平面二维溃坝水沙输移动床数学模型研究

为数值模拟溃坝洪水作用下泥沙输移及河床变形,建立了无结构三角形网格的平面二维水沙耦合数学模型。水动力学模型采用浑水流动方程,考虑了泥沙输移及床面冲淤变化对水流动量的影响;泥沙输移采用不平衡泥沙输移模式。模型数值计算格式采用守恒性较好的有限体积法,单元界面的对流通量采用基于近似黎曼解的Roe格式计算,扩散通量采用中心格式,不平衡泥沙输移方程采用坡度限制的二阶空间精度格式离散。模型经经典算例和小尺度瞬间全溃的动床实验资料检验,水面、床面及流速等计算结果与实验资料或解析解等比较吻合,分析了动床与定床水面及洪水传播速度的差异。在上述检验的基础上,采用动床模型对某河道型水库溃坝诱发的水沙运动进行了数值模拟,结果表明溃坝洪水下水流、泥沙及河床变形发生强烈的相互作用,采用水沙及河床变形耦合的数学模型是必要的。     

回归应力场下的大型地下岔管围岩稳定及衬砌结构分析

根据实测点反演研究区域的初始应力场是地下洞室围岩稳定性分析的首要工作。采用有限元模拟中常用的多元线性回归与逐步回归相结合的方法,结合某水电站地下尾水岔管段区域地形地质条件回归得到初始应力场,并在较准确的回归应力场下,研究该大型地下岔管在完建、运行和检修工况下衬砌厚度对围岩稳定及衬砌结构本身的影响,提出较合理的支护措施。     

龙门山区小流域降雨产流数值模拟研究

龙门山区小流域常由暴雨引发山洪泥石流等灾害,但由于数据的缺乏而无法明确其产流机制及发展过程.本文选取四川省龙溪河地区的山区小流域碱坪沟作为研究区域,利用基于物理概念的模型InHM对该流域的降雨产流过程进行分析.与实测流量数据的比较表明该模型在碱坪沟流域有较好的适用性.基于模拟结果分析了该流域土壤含水率以及地表/地下交换水量(入渗/出渗)在产流过程中的分布特征,结果表明:(1)土壤含水率以及地表/地下交换水量(入渗/出渗)在流域内不同位置分布不均匀;(2)在河道周边,Dunne产流机制占主要地位;(3)出渗常发生在河道周边;(4)流域内存在地下径流,且在总径流中占较大比例.该研究证实了InHM模型在西部山区小流域水文模拟中的适用性,也加深了对碱坪沟流域产流机制的了解,进而有助于明确该地区山洪泥石流灾害的产生机制.     

钢筋混凝土构件细观数值模拟分析

在混凝土材料细观力学分析模型的基础上,提出了一种钢筋混凝土构件非线性力学特性分析的细观数值方法。使用这种细观力学方法对轴压加载作用下某一钢筋混凝土柱的损伤破坏过程及宏观力学特性进行了数值模拟研究,并与试验结果和宏观力学模型方法分析结果进行了对比。研究表明：（1）细观尺度上,采用细观力学模型获得的钢筋混凝土柱的破环模式及宏观力学性能均与试验结果吻合良好,验证了本文细观力学方法的有效性和准确性;（2）相比于宏观尺度分析模型,细观力学模型考虑了混凝土的非均质特性,从而更真实地揭示了钢筋混凝土柱的破坏过程及破坏模式,且计算结果与试验结果对比也更为吻合。     

预应力锚索内锚段有限元精细化模拟

预应力锚索加固作为岩土工程的一种主要加固技术已得到日益广泛的应用,但现有的预应力锚索数值模拟方法却不能很好地反映其实际加固效果。针对预应力锚索内锚段模拟存在的难点问题,提出用精细化有限单元法进行模拟。该算法最突出的特点是详细地描述了钢绞线、砂浆和接触面等细部结构。算例表明,这种方法是合理和有效的,内锚段轴向位移和应力沿钢绞线方向由外到里呈指数性衰减。     

