地震波反演与土-结构动力相互作用分析

基岩地震动的确定是土-结构动力相互作用分析的关键步骤之一.本文基于一维剪切波动理论,利用MATLAB编制了自由场地表波向基岩波反演的计算程序,进行了数值验证,并对汶川地震同济大学实测地震波进行了反演计算,分析了反演基岩地震波与地表波的差异.在此基础上,采用ANSYS软件建立土-结构相互作用体系分析模型,以土层深处的反演地震波作为输入,对土-结构相互作用体系进行了地震反应分析,探讨了在El Centro波及汶川地震同济大学实测波二种不同反演波输入下,桩基承台及上部结构地震反应的差异,得到了有工程参考价值的结果.     

一种土的非线性弹性本构模型参数的反演方法

旨在提出一种土的非线性弹性本构模型参数反演的方法。以现今普遍实行的地基载荷试验为基础,依据遗传算法的组合优化理论,采用正演计算和遗传算法优化相结合的方式,建立了土层非线性弹性本构模型参数反演的方法;并依据某黄土场地地基载荷试验数据,实施了黄土土层非线性弹性本构模型参数反演的全过程。计算结果表明,所建立的方法可以实现土层非线性弹性本构模型中相互关联的多个参数的组合优化,并在对初始值要求较低的情况下,可以获得良好的参数反演精度。从而为土的变形特性分析和土与其中及相邻结构的共同作用分析,提供了较好的土体本构模型参数的确定方法。     

非数字式反演数据的量化单调消噪方法

力学反问题的数据处理有益于提高反演结果的准确度．针对两类反演数据之一的非数字式反演数据，提出了量化单调消噪方法及其多尺度分析，建立了两个由数据处理提升反演准确度的评价准则．末给出了一个数值试验，分别对测量数据和正演加噪数据进行优化处理，获得了准确度提高的反演参数．     

用同伦方法反演非饱和土中溶质迁移参数

非饱和土中溶质迁移参数反演问题可以归结为非线性算子方程的求解问题. 将同伦方法 引入该问题的求解，通过构造线性同伦将原问题转化为求解同伦函数最小值的无约束优化问 题. 同时在分析了同伦参数正则化效应的基础上，提出一种两段同伦参数修正方法. 即在求 解的初始阶段，根据拟Sigmoid函数调整同伦参数，以追踪同伦路径，保证计算稳定地进行； 在迭代的后期，采用与残差相关的同伦参数修正方法，以抵抗观测噪声对求解的影响. 数值 算例为求解带有平衡及非平衡吸附效应的一维非饱和土中溶质迁移模型参数反演问题，计算 结果表明了该方法的大范围收敛性及较强的抵抗观测噪声的能力.     

基于五次样条函数的基坑土层等效参数反演方法

根据五次样条函数的性质,利用弹性支点法,将土压力视为不连续的分布载荷集度,对支护结构的变形进行五次样条函数拟合,并通过逐次求导反演支护结构上的受力,最后结合工程情况反演基坑土层的等效参数。本文基于上述研究思路,成功反演了支护结构的分布载荷集度,提出了一种基于五次样条函数的基坑土层等效参数反演方法,反演的土层等效参数可用于基坑工程的动态化设计、施工方案优化和变形预测,并为邻近类似土层区域的基坑设计提供土层抗剪强度指标参考。     

海洋平台水动力系数识别及精度分析

论文利用新动态模型减缩方法对海洋平台结构进行自由度减缩,利用简化后的模型对水动力系数进行反演,改善了反演模型中解的不确定性,并对载荷反演中的病态问题进行了探讨,同时给出了反演结果的评估方法,为反演中测量数据的获取提供了依据,提高了反演结果的可靠性.     

