基于时域解耦算法的多液舱浮式结构物运动模拟

对于带有多个晃荡液舱的浮式结构物, 浮体的运动、外场水动力以及各舱内的液体晃荡力会实时相互决定, 发生复杂的耦合作用. 为准确模拟多液舱浮式结构物的运动, 本文引入一种有效的时域解耦算法. 该方法以模态分解法为基础, 通过对浮式结构物所受外域水动力和各液舱内非线性晃荡力进行模态分解, 最终形成时域解耦运动方程, 无需迭代求解过程即可显式计算浮式结构物的瞬时加速度. 该方法可避免传统迭代求解方法在迭代次数、截断误差和收敛特性等方面的不足, 减少解耦过程的计算耗时. 本文进一步结合边界元数值方法, 分别对单液舱浮式结构物和多液舱浮式结构物的工况开展数值模拟研究. 通过与单液舱浮式结构物的实验结果对比, 验证了本文时域解耦算法的有效性. 本文详细分析了晃荡力对单液舱浮式结构物运动的影响, 发现存在一个共振影响区间: 当外场波浪频率在该区间之外时, 可以在时域计算结果中观察到稳定的浮体运动; 在比该区间更低频的波况下, 液舱晃荡力与外场波浪力相位相反甚至可以相互抵消, 此时晃荡液舱的存在可以减弱浮体运动; 在比该区间更高频的波况下, 液舱内晃荡力与外场波浪力可以具有相同相位, 此时晃荡液舱的存在会加剧浮体的运动. 本文进一步研究了四液舱浮式结构物在波浪中的纵荡、垂荡和纵摇运动情况, 发现非线性液舱晃荡可对纵荡和纵摇运动产生影响, 但对垂荡运动影响很小.      

流体动力干扰对单排圆柱桩列波浪力的影响

多物体之间的流体动力干扰特性对超大型海洋结构物的设计和研究十分重要用波动源在截面周线上分布的方法，就垂直桩柱间三维流体动力干扰对波浪力的影响进行了系统的研究，桩柱的数目可达１００余根得到了柱间流体动力干扰力学机理的若干新的特性尤应指出的是，当桩柱根数超过某一数量后，桩柱上的受力表现出有规律的连续依赖性当柱数很大时，无论柱数是奇数还是偶数，中间大部分的桩柱都将表现出均匀的受力特征这些特性的发现对其他形式多体结构物流体动力干扰的研究也有重要的借鉴和指导意义     

水中悬浮隧道在波浪场中非线性动力响应的研究

针对水中悬浮隧道在波浪力作用下动力响应的问题,通过柔度系数法推导得到了悬浮隧道的等效刚度系数,考虑了不同自由度运动之间的耦合作用,建立了悬浮隧道管段的动力响应模型,在时间域内采用逐步积分法迭代求解其运动控制方程.波浪力采用Airy线性波理论和Morison方程计算.计算结果表明,在波浪力作用下悬浮隧道管段产生较大的横荡位移,且随着波频或锚索中预张力的减小,响应振幅增大.在悬浮隧道的动力响应分析中,若不考虑不同自由度运动之间的耦合作用,会过低估计垂荡响应的幅值.     

波浪作用下直立结构物附近强湍动掺气流体运动的数值模拟

波浪破碎卷入气体易对建筑物受力产生压力振荡, 了解波浪作用下建筑物附近掺气水流的运动特性是精确计算建筑物受力的前提. 基于OpenFOAM开源程序包和修正速度入口造波方法建立三维数值波浪水槽, 模型采用S-A IDDES湍流模型进行湍流封闭, 并采用修正的VOF 方法捕捉自由液面, 数值模拟了规则波在1:10的光滑斜坡上与直立结构物的相互作用过程, 重点分析了结构物附近的水动力和掺气水流运动特性. 结果表明, 建立的数值模型能精确地捕捉波浪作用下直立结构物附近的自由液面的变化以及气泡输运过程, 较好地描述气体卷入所形成的气腔形态以及多气腔之间的融合、分裂等过程; 波浪与直立结构物相互作用产生强湍动掺气水流, 其运动过程十分复杂; 掺气流体输运过程中水气界面周围一直伴随着涡的存在, 其中, 气泡的分裂与周围正负涡量剪切作用密切相关, 且其输运轨迹主要受周围流场的影响; 研究揭示了结构物附近湍动能与掺气特性的关系, 发现波浪作用下直立结构物附近湍动能的分布与掺气水流特征参数(气泡数量、空隙率)整体呈现一定的线性关系.      

