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1.
Bani Pramanik 《Pure and Applied Geophysics》1972,93(1):60-67
Summary In this note displacement of a thin perfectly conducting viscoelastic plate of Reiss type in contact with vacuum on both sides and in a uniform magnetic field has been discussed. The plate has been assumed to be acted on by an impulsive load. Solutions have been obtained for small and large values of time. Results have also been discussed for some particular cases. 相似文献
2.
The aim of the paper is to study the shear wave propagation in a viscoelastic layer over a semi-infinite viscoelastic half
space due to irregularity in the viscoelastic layer. It is of great interest to study the propaga-tion of shear waves in the
assumed medium having a non planar boundary due to its similarity to most of the real situations. The perturbation method
is applied to find the displacement field. The effect of complex wave number on dissipation factor is analysed. Finally, as
an application, the result obtained has been used to get the reflected field in viscoelastic layer when the shear wave is
incident on an irregular boundary in the shape of parabolic irregularity as well as triangular notch. It is observed that
the amplitude of this reflected wave decreases with increasing length of the notch, and increases with increasing depth of
the irregularity. 相似文献
3.
Effect of point source and heterogeneity on the propagation of SH-Waves in a viscoelastic layer over a viscoelastic half space 总被引：1，自引：1，他引：0
The present paper is concerned with the propagation of shear waves in a homogeneous viscoelastic isotropic layer lying over
a semi-infinite heterogeneous viscoelastic isotropic half-space due to point source. The inhomogeneity parameters associated
to rigidity, internal friction and density are assumed to be functions of depth. The dispersion equation of shear waves has
been obtained using Green’s function technique. The dimensionless angular frequency has been plotted against dimensionless
wave number for different values of inhomogeneity parameters. The effects of inhomogeneity have been shown in the dispersion
curves. graphical user interface (GUI) software in MATLAB has been developed to show the effect of various inhomogeneity parameters
on angular frequency. The topic can be of interest for geophysical applications in propagation of shear waves on the Earth’s
crust. 相似文献
4.
A method is presented for the determination of the transverse response of the idealized suspended span of an offshore pipeline to random seismic input. The method is based on spatial discretization of the pipe with nodal lumped masses. The earthquake is assumed to be a stationary random process characterized by a power spectral density function. The cross spectral density function between two random seismic excitations along the pipe length is defined with the help of a local earthquake power special density function, which is assumed to be the same for the two end supports of the pipeline, and a frequency dependent weighted function which decays exponentially with distance from the pipe supports. The solution is obtained in the frequency domain using the spectral approach and is presented in terms of r.m.s. displacements and stresses. The formulation adequately includes the pressure drag effect which tends to dampen the pipe motions. Utilizing this method of analysis, several idealized pipe sea bed configurations, in which the pipe is anchored between two end blocks and subjected to horizontal ground excitations normal to the pipe axis, have been analysed to predict the influence of certain important parameters on the response. 相似文献
5.
Tarkeshwar Lal 《Pure and Applied Geophysics》1970,82(1):259-269
Summary The theory of resistivity sounding on a three layer earth comprising an inhomogeneous interstratum has been presented. The electrical conductivity in the intermediate layer, embedded between two layers of uniform conductivity, is assumed to follow either generalised power law or exponential variation. A point source of current is placed on the surface. The electric potential functions on the ground surface have been obtained. The expressions for apparent resistivity over the above models for the Wenner and Schlumberger electrode configurations have been derived. 相似文献
6.
瑞利波具有能量大、信噪比高等特点,可以用来反演介质内部的力学信息,近年来在浅层地球物理勘探、深层地震学研究以及超声波无损检测等多个领域都有较广泛的应用。目前大多数瑞利波的应用中都假设介质是弹性的,然而实际中岩石、土壤和金属等介质都在一定程度上体现出了黏弹性。当介质的黏弹性较强时仍然采用弹性假设研究其中瑞利波的反演将增大误差,因此有必要考虑黏弹性介质中的瑞利波反演,但是目前这方面的研究仍不够深入。本文研究黏弹性介质中瑞利波频散曲线和衰减系数曲线的反演问题,给出其在半空间中联合反演的方法,并对该方法的误差进行分析。 相似文献
7.
R. K. VERMA 《Geophysical Prospecting》1973,21(1):1-25
Computations have been made for the effect of ground slope in combination with transmitter coil misorientation on different electromagnetic depth sounding systems and sets of frequency sounding master curves are presented for different angles. The effect of a thin air layer due to the elevation of coils above ground surface has been studied for different systems. Also discussed are the effects due to an error in transmitter-receiver coil separation. 相似文献
8.
