边坡工程中监测数据场三维云图实时动态可视化方法

实现监测物理量空间数据场的三维实时动态可视化表达,是边坡工程安全监测三维可视化在线分析的关键。空间数据场三维可视化最直观的表达形式是三维云图,其绘制方法包括面绘制和体绘制,而体绘制方法是实现三维数据场实时动态云图绘制的首选方法。鉴于X3D灵活的场景交互和丰富的三维几何造型节点,通过生成用于监测数据场三维云图显示的几何载体TEN模型,在提取监测点坐标并形成监测数据场的基础上,应用空间插值算法得到TEN网格节点的监测物理量数值,并按照特定颜色表映射到网格节点的颜色域值,提出基于X3D技术的空间数据场三维云图体绘制方法。以某水电站坝肩边坡和某水电站谷肩堆积体为例,应用该方法实现边坡和堆积体监测数据场三维分布云图的实时动态可视化显示,直观地揭示监测对象的变形趋势和可能的变形破坏模式,为该方法在水利水电和岩土工程的边坡及地下工程安全监测领域的应用提供参考。     

受施工扰动影响土体力学参数的可视化分析方法

结合具体工程,对受施工扰动后土体力学参数分析中应用科学计算可视化分析的方法进行研究,结合体视化的算法思想,建立了受工程施工扰动土体力学参数变化的可视化分析研究方法,提出采用直接体视的算法来实现受工程施工扰动土力学参数可视化表示的解决方案。建立了用于受基坑工程施工扰动土体力学参数可视化分析的体数据V,体数据中包含了基坑外部土体的土力学参数和位移场的三维信息。按照不同的施工阶段,建立不同时间序列的系列体数据集,利用这些体数据集,可直接可视地分析施工每一工况下的坑外土体内各种土力学参数的变化和土体位移的变化。     

移动环境下三维场景的实时渲染技术研究

讨论了移动三维图形的实时显示技术,通过建立LOD模型和采用分层分块的数据组织方式,并采用基于四叉树层次结构的视景体裁剪优化算法,来减少场景渲染的模型数据量,从而加速三维实体模型的显示速度,达到流畅连续地实时显示移动环境下三维场景的目的。     

Numerical evaluation of the effective elastic moduli of rocks

In this paper we describe a two-dimensional numerical algorithm to calculate overall elastic properties of rocks. We assume that rocks can be viewed as an assemblage of blocks divided by discontinuity surfaces such as large-scale fractures. For each block we use the concept of representative volume element. We model a representative volume element as a finite body containing multiple defects in the form of inhomogeneities, pores, and microcracks and use simplified assumptions regarding the shapes of the defects. Effective moduli for all blocks can be used as input data for a boundary element (or finite element) computer code to model behavior of rock masses at a different length scale as an assemblage of homogeneous blocks of different shapes and elastic properties. The approach is based on a numerical solution of a hypersingular integral equation for a representative volume element. The use of global approximations and a specially tailored fast multipole technique allows one to efficiently solve large-scale problems and accurately calculate the elastic properties of an equivalent homogeneous material. An additional benefit of the approach is that it allows for an accurate representation of the displacement and stress fields anywhere within the material. A series of computer experiments is conducted to demonstrate the efficiency and accuracy of the algorithm. The possible extension of the approach for three-dimensional problems is discussed.     

High-speed visualization of time-varying data in large-scale structural dynamic analyses with a GPU

Large-scale structural dynamic analyses generally produce massive amount of time-varying data. Inefficient rendering of these data seriously affects the quality of display of and user interaction with the analysis results. A high-speed visualization solution using a GPU (graphics processing unit) is thus developed in this study. Based on the clustering concept, a key frame extraction algorithm specific to the GPU-based rendering is proposed, which significantly reduces the data size to satisfy the GPU memory requirement. Using the key frames, a GPU-based parallel frame interpolation algorithm is also proposed to reconstruct the complete structural dynamic process. Particularly, a novel data access model considering the features of time-varying data and GPU memory is designed to improve the interpolation efficiency. Two case studies including an arch bridge and a high-rise building are presented, confirming the ability of the proposed solution to provide a high-speed and interactive visualization environment for large-scale structural dynamic analyses.     

