Study On Dynamic Characteristics Of The Axially Flying Beam

In this paper, vibration characteristics of the transverse oscillation of the axially flying beam is investigated, according to the flying speed,we divide the question into low and high speed conditions.Firstly, dynamic characteristics of the axially flying beam at low speed is investigated.The differential equation of transverse motion of the beam is derived by Newton's second law and Hamilton's principle Newton's second law.Then we apply the Galerkin method to truncate the partial differential equation into a set of ordinary differential equations, and the effect of the axially flying speed on the first order natural frequency of the beam is researched. It is found that the first order natural frequency decrease as the axial velocity increase, so there is a critical velocity of the axially flying beam.Then we take the arrow as the research object to make experiment to analyze the modal parameter of it.There are two methods in our experiment.In the first method,we measure the frequency response function by means of the dynamic signal analyzer 35670, then identyfy the first three order modes by means of I-DEAS software.In the second method, we record the flying process of the arrow with the help of high-speed camera, and make qualitative analysisand and quantitative analysis to it. According to the record,we can get the first order natural frequency.With the help of MSC.Patran/Nastran software,we make simulation of the arrow and get the first three modes,and the results keep consistent with the experimentSecondly, dynamic characteristics of the axially flying beam at high speed is investigated. The vibration characteristics,especially thermal vibration characteristic of the beam under aerodynamic heating is analyzed. the finite element method is used to analyze the temperature field and thermal stress. The temperature effect which has been taken as 'thermal load' forced on the body, then, such thermal stress is settled as general elasticity mechanics question. Secondly, the thermal stress is taken as'pre-stress', then, deduce extra stiffness matrix caused by pre-stress.Considered the mechanical property of the material changed with thermal, get the new system thermal stiffness and the nature frequency of the structure.By means of FEM method, we get the conclusions as followed: thermal stress and the mechanical property of the material variety can send the nature frequency down; the latter effect stronger; the nature frequency is decreased by the two factors, the higher the nature frequency is, the more it decrease.