MPS方法数值模拟减摇水舱晃荡流动问题

船舶六自由度运动中,横摇对船舶的安全性影响十分严重。船舶在设计建造时,常采用减摇装置来降低横摇运动对船舶安全的危害。其中,减摇水舱因其结构简单、经济、便于养护,且在低航速和无航速情况下仍能发挥作用而得到广泛应用。为对减摇水舱的减摇特性进行深入研究,该文采用基于半隐式移动粒子MPS方法开发的MLParticle-SJTU求解器,对三维矩形被动式减摇水舱的晃荡进行了数值模拟。首先,进行了减摇水舱和舱内液体晃荡在外界激励下耦合运动的模拟,并将模拟结果与空舱横摇情况进行对比,证明了减摇水舱的减摇效果。然后,将减摇水舱横摇角的历时变化曲线与实验结果进行对比,验证了MPS方法的适用性与可靠性。最后,分析了减摇力矩与外界激励力矩之间的相位差,解释了减摇水舱的工作原理。     

深海采矿船减摇水舱减摇效果评估

船舶在海上航行或作业时最容易发生横摇,在各种航速下减摇水舱都能减小船舶横摇运动,因此越来越多的船舶使用减摇水舱减小横摇.在此背景下,针对一艘深海采矿船,开展减摇水舱减摇效果评估计算.首先在规则波中进行频域分析,基于受力平衡原理,得到船舶-减摇水舱耦合运动方程.在频域内求解耦合运动方程,得到不同激励下的船舶横摇响应.定性...     

基于MPS方法数值模拟三维LNG液舱的晃荡问题

该文基于自主开发的无网格粒子方法求解器MLParticle-SJTU,将MPS方法(moving particle semi-implicit)应用到三维LNG液舱的晃荡问题中,分别研究了LNG液舱在单自由度纵摇和横摇激励下,装载高度和激励频率对液舱晃荡作用的影响。首先,对装载高度为70%H的LNG液舱在单自由度纵摇和横摇激励下的晃荡问题分别进行了数值模拟,并将计算结果与实验结果进行比较,验证了MPS方法的可靠性。其次,对比不同装载高度,不同激励频率下液舱晃荡的拍击压力和流场分布情况,分析了装载高度和激励频率对晃荡作用的影响,并分析了一阶固有频率和共振频率随装载高度的变化规律。数值结果表明:激励频率对晃荡幅度影响较大;当激励频率在一阶固有频率附近时,会发生剧烈的晃荡现象;52.5%H为危险装载高度,在共振频率下,产生的拍击压力最大。     

带液舱FPSO船内外流场耦合的数值分析

带液舱FPSO船舶运动时对液舱晃荡的影响明显,而被影响的液舱晃荡会反过来改变FPSO船舶运动性能。该文采用基于开源代码OpenFOAM平台自主开发的CFD求解器naoe-FOAM-SJTU,对带有液舱的FPSO进行内外流场耦合数值模拟,对放开横荡自由度和不放开横荡自由度下的FPSO船舶运动和液舱晃荡进行了模拟研究;并对这两种状态下的船舶运动曲线和液舱抨击压力进行了比较。     

红土镍矿运输船倾覆特性数值研究

为深入揭示易流态货物运输船倾覆发生特性,该文以一舱段为研究对象,采用Herschel-Bulkley和Bingham方程对含水量40%的流态红土镍矿应力-应变特性进行描述,结合VOF方法建立了流态货物舱内晃荡数值计算模型;采用简化物面非线性方法求解舱段外部流场,并建立了流态货物舱内晃荡和舱段间横摇耦合运动数值模型。该模型完整地考虑了流态货物海运过程中舱内晃荡力矩及其对舱段回复力矩削弱的共同作用。结果表明,流态货物舱内晃荡引起的横摇运动不对称现象以及较高的波浪幅值和共振频率是导致易流态货物运输船发生倾覆的主要因素。     