基于复形法的大跨屋盖结构有限元模型修正研究

根据环境振动测试的模态数据,首次采用复形法对广州国际体育演艺中心屋盖结构进行有限元模型修正研究,并与ANSYS一阶算法、改进BP神经网络算法和粒子群算法修正有限元模型进行对比分析。研究结果表明:修正后的有限元模型的模态频率与实测的模态数据比较吻合,复形法可以作为大跨屋盖结构有限元模型修正的一种有效方法。     

流形切割及有限元网格覆盖下的三维流形单元生成

 三维流形单元生成和接触搜索算法问题是制约三维数值流形方法发展的瓶颈问题。系统详细地研究三维流形单元的生成方法,在前人工作基础上,采用三维有限元网格生成技术生成数学网格;通过块体数据结构、块体识别算法等方面的改进,将三维块体切割技术发展成流形切割技术,来解决流形块体生成问题;将石根华博士在二维NMM程序中采用的物理覆盖系统编码算法,扩展成三维流形编码算法,进而实现三维流形单元的生成。并在此基础上开发三维流形切割程序3D_MC.f90,可以实现四面体及六面体网格覆盖下任意形状三维流形单元的生成。通过几个例子可以看出,三维流形切割程序生成的流形块体形态、流形单元的节点与单元编码等均满足三维流形单元定义要求,从流形切割角度来看,说明此算法是正确的。     

基于GIS和体视化技术的工程场地地震液化势3D可视化

工程场地地震液化势三维模型的建立及可视化研究的目的是用三维图形来描述地震动作用下场地液化势的空间分布特性,以此为城市防震减灾工作提供相应的支持。采用具有概率意义的饱和砂土抗液化强度经验公式来对场地进行地震液化势概率评价;采用一种基于"块"模型的数据结构来描述场地液化势三维实体;结合Kriging插值法和体视化技术进行场地液化势的三维可视化建模。研究表明:采用"块"数据模型来分割模拟三维液化势场,利用Kriging法对工程场地地震液化势进行空间数据三维插值,有助于揭示勘探孔以外任意空间点的土层液化势信息;基于液化势概率评价结果和体视化技术,采用Kriging插值法,以不同的色标体现场地液化势的风险程度,可以直观的三维图像形式呈现场地液化势的空间分布特性和变化趋势,通过剖切自动生成指定位置的二维剖面和三维切割体,工程场地液化势的三维分布特性得到有效的表达。     

基于显微CT试验的岩石孔隙结构算法研究

在对煤系地层泥岩样进行显微CT无损伤探测及其图像分析的基础上,用Matlab语言对岩石孔隙结构(孔隙孔径和孔隙率)的算法进行了研究。结果表明:显微CT扫描、数字图像处理和三维重构三者的结合为岩石类材料孔隙结构的定量研究提供了一种简单可行的新方法。对显微CT试验得到的CT单张横截面图像进行数字图像处理,计算出了基于CT单张图像的岩石孔隙率。对CT单张横截面图像进行压缩,生成不同分辨率的新图像,以新图像的像素大小作为孔径尺度,确定了基于CT单张图像的岩石孔径尺度和孔隙率之间的变化规律。将CT单张图像进行处理生成CT图像序列,用可视化重构算法中的体绘制算法对其进行三维重构,生成岩石的三维数字图像,计算了基于CT图像序列的岩石孔径、孔隙率及其二者之间的变化规律。以煤系地层中的泥岩为例,泥岩的孔隙率随孔径尺度的增加呈负指数规律减少,其计算结果与压汞法测定的孔径分布相吻合。     

Hybrid intelligent method optimization of a soft rock replacement scheme for a large cavern excavated in alternate hard and soft rock strata

