动导数数值预测中的相关问题

动导数是飞行器动态稳定性分析、弹道设计和控制系统设计的重要参数，其预测方法主要有工程近似方法、数值模拟和风洞试验。基于动导数、交叉导数的概念，介绍了强迫振荡法、自由振荡法等预测动导数的数值模拟方法，重点就超声速、高超声速动导数数值预测中存在的问题开展讨论，包括时间步长、子迭代步数的选取；振荡频率对辨识结果的影响；强迫振荡法和自由振荡法辨识动导数可能存在差异的原因分析；交叉导数和交叉耦合导数的辨识问题以及飞行器构型对动导数预测的影响等。并结合算例进行了具体分析，在总结现有研究经验的同时，针对当前研究中存在的困惑和难题，提出了相应的改进建议。

Problems in numerical prediction of dynamic stability derivatives

Dynamic stability derivative is one of the important parameters in the design of control system, the design of flight orbit, and the analysis of dynamic stability of vehicles. The prediction methods of the dynamic stability derivatives mainly include the engineering approximations, numerical simulations and wind tunnel tests. The concepts of dynamic stability derivative and cross derivative are reviewed, and the forced oscillation and free oscillation methods for numerically predicting the dynamic stability derivatives are introduced. The problems existing in the numerical prediction are specially discussed, including the choice of time-marching step and step number of sub-iteration, the effects of the oscillating frequency on the identification results, the analysis of the probable reasons which lead to the difference between the forced oscillation and free oscillation methods in dynamic derivative identification, the identification of the cross and cross coupling derivatives, and the identification of dynamic stability derivatives of the integrated internal-external flow vehicles. The discussions are made with computational cases and detailed analysis, in which both experiences and puzzles exist, and the corresponding suggestions for improvement are presented.