某水电工程坝肩边坡碎裂岩体强度参数反演研究

针对藏区某水电工程边坡存在大范围多区域碎裂岩体的特点,为求得岩体强度参数,对其逐一进行反分析。在分析其中某一区域的碎裂岩体时,先假设其他碎裂岩体强度较高,进行滑带搜索计算,直到滑带发生转移且安全系数满足实际要求,最后得出满足一定条件下的凝聚力与内摩擦角的线性关系。利用此线性关系,并结合工程实际,最终确定了较为合理的参数组合以供工程设计使用。     

A NEW NUMERICAL WAVE FLUME COMBINING THE 0-1 TYPE BEM AND THE VOF METHOD

A new coupling numerical wave model, based on both the Boundary Element Method (BEM) and the Volume Of Fluid (VOF) method, is established by taking advantages of the both methods to solve the wave-structure interaction problems. In this model, the wave transformation in front of structures is calculated by the 0-1 type BEM, and the intense wave motions near the structures are calculated by the VOF method. In this paper, the characteristics of the BEM and the VOF method are discussed first, and then the coupling treatments are described in detail. In the end, the accuracy and the validity of the coupling model are examined by comparing the numerical results with experiment results and other numerical results available for the interactions between regular waves with a monolayer horizontal plate.     

NUMERICAL SIMULATION OF THE HYDRODYNAMIC PERFORMANCE OF AN UNSYMMETRICAL FLAPPING CAUDAL FIN

A comprehensive numerical simulation of the hydrodynamic performance of a caudal fin with unsymmetric flapping motion is carried out. The unsymmetrical motion is induced by adding a pitch bias or a heave bias. A numerical simulation program based on the unsteady panel method is developed to simulate the hydrodynamics of an unsymmetrical flapping caudal fin. A CFD code based on Navier-Stokes equations is used to analyze the flow field. Computational results of both the panel method and the CFD method indicate that the hydrodynamics are greatly affected by the pitch bias and the heave bias. The mean lateral force coefficient is not zero as in contrast with the symmetrical flapping motion. By increasing the pitch bias angle, the mean thrust force coefficient is reduced rapidly. By adding a heave bias, the hydrodynamic coefficients are separated as two parts: in one part, the amplitude is the heave amplitude plus the bias and in the other part, it is the heave amplitude minus the bias. Analysis of the flow field shows that the vortex distribution is not symmetrical, which generates the non-zero mean lateral force coefficient.     

NUMERICAL STUDY OF FLOW AROUND AN OSCILLATING DIAMOND PRISM AND CIRCULAR CYLINDER AT LOW KEULEGAN-CARPENTER NUMBER

In order to identify the influence of shape corners on the instantaneous forces in the case of oscillating bodies, the simulated flow field is compared for two kinds of cross sections: diamond prism and circular cylinder. For these two flow configurations, the same Reynolds number and a Keulegan-Carpenter are considered. To compute the dynamic flow field surrounding the body, the Navier-Stokes transport equations in a non-inertial reference frame attached to the body are considered. Hence, a source term is added locally to the momentum equation to take into account the body acceleration. The proposed model is solved using the PHOENICS code. For the oscillating circular cylinder, the simulated results are in good agreement with the experimental data available in the litterature. After validation of this proposed model, flow field for diamond prism is determined. For both bodies, the process of the vortex formation is similar, with the formation of a recirculation zone in the near-wake containing a symmetric pair of vortices of equal strength and opposite rotation. The length of recirculation zone varies approximately linearly with time. However, the in-line force coefficient of the oscillating diamond prism is found to be greatest, since the recirculation zone is longer compared with that of the oscillating circular cylinder.     

碾压混凝土在水压与机械荷载耦合作用下断裂数值模拟分析

碾压混凝土软弱层面的断裂破坏是碾压混凝土坝稳定性研究的一个重要的方面,本文考虑了碾压混凝土的多相非均匀性细观结构特征。采用RFPA分析系统对在水压与机械荷栽共同作用下,碾压混凝土水平软弱层面破坏的全过程进行了模拟分析。通过模拟。给出了碾压混凝土层面破坏过程的应力、弹性模量以及水压力的分布图,得到了起裂荷我、失稳荷栽以及临界裂缝扩展长度等参数。并计算得到了各种工况下碾压混凝土的双K断裂韧度,对碾压混凝土层面破坏过程进行了分析。结果表明。起裂韧度、失稳韧度都随着初始荷裁的增加而产生的变化有一定的规律性。