Numerical model of energy dissipation and shallow-water sloshing motions in tank under different coupled excitations

Shallow-water sloshing motions in a three-dimensional rectangular tank are investigated. The Boussinesq-type equations in terms of velocity potential and the finite-difference scheme are applied for the solutions of numerical model. Through linking the rate of decay of the wave amplitudes to the energy dissipation due to the friction at the tank walls, a linear damping term is proposed and added into the free surface boundary condition. Taking the tank under excited frequencies near the lowest natural frequency, the maximum transient wave amplitudes and steady-state wave amplitudes of sloshing motions at the tank wall are presented and verified by the experimental results given in the literature. The characteristics of sloshing motions in tank under different coupled excitations are studied. The results indicate that coupled surge-sway excitations lead to the weaker nonlinear sloshing motions in tank than the single degree of freedom excitations. The intersection of sloshing wave crest lines finally tend to the diagonal line of the tank under the coupled surge-sway excitations with different amplitudes. And the irregular free surface oscillations appear at the corners of the tank excited by the coupled surge-sway-roll-pitch-yaw harmonic motions.

     

液舱晃荡的数值模拟

随着海上液化天然气的开采和卸载的发展,LNG船部分充满液舱的晃荡问题变得非常重要,成为一个重要的研究课题.文章采用VOF法对部分充满液舱的晃荡进行了数值模拟.结合动网格技术,针对二维矩形舱和三维立方体舱及薄膜型舱进行了计算.并将相关的横向力、波高和压力曲线与试验结果作对比,吻合较好.验证了此法的可行性和有效性.     

采用耦合有限元、边界元方法的矩形储液舱中液体晃荡数值仿真(英文)

Sloshing of liquid can increase the dynamic pressure on the storage sidewalls and bottom in tanker ships and LNG careers. Different geometric shapes were suggested for storage tank to minimize the sloshing pressure on tank perimeter. In this research, a numerical code was developed to model liquid sloshing in a rectangular partially filled tank. Assuming the fluid to be inviscid, Laplace equation and nonlinear free surface boundary conditions are solved using coupled FEM-BEM. The code performance for sloshing modeling is validated against available data. To minimize the sloshing pressure on tank perimeter, rectangular tanks with specific volumes and different aspect ratios were investigated and the best aspect ratios were suggested. The results showed that the rectangular tank with suggested aspect ratios, not only has a maximum surrounded tank volume to the constant available volume, but also reduces the sloshing pressure efficiently.     

Experimental and numerical study on tuned liquid dampers for controlling earthquake response of jacket offshore platform

Earthquake loading has to be considered when the offshore platform is constructed in active fault zone. Tuned liquid dampers (TLD) have been proposed to control the dynamic response of structures. Liquid sloshing experiments on cylinder tank show the sloshing happens more seriously when the frequency of external excitation is close to the fundamental sloshing frequency of liquid. Lumped mass method is employed to numerically analyze the controlling earthquake effect on TLD. Based on TLDs the feasibility to control earthquake response of jacket platform is studied and applied to CB32A oil tank platform. Using extra TLDs in CB32A to control the seismic response of the platform is researched by the model test and numerical simulation. Lumped mass method can simulate the behavior of TLD during earthquake very well and gives close numerical results compared with those from model experiments. It has been found that the ratio of the fundamental sloshing frequency of liquid to the natural frequency of platform is the key factor to control earthquake response. The larger ratio of water-mass to platform-mass is also useful to reduce vibration as well.     

液体晃荡荷载与液舱运动相位关系的数值研究

该文从相位角度出发,采用CFD的数值方法研究简谐激励下液体晃荡整体荷载与液舱运动的相位关系。首先,通过模型实验验证数值方法的可靠性,然后,以横荡激励下的二维矩形舱晃荡为例,研究不同载液率工况下,相位差和晃荡整体荷载幅值随激励频率的变化关系。结果表明:基于VOF法的数值模拟能较好地模拟液舱内液体晃荡;在自由面共振频率附近(0.8 f0~1.2 f0),相位差随激励频率增加而增大;频率比相同时,相位差随载液率的升高而增大;相位差90°时,相位差对应频率低于共振频率,且与晃荡荷载最大值对应频率基本相等。     

基于MSC.Dytran的液舱晃荡分析

液货船发展的关键技术之一是解决液舱内流体的晃荡问题。MSC.Dytran有限元程序能较好的模拟贮液容器的液面晃荡问题。以载液船舶液舱为研究对象,利用MSC.Dytran程序对矩形液舱在一确定装载水平下的液面晃动进行仿真分析,得到了不同时刻舱内液体的液面形状。     

三维矩形弹性液舱内液体晃荡数值模拟研究

为了解三维弹性液舱内液体晃荡情况,采用ADINA模拟不同激励频率下液舱内液体的晃荡,将所得的结果与解析解进行对比,得到不同载液率下弹性液舱内液体晃荡特点,得到液舱载液率、外界激励等参数变化对液体自由表面运动及晃荡荷载的影响.     

