基于TOUGH2和FLAC3D的水-气二相流-固耦合模型

要实现饱和-非饱和土体的水-气二相流-固耦合作用的数值模拟,关键是如何实现渗流场与应力场的耦合,目前,松弛耦合方法不仅精度能够满足一般的工程要求,而且求解方法易于实现,是多相流-固耦合问题研究的主要方向。本研究根据松弛耦合原理,利用TOUGH2/EOS3来模拟水-气二相渗流过程;利用FLAC3D来模拟土体变形;基于水-气二相渗流过程与力学过程的相互影响,给出饱和度-密度、孔隙水压力和气压力-有效应力、体积应变-孔隙率、孔隙率-固有渗透率,以及孔隙率-毛细压力等状态变量之间的耦合关系式;利用C++控制TOUGH2、FLAC3D在流固耦合过程中的有序运行并利用耦合关系式传递相关状态变量,以实现对水-气二相流-固耦合作用的模拟。利用该模型对一现场压气试验进行模拟,通过模型计算值与实测值的对比,验证了模型的准确性和有效性。     

An erosion-based model for abrasive waterjet turning of ductile materials

This paper presents an attempt to model the abrasive waterjet (AWJ) turning process considering material removal from the circumference of a rotating cylindrical specimen. The methodology involves the use of Finnie's theory of erosion to estimate the volume of material removed by the impacting abrasive particles. The proposed model considers the impact of jet at an angle to the workpiece surface to account for the curvature of the workpiece. Unlike earlier works, this model considers the continuous change in local impact angle caused by the change in workpiece diameter. The flow stress of the workpiece material is determined using a novel experiment involving the same abrasive and workpiece materials. The adequacy of the proposed model is examined through AWJ turning tests under various process parameter combinations. The final diameters predicted by the model are found to be in good agreement with the experimental results.     

湖泊水力调控对河湖连通伴生洪水风险的缓释影响

河湖水系连通是国家治水、用水的重要战略手段,复杂的河湖连通工程往往伴随着系列风险,其中如何量化评估湖泊水力调控对河湖连通风险的影响,有待深入研究.本文利用Vine Copula函数与水动力模型模拟技术,以沂沭泗水系下游河湖连通工程为例,研究了不同洪水重现期下,骆马湖水力调控对河湖连通伴生洪水风险的定量影响.结果表明,发...     

冲击荷载下大型箱涵输水安全性的数值分析

冲击荷载对大型箱涵输水安全的影响是工程界关注的重要问题,其研究涉及到冲击荷载传播、土～结构物～水相互作用等诸多方面。采用数值分析技术,土与箱涵之间设置接触面单元,水体采用任意拉格朗日欧拉法描述,采用罚方法模拟水与箱涵相互作用,研究了爆炸冲击荷载对大型箱涵输水安全性的影响。研究结果表明： ALE法可以较好揭示土中爆破对输水情况下钢筋混凝土结构物的影响;输水情况下水体能传递荷载到箱涵中墙上,并缓冲冲击荷载对边墙的过大影响,可改善结构整体安全性;有压输水情况对结构物安全影响最为明显。     

基于XFEM的强震区砼重力坝开裂与配筋抗震措施研究

已有震害表明,混凝土坝遭遇强烈地震将不可避免地产生开裂。扩展有限元法（XFEM）通过在相关节点的影响域上富集非连续位移模式,使得对非连续位移场的表征独立于单元边界,可以有效描述混凝土中的裂纹扩展。基于扩展有限元模型,采用合理的地震波动模型对国内某混凝土重力坝强震下的动力破坏过程进行了分析;针对大坝破坏情况,应用嵌入式滑移模型模拟了混凝土重力坝配筋前后的地震响应和破坏状况,据此评价局部配筋的抗震效果。研究表明,局部配置抗震钢筋虽无法防止裂缝的发生,但可有效限制坝体裂缝的开裂扩展范围及深度,减少裂缝的开度,有效改善坝体的抗震性能。     

