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.     

Numerical simulation of viscous liquid sloshing by moving-particle semi-implicit method

A meshless numerical simulation method,the moving-particle semi-implicit method(MPS)is presented in this paper to study the sloshing phenomenon in ocean and naval engineering.As a meshless method,MPS uses particles to replace the mesh in traditional methods,the governing equations are discretized by virtue of the relationship of particles,and the Poisson equation of pressure is solved by incomplete Cholesky conjugate gradient method(ICCG),the free surface is tracked by the change of numerical density.A numerical experiment of viscous liquid sloshing tank was presented and compared with the result got by the difference method with the VOF,and an additional modification step was added to make the simulation more stable.The results show that the MPS method is suitable for the simulation of viscous liquid sloshing,with the advantage in arranging the particles easily,especially on some complex curved surface.     

液舱晃荡与浮体非线性耦合运动分析(英文)

Nonlinear interactions among incident wave, tank-sloshing and floating body coupling motion are investigated. The fully nonlinear sloshing and body-surface nonlinear free surface hydrodynamics is simulated using a Non-Uniform Rational B-Spline (NURBS) higher-order panel method in time domain based on the potential theory. A robust and stable improved iterative procedure (Yan and Ma, 2007) for floating bodies is used for calculating the time derivative of velocity potential and floating body motion. An energy dissipation condition based on linear theory adopted by Huang (2011) is developed to consider flow viscosity effects of sloshing flow in nonlinear model. A two-dimensional tank model test was performed to identify its validity. The present nonlinear coupling sway motion results are subsequently compared with the corresponding Rognebakke and Faltinsen (2003)’s experimental results, showing fair agreement. Thus, the numerical approach presented in this paper is expected to be very efficient and realistic in evaluating the coupling effects of nonlinear sloshing and body motion.     

Numerical simulation of viscous liquid sloshing by moving-particle semi-implicit method

A meshless numerical simulation method, the moving-particle semi-implicit method （MPS） is presented in this paper to study the sloshing phenomenon in ocean and naval engineering. As a meshless method, MPS uses particles to replace the mesh in traditional methods, the governing equations are discretized by virtue of the relationship of particles, and the Poisson equation of pressure is solved by incomplete Cholesky conjugate gradient method （ICCG）, the free surface is tracked by the change of numerical density. A numerical experiment of viscous liquid sloshing tank was presented and compared with the result got by the difference method with the VOF, and an additional modification step was added to make the simulation more stable. The results show that the MPS method is suitable for the simulation of viscous liquid sloshing, with the advantage in arranging the particles easily, especially on some complex curved surface.     

Analysis on acoustic performance of floating raft vibration isolation system with liquid tank北大核心CSCD

［Objective］This paper aims to establish a dynamic model of a floating raft vibration isolation system with a liquid tank in order to study the mass effect of the liquid medium, tank form, structural stiffness and loading rate on acoustic performance. ［Methods］A floating raft system with a cuboidal or cylindrical liquid tank is taken as the research object, and a fluid-structure coupling finite element dynamic model is established. The dynamic force transmission rate and power flow are then used to evaluate the acoustic performance of the system. The influence of the mass effect of the liquid medium, tank form, structural stiffness and loading rate of tank volume on the acoustic performance of the floating raft system are analyzed.［Results］The results show similar laws obtained through the calculation and analysis of the floating raft system with two types of tanks. The structural stiffness of the tank affects the mass effect of the liquid medium in the tank to a certain extent. ［Conclusions］If full advantage is to be taken of the liquid mass effect in the tank with a large loading rate to improve the acoustic performance of the floating raft system, the design of the liquid tank and raft structure must have sufficient stiffness. In addition, under the condition that the floating raft structure has sufficient stiffness, its acoustic performance will improve significantly as the tank loading rate increases in the relevant low frequency range. © 2022 Journal of Clinical Hepatology. All rights reserved.     

