基于降阶模型的气动弹性主动控制律设计

流体/结构耦合数值模拟是目前解决复杂气动弹性问题精度最高的方法。但由于计算效率比较低,模型阶数过高,不能直接用于气动弹性系统的主动控制律设计。为了对主动控制系统设计提供高效高精度状态空间模型,研究了气动弹性系统的时域正则正交分解(POD)/降阶模型(ROM)方法,并引入平衡截断(BT)技术进一步降低时域POD/ROM的阶数,从而有效克服了时域POD/ROM阶数过高的缺点。在此基础上建立了基于POD-BT/ROM的气动伺服弹性降阶方程。以AGARD445.6机翼为例,说明了时域POD/ROM建模的各个细节,并将其用于气动弹性主动控制律的设计。计算结果表明,POD/ROM具有接近计算流体力学(CFD)/计算结构动力学(CSD)耦合计算的精度,同时又大大提高了计算效率约1～2个量级,是一种高精度高效率的气动弹性主动控制系统设计工具。     

高温压缩对高体份SiC_p/Al复合材料组织的影响

采用无压浸渗法制备出结构/热控一体化的高体份(～55%)SiCp/Al复合材料。对该复合材料进行了高温(高于基体熔点)压缩实验。利用XRD和SEM观察分析了高温压缩参数对复合材料相组成及组织形态的影响。研究结果表明:高温压缩后高体份SiCp/Al复合材料的相组成仍为Al,SiC及少量Si和Mg2Si,该复合材料具有较好的高温稳定性;高体份SiCp/Al复合材料高温压缩变形后,基体仍保持连续,颗粒在压力作用下会翻转、部分颗粒会破碎,颗粒尺寸及分布均匀性等组织特性受高温变形参数控制。随着变形温度的升高和应变速率的减小,SiC颗粒的尺寸一致性、圆整度及分布均匀性有所提高;高体份SiCp/Al能复合材料在基体熔点以上的材料状态可视为粘流体,并可认为其具有一定的流动性。变形温度和应变速率对复合材料流动性的影响,使复合材料高温压缩后组织特性呈现四个阶段。     

基于动态贝叶斯网络的弹头目标融合识别方法

通过分析导弹目标识别问题的特殊性,设计了适用于导弹目标识别的动态贝叶斯网络。根据导弹目标的特点,选取了几种具有较好普适性的目标特征,并给出了每种目标特征的条件概率。通过分析导弹目标识别流程,提出了合理的贝叶斯网络模型。最后经过仿真试验,证明该模型相比单特征识别模型识别概率有明显提高,并且具备较好的稳健性。     

叶轮式辅助心脏泵装置优化设计

叶轮式血液泵LAP-Ⅰ采用了航空叶轮机械中使用的设计思想方法,该装置是针对亚洲患者的临床应用而设计.综合航空叶轮机械技术和医学需求,采用整体转子和悬臂静子结构设计,并对其串列叶栅静子结构做了进一步的优化改进,得到叶轮式血液泵LAP-Ⅱ.计算流体动力学(CFD)模拟结果表明,血泵LAP-Ⅱ的压升性能达到医学需求,泵体内流动状况顺畅.最大比较剪切应力(S)值得到明显降低,流线显示血液通过泵体的最长时间得到减小,抗溶血应用性能得到提高.      

机载火控系统精度分析

火控系统动态精度试验是指在目标和飞机处于相对运动的状态下,检查系统输出值相对标准值的误差。本文介绍了飞机火控系统动态试验的程序和基于时间序列建模的理论。最后,对导弹与目标相对位置的误差以及火控跟踪雷达对目标的测距、测角误差进行了分析。     

前置肋片对凹槽火焰稳定器混合特性的影响

将前置肋片结构应用于超声速凹槽火焰稳定器中,数值模拟研究了前置肋片对凹槽火焰稳定器混合特性的影响.结果表明:与传统结构相比,在凹槽稳定器中加入前置肋片,能减小总压损失,增大凹槽内外喷口的穿透深度,并获得更为均匀燃料分布,有利于燃烧组织.      

