超大型海上浮式结构物总体强度和关键结构极限强度研究

发布时间：2019-02-15 15:13

【摘要】：超大型海上浮式结构物(Very Large Floating Structure,VLFS)是由若干个与半潜式平台结构相似的单模块通过连接器连接而成的一种新型海上结构物。它可用于海洋油气开发、后勤保障和岛礁渔民生活等,是目前海洋工程界的研究热点之一。近年来,国内对于超大型海上浮式结构物的研究越来越重视。本文以超大型海上浮式结构物(超大浮体)为研究对象,进行单模块总体强度直接计算方法研究;对关键结构(撑杆和连接器基座)进行极限强度分析,对连接器基座进行静强度分析,主要研究内容和结论如下:(1)超大浮体单模块波浪载荷长期预报及典型波浪载荷下结构总体强度分析。基于三维势流理论,采用SESAM有限元软件,对波浪载荷进行长期预报,确定超大浮体在各典型工况下的设计波参数,由设计波对平台进行波浪载荷传递分析,从而得到超大浮体典型波浪载荷下应力分布和变形情况。结果表明,超大浮体单模块结构总体应力分布均匀;但存在三处高应力区域,即立柱与上箱体连接处、立柱与下浮体连接处、撑杆喇叭口位置,其中撑杆结构强度最为薄弱。(2)对超大浮体撑杆结构进行极限强度有限元分析,计算两端受压、受拉、受剪切和受弯矩作用下的极限承载力,分析其失效模式,并讨论边界约束,初始缺陷、海水腐蚀等因素对撑杆结构极限承载力的影响。结果表明,撑杆结构受压失效模式表现为屈曲失效、塑性变形;受拉、受剪、受弯失效模式表现为屈服、塑性流动。边界条件、初始缺陷、腐蚀对撑杆结构的极限承载力有一定的影响,应该得到重视。(3)选取两种尺度的超大浮体连接器基座模型,进行不同工况下的静强度有限元分析。结果表明,两种模型连接器基座整体Von mises应力都不大,但存在两处高应力区域,一基座与连接器连接处,二立柱与上箱体连接处。两种模型在基座与连接器连接处应力不变,而模型二在立柱与上箱体连接处应力相比模型一更大。X方向的载荷对基座与上箱体连接部位影响较大;Z方向的载荷对立柱与上箱体连接处强度要求较大;X、Y和Z方向外力同时作用到基座上时,结构应力最大。(4)基于非线性有限元准静态法,对超大浮体上箱体两种模型进行连接器基座极限强度分析,得到不同方向极限承载力,分析结构最先发生破坏的位置。结果表明,两种模型连接器基座不同方向的极限承载能力相差不大,且远小于预报值,连接器基座具有较大的结构强度储备。模型二几何尺寸较大,结构柔性更大,变形更大。
[Abstract]:Super large floating offshore structure (Very Large Floating Structure,VLFS) is a new type of offshore structure which consists of several single modules similar to the semi-submersible platform structure connected by connectors. It can be used in offshore oil and gas development, logistic support and the life of reef fishermen. It is one of the research hotspots in marine engineering field at present. In recent years, more and more attention has been paid to the study of super-large floating structures at sea. In this paper, the direct calculation method of the single module total strength is studied, taking the super-large floating structure (super-large floating body) as the research object. The ultimate strength of key structures (brace and connector base) is analyzed, and the static strength of connector base is analyzed. The main research contents and conclusions are as follows: (1) long term prediction of single module wave loads of large floating bodies and analysis of the overall strength of structures under typical wave loads. Based on the theory of three-dimensional potential flow, the long-term prediction of wave load is carried out by using SESAM finite element software, and the design wave parameters of super-large floating body under various typical working conditions are determined, and the wave load transfer analysis of the platform is carried out by the design wave. The stress distribution and deformation of superlarge floating body under typical wave loads are obtained. The results show that the stress distribution of the single module structure is uniform. However, there are three high stress areas, namely, the connection between the column and the upper box, the connection between the column and the floating body, and the position of the supporting horn mouth, in which the strength of the brace structure is the weakest. (2) the finite element analysis of the ultimate strength of the super-large floating body brace structure is carried out. The ultimate bearing capacity under compression, tension, shear and bending moment at both ends is calculated. The failure modes are analyzed, and the effects of boundary constraints, initial defects and seawater corrosion on ultimate bearing capacity of bracing structures are discussed. The results show that the failure modes are buckling failure, plastic deformation, tensile failure, shear failure and bending failure mode. Boundary conditions, initial defects and corrosion have a certain impact on the ultimate bearing capacity of braced structures, which should be paid attention to. (3) two kinds of large floating connector base models are selected, and static strength finite element analysis is carried out under different working conditions. The results show that the integral Von mises stress of the two model connectors is not large, but there are two high stress regions, one is the connection between the base and the connector, and the other is the connection between the two columns and the upper box. The stress of the two models is invariant at the connection between the base and the connector, while the stress in the connection between the column and the upper box is bigger than that in the model 1. The load in the X direction has a great influence on the connecting position between the base and the upper box. The load in Z direction requires the strength of the connection between the column and the upper box. When the external forces in the direction of XY and Z act on the base at the same time, the stress of the structure is maximum. (4) based on the nonlinear finite element quasi-static method, the ultimate strength of the connector base is analyzed for the two models of the box on the super-large floating body. The ultimate bearing capacity in different directions is obtained, and the location of the first failure of the structure is analyzed. The results show that the ultimate bearing capacity of the two model connectors in different directions is not different and much less than the predicted value. The connector base has a large structural strength reserve. The second model has the advantages of larger geometry size, greater flexibility and larger deformation.
【学位授予单位】：江苏科技大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：U661.43

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