WAVE INTERACTION WITH PERFORATED CAISSON BREAKWATERS

The reflection coefficient of perforated caissons and the total horizontal forces acting on them were experimentally and numerically analyzed and discussed when wave propagates normally. To consider the viscosity effect of fluid and nonlinear action of waves on structures, the VOF (Volume Of Fluid) method combined with the k-ε turbulence model was used to simulate the interaction between waves and structures. Governing equations were solved with the finite difference method. Through 2D experimental study in the wave flume, the empirical relationship between the reflection coefficient of perforated caissons and the main affecting factors were obtained from the experimental data using the least square method. Also the correlation between the ratio of the total horizontal force acting on perforated caisson and the force acting on solid caisson and the main affecting factors were regressed from the experimental data.     

Optimal design of gating systems by gradient search methods

A numerical optimization technique based on gradient-search is applied to obtain an optimal design of a typical gating system used for the gravity process to produce aluminum parts. This represents a novel application of coupling nonlinear optimization techniques with a foundry process simulator, and it is motivated by the fact that a scientifically guided search for better designs based on techniques that take into account the mathematical structure of the problem is preferred to commonly found trial-and-error approaches. The simulator applies the finite volume method and the VOF algorithm for CFD analysis. The direct gradient optimization algorithm, sequential quadratic programming (SQP), was used to solve both a 2D and a 3D gating system design problems using two design variables. The results clearly show the effectiveness of the proposed approach for finding high quality castings when compared with current industry practices.     

空泡溃灭水锤的VOF计算方法

空泡溃灭水锤是核电厂冷却循环系统中较常出现的一种严重的水锤事故。空泡的形成和溃灭是复杂的两相、瞬态过程，对于这一现象的分析是相当困难的。作者尝试着把蒸汽泡的边界看成是冷水流动的自由面，在自由面上考虑蒸汽的凝结。对于自由面的ＶＯＦ算法用了ＶＯＦ算法，取得了令人满意的结果，不仅形象地描绘了空泡的形成和溃灭的过程，而且得到了与实验相符的空泡溃灭高压和弥合速度，因此可为管道设计提供理论基础。     

快速闸门断流的轴流泵起动过程三维数值模拟

针对轴流泵机组起动过程的研究是泵站安全稳定运行研究的重要环节。为了准确捕捉轴流泵机组在起动过渡过程中的动态特性,建立轴流泵机组的全流道三维模型,采用三维CFD计算软件Fluent,利用基于有限体积法的动网格技术,配合VOF多相流模型对快速闸门断流的轴流泵机组起动过程进行了三维瞬态数值模拟,获得了轴流泵机组起动过渡过程中的流态变化及外特性参数的变化规律。闸门开启时间为60s时,机组起动扬程在12s时达到最大值2.76m,为运行扬程的1.28倍。减小快速闸门开启时间能够降低机组最大起动扬程,但同时会加剧回流及闸门处的水流撞击。计算结果表明:动网格技术结合VOF多相流模型可以较好的应用于快速闸门断流的轴流泵机组起动过渡过程数值模拟中,其结果可为泵站水力设计及轴流泵机组的过渡过程研究提供参考。     

单体与三体高速船舶粘性流场数值模拟

为了检验CFD在船舶粘性流场计算中的有效性,基于RANSE方法,对单体船型DTMB 5415和三体船FA1粘性流场进行了数值模拟.自由面处理采用VOF方法,湍流模型选用SSTk-ω模型,计算结果与试验数据进行了比较,在傅汝德数不是很高时吻合较好.计算结果表明,CFD可以用来研究复杂船型流动问题,对于阻力、伴流等重要的水动力参数,CFD能够给出与试验相一致的结果;同时VOF方法可以比较好地捕捉船舶自由面波形,对于三体船,计算结果能够清晰地反映出主体和侧体之间强烈的兴波干扰现象,可以为船型优化提供重要的参考.     

无挡板搅拌槽内的自由表面湍流流场研究

基于VOF多相流模型,建立了自由液面搅拌流场的数值模型和模拟方法。以偏心和无挡板中心搅拌槽为例,分别使用标准k-ε模型和分离涡模型研究了搅拌槽内流体的时均速度分布,发现数值模拟结果与实验结果吻合较好,仅略低于实验值。整体而言,使用分离涡模型时模拟结果与实验值之间的误差不超过12%,而k-ε模型的模拟精度则较差。研究结果表明,分离涡模型和VOF模型相结合,能很好地模拟搅拌槽内流体的自由液面流动特性。     

涌潮冲击排桩式丁坝的数值模拟

为了研究钱塘江排桩式丁坝在涌潮作用下的受力机理,对涌潮冲击排桩式丁坝进行了数值模拟,采用标准κ ε紊流模型和体积函数法(VOF)追踪自由水面的方法,得出了丁坝附近的流场分布和自由水面的位置,揭示了丁坝上的涌潮压力在时间和空间上的变化规律：（1）当涌潮冲击丁坝时,涌潮压力急剧增大,约2 s后涌潮压力达到最大值,之后,有一段下降的过程,随后出现较小幅度的振荡,最后涌潮压力趋于稳定,并且在垂直方向上各高程处的涌潮压力最大值基本出现在同一时刻;（2）在潮前水位以上丁坝上的涌潮压力呈梯形分布,而在潮前水位以下丁坝上的涌潮压力随深度基本保持不变,呈矩形分布.     

围油栏形状优化的数值模拟

文中对传统围油栏进行形状优化,应用流体体积分数法(VOF),数值模拟优化后的围油栏对两种不同粘度油类拦油效果;通过分析、比较拦油失效速度、失效时间以及围油栏失效前的栏前受压,说明围油栏形状优化的可行性,以提高围油栏的拦油性能。     

THREE-DIMENSIONAL NUMERICAL SIMULATION OF AERATED FLOWS DOWNSTREAM SUDDEN FALL AERATOR EXPANSION-IN A TUNNEL

Air entrainment is known to be one of efficient and inexpensive methods to prevent cavitation damages in hydropower projects.The shape of sudden expansion-fall is used as a common device for mitigating cavitation erosions.The complex flow patterns with cavitation are numerically simulated by using the realizable k-εturbulence model and the air-water mixture model.The calculated results are compared well with the experimental results as well as those obtained with the k-εturbulence model with the Volume Of Fluid(VOF)Model.The calculated results agree well with the experimental data for the aeration cavity and wall pressure.Moreover,the air concentration near sidewall is simulated by a mixture model.It is found that the mixture turbulence model is superior to the VOF turbulence model.     

基于铀的激光氮化机理研究和数值模拟

针对工件铀的表面激光氮化工艺,考虑铀的固-液相变过程中各物理参数随温度的变化,结合计算流体软件FLUENT中流体体积函数(VOF)模型计算气-液相界面处的降膜解吸传质过程。进行了铀的瞬态激光氮化传热传质耦合数值仿真,仿真分析研究了不同工艺参数下瞬态温度场和流场的分布,同时获得渗氮量在铀表面和深度上的分布。分析结果表明,因激光局部加热引起的表面张力梯度导致的Marangoni对流对铀表面氮化过程中的传热和传质有很大的影响。其中渗氮量在不同工艺参数下的数值结果与试验结果相吻合,验证了数值模型的可行性,为激光氮化的理论分析和工艺指导提供了理论和方法。