3DFD Simulation of Asymmetric Wave Field by Side-wall Acoustic Tool in Open and Cased Wells

1. Introduction Side-wall acoustic logging tools, such as the Segmented Bond Tool (SBT) from Baker Atlas and the tools for open hole measurements, utilize acoustic transducers mounted on six pads to make compensated acoustic velocity and attenuation measurements which are not affected by mud weight, gas cut, fast formation effects, casing surface conditions or reasonable tool de- centralizing. Studies on the wave fields generated by these tools are very important to tool design and data int…     

全波场地震波数值模拟中的边界处理实践研究

在用有限差分法或有限元法模拟无界区域中的波动时,需要对计算区域的边界做特殊处理,以消除由于把地震波的传播设定在有限区域而产生的边界反射。为了这一目的,人们研究出了多种人工边界处理方法,完全匹配层（PML）吸收边界条件就是理想的方法之一,现已被广泛应用。本文将PML吸收边界条件应用于全波场地震波的数值模拟,数值计算实验表明,对qP波,匹配层的厚度为5个网格间距即可达到要求,而对qSV波与qSH波,为达到理想的吸收效果,匹配层的厚度应当增大,当厚度为13个网格间距时达到了理想的吸收效果。     

基于RFID物联网的应用研究

物联网是在计算机互联网的基础上,利用射频自动识别(RFID)技术,通过互联网实现物品的自动识别和信息的互联与共享。在简述RFID电子标签和物联网的基本原理基础上,通过在零售业中的应用实例讨论物联网的系统构架、关键技术及其应用。最后提出云计算、并行计算和数据挖掘等技术在物联网中的应用想法。     

弹性介质瑞雷面波交错网格有限差分法数值模拟

为了研究瑞雷面波在复杂地质条件下的传播规律和波场特征,采用交错网格高阶有限差分方法对浅层各向同性弹性介质进行了包括瑞雷面波和体波在内的全波场模拟.通过均匀半空间模型和层状介质模型的模拟,验证了含有瑞雷面波的全波场理论的正确性.     

一种带权限管理的EPC IS设计方案

EPC IS在物联网中处于核心地位,它担负着对大量EPC数据和PML文件的处理解析任务.在传统的EPCIS的基础上,结合可扩展的访问控制高标识语言(XACML),提出了一种带权限管理的EPC IS设计方案,以解决企业之间互相访问EPC IS所带来的一系列安全问题.首先介绍了传统的EPC IS的架构和作用以及所带来的安全隐患,然后引入了XACML,重点分析如何实现权限管理,最后针对跨企业的供应链管理系统给出一个带权限管理的EPC IS设计方案.     

交替方向隐式时域有限差分法中的Berenger理想匹配层

提出一种新方案．用于离散Berenger场分裂形式Maxwell方程．将理想匹配层吸收边界条件由通常的时域有限差分法推广到交替方向隐式时域有限差分法．和已有的离散方案比较，采用文中提出的离散方案可使理想匹配层吸收边界的反射误差成数量级地减小．     

Perfectly matched layers for transient elastodynamics of unbounded domains

One approach to the numerical solution of a wave equation on an unbounded domain uses a bounded domain surrounded by an absorbing boundary or layer that absorbs waves propagating outward from the bounded domain. A perfectly matched layer (PML) is an unphysical absorbing layer model for linear wave equations that absorbs, almost perfectly, outgoing waves of all non‐tangential angles‐of‐incidence and of all non‐zero frequencies. In a recent work [Computer Methods in Applied Mechanics and Engineering 2003; 192: 1337–1375], the authors presented, inter alia, time‐harmonic governing equations of PMLs for anti‐plane and for plane‐strain motion of (visco‐) elastic media. This paper presents (a) corresponding time‐domain, displacement‐based governing equations of these PMLs and (b) displacement‐based finite element implementations of these equations, suitable for direct transient analysis. The finite element implementation of the anti‐plane PML is found to be symmetric, whereas that of the plane‐strain PML is not. Numerical results are presented for the anti‐plane motion of a semi‐infinite layer on a rigid base, and for the classical soil–structure interaction problems of a rigid strip‐footing on (i) a half‐plane, (ii) a layer on a half‐plane, and (iii) a layer on a rigid base. These results demonstrate the high accuracy achievable by PML models even with small bounded domains. Copyright © 2004 John Wiley & Sons, Ltd.     

Numerical simulation of bistatic scattering from a target at low altitude above rough sea surface under an EM wave incidence at low grazing angle by using the finite element method

Astudyofscatteringfromavolumetrictargetaboverandomroughsurfaceisofgreatsignificanceintargetdetectioninterrainandoceanicclutters.Mostofanalyticalapproachestoroughsurfacescatteringarebasedonsomeapproximations,suchastheKirchhofftangentplaneapproximation,smallperturbationapproximation,two-scalemodelandothers[1].Analyticalstudyofscatteringfromanobjectabovethesurfacehasbeenlimitedtothemodelofasphereoracylinderaboveaplanarconductingsurface[2,3].Numericalmodelforsimulationofscatteringfromcomplextarget…     

Time‐domain hybrid formulations for wave simulations in three‐dimensional PML‐truncated heterogeneous media

We are concerned with the numerical simulation of wave motion in arbitrarily heterogeneous, elastic, perfectly‐matched‐layer‐(PML)‐truncated media. We extend in three dimensions a recently developed two‐dimensional formulation, by treating the PML via an unsplit‐field, but mixed‐field, displacement‐stress formulation, which is then coupled to a standard displacement‐only formulation for the interior domain, thus leading to a computationally cost‐efficient hybrid scheme. The hybrid treatment leads to, at most, third‐order in time semi‐discrete forms. The formulation is flexible enough to accommodate the standard PML, as well as the multi‐axial PML. We discuss several time‐marching schemes, which can be used à la carte, depending on the application: (a) an extended Newmark scheme for third‐order in time, either unsymmetric or fully symmetric semi‐discrete forms; (b) a standard implicit Newmark for the second‐order, unsymmetric semi‐discrete forms; and (c) an explicit Runge–Kutta scheme for a first‐order in time unsymmetric system. The latter is well‐suited for large‐scale problems on parallel architectures, while the second‐order treatment is particularly attractive for ready incorporation in existing codes written originally for finite domains. We compare the schemes and report numerical results demonstrating stability and efficacy of the proposed formulations. Copyright © 2014 John Wiley & Sons, Ltd.     

PML吸收边界条件在波导不连续性问题中的应用

采用矢量有限元方法结合PML吸收边界条件分析波导不连续性问题。利用PML吸收边界条件截断计算区域,可以减少内存消耗;采用模式正交性计算波导结构的S参数,可以获得更加精确的解。在结果验证阶段,分别对PML参数设置、厚度选择、波导介质不连续性以及波导结构不连续性模型进行分析,将计算结果与文献对比,验证了PML吸收边界条件的有限元法分析波导不连续性问题的准确性。