组合隔板抑制液舱晃荡机理的数值方法研究

液舱晃荡是船舶与海洋工程领域的热点问题,有效地抑制液舱晃荡、减小壁面冲击载荷关系着船体结构的安全。使用内嵌隔板是抑制舱内晃荡,减小壁面冲击载荷的有效手段。实际工程中,内嵌隔板的最优设计的前提是对隔板抑制晃荡的机理有深入了解。CIP法具有高精度、低耗散等特点,以THINC格式捕捉自由液面,可以再现液面破碎、翻卷、涡旋以及液滴飞溅等现象。基于此法,建立了数值液舱,对比了单一隔板和组合隔板抑制晃荡的效果。结果表明,内嵌隔板的安装在水平位置上应尽量靠近舱底中线,在垂直位置上应尽量靠近自由液面,且液面附近安装的双垂直隔板抑制晃荡能力最佳。     

双浮板液舱晃荡特性的数值研究

基于黏性流理论,采用动网格技术和6自由度模型,以及动量源方法,建立了双浮板液舱晃荡的数值模型。分别采用3种不同空间步长的网格离散计算区域,进行了网格收敛性验证。通过光滑液舱晃荡的模型试验和解析得到的爬高最大值,验证了数值模型的精确性。在载液率为50%,激励幅值为2 mm条件下,对双浮板液舱晃荡进行了数值计算,与光滑液舱相比,双浮板液舱晃荡的最大爬高明显减小。通过一个激励周期内双浮板液舱晃荡的波面显示发现,液舱晃荡模式由光滑液舱的驻波模式变为U管模式,晃荡模式的改变起到了明显地抑制液舱晃荡的效果。     

弹性液舱内液体晃荡实验研究

通过物理模型实验,对水平简谐激励下弹性矩形液舱内液体晃荡问题进行了研究。实验中给出了不同液深和不同激励振幅下弹性液舱内液体最低阶固有频率。采用影像采集与分析系统获得液舱内自由液面的形状和高度,通过压力采集系统得到舱壁上的压力分布。实验中分析了不同液深、不同激励频率下弹性和刚性液舱内自由液面高度和晃荡压力的变化特性。比较了弹性和刚性液舱内不同位置处自由液面高度随外界激励频率的变化规律,以及舱壁上不同位置处的压力峰值随外界激励频率的变化规律。结果表明:非共振情况下,弹性和刚性实验结果及理论值三者的波高和压力较为接近。共振情况下,弹性和刚性波高基本相等,在近舱壁处二者明显大于理论值,而在远离舱壁处二者与理论值存在一定差别;弹性压力较刚性压力略小,但二者与理论值差别较大。     

液舱三维晃荡运动二阶共振理论解及特性分析

从无旋运动的理论出发,并利用微扰法,推导了液舱三维晃荡运动二阶共振问题的理论解。考虑纵荡和横荡运动情况,对液舱三维晃荡二阶共振问题进行了分析。当两个晃荡方向的和频(即其外部激发频率的和)或差频(即其外部激发频率的差值)等于液舱固有频率时,二阶共振发生;当某一晃荡方向(横荡或纵荡)外部激发频率与另一晃荡方向(纵荡或横荡方向)液舱某一固有频率的和或差值等于液舱另一固有频率时,二阶共振也会发生。进一步研究了各个二阶共振激发频率下水深变化对晃荡振幅的影响。结果表明,对于两个晃荡方向外部激发频率的和频和单一晃荡方向(纵荡或横荡)某一个激发频率与另一晃荡方向(横荡或纵荡)某一个属于奇模的固有频率的和频所引发的共振情况,水深变化对共振振幅大小的影响比较大;而对于相应差频所引发的共振情况,水深变化对共振振幅大小的影响比较小。     

FLNG液舱晃荡压力影响因素及安全性评估研究

针对大型浮式液化天然气储卸生产装置FLNG的液舱晃荡压力变化特征,在深水试验池中开展带液舱模型的FLNG水池模型试验研究。通过试验,获得了FLNG在风浪流联合作用下的浮体六自由度运动,以及相应的液面高度变化数据。通过液舱的液面高度变化数据,提出平液面假设,并在此基础上,求得液舱晃荡引起的舱壁压力变化结果。研究中进一步讨论了液舱晃荡压力的影响因素,并将试验数据与CCS船级社规范计算结果进行对比,为FLNG液舱晃荡压力引起的结构安全性评估提供技术支持。     

