水下弹性圆柱的共振散射

当声波频率与水下弹性圆柱的某一模式的共振频率相符时,圆柱受声波激励产生的共振振动向周围介质辐射的声波最强。国内、外研究表明,对一般的金属圆柱而言(其弹性纵波与切变波速度大于水中声速),在与入射波方向相反的方向上,由于这种辐射声波与圆柱表面的几何反射波位相相反,因此两者干涉的结果形成了在共振频率上出现反向散射声振辐的极小值。本文揭示了一种新的情况,即对于弹性切变波波速小于水中声速的一种材料做成的圆柱体,无论是理论计算和实验测量,均表明在共振频率上出现反向散射振幅的极大值。     

对声波和弹性波传播模拟的Hamilton系统方法

建立了离散化网格上的准粒子体系，引入此体系的Hamilton系统描述，用来模拟声波和弹性波的传播.介绍了准粒子间相互作用的九点模型并给出互作用系数.证明了Hamilton系统方法 和声波、弹性波方程的关系，并给出两个方法中所使用物理量的关系.使用辛算法对给定的 介质模型进行数值模拟. 关键词： Hamilton系统方法 九点互作用模型 声波方程 弹性波方程 辛算法     

斜入射声场中无限弹性圆柱的共振、表面波及声散射

本文讨论斜入射声波场中无限长弹性圆柱体的声散射特性与柱体的共振和表面波特性之间的关系。由自由柱的三维简正波解,可求得柱的自由共振频率与相应螺旋表面波的相速度以及螺旋角的关系,进而可求得表面波相速度的频散关系与水中声波入射角的关系,通过与Flex等在有关论文中的结果相比较,表明在倾斜入射条件下,无限弹性柱的共振方式与形函数曲线中极小值的频率基本相符,这一现象与正横入射时的现象相类似。     

楔形弹性海底声矢量场分布规律研究

提出了基于弹性抛物方程的声矢量场计算方法,计算了楔形弹性海底的海洋环境中甚低频声矢量场和弹性海底地震波场分布,研究了声源深度和声源频率对声场分布的影响,仿真结果表明声波在具有弹性楔形海底的海洋环境中传播时存在能量泄漏现象,利用简正波理论解释了能量泄漏位置可由水深一波长比确定.     

弹性波通过一维复合材料系统的透射性质

提出了不同结构的一维弹性波复合材料系统模型,包括一维周期结构声子晶体、标准Fibonacci准周期结构声子晶体、广义Fibonacci准周期结构声子晶体以及完全无序结构的复合材料系统. 采用模式匹配理论法,数值计算了弹性波通过一维复合材料系统的透射系数. 计算结果表明,利用特殊的准周期结构声子晶体可获得比周期结构声子晶体更宽的带隙范围,准周期结构排列的复合材料系统相当于在周期结构中引入了缺陷体一样,带隙内出现了丰富的局域模式. 对弹性波/声波在复合材料系统中局域态性质的研究有助于弹性波/声波滤波器、导波器 关键词： 弹性波复合材料 局域化     

金属薄板弹性各向异性检测

当平面声波入射到液体中的金属薄板上时，透射系数将随声波入射角变化，根据这一规律，能够准确地测定声波入射面与金属薄板交线方向上金属板材料的弹性常数，测得金属薄板面内不同方向的弹性常数，对金属薄板弹性各向异性情况将有一清蜥的认识，由于测试过程采用微机控制、数据采集和处理，实现了各向异性测量的全自动化，该方法测试时间短、所需样品小且加工方便，并可测试金属薄板弹性各向异性的均匀度。     

海底沉积物压缩波速度与切变波速度的关系

基于连续介质假设,根据无吸收各向同性弹性介质通用方程分析沉积物声波传播关系,提出应用弹性结构分布因子表达的声速通用模型(GMSS,General Model of Sound Speed)分析海底沉积物的声速特性;通过研究Willey时间平均模型、Wood方程、Gassmann方程、Buckingham模型、Biot-Stoll模型和EDFM模型,可以表述成GMSS通用模型中的弹性结构分布因子的具体表达形式,得出GMSS通用模型在解释压缩波速度和切变波速度特性上具有一致性的特点。GMSS通用模型具有弹性结构分布因子、孔隙度、孔隙海水的等效密度和等效弹性模量、固相颗粒的等效密度、固相颗粒的等效体积弹性模量和等效切变弹性模量共7个参数,为研究海底沉积物压缩波和切变波速度提供了一种模型简单、参数少、通用性强的方法。但也需要从物理结构上以及应力应变关系上开展更为深入的分析和探寻GMSS模型的物理意义和参数测量的方法。      

水中有限弹性圆柱的窄脉冲回波响应与螺旋表面绕行波

用严格的解析方法求解有限长弹性柱的声散射问题是困难的,而近似的数值计算方法又缺乏物理的直观性.本文提出采用弹性螺旋表面波的声激励和再辐射理论分析模型,对入射声波方向在正横附近一定角度范围内(约±30°)有限弹性圆柱的脉冲回波响应作了分析,建立了用以估算回波时序、幅度和共振模式的基本关系式.给出了目标弹性特性与回波响应的直观物理联系。在水池中,实测了厚壁中空钢柱和铝柱的脉冲响应,实测脉冲回波时序与理论预报结果基本相符.     

