无限域地基有限元分析的简化粘弹性边界

本文提出一种能用于无限域地基动、静力有限元分析的简单人工边界——粘弹边界，采用一层边界单元来实现。该边界弹簧部分采用弹性半空间Mindlin解计算，边界单元采用具有粘性阻尼的粘弹材料，通过确定合理的弹性模量、泊松比和粘性阻尼系数，不仅可以使边界单元能够模拟无限域远场的弹性恢复力，同时可以模拟粘性边界。通过算例分析，验证了该边界的有效性，它可用于土-结构动力相互作用分析。     

考虑土骨架非线性的饱和土-结构相互作用分析

强地震作用下,饱和土体将进入非线性,有必要考虑非线性饱和土的地震响应以及非线性饱和土-结构相互作用问题。本文采用Biot饱和多孔介质模型,基于不规则加卸载准则的修正Davidenkov模型来描述近场区域内饱和土骨架的非线性特性,并采用集中质量显式有限元方法进行分析;远场区介质假定为线弹性饱和多孔介质,通过多次透射人工边界进行模拟;结构采用Newmark隐式时步积分方法进行分析。通过自编程序实现了非线性饱和土体的地震反应分析以及非线性饱和土-基础-结构相互作用分析。通过算例,对比分析了土体非线性对饱和土体、基础和结构反应的影响。     

波动数值模拟中透射边界的稳定实现

从波动能量在计算区内累积增大的观点出发,通过简单的一维弹性波模型,系统地阐明了在近场波动数值模拟中透射边界两类数值失稳--"高频振荡"和"零频飘移"的机理:前者源于对波动数值模拟无意义的高频波动在人工边界上的放大和波在有限计算区内多次反射产生的反复放大;后者则源于透射边界允许零频和接近零频的分量不断进入计算区. 由此提出了稳定实现透射边界的完整方案包括两项简单措施:第一,在全部计算区内按文中建议的方法注入小阻尼,以消除高频振荡;第二, 给出一种具有明确物理意义的消除零频飘移的算子算法. 最后,提供了三维波源问题和散射问题的详细数值试验结果.     

求解结构-无限地基动力相互作用的高阶透射边界频域方法

基于比例边界有限元法(scaled boundary finite element method,SBFEM)对结构-无限地基系统进行了频域的动力相互作用分析。通过一种新的高阶透射边界对无限地基进行模拟,该透射边界是基于无限域动力刚度矩阵的连分式解形式,连分式的系数通过以动力刚度矩阵表示的比例边界有限元方程递推计算。通过数值算例验证了该高阶透射边界的收敛性,并与解析解进行了比较,表明该方法具有较高的精度。最后对重力坝-库水-无限地基系统进行了频域分析,将计算结果与无质量地基模型进行了对比。对比结果表明,所提地基模型计算的结果与无质量地基模型的计算结果相比降低约20%。该方法可以有效地进行二维和三维大型结构-地基相互作用分析。     

地震波动数值模拟及稳定性研究

本文针对显式有限元-有限差分法进行了系统的研究,包括理论分析、算法改进以及实际应用.通过理论推导定量地研究了采用这种数值模拟方法对波动传播规律的影响,以及其在结合局部透射人工边界进行计算时的稳定条件.就采用该方法结合局部透射人工边界求解波源问题和散射问题的情况分别提出了改进计算的措施,并通过数值试验验证其有效性.     

三维土-结构动力相互作用的一种时域直接分析方法

本文提出了一种分析三维土-结构动力相互作用的时域直接方法。该方法采用集中质量显式有限元和透射人工边界模拟无限域地基,通过编制的FORTRAN程序实现;采用ANSYS软件对上部结构进行建模分析,并通过FORTRAN程序对ANSYS软件的调用,实现了土与结构系统在地震作用下的整体分析。该方法为显隐式相结合的方法,地基和上部结构可采用不同的时间步距进行分析,可大大提高效率。通过两算例,验证了该方法的可行性。     

较复杂介质波场计算中的一种透射边界

传统的人工边界是在声波或弹性波分解为内行和外行分量的基础上设计的.对于较复杂的介质模型（如粘弹介质、弹塑介质、塑性介质模型等）,地震波不能简单地分解为各自满足其运动方程的纵波、横波等成分,且地震波在传播过程中还有衰减现象,因此传统的人工边界已不能有效地用于非弹性的较复杂介质的波场模拟.本文提出了一种适合于更一般的地震模型的波场计算的透射边界条件,并以粘弹介质的一个较简单的二维几何模型为例,通过有限元数值求解这种透射边界和刚性边界下粘弹波的激发和传播,得到地面合成地震记录,证明了这种透射边界用于较复杂介质波场计算是可行的.     

