Investigation On Structural Dynamic Scale Model Design Of Launch Vehicles Based On The Discrete Similitude Method

Scale model test,as an important way to obtain the dynamic characteristics of launch vehicles,has the advantages of high efficiency,low cost and low technical risk.However,there are many limitations in applying traditional similitude method to scale model design of launch vehicles,especially the similitude distortion problem in scaling down smallsized structures.Therefore,the discrete similitude method suitable for the study of the similitude of complex structures is proposed and used as the theoretical framework of this dissertation.Then,the complete similitude relationship of dynamic characteristics for stiffened cylindrical shells is deduced by using the discrete similitude method.Furthermore,for two similitude distortion problems caused by skin thickness and rib sectional parameters,energy similitude correction method and equivalent similitude method are proposed in turn.And the similitude relationships with similitude distortion are deduced.Finally,taking the beam-element model of launch vehicle as the research object,the complete similitude relationship of dynamic characteristics is deduced,the problem of similitude distortion caused by the cross-sectional size of the bundled connecting rod is analyzed,and the corresponding solutions are put forward.In the process of research,the proposed similitude methods and the deduced similitude relationships are verified by comprehensive numerical simulation and some experiments.The main contents are as follows.A discrete similitude method is proposed to analyze the similitude of dynamic characteristics for complex structures.In view of the problem that the complex and fine structure can not be completely scale down,the discrete similitude method is proposed based on the theory of similar combination,and the similitude relationship of the free vibrational characteristics of the general structure is deduced and simplified.Finally,the advantages of the proposed discrete similitude method are analyzed.The complete similitude relationship of the dynamic characteristics for stiffened cylindrical shells is deduced with the discrete similitude method.Based on the similitude relationship of dynamic characteristics for plane shell elements,two kinds of partial similitude relationship of dynamic characteristics for cylindrical shells are established by using the discrete similitude method.Furthermore,by combining the two partial similitude relationships and restricting the section of ribs to be rectangular,the complete similitude relationship of dynamic characteristics for stiffened cylindrical shells is obtained.Finally,the correctness of the deduced similitude relationship and discrete similitude method is verified by numerical simulation.An energy similitude correction method,for solving the similitude distortion problem caused by the wall thickness of stiffened cylindrical shells,is proposed.On the basis of the complete similitude relationship of stiffened cylindrical shells,the similitude distortion problem caused by the wall thickness is analyzed.The distortion and size effectsare analyzed by numerical examples,and the intrinsic mechanism is revealed by using the strain energy ratio.The energy similitude correction method is proposed to correct the similitude problem quantitatively.Finally,the validity of the proposed energy similitude correction method is verified by numerical simulation.An equivalent similitude method,for solving similitude distortion problem caused by the sectional parameters of stiffened cylindrical shells,is proposed.On the basis of the wall thickness similitude distortion problem,the similitude distortion problem caused by the sectional parameters of the stiffeners is further analyzed.The equivalent similitude method is put forward by three kinds of equivalent analysis.For the local models and the whole models of the stiffened cylindrical shells,there similitude relationship is deduced respectively,and solution of the similitude distortion problem is proposed.Finally,the validity of the solution and the equivalent similitude method are verified by the numerical simulation.Based on proposed discrete similitude method and equivalent criterion,similitude of the global dynamic characteristics of launch vehicles is studied: Taking the beam-element model of launch vehicles as the research object,using the discrete similitude method and the deduced equivalent criterions,the similitude relationship of the three non coupling modes including the tension,bending and torsion for beam elements is deduced.Then,the complete similitude relationship for the global dynamic characteristics of launch vehicles is established.The problem of the similitude distortion problem caused by the connecting rod is analyzed,and the solution is proposed.The numerical simulation and test is used to verify the correctness of the deduced similitude relationship and the solution of the similitude distortion problem.To sum up,this paper establishes a systematic method system for the structural dynamic scale model of launch vehicles,and is a great value in theory and engineering application.