改进的二维滤波技术在浅层地声探测中的应用

利用声波反射原理探测地下浅层物体是一种较为有效的探测方法。经过多年的探索，我们已形成了以爆炸和锤击等有较高分辨率的瞬态信号作为声源，采用传感器直线阵接收，后续结合阵列信号处理技术完成目标信号的提取和成像处理的探测方案。该声探测系统在实测中，地表直达波对物体反射波的强干扰是限制探测灵敏度的主要原因之一。因此，抑制强干扰，提取有效信号，是实现目标正确探测和定位的先决条件。由于探测深度较浅，反射波和直达波混迭在一起，在频率域或时间域很难将强干扰和信号分开。于是就提出了利用直达波和反射波视速度的差异对频…     

长江口和杭州湾浮泥声参数测量

本文报导了用４种频率的超声波，对长江口和杭州湾的水底浮泥在不同重度下测得的声速和重度之间，声衰减与重度之间以及在一定重度下频率与声衰减之间的变化关系曲线。实验结果表明；在相同条件下，杭州湾浮泥的声衰减比长江口浮泥的声衰减大一点。     

基于回传射线矩阵法成层土中部分埋入黏弹性桩的波动响应研究

基于回传射线矩阵法获得桩顶作用半个正弦波脉冲时成层土中部分埋入黏弹性桩桩顶处速度导纳,利用Fourier逆变换与卷积定理获得瞬态半正弦激振力作用下桩顶处时域速度响应。比较均匀地基部分埋入桩受桩身材料阻尼与桩侧土体阻尼作用的桩顶速度响应,分析软(硬)夹层厚度、夹层土土性参数、桩底土土性参数变化对桩顶速度导纳及反射波影响。结果表明,桩身材料阻尼对桩顶速度导纳及反射信号均有衰减作用,且会使桩底反射波发生弥散现象;桩侧、桩底土体刚度变化会使速度导纳低频段曲线产生偏移量;桩侧、桩底土体阻尼变化对桩顶速度导纳及反射波较二者刚度变化影响更大。     

钛铜复合棒挤压过程的数值模拟

采用Deform-3D有限元软件对扁形钛铜复合棒的挤压过程进行了数值模拟研究,得到了挤压过程中钛和铜的流动规律及应变场分布.分析了挤压速度对产品表面质量、钛铜相对滑移量及钛层厚度的影响.结果表明:随挤压速度的加快,钛铜相对滑移量增加,而钛层厚度变化不大；当挤压速度为100mm/s时挤压产品的质量最好.     

锗酸铅晶体枝蔓晶生长的实时观察研究

利用实时观察方法对锗酸铅晶体生长枝蔓晶的生长过程进行了描述和分析．发现，枝蔓晶的产生与杂质相关，杂质作为一个成核中心，在其周围存在一个溶质扩散层，这个溶质扩散层的厚度随着晶体生长而增大．当该扩散层的厚度超过某个临界值时，出现枝蔓晶生长，溶质扩散层的临界厚度约为12μm．枝蔓晶主干的生长速度受分支出现以及主干转向的影响．     

大振幅平面声波在多层介质中的传播

本文用逐级近似法就一维情况下分析了大振幅平面声波在多层介质的界面上发生反射和透射的传播特性。在二级近似下计算了精确到二阶小量的二至三个界面各层的反射波和透射波的二次谐波，并推广至几个界面，得到一些规律性的结果。从拉格朗日坐标下的一级近似和二级近似的波动方程式出发，假定声波在多层介质中传播在各个界面仍是连续的，即各层界面的边界条件由界面两侧的压力平衡和质点速度相等来决定，由此求得各层界面在二级近似下的二次谐波的反射波和透射波。计算结果表明，二级近似下的反射波和透射波均由两部分组成，一部分是由一级反…     

圆柱形压缩机壳体声辐射特性参数研究

利用波数域法建立了在集中载荷作用下，压缩机壳体的波数域径向振动速度计算公式，进而用边界积分方程推导了压缩机壳体的远场辐射声压理论表达式。建立的壳体声辐射预估理论公式研究了制冷工质类型、壳体厚度、结构阻尼、力的作用方向、机芯等效刚性圆柱半径、壳体中心面半径等参数的变化对压缩机壳体声辐射的影响规律。研究结果对圆柱形压缩机壳体的低噪声优化设计有一定的指导意义。     