多种激励耦合作用下的二维液舱晃荡(英文)

In this research,liquid sloshing behavior in a 2-D rectangular tank was simulated using ANSYS-FLUENT software subject to single or multiple-coupled external excitations(such as sway coupled with roll,and sway and roll coupled with heave).The volume of fluid(VOF) method was used to track the free surface of sloshing.External excitation was imposed through the motion of the tank by using the dynamic mesh technique.The study shows that if the tank is subjected to multiple coupled excitations and resonant excitation frequencies,liquid sloshing will become violent and sloshing loads,including impact on the top wall,will be intensified.     

液舱内大幅晃荡引起的压强预报

本文基于流体体积(VOF)法就部分装载液体的液舱内的晃荡压强进行了二维数值计算.为了模拟大幅晃荡引起的冲击压强,重点对数值计算较为敏感的速度边界条件进行了数值处理.通过对某一矩形液舱内的液体晃荡的计算,得到了自由表面位置和压强的时间历经曲线.计算结果同实验值的比较显示:本方法可以用于计算预报大幅晃荡引起的载荷.     

液舱内流体晃荡特性数值研究

本文利用VOF法对矩形液舱内液体晃荡进行数值计算。首先对舱内无任何隔板时液体晃荡作了模拟,并与相关文献中的实验结果进行了比较;然后在舱底中间设置一道不同形式的防晃隔板,对液体晃荡进行了计算。从结算结果看,本文提出的方法可以用于分析液舱内液体的运动和载荷,为设计合理的液舱结构形式提供理论依据。     

液舱内三维液体非线性晃荡的数值模拟

晃荡是一种非常复杂的非线性液体流动现象,载液船舶的晃荡问题颇受关注,因为在外界的激励下液舱内会产生剧烈的晃荡现象,巨大的晃荡冲击力会造成结构的破坏.文中建立了三维晃荡数学模型及数值计算模型,借助处理自由表面的VOF(volume of fluid)方法对液舱内液体晃荡的自由表面进行追踪,编制程序实现了液舱内三维液体非线性晃荡的数值模拟,并就三维刚性液舱内粘性液体的自由晃荡和强迫晃荡做了分析,讨论了液体不同粘性系数对晃荡的影响.模拟结果证明了三维晃荡理论的可行性.     

基于Level-set法的液舱液体晃荡数值模拟

船舶液舱中液体晃荡现象已引起人们的深刻关注,液体晃荡载荷与效应成为航行中载液船舶安全性评估的重要内容之一.该文基于Level-set法,对一矩形液舱的两种工况下舱内的液体晃荡进行了数值模拟.通过计算,得到了液面起伏和压强的时间历经,结果显示Level-set方法可有效地模拟液体晃荡问题.     

Level-set法预报液舱内剧烈晃荡引起的冲击压强

基于Level-set法就部分装载液体的液舱内剧烈晃荡引起的冲击压强进行了二维数值计算.为了模拟大幅晃荡引起的冲击压强,重点对数值计算较为敏感的自山液面处的物性参数、初始化方程的求解等进行了,数值处理.通过对某一矩形液舱内的液体晃荡的计算,得到了自由表而位置和压强的时间历经曲线.计算结果同实验值的比较表明:本方法可以用于计算预报大幅晃荡引起的载荷.     

纵摇容器中液体晃荡的非线性数值模拟

在海洋工程领域,液体晃荡是一种普遍存在的物理现象。对于船舶而言,转动比平动有着更重要的影响。该文针对纵摇容器中的液体晃荡问题,采用高阶边界元方法建立自由水面满足完全非线性边界条件的时域数学模型。通过大地坐标系和随体坐标系之间的坐标变换,使得计算域仅控制在随体坐标系内。求解中采用半混合欧拉—拉格朗日方法追踪流体瞬时水面,运用四阶龙格库塔方法更新下一时间步的波面和速度势。通过与已发表试验和数值结果的对比,验证了建立模型的准确性。进而开展大量数值试验研究容器纵摇运动频率、纵摇转动中心和容器中布置一竖直隔板对晃动波面与荷载的影响。     

