Slamming load on a very large floating structure with shallow draft

The objective of this paper is to estimate the slamming load acting on a pontoon-type very large floating structure with a shallow draft. Experiments were carried out using elastic models with different rigidities in regular waves. The results revealed that the slamming load was strongly influenced by the rigidity of the model. The conditions under which slamming occurs depended on the extent of the bottom emergence and the velocity of the relative wave height at the bow of the model. These results were related to a simple procedure for estimating slamming load.     

超大型浮体结构碰撞损伤研究

基于LS-Dyna数值仿真软件,以双模块超大型浮体结构为研究对象,开展油轮与双模块超大型浮体结构发生碰撞的数值仿真分析.数值仿真中碰撞场景为邮轮撞击模块中部结构,材料模型采用线性强化弹塑性模型,并计人应变速率引起的材料强化,考虑碰撞发生时的接触及摩擦.通过本文的研究,获得了双模块超大型浮体结构变形及损伤规律,讨论了结构的吸能特性和运动规律等,可为超大型浮体结构的耐撞性设计提供参考.     

On the hydroelastic responses of a very large floating structure in waves

New numerical methods are presented for hydroelastic analyses of a very large floating structure (VLFS) of several kilometers length and width. Several methods are presented that accelerate computation without an appreciable loss of accuracy. The accuracy and efficiency of the proposed methods are validated through comparisons with other numerical results as well as with existing experimental results. After confirming the effectiveness of the methods presented, various characteristics of the hydroelastic behavior of VLFSs are examined, using the proposed methods as numerical tools. Received for publication on Dec. 3, 1999; accepted on Dec. 15, 1999     

超大型海上浮式结构物连接器基座强度分析

超大型海上浮式结构物(Very Large Floating Structure, VLFS)是由若干个单模块通过连接器连接而成的海上结构物,连接器是整个结构中最薄弱而又最关键的部分,因此有必要对连接器基座进行静强度分析和极限强度分析。文章采用以包含连接器基座的上箱体为研究对象,选取包含单个连接器基座和两个连接器基座的上箱体局部结构作为模型进行静强度分析,得到了两种模型连接器基座整体Von mises应力不大,但存在基座与连接器连接处、立柱与上箱体底甲板连接处两处明显的高应力区的相关结论。然后,采用非线性有限元准静态法对连接器基座进行极限强度分析,确定结构在危险工况下最先发生破坏的位置,得到基座连接器不同方向的极限承载力。结果表明,连接器基座在各个方向的极限承载力都远大于其载荷预报值,连接器基座具有较大的结构强度储备。文中的研究结果为超大浮体连接器基座的设计和安全可靠性分析提供了相关理论依据。     

超大型浮体模块柔性连接功能仿真模型试验研究

精确评估模块柔性连接性能对连接器和超大型浮体的结构安全性具有重要意义,而模型试验是获取超大型浮体模块柔性连接性能的必要手段。文章以横向浮筒式的浅吃水超大型浮体为研究对象,根据连接器动响应计算结果,设计了柔性连接器模型;通过不同幅值和载荷组合的连接器静态拉伸和压缩试验,研究了超大型浮体连接器的刚度特性,探讨了组合载荷对连接器刚度的影响;通过不同幅值和周期的连接器纵向动态载荷试验,研究了超大型浮体连接器在动态载荷作用下的结构响应,验证了超大型浮体连接器结构的安全性和适用性。试验结果表明在静态和动态载荷作用下文中设计的柔性连接器连接可靠、结构安全,连接器载荷、位移和应力测量结果可为验证连接器结构设计和计算方法提供依据。     

Elastic response characteristics of a very large floating structure in waves moored inside a reef

 This article describes the results of hydraulic model tests of the elastic response of a very large floating structure (VLFS) moored inside a reef in an isolated island. The distributions of strains and vertical displacements due to the elastic response of the VLFS were measured. The response characteristics were strongly affected by deformed nonlinear waves inside the reef. A two-step analytical method to compute the elastic response of a VLFS is proposed, and its validity is verified using the results of the hydraulic model tests. Received: May 2, 2002 / Accepted: March 17, 2003 RID="*" ID="*" Address correspondence to: S. Shiraishi (shiraishi@pari.go.jp) Acknowledgment. This study was supported by the Program for Promotions of Fundamental Transport Technology Research from the Corporation for Advanced Transport and Technology (CATT).     

