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71.
《中国航空学报》2023,36(1):75-90
The modeling of dynamic stall aerodynamics is essential to stall flutter, due to the flow separation in a large-amplitude pitching oscillation process. A newly neural network based Reduced Order Model (ROM) framework for predicting the aerodynamic forces of an airfoil undergoing large-amplitude pitching oscillation at various velocities is presented in this work. First, the dynamic stall aerodynamics is calculated by solving RANS equations and the transitional SST-γ model. Afterwards, the stall flutter bifurcation behavior is calculated by the above CFD solver coupled with structural dynamic equation. The critical flutter speed and limit-cycle oscillation amplitudes are consistent with those obtained by experiments. A newly multi-layer Gated Recurrent Unit (GRU) neural network based ROM is constructed to accelerate the calculation of aerodynamic forces. The training and validation process are carried out upon the unsteady aerodynamic data obtained by the proposed CFD method. The well-trained ROM is then coupled with the structure equation at a specific velocity, the Limit-Cycle Oscillation (LCO) of stall flutter under this flow condition is predicted precisely and more quickly. In order to predict both the critical flutter velocity and LCO amplitudes after bifurcation at different velocities, a new ROM with GRU neural network considering the variation of flow velocities is developed. The stall flutter results predicted by ROM agree well with the CFD ones at different velocities. Finally, a brief sensitivity analysis of two structural parameters of ROM is carried out. It infers the potential of the presented modeling method to depict the nonlinearity of dynamic stall and stall flutter phenomenon. 相似文献
72.
借鉴数学中的函数与反函数思想,由间隙环节的数学模型导出逆间隙环节。分析了飞机侧偏控制系统
中副翼、方向舵舵机间隙非线性特性所引起的极限环振荡,针对副翼、方向舵舵机的非线性特性设计了相应的逆间隙环节,把所设计的逆间隙环节引入侧偏控制系统。仿真结果表明,所设计的逆间隙环节能够显著地抑制侧偏控制系统中的极限环振荡。 相似文献
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74.
流量调节器管路系统在小流量大压降工况下会出现低频自激振荡现象,为了深入认识自激振荡产生机理,结合某型自稳流型流量调节器及管路系统,基于流量调节器弹簧振子动力学模型开展数值仿真研究。数值仿真得出自激振荡频率为94 Hz,与发动机试验结果一致。自激振荡产生机理是流量调节器的液动力受滑阀窗口型面变化率影响对系统形成正反馈作用,流量调节器综合刚度小于零时系统失稳。分析了流量调节器结构参数对系统稳定性的影响作用,三角形滑阀节流口流通面积能够抑制管路系统自激振荡。结合某型流量调节器负载特性试验系统进行验证,得出随着流量调节器压降升高,管路系统稳定性变差,获得的幅频特性,稳定边界与试验结果一致。 相似文献
75.
76.
主要阐述直或机贴地飞行时的驾驶员诱发振荡问题,导出了贴地突防和迅速停止动作、地形跟踪时的“海豚”运动和贴地飞行时滑雪运动条件下诱发振荡时操纵位移和稳定裕度的计算公式,计算了Z-8直长机的纵向试验结果,并进行了误差分析。计算结果表明,所研究的方法是可行的,可推广应用于各种直升机的闭环分析和计算。 相似文献
77.
某型飞机空中飘摆故障分析及防护措施 总被引:1,自引:0,他引:1
文韬 《长沙航空职业技术学院学报》2007,7(2):33-35
分析某型飞机平尾助力器故障导致飞机在空中飞行时产生飘摆现象的原因,提出修理改进措施及维护对策。 相似文献
78.
一种抑制电传系统PIO的非线性补偿方法 总被引:1,自引:0,他引:1
朱恩 《南京航空航天大学学报》1998,30(4):400-404
提出了一种不完全非线性补偿方法用来抑制电传系统飞行员诱发振荡,其补偿着眼点是电传系统内部的舵回路速率饱和。本文把新的补偿方法用于一个两回路的飞行控制系统中,其设计过程和仿真结果表明,该方法结构简单,可以有效抑制PIO,而且不影响原有系统的正常工作,便于工程应用。 相似文献
79.
80.
R. Modzelewska M.V. Alania 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
We show that the higher range of the heliolongitudinal asymmetry of the solar wind speed in the positive polarity period (A > 0) than in the negative polarity period (A < 0) is one of the important reasons of the larger amplitudes of the 27-day variation of the galactic cosmic ray (GCR) intensity in the period of 1995–1997 (A > 0) than in 1985–1987 (A < 0). Subsequently, different ranges of the heliolongitudinal asymmetry of the solar wind speed jointly with equally important corresponding drift effect are general causes of the polarity dependence of the amplitudes of the 27-day variation of the GCR intensity. At the same time, we show that the polarity dependence is feeble for the last unusual minimum epoch of solar activity 2007–2009 (A < 0); the amplitude of the 27-day variation of the GCR intensity shows only a tendency of the polarity dependence. We present a three dimensional (3-D) model of the 27-day variation of GCR based on the Parker’s transport equation. In the 3-D model is implemented a longitudinal variation of the solar wind speed reproducing in situ measurements and corresponding divergence-free interplanetary magnetic field (IMF) derived from the Maxwell’s equations. We show that results of the proposed 3-D modeling of the 27-day variation of GCR intensity for different polarities of the solar magnetic cycle are in good agreement with the neutron monitors experimental data. To reach a compatibility of the theoretical modeling with observations for the last minimum epoch of solar activity 2007–2009 (A < 0) a parallel diffusion coefficient was increased by ∼40%. 相似文献