二维弹性介质中瑞利波高阶有限差分模拟分析

为探讨瑞利波在复杂介质中的形成机理和传播规律,正确认识瑞利波实测结果,提高反演结果的精度,从弹性波方程出发,采用4×10阶高阶交错网格有限差分方法对弹性半空间介质进行全波场模拟。通过对均匀半空间介质、正常地层顺序地基模型和含有低速夹层地基模型的正演模拟,获得了它们各自的地震记录和瞬时快照。由模拟结果可知：以往常规的低阶...     

Multiscale RBF-based central high resolution schemes for simulation of generalized thermoelasticity problems

In this study, average-interpolating radial basis functions (RBFs) are successfully integrated with central high-resolution schemes to achieve a higher-order central method. This proposed method is used for simulation of generalized coupled thermoelasticity problems including shock (singular) waves in their solutions. The thermoelasticity problems include the LS (systems with one relaxation parameter) and GN (systems without energy dissipation) theories with constant and variable coefficients. In the central high resolution formulation, RBFs lead to a reconstruction with the optimum recovery with minimized roughness on each cell: this is essential for oscillation-free reconstructions. To guarantee monotonic reconstructions at cell-edges, the nonlinear scaling limiters are used. Such reconstructions, finally, lead to the total variation bounded (TVB) feature. As RBFs work satisfactory on non-uniform cells/grids, the proposed central scheme can handle adapted cells/grids. To have cost effective and accurate simulations, the multiresolution–based grid adaptation approach is then integrated with the RBF-based central scheme. Effects of condition numbers of RBFs, computational complexity and cost of the proposed scheme are studied. Finally, different 1-D coupled thermoelasticity benchmarks are presented. There, performance of the adaptive RBF-based formulation is compared with that of the adaptive Kurganov-Tadmor (KT) second-order central high-resolution scheme with the total variation diminishing (TVD) property.     

地震分析中的人工边界及其在LS-DYNA中的实现

 地震分析中的局部人工边界由于具有易于实现、稳定性较好的特点,目前在时域有限元法中得到广泛应用。基于球坐标系的膨胀波(P波)和剪切波(S波)理论,引入无限介质线弹性本构关系,并采用多个平面子波和远场散射波混合透射,推导一种新的三维黏弹性人工边界方程。在有限元分析中采用边界单元作等效处理,并将地震加速度记录转化为基底边界单元上的等效节点力进行输入,建立一种新的地震反应数值模拟技术。最后以人防工程结构的地震分析为例,利用有限元软件LS-DYNA分析弹性边界、透射边界及黏弹性边界对计算结果的影响。数值模拟表明,黏弹性人工边界简单实用,可解决地震动输入和自由场响应模拟问题,能更好地模拟人工边界外半无限介质的弹性恢复性能和能量辐射作用,并验证其有效性。     

基于Tikhonov正则化的灌注桩超声波衰减成像方法

采用Tikhonov正则化方法对一带有蜂窝缺陷体的混凝土灌注桩进行了超声波衰减图像重建,重建图像清晰显示出桩内蜂窝体的位置与形状,与速度成像结果相比较,两者吻合较好。又对一桥梁工程灌注桩进行了衰减图像重建与速度图像重建,所得图像均清晰显示出缺陷体的部位,且两者较为符合,后经钻孔抽芯验证,其结果证明了该衰减成像方法的有效性。实际工程中宜采用速度与衰减系数双参数进行成像,以相互验证,提高检测的可靠性。     

利用多次散射波监测介质性质变化的试验研究

 与传统的直达波检测相比,多次散射形成的尾波对介质性质变化具有很高的灵敏度。本研究建立了试验测试系统,对水泥和岩石样品开展散射波试验研究,分析尾波发育规律、尾波干涉数据处理方法和应用条件。得出岩石散射体的浓度和尺度、超声波偏振方向、频率对散射波和尾波形成具有重要影响;观测系统的高度重复性、稳定和高信噪比(SNR)尾波以及变窗口互相关扫描分析是获得高精度尾波干涉测量的关键。测试获得了水泥试件纵波、横波和尾波波速对应力变化的敏感性,与直达波相同,所有样品尾波波速都随应力的增大而增大,不同样品间增大的速率(应力敏感性)不同且随杨氏模量的增大而减小。将该方法用于水泥试件水饱和及楼房承载柱环境变化响应的监测,获得清晰的水泥试件水饱和进程,以及楼房承载柱尾波波速随环境湿度的变化,为利用多次散射波监测介质微弱变化和研究介质性质变化的精细过程创造条件。     

倾斜入射地震波作用下成层场地动力反应的界面子波算法

为提高成层半空间自由波场的一维化时域方法的计算效率和精度,分析了SH波在层状介质中的传播方式、旅行时间和反射系数等问题,基于惠更斯–菲涅耳波动观点,将波阻抗界面看作次级子波源(简称为界面子波),提出了倾斜入射地震波作用下成层场地动力反应的界面子波算法,并通过模型试算验证了此方法的正确性。与常规数值法相比,此方法无需划分网络单元,也无需处理人工边界条件,从而极大地减少了计算工作量和节点之间的传递误差,具有速度快、精度高、稳定性好等特点,是一种计算成层场地动力反应的实用方法。     

