渗流作用下边坡稳定有限元分析

基于二维无压稳定渗流基本原理,采用改进的单元渗透系数矩阵调整法模拟边坡渗流场,计算了土体单元的渗透力;以渗透力代替单元周边的孔隙水压力,采用有限元强度折减法分析渗流作用下边坡的稳定性.算例分析表明,采用有限元强度折减法进行渗流作用下边坡稳定性分析是可行的.     

考虑围压衰减时管涌动态模型研究及数值计算

管涌破坏发展的动态过程是个复杂而随机的过程.颗粒在形成管涌起动前与周围颗粒的作用力存在随时间衰减的过程,管涌形成前后由于约束的变化及渗透力作用下颗粒位移的徐变是围压衰减的根本原因.对处于渗流场中的泥沙颗粒间的作用及与流体的相互作用机理和规律进行了分析,提出了泥沙起动形成管涌的必要条件,并通过有限元法的数值计算模拟了管涌破坏发展的动态过程.     

箱形渗透试验仪中宽级配砂砾石渗流变形试验

为了解管涌现象形成和发展过程中土颗粒的移动规律,采用箱型渗透变形试验仪对不同级配的砂砾石进行了试验研究,并描述了渗透破坏过程。考虑固体介质的性质及特点,使用先进压力传感器记录试验中管涌过程,研究了宽级配砂砾石在渗流过程中的性质和特点。该试验为砂砾石的管涌破坏类型分类(发展型和非发展型)提供了合理的理论支持。     

吸力式桶形基础负压安装的渗流侵蚀过程研究

针对吸力式桶形基础负压安装渗流侵蚀效应,建立轴对称坐标下吸力桶在砂性土中负压沉贯的数值模型,应用包含土骨架、流体和液化土颗粒的三相耦合模型描述海床土体,计算负压作用下海床的渗流场分布,并模拟负压引起的渗流侵蚀过程.渗流侵蚀可改变不同区域土体的渗透率,进而引起水力梯度从内侧向外侧转移.基于孔隙水压力场的重新分布,揭示出负...     

悬挂式防渗墙防渗效果数值模拟

鉴于数值模拟技术在模拟土体渗流方向上几乎不受外界干扰、计算可重复性高等优势,以室内砂槽模型试验为背景,采用有限差分软件FLAC3D模拟了双层堤基中悬挂式防渗墙的贯入深度、布置位置对渗透变形的影响。结果表明,悬挂式防渗墙防渗效果随贯入深度的增加而更为显著;防渗墙布置在靠近下游位置时可抑制渗透变形在墙后背水侧发展,从而避免堤身沉降出现溃堤事故;数值模拟结果与室内模型试验数据基本吻合,说明运用数值模拟分析渗透变形是可行的。     

二滩高拱坝坝基灌浆帷幕防渗效果研究

以运行期的二滩拱坝为例,考虑高拱坝坝基存在断层及有自由面排水孔幕情况,利用三维渗流场有限元模拟法、改进排水子结构法和隐式复合材料单元法建立了高拱坝坝基渗流场有限元数值模型,模拟了灌浆帷幕和排水孔幕同时作用时的拱坝实际渗流场,再假设坝基灌浆帷幕失效模拟了该工况下的坝基渗流场,通过比较分析研究了高拱坝坝基灌浆帷幕的防渗效果。结果表明,灌浆帷幕失效后二滩高拱坝坝基渗流场依然可在排水孔幕作用下保持稳定,坝肩部位渗流场稳定性明显降低。     

某多层结构堤基土体渗透变形机理模拟研究

针对某多层结构堤基渗透稳定性问题,采用基于离散元理论的颗粒流方法,建立堤基概化颗粒模型并进行渗流模拟,研究多层结构堤基渗透变形发展过程及颗粒流失量、孔隙率等参数的变化规律。结果表明,对于上覆粘土,下部为级配不良中砂和级配不良细砾的土层结构,发生渗透破坏时土体颗粒流失主要发生在中砂层,渗漏通道表现为由渗流出口逐渐向上游发展,由于流失量持续增大,造成该土层逐渐被掏空并导致上覆粘土层塌陷破坏;细砾石层颗粒流失量较小且趋于稳定,不会演变为管涌破坏。     

