基于RANS法和边界层理论预报三维船体阻力

基于船体阻力成因和分类,应用二因次RANS法并结合EFD技术为研究手段,研究了船体各阻力成分和兴波波形,考虑边界层第一层网格高度对数值计算结果的影响,通过数值模拟计算和兴波波形比较,分析表明第一层网格无量纲高度y+值充分影响数值结果精度,总阻力在高傅汝德数下其数值误差有增大趋势,同一航速下摩擦阻力值随y+增加略微增大,剩余阻力值却明显减少,且自由面兴波随傅汝德数增大首部波高愈发明显,船中及尾部区域兴波向外扩散,船首尾肩部开尔文波系明显且波峰后移,其趋势与EFD波形一致,具有实用性。     

结合亚格子模型的Lattice-Boltzmann算法

介绍一种亚格子模型与LB(Lattic-Boltzmann)方法相结合的算法,并用其对亚临界雷诺数情况下的圆柱绕流问题进行数值模拟,得到流场的流线图以及圆柱表面的压力系数。通过与实验值相比较,发现数值结果与实验值是比较吻合的,证明该算法可以用于计算雷诺数较大的流体问题,同时具有LB方法计算效率高的优点。     

具有自由液面效应的圆柱绕流三维数值模拟

基于计算流体力学软件CFX、应用RNG k-ε湍流模型、结合流体体积法(VOF法)模拟均匀流场中半沉浸三维圆柱运动,分析自由液面对圆柱尾迹以及圆柱表面水动力特征参数的影响。结果表明:在自由液面流场中,雷诺数较高时,自由液面对流场流动的影响较小;而雷诺数一定时,自由液面对流场的影响随着傅汝德数的增加而增加;在自由液面作用下,圆柱的时均阻力系数和时均压力系数随流场的傅汝德数和雷诺数的增加而减小。     

基于SHIPFLOW的KCS船型兴波阻力数值计算

本文以韩国船舶与海洋工程研究所(KRISO)的集装箱船标模KCS为研究对象,利用CFD软件SHIPFLOW对其进行兴波阻力性能数值模拟,比较网格质量、傅汝德数对兴波阻力性能计算结果的影响。结果表明:傅汝德数相同,网格质量不同时,计算结果不同;网格质量相同,傅汝德数不同,计算结果与实验值有所差异,但是总体趋势与实验值较为一致。本文对不同网格质量、不同傅汝德数下的KCS船型作了兴波阻力的数值模拟,模拟结果具有一定可靠性,为基于兴波阻力的船型优化提供兴波阻力性能数值计算支撑。     

双层流体中浮箱拖航阻力的实验研究

在密度分层的双层流体中进行浮箱拖航的物理模型实验,通过改变拖航速度v、吃水深度b以及分界面位置研究浮箱阻力变化特点及规律。实验结果表明:单双层拖航阻力差值Fsd及阻力系数差值Csd随着拖航速度的增加,均呈现先增加后减小的变化趋势,且在分界面位置不变的情况下Csd达到峰值对应的内傅汝德数Fr极为相近,仅随吃水深度的增加略有减小;此外,当内傅汝德数Fr大于0.8时,阻力系数与吃水深度系数平方的比值大小只与内傅汝德数Fr有关,而与箱体的吃水深度无关。     

深V船型大型化应用分析

将深V船型应用于大型化高速船的实船设计中,采用非线性型线变换生成多样化的型线方案,运用势流CFD方法对各型线方案进行兴波阻力船型优化。通过相同主尺度及设计排水量条件下的船模阻力对比试验,验证了优化后的深V船型可以在保持高傅汝德数Fr阻力性能优势的同时,在低傅汝德数Fr时拥有与圆舭船型相当的阻力性能。运用切片理论对深V船型进行耐波性理论预报,并对预报结果进行耐波性试验验证。试验结果表明,切片理论适用于瘦长型深V船型的耐波性预报。     

基于多块结构网格的滑行艇巡航时流场研究

滑行艇是一种依靠动升力高速航行的船体,其流场复杂。为了捕捉滑行艇航行的流场特征,本文根据滑行艇的流场梯度变化建立合适的结构网格,采用RANS结合VOF方法对滑行艇不同航速的运动进行数值模拟,将不同体积傅汝德数下的滑行艇阻力的计算值与理论值和试验值进行对比,验证了数值方法的可靠性。详细分析了滑行艇航行的流场,包括水面兴波、方尾虚长度以及侧向喷溅现象。最后根据滑行艇的流场完整性,设计了外挂对转桨,并给出了自航滑行艇的流场特性。     

