采用逐时递推同化技术修正伶仃洋外海边界水位

采用变分同化技术修正伶仃洋二维潮流场的外海水位边界条件。由于计算分辨率较高,使计算量大而无法储存所有时刻、所有空间的物理量,以至通常的变得同化技术变得不可行。本文根据修正外海边界条件的计算特点,提出了逐时递推同化的思路。只储存六小时的计算物理量,每次仅同化修正一个小时的水位边界,而后逐小时向前递推。以伶仃洋二维潮流场为算例,应用逐时递推同化技术修正外海水位边界条件,得到了令人满意的结果。     

大型泵站水锤防护措施选型研究

针对SJZ泵站流量大、扬程高、卧式泵组转动惯量小、输水管线长的特点,泵站突然失电,无防护情况下全管线负压严重。为满足水锤防护后任何工况最小压力均需大于+2 m要求,水锤防护难度很大。本文通过水泵出口不同止回阀—液控球阀、液控活塞阀、轴流式止回阀与管线中防护设置—单向调压塔、双向调压塔及空气罐等16种组合方案计算和比较,考虑水锤防护效果、防冻、占地面积及成本等多种因素,最终方案选用泵后轴流式止回阀、水锤消除罐和双向调压塔组合的水锤防护措施,有效的降低管道的水锤压力,各项指标均满足规范规定,达到了设计要求。     

FINITE ELEMENT ANALYSIS OF A VERTICAL RECTANGULAR PLATE COUPLED WITH AN UNBOUNDED FLUID DOMAIN ON ONE SIDE USING A TRUNCATED FAR BOUNDARY

The dynamic pressure distribution on a rectangular plate attached to a rigid wall and supporting an infinitely large extent of fluid subjected to a harmonic ground excitation is evaluated in the time domain. Governing equations for the fluid domain are set considering the compressibility of the fluid with negligibly small change in density and a linearized free surface. A far boundary condition for the three-dimensional fluid domain is developed so that the far boundary is truncated at a closer proximity to the structure. The coupled problem is solved independently for the structure and the fluid domain by transferring the acceleration of the plate to the fluid and pressure of the fluid to the plate in sequence. Helmholtz equation for the three-dimensional fluid domain and Mindlin's theory for the two-dimensional plate are used for the solution of the interacting domains. Finite element technique is adopted for the solution of this problem with pressure as nodal variable for the fluid domain and displacement for the plate. The time dependent equations are solved in each of the interacting domain using Newmark-b method. The effectiveness of the technique is demonstrated and the influences of surface wave, exciting frequency and flexibility of the plate on dynamic pressure are investigated.     

NUMERICAL SIMULATION OF LEVEE BREACH FLOWS UNDER COMPLEX BOUNDARY CONDITIONS

Levee or dam failure can cause a significant disaster in most cases. A good prediction of the flood process especially in a real complex terrain is necessary for working out emergency plans for levee or dam breaches. Numerical simulations of levee or dam breach flow were carried out often with constant flow parameters and in relatively simple channels rather than in natural rivers with complex boundaries. This article presents our dedicated studies on the 2-D numerical model of levee or dam breach hydraulics with finite difference schemes. The good performance of the model is demonstrated by comparisons with the theoretical solution of an idealized dam-break flow over a frictionless flat rectangular channel. The model is also validated through its stability and conservation properties. The model is applied to simulate the flood propagation under complex boundary conditions, and the unsteady flood process in a river and in the dry floodplain with a complex bed terrain simultaneously. Furthermore, with respect to engineering practice, the numerical solutions can give special guidance to the effects of parameters such as the flood depth at different sites and the inundated area at different time periods after the levee breach and the travel time of the flood waves, which may be very important for practicing engineers in an efficient flood management.     

LBM的一种新的边界处理方法

近年来,LBM取得了长足的进展,理论和应用方面都有了新的突破,各种新的模型和边界处理方法不断被提出.在这些边界处理方法基础上,本文提出了一种新的边界处理方法,该方法是用邻点和次邻点的宏观值二阶插值得到边界上的宏观值,再用邻点的分布函数的非平衡部分来外推得到边界处的分布函数.此方法可用于压力边界或速度边界,具有二阶精度,采用该处理方法对Poiseuille流、Couette流和Cavity流进行了数值模拟,并与其他几种边界处理作了比较,其结果要好于其他几种边界处理.     

改进的非线性波传播数值模型的验证和应用

基于吸收入射边界上反射波的方法,并通过将统一边界条件表达式推广到适应不规则波的情况,改进了非线性波传播的数值模型.将利用模型的线性版本(略去非线性项)所计算得到的台阶地形上波浪的反射和透射系数与相应的解析解进行了定量比较.在斜坡地形上数值模拟了不规则波的传播,并将数值结果和物理模型实验值进行了比较.在下游边界分别为开边界和全反射边界的等水深的水槽内数值模拟了不规则波的传播变形,讨论了非线性作用的影响.在侧边界和下游边界均为全反射的固壁边界、二维的等水深水域内,数值模拟了波浪斜向入射时所产生的波浪变形.计算结果表明,对上述各种算例,改进后的非线性波传播数值模型均能进行有效地数值模拟.     

掺气坎空腔回水问题分析

以研究空腔回水的重要性为出发点,概述空腔回水的危害、掺气坎空腔回水的影响因素及目前解决空腔回水的一些措施.提出在研究空腔回水的过程中,可始终围绕来流条件与边界条件两大前提,由"果"追"因",以达到高效减轻回水的目的.     

增材制造技术中的流固耦合度影响因素

对流固界面的耦合程度为增材制造技术带来的挑战进行报道.以流体柱体外围绕无限远各向同性固体模型为基准,在角频率—波数域建立流体满足的声波方程、固体满足的弹性波方程和流固耦合边界条件.引入流固耦合度这一概念,导出法向位移断续、法向应力断续、切向应力为零的流固界面不完全耦合边界条件,考察不同中心频率的单极子声源在模型中激发的...     

论非均匀悬移质二维不平衡输沙方程及其边界条件

本文深入研究了非均匀悬移质不平衡输沙的内在机理，较严格的推导了其方程，引进和定义了水量百分数、悬移质级配、平均沉速。根据泥沙交换强度理论，专门研究了方程的底部边界条件，在一定简化下给出了底部边界条件的具体表达式及有关结果，并与以往经验数据基本符合。     

1960年以来渭河下游河道的自动调整作用

1960年以来,渭河下游河道来水来沙条件和边界条件都发生了较大的变化,河道纵横剖面形态针对这些变化进行了相应的调整,通过分析河相关系、主槽面积、河底高程以及弯曲系数的调整规律,对渭河下游河道的自动调整作用进行了研究。