The role of mud erosion under waves in governing cohesive sediment transport in estuarial and coastal waters is well known. A laboratory study was conducted in order to elucidate the mechanism by which soft muds erode under progressive waves in a flume. Two types of cohesive sediment were used, a commercial kaolinite and an estuarial mud. Beds were formed by pouring in a pre-prepared sediment-water slurry and allowing the deposit to consolidate for a period ranging from 2 to 14 days. A multi-layered hydrodynamic model, which considers the mud to be viscoelastic, has been developed and used to evaluate the bed shear stress at the oscillating mud-water interface. The viscoelastic property of the mud has been confirmed by rheological measurements, and model results on velocity, pressure and wave attenuation verified against flume data. Concentration profiles indicate a distinct evolutionary pattern resulting in a highly stratified suspension. Just above the bed, a thin layer of fluid mud is generated. Above this layer, the suspension concentration is significantly lower. This two-layered feature of the concentration profile is related to the oscillatory response of the mud and water layers, and the associated momentum exchange and mass diffusion characteristics. An expression relating the rate of erosion to the bed shear stress in excess of bed shear resistance has been developed. Generation of fluid mud during erosion is a significant feature of the role of waves over mud. 相似文献
9.
T. LEE 《Geophysical Prospecting》1981,29(3):462-469
A direct interpretation scheme is developed which is capable of determining most of the geological features of a ground which can be assumed to be two dimensional in structure. This scheme extends the earlier work of Pekeris (1940) and Koefoed (1968) to the case where the basal layer of a ground is undulating. It also has a limited use for finding the parameters of a dipping dyke in the lower medium. Though the top and dip of the dyke can be determined, this is not true for the thickness. 相似文献
10.
Interceptor trenches are an effective ground water control method at waste management sites. Trenches may be installed without disturbing the wastes, and the withdrawal of ground water recovers contaminants that have left the waste management perimeter. The rapid and steep depression of the piezometric surface on both sides of the trench is positive proof of a barrier to horizontal flow across the trench in the affected permeable units.
Historically, the construction of interceptor trenches has been very difficult. A new and efficient installation method has been developed and successfully utilized for several applications at a petrochemical facility on the Texas coastal plain. Rapid and cost-effective installation is made possible by innovations in sump and trench construction and the tie-in between the two.
The sump is constructed first using standard well construction techniques to drill a 96-inch diameter hole to contain the 42-inch diameter polyethylene pipe sump. A European designed and fabricated trenching machine then excavates the trench, inserts the drainage pipe and backfills with sand and/or gravel in one operation. A specially designed perforated pipe entry door built into the side of the sump barrel provides for efficient and safe connection of the drainage pipe to the specially designed collection sump. The effectiveness of interceptor trenches has been confirmed in full scale applications through the reversal of flow gradients and the prevention of continued horizontal migration of ground water contaminants. 相似文献
Historically, the construction of interceptor trenches has been very difficult. A new and efficient installation method has been developed and successfully utilized for several applications at a petrochemical facility on the Texas coastal plain. Rapid and cost-effective installation is made possible by innovations in sump and trench construction and the tie-in between the two.
The sump is constructed first using standard well construction techniques to drill a 96-inch diameter hole to contain the 42-inch diameter polyethylene pipe sump. A European designed and fabricated trenching machine then excavates the trench, inserts the drainage pipe and backfills with sand and/or gravel in one operation. A specially designed perforated pipe entry door built into the side of the sump barrel provides for efficient and safe connection of the drainage pipe to the specially designed collection sump. The effectiveness of interceptor trenches has been confirmed in full scale applications through the reversal of flow gradients and the prevention of continued horizontal migration of ground water contaminants. 相似文献
11.
The resistance of a soil layer to steady horizontal vibration of an elastic pile is theoretically investigated. The pile is assumed to be vertical and of circular cross-section. The soil is modelled as a linear viscoelastic layer with hysteretic material damping. A closed form solution is obtained for the resistance of the soil layer to the motion. This resistance depends on shear modulus of soil, frequency, pile slenderness, material damping and Poisson's ratio. A parametric study of the effect of these parameters is included. The soil layer resistance is expressed in a form which can be used directly in the solution of the soil-pile interaction problem which is treated in a subsequent paper. The approach also applies for rigid deeply embedded footings. 相似文献
12.
沉陷区域埋地管线数值模拟分析 总被引：4，自引：0，他引：4
场地的不均匀沉陷是导致埋地管线破坏的重要原因之一。本文考虑了材料非线性、几何非线性以及管土接触非线性,将管线计算分析模型模拟为四节点薄壳单元结构,周围填覆土体采用八节点六面体单元划分。管土相互作用模拟为三维刚性与柔性的面面接触单元结构,并采用线性位移加载来模拟土体的沉陷作用,对三维薄壳有限元模型进行数值计算分析。通过比较不同参数,如沉陷长度、沉陷深度、埋深、管径、径厚比、土特性等对管线的反应影响,得出管线在沉陷情况下的应力和应变的关系,通过算例分析,说明了该方法能更好地模拟管线的破坏过程,该方法将为沉陷区域埋地管线数值模拟提供理论分析依据。 相似文献
13.
