海洋浮式结构流固耦合动力建模分析

讨论了海洋大体积结构的流固耦合分析数学模型,建立了不可压缩理想流体中流固耦合系统结构运动微分方程,给出了用干模态分析方法计算流体附加质量矩阵、流体阻尼阵和流体附加刚度矩阵以及广义力的计算公式.     

海洋浮式结构流固耦合动力建模分析

讨论了海洋大体积结构的流固耦合分析数学模型，建立了不同压缩理想流体中流固耦合系统结构运动微分方程，给出了用干模态分析谅都督充体附加质量矩阵、流体阻尼阵和流体附加刚度矩阵以及广义力的计算公式。     

基于数值波浪水池的柔性浸没短板流固耦合研究

浸没于水中的柔性板壳可作为水下防波堤、波浪能装置等海洋工程结构的简化模型。论文基于Stokes五阶波浪和人工阻尼消波理论对软件ANSYS Fluent进行二次开发，在构建的数值波浪水池中，对柔性浸没短板的有限元结构模型进行双向流固耦合计算。改变板壳结构刚度、沉没深度等参数，分析短板的水弹性振动和波浪的透射系数。仿真结果表明，短板在特定的板壳结构刚度和沉没深度下会发生共振，并能有效反射波浪。搭建的双向流固耦合计算平台能对复杂的流固耦合现象准确地仿真，为研究柔性浸没短板与波浪相互作用提供可靠的工具。     

基于有限元法的流体与结构的耦合研究

对有限元法离散流固耦合方程进行了简要的介绍,给出了粘性流体与弹性结构的全耦合模型。流体采用k-ε湍流模型进行了有限元计算,采用ALE描述实现固体Lagrangian描述到流体Eulerian描述的过渡,使大变形带来的流体域网格畸变得以避免。对流固耦合方程,采用流固全耦合的迭代算法进行了迭代求解,最后模拟了高雷诺数下湍流流动中冲击致使涡轮结构旋转的过程。计算结果表明,流固耦合的算法是可靠的。     

水中三维结构的湿模态分析方法

水中任意几何形状结构的流固耦合振动特性的研究对船舶及海洋工程应用具有很大的价值。本文利用三维水弹性分析方法计算流体附加质量和恢复力系数，然后求解由结构的干模态广义质量、广义刚度及流体附加质量、流体恢复力系数所构成的耦合特征方程，从而获得结构的湿模态及特征频率。计算结果与整体弹性船模式试验结果吻合。     

弹性螺旋桨流固耦合振动特性分析

[目的]研究弹性螺旋桨在水流中的振动响应特性。[方法]基于CFD/FEM流固耦合方法,利用Workbench平台中的ANSYS-CFX模块对螺旋桨进行双向流固耦合水动力求解,分析弹性螺旋桨变形及应力应变响应特性;考虑到流固耦合对固有特性的影响,利用ACT_Acoustic模块计算桨叶湿模态,结合弹性螺旋桨固有特性和流固耦合水动力结果进行弹性螺旋桨频谱分析。[结果]流固耦合水动力结果相较不考虑流固耦合的定常计算结果更接近试验回归曲线;与干模态相比,弹性螺旋桨前5阶湿模态固有频率减小19%～37%,且四阶和五阶干湿模态振型存在交错情况。频谱分析结果表明,水动力轴向推力和扭矩是弹性螺旋桨在流场中振动响应的主要影响因素,且主要引起弹性螺旋桨的一阶湿模态悬臂振动;桨叶面上,从叶梢处到导边和叶中部分,再到随边部分,最后到叶根处,结构响应逐渐降低。[结论]所做研究可为弹性螺旋桨流固耦合计算分析提供方法途径,也为螺旋桨流固耦合振动噪声分析打下了一定基础。     

不同碰撞角度下水-船-墩流固耦合数值模拟研究

为研究不同碰撞角度下流体对船桥碰撞过程的影响，本文建立了水-船-墩精细化流固耦合模型，流体域采用ALE描述，船-桥结构采用Lagrange描述，通过罚函数算法实现结构-流体间的耦合。通过数值造波结果与解析解对比，验证了数值水池和耦合接触算法的可靠性。随后在0°～45°范围内开展了碰撞数值模拟，并与附加质量模型在能量转化、碰撞力、桥墩内力及位移、船舶损伤及航迹方面进行了对比。结果表明：流体对碰撞力影响较小；附加质量模型会略微夸大桥墩位移，但差别较小；两种模型的船舶撞损差别较大，不考虑流体时将夸大船舶撞损程度，最高可达21%；流体对船舶航迹与姿态会产生显著影响，流固耦合模型中船舶会明显滞后于附加质量模型。     