基于无网格MPS方法数值分析方舱破舱进水问题

采用移动粒子半隐式法(moving particle semi-implicit,简称MPS)对自由漂浮二维方舱的破舱瞬时进水过程进行数值模拟。首先,采用基于GPU平台自主开发的MPS软件模拟破舱进水问题,并与其他方法得到的数值模拟结果进行对比验证。然后,对该二维方舱的各种模型进行了数值模拟,其中开孔位于不同位置以表示舷侧不同高度下的损坏。此外,还研究了不同类型的挡板对破舱进水后方舱稳定性的影响。结果表明损坏的孔洞和内部挡板会影响损坏舱段的运动特性,开孔距静水面的距离越大引起舱段的横摇等运动幅度越大,垂直挡板比水平挡板对舱内洪水的影响更大。     

液舱晃荡实验风险分析方法研究

以液舱晃荡实验为风险评估对象,利用事故树分析法进行风险辨识,确定风险评价指标体系,然后在此基础上建立了实验风险的模糊综合评判模型,对实验风险进行评估。同时,对风险因素进行排序,确定主要的风险控制对象。     

基于MPS无网格方法的孤立波传播的数值模拟

在MPS无网格方法中,引进预定候选粒子集概念用以生成邻接粒子集矩阵,使该部分的机时耗费缩短为引进前的1/11;采用Bi-CGSTAB方法求解压力泊松方程,显著地提高了求解速度.模拟了孤立波在数值波浪水槽中的传播及其与直墙作用时的爬升、回落过程,结果表明模拟波面结果与解析值及实测结果基本相符,针对不同波高的孤立波计算得到的墙前最大爬升值与实测结果也是一致的.     

考虑晃荡效应的独立B型LNG液舱结构多目标优化

独立B型LNG液舱内部设置舱壁板材及多种桁材,有效缓解了液舱晃荡效应。针对晃荡载荷下的独立B型LNG液舱结构多目标优化,利用规范中的公式计算晃荡载荷,并引入液舱晃荡系数,以期综合反映液舱内部构件对晃荡特性的影响,在此基础上进一步建立以液舱结构重量和液舱晃荡系数为目标的多目标优化模型,采用多目标遗传算法(NCGA),计算得到改进的独立B型LNG液舱结构设计方案。     

MPS法高精度自由表面识别方法研究

为了提高粒子法即移动粒子半隐式法(Moving Particle Semi-implicit method, MPS法)中自由表面粒子的识别精度,降低由粒子误判引起的非物理压力振荡,对MPS法的自由表面识别方法进行了改进。在原始自由表面判别标准的基础上增加辅助判别条件,提出2种新的自由表面判别法即压力判别法和填充率判别法。利用对静水问题和溃坝流问题的模拟计算,对比分析选用不同自由表面判别法得到的数值计算结果,揭示粒子识别精度对压力计算的重要影响。研究结果表明:新提出的压力判别法和填充率判别法可以有效地提高自由表面粒子的识别精度,减轻压力计算中的非物理压力振荡现象,从而提高压力计算的稳定性以及整体数值计算的模拟精度。     

改进的移动粒子半隐式法模拟楔形体入水砰击

移动粒子半隐式法(Moving-Particle Semi-Implicit Method,MPS)是一种新的基于拉格朗日(Lagrange)理念的无网格方法,适用于模拟自由液面的大变形和水流的喷射现象。用基于大涡模拟的改进MPS法首先模拟了矩形体的入水砰击,砰击压力的计算结果证明了这种方法的正确性,然后模拟了楔形体的匀速入水砰击,并与实验结果进行了对比,验证了大涡模拟改进MPS法在砰击问题中的适用性。     

Numerical simulation of solitary wave propagation based on MPS method

The concept of candidate particle set is introduced in the MPS gridless numerical method to generate neighboring particle set matrix, which can reduce the CPU time to 1/11 of that before introduction. The Bi-CGSTAB (bi-conjugate gradient stabilized) algorithm is applied to solving the Poisson pressure equation, by which the solving speed is significantly accelerated. The process of solitary waves propagating over a numerical flume and interacting with a vertical wall is simulated. The simulated results of water surface elevation are in good agreement with the analytical solution as well as the measured data. The predicted maximum values of the run-up of solitary waves with various relative incident wave heights agree well with the measured results.     

