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221.
The model studied in this paper presents an extension of previous work for a shear wall on a semi-circular rigid foundation in an isotropic homogeneous and elastic half-space. The objective is to develop a soil-structure interaction model that can later be applied to the case of a flexible foundation. As shown in the Introduction below, Luco considered the case of a rigid foundation subjected to vertical incident plane SH waves, and Trifunac extended the solution for the same rigid foundation subjected to SH waves but for arbitrary angles of the incidence. In this paper, a new approach and model are presented for the same semi-circular rigid foundation with a tapered-shape (instead of rectangular) superstructure. The analytical expression for the deformation of the semi-circular rigid foundation below this tapered shear wall with soil-structure interaction in an isotropic homogeneous and elastic half-space is thus derived. Results are then compared with those of Trifunac discussed in the section below. This problem formulation can and will later be extended in the case of a flexible foundation that is semi-circular or arbitrarily shaped. 相似文献
222.
S.C. Mohapatra 《地球物理与天体物理流体动力学》2014,108(6):615-638
Expansion formulae associated with the interaction of oblique surface gravity waves with a floating flexible plate in the presence of a submerged horizontal flexible structure are derived using Green’s integral theorem in water of finite and infinite water depths. The associated Green’s functions are derived using the fundamental solution associated with the reduced wave equation. The integral forms of the Green’s functions and the velocity potentials are advantageous over the eigenfunction expansion method in situation when the roots of the dispersion relation coalesce. As an application of the expansion formulae, diffraction of oblique waves by a finite floating elastic plate in the presence of a submerged horizontal flexible membrane is investigated in water of finite depth. The accuracy of the numerical computation is demonstrated by analysing the convergence of the complex amplitude of the reflected waves and the energy relation. Effect of the submerged membrane on the diffraction of surface waves is studied by analysing the reflection and transmission coefficients for various parametric values. Further, the derivation of long wave equation under shallow water approximation is derived in a direct manner in the appendix. The concept and methodology can be easily extended to deal with acoustic wave interaction with flexible structures and related problems of mathematical physics and engineering. 相似文献
223.
The intermittent structure of turbulence within the canopy sublayer (CSL) is sensitive to the presence of foliage and to the
atmospheric stability regime. How much of this intermittency originates from amplitude variability or clustering properties
remains a vexing research problem for CSL flows. Using a five-level set of measurements collected within a dense hardwood
canopy, the clustering properties of CSL turbulence and their dependence on atmospheric stability are explored using the telegraphic
approximation (TA). The binary structure of the TA removes any amplitude variability from turbulent excursions but retains
their zero-crossing behaviour, and thereby isolating the role of clustering in intermittency. A relationship between the spectral
exponents of the actual and the TA series is derived across a wide range of atmospheric stability regimes and for several
flow variables. This relationship is shown to be consistent with a relationship derived for long-memory and monofractal processes
such as fractional Brownian motion (fBm). Moreover, it is demonstrated that for the longitudinal and vertical velocity components,
the vegetation does not appreciably alter fine-scale clustering but atmospheric stability does. Stable atmospheric stability
conditions is characterized by more fine scale clustering when compared to other atmospheric stability regimes. For scalars,
fine-scale clustering above the canopy is similar to its velocity counterpart but is significantly increased inside the canopy,
especially under stable stratification. Using simplified scaling analysis, it is demonstrated that clustering is much more
connected to space than to time within the CSL. When comparing intermittency for flow variables and their TA series, it is
shown that for velocity, amplitude variations modulate intermittency for all stability regimes. However, amplitude variations
play only a minor role in scalar intermittency. Within the crown region of the canopy, a ‘double regime’ emerges in the inter-pulse
duration probability distributions not observed in classical turbulence studies away from boundaries. The double regime is
characterized by a power-law distribution for shorter inter-pulse periods and a log-normal distribution for large inter-pulse
periods. The co-existence of these two regimes is shown to be consistent with near-field/far-field scaling arguments. In the
near-field, short inter-pulse periods are controlled by the source strength, while in the far-field long inter-pulse periods
are less affected by the precise source strength details and more affected by the transport properties of the background turbulence. 相似文献
224.
