Hydroelastic analysis of oblique irregular waves with a pontoon-type VLFS edged with dual inclined perforated plates

The fluid-structure interaction of oblique irregular waves with a pontoon-type very large floating structure (VLFS) edged with dual horizontal/inclined perforated plates has been investigated in the context of the direct time domain modal expansion theory. For the hydroelastic analysis, the boundary element method (BEM) based on time domain Kelvin sources is implemented to establish water wave model including the viscous effect of the perforated plates through the Darcy’s law, and the finite element method (FEM) is adopted for solving the deflections of the VLFS modeled as an equivalent Mindlin thick plate. In order to enhance the computing efficiency, the interpolation-tabulation scheme is applied to assess rapidly and accurately the free-surface Green function and its partial derivatives in finite water depth, and the boundary integral equation of a half or quarter VLFS model is further established taking advantage of symmetry of flow field and structure. Also, the numerical solutions are validated against a series of experimental tests. In the comparison, the empirical relationship between the actual porosity and porous parameter is successfully applied. Numerical solutions and model tests are executed to determine the hydroelastic response characteristics of VLFS with an attached anti-motion device. This study examines the effects of porosity, submerged depth, inclined angle and gap distance of such dual perforated anti-motion plates on the hydroelastic response to provide information regarding the optimal design. The effects of oblique wave angle on the performance of anti-motion and hydroelastic behavior of VLFS are also emphatically examined.     

斜坡型潜导堤波浪力特性的数值研究

为研究各水位期不同波高作用条件下,斜坡型潜堤所受波浪力的特性,基于某潜导堤工程设计与物理模型资料,采用FLUENT软件建立二维波浪数值水槽,用物理模型试验数据验证模型的可靠性,对不同淹没水深和波高下斜坡型潜导堤所受波浪力进行数值计算,分析波浪力与相对波高、相对淹没水深之间的关系,结合其他形式潜堤波浪力的经验计算公式拟合得出该斜坡型潜导堤堤顶面最大波浪力计算公式。结果表明:波浪力大小受相对波高、相对淹没水深的影响较为显著,其影响机理与波浪场流体运动特征相关;相对于波高的变化,波浪力对淹没水深的变化更为敏感,且波浪力在不同的淹没水深区间和不同的作用位置均呈现出不同的变化规律。     

带横隔板开孔沉箱所受波浪力的研究

研究了斜向波与无限多开孔沉箱的相互作用。依照结构物的几何形状,整个流域被分成无限多个子域,在每个子域内应用特征函数展开法求解速度势。对于沉箱内的波浪运动,引入相位差概念;同时,在构造反射波模型时,考虑了结构物的几何形状影响。进行了数值试验,分析了开孔沉箱水平波浪力及横隔板受力特点,详细讨论了波浪入射频率、入射角度、相对消浪室宽度及开孔影响系数对开孔沉箱波浪力的影响。     

基于高阶面元法的浅水域中船-船水动力相互作用数值预报

文章开发了一种基于非均匀有理B样条（NURBS）的三维高阶面元法对浅水域中两船会遇和追越时的船-船水动力相互作用进行预报。该方法采用NURBS精确表达船体曲面,采用配置点法满足离散的边界积分方程,在边界面上的源强分布确定之后采用B样条表达物面速度势分布。基于低速假设,忽略了自由面的兴波效应,采用无穷镜像法处理刚性自由面和浅水效应,采用时间步进法在时域内求解速度势。将文中计算结果与基于RANS方程求解的CFD方法和细长体理论方法计算结果比较,验证了该方法的有效性。在此基础上,分别在不同水深、船间横向间距和船速下进行了系列的计算,分析了这些因素对船-船水动力相互作用影响。结果表明,在相同的工况下,船-船会遇时相互作用力比追越时更大,对水深变化更敏感,而对横向间距不如追越时敏感。     

