各向异性成层地基中Rayleigh波的弥散特性

利用有限单元法及解析法推导了各向异性层地基中Ｒａｙｌｅｉｇｈ面波的弥散特征方程及各模态波位移分布的计算公式，可用于计算上软下硬地基，上硬下软地基及夹层地基Ｒａｙｌｅｉｈｔ面波的弥散曲线及位移分布。本文主要对各向异性上软下硬地基中Ｒａｙｌｅｉｇｈ面波弥散特性及位移分布规律进行了讨论。     

利用Love波特性计算地基动力响应

本文利用Love波弥散特性在频域上对地基出平面振动及扭振问题进行了研究。在计算区域内结构将采用有限单元划分,而在边界上则根据Love 面波特性使用传递边界有限单元。本文同时讨论了不同模态波对结构动力响应的贡献。本文方法也适合于静力分析。     

地基含倾斜界面对Love波弥散特性

利用有限元法及解析法相结合的方法建立了地基含有倾斜层时Ｌｏｖｅ波弥散特征方程和位移计算公式，利用这一方法研究了该类地基Ｌｏｖｅ波弥散特性，并与水平成层地基进行比较。     

地基含倾斜界面时Love波弥散特性

利用有限元法及解析法相结合的方法建立了地基含有倾斜层时Ｌｏｖｅ波弥散特征方程和位移计算公式。利用这一方法研究了该类地基Ｌｏｖｅ波弥散特性，并与水平成层地基（α＝０°）进行比较     

2.5D有限元建模关键问题——边界条件、网格划分及计算域选取

为了提高2.5D有限元数值计算的求解精度及建模效率,分析了移动荷载作用下地基系统的动力响应特点,确定了计算域选取及网格划分的基本规则,评价了地基分层对波场的影响及边界的波动吸收效果,提出了可以规避边界影响的建模思路。分析结果表明:当计算域尺寸满足低频振动要求(约60 m)时,反射波对计算结果的影响可以忽略;建模时可以采用辐射状网格划分,最小网格尺寸需满足高频振动要求(约0.5-1.0 m)。荷载运行速度小于地基瑞利波速时没有波动传播现象,建议直接采用固定边界;荷载运行速度大于地基瑞利波速时可以通过切取局部计算域的方式规避反射波的影响,此时计算域半宽和纵向空间范围的选取需要遵循与马赫锥锥角和列车全长相关的几何关系。荷载影响深度内的地基分层会扰乱地基波场,当地基上覆软弱土层或软弱夹层时,波动会在软土层聚集并在加载点后形成多个马赫锥。     

用Love面波特性计算动力响应的进一步探讨

根据上软下硬地基中Ｌｏｖｅ面波的能流分布规律，提出了利用Ｌｏｖｅ面波的第一模态波模拟水平方向传播波，而竖直方向传播波则采用半无限单元来模拟。通过算例来验证本文方法的可靠性和精确性，并讨论了传统的传递边界法的可靠性，对这两种方法进行了比较。最后讨论了衰减系数φ对计算结果的灵敏性。     

利用瑞利波速度弥散特性反演地基参数

文献[1]利用有限元与半无限元相结合的方法已能精确有效地计算成层地基R波速度的理论弥散曲线.在此基础上,本文利用阻尼最小二乘法推导了R面波法反分析成层地基土的有关参数的公式,给出了应用实测的R波弥散曲线反演土层参数的方法,并编制了相应的计算机程序.最后,通过计算实例验证了本文方法的可靠性和实用性.     

流体—固体成层介质中瑞利波特性的进一步讨论

利用解析法建立了两流体固体介质中斯通利波的特征方程及其位移计算公式，并进一步分析讨论了流体固体介质中瑞利波的弥散特性和传播规律。两半无限流体固体介质中斯通利波波速度是非频散的，波速比ｃ／ Ｖｓ 比匀质半空间中瑞利波波速比小，且ｃ／ Ｖｓ 受泊松比μ影响较小，一般情况模量比ｑ 对ｃ／ Ｖｓ 影响很小。流体固体成层介质中瑞利波具有弥散性，波长短时，相速度ｃ 趋于最上层固体的斯通利波波速，波长长时则趋于最下层固体的瑞利波波速     

饱和土中Love波弥散特性

本文利用有限元法推导了饱和土中Ｌｏｖｅ面波的弥散特性方程，讨论了饱和土中Ｌｏｖｅ面波波速度的弥散特性及位移分布规律，并与相应弹性地基Ｌｏｖｅ面波的波速度弥散曲线进行了比较。     

Rayleigh波作用下桩-土-桥梁结构动力相互作用问题研究

基于等效粘弹性人工边界单元建立了可考虑成层介质及Rayleigh波输入的二维有限元时域模型,计算了Rayleigh波作用下成层介质与均匀介质的自由场反应,与理论解比较表明有限元计算结果具有较好的工程精度。针对Rayleigh波作用下桩-土-典型刚构桥梁结构动力反应进行了分析,考虑了场地条件的不同、软夹层位置的改变、不同频率Rayleigh波的输入以及桩长对Rayleigh波传播与场地地震反应的影响,对影响因素进行了讨论。     

层状场地脉动卓越频率对应的理论计算深度研究*

地脉动观测是一种简便有效的场地土层动力特性测试方法。本文依据场地脉动能量中瑞利波为主的特性,基于层状场地瑞利波弥散特征曲线,研究了不同场地条件下脉动卓越频率对应的瑞利波波长与场地自振频率理论计算深度之间的关系。计算结果表明：场地一定深度范围内土层剪切波速差异特性是其主要影响因素。如果土层波速差别较小或者某一波速占主导地位,则理论计算深度与瑞利波波长比值约为1/4a(a为瑞利波波速与剪切波速之比),与均匀场地结果接近;反之,土层波速差异越大,两者比值与1/4a偏离越远,且1/4a为比值上限。     