钴的晶体结构对镀钴空心玻璃微球电磁性能的影响

采用化学镀方法在空心玻璃微球表面复合磁性金属钴,制备了镀钴空心玻璃微球,并对其进行了真空退火热处理。经过化学镀的空心玻璃微球表面包覆了一层均匀、致密的金属镀层;镀钴空心玻璃微球(2.5g/cm3)镀层晶体结构对其电磁性能产生影响。当镀层Co含量为95%时,介电常数实部在11GHz处达到35,虚部在13GHz处达到22;在经过热处理后,镀层发生晶相转变,介电常数实部和虚部均得到提高。另外,热处理能降低钴镀层的矫顽力,改善其软磁性能。     

Studies of Electromagnetic Properties of MWCNTs after Electroless Plating with Co-Fe Alloy

A method of electroless plating is utilized to deposit Co-Fe alloy on the surface of multi-walled carbon nanotubes (MWCNTs), and electromagnetic parameters of MWCNTs with and without electroless plating are discussed. The MWCNTs covered by Co-Fe is a desirable light absorbent in wide wave band by utilizing electroless plating process in experiments. Field-emission scanning electron microscope (FESEM) and field-emission transmission electron microscope (FETEM) images as well as energy dispersive spectroscopy (EDS) results are presented to show the morphology, components and electromagnetic parameters of MWCNTs. Electromagnetic properties of MWCNTs are enhanced after electroless plating observed from contrast of results between MWCNTs with and without plating. In conclusion, the covering Co-Fe on the surface of MWCNTs in 2-18 GHz frequency range has better electromagnetic properties. When the material is in the 6.5 GHz electromagnetic waves, the reflection loss is up to ?10 dB, and the bandwidth more than ?4 dB is 5 GHz. The excellent electromagnetic properties make it probable for MWCNTs to be utilized as absorbent in electromagnetic shielding materials.     

Forming Characteristics of Al-alloy Large-diameter Thin-walled Tubes in NC-bending Under Axial Compressive Loads

Tube thinning control without wrinkling occurring is a key problem urgently to be solved for improving the forming qualities in numerical control (NC) bending processes of large-diameter Al-alloy thin-walled tubes (AATTs). It may be a way solving this problem to exert axial compression loads (ACL) on the tube end in the bending. Thus, this article establishes a three-dimensional (3D) elastic-plastic explicit finite element (FE) model for the bending under ACL and has its reliability verified. Through a multi-index orthogonal experiment design, a combination of process parameters, each expressed by a proper range, for this FE model is derived to overcome the compression instability on tube ends. By combining the FE model with a wrinkling energy prediction model, an in-depth study is conducted on the forming characteristics of large-diameter AATTs with small bending radii and it can be concluded that (1) The larger the tube diameters and the smaller the bending radii, the larger the induced tangent tension stress zones on tube intrados, by which the tube maximum tangent compression stress zones will be partitioned in the bending processes; thus, the smaller the ACL roles in decreasing thinning degrees and the larger the compression instability possibilities on tube ends. (2) The tube wrinkling possibilities under ACL are larger than without ACL acting in the earlier forming periods, and smaller in the later ones. (3) For the tubes with a size factor less than 80, the ACL roles in decreasing thinning degrees are stronger than in increasing wrinkling possibilities.     

主燃孔对模型燃烧室流场的影响

为了深入了解主燃孔参数变化对双级轴向旋流器模型环形燃烧室内气流组织与气动性能的影响,采用PIV测速仪对该燃烧室内冷态和液雾燃烧流场进行测量,试验研究在冷、热态情况下不同主燃孔参数对模型燃烧室内回流区的形成、轴向平均速度u,轴向脉动速度Urms,雷诺剪切应力u′v′分布的影响。研究结果表明:主燃孔参数变化对燃烧室内冷、热态流场有着重要的影响;燃烧室在燃烧情况下所得的中心回流区长度要比冷态短,但回流负速度、脉动速度和雷诺应力都明显大于冷态,所得的研究结果可为燃烧室优化设计提供有用的依据。