基于无单元法的应力场与渗流场耦合分析模型

应用迭代解耦技术建立了基于无单元法的应力场与渗流场耦合分析计算模型并研制开发了计算程序。以矩形坝为例,计算比较了有无耦合作用时的坝体应力场和渗流场。结果表明,耦合作用时坝体的位移略小但分布规律一致;坝体的水平正应力分布差别较大,垂直正应力、剪应力和等势线变化较大,但分布规律一致。计算结果符合一般规律,用无单元法进行应力场和渗流场耦合分析是可行的。     

堤基管涌破坏过程中的声发射信号特性研究

通过自行设计砂槽模型,开展了堤基管涌连续破坏的室内试验,研究了堤基管涌连续破坏过程中的声发射信号特性。通过对比分析管涌连续破坏过程中测压管水头的变化与声发射特性参数,发现管涌连续破坏过程中有明显的破坏阶段性,可分为未发生管涌、管涌发生初期、管涌发生后期3个阶段。通过分析管涌连续破坏各个阶段声发射信号的波形,发现堤基管涌连续破坏过程的声发射信号多为突发型信号。利用二进离散小波包对声发射信号进行频谱分析,发现管涌连续破坏各个阶段的声发射信号主频主要集中在[0 62.5]kHz频带,管涌发生初期和管涌发生后期的声发射信号主频范围为20~30kHz,未发生管涌阶段则主频偏小为2~7kHz。     

文登市抽水蓄能电站三维渗流场的有限元分析

针对抽水蓄能电站工程区中众多地下洞室和排水措施影响下渗流场的复杂性问题,给出了求解有自由面渗流场改进的截止负压法、模拟高压隧洞子结构法、模拟地下厂房密集排水孔改进的排水子结构法等,并采用IDL语言编制了基于子结构法的三维渗流场有限元计算软件GWSS,计算了文登市抽水蓄能电站工程区复杂渗流场,研究了高压输水隧洞和引水管道下水平段的钢筋混凝土衬砌开裂状态下内水外渗及工程区复杂渗流场的分布特征。结果表明,在高压隧洞下水平段上部设置排水洞和排水孔幕的排渗方案,对衬砌开裂状态下高压渗水有显著排水降压作用。     

Matrix free meshless method for transient heat conduction problems

In the paper, the element free Galerkin method (EFGM) is applied to calculate two-dimensional unsteady state heat conduction problems. As is well known, most of the meshless methods have higher computational cost than that of finite element method (FEM). In order to overcome this shortcoming especially for transient heat conduction problems, mass lumping procedure is adopted in EFGM, which can decrease the computational cost evidently. Moreover, this technique which can simplify the solution procedure makes the essential boundary conditions enforced directly. The results obtained by EFGM combining mass lumping technique are compared with those obtained by finite element method as well as analytical solutions, which shows that the solutions of the present method are in good agreement with FEM’s and analytical solutions.     

Systematic correction of stiffness of a finite element model by means of measured eigenvalues and derivation of concrete identification factors of a dowel connection

The correct dynamic behaviour of a real structure can be described by an analytical finite element model only when the parameters of the finite element model are correctly assumed. The dynamic prediction is closely related to the choice of the boundary stiffness, the intermediate elements and the geometric properties of open-cross-section beams.First, laboratory tests are carried out on a test set-up which consists of a piping support, anchorage elements and a concrete block. The test parameters include the variation of dowel tightening torque, the anchor plate stiffness and the concrete block. The first comparison of analytical and test results did not show good agreement. The uncertain stiffness of the finite element model is systematically adjusted by means of indirect parameter identification with measured eigenvalues. A high degree of agreement is obtained between the analytical and measured eigenvalues at the end of the iterative procedure. The required concrete stiffnesses are derived from a spring model which includes all important stiffness terms of a dowel connection. The typical concrete identifications are derived from the affected pressure concrete cones. For similar dowel connections the equivalent concrete stiffness can be analytically determined using the derived identification factors.     