自适应有限元不同网格间力学结果传递方法及程序实现

对于依赖于加载历史的自适应有限元分析问题,不同网格间力学结果的传递过程起着重要作用。基于按距离加权平均的改进插值方法,研究分步加载时自适应有限元不同网格间力学结果的继承问题。为使传递结果合理并减小计算工作量,插值方法采取选择邻近数据点、考虑方向影响、适当提高结果场的光滑性并使其通过全部已知数据点等措施;针对开挖过程中结构介质不断改变、开挖工作面不断移动及不同开挖步引入的介质之间场变量不连续等特点,采取分区划分网格并插值方式,构造不同网格间应力及位移结果的传递过程。所述传递过程,能为自适应有限元模拟多步骤开挖及弹塑性增量荷载分析等各种分步加载计算问题的解决提供有利条件。最后,给出2个算例以验证传递过程的可靠性。按增量荷载初应力方法对厚壁筒弹塑性分析表明,其结果与理论解吻合;模拟多步开挖的工程实例计算结果亦展示出所述传递方法的有效性。     

数值流形方法的网格自动剖分技术及其数值方法

数值流形方法包含数学覆盖与物理覆盖双重网格，数学网格用以构造流形单元的插值函数，物理覆盖确定了流形单元的积分区域。数值流形方法的前处理一直是一个难题。讨论了数值流形方法的网格自动生成技术，解决了数值流形方法的前处理问题。无论是连续性材料还是非连续性材料，数学覆盖都保持不变，因此，借助现有的有限元技术生成数值流形方法的数学网格，利用面向对象的编程方法生成了数值流形方法的物理网格。实例应用表明，这种方法是可行的和有效的。     

一种用于随机突变量的数据可靠性处理算法

对于随机突变参量的数据可靠性处理,本文提出了一种新的基于自适应预报的数据处理器算法.该算法将被测参量的变化规律用一参数慢时变的时间序列模型描述,以被测参量变化趋势的自适应一步预报值及其95%置信限构成判据,对测量数据进行处理,剔除或抑制其中的不良数据.仿真实例表明本算法克服了现有大多数算法在处理随机突变数据时遇到的困难,效果明显.     

Identification of the hygrothermal properties of a building envelope material by the covariance matrix adaptation evolution strategy

This paper proposes the application of the covariance matrix adaptation (CMA) evolution strategy for the identification of building envelope materials hygrothermal properties. All material properties are estimated on the basis of local temperature and relative humidity measurements, by solving the inverse heat and moisture transfer problem. The applicability of the identification procedure is demonstrated in two stages: first, a numerical benchmark is developed and used as to show the potential identification accuracy, justify the choice for a Tikhonov regularization term in the fitness evaluation, and propose a method for its appropriate tuning. Then, the procedure is applied on the basis of experimental measurements from an instrumented test cell, and compared to the experimental characterization of the observed material. Results show that an accurate estimation of all hygrothermal properties of a building material is feasible, if the objective function of the inverse problem is carefully defined.     

Estimating small structural motions based on sparsity enforcement

This paper proposed a novel, efficient method to estimate challenging small structural motions from noisy video. To eliminate the phase limitation, ill-posed problem, and high computational burden, the structural motion function is resampled and recovered. Because video signals have tremendous redundancies in spatial, block, and time domains, the objective is achieved by enforcing three levels of sparsity constraints. In the first step, the ill-posed optimization is solved using the multi-hypothesis prediction embedded with the Tikhonov regularization, to resample and recover the video signal in the spatial domain. The second step is to characterize the measurement uncertainty in the block domain, in which two weight matrices are proposed into the regularization terms of the sparse coding. Finally, the temporal correlation of video frames is exploited by the reweighted residual sparsity. The superiority of the sparsity-enforcement method over existing methods was demonstrated through several case studies. Among the comparisons, the sparsity-enforcement method yielded video magnifications, structural motions, and modal information more accurately. Meanwhile, it has the lowest computational burden.     