基于CFD方法对波浪中FLNG分段液舱晃荡耦合运动的研究

作为液化天然气运输船,FLNG船在世界范围内引起广泛关注。在FLNG载液运输的过程中,船体会受复杂海洋环境影响产生摇晃,船体运动会带动液舱内液体产生晃荡,同时这种晃荡现象反过来也会与船体运动产生耦合作用。由于船舶运动与液舱内液体晃荡耦合作用的重要性,该问题十分具有研究价值。该文主要应用CFD方法,同时对液舱内部与外部流场进行模拟。对规则波中带双液舱FLNG分段的液舱晃荡耦合运动问题进行研究。该文应用的求解器是课题组基于Open FOAM自行开发的海洋工程水动力学求解器naoe-FOAM-SJTU。首先对空舱FLNG分段在不同频率规则波中的横摇运动进行模拟,并与文献结果进行对比,验证了求解器的准确性。接着针对液舱充液率24.3%的情况,对分段在不同波浪频率下的运动情况进行计算研究。在比对参考文献后,发现该文求解器的模拟结果比文献中的势流计算结果更加贴近文献中给出的物理实验结果。随后,研究在波浪频率相同时,五种不同充液率情况对FLNG分段液舱晃荡耦合运动的影响,并分析FLNG分段内外壁所受力矩相位差对耦合运动幅值造成的影响。最后将上述工况的波高增大一倍,再次研究在不同充液率下FLNG分段耦合运动受不同波陡的波浪的影响情况及规律。研究结果表明,naoe-FOAM-SJTU求解器可以有效模拟波浪环境下液舱晃荡-船体运动耦合问题,并可以对整个流场进行可视化展示与分析,从多角度分析这一复杂现象的机理。     

基于MPC的船舶横摇运动控制方法研究

船舶在恶劣海况下会产生大幅横摇运动，严重影响船舶航行安全。如果能对船舶运动趋势进行预测，并采取一定措施进行减摇控制，将大幅提升船舶安全性。该文基于AQWA软件计算船舶运动响应，利用系统识别对波浪的记忆效应进行近似估计，结合横风横浪中单自由度横摇运动方程和船舶运动状态方程，采用模型预测控制(MPC)方法进行船舶横摇运动控制，进而达到减小横摇运动的目的。通过对标准船模5415在规则波和不规则波条件下的横摇运动及其控制模拟，结果表明：MPC方法可有效减小横摇运动幅值，可以很好地解决船舶横摇运动控制的非线性问题，因此该方法适用于船舶时域运动控制研究。该研究为横浪条件下多自由度船舶运动控制奠定了基础。     

迎浪船舶的参数横摇分析

本文该文建立了三维非线性时域模拟运动方程;应用泰勒展开得到参数共振项系数;基于势流理论给出了非线性运动方程中来波影响项系数的确定方法.分析了发生参数横摇的范围和幅度;对船舶在不同波高、不同遭遇频率下的参数横摇幅值进行了系列预报,得到船舶参数横摇的发生区域图.     

不同液舱结构形式对晃荡的影响分析

本文就不同液舱结构形式对晃荡所产生的影响进行了分析研究。根据晃荡问题的特点及其液舱结构形式，建辛了数学模型。采用有限差分法离散流体运动方程，VOF法追踪自由表面，通度系数概念处理液舱内的障碍物。最后通过编制的计算程序，计算分析了不同结构形式液舱的防晃效果。     

随机海浪下的船舶非线性横摇与安全池研究

船舶大幅横摇运动是复杂的非线性问题,也是导致船舶倾覆的主要原因之一.该文通过对随机海浪下船舶非线性横摇运动进行分析,建立了横摇运动微分方程,采用数值方法在时域内对微分方程进行积分,模拟了船舶横摇运动响应,并研究了—实船在随机海浪中安全池的破损情况,得出该船的生存概率,分析了不同有义波高和航速下生存概率的变化.研究表明,数值方法以及安全池理论可用于预测船舶在随机海浪中的生存概率,从而可为船舶稳性衡准提供相关的参考.     

