超声速射流离散频率噪声的屏蔽抑制及对流动的影响

根据对超声速射流离散频率噪声产生的反馈机理的认识,提出了一种能够有效地破坏反馈环的形成,从而抑制射流离散频率噪声的喷嘴屏蔽方法.这种方法是通过阻隔反馈声波使其不能到达喷嘴唇口、同时屏蔽物不与射流接触来实现降噪的目的.实验结果表明,对于合适的屏蔽罩参数,正常降噪效果可达5分贝以上.应用激光多普勒测速技术测量了超声速自由射流在采取屏蔽降噪措施前后轴线速度的分布,发现屏蔽后射流势核长度增加近50%,表明这种降噪方法有助于射流推力的提高,但不利于射流的掺混.     

用刚度替换法求解变截面排架柱的水平位移

本文介绍一种求解变截面排架柱水平位移的新方法：刚度替换法，同时推导出刚度替换法则。应用此法，可使变截面排回柱位移的求解过程大大简化。这一方法对求解单层变截面排架的位移及内力有着重要的意义。     

固体发动机柔性喷管扩张段刚度分析

基于某发动机柔性喷管结构，用弹簧模型替代柔性接头，建立计算模型，对不同控制力作用下的柔性喷扩张段支耳的轴向和径向刚度进行了三维有元分析计算，本计算分析，对固体发动机推力向量控制有一定的参考价值。     

实现DDS的波形存储表幅度值压缩方法

简介直接数字频率合成器的原理 ,提出在自行设计 DDS时采用波形存储表幅度值压缩方法以降低输出频谱的杂散。文中阐述正弦相位差法、Nicholas优化结构等幅度值压缩方法的有关原理和具体实现方法 ,并提出一种在现有方法上进一步提高压缩比的改进办法 ,最后 ,给出在 Matlab中 Simulink下的仿真验证结果     

基于高阶谱约简的变结构模糊神经网络

针对先验知识不完备和不确定的情况下海量数据造成的冗余和互斥，模糊神经网络结构变得复杂化并不能很快逼近和分类输出对象的情况，提出了一种基于高阶谱完成规则约简的变结构模糊神经网络的模型。相同结论属性的模糊规则的条件属性值可以被认为是由若干个谐波成分组成的平稳信号，并且此信号可以采用高阶谱分析来估计其谐波成分，规则的最小约简集与谐波对应。在完成了谐波估计后，神经网络结构和连接权值发生改变，神经网络的性能也得到优化。最后给出了此模型在航迹融合中应用的一个例子，得到了较好的结果。     

A multi-disciplinary plan for easier access, management, and analysis of science data

NASA's COST LESS Team is pursuing strategies to reduce the cost and complexity of planning and executing space missions. The team's technical goal is to reverse the trend of constructing unique solutions for similar problems. To this end, the team is exploring ways to represent mission functionality in terms of building blocks and is discovering approaches that could accommodate the same building blocks for seemingly disparate activities, such as organizing processed telemetry data, controlling onboard experiments, searching science archives, reducing and presenting information to science users, and supporting educational outreach. Reusable object technology (UOT), a research undertaking by the authors, is showing promise in recognizing similarities in functions which were previously viewed as unique because they appeared in different programs or mission phases. Since UOT is aimed at being implementation independent (i.e. the function performed could be accomplished manually, by an automated process, by a specialized instrument, etc.), no premature judgment for automation or autonomy need be made. In this paper, the authors attempt to strike a balance between theory and reality as they describe UOT, including its beginnings, its underpinning, its utility, and its potential for achieving substantive reductions in cost and complexity for the Agency's space programs. The authors discuss their collaboration with the Center for EUV Astrophysics, University of California, Berkeley to reduce the cost and complexity of science investigations. Their multi-disciplinary plan incorporates both UOT and a complementary technology introduced in this paper, called interactive archives.     

Numerical analysis of broadband noise reduction with wavy leading edge

Large Eddy Simulation(LES) is performed to investigate the airfoil broadband noise reduction with wavy leading edge under anisotropic incoming turbulence. The anisotropic incoming turbulence is generated by a rod with a diameter of 10 mm. The incoming flow velocity is 40 m/s and the corresponding Reynolds numbers based on airfoil chord and rod diameter are about 397000 and 26000, respectively. The far-field acoustic field is predicted using an acoustic analogy method which has been validated by the experiment. A straight leading edge airfoil and a wavy leading edge airfoil are simulated. The results show that wavy leading edge increases the airfoil lift and drag whereas the lift and drag fluctuations are substantially reduced. In addition, wavy leading edge can significantly change the flow pattern around the leading edge and a pair of counter-rotating streamwise vortices stemming from each wavy leading edge peak are observed.An averaged noise reduction of 9.5 dB is observed with the wavy leading edge at the azimuthal angle of 90°. Moreover, the wavy leading edge can mitigate noise radiation at all the azimuthal angles without significantly changing the noise directivity. The underlying noise reduction mechanisms are then analyzed in detail.     

大型客机气动设计综述

中国大型客机研制过程中追求"三减，四性"：减阻、减重、减排，安全性、经济性、舒适性、环保性。中国大型客机采用翼下常规布局形式，放宽静稳定技术，发动机选用CFM公司Leapx-1C发动机，这对气动设计技术在工程适用性上提出了极高的要求。大型客机是中国第1架完全自主知识产权民用飞机，本文综述了其设计过程中采用的先进气动优化设计方法、CFD分析和充分的风洞试验验证，说明了超临界机翼设计、高效增升装置设计、飞机/发动机一体化设计、尾翼设计、翼梢小翼设计和部件精细化减阻设计技术，能实现大型客机的减阻应用设计。研究表明，中国大型客机在气动设计水平和设计方法上取得了一系列的进展和突破，实现了设计具有较强竞争力的先进民用飞机的目标。     

挠性框架对陀螺飞轮性能影响分析

挠性框架是实现陀螺飞轮输出三轴控制力矩、测量外界角速度的关键部件。通过数值计算分析了挠性框架平衡环的惯量特性、内/外弹性元件的摆动刚度,以及倾侧角度对陀螺飞轮整机性能指标的影响。分析结果表明:降低挠性框架剩余刚度系数可以提高陀螺飞轮转子摆角控制精度,降低控制力矩。     

基于改进证据网络的空战动态态势估计方法

针对无人机空战态势估计既需要综合考虑多类型因素影响,又需要具有不确定性推理能力的特点,建立了一种基于改进证据网络的动态态势估计模型并设计了威胁等级评估推理方法。首先,考虑空战决策时间较短的特点,提出变量框架等级缩减方法以提高网络运行效率;然后,针对空战态势信息具有大不确定性的特点增加冲突数据自适应融合算法以及网络证据的时间序列预测,提高证据的合理性;最后,引入时空融合思想和变权机制将前一时刻的威胁信息作为评判后一时刻威胁的重要标准,应用威胁在时间维度上的递归合成增加信息在时间方向的传递,改善了由于证据失真引起的评估结果的不合理性问题,并通过仿真验证了该方法的有效性。