运输类飞机起落架地面操纵载荷计算

为了使运输类飞机起落架的设计更好地满足适航规范的要求,介绍一种针对CCAR25部规范要求的计算起落架地面操纵载荷的流程,并提出根据轮胎、缓冲支柱压缩状态计算起落架基本尺寸数据和飞机姿态的旋转"虚拟接地点"方法。通过上述流程能够计算得到起落架地面操纵载荷结果,包括飞机在某种地面操纵工况下的姿态、地面坐标系和飞机坐标系下的地面操纵载荷以及起落架基本尺寸数据。通过对转弯地面载荷工况的计算与分析,表明计算流程和旋转"虚拟接地点"方法是准确可靠的且能较好地满足CCAR25部规范要求。     

基于多点约束的大展弦比机翼静气动弹性计算

基于雷诺平均N-S方程和多块结构网格技术计算大展弦比机翼的气动力.机翼采用梁模型结构,利用有限元方法计算结构变形.建立基于多点约束(MPC,Multi-Point Constrain)的气动、结构数据的双向传递方法.采用MPC数据插值方法快捷地实现自主研发的计算流体力学(CFD,Computational Fluid Dynamics)程序和NASTRAN计算结构力学(CSD,Computational Structural Dynamics)软件的耦合计算,发展出可以考虑结构非线性的静气动弹性CFD/CSD耦合计算方法,该方法比只考虑单方向变形的柔度法更精确.开展了某大展弦比机翼的静气动弹性数值计算分析,结果显示只考虑机翼纵向变形而忽略展向变形对计算结果会有一定影响,而该算例几何非线性影响较小.     

油画中的东方神韵--访青年油画家孟涛

初识孟涛，就被他画中的东方神韵所吸引．用油画来画心中的山水，画中国画所特有的意境．的确有其独创性。     

天气预报不准需要理由吗？

古人云:天有不测风云。这是真理,在任何时候都适用。在古代,天气预报是一种神话,而在现代社会,天气预报是有局限的科学,是人类一种高级的智力游戏。责怪天气预报的不准确,是个世界性的现象。在生活中,有一个流传很广的说法:很多人说假话,天气预报倒是特别想说真话,可就是说不准     

基于改进稀疏A~*算法的无人机航路规划

为使无人机具有在复杂环境下快速有效规划的能力,针对无人机航路规划中的稀疏A*算法进行改进,提出基于预生成点的变步长稀疏A*算法。算法在存在可行航路的紧密威胁障碍之间预先生成备选航路点,然后通过带有约束条件的稀疏A*算法进行航路规划,且在航路规划过程中结合变步长思想,更好地规避威胁,并加快搜索,最后对生成的航路实现二次优化。仿真结果表明,相比稀疏A*算法,改进的稀疏A*算法收敛速度快,具有更强的鲁棒性、可行性,且生成航迹具有更好的飞行品质。     

Performance evaluation of digital beamforming strategies for satellite communications

Smart antennas are becoming one of the promising technologies to meet the rapidly increasing demands for more capacity of satellite communication systems. A main component in a smart antenna system is beamforming. Because of the limitations of analog beamforming, digital beamforming will be employed in future satellite communication systems. We evaluate the performance of various digital beamforming strategies proposed in the literature for satellite communications: 1) single fixed beam/single user, 2) single fixed beam/multiple users, 3) single adaptive beam/single user, and 4) single Chebyshev dynamic beam/multiple users. Multiple criteria including coverage, system capacity, signal-to-interference-plus-noise ratio (SINR), and computation complexity are used to evaluate these satellite communication beamforming strategies. In particular, a Ka-band satellite communication system is used to address the various issues of these beamforming strategies. For the adaptive beamforming approach, subarray structure is used to obtain the weights of a large 2D antenna array, and a globally convergent recurrent neural network (RNN) is proposed to realize the adaptive beamforming algorithm in parallel. The new subarray-based neural beamforming algorithm can reduce the computation complexity greatly, and is more effective than the conventional least mean square (LMS) beamforming approach. It is shown that the single adaptive beam/single user approach has the highest system capacity.     

Improved field-weakening control for IFO induction motor

Generally, good transient response and high conversion efficiency of a field-weakened indirect field-oriented (IFO), induction motor drive are difficult to obtain simultaneously owing to their contradictory behaviors. Moreover, its operating performance is quite sensitive to the flux level, detuned effect, and parameter variations. An improved field-weakening control approach for an IFO induction motor drive is developed here. In the proposed method, the saturated magnetizing inductance is represented by a fitted quadratic polynomial of flux current. And the normal d-axis flux current command is composed of a no-load, a load-compensating, and a transient compensating component. The first one is represented by a third-order polynomial of rotor speed, which is estimated at no-load to consider the effects of nonlinear magnetizing inductance and the limitation of motor rated voltage. As for the latter two compensating current command components, they are utilized to further weaken the field such that current tracking performances during loaded cases and transient period can be improved. And hence the torque-generating capability is also enhanced accordingly. During steady-state operation, the slip angular speed command or the flux current command is tuned using the proposed approach to let the motor quickly reach a stable operating condition with better efficiency. Experimental results show that good dynamic responses and better energy conversion efficiencies can be simultaneously obtained by the proposed field-weakening control method.     

美军机载导弹防御武器发展现状研究及启示

从美国网络中心机载防御单元(NCADE)的需求背景入手,分析了其技术方案和作战特点,就发展助推段/上升段机载导弹防御武器的必要性、发展思路、关键技术等进行了分析,提出了利用成熟空空导弹派生机载导弹防御武器的初步解决方案。     

海洋目标天基综合感知技术

在分析海洋运动目标特征的基础上,阐述海洋目标感知卫星采用单一手段带来的局限性以及效能受到的影响,提出海洋目标天基综合感知的概念.根据不同卫星感知手段的特点,设想对海洋目标采用单星多手段综合感知,利用功能互补,解决感知系统覆盖与分辨率的矛盾,解决高发现概率与高定位精度的矛盾.通过多元数据融合,提高卫星功能密度,单星即可成...