the distribution of thermal stress in the cross section of beam element has no impact on its initial stress stiffness matrix. By applying this to beam, it is concluded that the distribution of thermal stress in the cross section of beam has little impact on its nature frequency. But the change of elasticity modulus of part of beam has more influence on the nature frequency and mode of vibration.(2) Three kinds of modal parameter identifications are studied which are orthogonal polynomial fitting method(OPF), vector fitting method(VF) and EMD method. The availability of OPF and VF in identifying nature frequency and mode shape is verified by fitting the FRF of a multi-DOF beam. The availability of EMD in identifying nature frequency and damping ratio is verified by using it on measured free vibration datas of a cantilever.(3) Thermal modal test system is builded and tested at room and high temperature. FRF and free vibration datas are collected on which OPF, VF and EMD are used. It turns out that OPF, VF and EMD are effective but each have advantages and disadvantages. OPF is more accurate in identifying mode of vibration and so is VF in nature frequency and EMD in damping ratio.(4) Based on those modal parameter identification methods and thermal modal test, the following conclusions were summarized. Natural frequences will decrease and more and more close to each mode with increasing temperature; Modal damping ratio will increase under the same vibration amplitude as the temperature rises.