波浪作用下直立结构物附近强湍动掺气流体运动的数值模拟

波浪破碎卷入气体易对建筑物受力产生压力振荡,了解波浪作用下建筑物附近掺气水流的运动特性是精确计算建筑物受力的前提.基于OpenFOAM开源程序包和修正速度入口造波方法建立三维数值波浪水槽,模型采用S-A IDDES湍流模型进行湍流封闭,并采用修正的VOF方法捕捉自由液面,数值模拟了规则波在1:10的光滑斜坡上与直立结构物的相互作用过程,重点分析了结构物附近的水动力和掺气水流运动特性.结果表明,建立的数值模型能精确地捕捉波浪作用下直立结构物附近的自由液面的变化以及气泡输运过程,较好地描述气体卷入所形成的气腔形态以及多气腔之间的融合、分裂等过程;波浪与直立结构物相互作用产生强湍动掺气水流,其运动过程十分复杂;掺气流体输运过程中水气界面周围一直伴随着涡的存在,其中,气泡的分裂与周围正负涡量剪切作用密切相关,且其输运轨迹主要受周围流场的影响;研究揭示了结构物附近湍动能与掺气特性的关系,发现波浪作用下直立结构物附近湍动能的分布与掺气水流特征参数(气泡数量、空隙率)整体呈现一定的线性关系.     

破碎带波浪的数值模拟

基于一组色散关系得到改进的完全非线性Boussinesq方程建立了一个波浪模型可以模拟近岸水域的波浪变浅、破碎以及在海滩上的爬高等多种变形。波浪破碎引起的能量衰减是在动量方程中引入一个在空间和时间上都只作用于波前的涡粘项来模拟。动海岸线边界用窄缝法处理。波浪爬高用非线性浅水方程推导的非破碎波浪在斜坡上爬高的解析解来验证。本模型还模拟了波浪在斜坡上不同类型的破碎变形过程,并将其波高和平均水位的沿程变化和物理模型实验的结果比较,两者符合良好。     

部分浸入水中的柔性梁非线性自由振动

研究了浸入水中的柔性梁非线性自由振动,假设其底端具有线弹性扭转弹簧支撑,顶端附有不计体积的集中质量块.推导了梁的运动控制方程和边界条件,由于考虑了大挠度,法向运动和轴向运动是非线性耦合的,使用Morison方程给出了流体力的表达式,利用有限差分法和Runge-Kutta法数值分析了梁在真空中和在水中的自由振动,讨论了参数对振动模态、固有频率等的影响.     

基于时域解耦算法的多液舱浮式结构物运动模拟

对于带有多个晃荡液舱的浮式结构物,浮体的运动、外场水动力以及各舱内的液体晃荡力会实时相互决定,发生复杂的耦合作用.为准确模拟多液舱浮式结构物的运动,本文引入一种有效的时域解耦算法.该方法以模态分解法为基础,通过对浮式结构物所受外域水动力和各液舱内非线性晃荡力进行模态分解,最终形成时域解耦运动方程,无需迭代求解过程即可显式计算浮式结构物的瞬时加速度.该方法可避免传统迭代求解方法在迭代次数、截断误差和收敛特性等方面的不足,减少解耦过程的计算耗时.本文进一步结合边界元数值方法,分别对单液舱浮式结构物和多液舱浮式结构物的工况开展数值模拟研究.通过与单液舱浮式结构物的实验结果对比,验证了本文时域解耦算法的有效性.本文详细分析了晃荡力对单液舱浮式结构物运动的影响,发现存在一个共振影响区间:当外场波浪频率在该区间之外时,可以在时域计算结果中观察到稳定的浮体运动;在比该区间更低频的波况下,液舱晃荡力与外场波浪力相位相反甚至可以相互抵消,此时晃荡液舱的存在可以减弱浮体运动;在比该区间更高频的波况下,液舱内晃荡力与外场波浪力可以具有相同相位,此时晃荡液舱的存在会加剧浮体的运动.本文进一步研究了四液舱浮式结构物在波浪中的纵荡、垂荡和纵摇运动情况,发现非线性液舱晃荡可对纵荡和纵摇运动产生影响,但对垂荡运动影响很小.     

