Floating structures as spar, semi-submersibles and TLP have been proposed for offshore wind turbines for deep waters (>60m) according to the report of Arapogianni, Moccia, Williams, & Phillips (2011), where bottom fixed sub-structures are technically and economically not feasible. Several floating concepts have been designed and just some of them were deployed as Hywind (Statoil, 2015) and WindFloat (Roddier, Cermelli, Aubault, & Weinstein, 2010), but still they are prototypes that require further improvements in order to achieve it techno-economic feasibility. At the Centre for Ships and Ocean Structures (CeSOS) NTNU a braceless concept was developed for deep waters called CSC. This floater consists on one central column supporting the wind turbine and three side columns connected each of them at the bottom to the central one through pontoons. These cantilever columns might induce large dynamic stress at the connection section on the pontoon as well on the cross section closer the central column. The project objective is to propose a structural connection between the central and outer columns at the top avoiding wave loads and check its stress reduction on the pontoon. The design methodology involves a stability analysis using numerical tool from Det Norske Veritas (DNV) Genie and HydroD. The wind turbine from the National Renewable Laboratories (NREL) in E.E.U.U. of 5MW was employed to estimate the loads and workability of the floater. The hydrodynamics analysis is going to be done in frequency domain based just in wave loads. Through the hydrodynamic loads the stresses are estimated assuming rigid body behavior. It estimation are done by Euler-Bernoulli theory and via Finite Element Method using beams and shell elements. The results show that the upper beams reduce significantly the dynamic axial stress on the pontoon, increasing the floater strength. The FEM using beam elements is a simple and reliable numeric approach to obtain global loads and the stress distribution on the structure. The FEM shell mode could predict the stress for the simplest case but it requires more computational effort in order to set up the mesh model and achieve satisfactory results.The Euler-Bernoulli method under predict the stress on the pontoons as the whole structure of pontoon-brace does not fulfill the beam theory assumptions.
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机译：根据Arapogianni，Moccia，Williams和Phillips（2011）的报告，针对深水（> 60m）的海上风力涡轮机，已提出了诸如翼梁，半潜水器和TLP的浮动结构，其中底部固定的子结构在技术上和在经济上不可行。已经设计了几种浮动概念，其中只有一些被部署为Hywind（Statoil，2015）和WindFloat（Roddier，Cermelli，Aubault和Weinstein，2010），但它们仍然是原型，需要进一步改进才能实现这一目标。经济可行性。在NTNU的船舶和海洋结构中心（CeSOS），为深水开发了一种无支撑的概念，称为CSC。该浮子由一个支撑风力涡轮机的中央立柱和三个侧面立柱组成，每个侧面立柱的底部通过浮桥连接到中央一个。这些悬臂柱可能会在浮桥的连接部分以及靠近中心柱的横截面上引起较大的动应力。该项目的目标是在顶部的中心柱和外部柱之间建立结构连接，避免波浪载荷，并检查其在浮桥上的应力降低。设计方法涉及使用Det Norske Veritas（DNV）Genie和HydroD的数值工具进行稳定性分析。欧盟国家可再生能源实验室（NREL）的风力发电机用5MW的浮力估算浮子的载荷和可加工性。仅在波浪载荷的基础上，将在频域中进行流体动力学分析。通过流体动力载荷，假定刚体行为，就可以估算应力。它的估计是通过Euler-Bernoulli理论以及使用梁和壳单元的有限元方法完成的。结果表明，上部梁显着减小了浮桥上的动态轴向应力，提高了浮子的强度。使用梁单元的有限元分析是一种简单可靠的数值方法，可获取整体载荷和结构上的应力分布。有限元壳模式可以预测最简单情况下的应力，但是为了建立网格模型并获得令人满意的结果，它需要更多的计算工作。Euler-Bernoulli方法在预测浮桥整体应力的情况下对浮桥进行应力预测。支撑不满足梁理论的假设。
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