多层垂直对称轴横向各向同性介质精确走时计算   总被引：1，自引：0，他引：1       下载免费PDF全文

唐巍  李磊 《地震学报》2008,30(4):367-376

给出了计算多层垂直对称轴横向各向同性（VTI）介质精确射线路径和走时的方法,所用的体波相速度公式、群速度公式和Snell定律都是严格的显式解析公式. 任意基本波的射线路径和走时计算问题都可以转化成一个等效的透射问题,再用文中的公式来计算,具体实现方法用一个多次波和一个首波的实例给出. 最后分别用精确公式和Thomsen近似公式计算了相同模型相同基本波的走时曲线. 比较两者计算结果可发现, 近似公式反复使用会使误差积累,同时揭示了近似公式适用范围的局限性,强调了使用近似公式需要注意其适用范围的重要性.   相似文献   

横观各向同性冻土弹性常数及强度预测   总被引：1，自引：0，他引：1  

王正中  牟声远  牛永红  陈立杰  刘军  刘旭东 《岩土力学》2008,29(Z1):475-480

在分析冻土形成过程及其组构前提下,从冻土细观结构特征出发,将冻土视为由冰层与干硬土层黏结组成的横观各向同性固体介质。根据复合材料力学理论,求出冻土各向同性面内及面外的弹性模量和泊松比;基于Tsai-Wu 准则,预测了横观各向同性冻土的强度。根据实验数据,分析了不同组分对冻土弹性常数及强度的影响。在工程应用中可根据环境温度及土质、系统有无水分补给、温降速度与冻结速率是否同步、冻土受力方向与冻结封面方向的具体情况选用即可,从而大幅降低室内外试验次数。为冻土工程数值计算奠定了基础,为进一步了解冻土力学特性提供了理论依据  相似文献   

Axisymmetric transient waves in transversely isotropic half-space     

Morteza Eskandari-Ghadi  Siamak Sattar 《Soil Dynamics and Earthquake Engineering》2009

A transversely isotropic material in the sense of Green is considered. Using a series of potential functions proposed in [Eskandari-Ghadi M. A complete solution of the wave equations for transversely isotropic media. J Elasticity 2005; 81:1–19], the solutions of the transient wave equations within a half-space under surface load are obtained in the Laplace–Hankel domain for axisymmetric problems. The solutions are investigated in detail in the special case of a surface point force pulse varying with time as Heaviside function. Using Cagniard–De Hoop method, the inverse Laplace transform and inverse Hankel transform of the solutions are then obtained in the form of integrals with finite limits. For validity of the analytical results, the final formulations for surface waves are degenerated for an isotropic material and compared with the existing formulation obtained by Pekeris [The seismic surface pulse. Proc Natl Acad Sci USA 1955;41:469–80], to show that they are exactly the same. The numerical evaluations of the integrals for some transversely isotropic materials as well as an isotropic one are obtained. The present approach is then numerically verified by comparing a particular case of displacements for the surface of an isotropic half-space subjected to a point load of Heaviside function with the solutions obtained by Pekeris [The seismic surface pulse. Proc Natl Acad Sci USA 1955;41:469–80]. In addition, the wave equations for the mentioned medium are obtained on the vertical line directly under the applied surface load. The final formulations are degenerated for an isotropic material and compared with the existing formulation given in Graff [Wave motion in elastic solids. New York: Dover Publications Inc; 1975 [New Ed edition, November 1991]], to show that they are also exactly the same. Then equations are presented in graphical forms using an appropriate numerical evaluation.  相似文献   