Optimization of a soft rock replacement scheme for a large cavern excavated in alternating hard and soft rock strata is a complicated non-linear mechanical problem having a large parameter search space. Obtaining a global optimum solution is the key to the problem. A hybrid intelligent method is proposed for this purpose. It is an integration of an evolutionary neural network and finite element analysis using a genetic algorithm. The non-linear relation of the soft rock replacement scheme with the displacement and damage zone of the cavern due to excavation in the given geological conditions is learnt and represented by a forward neural network whose structure and connection weights are global optimally recognized by using the genetic algorithm. The learning samples are obtained from finite element calculations. The optimal soft rock replacement scheme, having the minimal displacement and damage volume induced by cavern excavation, is searched in a global space using the genetic algorithm. The new methodology is used to evaluate soft rock replacement schemes for the Shuibuya cavern in China excavated in strata consisting of alternating soft and hard rocks. The results indicate that the new methodology can recognize the optimal soft rock replacement scheme for a large cavern in such complicated geological conditions and the neural network model can provide a solution which is close to the finite element analysis for the same geological and construction conditions.     

基于浮动车的城市道路行程时间预测算法研究

装载GPS的浮动车在社会交通流中比重越来越高,已成为主要的行程时间采集手段。研究了基于浮动车的城市道路路段行程时间预测算法,输入数据包括静态空间属性数据、行程时间历史备份数据和基于GPS采集的动态交通行程时间数据,并以5 min为预测间隔进行20 min短时行程时间预测。最后经2.1 km含3个交叉口的路段预测验证,表明该算法单方向单次最大误差23.0%;经过滚动预测,单方向平均绝对误差为5%~6%,精度满足用于城市道路路段的信息发布要求。     

不连续岩体温度场的复合单元模型初步研究

 基于复合单元法原理和不稳定温度场的隐式解法,提出针对不连续岩体温度场的复合单元法。该算法的特点是每个复合单元可以含有任意的不连续面,如断层或节理,且当结构中含有需在计算中离散处理的不连续面时,网格的生成不受不连续面的数量、位置和方向的影响。初步研究针对含1条节理的复合单元模型展开,假定岩块中无对流和辐射影响,推导岩块子单元和不连续面的热传导计算式,得到不连续岩体温度场的复合单元算法基本方程组,然后将该算法整合到传统有限元分析程序中。分别采用传统有限单元和复合单元法模拟热水流过单条裂隙时岩体温度场的变化过程,二者的计算结果非常接近,表明不连续岩体温度场的复合单元算法是合理和有效的,但其配套的温度场等值线后处理程序有待进一步完善。该算法的提出为深部岩体的多场耦合研究提供又一思路。     

沉管隧道地震响应分析的并行计算

采用全三维非线性建模方法建立了沉管隧道总体有限元模型,模型规模上节点总数超过100万,单元总数超过120万。由于系统的非线性,以及地震激励是一种时间历程,沉管隧道地震响应数值模拟的实质是一个超大规模非线性系统的瞬态响应计算问题,因此导致目前在地震安全性评价领域普遍采用的串行算法、串行软件和普通的计算机无法胜任此工作。根据所用超级计算机的体系结构特点,采用并行区域分解算法,通过对沉管隧道总体模型合理分区来进行地震响应分析。地震波载荷选用调幅后的唐山地震波,应用通用的非线性动力分析有限元程序LS-DYNA进行求解,计算结果可为隧道的抗震设计提供有力依据。     

地下工程问题的可视化分析方法

针对地下工程施工的特点和目前数据分析中所存在的问题,对地下工程问题分析中应用科学计算可视化分析方法进行了研究;结合体视化的算法思想,建立了地下工程问题的可视化分析方法;提出了采用基于表面重建和直接体视的算法来实现地下工程问题的可视化解决方案,并对地下工程施工的可视化分析方法进行了探索。     

分阶段结构损伤诊断方法

在现有分步损伤诊断方法的基础上,提出了一种3阶段结构损伤诊断方法.通过对遗传算法的特点进行分析,提出以逐步评定并排除无损单元的思路来处理结构损伤诊断问题.提出的分步方法中,应用了多次灵敏度遗传算法计算来进行无损单元排除,同时结合残余力向量指标对损伤大致位置进行判断.算例证明,在单纯用1种方法难以完成损伤诊断的情况下,用...     