Minimizing differential deflection in a pontoon-type,very large floating structure via gill cells

When a pontoon-type, very large floating structure is heavily loaded in the central portion, it will deform with its central deflection much larger than its corner deflections. The resulting differential deflection, if large enough, may cause machines and equipment sensitive to differential deflection to cease operation or the floating structure to be subjected to additional large stresses. In this paper, we introduce the so-called gill cells which are compartments within the floating structure with holes or slits at the bottom floor to allow water to flow in and out freely. It will be shown herein that these gill cells reduce the differential deflection and the bending stresses significantly while maintaining the structural stiffness integrity by using the example problem of a super-large floating container terminal.     

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     

A B-spline Galerkin scheme for calculating the hydroelastic response of a very large floating structure in waves

This paper presents an effective scheme for computing the wave-induced hydroelastic response of a very large floating structure, and a validation of its usefulness. The calculation scheme developed is based on the pressure-distribution method of expressing the disturbance caused by a structure, and on the mode-expansion method for hydroelastic deflection with the superposition of orthogonal mode functions. The scheme uses bi-cubic B-spline functions to represent unknown pressures, and the Galerkin method to satisfy the body boundary conditions. Various numerical checks confirm that the computed results are extremely accurate, require relatively little computational time, and contain few unknowns, even in the region of very short wavelengths. Measurements of the vertical deflections in both head and oblique waves of relatively long wavelength are in good agreement with the computed results. Numerical examples using shorter wavelengths reveal that the hydroelastic deflection does not necessarily become negligible as the wavelength of incident waves decreases. The effects of finite water depth and incident wave angle are also discussed.     

超大型浮体结构考虑非线性项的波浪力响应计算

为求解超大型浮体结构波浪响应问题,将其简化成弹性梁板模型。以有限元软件为基础来建立超大型浮体结构的弹性梁板模型,在势流理论的基础上,将速度势分解为入射势、绕射势和辐射势三部分,并利用格林函数法推导出一阶、二阶波浪速度势的表达式。以此为理论基础,编制了相应的计算程序来计算浮体结构所受到的二阶波浪力,最后建立了梁板模型的水弹性响应方程,对非线性波浪力作用下的浮体结构的水弹性响应进行求解分析,并分析了波向对响应振幅的影响。     

Analysis of the slowly varying drift force on a very large floating structure in multidirectional random seas

In designing the mooring system of a very large floating structure (VLFS), it is essential to estimate the slowly varying drift force in random seas. For a small vessel, Hsu's method or Newman's approximation may be used to simulate this slowly varying drift force. However, based on experiments and/or field observations, it was found that the slowly varying drift force acting on a VLFS could be reduced to a great extent from the simulated values based on those methods. Thus, the conventional methods are not applicable for a VLFS. This discovery led to the development of several methods for estimating the slowly varying drift force on a VLFS, e.g., Namba et al. (J Soc Nav Archit Jpn 186:235–242, 1999), and Shimada and Maruyama (J Soc Nav Archit Jpn 190:347–351, 2001). However, Namba's method is only applicable to a pontoon-type VLFS with a shallow draft, and Shimada's method is too simplified to account for the general shape of a VLFS and elastic deformation. These methods have been expanded in this article, and by our proposed method, any shape of VLFS and the effect of elastic deformation of the VLFS can be included. Formulations and several numerical examples are given.     

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.     