声波全波测井数字记录

一、前 言 常用的补偿声波测井仪只测量声波波列中纵波的首波,而其余大量有用的声波信息没有得到利用. 声波全波测井测量的是整个声波波列.它能提供地层纵波、地层横波和诱导波的数据.从而扩大了声波测井的应用范围,并为进一步利用声波波列的其它信息提供了原始资料. 声波全波测井是一种较新而重要的测井方     

海面随机起伏对噪声场空间特性的影响规律

对于1 k Hz以上声波,海面起伏会对浅海声传播产生显著影响,现有的噪声预报模型在建模过程中基本没有考虑海面起伏的影响.针对这一问题,本文基于传输理论建立了随机起伏界面下噪声场垂直相关性和指向性模型,仿真分析了海面起伏对噪声强度、垂直相关性与指向性的影响.结果表明,对于表面噪声,海面随机起伏使声波能量从中间阶简正波向低阶和高阶简正波转移,而对噪声强度起主要贡献的一般是中间阶简正波,所以海面起伏使得噪声强度减弱;简正波之间能量的耦合导致垂直平面上不同掠射角方向上到达的声波响应发生变化,经由海面反射大掠射角到达的声波响应以及中小角度到达的声波响应变弱,而经由海底反射大掠射角到达的声波响应变强;海面随机起伏还会扰动各阶简正波相位,使不同阶简正波互相关性变弱,致使噪声场的空间相关性也变弱.     

Third-order elastic constants and pressure derivatives of the second-order elastic constants of β-tin

The second- and third-order elastic constants and pressure derivatives of second-order elastic constants of tetragonal β-tin have been obtained using the deformation theory. The strain energy density derived using the deformation theory is compared with the strain dependent lattice energy obtained from the elastic continuum model approximation to get the expressions for the second- and third-order elastic constants. Higher order elastic constants are a measure of the anharmonicity of a crystal lattice. The 12 non-vanishing third-order elastic constants and the six pressure derivatives of the second-order elastic constants in tetragonal β-tin are obtained in the present work and are compared with the available experimental values. The second-order elastic constant C₃₃ obtained in the present study is in reasonable agreement with the experimental values. The third-order elastic constants are generally one order of magnitude greater than the second-order elastic constants as expected of a crystalline solid. The third-order elastic constant C₃₃₃ is higher in magnitude than all other values. This shows a greater anharmonicity of β-tin along the c-axis direction of the crystal.     

具有立方晶系结构的多晶体材料的弹性常数——Y弹性常数

提出了一个新的物理参量“Ｙ弹性常数”,并阐述了其物理含义.并将其应用于具有立方晶系结构的多晶体材料,推导了立方晶系结构的多晶体材料的Ｙ弹性常数,通过算例与具有立方晶系结构的多晶体材料的X射线弹性常数进行了比较.运用这个Ｙ弹性常数进一步推导出的多晶体材料整体的机械弹性常数的表达式与Krner的研究结果完全符合. 关键词： Y弹性常数 立方晶系 多晶体材料     

具有六方晶系结构的多晶体材料弹性常数——Y弹性常数

利用最近提出的新的物理参量——Ｙ弹性常数,将其应用于具有六方晶系结构的多晶体材料.推导了六方晶系结构的多晶体材料之Ｙ弹性常数,通过算例与具有六方晶系结构的多晶体材料之X射线弹性常数进行了比较.运用这个Ｙ弹性常数进一步推导出的多晶体材料整体之机械弹性常数的表达式与Kneer的研究结果中的表达式虽然形式不同,但针对具体材料所计算的结果却完全符合. 关键词： Y弹性常数 六方晶系 多晶体材料     

Elastic constants for NaCl and KCl solids at high temperatures

In the present study we derive new relationships to predict the temperature dependence of elastic constants. Proposed relationships are applied to study elastic constants of NaCl and KCl. A linear relationship between thermal expansivity and elastic constants at high temperatures is found to exhibit for solids. The extrapolated data on elastic constants in very high temperature region obtained in the present study are useful to understand the thermoelastic properties of NaCl and KCl. A close agreement between theory and experiment reveals the validity of the formulations used.     