滑行艇升沉纵摇运动的二维数值预报

基于CFD软件对滑行艇二维简化模型在均匀来流中的运动响应进行数值分析。根据滑行艇的流体动力数值计算结果实时求解滑行艇的运动响应特性,对4种不同傅汝德数下滑行艇的纵摇与垂荡耦合运动特性进行研究,得到艇体升沉幅值、纵摇角随时间的变化特性,以及阻力、升力和力矩随傅汝德数的变化规律,并分析了艇体达到稳定状态所需时间和滑行过程中艇底动压力的变化特性。研究表明:傅汝德数1.5时达到稳定滑行状态的时间仅为80 s;除了在傅汝德数2.0时发生严重振荡,其余3种情况下滑行艇均能够趋于一种"动平衡"状态。     

低雷诺数圆柱绕流的大涡模拟分析

以二维圆柱为研究对象,采用大涡模拟的方法对圆柱绕流进行数值模拟。计算的雷诺数Re=400。计算结果能够清晰地反映卡门涡街的周期性脱落。通过对圆柱表面压力分布的深入探究,揭示圆柱尾流中产生周期性旋涡脱落的原因。研究结果中的阻力、升力呈周期性变化规律以及斯特劳哈尔数(St)都与前人实验结果较好吻合,说明大涡模拟能够对低雷诺数的圆柱绕流进行准确的模拟。     

海上平台支撑柱绕流特性的大涡模拟分析

海上平台是开采海洋资源的关键建筑,而支撑柱在平台中起着至关重要的作用。本文建立在海水作用下支撑柱做单圆柱绕流、串列双圆柱绕流和并列双圆柱绕流的二维流场模型,运用大涡模拟方法,对这3种模型进行数值模拟,得出其瞬时流场速度云图和圆柱受力特性曲线图。模拟计算层流和湍流情况下的圆柱绕流,通过模拟结果分析流场、升力系数和阻力系数的变化规律。     

基于CFD的三体船侧体布局优化

三体船构型复杂,侧体布局对其阻力性能有很大的影响。基于计算流体动力学(Computational Fluid Dynamics, CFD)理论,利用SHIPMDO-WUT软件平台构建一种侧体布局自动优化方法。以某高速三体船为例,进行侧体布局的优化,结果表明:在4个不同弗劳德数下,优化船较母型船的兴波阻力均有所下降,总阻力也相应减小。得出在4个不同弗劳德数下总阻力最小的侧体布局方案,表明该方法的可行性与有效性。研究内容可为三体船减阻优化设计提供参考依据。     

Comparison of CFD and EFD for the Series 60 C B= 0.6 in steady drift motion

 This paper presents comparisons of computational and experimental fluid dynamics results for boundary layers, wakes, and wave fields for the Series 60 C _B= 0.6 ship model in steady drift motion. The numerical method solves the unsteady Reynolds-averaged Navier–Stokes and continuity equations with the Baldwin–Lomax turbulence model, exact nonlinear kinematic and approximate dynamic free-surface boundary conditions, and a body/free-surface conforming grid. The experimental and computational conditions, i.e., Froude numbers of 0.16 and 0.316 for the experiments, and Froude numbers of 0 and 0.316 for the computations, allow comparisons of low and high Froude number results, respectively, which allows an evaluation of Froude number effects and validation of the computational fluid dynamics at both low and high Froude numbers. This article gives an overview of this numerical approach, and the computational conditions and uncertainty analysis are described. Results are presented for the wave and flow fields, with emphasis on the important flow features of drift- and wave-induced effects in comparison with the experiments. Finally, conclusions from the present study are given, together with recommendations for future work. Received: August 31, 2001 / Accepted: March 25, 2002     

Two-dimensional numerical simulation of water splash phenomena with and without surface tension

Two-dimensional numerical analyses were conducted and analyzed to simulate water splash produced by free falling object models starting from the resting position. The equilateral prism-shaped object models were allowed to fall onto the free surface of the water. The moving-particle semi-implicit (MPS) method was used to solve the unsteady Navier-Stokes equation for incompressible fluid flows with and without the surface tension effect. Froude numbers of 0.75, 1.0, and 1.25 were used with different model sizes for the entry velocity at the free surface. Splashes obtained by numerical computation closely agreed with the experimental results. The surface tension force, the Froude number, and the Weber number were found in these calculations to play major roles in determining various types of splash shapes. Model size was found to influence splash phenomena, even if the Froude number remained the same. The dependencies on these two nondimensional numbers and the fundamental law of similarity on water splash with and without the surface tension effect were thoroughly investigated in this research. Several two-dimensional numerical simulations are presented in this article to describe the hydrodynamic behaviors of water splash with and without the surface tension effect.     

