针对运载火箭“摆动发动机-伺服回路”负载频率低,可能影响全箭弹性模态稳定性的问题,首先建立了包含“发动机-伺服回路”动力学模型的全箭动力学模型,分析了“发动机-伺服回路”负载频率对伺服机构传递函数和控制系统开环传递函数特性的影响,指出了“发动机-伺服回路”负载频率与箭体弹性模态之间的动力学耦合关系,给出了保证弹性模态稳定的谐振频率判据,最后计算了保证全箭弹性模态稳定的负载频率边界值,并通过仿真算例验证了结果的正确性.研究结果表明,“发动机-伺服回路”局部的负载频率通过惯性负载力矩作用与全箭弹性模态形成耦合,当负载频率位于上、下边界值范围之内时就会导致某些弹性模态不稳定,因此在实际工程中应对负载频率进行限制,以保证运载火箭的飞行安全.%In view of the fact that the instability of the launch vehicle' s modes probably caused by the low load harmonic oscillation frequency of the "swiveled engine-servo loop" , firstly, the launch vehicle's dynamic model including the dynamic model for "engine-servo loop" is established. The influences of the load frequency of the "engine-servo loop" on servo system' s transfer function as well as the open loop transfer function of the control system are analyzed. Secondly, the dynamical coupling between the load frequency of the "engine-servo loop" and vehicle' s elastic modes is analyzed. The criterion of the harmonic oscillation frequency which ensure the stability of the vehicle' s elastic modes is given. Finally, the boundary value of the load frequency which ensures the stability of the vehicle' s elastic modes is computed. The correctness of the results is validated by some simulation examples. The results of the research show that the load local frequency of the "engine-servo loop" is coupled with vehicle' s modes by inertia) load feedback torque and some elastic modes will be unstable when the load frequency lies in the boundary which is composed of upper and lower limit. The load frequency must be limited in actual engineering so that the launch vehicle' s flight safety could be guaranteed.
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