A numerical study of the effects of bottom and sidewall stiffeners on sloshing behavior considering roll resonant motion

In the present study, aiming to provide practical guidance for the structural design, the effects of the small bottom and sidewall stiffeners on sloshing loads in shallow and intermediate liquid conditions are investigated numerically. The interaction between the highly nonlinear free surface flow and a large number of small stiffeners is modeled based on the Moving Particle Semi-implicit method. 2D models of a rectangular clean tank and tanks with small sidewalls or bottom stiffeners are considered. For filling ratios ranging from 5% to 20%, harmonic angular motions with periods around the analytical sloshing resonant ones are applied. Simulation snapshots and computed pressure time series, pressure variation, wave run-up, maximum fluid velocity, and kinetic energy were provided to clarify the complex interaction between the small baffles and the shallow free surface flow. As a result, except for the tanks with bottom stiffeners in shallow liquid conditions, in which the response under actual resonant frequency should be considered, the response computed using the clean tank excited by its resonant period can be adopted as a conservative estimation for the sloshing loads of actual tanks with small stiffeners.     

频域范围内液舱晃荡对FLNG运动影响的研究

FLNG是一种新型的浮式海洋结构物,其外形与FPSO相似并配备天然气的液化装置以及LNC储罐.FLNG概念的出现使得海上边际油气的开发不再依赖于长距离的管道运输,从而节约了此类油气田的开发成本.文中基于WADAM并针对液舱晃荡与船体运动之间的相互影响进行了频域范围内的研究,在研究过程中将液舱内湿表面包含于船体外湿表面中从而形成一个统一的边界表面.通过计算得出考虑液舱晃荡与忽略液舱晃荡两种情况下的六自由度运动的RAO.对于两种情况下的计算结果进行分析研究,从而得到液舱晃荡对船体运动影响的重要规律.     

二维矩形弹性液舱内液体晃荡数值模拟研究

阐述ADINA数学模型及相关数值方法,以二维矩形刚性液舱模型为例模拟液体晃荡,将所得的结果与解析解进行比较,验证该模型的有效性;通过数值模拟,研究二维矩形弹性液舱内的液体晃荡,分析不同刚度、不同频率对液体晃荡自由液面波高运动的影响。     

浅液深和挡板影响下遭受横摇激励的晃荡问题数值研究（英文）

Sloshing is relevant in several applications like ship tanks,space and automotive industry and seiching in harbours.Due to the relationship between ship and sloshing motions and possibility of structural damage,it is important to represent this phenomenon accurately.This paper investigates sloshing at shallow liquid depths in a rectangular container using experiments and RANS simulations.Free and forced sloshing,with and without baffles,are studied at frequencies chosen specifically in proximity to the first mode natural frequency.The numerically calculated free surface elevation is in close agreement with observations from experiments.The upper limit of the resonance zone,sloshing under different filling depths and roll amplitudes and sloshing with one,two and four baffles are also investigated.The results show that the extent of the resonance zone is reduced for higher filling depth and roll amplitude.It is also found that the inclusion of baffles moves the frequency at which the maximum free surface elevation occurs,away from the fundamental frequency.Finally,a submerged baffle is found to dissipate more energy compared to a surface piercing baffle and that the effect of several submerged baffles is similar to that of a single submerged baffle.     

矩形液舱横荡流体载荷的Fluent数值模拟

采用CFD软件Fluent对二维矩形液舱不同舱内水深、不同激振频率时的横荡进行数值计算,并将数值结果与实验结果进行比较。结果表明,Fluent可以模拟自由面的翻卷和破碎运动现象,其对于距自由面较深点处流体载荷的计算结果与实验值相符合,但对于自由面附近点,尤其是舱顶上点处的砰击载荷,其计算结果与实验值差别较大。因此,对大幅晃荡的数值模拟仍需进一步研究。     

Seismic response of liquid-filled tank with baffles

In thispaper, the effects of a rigid baffle on the seismic response of liquid in a rigid cylindrical tank are evaluated. A baffle is an annular plate which supplies a kind of passive control on the effects of ground excitation. The contained liquid is assumed incompressible, inviscid and has irrotational motion. To estimate the seismic response, the method of superposition of modes has been applied. To analyze the rigid tank response, Laplace＆#39;s equation is considered as the governing equation of the fluid domain, in both time and frequency domains. The boundary element method （BEM） is employed to evaluate the natural modes of liquid in a cylindrical tank. To gain this goal, the fluid domain is divided into two upper and lower parts partitioned by the baffle. Linearized kinematic and dynamic boundary conditions of the free surface of the contained liquid have been considered.