When the magnitude of sub-scale ographic forcing is comparable with explicitly ordinary dynamic forcing, the drag effect reduced by ographic gravity wave is to be significant for maintaining dynamic balance of atmospheric circulation, as well as the momentum and energy transport. Such sub-scale ographic forcing should be introduced into numerically atmospheric model by means of drag being parameterized. Furthermore, the currently mature ographic gravity wave drag (OGWD) parameterization, i.e., the so-called first-generation (based on lineal single-wave theoretical framework) or the second-generation drag parameterization (including an important extra forcing by the contribution of critical level absorption), cannot correctly and effectly describe the vertical profile of wave stress under the influence of ambient wind shearing. Based on aforementioned consideration, a new two-wave scheme was proposed to parameterize the ographic gravity wave drag by means of freely propagating gravity waves. It starts with a second order WKB approximation, and treats the wave stress attenuations caused by either the selective critical level absorption or the classical critical level absorption explicitly; while in the regions where critical levels are absent, it transports the wave stress vertically by two sinusoidal waves and deposits them and then damps them according to the wave saturation criteria. This scheme is thus used to conduct some sample computations over the Dabie Mountain region of East China, as an example. The results showed that the new two-wave scheme is able to model the vertical distribution of the wave stress more realistically. 相似文献
225.
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227.
深部储层地震资料通常照明度低、信噪比低、分辨率不足,尤其是缺乏大角度入射信息,对深部储层流体识别存在较大影响.Gassmann流体项是储层流体识别的重要参数,针对深层地震资料的特点,本文首先在孔隙介质理论的指导下,推导了基于Gassmann流体项与剪切模量的两项AVO近似方程.通过模型分析,验证了该方程在小角度时与精确Zoeppritz方程误差很小,满足小角度入射条件下的近似精度要求.然后借助Connolly推导弹性阻抗的思想,推导了基于Gassmann流体项与剪切模量的两项弹性阻抗方程.针对深部储层地震资料信噪比差的特点,利用奇偶反射系数分解实现了深部储层基追踪弹性阻抗反演方法,最后提出了基于基追踪弹性阻抗反演的Gassmann流体项与剪切模量的求取方法,并将提取的Gassmann流体项应用于深部储层流体识别.模型测试和实际应用表明该方法稳定有效,具有较好的实用性. 相似文献
228.
229.
应用于大规模三维数据反演的拟线性近似方法的计算精度和应用范围至今仍是一个比较模糊的概念。本文首先实现了基于拟线性近似方法(对角拟线性近似、标量拟线性近似、拟解析近似和局部拟线性近似)的三维电磁场数值模拟,然后通过正演计算,对这些方法的计算精度进行了系统的对比研究。理论研究结果表明:对角拟线性近似方法精度最高,适用范围最广,对电性变化在3~4个数量级内的地电模型都能给出精确的计算结果;拟解析近似方法计算精度只低于对角拟线性近似方法,它适用于异常电导率与背景电导率比值为2~3个数量级的地电模型;标量拟线性近似方法和局部拟线性近似方法的精度较低,只适用于异常电导率与背景电导率比值小于2个数量级的情况。 相似文献
230.
实验研究了韵律层结构和超声波探测频率对弹性波波速和波形的影响。实验中所使用的超声波频率为 2 4 0kHz ,韵律层由不同厚度的钢板和有机玻璃板构成。研究表明 ,当λi/di<4 (i=1 ,2 ) (λi 为超声波在介质i中传播时的波长 ,di 为韵律层中介质i的厚度 )时 ,韵律层的波速近似等于 2种介质的时间平均速度 ;当λi/di>5 (i=1 ,2 )时 ,其速度开始显著地降低 ,并趋向于有效介质波速的Reuss下限 (VRp)。韵律层的结构对于透射波的波形有显著的影响。特别是当λi/di 接近于 6时 ,透射波波形非常简单 ,并且其透射波的振幅显著地降低。因此波形简单并不一定对应着简单的介质结构。由于弹性波在韵律层中的传播速度以及波形与探测频率有关 ,因此在利用地震测深结果分析岩石圈结构 ,推断其物质组成时应该充分考虑地震测深频率和地壳结构对分析结果的影响 相似文献