基于Level-set法和通度概念液体晃荡特性研究

液体晃荡现象在诸多工程领域具有深刻的研究意义,并引起了广泛的关注。基于Level-set方法,借助流场通度的概念,模拟了流场内具有障碍物的液体晃荡现象。选取不同形式的防晃结构分析研究对晃荡的抑制效果,得到几点关于防晃结构的设计与选择的重要结论。计算结果表明,通度系数法与Level-set方法的结合使用,能够有效地处理流场内带有障碍物的液体晃荡问题,该方法具有一定的可行性和应用前景。     

Numerical simulation of three-dimensional sloshing phenomena using a finite difference method with marker-density scheme

In the present study, three-dimensional sloshing phenomena occurring in liquid cargo tanks are numerically simulated. The Navier-Stokes equations and continuity equation are used for the governing equations, and solved with a finite difference method in a rectangular fixed staggered mesh system. The positions of free surface are defined by the Marker density method satisfying the free-surface boundary conditions, and the flows of the gas and liquid regions are simulated simultaneously. The irregular leg length and star method is employed on the cells near the free surface for the computations of pressure. The computation results are compared with other experimental results to verify the consistency of the present numerical method, and the agreements are reasonably good. Furthermore, the flow characteristics inside a partially filled liquid tank of a real sized ship oscillating regularly and irregularly are computed to verify the possibility of practical application of the present method.     

New modified gradient models for MPS method applied to free-surface flow simulations

In this paper, two modified pressure gradient models based on Taylor series expansion are proposed to enhance the higher order source term MPS (MPS-HS) method. The modified models consist of gradient correction matrices applied to the existing (base) pressure gradient models. To validate the modified pressure gradient models first hydrostatic pressure test is simulated and compared to both the base and modified MPS methods. Using the modified models are shown to reduce unphysical pressure oscillations observed in the base models. Second, an evolution of an elliptical drop in a 2D flow field is examined and shown to verify the models. Third, the proposed models illustrated appropriate stability and consistency properties against analytical solutions when an altered gravitational acceleration was superimposed to the hydrostatic pressure test. In addition, an improved performance is observed when Higher order Laplacian (HL) and Error-Compensating Source (ECS) of the Poisson Pressure Equation (PPE) schemes are coupled with the modified pressure gradient models compared to coupling them with the base gradient models. Finally, the modified MPS methods enhanced performances are validated in a free-surface flow simulation for a dam break problem with impact pressure, and a violent sloshing flow in a rectangular tank when compared to the base MPS methods against an existing experimental data.     

Experimental and numerical investigation of sloshing using different free surface capturing methods

We investigated the use of numerical methods to predict liquid sloshing phenomena in a moving tank and compared our results to model test measurements. The numerical techniques for the free surface, based on the so-called finite Volume-of-Fluid (VoF) approach, comprised an incompressible VoF method, an incompressible coupled Level-Set and Volume-of-Fluid (clsVoF) method, and a compressible VoF method. We assessed the capability of these three numerical methods to achieve suitable numerical predictions of sloshing phenomena, specifically, air pockets and bubbles on the free surface inside a test tank. To observe the described sloshing phenomena, we simulated tank motions leading to well defined single impact wave motions. We performed repeated physical tests for validation purposes. Computed velocity and pressure time histories were compared to experimental data we obtained from Particle Image Velocimetry (PIV) and pressure sensor measurement. Grid sensitivity and turbulence model studies were performed. We demonstrated that the compressible VoF method was the most suitable method to obtain accurate predictions of sloshing phenomena.     

Three-dimensional liquid sloshing in a tank with baffles

A numerical model has been developed to study three-dimensional (3D) liquid sloshing in a tank with baffles. The numerical model solves the spatially averaged Navier-Stokes equations, which are constructed on a non-inertial reference frame having six degree-of-freedom (DOF) of motions. The large-eddy-simulation (LES) approach is employed to model turbulence by using the Smagorinsky sub-grid scale (SGS) closure model. The two-step projection method is employed in the numerical solutions, aided by the Bi-CGSTAB technique to solve the pressure Poisson equation for the filtered pressure field. The second-order accurate volume-of-fluid (VOF) method is used to track the distorted and broken free surface. The baffles in the tank are modeled by the concept of virtual boundary force (VBF) method. The numerical model is first validated against the available analytical solution and experimental data for two-dimensional (2D) liquid sloshing in a tank without baffles. The 2D liquid sloshing in tanks with baffles is then investigated. The numerical results are compared with other results from available literatures. Good agreement is obtained. Finally, the model is used to study 3D liquid sloshing in a tank with vertical baffles. The effect of the baffle is investigated and discussed.