ABAQUS模拟土-结构相互作用时人工边界的选取

利用有限元数值模拟方法研究半无限空间中的动力响应问题时,人工边界的选取对于计算结果的可靠性与准确性有直接的影响。本文利用ABAQUS有限元软件计算土-结构地震响应,分析了选用不同人工边界对计算结果的影响。通过与远置边界自由场和土-结构模型的数值结果对比,讨论了底边界分别采用固定边界和黏性边界;侧边界分别采用固定边界、绑定边界、竖向约束边界和黏性边界时的计算误差。研究表明,利用ABAQUS软件计算土-结构动力相互作用影响时,黏性边界适合作为非刚性地基问题的底边界,固定边界适合作为刚性地基问题底边界。对于侧向边界当采用相对计算宽度较小模型时,固定边界和黏性边界无法再现自由场和土-结构响应;绑定边界和竖向约束边界可以模拟精确的自由场响应,并在动力土-结构作用分析中具有良好的性能。     

场地地震波动模拟中透射边界稳定性问题研究

本文对场地地震波动模拟中透射边界的稳定性问题进行了一系列研究。对已有的透射边界稳定措施做了比较分析,并给出了不同措施的适用性。结合粘弹性边界的物理模型提出了一个新的消除透射边界飘移失稳的措施,参考高频滤波的思路探讨了一种新的消除透射边界葛频振荡失稳的措施,并用数值试验验证了这两种新的透射边界稳定方法的有效性。将显式行限元一有限差分方法结合透射边界的数值解法的计算结果与解析结果作对比分析,验证这弹一套数值解法的计算精度。利用二维模型模拟了自贡土层和山脊地形的场地效应,利用显戈有限元一有限差分方法结合透射边界这套数值解法进行数值模拟计算,应用汶川地震的实示强震观测记录来验证这套数值解法对于实际地震波动模拟的有效性。     

流体饱和多孔介质黏弹性动力人工边界

基于Biot流体饱和多孔介质本构方程，采用平面波和远场散射波经验叠加来反映外行波传播，以经验参数反映人工边界外行波动的衰减和多角度透射特性。在人工边界处分别施加反映固相和液相介质传播效应的弹簧及阻尼来模拟人工边界以外的无限域介质对来自有限域的外行波的能量的吸收作用。从而形成一种流体饱和多孔介质的黏弹性动力人工边界。数值算例表明：边界的精度和稳定性高于现有的黏性边界、黏弹性人工边界及一阶透射边界。     

采用多种有限元子结构的混合试验系统

采用子结构混合实验方法进行复杂结构的地震响应模拟。在混合实验中,根据结构的特征划分为多个子结构,每个子结构被封装起来,只有边界上的力和位移作为子结构间相互作用的变量,利用拟牛顿法保持整体结构的平衡和协调。目标结构为SRC框架剪力墙结构体系,结构顶部设置11层高的钢塔。在混合实验中,该结构被分为3个子结构,SRC部分为第一个子结构,采用OpenSees进行模拟;钢塔的第1层比较薄弱,是变形集中区域,采用实验进行模拟;钢塔其余部分采用ABAQUS有限元程序进行模拟。实验得到准确的地震响应,表明本文提出的混合实验方法可有效地结合多个有限元程序,充分利用各个有限元程序的优点进行复杂结构的地震响应模拟。     

A new analytical solution solved by triple series equations method for constant-head tests in confined aquifers

The constant-head pumping tests are usually employed to determine the aquifer parameters and they can be performed in fully or partially penetrating wells. Generally, the Dirichlet condition is prescribed along the well screen and the Neumann type no-flow condition is specified over the unscreened part of the test well. The mathematical model describing the aquifer response to a constant-head test performed in a fully penetrating well can be easily solved by the conventional integral transform technique under the uniform Dirichlet-type condition along the rim of wellbore. However, the boundary condition for a test well with partial penetration should be considered as a mixed-type condition. This mixed boundary value problem in a confined aquifer system of infinite radial extent and finite vertical extent is solved by the Laplace and finite Fourier transforms in conjunction with the triple series equations method. This approach provides analytical results for the drawdown in a partially penetrating well for arbitrary location of the well screen in a finite thickness aquifer. The semi-analytical solutions are particularly useful for the practical applications from the computational point of view.     

基于统计检验法研究Amurian板块相对独立性

Amurian 板块是Zonenshain等提出的提出的东北亚地区内部一个构造亚板块.Amurian板块自提出以来就一直受到地学界的广泛重视.它到底是欧亚大陆的一部分,还是独立于欧亚大陆之外的一个独立次级构造块体?这个问题一直是是东亚,乃至欧亚大陆构造动力学研究的核心问题之一.许多学者从地质和地球物理学两个角度研究了Amurian板块存在的可能性.但是复杂的构造特征和稀少且弥散的地震分布使得Amurian问题充满了争议.全球卫星定位系统(GPS)技术的不断进步使得在短时间获得高精度、大范围、准实时的地壳运动观测数据,并确定地壳运动速度场成为可能.本文利用东北亚地区最新GPS资料,从大地测量学角度对东北亚地区的地壳运动特征进行分析,基于统计检验方法重点研究Amurian板块相对欧亚大陆的独立性及其边界等问题.     