排架支撑式渡槽排架损伤下地震响应分析

以洗耳河渡槽为例,以弹塑性梁单元模拟排架,采用有限体积法、ALE及二阶迎风格式模拟槽内水体,建立了二维槽—水耦合体,分析了横向地震作用下的排架损伤下渡槽动力非线性响应,并与线弹性梁单元模拟排架的分析结果进行对比。结果表明,在所选地震波横向作用下,排架发生损伤造成了刚度下降、结构振动周期延长,从而逼近水体的一阶晃动周期,引起了槽—水耦合体内水体的大幅晃动;排架损伤后槽底水平位移增大而水平加速度减小,槽内水体作用于槽体底部的动水压力、倾覆力矩、倾覆力减小。     

A coupled meshless-finite element method for fracture analysis of cracks

This paper presents a coupling technique for integrating the element-free Galerkin method (EFGM) with the traditional finite element method (FEM) for analyzing linear-elastic cracked structures subject to mode-I and mixed-mode loading conditions. The EFGM was used to model material behavior close to cracks and the FEM in areas away from cracks. In the interface region, the resulting shape function, which comprises both EFGM and FEM shape functions, satisfies the consistency condition thus ensuring convergence of the method. The proposed method was applied to calculate mode-I and mode-II stress–intensity factors (SIFs) in a number of two-dimensional cracked structures. The SIFs predicted by this method compare very well with the existing solutions obtained by all-FEM or all-EFGM analyses. A significant saving of computational effort can be achieved due to coupling in the proposed method when compared with the existing meshless methods. Furthermore, the coupled EFGM–FEM method was applied to model crack propagation under mixed-mode loading condition. Since the method is partly meshless, a structured mesh is not required in the vicinity of the cracks. Only a scattered set of nodal points is required in the domain of interest. A growing crack can be modeled by simply extending the free surfaces, which correspond to a crack. By sidestepping remeshing requirements, crack-propagation analysis can be dramatically simplified. A number of mixed-mode problems were studied to simulate crack propagation. The agreement between the predicted crack trajectories with those obtained from existing numerical simulation and experiments are excellent.     

考虑流固耦合的泵站压力管道激振特性有限元分析

为探究大型高扬程泵站压力管道运行时高频激振的诱因和振动特性,以甘肃省景电二期总干七泵#1压力管道为研究对象,采用附加水体质量法建立基于ANSYS有限元的简化流固耦合仿真模型,对压力管道的激振特征进行数值模拟,分析不同机组启闭工况下压力管道的振动模态及位移变形规律,揭示压力管道的主要振动变形特性。结果表明,在多种运行工况下,压力管道弯管段和大小管连接段振动比较明显,且高阶模态的振型振幅高于低阶模态,不易被激振的出水管随着阶次的增高也逐渐产生振动变形。经DASP测试系统现场振动监测表明,数值模拟结果与现场测试结果吻合良好。该结论可为高扬程泵站压力管道避振、减振优化设计提供技术支撑,也为同类泵站工程的更新改造设计和安全运行提供理论依据。     

尾矿坝土工席垫三维有限元模拟及效果分析

为了快速有效地降低尾矿坝浸润面,结合某尾矿坝加高扩容工程,根据其初期排渗系统已部分失效的现状,拟定了后期扩容加高中土工席垫的排渗布置措施,为简化计算,建立包含土工席垫及其排渗管的尾矿库精细准三维渗流有限元分析模型及等效渗流分析模型,研究了土工席垫的等效模拟方法及相应的等效渗透系数,并将简化成果应用于尾矿坝全库整体模型的三维渗流计算分析,模拟土工席垫排渗措施的排渗效果,并研究其部分失效工况的尾矿坝渗流场。结果表明,采用土工席垫排渗措施后,可增大浸润面埋深,有效控制浸润面;土工席垫部分失效后,排渗效果稍微减弱,建议土工席垫由铺设3排改为铺设4排,其余保持不变,以更好地保证尾矿坝渗流稳定性。     

细砂管涌破坏试验及渗透变形分析

建立颗粒孔隙通道物理模型对渗流场中的颗粒进行力和力矩的平衡分析,以判断颗粒的运动状态;通过室内方形玻璃槽渗透破坏试验,从细观角度观察颗粒的起动和移动轨迹,通过各级水头下流量的变化、渗漏通道发展过程中涌砂量的变化、流速随水力梯度的变化及孔隙水应力的变化对颗粒迁移、渗漏通道发展过程的影响进行了分析,并将临界水力梯度的理论值与试验值进行比较,两者吻合度较高。     

乌塔沟分洪道试验段堤防渗流场分析与渗控研究

基于稳定饱和渗流基本理论,采用等效连续介质模型建立了乌塔沟分洪道试验段有限元模型,分析了试验段堤体及周围土体的渗流特性和渗透破坏情况,提出了渗流控制措施并进行了比较。计算结果表明,选取经济可靠的防渗措施可确保堤防安全度汛。