横观各向同性含液饱和多孔介质黏弹性瞬态反应     

王俊林  祝彦知  张天航 《岩土力学》2007,28(7):1315-1322

在考虑横观各向同性含液饱和多孔介质固体骨架和流体可压缩性以及固体骨架的黏弹性特征下,基于横观各向同性含液饱和多孔介质u-w形式的三维动力控制方程,以固相位移u、液相相对位移w为基本未知量,综合运用Laplace变换、双重Fourier变换等方法,在直角坐标系下通过引入中间变量,将六元2阶动力控制方程组化为两组各含4个未知变量的常微分方程组,给出了直角坐标系下横观各向同性含液饱和多孔介质三维黏弹性动力反应的积分形式一般解;作为理论推导的验证,通过引入初始条件和边界条件,对横观各向同性含液饱和多孔介质半空间黏弹性瞬态反应问题进行了求解。解答的退化验证表明,所推导的理论解是正确的。  相似文献   

各向异性双相介质中多极源声波测井理论研究   总被引：4，自引：0，他引：4  

张碧星  王克协 《地球物理学报》2000,43(5)

将各向异性地层模拟为横向各向同性双相介质 ,使其对称主轴与井孔中心轴线相垂直 .本文针对井孔模型下的多极源声波测井问题提出了一种解析的摄动方法 .将各向异性双相介质看作是由对应的各向同性双相介质加上摄动部分而组成 ,并引入 5个关于弹性模量偏离各向同性时的摄动量 ,对对称主轴与井轴垂直的各向异性双相介质的多极源声波测井问题进行了系统的理论研究和分析 ,严格求解了井孔内外的零级和一级近似声波场 .发现在n级多极源激发下 ,井孔中不仅出现n级多极声场 ,而且还能激发出与各向同性地层时不相同的高于和低于n级的多极声波场  相似文献   

On the strength of transversely isotropic rocks          下载免费PDF全文

《国际地质力学数值与分析法杂志》2018,42(16):1917-1934

Accurate prediction of strength in rocks with distinct bedding planes requires knowledge of the bedding plane orientation relative to the load direction. Thermal softening adds complexity to the problem since it is known to have significant influence on the strength and strain localization properties of rocks. In this paper, we use a recently proposed thermoplastic constitutive model appropriate for rocks exhibiting transverse isotropy in both the elastic and plastic responses to predict their strength and strain localization properties. Recognizing that laboratory‐derived strengths can be influenced by material and geometric inhomogeneities of the rock samples, we consider both stress‐point and boundary‐value problem simulations of rock strength behavior. Both plane strain and 3D loading conditions are considered. Results of the simulations of the strength of a natural Tournemire shale and a synthetic transversely isotropic rock suggest that the mechanical model can reproduce the general U‐shaped variation of rock strength with bedding plane orientation quite well. We show that this variation could depend on many factors, including the stress loading condition (plane strain versus 3D), degree of anisotropy, temperature, shear‐induced dilation versus shear‐induced compaction, specimen imperfections, and boundary restraints.  相似文献   

Static analysis of vertically loaded pile group in multilayered transversely isotropic soils     

Zhi Yong Ai  Yuan Feng Chen  Xiao Bin Jiang 《国际地质力学数值与分析法杂志》2020,44(15):2114-2131

In this paper, a coupling approach is presented to study the static responses of vertically loaded pile group embedded in multilayered transversely isotropic soils. The individual pile in pile group is modeled by the finite element method, while the analytical layer-element method is applied to represent the soil's behavior. Then, the interaction equation of piles and soils is obtained by considering the force equilibrium and displacement compatibility conditions and solved by a FORTRAN program. The results computed by the proposed approach compare favorably with those from some existing solutions and field test. Some typical parametric analysis cases are investigated to study the effect of soil anisotropy, pile stiffness ratio, and pile spacing on the behavior of vertically loaded pile group.  相似文献   

Crustal laminations in deep seismic profiles in France and neighbouring areas     

C. Bois  M. Cazes  A. Hirn  P. Matte  A. Mascle  L. Montadert  B. Pinet 《Geophysical Journal International》1987,89(1):297-304