双层多孔薄壁结构在斜浪环境中的波浪反射与透射分析的多域边界元法研究（英文）

In the present paper, we examine the performance of an efficient type of wave-absorbing porous marine structure under the attack of regular oblique waves by using a Multi-Domain Boundary Element Method(MDBEM). The structure consists of two perforated vertical thin barriers creating what can be called a wave absorbing chamber system. The barriers are surface piercing, thereby eliminating wave overtopping. The problem of the interaction of obliquely incident linear waves upon a pair of perforated barriers is first formulated in the context of linear diffraction theory. The resulting boundary integral equation, which is matched with far-field solutions presented in terms of analytical series with unknown coefficients, as well as the appropriate boundary conditions at the free surface, seabed, and barriers, is then solved numerically using MDBEM. Dissipation of the wave energy due to the presence of the perforated barriers is represented by a simple yet effective relation in terms of the porosity parameter appropriate for thin perforated walls. The results are presented in terms of reflection and transmission coefficients. The effects of the incident wave angles, relative water depths, porosities, depths of the walls, and other major parameters of interest are explored.     

Experimental and numerical study of the effects of heave plate on the motion of a new deep draft multi-spar platform

The heave motion of a floating structure is critical, as a favorable heave characteristic permits dry tree systems, amongst other benefits. The heave response can be suppressed by installing heave plates. However, the associated hydrodynamic effects, which include viscous damping and added mass, are very complicated. Moreover, there are limited experimental investigations to understand the heave plate effects on actual platform designs. This paper aims to study the abovementioned issue based on a novel deep draft multi-spar (DDMS) platform, for four different configurations (with/without upper and lower heave plates). A set of experiments (free decay, regular and irregular wave tests) are conducted, and compared with time domain and linearized frequency domain analyses. Amongst other things, the investigations and discussions include the added mass and damping coefficients for the platform and heave plates, comparison of experimental and numerical results, and the influence of the heave plates on the surge, heave and pitch motions.     

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.     

无航速三体浮驳水动力特性频域分析

为了研究不同工作条件下无航速三体浮驳的水动力特性的变化规律,根据势流理论和波浪的辐射/衍射理论对无航速三体浮驳的水动力特性进行了分析,并以某三体浮驳为例应用水动力计算软件AQWA对其在不同工况下进行了水动力计算。分别求得了该三体浮驳在不同水深、不同吃水深度时的附加质量、附加阻尼、不同波向下的波浪激励力和幅值响应算子随波频的变化曲线,并对其进行了对比分析。结果表明,水深对三体浮驳附加质量、附加阻尼、波浪激励力和幅值响应算子均有较大的影响,特别是在低波频时影响较为显著;水深大于20倍吃水深度后三体浮驳的水动力系数可按照无限水深进行近似计算。吃水深度对三体浮驳纵荡和横荡幅值响应算子几乎无影响,对垂荡和纵摇幅值响应算子的影响较小,对横摇和艏摇幅值响应算子的影响较大。     

Water wave scattering by a sphere submerged in uniform finite depth water with an ice-cover

Using the multipole method, we formulate the problem of water wave scattering by a submerged sphere in uniform finite water depth with an ice-cover, the ice-cover being modelled as an elastic plate of very small thickness. This leads to an infinite system of linear equations which are solved numerically by standard techniques. The vertical and horizontal forces on the sphere are obtained and depicted graphically against the wave number for various values of the depth of water and flexural rigidity of the ice-cover to show the effect of the presence of ice-cover and also the effect of varying depth of water on these quantities. When the flexural rigidity is taken to be zero, the numerical results exactly coincide with the curves of the vertical and horizontal forces on the sphere for the cases of uniform finite depth water with a free surface.     

弹性浮板对水波的衍射与动弯矩分析

文章基于水波理论和Mindlin厚板动力学理论,采用Wiener-Hopf方法,分析研究了水面上弹性浮板对水波的衍射与动弯矩分布问题.为确定极点,首先分析求解了有限水深的导波问题.而后将原来混合边值问题的求解归结为求解无穷线性代数方程组的问题.文中将分析计算结果与前人的计算结果及实验数据进行了对比,并对结果进行了分析讨论.最后,分析了结构几何参数和物理参数挠度和动弯矩分布的影响.     

