强度折减法在滑坡稳定性分析中的应用

沁水县侯村煤矿边坡处治后,I~III段使用良好,IV段抗滑挡墙失效。本文采用有限元强度折减法计算,强度指标比原定的降低了1.29倍。同时,在折减过程中,通过计算分析剪应力集中部位,确定滑面是在老滑面的基础上发展的部分新滑面,形成新的剪出口。利用折减后强度参数,计算对比新滑面与次级滑面的滑坡推力,认为挡墙破坏为新滑面推力过大所致,与原设的“次级滑面为最危险滑面”情况不符,计算结果与实际情况较吻合。     

Full-scale experimental modal analysis of an arch dam: The first experience in Iran

Forced vibration field tests and finite-element studies were conducted on the Shahid Rajaee concrete arch dam in Northern Iran to determine the dynamic properties of the dam–reservoir–foundation system. The first forced vibration tests on the dam were performed with two different types of exciter units, with a limited maximum force, bolted on the dam crest for alternative in-phase and out-of-phase sequencing. Because of an insufficient number of recording sensors, two arrangements of sensors were used to cover sufficient points on the dam crest and one gallery during tests. Two kinds of vibration tests, on–off and frequency sweeping, were carried out on the dam. The primary natural frequencies of the coupled system for both symmetric and anti-symmetric vibration modes were approximated during on–off tests in two types of sequencing of exciters, in phase and out-of-phase, with a maximum frequency of 14 Hz. The principal forced vibration tests were performed at precise resonant frequencies based on the results of the on–off tests in which sweeping around the approximated frequencies at 0.1 Hz increments was performed. Baseline correction and suitable bandpass filtering were applied to the test records and then signal processing was carried out to compute the auto power, cross power and coherence spectra. Nine middle modes of vibration of the coupled system and corresponding damping ratios were estimated. The empirical results are compared against the results from calibrated finite-element modeling of the system using former ambient vibration tests, considering the dam–reservoir–foundation interaction effects. Good agreement is obtained between experimental and numerical results for eight middle modes of the dam–reservoir–foundation system.     

黄河上游某电站近坝滑坡稳定性研究

黄河上游某电站库首滑坡距大坝仅400多米,一旦失稳将会对大坝造成严重危害。笔者采用工程地质分析法及有限元数值模拟研究了滑坡的成因机制及应力场特征,在此基础上采用极限平衡法演算了滑坡在各种工况下的稳定状况。表明滑坡在蓄水过程中有可能产生下滑失稳。     

考虑饱和-非饱和渗流、温度和应力耦合的三维有限元程序研制

在探索多场耦合理论基础上,研制出了一个考虑饱和-非饱和渗流场和温度场对应力场作用的三维弹塑性有限元程序,该程序采用了以下简化假设：不考虑力学过程和渗流过程对温度场产生的影响,而只考虑变温对力学过程产生的影响;不考虑力学过程和温度场对渗流场产生的影响,而只考虑渗流场对力学过程产生的影响。经与弹性力学解析解对比,验证了该程序计算结果是合理的。     

A nonlinear PDE formulation for offshore vessel pipeline installation

In this paper a nonlinear dynamic PDE formulation for a pipe string suspended from a pipelay vessel to the seabed in a pipelay operation is developed. This model extends a three-dimensional beam model capable of undergoing finite extension, shearing, twist and bending, to apply for marine applications by adding the effects of restoring forces, hydrodynamic drag and seabed interaction. The model is validated against the natural catenary equation and the FEM code RIFLEX. The model is extended to include the pipelay vessel dynamics by applying a potential theory formulation of a surface vessel, suited for dynamic positioning and low speed maneuvering, as a boundary condition for the PDE. This system is found to be input-output passive and stable. Pipeline installation applications where the presented model is suited are e.g., analysis and simulation of the installation operation, operability analysis, hardware-in-the-loop (HIL) testing for vessel control systems, and automation of the pipelay operation.     

某边坡变形破坏机理的数值分析

某花岗岩矿岩土体主要有填土、粉质粘土、淤泥及淤泥质土、含泥中粗砂、粘土、残积砂质粘土,其下为花岗岩基岩。边坡最大高度75m,其中残积土层以上的土质边坡高度约50m。本文运用有限元强度折减法对该边坡的稳定性进行了研究,得出了潜在的破坏模式及各个滑动部分的安全系数。分析结果表明,本边坡存在3个潜在滑动面,其中两个为浅层滑动面,另一个为深层滑动面。两个浅层滑动面的稳定系数在1.13～1.17,处于临界状态。深层滑动面稳定性系数在1.29,目前尚处在相对稳定状态。根据分析结果,提出了如下加固措施:（1）对滑坡体进行削坡处理;（2）在其滑动面下方设置抗滑台阶;（3）采用预应力锚索框架梁结合肋柱进行加固处理。     

Direct scantling assessment of propeller blades

Traditionally, propeller design has been focused on all activities necessary to obtain a propeller featuring a high efficiency, avoiding erosive cavitation for given operating conditions and having adequate structural strength. In recent years, more and more challenging requirements have been imposed, such as the reduction of radiated noise and pressures pulses, requiring more precise analyses and methods in the optimization of the propeller performance. On the other hand, the evaluation of the propeller strength still relies on simplified methods, which basically consider the blade as a cantilever beam subjected to characteristic static forces. Since the loads acting on a blade are variable in the blade revolution and in different operating conditions throughout the ship life, a procedure to account for the influence of fatigue phenomena is proposed. The fatigue assessment could reduce the safety factor in the propeller scantling rules and allow improving the quality of propeller design (e.g. obtaining higher efficiency, margin on cavitation phenomena, less noise).     

方钢管混凝土柱-钢梁平面框架耐火性能研究

建立了局部火灾下多层多跨矩形钢管混凝土柱-钢梁平面框架温度场和力学性能分析的有限元模型。在考虑楼板影响的基础上,研究了保护层厚度不同时钢管混凝土框架结构的温度场分布规律。研究了不同受火工况条件下钢管混凝土框架结构的变形和破坏规律、耐火极限状态、受火梁的内力状态以及结构耐火极限的规律。分析表明,梁保护层厚度影响钢梁温度分布形式;火灾下,框架结构发生了受火梁的整体屈曲破坏。     

汶川地震震前龙门山以西地壳垂直隆升机理分析

结合流动GPS观测速度场及层析成像结果,构建跨龙门山断裂剖面的二维有限元分层模型,分两种情况讨论汶川地震前龙门山前缘地壳垂直隆升的物理机制,以及中、下地壳软物质垂向和横向的不均匀性对地壳隆升作用的影响。分析认为：川西高原相对四川盆地的差异抬升和龙门山以西地壳缩短的共同作用是汶川地震震前龙门山前缘地壳垂直隆升的可能原因。     

移动荷载作用下土岩组合基坑吊脚桩变形分析

以青岛地区特有的土岩组合地质条件为背景,采用现场监测和Plaxis有限元模拟相结合的方法,研究了土岩基坑中吊脚桩在龙门吊移动荷载作用下的变形规律及动力响应。结果表明：桩身变形模拟结果与实测值吻合较好,基坑的变形主要发生在基坑上部软弱土层,吊脚桩嵌岩处产生应力集中;在龙门吊移动荷载作用下,桩顶水平位移较大,但其动力响应最小,而嵌岩处水平位移较小,但其动力响应最大;嵌岩处、桩身最大正弯矩处及最大负弯矩处的土压力动力响应较大,且移动荷载刚经过时刻影响最大。研究成果可为类似土岩结合地区深基坑支护设计提供参考。