Investigation Of The Dynamic Behaviorfor POGO Vibration System In Liquid Rockets

The structure of liquid rockets is very complicated which has a lot of propellant fluid in it. During flight, its flying velocity can be increased from zero to several kilometers per second, going through different environments, usually accompanied with various dynamic phenomena. With consuming the propellant fluid, instable POGO vibration will happen in liquid rockets with coupled propulsion system and its longitudinal vibration system. POGO vibration will produce a vibration environment that the sensitive element, instruments and astronauts cannot bear in liquid rockets. It also induce a lot of adverse affection to the working process of engine system from the fluid pulsation of propulsion system. So it is very necessary to study the mechanical and physical mechanisms of POGO vibration system in liquid rockets and establish the influence law of various physical parameters on the dynamic behavior of POGO vibration system. For this purpose, the main research contents are as follows.Based on the fluid pulsation characteristics and the structural characteristics of each component unit of propulsion system in liquid rockets, its dynamic model of flow disturbance is established according to the fluid mass conservation, momentum conservation and energy conservation laws. By considering the coupled conditions from each component unit in propulsion system，the dynamic model of propulsion system in liquid rockets is established. The dispersed fourier transformation method is adopted to analyze the influence of nonlinear characteristics of pump on the frequency and response of the propulsion system in liquid rockets.The modal effective mass theory is used to propose a method that automatically identifies longitudinal modal of rocket body structural system from the whole modes of liquid rockets. The effectiveness and advantage of this automatic identification method are discussed by taking the vibration characteristics of system with lumped mass for a computing example. By considering the forces acted on rocket body structural system from flow disturbance of propulsion system in liquid rockets, the structural modal theory is employed to establish the dynamic model of longitudinal vibration system of rocket body structure.By considering the coupled relationship between the propulsion system and longitudinal vibration system in liquid rockets, the dynamic model of POGO vibration system in liquid rockets is established. Through the eigenvalue analysis of POGO vibration system in liquid rockets, the necessity of suppressing POGO vibration is further illustrated by the method of installing accumulator in project. The Rugge-Kutta method is used to simulate the response of POGO vibration system. The influence of nonlinear characteristics of pump in engine system on the response of POGO vibration system is researched under the conditions that POGO vibration system is balance and stable in liquid rockets.The small perturbation theory of vibration system and the complete differential theory are adopted to investigate the linearized problem for dynamic model of nonlinear fluid pulsation of each component unit in propulsion system during working state and nearby, the equivalent linearization dynamic model of propulsion system in liquid rockets is established. By considering the coupled relationship of linearity propulsion system and longitudinal vibration system of rocket body structure, the equivalent linearization dynamic model of POGO vibration system in liquid rockets is established. The Routh-Hurwitz Criterion of stability theory is adopted to investigate the critical parameter equation of POGO vibration system. And the effects of physical parameters on stability of the POGO vibration system are discussed with numerical method. Based on the stability condition of POGO vibration system and the distribution laws of the main parameters that may affect stability of the POGO vibration system, The Monte Carlo method is used to carry out computer experiments to simulate the target practice of POGO vibration system in liquid rockets.Pointed at the condition that POGO vibration system is stable in liquid rockets, based on the equivalent linearization dynamic model of the propulsion system and POGO vibration system in liquid rockets. Interval method that analyzes frequency characteristic sensitivity of propulsion system is proposed with interval mathematics as theoretical basis. The influence of physical parameters of propulsion system on its frequency characteristic is discussed with numerical method. The dynamic sensitivity theory is employed to establish the time domain analysis model of sensitivity of longitudinal vibration response in liquid rockets, and the effects of the fluid inertia, resistance and stiffness of propulsion system on the longitudinal vibration response in liquid rockets are investigated with the Newmark integral method.