目前完全弹性介质中面波频散特征的研究已较为完善,多道面波分析技术(MASW)在近地表勘探领域也取得了较好的效果,但黏弹介质中面波的频散特征研究依然较少.本文基于解析函数零点求解技术,给出了完全弹性、常Q黏弹和Kelvin-Voigt黏弹层状介质中勒夫波频散特征方程的统一求解方法.对于每个待计算频率,首先根据传递矩阵理论得到勒夫波复频散函数及其偏导的解析递推式,然后在复相速度平面上利用矩形围道积分和牛顿恒等式将勒夫波频散特征复数方程的求根问题转化为等价的连带多项式求解问题,最后通过求解该连带多项式的零点得到多模式勒夫波频散曲线与衰减系数曲线.总结了地层速度随深度递增和夹低速层条件下勒夫波频散特征根在复相速度平面上的运动规律和差异.证明了频散曲线交叉现象在复相速度平面上表现为:随频率增加,某个模式特征根的移动轨迹跨越了另一个模式特征根所在的圆,并给出了这个圆的解析表达式.研究还表明,常Q黏弹地层中的基阶模式勒夫波衰减程度随频率近似线性增加,而Kelvin-Voigt黏弹地层中的基阶模式勒夫波衰减程度随频率近似指数增加,且所有模式总体衰减程度强于常Q黏弹地层中的情况. 相似文献
14.
Soil pipe collapses in a loess pasture of Goodwin Creek watershed,Mississippi: role of soil properties and past land use 
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下载免费PDF全文 Little is known about the association of soil pipe collapse features with soil properties or land use history. Three loess covered catchments in northern Mississippi, USA were characterized to investigate these relationships. Soil pipe collapses were characterized for their size, type feature and spatial location along with soil properties across the three catchments. Although mapped as the same soil, one of the catchments did not contain pipe collapse features while the other two had 29.4 and 15.4 pipe collapses per hectare. These loess soils contained fragipan layers that are suspected of perching water, thereby initiating the piping processes. Pipe collapses associated with subsurface flow paths were not always consistent with surface topography. The surface layer tended to be non‐erodible while layers below, even the upper fragipan layers, were susceptible to erosion by pipeflow. Soil properties of the lowest fragipan layer were highly variable but tended to prevent further downward erosion of soil pipes and thus formed a lower boundary for gullies. Middle to lower landscape positions in one of the piped catchments contained anthropic soils that were highly erodible. These anthropic soils were previously gullies that were filled‐in in the 1950s when forested areas, assumed to have been established when land was previously converted from crop to forest land, were converted to pasture. Three decades after this land use change from forest to pasture, pipe collapses became evident. In contrast, the adjacent catchment that does not exhibit pipe collapse features experienced severe sheet and rill erosion prior to the 1930s while in cotton production. The surface horizons above the lower fragipan layer were completely removed during this period, thus the top‐soil layer that tends to form a bridge above soil pipes in the more erodible subsoil layers was removed. This study showed that knowledge of soil characteristics or topography alone do not explain the distribution of soil pipe collapses as past land use can play a definitive role. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
15.
Using controlled liquefaction, a seismic isolation technique is introduced by which a large area with dozens of structures can be seismically isolated. The proposed Large Scale Seismic Isolation (LSSI) is in many ways similar to conventional base isolations. The required bearing is provided by a fully undrained pre-saturated liquefiable layer which has substantial vertical stiffness/capacity and minimal lateral stiffness. Moreover, required energy dissipation would be provided through material damping and Biot flow-induced damping within the liquefied layer. LSSI consists of a thick nonliquefiable crust layer and an underlying engineered pre-saturated liquefiable layer bounded by two impermeable thin clay layers. The liquefiable layer should be designed to trigger liquefaction as soon as possible within the early seconds of a design level seismic event. Adopting the energy-based GMP liquefaction theory, optimum gradation of the liquefiable layer is also investigated. It turned out that LSSI would effectively reduce acceleration response spectrum within short to medium periods. Contribution of the proposed LSSI is more pronounced in the case of stronger ground motions such as near field events as well as ground motions with longer return periods. 相似文献
16.