有限覆盖无单元法在多裂纹岩体

考虑基于有限覆盖的流形方法和以Galerkin插值技术为基础的无单元方法的各自优点，将所提出的有限覆盖无单元法推广应用于多裂纹岩体断裂特性等非连续问题的数值计算与分析。在简要阐述有限覆盖无单元方法基本原理的基础上，首先对含有单条裂纹的岩体进行了计算与分析，通过与其他方法的比较验证了所建议方法的有效性和合理性，进而对含有多条裂纹的复杂岩体的断裂特性及其裂纹的扩展过程进行了数值模拟与预测。     

An accurate predictor-corrector time integration method for structural dynamics

In this paper, a new accurate predictor-corrector time integration method is proposed, which has an appropriate stability domain. The dispersion error of the suggested approach is considerably smaller than that of the central difference scheme. Moreover, the presented technique introduces effectively numerical damping, which can be used to remove the spurious highfrequency components from the numerical responses. The authors’ approach has second-order accuracy for structures with and without damping. It is worth mentioning that the scheme solves the nonlinear problems without using iterative processes. The new algorithm is tested by using several linear and nonlinear numerical examples, and the outcomes are compared against the results of the central difference and explicit second-order Runge-Kutta schemes. The findings confirm the high accuracy and good performance of the suggested technique.     

两种GPS坐标转换方法及解的稳定性分析

主要探讨了GPS坐标转换的方法,对两种不同的转换方法进行了数值稳定性和精度分析,结果表明：空间七参数转换方法可适用于大范围的坐标转换,但方程经常病态,稳定性差,平面相似变换法方程相对稳定,但只适用于小范围的坐标转换。     

Quantification and relative comparison of different types of uncertainties in sewer water quality modeling

Quantifiable sources of uncertainty have been identified for a case study of integrated modeling of a sewer system with a more downstream wastewater treatment plant and storage sedimentation tank. The different sources were classified in model input and model-structure-related uncertainties. They were quantified and propagated towards the uncertainty in the event-based prediction of sewer emissions (flow, and physico-chemical water quality concentrations and loads). Based on the concept of variance decomposition, the total prediction uncertainty was split into the contributions of the various uncertainty sources and the different submodels. Although the results strongly depend on the water quality variable considered, it is in most general terms concluded that the uncertainty contribution by the water quality submodels is an order of magnitude higher than that for the flow submodels. Future model improvement should therefore mainly focus on water quality data collection, which would reduce current problems of spurious model calibration and verification, but also of knowledge gaps in in-sewer processes.     

Stochastic wave models for stationary and homogeneous seismic ground motion

A fundamental theory of stationary, homogeneous stochastic waves is developed and a technique for digitally generating samples of such waves is introduced as a further extension of the spectral representation method. This is done primarily for the purpose of developing an analytical model for propagating seismic waves that can account for their stochastic characteristics in the time and space domain. From this model, the corresponding sample seismic waves can be digitally generated with great computational efficiency. The efficacy of this technique is demonstrated with the aid of a numerical example in which a sample of a stationary, homogeneous, two-dimensional, dispersive Rayleigh wave consistent, in its analytical form of spatial variability, with Lotung, Taiwan dense-array data is digitally generated. Although the stochastic wave model considered in this work is stationary and homogeneous, it is a straightforward task to extend the methodology introduced to nonstationary and / or non-homogeneous stochastic waves characterized by an evolutionary power spectrum.     

Adaptive radial-based importance sampling method for structural reliability

In this paper an adaptive radial-based importance sampling (ARBIS) method is presented. The radial-based importance sampling (RBIS) method, excluding a β-sphere from the sampling domain, is extended with an efficient adaptive scheme to determine the optimal radius β of the sphere. The adaptive scheme is based on directional simulation. The underlying basic methods are presented briefly. Several numerical examples demonstrate the efficiency, accuracy and robustness of the scheme. As such, the ARBIS method can be applied as a black-box and is of particular interest in applications with a low probability of failure, for example in structural reliability, in combination with a small number of stochastic variables.     

爆炸与冲击中的非线性岩石力学问题(I)：一维块系岩体波动特性的试验研究

与岩体构造层次相关的摆型波现象正逐渐形成非线性岩石力学的重要研究方向,并在诱发地震、岩爆及其他地震动事件的研究中展现出了重要的应用前景。利用自行研制的块系岩体动态力学性能测试试验系统,进行一维块系岩体模型的波动特性试验研究,测得一维冲击条件下块体振动的的频谱、振幅、波速特征,获得了迥异于连续介质中波动特性的摆型波特征现象,试验结果表明：一维冲击作用下,在冲击振动通过块系构造岩体向前传播的过程中,发生了从高频振动向低频振动的转移;相邻岩块间发生位移相差很大、甚至位移符号相反的相互对应的摆动;随着冲击比例距离的增加,块系岩体各块体加速度、位移幅值按指数形式衰减;摆型波传播的速度远远小于连续介质中纵波的传播速度,主要取决于块体间的裂隙宽度以及块体的运动速度。     

用于小高层住宅的模糊PID变频供水系统

为保证小高层住宅供水压力稳定性并达到节能,采用了模糊自适应PID控制技术,利用模糊推理在线自动整定PID控制器的参数,较好地克服了传统PID控制器稳定性差、参数整定困难的缺点.将供水母管压力与设定压力的偏差经模糊自适应PID运算,通过可编程控制器调节变频器的输出,可自动调整水泵运行的台数和电机转速,实现闭环自动调节恒压供水.