基于无迹卡尔曼滤波的高层建筑风荷载反演

基于无迹卡尔曼滤波提出了一种高层建筑风荷载的反演算法，该方法利用有限测量楼层的风致响应数据，实时识别结构的未知风荷载和风致响应。通过典型高层建筑的风洞试验进行风荷载反演实例分析，验证了该方法的准确性和适用性，评估了模态参数误差、测量噪声水平对风荷载反演的影响。研究结果表明，文中提出的算法对模态参数误差不敏感，在一定噪声水平下反演的结果基本能够满足实际工程需要，该算法为实时评估高层建筑的风荷载和风致响应提供了有效的工具。     

弹性动力学反问题的非线性及其迭代反演

分析了弹性动力学反问题的非线性及在迭代反演过程中表现出的复杂非线性现象。迭代反演的结果依赖于反演系统参数和迭代初值,而系统参数对应的Mandelbrot集和迭代初值对应的Julia集都是复杂的分形集。随反演系统状态参数的变化,完全确定性的反演系统却可能产生一系列无规则的,不可预测的迭代输出序列。反演迭代过程中出现的分形和混沌现象反映了表面简单的反演迭代后隐藏的复杂性,正是这种复杂性给迭代系统参数的合理选择带来困难,进而使反演迭代不总能给出满意的结果。     

岩石力学位移反演分析回顾及进展

回顾综述了岩石力学反演分析的研究进展，重点介绍了位移反分析法的分类、结果评价及研究特点，讨论了需进一步探讨的问题．     

共和干热岩地热井GR2井区三维地应力场反演分析

GR2 地热井位于共和恰卜恰镇，干热岩地热井井深达到4000 米，大深度井区极大增加了反演的难度．井区附近20 千米内无大型构造，附近地应力场的主要影响因素为板块构造应力和自重应力．由于井中未进行三维地应力场测井工作，所以我们以地面地应力调查结果和震源机制解反演结果为依据，基于MIDAS GTS 和大比例尺高清卫星云图建立有限元数值模型，使用改进的边界法进行反演计算，最终预估了井中地应力场分布特征．对于后续的井网布置以及干热岩井场开采具有重要意义．     

Cotransport of Suspended Colloids and Nanoparticles in Porous Media

The objective of this study is to develop a model for cotransport of colloids and nanoparticles (NPs) in porous media under two particle capture mechanisms. The particle capture rate is proportional to the capture probability, which is a function of retained concentration, called the filtration function. Laboratory bench-scale experiments of individual transport of NPs and colloidal-size kaolinite clay particles through packed columns produced breakthrough curves (BTCs) that monotonically increased with time and stabilised at some value lower than the injected concentration. We discuss the filtration function that corresponds to BTCs stabilising at the concentration lower than the injected value. This so-called binary filtration function incorporates two particle capture mechanisms. The analytical transport model with a binary filtration function was capable to fit successfully BTCs obtained from individual transport experiments using kaolinite and NPs conducted by Chrysikopoulos et al. (Transp Porous Med 119(1):181–204, 2017). Assuming that the electrostatic particle–solid matrix interaction and the fraction of the solid matrix surface area occupied by a single attached particle (kaolinite or NP) are the same for individual transport of either kaolinite particles or NPs and for simultaneous cotransport of kaolinite particles and NPs, the proposed binary filtration function was extended for the cotransport case. Although the breakthrough data from cotransport experiments with kaolinite particles and NPs have six degrees of freedom, the developed cotransport model successfully matches the BTCs by tuning two constants only. This validates the developed model for cotransport of two colloidal populations with different attachments and straining rates.

     

Parameterizing the Leaching Surface by Combining Curve-Fitting for Solute Breakthrough and for Spatial Solute Distribution

Multi-compartment samplers (MCSs) measure unsaturated solute transport in space and time at a given depth. Sorting the breakthrough curves (BTCs) for individual compartments in descending order of total solute amount and plotting in 3D produces the leaching surface. The leaching surface is a useful tool to organize, present, and analyze MCS data. We present a novel method to quantitatively characterize leaching surfaces. We fitted a mean pore-water velocity and a dispersion coefficient to each BTC, and then approximated their values by functions of the rank order of the BTCs. By combining the parameters of these functions with those of the Beta distribution fitted to the spatial distribution of solutes, we described an entire leaching surface by four to eight parameters. This direct characterization method allows trends to be subtracted from the observations, and incorporates the effects of local heterogeneity. The parametric fit creates the possibility to quantify concisely the leaching behavior of a soil in a given climate under given land use, and eases the quantitative comparison of spatio-temporal leaching behavior in different soils and climates.     