On maximum forces exerted by floating ice on a structure due to constrained thermal expansion of ice

The problem of interaction between a floating ice cover and an engineering structure is considered, in which the ice–structure contact forces are caused by an increase in ice temperature due to solar radiation in situations, when the lateral thermal expansion of ice is constrained. The focus is on the determination of the maximum thermally-induced horizontal force exerted on a structure wall, assuming that the magnitude of this force is bound by the smallest force capable of fracturing the ice cover due to its buckling. The ice cover is modelled as a rectangular plate of uniform thickness, with its four edges being constrained by vertical rigid walls, and it is assumed that ice deforms, and eventually fails, by the mechanism of viscous creep buckling. The plate is subjected to in-plane axial compressive stresses developing in ice to prevent its thermal expansion due to solar heating, and is transversely (vertically) bent by the forces caused by the reaction of underlying water. The floating ice is treated as a material whose elastic and viscous properties depend on temperature and the ice porosity, and therefore they vary with time and the depth of ice. The results of numerical simulations, conducted for a variety of the ice plate horizontal dimensions, thicknesses and daytime temperature-change scenarios, illustrate the evolution of the plate deflection surface prior to its failure, and show the time variation of the maximum forces exerted by ice on a structure wall as functions of the ice thickness and maximum daytime temperature rise at the top surface of ice.     

水波与双圆型透水板的相互作用（英文）

In this paper we have investigated the reflection and the transmission of a system of two symmetric circular-arc-shaped thin porous plates submerged in deep water within the context of linear theory. The hypersingular integral equation technique has been used to analyze the problem mathematically. The integral equations are formulated by applying Green's integral theorem to the fundamental potential function and the scattered potential function into a suitable fluid region, and then using the boundary condition on the porous plate surface. These are solved approximately using an expansion-cum-collocation method where the behaviour of the potential functions at the tips of the plates have been used. This method ultimately produces a very good numerical approximation for the reflection and the transmission coefficients and hydrodynamic force components. The numerical results are depicted graphically against the wave number for a variety of layouts of the arc. Some results are compared with known results for similar configurations of dual rigid plate systems available in the literature with good agreement.     

双层开孔直立式板结构的消波性能试验

在波浪与双层开孔直立式消浪板结构相互作用的模型试验中,给出了双层开孔直立式消浪板不同开孔形式在规则波作用下的透射系数.利用透射系数来反映结构的消波性能.分析了透射系数与水深、波浪要素之间的无量纲关系曲线.试验结果表明,双层开孔直立式消浪板结构具有消能好的优点.     

开孔平板水下振动及声辐射特性

采用有限元与间接边界元相结合的方法,以开有圆孔、四边简支、无障板的钢制平板为对象,开展开孔板水下振动及声辐射特性研究。首先,计算开孔板在空气中和水中的固有频率。在空气中,开孔板的固有频率较无孔板低,随着开孔面积增大,大部分固有频率降低;在水中,由于开孔可明显降低平板水下振动的附连水质量,开孔板的固有频率升高,且随开孔面积的增大,固有频率升高。然后,开展单位力激励下开孔板的水下振动声辐射研究,相同激励下,开孔板大部分频段的辐射噪声和辐射效率明显降低,且随着开孔面积的增大,降低量增大,辐射声功率和辐射效率的峰值向高频移动。研究结果表明,开孔可显著改变平板水下振动与声辐射特性。     

不对称流动对航道中航行船舶的影响

本文利用能够处理不对称自由面流动的改进的Dawson's方法来研究当船偏离航道航行时航道岸壁及水深对船舶所受的水动力的影响.计算结果与模型试验进行了比较,结果表明当航道水深不是很浅时,本文提出的方法和计算程序可以给出比较满意的结果,同时还可以发现当船舶偏离中心航道航行时,船两侧湿表面压力以及水面变化也是不对称的,水深以及岸边距离都能影响船体所受水动力及船波.     