Summary. Remarkable crustal features appear on the ECORS profiles carried out in northern France and the Bay of Biscay as well as on the SWAT profiles shot in the western Channel and the Celtic Sea. The most striking one is the occurrence of flat laminations in the lower crust. Dipping events and laminations are also present in the upper and lower crust, especially in the SWAT profiles. They can readily be related to tectonic events, Variscan in age, some of them identified in the field. The flat laminations in the lower crust are at first interpreted as resulting from delamination, shearing, magmatism and metamorphism at the crust-mantle transition during the Variscan orogeny. This interpretation raises some difficulty concerning the space and time correlation of the laminations with the Variscan orogeny. They seem to have been emplaced after the Permian-Triassic infilling of the Plymouth Bay basin and before the early Cretaceous opening of the Bay of Biscay. An early to middle Jurassic age is suggested, a period when large cratonic basins were formed without noticeable extension. Heat flow increase and magmatism are proposed as a second hypothesis for the formation of the lower crust laminations. Choosing between orogenic and non-orogenic causes of these laminations will require further deep seismic profiles together with good velocity determination.  相似文献   

巴丹吉林沙漠北缘拐子湖近地层湍流能谱特征分析     

郑新倩 《沙漠与绿洲气象(新疆气象)》2017,11(5):63-69

利用2013年6月巴丹吉林沙漠拐子湖地区流沙下垫面的陆气通量观测资料,计算并分析了该研究区不同大气稳定层结条件下的湍流速度各分量谱和温度谱及湍流的局地各向同性特征。结果表明:该研究区风速各分量的湍流强度随平均风速的增加而逐渐减小,当平均风速2 m/s时,风速各分量的湍流强度逐渐稳定且基本限定在0.5以内。在不同大气稳定度下,湍流速度和温度能谱曲线在惯性副区内逐渐有合并趋势且遵循Kolmogorov提出的-2/3定律,速度各分量谱在高频段均满足各向同性且符合低频限制理论。随着稳定度的增加,风速分量的能谱曲线逐渐降低且向高频端移动,风速分量和温度能谱对应的谱峰长度则逐渐减小。该研究区水平湍流尺度范围为9.0~600 m,垂直湍流谱峰波长为10.79~75 m。该结果介于草地和森林下垫面之间,与塔克拉玛干沙漠腹地的试验结果较为接近。  相似文献   

Turbulence Spectra And Dissipation Rates Above And Within A Forest Canopy   总被引：4，自引：0，他引：4  

Shuhua Liu  Heping Liu  M. Xu  M. Y. Leclerc  Tingyao Zhu  Changjie Jin  Zhongxiang Hong  Jun Li  Huizhi Liu 《Boundary-Layer Meteorology》2001,98(1):83-102

Three velocity componentsand temperature were measured usingthree-dimensional sonic anemometers/thermometers attwo levels, above and within a forest canopy, in theChangbai Mountains of northeast China. Turbulencespectral structure, local isotropy anddissipation rates above and within the forest canopywere calculated using the eddy correlation method.Results show that the normalized turbulent spectralcurves have -2/3 slopes in the inertial subrange.While the shapes of the spectra are in good agreementwith the Kansas flat terrain results, the atmosphericturbulence is anisotropic above the forest canopy. Dueto breaking down of large eddies by the foliage,branches and trunks, the spectral peak frequencies forvelocity and temperature are higher withinthan above the forest canopy. Compared withmeasurements from previous studies over flat terrain,the velocity and temperature spectra above andinside the forest canopy appear to shift toward higherfrequencies. The turbulence is approximately isotropicin the inertial subrange within the forest canopy, and isanisotropic above the forest canopy. The turbulentkinetic energy and heat energy dissipation rates aboveand inside the forest canopy are much larger thanthose obtained by Kaimal and Hogstrom over grasslandand grazing land. The distinct features in the resultsof the present experiment may be attributed to thedynamic forcing caused by the rough surface of the forestcanopy.  相似文献