Single and Dual-Domain Models to Evaluate the Effects of Preferential Flow Paths in Alluvial Sediments

Typical features of preferential flow paths were evidenced by numerical tests of convective transport of conservative solutes performed in three blocks of alluvial sediments at the scale of depositional elements. The numerical experiments are analysed with standard single-domain models (SDMs) and with dual-domain models (DDMs): the model parameters are identified by minimisation of the misfit between the ??experimental?? and the modelled cumulative breakthrough curves (BTCs) and between the ??experimental?? and the modelled temporal moments of the BTCs. The results for the SDMs show different behaviours for the three model blocks and for the different flow directions, in good agreement with their hydrostratigraphic characteristics. The results for the DDMs sometimes correspond to cases for which one of the two domains is dominant and its values of diffusivity and average velocity are close to those obtained for the SDM; in some cases the DDM performs much better than the SDM and correctly represents the effects of preferential flow paths. Finally the relevance of the DDM is analysed in the framework of multi-objective optimisation: a proper choice of the objective-functions yields Pareto sets whose geometries are different for single- and dual-domain media.     

Asymptotic Analysis of Solute Transport with Linear Nonequilibrium Sorption in Porous Media

We analysed the asymptotic behaviour of breakthrough curves (BTCs) obtained after a single pulse injection in a 1D flow domain. Five different types of solute transport with nonequilibrium sorption were considered. The properties of the porous medium were assumed to be spatially constant. For long times, the concentration at a fixed position in time was found to decay like exp(–t) where depends on both the transport parameters and the parameters describing the nonequilibrium process. The results from the asymptotic analysis were compared with 1D numerical transport calculations. For all cases examined a good agreement between numerical calculations and the asymptotic analysis was found. The results from the asymptotic analysis provide an alternative way to determine transport and sorption related parameters from BTCs. The derived relationships between and the model parameters are however only valid for large times. This requires that the very low concentrations need to be measured and not only the bulk mass, too. By either increasing or decreasing the velocity during BTC experiments additional asymptotic equations are obtained which can be used to determine the value of the model parameters. The results from the asymptotic analysis can also be used in standard inverse modelling techniques to either obtain good initial guesses or to reduce the parameter space. The fact that linear nonequilibrium processes decay like exp(–t) can be used to qualitatively evaluate observed BTCs. The asymptotic analysis can also be easily extended to a larger class of transport problems (e.g. transport of solutes with microbial decay) provided that the overall transport problem remains linear in the concentration.     

The Penetration Processes of Red Mud Filtrate in a Porous Medium by Seepage

This study investigated the effect of flow velocity, the concentration of red mud particles, and the concentration of \(\hbox {OH}^{-}\) ions on the penetration processes of red mud filtrate with fine particles in a porous medium by seepage. The results show that the peak concentrations of the breakthrough curves (BTCs) of red mud particles with high alkalinity are much higher than that with low alkalinity, indicating that the existence of \(\hbox {OH}^{-}\) ions enhances the repulsive interaction between red mud particles and between red mud particles and the matrix and promotes the migration of red mud particles. The red mud particles are more easily absorb onto the surface of porous medium or embedded in the matrix due to the greater adsorption between red mud particles and porous dielectric matrix than silicon powders. The penetration velocity of these red mud particles is often slower than water velocity due to the capture effect by straining and the detours path effect, especially in the case of high injection concentration and low alkalinity. Both the recovery rate and modal size of recovered particles increase with the increase in flow velocity, and the recovery rate of particles with high alkalinity is higher than that of particles with low alkalinity, which can be attributed to the stronger repulsive interaction between particles and between particles and the matrix. An analytical solution for the migration of particles in a porous medium in which the contaminant intensity varies with time has been developed from the elementary solution, and the predicted BTCs for a repeated three-pulse injection are in good accordance with the experimental results.     

