Research On Time Varying Modal Parameter Identification Method Of Liquid Filled Rocket Tank

In many practical systems, the system parameters are unstable and are changingover time. And because of the continuous variability and complexity of thetime-varying parameters of current structural systems, methods of the time varyingsystem parameters identification remain to be further developed, so researches onvariable structure system parameter identification methods are very important andhave theoretical significances and extensive engineering application values.In this paper the fluid-structure interaction theory is studied in the bases ofwater filled rockets tank’ vibration problem and finite element software ANSYS isused for the water filled rocket tank’s simplified model (variable mass offluid-filled cylindrical shell) for modal analysis.In this paper, firstly, we have donemany researches on the time-varying system parameter identification methods.Many time-varying system parameters identification methods have beensummarized at home and abroad, and put forward the deficiencies of existingmethods. Then two kinds of time varying parameter identification methods whichare called an identification method of using broken line to approx imate time varyingparameter and an identification algorithm with auto-regulation forgetting factor forfast time varying system are studied. The two methods are used for short-termtime-varying system parameter identification in simulations. According to theresults of the simulations, the applicable conditions of the two kinds ofidentification methods are analyzed. The results of the simulations indicate theeffectiveness of the two methods. Furthermore the sensitivities of the twoidentification methods are studied by setting different noise levels in thesimulations.Secondly, studies on the relationship of the sub-interval size of theidentification method of using broken line to approximate time varying parameterand changing rate of the system frequency. Then I pay much more attention to thesub-interval size of the identification method of using broken line to approximatetime varying parameter, for its unreasonableness of the sub-interval size, animproved method of the sub-interval size has been put forward in this paper. Andsome simulations has been studied, according to the results of the simulations, wecan see the accuracy of the improved identification method of using broken line toapproximate time varying parameter. Finally, experiments of a liquid filled rocketpropellant tank are adopted to demonstrate the efficiency of the improvedidentification method of using broken line to approximate time varying parameter and the identification algorithm with auto-regulation forgetting factor for fast timevarying system.A study of a liquid filled rocket propellant tank’s vibration characteristics hasbeen researched. For the importance of the liquid filled rocket propellant tank’svibration characteristics to the whole rocket’s structural dynamics characteristics,and in many cases, the liquid filled rocket propellant tank’s modal parameters aretime-varying. In this paper, liquid filled rocket propellant tank’s vibration issuesstudied. Mainly through experimental methods, collecting different cond itions ofliquid filled rocket propellant tank’s vibration response data, then using theimproved identification method of using broken line to approximate time varyingparameter and the identification algorithm with auto-regulation forgetting factor forfast time varying system to identified the parameters of the liquid filled rocket. Inthe end, the changed regularity of the modal parameter liquid filled rocket propellanttank’s vibration characteristics has been obtained. Namely, in the case of the samefluid, the variable mass of fluid-filled cylindrical shell’s vibration modal frequencieswill be decreased with the increasing liquid positions in the variable mass offluid-filled cylindrical shell; In the case of different fluid, the variable mass offluid-filled cylindrical shell’s vibration modal frequencies will be decreased with theincreasing liquid’s density; In the case of different flow velocity, the variable massof fluid-filled cylindrical shell’s vibration modal frequencies will be varied with theflow velocity, that is the variable mass of fluid-filled cylindrical shell’s first ordervibration modal frequency will be decreased with the increasing flow velocity.