关于岩石三阶弹性常数的超声测量方法

油气储层岩石的三阶弹性常数反映了该岩石的速度应力敏感性,是利用声波测井或地震资料进行原位地应力反演的基本参数。本文阐述了利用声弹性理论在实验室测量岩石三阶弹性常数的原理与方法,并给出了部分实验结果。这些参数将为研究声波在预应力声场中传播规律的提供基础数据,同时也为定量分析利用交叉偶极声波测井评价地应力的精度提供了依据。不同岩石的三阶弹性常数较大差异表明,通过速度各向异性进行应力反演时必须考虑岩石本身非线性的差异。     

RUS study of the elastic constants in silver halide crystals

By using RUS method, the temperature dependence of the elastic constants in the silver halide crystals has been measured above room temperature. The elastic constants decrease linearly with increasing temperature. Numerical calculations are presented for the contribution of the multipole polarization to the elastic constants in the silver halide crystals. The calculated values of the deviation from the Cauchy relation are about a quarter of the experimental values. The multipole polarization significantly affects the elastic constants and contributes to the violation of the Cauchy relation.     

Higher order elastic constants and generalized Gruneisen parameters of elastic waves and low temperature thermal expansion of gadolinium

Expressions for the higher order elastic constants are derived using the sublattice displacements to the second degree in strains. These expressions are used to obtain the higher order elastic constants and their pressure derivatives in gadolinium. The higher order elastic constants are used to find out the generalized Gruneisen parameters of the elastic waves propagating in different directions in gadolinium. The Brugger gammas are evaluated and the low temperature limit of the Gruneisen gamma is obtained. The results are compared with the available reported values.     

Third-order elastic constants of the alloy Fe72Pt28

The complete sets of second- and third-order elastic constants of the cubic Fe₇₂Pt₂₈ have been obtained using the strain energy density derived from interactions up to three nearest neighbours of each atom in the unit cell. The finite strain elasticity theory has been used to get the strain energy density of Fe₇₂Pt₂₈. The strain energy density is compared with the strain-dependent lattice energy density obtained from the continuum model approximation and the expressions for the second- and third-order elastic constants of Fe₇₂Pt₂₈ are given. The second-order potential parameter is deduced from the measured second-order elastic constants of Fe₇₂Pt₂₈ and the third-order potential parameter is estimated from the Lennard-Jones inter-atomic potential for Fe₇₂Pt₂₈. The inter-lattice displacements; the three independent second-order elastic constants and the six independent third-order elastic constants of Fe₇₂Pt₂₈ are also determined. The second-order elastic constants are compared with the experimental elastic constants of Fe₇₂Pt₂₈. We also study the effect of pressure on the second-order elastic constants of Fe₇₂Pt₂₈.     

Third-order elastic constants of ZnS and ZnSe

The complete set of non-vanishing third-order elastic constants of the semiconductors ZnS and ZnSe is obtained theoretically. The strain energy density is estimated using finite strain elasticity theory by considering the interactions up to two nearest neighbours of each atom in the unit cell of these compounds. This energy density is compared with the strain dependent lattice energy density from the continuum model approximation. The second-order parameter of the potential function φ is obtained from the measured principal axis C_ij. The third-order potential parameter is estimated by assuming a Lennard-Jones type of interatomic potential. The interlattice displacements as well as the second-order elastic constants are evaluated along with the six third-order elastic constants of ZnS and ZnSe. Using these second- and third-order elastic constants of ZnS, the pressure derivatives of second-order elastic constants are evaluated. The second- and third-order elastic constants of ZnSe are compared with the available experimental values. The third-order elastic constants show anisotropy in different directions.     

Anharmonic properties of rocksalt structure solids

An effort has been made for obtaining the anharmonic properties of rocksalt structure solids starting from primary physical parameters viz. nearest-neighbor distance and hardness parameter assuming long- and short-range potentials at elevated temperatures. The elastic energy density for a deformed crystal can be expanded as power series of strains for obtaining coefficients of quadratic, cubic and quartic terms which are known as the second-, third- and fourth-order elastic constants, respectively. When the values of the higher-order elastic constants are known for a crystal, many of the anharmonic properties of the crystal can be treated within the limit of the continuum approximation in a quantitative manner. In this study, higher-order elastic constants are computed up to their melting temperature for rocksalt structure solids, which are alkali cyanides, sodium and potassium halides. The first order pressure derivatives of second- and third-order elastic constants, the second-order pressure derivatives of second-order elastic constants and partial contractions are also evaluated at different temperatures for these substances. The results thus obtained are compared with experimental data and found in well agreement with present values.