海洋大气间气泡的气体输运1)

研究球形小气泡在理想流体的波浪场中的气体扩散过程,把小雷诺数下均匀来流绕流球形气泡的气体交换结果与气泡运动方程耦合在一起进行求解.讨论了溶解于水中的气体浓度、波浪、气泡半径、气泡初始深度对单个气泡气体扩散量的影响.由于气泡云对气体的输运,溶解于水中的气体可出现过饱和状态.对10 m/s风速下气泡云的气体输运量进行了计算,得到水中O     

港口非线性波浪耦合计算模型研究

建立了外域用差分法求解高阶Boussinesq方程、内域用边界元法求解Laplace方程的二维船 非线性波浪力时域计算的耦合模型. 研究了该类耦合模型的匹配条件、耦合求解过程和内域、 外域公共区域长度的确定. 该耦合模型计算结果与只用边界元求解Laplace方程模型的计算 结果和实验结果对比表明，该耦合模型不仅计算精度高，而且计算效率快，适用于研究较大 区域内波浪对物体的非线性作用.     

Recent progresses in studies on wave-current loads on foundation structure with piles and slab

The foundation structure with piles and slab is widely used in offshore wind farm construction in shallow water. Experimental studies on the hydrodynamic loads acting on the piles and slab under irregular waves and currents are summarized with discussion on the effects of pile grouping on the wave forces and wave impact loads on the slab locating near the free surface. By applying the theoretical solution of the wave diffracted by the slab and using the Morison equation to evaluate the wave force on the piles, the effects of the slab on the wave forces acting on the piles are analyzed. Based on the Reynolds-averaged Navier-Stokes (RANS) equations and the volume of fluid (VOF) method, a numerical wave basin is developed to simulate the wave-structure interaction. The computed maximum wave force on the foundation structure with piles and slab agrees well with the measured data. The violent deformation, breaking, and run-up of the wave around the structure are presented and discussed. Further work on the turbulent flow structures and large deformation of the free surface due to interaction of the waves and foundation structures of offshore wind farms needs more efficient approaches for evaluating hydrodynamic loads under the effects of nonlinear waves and currents.     

Frequency-domain analysis of non-linear wave effects on offshore platform responses

In this study, the effects of second-order non-linear random waves on the structural response of slender fixed offshore platforms are investigated based on frequency-domain Volterra-series approach and previously proposed correlation function/FFT-based cumulant spectral method. The cumulants of non-Gaussian water particle kinematics are derived and, Morison force is approximated in cubic functional transformations of Gaussian processes. Volterra series is applied to evaluate the power spectra of wave force and induced structural displacement. The more convenient and more efficient power spectral and tri-spectral analyses by cumulant spectral method are presented as well. The thereby estimated variance, skewness and kurtosis excess agree well with time-domain simulation results. It is found that non-linear wave effects result in stronger non-Gaussian behavior of wave force and structural response, especially in seas of finite water depth.     

A 1D Roe decomposition of a system of equations governing wave height transformation

A Roe‐type decomposition for a system of equations governing onshore/offshore wave transformation in coastal waters is derived. The equation set approximated pertains to coastal waters prior to wave breaking, and is based on depth‐averaging and time‐averaging of the Euler equations. The equations are those used in many commercial codes for simulation of wave height and wave‐averaged currents. This novel approach uses a combination of some standard Roe averages, together with physical reasoning and power series expansions to derive a Roe‐averaged Jacobian (with real, linearly independent eigenvectors) and ensures conservation, and thereby effects the decomposition. It is shown that the resulting derived Roe‐averaged quantities are accurate to a high degree, by comparing them with their analytical equivalents for a wide range of nondimensional water depths and slopes likely to be encountered in coastal problems. Numerical tests of time‐invariant wave height transformation and wave group propagation are undertaken; these indicate good performance of the scheme in practice. Copyright © 2011 John Wiley & Sons, Ltd.     

随机波浪作用下近岸波流场的数值模拟

结合近岸波浪抛物型缓坡模型和近岸波流场模型,对近岸不规则波浪及其破碎后所产生的流场进行了数值模拟. 在不规则波浪场的模拟中,采用JONSWAP波浪谱对入射单向不规则波浪要素按等分频率法进行离散,应用考虑波浪不规则性和破碎效应的抛物型缓坡方程对波浪场进行数值模拟,并基于抛物型缓坡方程中的波浪势函数等参数计算波浪辐射应力,以波浪辐射应力为主要动力因素基于近岸流数学模型对近岸波浪破碎所产生的近岸流场进行数值模拟,并对数值模拟结果进行了验证. 模拟结果表明该模型可有效地用于研究波浪破碎产生的近岸波流场.      

