利用Golay码测量长骨中传播的超声导波

近年来利用超声导波评价长骨状况已成为研究热点之一。但是超声导波信号在长骨的皮质骨层传播时会遭遇很大的衰减,尤其是当皮质骨层上附有软组织时,接收到的导波信号很小。为了提高信噪比,增大接收到的导波信号幅度,引入Golay码编码的超声信号作为激励。仿真结果表明,Golay码激励并解码后的L(0,5)导波模式与单脉冲激励得到的模式波形几乎完全一致,证明了利用Golay码作为激励,产生超声导波的可行性。在离体牛胫骨实验中,Golay码在提高信噪比的同时,还可以增加超声导波的测量距离。说明把Golay码应用到超声导波的测量上很有潜力。     

基于SEA方法的商用车噪声分析与预测

针对商用车驾驶室内噪声问题,采用统计能量方法(SEA),建立了驾驶室噪声仿真模型。通过试验方法,获取模态密度、结构损耗因子及输入激励等模型参数。实车测试与仿真结果的总体误差在2d B(A)以内,验证了模型的准确性。在此基础上,应用声学包设计方法优化车内噪声,降噪效果较好,具有一定的工程参考价值。     

基于小波变换和压缩感知的低速率语音编码方案

本文提出一种新的低速率语音编码方案,基于语音信号小波变换高频系数的稀疏性,利用压缩感知原理,将小波变换高频系数进行压缩感知投影成数据量大大减少的观测序列,然后对观测序列采用码激励线性预测技术进行编解码,根据解码后的观测序列,利用线性规划技术对小波变换高频系数进行重构,小波变换低频系数采用矢量量化技术编解码,并采用后置低通滤波器改善解码后小波高低频系数合成语音的听觉效果。该编码方案在低数码率(2.64～3.5 Kb/s)时得到的重构语音平均MOS分为3.0～3.4,达到4.8 Kb/s码激励线性预测语音编码质量。     

基于正交设计的SEA空腔结构吸声降噪优化研究

针对空腔结构建立SEA(统计能量分析方法)的仿真模型,通过设置多源激励得到目标空腔的噪声特性。考虑板件和吸声材料的降噪参数,并采用正交设计的方法对降噪参数进行仿真优化设计,得到了频带声压级的降噪处理的最优组合。     

基于FPGA的曼码编解码模块实现

本文提供了一种基于FPGA的曼彻斯特码编解码模块,利用FPGA进行曼码的编解码,完成单芯测井系统的通讯传输。整个系统主要分为编码模块和解码模块。测井过程中,地面系统通过编码模块产生命令信号,经过驱动电路和电缆后,发送到井下仪器。井下仪器将采集到的数据,经过电缆,驱动电路,发送到地面系统。地面系统通过解码模块恢复成原始数据。与采用专用编解码芯片相比,该方案成本更低,而且根据需要进行功能扩展,更加灵活。该解码方式已经在多个实际测井作业中成功运行,具有良好的工程实用价值。     

重型商用车内高频噪声的预测与分析

运用统计能量分析法,建立了车内噪声分析预测SEA模型。采用理论与试验相结合的方法确定了各子系统的模态密度和损耗因子。通过试验测量了各个工况下车身的振动激励与声压激励。输入参数与激励至模型中仿真计算得到的驾驶员头部声腔噪声声压级结果与试验结果对比,最大误差不超过2dB(A),这说明了建立的SEA模型预测车内噪声的准确性。进行能量传递路径分析,找出了噪声贡献最大的子系统,进而提出两种优化降噪方案并仿真,结果显示均能使室内声压级降低1.5dB(A)左右。     

基于Gray码和线移条纹的结构光3D测量技术

结构光3D测量的线移条纹进行编码,以亚像素定位技术提取Gray码条纹边缘和线移条纹中心,将其上点作为图像采样点进行解码的方法.消除了Gray码固有的一位解码误差对投射角求取的影响,同时提高了采样密度.文中具体介绍该方法的编码解码原理,分析了编码图案正交投射对测量准确度的影响,给出了仿真实验结果.测量误差约为0.04%.     

面向无线链路压缩数据可靠传输的高效纠删编码

机上载荷获取的视频图像数据经压缩后在误码率为1×10-5的无线通信链路中传输时极易受到干扰,从而使得地面终端无法正常解码显示。本文通过分析无人机测控下行链路数据传输误码模型,设计了一种高效的纠删编码技术以提高压缩后码流的抗误码性能。该算法首先将编码后的数据按照一定数量的字节数进行分帧,对分帧后的数据按列进行改进后的快速范德蒙纠删编码;然后对编码后的数据再按帧格式进行快速循环冗余校验(CRC)编码;最后将编码后的码流送入信道传输。仿真结果表明,该纠删编码抗误码技术能够将误码率为1×10-5信道降低到1×10-8左右,可以使得经过高压缩比后的视频码流正确解码显示。此外设计时使用的纠删编解码技术运算量低、延迟小、非常易于硬件实现。提出的高效纠删编码技术已成功应用于多项无人机测控系统。     