矩形水箱中模拟浅水晃荡的不同湍流模型性能研究（英文）

Liquid sloshing is a common phenomenon in the transportation of liquid-cargo tanks. Liquid waves lead to fluctuating forces on the tank walls. If these fluctuations are not predicted or controlled, for example, by using baffles, they can lead to large forces and momentums. The volume of fluid(VOF) two-phase numerical model in Open FOAM open-source software has been widely used to model the liquid sloshing. However, a big challenge for modeling the sloshing phenomenon is selecting a suitable turbulence model. Therefore, in the present study, different turbulence models were studied to determine their sloshing phenomenon prediction accuracies. The predictions of these models were validated using experimental data. The turbulence models were ranked by their mean error in predicting the free surface behaviors. The renormalization group(RNG) k–ε and the standard k–ωmodels were found to be the best and worst turbulence models for modeling the sloshing phenomena, respectively; moreover, the SST k–ω model and v2-f k-ε results were very close to the RNG k–ε model result.     

Numerical simulation of 2D and 3D sloshing waves in a regularly and randomly excited container

In this paper,various aspects of the 2D and 3D nonlinear liquid sloshing problems in vertically excited containers have been studied numerically along with the help of a modified-transformation.Based on this new numerical algorithm,a numerical study on a regularly and randomly excited container in vertical direction was conducted utilizing four different cases： The first case was performed utilizing a 2D container with regular excitations.The next case examined a regularly excited 3D container with two different initial conditions for the liquid free surface,and finally,3D container with random excitation in the vertical direction.A grid independence study was performed along with a series of validation tests.An iteration error estimation method was used to stop the iterative solver（used for solving the discretized governing equations in the computational domain） upon reaching steady state of results at each time step.In the present case,this method was found to produce quite accurate results and to be more time efficient as compared to other conventional stopping procedures for iterative solvers.The results were validated with benchmark results.The wave elevation time history,phase plane diagram and surface plots represent the wave nonlinearity during its motion.     

Dynamic interaction of parallel moving ships in close proximity

Nowadays,there are many studies conducted in the field of marine hydrodynamics which focus on two vessels traveling and floating in sufficiently close proximity to experience significant interactions.The hydrodynamic behavior of parallel moving ships in waves is an interesting and important topic of late.A numerical investigation has been carried out for the prediction of wave exciting forces and motion responses of parallel moving ships in regular waves.The numerical solution was based on 3D distribution technique and using the linear wave theory to determine the exciting forces and ship＇s motion.The speed effects have been considered in the Green function for more realistic results.The numerical computations of wave exciting forces and motion responses were carried out for a Mariner and Series 60 for the purpose of discovering different Froude numbers and different separation distances in head sea conditions.Based on the numerical computations,it was revealed that the sway,roll and yaw have a significant effect due to hydrodynamic interaction.     

风机塔架与叶片相互作用的数值模拟(英文)

Numerical simulations of wind turbine blade-tower interaction by using the open source OpenFOAM tools coupled with arbitrary mesh interface(AMI) method were presented.The governing equations were the unsteady Reynolds-averaged Navier-Stokes(RANS) which were solved by the pimpleDyMFoam solver,and the AMI method was employed to handle mesh movements.The National Renewable Energy Laboratory(NREL) phase VI wind turbine in upwind configuration was selected for numerical tests with different incoming wind speeds(5,10,15,and 25 m/s) at a fixed blade pitch and constant rotational speed.Detailed numerical results of vortex structure,time histories of thrust,and pressure distribution on the blade and tower were presented.The findings show that the wind turbine tower has little effect on the whole aerodynamic performance of an upwind wind turbine,while the rotating rotor will induce an obvious cyclic drop in the front pressure of the tower.Also,strong interaction of blade tip vortices with separation from the tower was observed.     

基于镜像SPH的三维容器液体晃荡研究

基于SPH方法对液体在三维矩形容器中的非线性晃荡问题进行了数值模拟研究。采用镜像粒子边界建立三维模型,成功解决传统SPH方法在容器壁产生缝隙的问题。对横荡和横摇两种容器运动形式进行数值模拟,在液面时间历程、不同时刻液体形态、点压强以及液体晃荡作用力等方面与其他学者的实验研究结果和数值计算结果进行对比验证,表明此三维模型的正确性。     

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.

     

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.     

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.     