General well function for soil vapor extraction

This paper develops a well function applicable to extraction of groundwater or soil vapor from a well under the most common field test conditions. The general well function (Perina and Lee, 2006) [12] is adapted to soil vapor extraction and constant head boundary at the top. For groundwater flow, the general well function now applies to an extraction well of finite diameter with uniform drawdown along the screen, finite-thickness skin, and partially penetrating an unconfined, confined, and leaky aquifer, or an aquifer underneath a reservoir. With a change of arguments, the model applies to soil vapor extraction from a vadose zone with no cover or with leaky cover at the ground surface. The extraction well can operate in specified drawdown (pressure for soil vapor) or specified flowrate mode. Frictional well loss is computed as flow-only dependent component of the drawdown inside the extraction well. In general case, the calculated flow distribution is not proportional to screen length for a multiscreen well.     

上海软土地震响应的振动台模型试验及其三维数值拟合分析

对上海典型软土地铁车站结构振动台模型中的自由场振动台模型试验建立了三维计算模型,包括计算范围的确定,材料本构模型的选取,动力边界条件的选用以及地震波的输入等4个方面.用该模型对自由场振动台模型试验进行了三维的拟合分析,并将计算结果与实测结果以及二维拟合分析结果进行了比较分析,表明三者吻合较好.说明该计算模型可用来模拟模型土的动力特性,可为建立上海软土三维地震响应的计算方法提供基础.     

Transitional, entraining, cloudy, and coastal boundary layers

Atmospheric boundary layers are marvelously varied and complex. Recent research has examined some of that variety. Boundary layers over land undergo drastic changes throughout the day as the sun rises and sets, and as clouds form and dissipate. Air is entrained at the top of the boundary layer at varying rates. As air moves over the coast, the boundary layer reacts to changes in surface forcing. All of these changes affect pollutant transport and weather formation. In this paper, research attempting to understand transitional, cloud-topped, and coastal boundary layers, and boundary-layer top entrainment, is reviewed.     

Transient analysis of concrete gravity dam-reservoir systems by Wavenumber-TD approach

The Wavenumber approach was initially introduced as an ideal substitute for the rigorous type of analysis which had been the basis of extensive studies in seismic analysis of concrete gravity dams. The former technique is formulated in the context of pure finite element programming, while the latter relies heavily on a two-dimensional semi-infinite fluid element (i.e., hyper-element). Recently, a variation of Wavenumber method was proposed which was referred to as Wavenumber-TD approach. The approximation to the original technique improves its realm of application and allows it to be carried out in time domain as well as frequency domain. In that study, the formulation was examined for harmonic type of excitation which proved to be promising. Herein, this will be evaluated for its real intended application, which is transient analysis of dam-reservoir systems. For this aim, the prepared special purpose finite element program is modified and the analysis of Pine Flat dam is considered as a typical example. Several models are considered with different values of normalized reservoir length. In each case, the reservoir truncation surface is treated by Wavenumber-TD and the extensively utilized Sommerfeld conditions. The dynamic loading considered is the S69E component of Taft earthquake record. Furthermore, two types of reservoir bottom condition of full reflective as well as absorptive, are adopted. Overall, this will allow for a thorough examination and evaluation of Wavenumber-TD approach in regard to its effectiveness.     

Influence of boundary conditions on the out‐of‐plane response of brick masonry walls in buildings with RC slabs

In modern unreinforced masonry buildings with stiff RC slabs, walls of the top floor are most susceptible to out‐of‐plane failure. The out‐of‐plane response depends not only on the acceleration demand and wall geometry but also on the static and kinematic boundary conditions of the walls. This paper discusses the influence of these boundary conditions on the out‐of‐plane response through evaluation of shake table test results and numerical modelling. As a novum, it shows that the in‐plane response of flanking elements, which are orthogonal to the wall whose out‐of‐plane response is studied, has a significant influence on the vertical restraint at the top of the walls. The most critical configuration exists if the flanking elements are unreinforced masonry walls that rock. In this case, the floor slabs can uplift, and the out‐of‐plane load‐bearing walls loose the vertical restraint at the top. Numerical modelling confirms this experimentally observed behaviour and shows that slab uplift and the difference in base and top excitation have a strong influence on the out‐of‐plane response of the walls analysed. Copyright © 2016 John Wiley & Sons, Ltd.     

一种改善区域地磁场模型边界效应的方法

针对目前建立区域地磁场模型截断阶数受限,地磁图精度偏低等缺陷,研究了运用Taylor多项式拟合法建立区域地磁场模型所存在的边界效应问题.从理论上深入分析了产生边界效应误差的根源,提出了采用边界插值约束的Taylor多项式拟合法,在改善区域地磁模型边界效应的同时,提高了模型拟合的截断阶数,进而绘制出较高精度的区域地磁场图,同时对该技术和现有补充国际地磁参考场值方法进行了比较分析,最后进行了仿真试验.试验证明,该技术具有优于补充国际地磁参考值的方法,能克服现有区域地磁场模型的边界效应问题,提高了区域地磁场模型的拟合精度.