Dynamics Modeling And Analysis Of Time-varying Mass Flexible Structures

With the size and diameter increasing of new launch vehicle structures, the overallstiffness of rocket structure declines and the flexibility increases constantly, which giverise to that the whole rocket rigid-flexible coupling dynamics problem caused by widerange movement of aircraft become more and more prominent. Meanwhile, with theincreasing rates of rocket fuel combustion, the mass parameters time-varying dynamicsproblems caused by the rapid changes of rocket structural mass parameters with time arebecoming increasingly prominent. Therefore, it is of great significance to construct amore precise dynamics model of flexible structures with time-varying mass parameters inthe design and development of a new large launch vehicle.In this thesis, dynamics modeling and analysis methods of flexible structures withtime-varying mass parameters are researched from two perspectives of the structuraldynamics and flexible multi-body dynamics. Firstly, structural dynamics equations of asingle degree of freedom system, two degrees of freedom system and multi degrees offreedom system are established, from which the universal form of the structuraldynamics equations of flexible structures with time-varying mass parameters areextracted. Then, the general form of element matrix with time-varying mass parametersis derived based on the finite element method. According to the characteristics of thegeneral form of element matrix with time-varying mass parameters, an improved methodcalculating the overall mass matrix of the finite element model with time-varying massparameters is proposed, which can effectively reduce the amount of computation underthe condition with time-varying mass parameters. Secondly, the effectiveness ofstationary-basis method is verified by comparing the simulation results. Finally, a newmodeling approach for rigid-flexible coupling dynamics model of flexible structureswith time-varying mass parameters considering the influence by the time derivative ofmode shapes is developed by means of improving Wilson, H.E.’s [17] method based on the stationary-basis method. Thus the numerical instability caused in the calculation ofthe time derivative of the mode shapes, which is prevented by the above new method, isavoided. Meanwhile, by this method the calculation of the initial time structural modesinformation is only needed. Consequently the calculation scale is greatly reduced. Finally,the effectiveness of the new method is verified by contrasting the numerical simulationresults of the original method and the new method.