四柱结构近场干涉的粘流分析（英文）

The hydrodynamic analysis of multi-floating bodies is important and widely used in marine engineering. In this study, we systematically simulated the wave diffraction problem of a fixed vertical four-cylinder structure in regular waves in the time domain in a viscous numerical wave tank. The hydrodynamic interaction of waves with a bottom-mounted structure consisting of four vertical cylinders arranged at the corners of a square shows a complicated interference phenomenon. In this paper, we illustrate and analyze the run-up around the structure and the corresponding wave forces. To investigate the viscous effect on the near-trapping phenomenon, we pay particular attention to investigating the waves near-trapped inside the four-cylinder structure,and make a comparative study of the viscous-and inviscid-flow solutions with the experimental measurements. The results show that the maximum wave elevation occurs on the inner side of the leeside cylinder, and that the wave elevations on the outer side of the cylinders are lower than those on the inner side. We can conclude that viscosity has an obvious damping effect on wave elevations inside the structure. The cylinders show a tendency to drift apart from each other when the near-trapping phenomenon occurs.     

有限域液体附加质量对板结构振动特性的影响

基于附加质量法、公式估算法以及流固耦合有限元方法对有限域流体与结构耦合振动特性进行计算分析,以方箱底板单面接触有限域的液体,以及双面分别接触有限域液体和无限域液体工况为例,通过一系列计算得出工程中处理附连水质量影响的一般方法和经验。给出处理有限流体域问题时附加质量法的一般适用准则,即当浸水参数h/b0.1时,利用附加质量法具有足够的工程计算精度,而当h/b>0.1时,建议采用流固耦合方法进行计算。     

Investigation of heave response of the deepwater octagonal FDPSO using various heave plate configurations

Heave plates can be employed to control undesirable heave motion amplitudes of the deepwater octagonal Floating, Drilling, Production, Storage, and Offloading (FDPSO) platform. Numerical simulations and model tests were applied to analyze and investigate the hydrodynamic response and the feasibility of the heave plate configurations. The diameter and the depth below the free surface of a single-layer heave plate, as well as the spacing of two-layer heave plates, were considered as the primary variables when studying the effect of heave plates on FDPSO hydrodynamics. The analysis results indicate that the heave plate diameter significantly affects the heave hydrodynamics, and heave performance could be improved with an increased diameter. In addition, increasing the depth below the free surface of a single-layer heave plate does not effectively suppress the heave motion within the range of draft depths tested. The target FDPSO obtained better heave characteristics with increased spacing between the two-layer heave plates. Furthermore, the global performances of the octagonal FDPSO with these typical heave plate configurations were comparatively analyzed. The results indicate that from a hydrodynamic point of view, the single-layer heave plate configuration has an advantage over the two-layer heave plate configuration.     

Hydroelastic responses and interactions of floating fuel storage modules placed side-by-side with floating breakwaters

This paper is concerned with the hydroelastic responses and hydrodynamic interactions of two large floating fuel storage modules placed side-by-side with the presence of floating breakwaters. These modules and breakwaters form the floating fuel storage facility (FFSF). The floating storage modules and breakwaters are modeled as plates and the linear wave theory is used to model the water waves in the numerical model. The numerical model is verified with existing numerical results and validated with experimental test. Numerical simulations are performed to determine the hydroelastic behavior and hydrodynamic interactions of floating storage modules placed adjacent to each other and enclosed by floating breakwaters under various incident wave angles. The effects of breakwaters, drafts, channel spacing formed by the two adjacent modules and water depth on the hydroelastic responses of the modules are investigated. The wave induced responses of multiple floating storage modules enclosed by floating breakwaters are also examined.