波浪前缘静子叶片对高速轴流风扇单音噪声的影响

航空发动机压气机噪声与大型风洞压缩机噪声问题日益凸显,相关研究机构迫切需求新的降噪手段以指导大型叶轮机械降噪设计。为了探索波浪前缘静子叶片在大型叶轮机械降噪中的应用前景,采用非定常雷诺平均Navier-Stoke（URANS）方程与FW-H方程混合方法对基准静子叶片和3种波浪前缘静子叶片的降噪效果进行了数值模拟,研究对象静子来流平均马赫数约为0.49,基于静子叶片弦长的雷诺数约为1 040 000。数值预测结果显示：波浪前缘静子叶片可以显著降低高速轴流风扇单音噪声,但会对风扇的气动性能产生少许不利影响;相较于基准静子叶片,3种波浪前缘静子叶片可以在1BPF时降低风扇入口声功率级0.97~1.5 dB,2BPF时降低风扇入口声功率级2.89~4.9 dB,3BPF时降低风扇入口声功率级3.32~4.72 dB;同时,总压比降低0.1%~0.8%,等熵效率降低0.1%~0.3%。进一步研究表明：不同频率下声源振幅和相位关系是风扇单音噪声强度的主要影响因素,总的来说,幅值的增加会降低声源强度,然而通过改变声源相位关系的降噪方式则需要兼顾径向模态与波长两个方面。     

Multi-disciplinary design optimization with fuzzy uncertainties and its application in hybrid rocket motor powered launch vehicle

In this paper, an Uncertainty-based Multi-disciplinary Design Optimization (UMDO) method combining with fuzzy theory and Multi-Discipline Feasible (MDF) method is developed for the conceptual design of a Hybrid Rocket Motor (HRM) powered Launch Vehicle (LV). In the method proposed, membership functions are used to represent the uncertain factors, the fuzzy statistical experiment is introduced to analyze the propagation of uncertainties, and means, standard deviations and credibility measures are used to delineate uncertain responses. A geometric programming problem is solved to verify the feasibility of the Fuzzy-based Multi-Discipline Feasible (F-MDF) method. A multi-disciplinary analysis of a three-stage HRM powered LV involving the disciplines of propulsion, structure, aerodynamics and trajectory is implemented, and the mathematical models corresponding to the F-MDF method and the MDF method are established. A two-phase optimization method is proposed for multi-disciplinary design optimization of the LV, including the orbital capacity optimization phase based on the Ziolkowski formula, and the scheme trajectory verification phase based on the 3-degree-of-freedom point trajectory simulation. The correlation coefficients and the quadratic Response Surface Method (RSM) based on Latin Hypercube Sampling (LHS) are adopted for sensitive analysis of uncertain factors, and the Multi-Island Genetic Algorithm (MIGA) is adopted as the optimization algorithm. The results show that the F-MDF method is applicable in LV conceptual design, and the design with the F-MDF method is more reliable and robust than that with the MDF method.     

基于合作博弈论的水下声传感器网络

声学传感器节点之间的合作面临声学信道故障、声学信号的长传播延迟、有限带宽和连接丢失等挑战,成为水下探索和海底监测研究中的关键问题。在节点合作中,可以利用合作通信博弈改善节点之间的合作问题。首先,介绍了水下声传感器网络中影响合作的各种因素,围绕水下通信的可靠性、能耗性、安全性等方面,提出水下合作的分类,并且从不同的角度研究了用于水下声传感器网络的各种合作技术;其次,通过回顾博弈论在节点相互合作中的应用,分析了不同的合作博弈方法,比较了它们在不同指标上的性能;最后,介绍了水下声传感器网络的开放性问题和未来研究方向。     

Modeling and flapping vibration suppression of a novel tailless flapping wing micro air vehicle

This paper establishes and analyzes a high-fidelity nonlinear time-periodic dynamic model and the corresponding state observer for flapping vibration suppression of a novel tailless Flapping Wing Micro Air Vehicle(FWMAV), named NPU-Tinybird. Firstly, a complete modeling of NPU-Tinybird is determined, including the aerodynamic model based on the quasi-steady method, the kinematic and dynamic model about the mechanism of flapping and attitude control,combined with the single rigid body dynamic mod...     

基于分类特征的零件信息描述及工序图自动绘制方法

应用面向对象技术的设计思想提出了分类特征的轴向位置码层次式信息描述法。在此基础上,对特征进一步分析,总结出特征的绘图属性集,提出了基于特征的工序图设计方法     

含钉孔有限大板应力集中系数的解析变分解法

导出满足弹性理论平面问题所有支配方程的应力场与位移场的罗朗级数展开式;用变分方法满足含钉孔有限大板边界条件并确定级数中的系数与应力集中系数;最后进行收敛性验证并给出系统计算曲线。     

钉孔挤压强化弹塑性计算中形变理论适用性探讨

本文为了检验形变理论在计算钉孔挤压残余应力场的可用性,对同一模型分别釆用全量法和增量法进行有限元计算,计算结果表明:在小的挤压量下,即δ≤2％(挤压量δ定义为(D_棒-D_板)/D_板×100％),两种方法均可釆用,当挤压量较大,即δ>2％时,全量法的结果与边界条件吻合得不好,而增量法符合得很好。从实验结果看,用全量法计算的残余应力计算试件的疲劳裂纹起始寿命与实验结果相差较大,而增量法计算的该寿命则与实验结果接近。工程中的挤压过程大都釆用较大的挤压量,所以,形变理论不适合计算钉孔挤压的残余应力场。     

一般非线性边值问题的高精度方法

介绍了满足边界条件y(a)=A 和y(b)=B 的一般二阶非线性常微分方程y″=f(x,y,y′)的六阶三对角有限差分法;在右端项一般形式下,推广了文献[2]的结果。并在适当条件下证明了该方法的收敛性和稳定性,同时用数值试验证实了上述结论的正确性。     

求解Navier—Stokes方程的指数型差分法

我们以Burger's方程为例,推导了指数型差分格式,并证明了这格式是无条件稳定和高精度的。此外,我们利用这格式来求解一维单个和多个Navier-Stokes方程,取得了令人满意的结果。把这格式进一步推广,得到求解二维Navier-Stokes方程组的格式,并从理论上证明了这一推广格式的一系列优点,还以此来求解实践问题,得到了与实验和理论非常符合的结果。