The Study Of Extraction Of Structural Free-Free Modes

For the problem of the mode test boundary transformation, it has been one of the topics concerned in aviation and spaceflight field all the time. The large scale mother vehicle size and the weight are too big to carry out free-free mode test under the original experimental tower and the old supporting system condition, so as to be compelled to have the structure supporting in some rigidity or the certain elastic basis, and carry on the mode test in the restraint condition. Therefore it is required to extract modes of free-free structure from constrained test data. But it just started regarding this method research, and was needed to be improved not only test but also theory, therefore, it has great significance for this question research.On the basis of the consideration of the above, the article embarks from the multi-degrees of freedom structure secular equation, in view of the different boundary condition, considered Zhang D Wen method and one general perturbation method two elementary theories methods, and has established the corresponding procedure. At the same time, we have conducted the thorough value simulator study in view of the different finite element model to two kind of elementary theories, and has carried on the comparative analysis to the analogue result, obtains them under the different supporting condition respective characteristic. Finally further optimizes using the model revision technology to the theory method.At the same time, this article has carried on the mode test to my school mechanics laboratory cantilever beam structure and the model wing two kind of structures, and particularly researched for the mode test as well as carried on processing to the test data. Using Guyan static state reduction and vector expansion carries on the degree of freedom match, and extracts free mode from test data based on the constrained condition. Finally the results are contrasted analyzed to those obtained through the computer numerical simulation.The result indicates, extraction of free-free mode from constrained test data not to lose is a effective solution for large scale mother vehicle structure dynamic characteristic.