30000方LNG船液货舱传热分析

针对国内第一艘在建中小型TYPE C型LNG船,提出了其货舱温度场的分析模型。基于工程传热学的原理,应用VBA计算程序,计算得到了各关键点的温度分布与热流密度,并与液货罐供应商TGE集团的报告对比。结果表明：若参数值相同,则计算值与报告值完全吻合。这说明,计算模型正确。这能够为TYPE C型液货舱的传热分析尤其是控制LNG蒸发率提供有力的指导。     

Comparison of simulation results and field data on currents and density in Tokyo Bay

A multilevel model was applied to the calculation of permanent current and density variation in Tokyo Bay, and the change of the state of stratification and the accompanying current field was simulated. In the numerical simulation, the observed field data such as wind conditions and atmospheric temperature were used as input to the calculation, and the results were compared with the observed values of currents, salinity, and sea temperature. Comparison of simulation results and observed data revealed that the numerical simulation could describe well the current and density field governed by wind under stratified conditions. In particular, the long-term variations of the vertical structure of salinity and temperature from summer to autumn could be predicted qualitatively, as could the long-term variations of the vertical structure of salinity and temperature from summer to autumn. Additionally, the effects of boundary conditions on the results of numerical simulations were examined. As a result, it was clarified that the simulation results of salinity stratification were strongly affected by the boundary conditions such as river discharge and the vertical structure of salinity at the open boundary adjacent to the outer ocean.     

An experimental study on water entry of horizontal cylinders

Complex hydrodynamics of a circular cylinder entering into water horizontally for low Froude numbers is experimentally studied. A high-speed digital video camera system is used to record the water entry process. The emphasis of this study is to investigate the three-dimensional effect on the water entry of the horizontal cylinders. A new experimental setup is built for this purpose and great effort is put on taking high quality pictures of the free surfaces. In the experiment four length to diameter ratios, two cylinder-water density ratios, and two release heights are investigated. For comparison, experiment with a sphere is also carried out. Quantitative analysis is performed based on the digital video images and the results are presented. The results obtained from this study can be used not only for understanding the physics but also for the purpose of validation of numerical models.     

Controls on stratification in the Rhine ROFI system

Stratification in the Rhine ROFI is very variable; the mean water column stability is controlled by the combined effect of tidal, wind and wave stirring which, at times, brings about complete vertical homogeneity. Control by the mixing variables has been elucidated by a regression analysis of mean stratification on the components of the windstress and significant wave height. There is strong partial correlation with all three variables which explains between 56% and 65% of the variance in two time series of observations in October 1990 and September 1992, respectively. During periods of low stirring the water column was observed to re-stratify over the whole inshore region through the relaxation of the horizontal gradients under gravity and with the influence of rotation. Superimposed on the mean stratification there is strong semi-diurnal variation, occurring throughout the stratified region at times of reduced mixing. The amplitude of this semi-diurnal variation is of the same order as the mean stability and frequently results in conditions being mixed or nearly mixed once per tide. This semi-diurnal variation results primarily from cross-shore tidal straining which interacts with the main density gradient to induce stratification. The hypothesis that water column stability is controlled by the combination of these processes has been tested using a reduced physics model which has been successful in reproducing the main features of both the mean and semi-diurnal components of stratification.     

Determining the hydrodynamic forces on a planing hull in steady motion

A combination of methods was developed that can determine hydrodynamic forces on a planing hull in steady motion. Firstly, a potential-based boundary-element method was used to calculate the hydrodynamic pressure, induced resistance and lift. Then the frictional resistance component was determined by the viscous boundary layer theory. Finally, a particular empirical technique was applied, to determine the region of upwash geometry and determine spray resistance. Case studies involving four models of Series 62 planing craft were run. These showed that the suggested method is efficient and capable, with results that are in good agreement with experimental measurements over a wide range of volumetric Froude numbers.     

水下导航拖曳载体水动力性能分析

三体船型适合作为水下导航系统的载体平台,其主体对整个载体的稳定性有较大影响。采用数值计算的方式分析主体封闭和开敞条件下,载体在静水拖曳直航工况下的水动力性能。结果表明:封闭主体与迎流有一个较大的接触角度,使得来流在主体前方的迎流区形成一个很大的流动停滞区,不利于载体的纵向稳定。当主体采用全开敞结构时,流体在整个舱室内几乎没有流动停滞区和飞溅,对应的载体稳定性相对较高,且压差阻力在总阻力中发挥主导作用。随着Fr值的增大,载体的横倾幅值不断增大,但变化不大。载体的纵向稳定性受Fr的影响较大,且在Fr的值接近0.428时,纵倾值突变到4.8°左右。