Effects of excitation angle and coupled heave–surge–sway motion on fluid sloshing in a three-dimensional tank

Sloshing waves in moving tanks is an important engineering problem, and most studies of this phenomenon have focused on tanks that are excited by forcing motion in a limited number of directions and with fixed excitation frequencies throughout the forcing. In practice, the excitation comprises multiple degree of freedom motion that potentially couples surge, sway, heave, pitch, roll, and yaw motions. In the present study, a time-independent finite difference method is used to simulate fluid sloshing in three-dimensional tanks filled to an arbitrary depth for various excitation frequencies and multiple degree of freedom motion. The numerical scheme developed here was verified by rigorous benchmark tests. The coupled motions of surge and sway are simulated for various excitation angles, frequencies and water depths. Five kinds of sloshing waves found under coupled surge–sway motions: diagonal, single-directional, square-like, swirling, and irregular waves. The effect of excitation angle on the frequency responses of different sloshing waves is analyzed and discussed in the present study. Further, the components of horizontal force of various sloshing waves are also presented. The coupled effect of surge, sway and heave motions is also discussed, and the results show that unstable sloshing occurs when the excitation frequency of the heave motion is twice the fundamental natural frequency. Moreover, the effects of heave motion on the different types of sloshing waves are explored. It is found that heave motion causes all of the sloshing waves to change type.     

基于全时域势流理论的船舶与液舱晃荡耦合运动的数值计算

基于三维线性有航速时域势流理论计算船体时域运动外域波浪力,同时采用三维全非线性时域势流理论来计算舱内液体的非线性晃荡所诱导力与力矩,进而建立了波浪中载液船舶耦合运动方程。该方法能够完整地考虑波浪、船体和液舱晃荡之间的实时耦合作用。研究结果表明:通过模型实验和数值模拟计算的对比,数值模拟计算能够清晰显现出液舱晃荡对船体全局运动影响,无航速船体运动RAO与模型实验结果吻合良好,有航速运动计算合乎预期。     

计及弹性支撑效应的独立液舱晃荡数值分析研究

文章针对弹性支撑结构作用下的液舱晃荡问题,采用基于Hilber-Hughes-Taylor(HHT)格式的隐式直接积分法求解液舱运动,应用VOF法求解流体晃荡,并结合部分单元参数的概念处理棱形液舱边界,建立了液舱运动与流体晃荡双向耦合迭代算法。以独立液舱为研究对象,通过耦合求解弹性支撑液舱晃荡,并与非弹性支撑液舱晃荡进行比较,分析了在不同刚度的弹性支撑结构作用下液舱液体运动及晃荡载荷的变化规律。该文建立的分析方法为含弹性支撑的独立液舱晃荡载荷预报提供了一种快速、有效的分析手段。     

独立B型LNG棱形液舱晃荡载荷数值分析

针对独立B型棱形液舱的结构特点,采用基于Hilber-Hughes-Taylor格式的隐式直接积分法求解液舱运动,应用VOF法求解流体晃荡,结合部分单元参数的概念处理棱形液舱边界,计算了计及弹性支撑效应的独立B型液舱晃荡。通过目标船计算,发现计及弹性支撑效应的液舱晃荡载荷会略大于不计及弹性支撑效应的晃荡载荷;通过不含内部构件弹性支撑液舱、含内部构件弹性支撑液舱和含内部构件非弹性支撑液舱晃荡的比较,分析了独立B型液舱晃荡载荷的特点以及内部构件对波面的限制作用。探讨的计算方法可为独立B型棱形液舱晃荡载荷的预报和分析提供一定的参考。     

两种运动平台下晃荡冲击荷载的实验研究

由液体晃荡引起的冲击荷载主要与外部激励(激励频率和激励幅值)和装载率相关。大尺度物理模型实验通过运动平台在室内复现液舱的运动,进而实现在室内对储液舱内晃荡载荷的研究。因此,平台的运动能力、运动的精确性对液体冲击载荷的实验结果非常关键。为了研究不同类型运动平台的运动性能及其对储液舱内冲击载荷的影响,文中以大比尺二维矩形舱为模型,分别在单自由度运动平台和六自由度运动平台开展系统的液体晃荡冲击实验。实验结果表明:仅考虑水平运动,单自由度平台的精度要高于六自由度平台;在个别工况下,两个平台下冲击荷载时程和特征值的对比结果出现了一定差别,但是晃荡冲击荷载的整体趋势基本一致。通过评价单自由度和六自由度两种类型的运动平台在液体晃荡研究领域应用的适用性,为大尺度室内晃荡模型实验中运动平台的选择提供参考