On dispersion relations of Rayleigh waves in a functionally graded piezoelectric material (FGPM) half-space

For propagation of Rayleigh surface waves in a transversely isotropic graded piezoelectric half-space with material properties varying continuously along depth direction, the Wentzel–Kramers–Brillouin (WKB) technique is employed for the asymptotic analytical derivations. The phase velocity equations for both the electrically open and shorted cases at the free surface are obtained. Influences of piezoelectric material parameters graded variations on Rayleigh wave dispersion relations, particles’ displacements magnitude and corresponding decay properties are discussed. Results obtained indicate that coupled Rayleigh waves can propagate at the surface of the graded piezoelectric half-space, and their dispersion relations and the particles displacements ellipticity at the free surface are dependent upon the graded variation tendency of the material parameters. By the Rayleigh surface waves phase velocities relative changing values combined with the relationship between the wave number and the material graded coefficient, a theoretical foundation can be provided for the graded material characterization by experimental measurement.     

Dispersion and characteristic surfaces of waves in hybrid multilayered piezoelectric circular cylinders

The frequency and group velocity dispersion behaviors, and characteristic surfaces of waves in a hybrid multilayered piezoelectric circular cylinder are investigated. The associated frequency dispersion equation is developed using an analytical-numerical method. In this method, the cylinder is modeled using the three-nodal-line layer element; the coupling between the elastic field and the electric field is considered in each element. A system of governing differential equations of each layer element is obtained following the Hamilton Principle. The phase velocity and slowness as well as the group velocity and slowness are established in terms of the Rayleigh quotient. Six characteristic wave surfaces, e.g. the phase velocity, slowness and wave surfaces as well as the group velocity, slowness and wave surfaces, are introduced to visualize the effects of anisotropy and piezoelectricity on wave propagation. A corresponding program code is developed and numerical examples are presented for hybrid multilayered piezoelectric circular cylinders with two ratios of radius to thickness.     

重力对具有表面层的半空间中Rayleigh波的影响

重力对具有表面层的半空间中Rayleigh波具有重要的影响,假设表面层和半空间均为均匀各向同性介质,首先利用考虑重力作用的运动方程得出了重力影响下具有表面层的半空间中Rayleigh波的弥散方程。该方程经退化后得出了不受重力作用时的弥散方程,且与忽略重力时得到的方程完全一致。然后利用数值方法得到了重力影响下的Rayleigh波弥散曲线,分析了泊松比和表面层的厚度的影响,结果表明泊松比和表面层的厚度对弥散曲线具有明显影响。     

声表面波滤波器的离散Green函数分析法

日本学者Hashimoto提出栅格有效介电常数和离散Green函数,并结合有限元方法分析了短路金属栅阵中声表面波的传输特性。由此开发了相应的Fortran应用程序。国际上许多从事声表面波器件的研发公司都使用该程序设计他们的产品。以Rayleigh波在128°YX-LiNbO3基片、铝金属栅中传播为例,给出根据Hashimoto程序运算的结果,读取禁带下边缘和禁带上边缘所对应的相对频率的数值,代入COM理论色散关系的数学表达式中,该表达式的图形就是由COM理论色散关系而确定的波数色散曲线,以提取耦合模参数。     

Improved Rayleigh Wave Velocity Measurement for Nondestructive Early-Age Concrete Monitoring

A modified one-sided technique is proposed for Rayleigh wave (R-wave) velocity measurement in concrete. Wave scattering from material heterogeneity and near-field effects may disrupt sensed R-wave signals in concrete, which is manifested as signal dispersion. Conventional one-sided measurement techniques for concrete do not consider dispersion of R-waves. In this study, the maximum energy arrival concept is adopted to determine the wave velocity by employing continuous wavelet transform. Experimental and numerical studies are performed to show the effectiveness of the proposed method. The method is applied to monitor the strength development of early-age concrete exposed to various curing conditions. Results reveal that the proposed method can be effectively used to measure the R-wave velocity in concrete structures and further to monitor the development of compressive strength in early-age concrete, regardless of the concrete moist curing condition.     

Rayleigh波作用下地下结构的动力反应分析

基于粘弹性人工边界提出了Rayleigh波的时域波动输入方法,在此基础上研究了Rayleigh波作用下地下隧道的动力反应特性,重点研究了埋深对结构动力反应的影响。结果表明提出的波动输入方法具有良好的模拟精度;Rayleigh波对浅埋地下结构的动力反应影响显著;存在临界埋深D0,当结构埋深D>D0时,随着埋深的增加,结构动力反应逐渐减小;当D相似文献   

Elastodynamic Doppler effects

Summary The Doppler effect is discussed for flexure waves in beam and plate, three body waves (P, SV, SH) in an infinite solid, modal SH waves in a thick plate and a Rayleigh wave on the surface of a semi-infinite solid. The exact closed form solution for each elasto-dynamic problem is obtained and the simple equation for the Doppler frequency shift is derived for all waves. It is shown that the Doppler frequency shift takes place continuously in the 2D plane problems, and that the most sensible wave for the Doppler frequency shift is the non-dispersion wave, such as the body wave and Rayleigh wave. The flexural and modal waves, which have the dispersion nature, are less sensible. Dedicated to Professor Franz Ziegler on the occasion of his 70th birthday