Shallow-water sloshing motions in rectangular tank in general motions based on Boussinesq-type equations

Based on the highly accurate Boussinesq-type equations in terms of velocity potential, the shallow-water sloshing in a two-dimensional rectangular tank is studied. The rectangular tank in harmonic sway, heave and roll motions with small excitation amplitudes is considered. The total velocity potential is divided into two parts: the particular solution and the remaining part to be determined by the Boussinesq-type equations. The Stokes-Joukowski potential is adopted in the particular solution for the roll excitation motion. The comparisons of the numerical results indicate that the shallow-water sloshing motions in a rectangular tank can be predicted well based on the Boussinesq-type equations.     

用MPS方法数值模拟低充水液舱的晃荡

液体晃荡是一种非线性的自由面流动现象.在低充水率下,由于液体具有很大的运动空间,晃荡现象具有强烈的非线性特征,自由面的变形较大,剧烈时甚至会翻卷和破碎,这给数值模拟带来很大挑战.本文基于移动粒子半隐式法(Moving Particle Semi-Implicit,MPS)对低充水率的液舱晃荡问题进行了数值模拟.结果表明:当激励频率等于共振频率时,液体撞击到了液舱的顶板,并出现了飞溅现象,此时液体对侧舱壁产生了较大的抨击压力;在低于共振频率时,自由面出现了破碎波及波前的翻卷和融合等现象,抨击压力相对较小.计算结果表明,MPS方法能够很好地预测晃荡引起的拍击现象,数值计算得到的压力能够与实验结果很好地吻合.在自由面的追踪上,MPS方法具有很大的灵活性,能够很好地处理自由面的破碎、融合及液体的飞溅等流动现象.     

基于CIP法的波物相互作用强非线性数值模拟

极端波浪环境作用下,浮体易发生上浪拍击等强非线性现象,这一问题也是波浪与浮体相互作用研究的难点之一。该文基于高阶CIP(Constrained Interpolation Profile)法,采用THINC(Tangent of Hyperbola for Interface Capturing)数值技术精确捕捉自由液面,建立了二维多相流强非线性数值水槽模型。通过模拟线性波和孤立波的生成、传播过程,对该模型的收敛性、稳定性及造波性能进行了全面的验证与分析。利用该数值模型模拟和分析了极端波浪对浮体的强非线性作用。     

Laboratory investigation of the hydroelastic effect on liquid sloshing in rectan- gular tanks

A sloshing experiment is conducted to study the hydroelastic effect in an elastic tank. For this purpose, a translational harmonic excitation is applied to a 2-D rectangular tank model. The lowest-order natural frequencies of the liquid in the tank are determined through the sweep test. The wave elevation and the sloshing pressure are obtained by changing the excitation frequency and the liquid depth. Then the characteristics and the variation of the elevation and the pressure are discussed. The results are compared with the experimental results and the theoretical calculations in a rigid tank. Our analysis indicates that, in the non- resonant cases, the elastic results, the rigid experimental results and the theoretical values are all close to each other. In contrast, under the resonant condition, the elastic experimental result is slightly smaller than the rigid one. Also, the theoretical values are smaller than the experimental results at the resonant frequency.     

SIMULATION OF TANK SLOSHING BASED ON OPENFOAM AND COUPLING WITH SHIP MOTIONS IN TIME DOMAIN

Tank sloshing in ship cargo is excited by ship motions, which induces impact load on tank wall and then affects the ship motion. Wave forces acting on ship hull and the retardation function are solved by using three-dimensional frequency domain theory and an impulse response function method based on the potential flow theory, and global ship motion is examined coupling with nonlinear tank sloshing which is simulated by viscous flow theory. Based on the open source Computational Fluid Dynamics (CFD) development platform Open Field Operation and Manipulation (OpenFOAM), numerical calculation of ship motion coupled with tank sloshing is achieved and the corresponding numerical simulation and validation are carried out. With this method, the interactions of wave, ship body and tank sloshing are completely taken into consideration. This method has quite high efficiency for it takes advantage of potential flow theory for outer flow field and viscous flow theory for inside tank sloshing respectively. The numerical and experimental results of the ship motion agree well with each other.     