考虑流固耦合影响的水中桩基结构振动特性分析

水-结构的耦合振动是一个比较复杂的问题,在设计中,只有考虑水体对结构基频及阻尼比等振动特性的影响,才能使结构设计更为合理、可靠。以往研究多分析水体的附加质量效应对桩柱基频的影响,对水深、桩径、上部结构等因素的影响尚缺乏进一步的研究,对水体的阻尼比增大效应也缺乏定量分析。鉴于工程的需要,利用有限元分析软件ADINA建立水体-桩基结构相互作用的三维有限元数值模型,对流固耦合作用下结构的基频和阻尼比进行计算,分析多种因素对水中结构振动特性的影响,并给出水体产生的阻尼比推荐值。结果表明,水体会引起结构基频降低及结构阻尼比增大,流固耦合作用对振动特性的影响不容忽视。     

考虑铺层的复合材料螺旋桨流固耦合计算及验证

为了验证考虑铺层的复合材料螺旋桨流固耦合算法的正确性,利用ANSYS/CFX软件,对±45°对称铺层的玻璃纤维增强材料螺旋桨建立流体模型和结构模型,实现双向流固耦合稳态求解,得到不同进速系数下的敞水性能,模型桨敞水试验结果表明,数值计算与试验吻合良好,均满足工程应用的要求,验证了采用ANSYS/CFX双向流固耦合算法计算复合材料螺旋桨的正确性。     

水下结构声固耦合振动的特征值计算

针对水下结构声固耦合振动计算中出现的非对称矩阵(与频率相关)的特征值问题,本文基于共轭子空间迭代法,提出了计算水下结构振动固有频率和振型的双重迭代算法.数值算例表明:该算法收敛性好,用于水下结构声固耦合振动的特征值计算是有效的.文中分别将流体视为不可压缩和可压缩两种情况建立了流固耦合方程,计算了板、加筋板和方箱振动的固有频率和振型,将干模态和湿模态、不可压缩流体和可压缩流体的计算结果进行了比较,并分析了结构刚度和流体边界条件对附加水质量影响系数的影响.     

结构刚度变化对船舶水弹性响应的影响

水弹性力学是研究水动力、惯性力和弹性力之间相互作用的力学分支。本文利用三维线性频域水弹性程序计算了某船在单位幅值正弦规则波中的水弹性响应 ,在结构质量分布不变的前提条件下 ,研究了结构刚度变化对结构水弹性响应的影响 ,得到了一些很有价值的结论。     

基于离散模块梁单元水弹性理论的复杂连接处建模方法

[目的]在离散模块?梁单元(DMB)水弹性理论框架下,提出针对连接形式复杂的超大型浮体结构(VLFS)的新的建模方法,并与已有方法进行对比分析.[方法]首先,概述基于DMB的水弹性分析方法,给出求解连续VLFS结构在波浪作用下的动力响应步骤;然后,针对VLFS复杂连接处进行建模,通过定义连接处的刚度矩阵,对与连接处相邻...     

Study on sloshing in cargo tanks including hydroelastic effects

The sloshing problem in cargo tanks is studied through experiments and numerical analysis. The fluid motion is described using a higher-order boundary element method and the structural response by a thin plate theory. It was found that hydraulic jumps are formed when the excitation frequency is close to the resonance frequency in the case of low filling depth. In the case of high filling depth, the flow resonates and hits the top of the tank, thus inducing a large impact pressure. The pressure on the flexible plate shows amplified initial peaks followed by oscillatory components, the frequency of which coincides with the natural frequencies of the plate in water as a result of hydroelastic effects. Received for publication on Nov. 18, 1998; accepted on May 14, 1999     

Hydroelastic analysis of a very large floating plate with large deflections in stochastic seaway

The hydroelasticity of a very large floating plate with large deflections in multidirectional irregular waves is discussed. After a brief introduction on wave loads on a flexible structure, the paper derives the generalised fluid force acting on a floating structure in multidirectional irregular waves. The nonlinear sectional forces induced by the membrane forces in the plate are deduced. The hydroelastic response equations of a floating plate with large deflections in multidirectional irregular waves are established, and a solution method in the frequency domain is discussed including extreme value statistics. A very large floating structure is chosen as an example. The numerical results show that the influence of the membrane forces on the vertical displacements and the bending moments is noticeable but not that large.     