超大型海上浮式基地柔性连接器设计及强度分析

超大型海上浮式基地（VLFB）连接器的设计是 VLFB 设计过程中非常关键的环节。文章采用 Sesam/GeniE建立 VLFB 模块水动力模型,计算出不同刚度连接器在4个海况下的最大载荷值,选取了合适的连接器刚度,并计算出此刚度下的连接器在5个海况下不同浪向角的连接器载荷,选取7级海况45°浪向角的载荷作为设计载荷值,提出了一种柔性连接器的设计方案,并用 Abaqus 建模进行非线性分析,结果表明方案符合设计要求,为VLFB 连接器的设计提供了参考。     

Time-domain analyses of elastic response and second-order mooring force on a very large floating structure in irregular waves

Real sea areas where very large floating structures are installed are random wave fields. Then, it is necessary to analyze the responses in the time domain due to directional waves. There exist hydroelastic deflections and slow drift motions in the responses of VLFSs in ocean waves. However, it is very time consuming to solve the equations of motion in the time domain and obtain these responses due to directional waves. It is unnecessary to solve such equations in the time domain, if mooring forces can be turned into on equivalent linear system. In this paper, we analyze the time-series responses without solving the equations of motion in the time domain. And, the corresponding model tests in uni- and two-directional irregular waves are carried out. The present method is validated by comparisons between the analytical and measured results of time histories, and moreover, the analytical method of a slowly varying wave drift force is also validated.     

新概念超大型浮式海基规划与设计

阐述基于载荷设定、弹性响应分析、结构建模、安全性/功能性评估及维护管理等关键构建要素的——新概念超大型浮式海基规划与设计流程。     

超大型多模块浮动平台柔性连接器刚度配比优化

连接器是超大型多模块浮动平台的关键部件,其刚度特性对多模块浮动平台的动力学响应影响很大,如何合理地安排连接器的各向刚度对连接器的设计至关重要.本文提出了一种通用的优化流程以寻求连接器的最优刚度配比.考虑实际工程需求,基于线性加权和法构建了优化问题的目标函数,并采用遗传算法寻求目标函数的全局最优解.针对不同模块数量的链式浮动机场,开展了不同海况下连接器最优刚度配比研究.结果表明,连接器采用纵向小刚度、横向和垂向大刚度对链式浮动机场的动力学性能最为有利.本文提出的连接器刚度配比优化算法可为不同类型超大型多模块浮体系统的连接器结构设计提供理论指导.     

基于浮体Morison方程的半潜式超大型浮式结构波浪力简化计算方法

研究了半潜式超大型浮式结构中移动式海上基地（MOB）在高海况随机波作用下波浪力的简化计算方法。文中基于修正后的浮体Morison方程,经理论推导得出了MOB结构波浪力的计算公式。以MOB结构“三模块模型”为例,研究其在6级海况条件下基于Bretschneider谱模拟的随机不规则波中浪向角变化在0°~90°范围内,各模块的波浪力-历时规律,将本文简化算法的计算结果统计值与势流理论的结果相互对比,并对二者进行误差分析。结果表明：运用本文简化算法得到的MOB波浪力统计结果与势流理论的结果吻合程度高,且二者之间的相对误差在工程允许的范围之内,可充分验证本文方法的正确性、合理性与可行性。本文算法相比于势流理论而言更加简单,建议在结构初步设计阶段运用该方法可高效地评估大量不同工况下MOB结构的波浪荷载,研究成果可为半潜式超大型浮式结构动力响应研究奠定基础。     

超大型浮体柔性连接器疲劳强度模型试验

为了保证超大型浮体的作业安全,需要精确评估连接器结构疲劳强度。文章针对一种由尼龙柔性夹层和环肋加强圆管轴构成的铰接式连接器,开展了疲劳强度模型试验,测量了热点应力、疲劳寿命和裂纹扩展。考虑接触、柔性层以及开孔的影响,采用三维有限元方法计算了连接器结构应力,分别基于S-N曲线和裂纹扩展,给出了柔性连接器疲劳寿命评估方法。比较分析表明,计算得到的连接器结构应力和疲劳寿命与模型试验结果吻合,文中方法可用于柔性连接器结构疲劳强度设计     

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.