The analysis of second-order sloshing resonance in a 3-D tank

Based on the potential theory and perturbation techniques, the problem of second-order sloshing in a three-dimensional tank in combination with surge and sway motions is analyzed. When excitation is applied in both horizontal directions, the second-order resonance can occur when the sum frequency or the difference frequency of any two excitation components is equal to one of the natural frequencies. The resonance can also occur when the sum or difference frequency of one of the excitation frequencies and one of the natural frequencies is equal to another natural frequency.     

船舶横摇的参数激励及对安全性的影响

本文研究了横浪情况下的横摇参数激励问题，在时域域范围内求解了横摇参数激励方程，分析了参数激励对横摇运动响应和船舶安全性的影响。     

Effect of internal sloshing on added resistance of ship

The motion responses of ships carrying liquid cargo are affected not only by external wave excitation, but also by internal sloshing-induced forces and moments. Sloshing flow is coupled with the ship motion. This means the added resistance in waves may change when sloshing occurs inside the tank of the ship. In this study, the motion responses and added resistance of a ship, coupled with the sloshing-induced internal forces and moments are considered by using the linear potential theory. The three-dimensional Rankine panel method, in which the physical quantities are represented by using B-spline basis function, is applied. The sloshing flow of inner tanks is also simulated by using the Rankine panel method and linearized boundary value problem. To study the added resistance, a near-field method, which integrates the second-order pressure on a body surface, is applied. The model ship is a blunt modified Wigley model with two inner tanks. Numerical results obtained without inner tanks are compared with the experimental data, and then the effect of filling ratio of inner tanks on ship motion and added resistance are observed. The components that induce added resistance are examined, and the effects of surge motion on sloshing flow and added resistance are briefly considered. This study shows that the sloshing flow inside the inner tanks may significantly influence not only the motion responses, but also added resistance, especially, when the incident wave frequency approaches the resonance frequency of the sloshing flow.     

土石坝-覆盖层-基岩体系动力相互作用研究

在我国西部强震区拟建的土石坝多坐落于覆盖层上,覆盖层土体具有动力非线性和饱和特性,土石坝-覆盖层-基岩体系动力相互作用复杂。为研究土石坝-覆盖层-基岩体系动力相互作用特性,分别采用地震动一致输入方法(联合地震惯性力和约束边界)和非线性波动输入方法(联合自由场非线性动力响应和非线性人工边界),对覆盖层上土石坝进行有限元动力反应分析,考虑了覆盖层厚度、土体动力特性、地震强度及地震波频谱特性的影响效应,着重讨论了大坝的加速度反应峰值。结果表明:在覆盖层土体饱和特性的影响下,一致输入方法不能合理模拟大坝体系动力的相互作用,所获得的坝体竖向加速度反应误差显著。非线性波动输入方法理论上更为严密,其所获得的坝顶竖向加速度峰值较一致输入方法降低明显,降低率为20%～62%,且当输入地震动以高频成分为主时一致输入方法的误差较大。对于坝顶水平向加速度峰值,非线性波动输入方法较一致输入方法的降低率为5%～32%。当土体材料阻尼效应明显时一致输入方法的误差较小,当输入地震动以低频成分为主时其误差较大。一致输入方法会明显低估覆盖层上土石坝的极限抗震能力。当土石坝可能遭受竖向分量较大的近场地震时,有必要采用非线性波动输入方法评价大坝抗震性能。