Settlement performance of pad footings on soft clay supported by stone columns: A numerical study

The settlement behaviour of small loaded areas (such as pad and strip footings) on soft soil supported by stone columns is poorly understood. The lack of confinement associated with peripheral columns and the sharp stress decay with depth are features which are incompatible with the widely-used unit cell method for infinite column groups thereby rendering small group behaviour particularly difficult to analyse. Useful field data is virtually non-existent and although innovative laboratory modelling has been insightful, the findings cannot easily be extrapolated to field scale. In this study, a 3-D finite element analysis in conjunction with an elastic–plastic soil model is used to identify the effect of variables in the design process and interactions between them: these include column arrangement, spacing, length, and Young׳s modulus of the column material. A simplified method is proposed to relate the settlement of small groups to a reference unit cell settlement predicted by current analytical approaches.     

Finite element modeling of concrete beams prestressed with external tendons

In this study, a numerical model based on the finite element method incorporating an arc-length solution algorithm for materially and geometrically nonlinear analysis of concrete beams prestressed with external tendons is established. The second-order effects are taken into account. The effects of external tendons are expressed by equivalent nodal loads of the beam element and therefore analysis of externally prestressed concrete beams can be conducted with the ordinary bonded concrete beams. The section tangent stiffness matrix is derived by the layered approach, and then the nonlinear beam flexural theory is utilized to determine the element tangent stiffness matrix. An updated normal plane arc-length solution algorithm is used to trace the nonlinear response of the beams from zero loads up to ultimate loads. This algorithm can deal well with the changes of response during loading, so that the possible limit points on the load–deflection response prior to the ultimate limit state can be easily passed. Results predicted by the analysis are in good agreement with the experimental data.     

不连续岩体的三维弹粘塑性复合单元模型研究

阐述了复合单元法的原理，并在此基础上提出了针对不连续岩体的算法。该算法最突出的特点是每个复合单元可以含有几个不连续面，如断层或节理。该算法的主要优点是可以方便地整合到传统有限元分析程序中，且当结构中含有较多需在计算中离散处理的不连续面时，计算网格的生成不受不连续面的数量、位置和方向的影响。算例表明这种新方法是合理和有效的。     

三维有限元并行计算及其工程应用

针对水利工程中的人型复杂三维结构对大规模数值计算的需求，基于J—PCG方法(Jacobi预处理共轭梯度法)，建立了有限元EBE(element-by—element)方法和分布存储并行机上的计算算法。该算法不用考虑网格拓扑结构和单元的排序，同时小形成整体刚度矩阵，而且避免了对复杂的三维结构进行区域分解。采用上述算法编制了三维有限元并行求解的PFEM(parallel finite element method)程序，并在网络机群系统上实现，然后将其应用到二滩拱坝-地琏系统和水布娅地下洞室的三维有限元数值计算中。数值计算结果表明，三维有限元并行EBE方法非常适合于水利工程中三维复杂结构的人规模数值计算。     

基于布谷鸟搜索算法的温度驱动损伤识别方法

基于振动的损伤识别方法数据分析过程复杂,且易受环境不确定因素影响,为解决该问题,提出了一种基于布谷鸟搜索算法的温度驱动损伤识别方法。分析中将温度视为结构的可测激励,对基于温度诱导应变的结构损伤参数识别公式进行了推导,进而利用实测的温度诱导响应值与有限元模型计算的温度诱导响应值构造目标函数,基于改进的布谷鸟搜索算法对有限元模型中的损伤参数进行更新,从而实现损伤的准确判别。通过一根两端弹性约束的H型钢梁,以及一榀Benchmark钢框架模型的数值仿真分析,验证了所提方法的损伤识别效果。分析结果表明：基于布谷鸟搜索算法的温度驱动损伤识别方法可对不同程度、不同位置及不同数量的损伤进行有效识别,即使在较高的噪声干扰下,仍能取得较好的识别结果。相比于基于振动的有限元模型损伤参数识别方法,该方法无需施加外部激励,输入与输出数据（温度与温度响应）方便可测,损伤识别所需的数据量较少,受噪声干扰影响小,可对结构的损伤进行有效定位与量化。