超薄弹性层低频超声频域定征方法

本文提出一种定量无损估计超薄弹性层声速、厚度和密度参数的低频超声波频域定征方法。这里“超薄”的概念是指材料厚度远小于材料中声波波长，导致在时域上材料前后界面的多次回波信号相互混迭。本文采用超声纵波垂直入射超薄层材料，分析了水浸耦合和耦合剂耦合两种情况下，材料反射波和透射波的组成，定义和推导了材料的反射与透射传递函数，提出了在最小二乘误差意义上分别使用材料传递函数幅度谱、相位谱和复谱对各参数进行反向估计的算法，分析了影响估计准确性的各种因素，研究了灵敏度函数在误差传递中的意义。实验结果表明该方法能够对厚度小于百分之一声波波长的超薄弹性层进行无损定征。     

超声治疗中耦合液对声聚焦影响的研究

本文推导了凹球面聚焦换能器产生的声波经耦合液进入软组织后的声场计算公式，并对不同耦合液，耦合层厚度，温度对声聚焦的影响进行了研究，得到一一些对超声热疗具有指导意义的结果。     

电参数对Mg-7Gd-5Y-1.5Nd-0.5Zr镁合金微弧氧化膜的影响

针对Mg-7Gd-5Y-1.5Nd-0.5Zr高强耐热镁合金,采用微弧氧化工艺制备了表面防护层,研究了电流密度、电压、频率以及占空比等电参数对膜层厚度及形态的影响规律.研究表明,电压对氧化膜厚度影响显著,电流密度对氧化膜厚度有影响但不显著,占空比和频率对氧化膜厚度影响较小.随着电流及电压的增加,膜层表面微孔的尺寸逐渐增大;随频率和占空比的增加,膜层表面微孔的尺寸先增大后减小.     

海面噪声垂直相干特性反演地声参数

声学反演是快速、低成本获取浅海局部地声参数的有效方法之一,其中,利用海面噪声的垂直相干函数反演海底参数,只需要两个垂直排列的水听器,不需要专门的发射声源,隐蔽性好,有较高的军事应用价值.通过已有的海面噪声场模型,分析了海底声速、密度及衰减系数对噪声垂直相干函数的敏感度,并利用中国某海区的海洋环境噪声试验数据,结合差异进...     

Anomalies of the Boundary Reflection of Ultrasound from the Film of a Dissipative Medium

Theoretical consideration has been given to the reflection of continuous and pulsed longitudinal and transverse acoustic waves from the film of a dissipative medium which is in contact with a solid-state half-space. It has been shown that the reflection coefficient and its phase substantially depend on the coefficient of attenuation of ultrasound in the dissipative-medium film and on its phase thickness. The shape of the reflected acoustic pulsed signal has been calculated using software. The application of the results obtained to investigation of the acoustic properties of viscous fluids is discussed.     

X射线反射法分析ZnO基薄膜的厚度、密度和表面粗糙度

采用X射线反射法(XRR)测试了在SiO_2玻璃衬底上磁控溅射沉积的单层ZnO基薄膜的反射强度,得到了反射强度随掠入射角变化的曲线;讨论了薄膜厚度、密度和表面粗糙度与反射曲线的关系,最后通过拟合XRR曲线获得了所制备薄膜的厚度、密度和表面粗糙度分别为55.8 nm,5.5 g·cm~(-3)和1.7 nm,与利用XRR数据直接计算出的薄膜厚度56.2 nm仅相差0.4 nm,表面粗糙度也与AFM测试的结果基本相符。可见XRR能无损伤、精确且快速地测试薄膜试样的厚度、密度和表面粗糙度等参数。     

P1波在非饱和土地基表面的反射特性

非饱和土是地表天然土体中最常见的一种形式。与饱和土不同,非饱和土内可传播四种体波:一种剪切波(S波)和三种压缩波(P1波、P2波、P3波)。其中P1传播特性与饱和土中的快压缩波相似:传播速度最快,且衰减系数最低。因此,该文运用非饱和孔隙介质理论阐述了弹性波在非饱和土中的传播特性,分析了平面P1波在非饱和土介质自由边界上的反射问题。根据边界条件,分别导出了在非饱和土自由边界上的四种反射波:反射P1波、反射P2波、反射P3波及反射S波的振幅反射系数及能量反射系数的理论表达式,并且在此基础上进行了数值计算。算例中讨论了四种反射波的振幅反射系数及能量反射系数受P1波入射角及地基土体饱和度变化的影响情况。结果表明:各反射波的振幅反射系数及能量反射系数不仅与入射角有关,也受到饱和度变化的影响。这些结论对土动力学的理论研究以及工程地震勘探具有一定指导意义。     