软土地区盾构法隧道施工三维数值模拟

本文采用三维有限元方法,考虑软土的固结作用和隧道开挖与周边建筑物变形的相互作用,对隧道施工的全过程进行数值模拟,分析盾构法隧道施工对周边建筑物的影响。数值计算结果表明:在考虑流固耦合的条件下,盾构法隧道开挖时3~4倍洞径范围内的土体变形可能会超过土体位移的规范规定值,施工中应加强该距离范围内的土体和周边建筑物的监测;盾构法仅对开挖掌子面处附近局部区域的孔隙水压力有影响,说明软土地区盾构法隧道施工对地下水的扰动很小;通过监测数据与计算值的对比分析可以得出,典型监测点的变形规律与监测规律相同,说明在工程条件相似的软土地区采用数值模拟对盾构法隧道施工进行预测和仿真分析是可行的,具有一定的工程参考价值。     

Double-shear tests of high-strength structural bolts at elevated temperatures

The behavior of high-strength structural steel at elevated temperatures, especially under shear loading, is not well established in the literature. This paper presents results from recently conducted tests on high-strength structural bolts subject to double shear loading at elevated temperatures. The parameters varied between tests included the bolt grade, bolt diameter, and temperature. Bolt grades A325 and A490 were tested. For each bolt grade, three different diameters were tested (19 mm (3/4 in), 22 mm (7/8 in), and 25.4 mm (1 in)) at five different temperatures (20 °C, 200 °C, 400 °C, 500 °C, and 600 °C). At least three tests were conducted for each combination of parameters. Degradations in the mechanical and material properties including stiffness, strength, and deformation at fracture, are characterized and presented herein. The results from these experiments fill a critical knowledge gap currently present in the literature regarding the behavior of high-strength structural bolts under shear loading at elevated temperatures. These data will ultimately provide a thorough understanding of the overall behavior of structural steel systems under realistic fire loading by clarifying the (i) shear behavior of high-strength structural steel bolts at elevated temperatures, and (ii) degradation in the mechanical and material properties of high-strength steel bolts with increasing temperatures.     

基于 Z-numbers 模糊数的改进 PROMETHEE 法

针对评价值为模糊数的工程方案优选问题,通过 Z-numbers 模糊数方法建立模糊评价矩阵,考虑了各决策主体的可靠程度,将模糊推理引入 PROMETHE 方法,对方案进行优先排序。运用 Matlab 的模糊推理系统工具箱构建模糊规则模型,计算每两对方案的差别度,采用模糊语言评价代替优先函数的选择,得到各方案在不同属性下的优先指数,并根据综合优序级别值对各备选方案进行排序,获得最优方案。最后通过一个工程案例进行计算和分析,证明了该方法对工程方案优选问题具有良好的实践价值。     

距离势离散单元法

 势函数离散单元法在接触力计算中存在势函数物理意义不明确、接触力计算与客观实际不符等重大缺陷。在已有研究的基础上,提出一种新型任意形状块体距离势离散单元法。该方法将势函数定义为接触体间归一化的距离函数,可以客观衡量单元间的嵌入程度,具有明确的物理意义,真实反映单元的接触刚度,使法向接触力计算更为合理。此外,新方法重新定义了切向方向矢量,提出切向接触力计算方法。新方法保留原势函数法所有优点,同时完善接触力计算受单元形式影响的不足,并突破三角形单元的限制,能够应用于任意凸多边形单元。通过若干算例说明新方法的正确性和有效性,可用于精确描述复杂非连续介质的运动过程。     

Numerical study on lateral buckling of fully bonded sandwich pipes

Sandwich pipes (SP) are promising subsea pipelines for deep-water applications. Thus, their lateral buckling response is a significant design aspect. The temperature field of SP denotes the load in lateral buckling analysis, and it is calculated using the heat transfer differential equation in this study. A general temperature field formula is proposed for an arbitrary multilayer SP, and this formula is verified by finite element models. Another finite element model based on the fiber shell element is then constructed to investigate the lateral buckling response of SP. They are validated by existing experimental and numerical results. The evolution of the lateral buckling profiles and of stress distribution are studied in consideration of nonlinear pipe-soil interaction and nonlinear material constitutive law. Moreover, the influence of initial imperfections and pipe-soil interaction on lateral buckling response is examined. Finally, a formula is approximated for a SP with a half-wave sinusoidal imperfection profile on the basis of dimensionless analysis and numerical results. This formula is convenient for engineering applications.