Dynamics of dual pontoon floating structure for cage aquaculture in a two-dimensional numerical wave tank

The trend of using floating structures with cage aquaculture is becoming more popular in the open sea. The purpose of this paper is to investigate the dynamic properties of a dual pontoon floating structure (DPFS) when attached to a fish net by using physical and numerical models. A two-dimensional (2-D) fully nonlinear numerical wave tank (NWT), based on the boundary element method (BEM), is developed to calculate the wave forces on the DPFS. The wave forces on a fish net system are then evaluated using a modified Morison equation. The comparisons of dynamic behaviors between numerical simulations and experimental measurements on the DPFS show good agreement. Results also display that a fish net system causes the resonant response of body motions and mooring forces to be slightly lower due to the net's damping effect. Finally, for designing the rearing space of cage aquaculture, the influences which net depth and net width have on the DPFS dynamic responses are also presented in this paper.     

Investigations on the porous resistance coefficients for fishing net structures

The porous media model has been successfully applied to numerical simulation of current and wave interaction with traditional permeable coastal structures such as breakwaters. Recently this model was employed to simulate flow through and around fishing net structures, where the unknown porous resistance coefficients were adjusted by fitting the available experimental data. In the present paper, a new approach was proposed to calculate the porous resistance coefficients based on the transformation of Morison type load model. The transformation follows the principle that the total forces acting on a net panel from Morison type load model should be equal to the forces obtained from the porous media model. In order to account for the interaction effects in-between the twines, two coefficients were introduced, and they were calibrated by minimizing the least square error function. Extensive validation cases were carried out to examine the performance of the numerical model. This includes steady current flow through plane net panels and circular fish cages, and wave interaction with plane net panels. A variety of fishing nets with different solidity ratios were used in the validation cases, from which it was seen that the overall agreement between the numerical and experimental results is fair.     

规则波作用下垂直圆柱局部波浪力

在ＫＣ为４０～３５，雷诺数Ｒｅ为６×１０３～２×１０４参数范围内就规则波作用下垂直圆柱局部波浪力进行了实验研究．给出横向力随ＫＣ数类型变化的划分．基于Ｓｔｏｋｅｓ二阶波理论和Ｍｏｒｉｓｏｎ公式得到圆柱阻力系数ＣＤ，惯性力系数ＣＭ和最大升力系数ＣＬｍａｘ沿桩柱的分布及其随ＫＣ数的变化规律．结果表明，在波表面间歇区的桩柱的局部水动力系数变化显著，越向波峰位水动力系数ＣＤ和ＣＬｍａｘ越减小，而ＣＭ值却越增高．     

Numerical study of breaking waves by a two‐phase flow model

A two‐phase flow model, which solves the flow in the air and water simultaneously, is presented for modelling breaking waves in deep and shallow water, including wave pre‐breaking, overturning and post‐breaking processes. The model is based on the Reynolds‐averaged Navier–Stokes equations with the k ?ε turbulence model. The governing equations are solved by the finite volume method in a Cartesian staggered grid and the partial cell treatment is implemented to deal with complex geometries. The SIMPLE algorithm is utilised for the pressure‐velocity coupling and the air‐water interface is modelled by the interface capturing method via a high resolution volume of fluid scheme. The numerical model is validated by simulating overturning waves on a sloping beach and over a reef, and deep‐water breaking waves in a periodic domain, in which good agreement between numerical results and available experimental measurements for the water surface profiles during wave overturning is obtained. The overturning jet, air entrainment and splash‐up during wave breaking have been captured by the two‐phase flow model, which demonstrates the capability of the model to simulate free surface flow and wave breaking problems.Copyright © 2011 John Wiley & Sons, Ltd.     

Numerical and experimental study on the dynamic behavior of a sea-star tension leg platform against regular waves

This paper describes an experimental work on a 1: 100 scaled model of a miniature sea-star tension leg platform (TLP) in a wave flume. Two different numerical models are developed: finite element model (FEM) based on the Morison equation and boundary element model (BEM) based on a 3D diffraction/radiation theory. The developed codes are used to calculate hydrodynamic forces and related coefficients. The nonlinear hull/tendon coupled dynamic equation of a mini seastar TLP is solved by using a modified Euler method (MEM). The results of numerical modeling of the motion response behavior of the platform in different degrees of freedom are compared with experimental data. This comparison shows good agreement between the results. Furthermore, this modeling reveals that the first-order diffraction method and quasi-static tendon modeling are sufficient in general for the hydrodynamic analysis of the sea-star TLP.