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961.
962.
根据齿轮啮合原理,准确求出复杂的齿廓曲线;采用MATALB—APDL混合建模方法,创建精确的齿轮有限元模型。在不同网格密度等级下,分别对齿轮的齿面变形、齿根应力分布进行分析。对照经验公式的计算结果,得出如下结论:在齿轮数值模拟中,由于有限元软件计算中舍入误差的存在,网格划分合理与否将直接影响仿真程度的高低;网格密度等级对齿面最大变形的仿真结果有较大影响,而对齿根应力影响甚微。 相似文献
963.
In this paper, we consider the double-satellite localization under the earth ellipsoid model of the Wideband Geodetic System(WGS-84) using the Time Difference of Arrival(TDOA)and the Angle-of-Arrival(AOA).Several closed-form solution algorithms via the pseudolinearization of the measurement equations are presented to efficiently estimate the location.These algorithms include the Weighted Least Squares(WLS), the Constrained Total Least Squares(CTLS), and the Taylor-Series Iteration(TSI).Performance comparison of the proposed methods with the Cramér-Rao Lower Bound(CRLB) in the simulation is shown to demonstrate that the proposed algorithms are feasible and have stable performance. 相似文献
964.
This article deals with the disturbance attenuation control of aircraft flying through wind shear via Linear Parameter Varying(LPV) modeling and control method. A Flight Dynamics Model(FDM) with wind shear effects considered was established in wind coordinate system. An LPV FDM was built up based on function substitution whose decomposing function was optimized by Genetic Algorithm(GA). The wind disturbance was explicitly included in the system matrix of LPV FDM. Taking wind disturbance as external uncertainties, robust LPV control method with the LPV FDM was put forward. Based on ride quality and flight safety requirements in wind disturbance, longitudinal and lateral output feedback robust LPV controllers were designed respectively,in which the scheduling flight states in LPV model were actually dependent parameters in LPV control. The results indicate that LPV FDM can reflect the instantaneous dynamics of nonlinear system especially at the boundary of aerodynamic envelope. Furthermore, the LPV FDM also can approach nonlinear FDM's response in wind disturbance special flight. Compared with a parameter-invariant LQR controller designed with a small-disturbance FDM, the LPV controllers show preferable robustness and stability for disturbance attenuation. 相似文献
965.
良好的机组配合可以有效提高飞行的安全性。首先通过国外军用直升机发生的一些典型事故,分析了不良机组配合的具体表现,然后指出机组配合对于军用直升机的重要性。最后,借鉴国内外的有效经验,对机组如何进行良好配合并提高安全性提出了一些建议。 相似文献
966.
Yongling FU Xu HAN Nariman SEPEHRI Guozhe ZHOU Jian FU Liming YU Rongrong YANG 《中国航空学报》2018,31(3):584-596
Electrohydrostatic actuator (EHA) is a type of power-by-wire actuator that is widely implemented in the aerospace industry for flight control, landing gears, thrust reversers, thrust vector control, and space robots. This paper presents the development and evaluation of position-based impedance control (PBIC) for an EHA. Impedance control provides the actuator with compliance and facilitates the interaction with the environment. Most impedance control applications utilize electrical or valve-controlled hydraulic actuators, whereas this work realizes impedance control via a compact and efficient EHA. The structures of the EHA and PBIC are firstly introduced. A mathematical model of the actuation system is established, and values of its coefficients are identified by particle swarm optimization. This model facilitates the development of a position controller and the selection of target impedance parameters. A nonlinear proportional-integral position controller is developed for the EHA to achieve the accurate positioning requirement of PBIC. The controller compensates for the adverse effect of stiction, and a position accuracy of 0.08 mm is attained. Various experimental results are presented to verify the applicability of PBIC to the EHA. The compliance of the actuator is demonstrated in an impact test. 相似文献
967.
Graphene nanosheets(GNSs) strengthened AgCuTi composite filler(AgCuTi_G) was used to braze C/C composite and Ti-6Al-4V. The effects of GNSs on the wettability of AgCuTi_G filler on the C/C composite surface and the interfacial microstructure and mechanical properties of brazed joints were investigated. The results indicate that the addition of GNSs reduced the wettability of AgCuTi_G. The interfacial microstructure of brazed joints evolved with the addition of GNSs, where Ti_3Cu_4 and TiCu_4 were converted to TiCu and the thickness of the reaction layer adjacent to the base material decreased. The maximum shear strength of joints brazed at 0.3 wt% GNSs was 23.3 MPa(880℃/10 min). Further adding GNSs deteriorated the shear strength of the joints. Fracture of the joints occurred in the C/C composite substrate and the TiC layer adjacent to C/C composite. 相似文献
968.
Background noise is inevitable when sensor arrays are used for aeroacoustic measurements in wind tunnels. The direct removal of background noise, however, would affect the measurement accuracy. In particular, the existing array signal processing algorithms are either invalid or inefficient for removing the noise that is coherent with the signal of interest. In this paper, an intelligent algorithm is developed to localize the coherent sound sources and background noise in real time by iteratively checking the collected data from the array. The proposed method can automatically adjust the suboptimal fading factor to extract useful information as much as possible in residual sequence. This algorithm is tested in simulations and then demonstrated in an experiment.Compared to the two existing methods, the results indicate that the new method has a good phase-shift tracking ability and rapid estimation-error convergence speed, and can achieve an acceptable performance even for low-cost acoustic sensors. Overall, the proposed method should assist array beamforming and hence benefit aeroacoustic measurement. 相似文献
969.
970.
为在远距离范围内实现高精度的激光测速测距,提出了一种联合利用伪随机码相位调制和外差探测技术的激光测速测距方法,并搭建了实验验证平台。当激光出射功率为2mW、参考光功率为117 、调制速率为100MHz、单周期内伪随机码序列长度为81.9 时,该系统在对位于约8 m处、径向速度约为1.4 m/s的目标进行测试时,可以实现0.138m的测距精度,以及4.16cm/s 的测速精度。实验结果证实,该套系统可实现高精度的径向速度和距离测量,且系统工作状态为长脉宽低峰值功率,为远距离的激光测速测距系统设计开辟了一条新途径。 相似文献