客车降噪材料应用研究

吸音隔音材料广泛应用于客车车内降噪,但其降噪效果实际会受到施工状态和客车本身噪声特性差异的影响。文章对客车发动机舱降噪材料进行了试验研究,根据车内噪声测试结果,对多种吸音隔音材料的降噪效果进行了评价,并利用阻尼材料弥补多孔材料对低频噪声降噪效果差的缺点。改善后的复合材料经测试,对300 Hz以下的低频噪声降噪达到1.7 dB（A）,对300 Hz以上的高频噪声降噪达5.7 dB（A）,总降噪量达4 dB（A）,显著改善了车内噪声。     

准正交空时组码系统的天线选择准则研究

论文利用准正交空时码(QSTBC)系统的等效信道矩阵的准正交性和格拉姆矩阵的稀疏性,提出了一种简单分离QST-BC系统接收信号的方法;应用协方差阵求解分离信号噪声项的平均功率(自方差),对4天线的Jafarkhan i码和TBH码的QST-BC码阵系统,分别推导出QSTBC-M IMO瞬时输出信噪比最新表达式。该法也可推广到任意4和8发射天线码的QSTBC系统和不等振幅复星座调制信号中。文中利用此瞬时输出信噪比作为系统发射天线子集的选择准则和收发两端天线子集选择的依据。大量仿真结果表明:无论采用何种QSTBC码型,准正交系统性能都将得到相当的改善;采用此最优选择准则所选择的天线组,其性能较之于选择信道增益系数最大和基于迫零准则要好很多。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

Quantum Cooperative Robotics and Autonomy

The intersection of Quantum Technologies and Robotics Autonomy is explored in the present paper.The two areas are brought together in establishing an interdisci...     

考虑进油孔有限长滑动轴承油膜力的近似解析解

针对具有进油孔的有限长滑动轴承油膜力求解问题,采用变分原理和分离变量法,求得了有限长滑动轴承油膜压力分布的近似解析表达式。将油膜压力分布的近似解析表达式在油膜存在区域上进行积分,即得到了油膜力。将提出的计算有限长滑动轴承油膜力方法与无限长轴承模型、有限元方法的计算结果进行了比较,发现了提出的方法与有限元方法的计算结果很接近。最后,研究了进油孔位置和进油压力对油膜存在区域、油膜力等的影响,研究结果表明进油孔位置和进油压力对油膜存在区域和油膜力有较大的影响。     

三绕组变压器的双绕组等效建模及在Matpower中的应用

针对实际电网存在着大量的三绕组变压器,但国际上一些著名商业软件,如BPA仿真软件、Matpower这一权威潮流计算开源软件,均只提供双绕组变压器模型,限制了其在具有三绕组变压器的电力系统中的应用的问题,潮流计算是自主开发的电力系统各种应用软件的核心模块,因此依托国际权威开源程序进行二次开发,是一种较好的选择。对Matpower要求的数据格式进行了归纳,对变压器的一般的等值电路及带理想变压器的等值电路和带标幺值的等值电路进行了分析研究,提出了三绕组变压器转换为双绕组等效模型的建模方法,使得原先只适应双绕组变压器的潮流计算软件可以适用于三绕组变压器电网的潮流计算;最后以Matpower软件为例进行了案例计算,并用PSASP仿真软件进行对比验证。研究结果证明,所提出的建模方法是有效的。     

On the Relation of Load to Average Gap in the Contact Between Surfaces with Longitudinal Roughness

A computer simulation model for the contact between longitudinally-oriented rough surfaces has been formulated. This model closely duplicates the actual surf ace contact deformation behavior by taking into account the elastic interactions between the asperities. There were no assumptions made about the shapes, or any deformation behavior of the asperities, except for their obeying the laws of elasticity. The plastic deformations on the high asperity peaks were taken into account by setting a ceiling on their contact pressures at the material hardness value. The simulations used real surface profiles which were digitized from unworn circumferentially ground steel surfaces. Each pair of these profiles was mathematically combined to form an equivalent rough profile pressing against an infinitely rigid flat and having the appropriately adjusted elastic modulus. A total of 28 different pairs of profiles were used in the simulations. Each contacting pair was subjected to 30 different load levels and the local contact pressures and deformations were calculated. The contact simulations yielded some important mathematical relationships between parameters, such as the real area of contact, average gap, and average asperity load through statistical curve fitting. Two analytical functions were generated to relate the average load to average gap and the real area of contact to load.     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

电站锅炉模糊风险评价方法研究与应用

针对电站锅炉风险等级评价问题,将模糊综合评价技术应用到电站锅炉风险等级评价中。开展了电站锅炉失效影响因素及模糊评价因素的重要程度分析,建立了一套科学合理适于在线评价的电站锅炉风险评价体系,提出了模糊综合评价技术与改进的模糊层次分析法相结合的模糊风险评价方法,利用改进的模糊层次分析法计算了指标体系中各层指标权重。对某一台电站锅炉的实际运行工况影响子因素进行了模糊风险评价,采用模糊合成算子进行模糊综合运算得到电了站锅炉运行工况影响子因素的评价向量。研究结果表明:电站锅炉的运行工况影响子因素的风险评价等级为第6级,失效可能性等级为小,该电站锅炉运行工况良好。     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.