本文旨在构建适用于滞弹性近场时域波动有限元模拟的高精度人工边界条件：完美匹配层（Perfectly Matched Layer：PML）,其中阻尼介质时域本构基于广义标准线性体建立.与以往研究不同,本文采用复坐标延拓技术变换弱形式波动方程构建了可直接用有限元离散的弱形式时域PML,规避以往独立对无限域内波动方程及界面条件进行延拓可导致的PML场方程和界面条件匹配不合理引发数值失稳、计算精度低下等问题.其次,针对PML中多极点有理分式与频域函数乘积的傅里叶反变换难以计算的问题,利用PML精度对复坐标延拓函数中延拓参数微调不敏感这一特点,明确给出了参数微调准则以规避多重极点,进而利用有理分式分解给出了一种普适、简便的计算方法,极大地简化了PML计算.基于该方法可实现任意高阶PML.最后,将本文构建滞弹性PML与高阶勒让德谱元（高精度集中质量有限元）结合得到滞弹性近场波动谱元离散方案.基于算例验证了滞弹性PML的计算效率、精度及新离散方案的长持时稳定特性.新离散方案可应用于计入实际介质阻尼的地震波动正、反问题数值模拟,提高波形模拟的精度以及地下波速结构反演的精度和可靠性. 相似文献
17.
Simplified design methods for obtaining the maximum strain in pipelines crossing active faults proposed by Newmark, Kennedy and Wang have not considered the section deformation of the pipe. In this study, a new simplified method is developed for obtaining the maximum strain in steel pipes crossing faults considering non‐linearity of material and geometry of pipe section. It is assumed that the pipe will bend near the fault and the geometry of pipe in the longitudinal direction will change according to a bent deformation. On the other hand, the relation between maximum strain and bent angle has been obtained using a beam–shell hybrid FEM for different pipe‐fault conditions. The developed method can be used for calculating the maximum strains for fault‐crossing steel pipes with different angles of crossing both in tension and compression, by considering the deformation of the pipe cross‐section. Copyright © 2001 John Wiley Sons, Ltd. 相似文献
18.
Paul J. Sanders 《Ground Water Monitoring & Remediation》1984,4(1):39-42
A composite tape has been developed which can be the link to various sensing devices for measuring ground water parameters. The tape consists of a standard steel engineering tape with two conductors at the edges of the tape, similar to a TV antenna wire. The tape coating is clear Tefzel®, which has outstanding chemical and physical resistance. At the bottom end of the tape is a probe which can sense either water level by conductivity, a layer of organic liquid by an optical device, temperature by advanced semiconductor temperature transducers, pH, dissolved oxygen, absolute conductivity, or any other measurement that can be made with a small in situ probe.
The steel tape itself provides one of three conductors and, because of its thin, flat shape, provides an excellent ground plane for electronic noise reduction. A multiplexing circuit commonly used in the electronics industry is placed inside the probe tip housing and routinely allows up to 16 signals to be transmitted to the hub at ground level. Most probes can be powered with a common 9V rechargeable battery. Signals are given either by low power-consuming light-emitting diodes (LEDs) ∼ 5 milliamperes (mA), piezo-audible alarms ∼ 3mA, or liquid crystal displays ∼ l-2mA
This configuration allows for extremely accurate depth profiles of the desired parameters. 相似文献
The steel tape itself provides one of three conductors and, because of its thin, flat shape, provides an excellent ground plane for electronic noise reduction. A multiplexing circuit commonly used in the electronics industry is placed inside the probe tip housing and routinely allows up to 16 signals to be transmitted to the hub at ground level. Most probes can be powered with a common 9V rechargeable battery. Signals are given either by low power-consuming light-emitting diodes (LEDs) ∼ 5 milliamperes (mA), piezo-audible alarms ∼ 3mA, or liquid crystal displays ∼ l-2mA
This configuration allows for extremely accurate depth profiles of the desired parameters. 相似文献
19.
Interaction between soil and an elastic pile vibrating horizontally is theoretically examined. The soil is modelled as a linear, viscoelastic layer overlying rigid bedrock. The pile is assumed to be vertical and point bearing. This study utilizes the definition of soil resistance presented in a preceding paper.1 A direct solution is developed which yields closed form formulas for pile displacement, stiffness and damping. A parametric study clarifies the role of the parameters involved, illustrates the interaction between the soil and the pile and shows the stiffness and damping properties of the soil-pile system for typical values of the governing parameters. 相似文献
20.
The soil is assumed to be a horizontally layered viscoelastic medium over a rigid base. A semi-analytical method is used to calculate the Green functions for line loads in the frequency domain. The displacements in the soil are then obtained by spatial convolution and Fourier transforms from the frequency to the time domain. The influence of significant parameters is studied for a homogeneous layer. Maximum response is obtained when the air pressure wave velocity equals the Rayleigh wave velocity in the soil. The response spectra computed for an actual soil profile, which is subjected to an air pressure wave from a deflagration-type explosion, show predominant response at frequencies, which are significantly higher than those of earthquake motion. 相似文献