预报超大型浮式结构物水弹性响应方法的比较

超大型海洋浮式结构物(VLFS)在利用海洋空间和开发海洋资源方面有着很大的实用价值.但如何精确有效地计算和预报其在波浪中的水弹性响应是设计过程中的一个非常重要的技术问题.目前,很多学者提出了不同的简化方法来预报VLFS的水弹性响应.文章全面地介绍了关于计算VLFS水弹性响应的解析方法和数值方法的研究现状,并将相应的数值结果与已有的试验数据相比较,进行了分析讨论.     

三维水弹性力学中的结构广义质量计算

该文给出了三维水弹性力学中弹性模态位移振型归一化时广义质量的计算方法,并应用三维有限元方法计算了箱式大型浮体结构的固有频率和广质量,经与均匀梁解析解的比较表明,两种方法差异不大,因此,采用均匀染解析解来计算这种结构的固有频率和广义质量是完全可行的,简化了计算工作。     

Time-domain,shallow-water hydroelastic analysis of VLFS elastically connected to the seabed

In order to ensure the safe operation of a VLFS, a combination of mooring, breakwater and other motion reducing systems is employed. In the present work, the transient hydroelastic response of a floating, thin elastic plate, elastically connected to the seabed, is examined. The plate is modelled as an Euler-Bernoulli strip, while the linearized shallow water equations are used for the hydrodynamic modelling. Elastic connectors are approximated by a series of simple spring-dashpot systems positioned along the strip. A higher order finite element scheme is employed for the calculation of the hydroelastic response of the strip-connector configuration over the shallow bathymetry. After the definition of the initial-boundary value problem, its variational form is derived and discussed. Next, on the basis of the aforementioned formulation, an energy balance expression is obtained. The effect of variable bathymetry on the response of a two connector-strip system is examined by means of three seabed profiles featuring a flat bottom, an upslope and a downslope environment. For the flat bottom case, the strip response mitigating effect exerted by the employment of two and three elastic connectors is considered. Finally, by means of the derived energy balance equation, the energy exchange is monitored, providing a valuable insight into the transient phenomena that take place in the studied configurations.     

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.     

箱式超大型浮体在不平底部海域中的水弹性响应

采用作者们(2007)提出的函数展开法描述箱式超大型浮体漂浮在不平底部海域中的水弹性响应问题.将速度势沿静水面位置展开,其系数是水平位置的函数.根据速度势满足拉普拉斯方程就可将这些系数简化到只有两个未知函数.海底条件和平板动力学方程或联合的自由面条件可以分别在Ⅰ区和Ⅱ区建立两个方程用于确定这两个未知函数.不同区域的解要在公共界面上进行匹配.在求解水弹性问题时,展开法必须要截断,从原理上来说,保留的项数越多,其解可以适用于更高阶的kh,其中k是波数,h是水深.作为一个例子,文中给出了只保留一项的结果,而这正好是人们所熟悉的浅水方程.     

基于直接计算方法的海上超大型浮式结构物单模块强度分析

海上超大型浮式结构是由若干个与半潜平台相似的浮体通过连接器相连而成的一种新型海上结构,目前对其结构强度分析较少。文章基于直接计算方法,采用SESAM/Hydro D进行超大浮体单模块水动力分析并预报其波浪载荷,进而调用SESAM/Sestra模块进行超大浮体总体强度有限元分析。分析表明,超大浮体的三个连接部位出现了较大应力集中。选取这三处连接部位作为关键节点,采用ANSYS计算该三处关键节点的局部强度。研究结果表明,在横撑与下浮体连接处总体和局部应力均最大,该部位是易产生疲劳破坏的部位,需要重点研究。     

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。     

碰撞事故时超大型浮体模块连接处荷载特性研究

精确评估模块连接处荷载特性对超大型浮体的水动力设计及结构安全性研究具有重要的工程意义。文章以5模块半潜式超大型浮体为研究对象,考虑碰撞荷载和风、浪、流环境荷载的联合作用并采用AQWA软件对超大型浮体模块连接点处的受力特性开展了数值计算。船舶碰撞荷载简化为矩形脉冲,采用定常风、定常流以及JONSWAP波谱,探讨了船舶碰撞角度、撞击位置、环境荷载等因素对模块连接点受力特性的影响。该文的研究成果可为事故荷载作用时超大型浮体连接器结构设计和强度计算提供一定依据。     

新型超大型浮式海上基地消浪室方案试验研究

新型超大型浮式海上基地（VLFOB）设计采用了由两层直立开孔式消浪墙组成的消浪室结构。根据内、外消浪墙开孔率的不同,提出6组消浪室方案。通过模型试验研究,对比分析不同消浪室方案下的消波效率和VLFOB水动力性能,结果表明：一般地,消浪室开孔率越小,消波效率越高,VLFOB的纵荡幅值和系泊力越大,单体间连接载荷相对较大;相同消浪室方案下,入射波能级提高使得消波效率降低;采用内外开孔率分别为0.16和0.24的消浪室方案,不仅消波效率较高,而且单体间的连接载荷也较小。     

Analysis on the applicability of VLFS for China

With the advantages on rapid construction,no limitation of extent,less influence on environment, the VLFS has been turned into the focus of coastal and offshore engineering studying.As the platform,VLFS was built as airport,huge oil house etc,and would play the role of ocean economics,politics and military.The restrictive condition of VLFS is strong wave by monsoon,seismic,serious bomb etc.The floating breakwater should be put forward to shelter VLFS.The analysis of wave condition including typhoon route,archipelago and water depth is performed in this paper.The advantage and disadvantage are compared between VLFS and the marine structure from land.