本論文ではスパー型浮体式洋上風車の最適化について紹介する。岸を離れるにしたがって急速に深くなるわが国の周辺の海域の特徴を考えると、ヨーロッパで展開されている海底設置型のタワー式は難しく、浮体式にせざるを得ない。洋上の風力エネルギーの資源量は陸上をはるかに上回る。浮体式洋上風車の開発における主たる目標はコスト低減である。著者らはスパー型風車に着目し、これまで研究を行ってきた。本研究では、3次元応答解析法の開発と改良、検証を紹介し、ついで開発したプログラムを用いた浮体の最適化を紹介する。目的関数はコストに直接関係する重量とし、スパーのコラム高さ主たる変数として最適な形状を求めた。

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The coastal areas of Japan are estimated to have vast offshore wind energy potential. In order to use large quantities of offshore wind energy, developing a floating body for offshore wind power generation applicable to deep sea areas. Several researches have been made to meet the requirements.
In this study, we proposed truss spar and semi-submersible bodies, they have a long track expand about deep water drilling rig operation results. And solved the response and stress characteristics of the floating bodies. And the optimum floating body size and the mooring facilities were determined by the analysis systems.

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With the progress of ocean development, new type of ocean structures are being commenced to be developed. However, it is not known yet how presently existing mooring systems can cope with these new type of ocean structures. Then, investigation and analysis of characters of existing mooring systems are carried out firstly. The range where characteristics of each existing mooring system can expand is investigated, and the future style of it is studied. The possibility that the ranges of existing mooring systems and their expanding ranges can cope with the mooring characteristic demands of new type of ocean structures is discussed.

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In order to be sure there is vast offshore wind energy potential on the Japanese coastal areas, we observed offshore wind climate on the Pacific Ocean near Fukushima pref. And to use the energy, we developed offshore wind power generation systems. At first, this paper presents the observation result that shows wind climate characteristics are good for wind turbines as well in Europe. Also, we developed two types of offshore wind power generation systems, one is installed on seabed and another is floated on water. And both can be safe from Japanese severe natural conditions.

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A number of papers on structural mechanics and strength of tubular joints of offshore structures have been published. Most papers of them treated simple nonstiffened joints and only small number of papers treated stiffened joints of members with small diameter, where simple gussets or ring stiffeners were used as stiffening elelmets.
Foundamental knowledges are needed, which are useful to initial design of stiffened joints of a large diameter member with small diameter members such as column to brace jojnts in semisubmersibles.
In this paper, effects of several kinds of stiffening elements used in joints mentioned above are discussed by both experiments using acrylic models and numerical calculations using a FEM program newly developed for the purpose of behavior analysis of shell structures with complicated construction. The joint models mainly discussed are T type of joints subjected to axial load of brace. A TY type of joint model is also studied experimentally and theoretically. The types of stiffening elements used in the models were diaphragm, vertical bulkhead, ring girder, vertical girder, piercing brace and so on. Each specimen of joint was fabricated as combination of a standard non-stiffened joint structure and a set of stiffening elements inserted in a chord member of the joint.
Finally, taking weights of stiffening elements into consideration, stiffening efficiency of joint models treated are compared. This comparison resulted in such a conclusion that a joint stiffened by a diaphragm and a partially piercing brace is the most effective as a T type of jojnt.

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