FEM modeling and analysis in prevention of the waterway dredgers crane serviceability failure

This paper gives a proposal of one suitable concept for FEM structural modeling and analysis of cranes which are a common part of the waterway dredger facilities. These dredgers typically contain two cranes: main jib crane between the catamaran-like pontoons and auxiliary crane in the bow zone. Discussion here is dedicated towards advantages and weaknesses of various FE models for the crane structures, in order to avoid of frequently failures of serviceability state of a main crane. Basic goal is to emphasize the benefits of sophisticated but practical numerical model in comparison with the simpler and inadequate models for prediction of a real structural behavior of jib cranes. In that sense results of our research could be sort of template for FE modeling phase in an efficient design of such structures.     

On the Possibility of Monitoring of Adhesive Joints of Bodies by Sounding with Plane Transverse Electric Waves

The reflection factor is analytically determined for a plane transverse electric wave reflected from an adhesive joint of a plate with a semiinfinite body in the presence of an intermediate layer whose dielectric permittivity linearly varies over the thickness of the layer. By analyzing the quantitative frequency dependences of the reflection factor for the investigated object, we conclude that the intermediate layer can be detected and its thickness can be approximately evaluated by comparing the theoretical results with the experimental data on sounding with 3–5-mm waves.__________Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 1, pp. 89–92, January–February, 2005.     

Determining surface orientations of transparent objects based on polarization degrees in visible and infrared wavelengths

Techniques for modeling an object through observation are very important in object recognition and virtual reality. A wide variety of techniques have been developed for modeling objects with opaque surfaces, whereas less attention has been paid to objects with transparent surfaces. A transparent surface has only surface reflection; it has little body reflection. We present a new method for obtaining surface orientations of transparent surfaces through analysis of the degree of polarization in surface reflection and emission in visible and far-infrared wavelengths, respectively. This parameter, the polarization degree of reflected light at the visible wavelengths, is used for determining the surface orientation at a surface point. The polarization degree at visible wavelengths provides two possible solutions, and the proposed method uses the polarization degree at far-infrared wavelengths to resolve this ambiguity.     

斜面型厚度变化板中导波的研究

针对单一模式导波入射的情况，利用混和边界元模型计算了斜面型散射区域的反射系数和透射系数与各种入射模式、入射频率以及斜面倾角变化的关系，研究了在单一模式导波入射时导波与散射体的相互作用。文章的结果可以用来提高大量实际的无损检测工程中的检测灵敏度与能量的穿透能力，尤其是在那些发生了斜面状厚度变化波导中的情形。     

Water-wave Scattering by an Ice-strip

The problem of water-wave scattering by a strip of ice-cover floating on the surface of deep water is investigated here. The ice-cover is modelled as a thin elastic plate of very small thickness. The problem is reduced to that of solving two singular integral equations of Carleman type over a semi-infinite range and are solved approximately by casting them into two separate Riemann-Hilbert problems by assuming the strip width to be large. The reflection and transmission coefficients are derived approximately. Numerical results for the reflection coefficient are presented graphically against the wave number and also against the ice-cover parameter. The oscillatory nature of the reflection coefficient against the wave number as well as the ice-cover parameter is found to be one of the main features of the curves. It is also seen that, in the limiting case when the ice-cover parameter tends to zero (i.e., the ice-cover is almost absent), the amount of reflection is negligible     

Applicability of the method of fundamental solutions to interaction of fully nonlinear water waves with a semi-infinite floating ice plate

In this research effort, a meshless numerical model was developed to study the hydroelastic interaction of an incident wave with a semi-infinite horizontal floating plate. It is assumed that the fluid is homogenous, inviscid and incompressible. Fundamental solution of the governing Laplace equation is considered to be radial basis functions. In this method, only a few boundary points are located on the boundary. Moreover, there are a few source points that are located outside the computational domain. Two additional source points are introduced to deal with the plate's edge conditions. The problem is solved using collocations at only a few boundary points. When density and thickness of the plate are reduced to zero, good agreements with other numerical works are observed.