Time-domain numerical and experimental analysis of hydroelastic response of a very large floating structure edged with a pair of submerged horizontal plates

This paper is concerned with the hydroelastic problem of a pontoon-type, very large floating structure (VLFS) edged with the perforated plates, non-perforated plates or their combination anti-motion device both numerically and experimentally. A direct time domain modal expansion method, taking amount of the time domain Kelvin sources in hydrodynamic forces, in which the fluid flows across the perforated anti-motion plate by applying the Darcy's law, is applied to the fluid–structure interaction problem. A quarter of numerical model is built based on the symmetry of flow field and structure in hydrodynamic forces, and special care is paid to the rapid and accurate evaluation of time domain free-surface Green functions and its spatial derivatives in finite water depth by using interpolation–tabulation method. Using the developed numerical tools and the model tests conducted in a wave basin, the response-reduction efficiency of the perforated plates is systematically assessed for various wave and anti-motion plate parameters, such as plate width, porosity and submergence depth. As a result of the parametric study, the porosity 0.11 is selected as the optimal porosity, and the relationship between the porosity and the porous parameter is developed by using the least-squares fitting scheme. After simulation and verification, the dual anti-motion plates which are the perforated-impermeable-plate combination attached to the fore-end and back-end of the VLFS, are designed for more wave energy dissipation and added damping. Considering variation of the water depths in offshore, discussion on the effectiveness of these anti-motion devices at different water depths is highlighted.     

Connection design for two-floating beam system for minimum hydroelastic response

This paper is concerned with the connection design for a two-floating beam system for minimum hydroelastic response. The frequency domain approach is used for the hydroelastic analysis. The fluid is modelled as an ideal fluid, and the floating beams are modelled by the Euler–Bernoulli beam theory. The boundary element method (BEM) and the finite element method (FEM) are applied to solve the governing equation of the fluid motion and the beam equation of motion, respectively. The study aims to investigate the optimum location and rotational stiffness of the connection for the two-floating beam system with the view to minimize the compliance. The study also investigates the effects of relative beam stiffnesses on the hydroelastic response of the two-floating beam system.     

考虑基础柔性的隔振系统功率流特性分析

根据舰船机械设备安装特性及隔振要求,建立包含机械设备、隔振器和柔性基础的数学模型并对其求解,得到隔振系统在简谐激励下的响应及传递功率流计算公式,讨论了隔振系统中设备质量、隔振器刚度和阻尼、柔性基础刚度和阻尼等参数对隔振能力的影响。理论表明,适当增大机械设备质量、隔振器阻尼及柔性基础阻尼能提高系统隔振能力,较大的隔振器刚度不利于隔振,而基础板柔性对隔振系统的影响与激励频率有关,并给出了柔性基础隔振设计中参数选取的一般规律。     

Hysteretic damping model for laterally loaded piles

Fatigue assessment is a critical design aspect for many offshore structures. Soil-foundation interaction has a direct impact on the system dynamic response of these structures. While the stiffness of the soil-foundation interaction influences the system's natural frequency, the damping influences the amplification of the structural response to environmental excitations. This paper presents a simplified model for estimating the soil damping due to nonlinear soil response for pile foundations, which have wide applications in the offshore industry, such as for supporting jacket platforms, wind turbines and wellhead facilities. The proposed model is fundamentally linked to the damping response of the soil measured at element level therefore it offers design engineers an efficient and accurate way to estimate soil-pile interaction damping based on site-specific soil data. Approaches to include the suggested model for structural analysis are also proposed.     

船舶对称响应的非线性水弹性微分分析法

本文给出了一个预报波浪诱导的船舶垂向运动和结构总体动响应的非线性时域水弹性力学微分分析法，这一理论是控制论的分析方法应用于船体与流体非线性相互作用研究领域的尝试，其流固耦合系统的非线性时域水动作用过程（含记忆效应）由一阶非齐次偏微分方程组来描述，理论预报与Ｓ１７５弹性材料船模型实验比较，结果令人满意。     

Numerical calculation method for the hydroelastic response of a pontoon-type very large floating structure close to a breakwater

This paper presents an effective scheme for calculating the wave-induced hydroelastic response of a pontoon-type very large floating structure (VLFS) when it is near a breakwater. The basic numerical calculation method is the one previously developed by the same author for a VLFS in the open sea (no breakwater), which is expanded to include the effect of the hydrodynamic mutual interaction between the breakwater and the floating structure. The efficiency and accuracy of the proposed method are validated through comparisons with other numerical results and with existing experimental results. After that confirmation, various numerical calculations were conducted, paying special attention to the resonance phenomena which will occur depending on the relation between the wavelength and the clearance between the breakwater and the floating structure. The irregular frequency phenomenon which appears in the calculation of the fluid dynamic problem is discussed in the appendices, including a method for its elimination. Received: October 31, 2000 / Accepted: December 19, 2000