Mobility and Interaction of Heavy Metals in a Natural Soil

We study the mobility and interaction under competing conditions observed for copper ( $\text{ Cu}^{2+}$ ) and zinc ( $\text{ Zn}^{2+}$ ) ions in the context of laboratory-scale experiments performed in natural soil columns. The experiments focus on the analysis of solute breakthrough curves (BTCs) obtained after injection of an aqueous solution containing similar concentrations of the two metal ions into a soil column fully saturated with double deionized water. Transport of the competing ions is tested for the same soil under aerobic and anaerobic conditions. Measurements show that the species with lower affinity for the soil, $\text{ Zn}^{2+}$ , migrates occupying all available adsorption sites, and is then progressively replaced by the ion with higher affinity, $\text{ Cu}^{2+}$ . The two ions are displaced in the system with different effective retardation. The slowest species replaces the sorbed ions, resulting in observed $\text{ Zn}^{2+}$ concentrations that display a non-monotonic behavior in time and which, for a certain period, are larger than the concentration supplied continuously at the inlet. In the absence of a complete geochemical characterization of the system, we show that the measured concentrations of both metals can be interpreted through simple models based on a set of coupled partial differential and algebraic equations, involving a small subset of aqueous and adsorbed species that are present in the system. Depending on the model considered, the relationship between aqueous and adsorbed ion concentrations is described at equilibrium by a Gaines–Thomas (GT) formulation, a competitive Sheindorf–Rebhun–Sheintuch (SRS) isotherm, or an Extended Langmuir (EL) isotherm, respectively. The GT formulation provides the best interpretation of the observed behavior among the models tested. We find that employing these simple models, which account only for the main governing reactive processes, allows reasonable estimation of the observed BTCs in experiments where only partial geochemical datasets are available.     

Single- and Dual-domain Models of Solute Transport in Alluvial Sediments: the Effects of Heterogeneity Structure and Spatial Scale

Fine-scale heterogeneity of alluvial aquifers controls solute transport in groundwater at the scales relevant for practical applications: the architecture of sedimentary structures might create preferential flow paths (PFPs) or hydraulic barriers, which affect the breakthrough curves (BTCs). Objective of this paper was the assessment of the relevance of single- and dual-domain models for different heterogeneity patterns and scale lengths in alluvial sediments. Three case studies have been analysed with a classical single-domain model (SDM) and with three dual-domain models (DDMs): a dual-porosity model (DPorM) and two dual-permeability models (DPerM), which differ for the presence or the absence of solute exchange between the two domains. The first case study includes numerical tracer tests in metre-scale blocks of alluvial sediments; the second is a laboratory experiment of tracer injection in a decimetre-scale column of homogeneous sand; the third is a field tracer test performed at hectometre scale at the Cape Cod site. The relevance of the solute exchange in the DDMs is analysed with the characteristic advection and exchange times and with the Péclet and Damköhler numbers. The SDM is satisfactory for alluvial sediments with unstructured heterogeneity. The uncoupled DPerM is shown to be a better approach than the DPorM in sediments with PFPs; in this case, the coupled DPerM does not improve significantly the results of the uncoupled DPerM. A minor difference between the results of the three DDMs is observed for sediments in which the non-Fickian behaviour is not clearly determined by the presence of PFPs.     

弹性动力学反问题的数值反演方法

系统介绍了弹性动力学反问题中各种数值反演方法,包括各种近似下的线性化反演方法;非线性迭代反演方法;确定性和非确定性搜索的优化反演方法;大范围收敛的同伦反演方法以及多尺度反演方法。阐述了各类反演方法的原理、特点、适用范围和存在的局限性,指出了数值反演方法进一步研究的方向。      

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综述了连续介质方法在碳纳米管研究中的最新进展. 主要叙述梁、壳模型, 膜模型,多尺度方法,分子结构力学方法,非局部连续介质方法,以及无网格法的基本原理、 基本方法,及其最新进展,指出其局限性,并预测连续介质方法在碳纳米管研究的发展趋势 和方向.     

无单元法研究和应用现状及动态

无单元法(也称无网格方法)是一种新兴的数值计算方法,它是有限元等传统数值分析方法的重要补充和发展,极大地简化了前处理工作与裂纹扩展等问题的计算分析.近年来,无单元法得到了迅速发展,受到了国际计算力学界的高度重视.简要介绍了国内、外无单元法的发展动态和应用现状,评述了无单元法的最新研究成果,归结出无单元法的一些优点及目前尚有待解决的一些问题.最后指出了无单元法在工程应用中将有着广阔的发展前景.