講演概要

1. 必ずしも完全な形ではないにしろ、総体としての「人類」に国際法上の法人格が、人類史上初めて与えられることになった。
2. 海洋に対する主権国家の「権利」は、主権国家の「義務」へと変質した。
3. 海洋空間における「環境」と「開発」の調和に関する法的枠組問題が、国際レベルで最も急を要する課題となった。

The use of the ocean in the urban development seems to be promising in view of the fact that further use of land is limited in urban areas due to vast growth of population and needs of many housings, business buildings, shops, infrastructures, factories and transportations. In such marine countries as Japan, the use of ocean space is encouraged on the standpoint of invulnerability to earthquakes, reduction of gravity forces, global warming, attraction of waterfront and easiness in transportations. This paper discusses the feasibility of such floating structures serving as infrastructure.
[ top | back ]

Singapore is a unique city-state. It is one of the smallest countries in the world with a relatively tiny island area of about 660 square kilometers today. As Singapore is without any natural resources, her people are, and will always be, the most precious resource. Presently, her population is about 4 million and this number is expected to grow to about 5.5 million in the year 2040. In anticipation of the projected population growth , economic growth as well as the recognition for enhancement of quality living and working environment that are sustainable into the future, Singapore is continually seeking and developing innovative ways to optimize both her land space and sea space.

This paper focuses on the multiple utilization of the precious sea space in Singapore coastal waters. These usages include port and harbour development for Singapore's megaports that serve ships plying a region stretching from India to Japan and beyond, land reclamation for airport, utility, residential, industrial and recreational needs, marinas for leisure activities, landfill for waste materials, coastal fisheries, and floating structures for piers and industrial purposes. The paper will trace the historical developments of the abovementioned usages, and also highlight the new innovative technologies used. New concepts for future utilization of sea space will also be discussed.
[ top | back ]

Time-domain, hydroelastic analysis of offshore structures can be　described as a two-field problem. The structural motion must be transferred to the fluid model and the resulting fluid pressure at the fluid-structure interface must be transmitted from the fluid model to the　structure. The displacement and pressure mapping is difficult and　mathematically imprecise when the structural mesh and the fluid mesh describe two distinct three-dimensional surfaces. In this paper, three mapping strategies based on the Penalized Discrete Least-Squares (PDLS) stress recovery (smoothing) technique are presented. These strategies attempt to conserve the work done by hydrodynamic forces when obtaining the global structural nodal forces. The merits and the disadvantages of these strategies are discussed and illustrated with several examples.
[ top | back ]

Floating causeways are used by the U.S. Navy to transport materiel from ships to shore when the water depth is very shallow. This work is on one of the 1200ft-long (365.7m), floating causeways (FC) called INLS, and which is moored in shallow water of depth less than 32 ft (9.8m). The FC is made up of modules connected to each other either flexibly or rigidly. The width of a module is 24ft (7.3m), but the length varies from 80ft (24.4m) to 160ft (48.8m). Several different mooring-line arrangements and mooring lines with different properties are investigated. The study also allowed the presence of ship(s) tied to the FC during both the static and dynamic analysis of the problem.

The overall objective of this study is to estimate the mooring-line tensions as a result of steady current, and wave action. In the static analysis, the modules are assumed flexible. The goals of the static analysis is to obtain a realistic mooring-line arrangement, and to establish a configuration on which the dynamic, wave motion analysis is based. In the dynamic analysis, the modules are assumed to be rigid but the connectors are flexible. Linear theory is used to estimate the response of the FC and the resulting mooring-line tensions.

We will describe the physical and mathematical models used in the study. Various mooring-line arrangements are included in the study to simulate when some of the anchors are dragged.

The static analysis shows that there can be substantial differences in mooring tensions depending on the site, metocean, and mooring data specified. Some of the sensitivity is due to the very shallow depth in that significant tensions can result from small displacements of the FC. Load balancing between mooring lines is therefore quite difficult to achieve.

The dynamic analysis shows that extremely large mooring tensions are estimated, and that they are partly a result of resonance, and partly a result of very large, catenary-line stiffness in this shallow-water problem. In addition, the very large horizontal distance water particles move in shallow water causes the FC to have extreme horizontal motions that in turn contribute to the very large mooring tensions predicted. However, modifying the line stiffness can reduce the extreme tensions dramatically. Moreover, the viscous damping that is not considered in the present study can be a source of significant reduction in mooring-line tensions. A follow-up study on this issue will also be discussed briefly.
[ top | back ]

A new type Very Large Floating Structure using Submerged Plates (Sub-Plate VLFS) is proposed for extending the operational area of VLFS to deeper sea with reducing environmental problems. The system consists of a Floating Breakwater using Submerged Plate (FBSP) and a VLFS with submerged plate. FBSP not only decreases incident wave height for VLFS but also generates a steady flow, which enhances the exchange of seawater around VLFS. A series of experimental and numerical studies on the wave dissipating capacity, motion, mooring forces and structural strength of Sub-Plate VLFS has been performed, and the high feasibility of the system for the sea of 100m depths has been demonstrated. This paper deals with the basic concept of the system, together with the conceptual design of proto-type system and its performance as a breakwater.
[ top | back ]

In recent research, it has been cleared that the motions of pontoon type very large floating structures (VLFS) are dominated by the dispersion wave that is induced by the floating structure and the fluid interaction. Incident wave excites the weather side of the structure, and then the deformation is propagated over all the structure. The deflection wave propagation to the main part of VLFS is not desirable, because the deformation requires the large area of high strength structures and the motion might affects the function of VLFS. In this study, the edge shape of VLFS that restrains the deformation propagation has been investigated. To evaluate the effect of the improved edge form, a program to calculate the response of VLFS that has arbitrary horizontal outline has been developed. It has been confirmed that the notched edge reduces the deformation of the inner area of VLFS. Furthermore, to reduce the motion effectively, a relation between the edge form and the incident wavelength was investigated.
[ top | back ]

著者らは，振動水柱型波エネルギー吸収装置を利用した超大型浮体の弾性応答低減方法を提案してきた。本論では，振動水柱上部の空気室内の空気圧縮及び自由表面の挙動を直接流体力解析時に考慮する方法を紹介する。理論計算方法は3次元問題を直接解く方法と，ゼロ喫水仮定により平面2次元問題で解く方法を示す。これらの理論計算結果同士の比較により計算方法の妥当性を検証する。弾性変形予測についてはゼロ喫水仮定下では計算結果が安全側になる傾向があること，また波漂流力予測においてはゼロ喫水仮定下では危険側になることを確認する。
[ top | back ]

The objective of this project is to determine the ultimate strength of imperfect stiffened and unstiffened plates subjected to compressive inplane loads. The imperfections can be due to initial deflection, welding residual stresses, presence of holes, corrosion, dents, or cracks. The resulting strength equations are to be used for guidance in design, and therefore have to in a simple closed-form format.

The approach adopted in the paper is to perform extensive parametric non-linear finite element analyses for many stiffened and unstiffened plates with varying geometric properties, e.g., aspect ratios, plate thickness, stiffeners dimensions, etc. The ultimate strength of each stiffened or unstiffened plate is then determined with the presence of one or more type of damage of increasing severity, using non-linear finite element program. Both, material and geometric (large deformation) non-linearities are included in the finite element analyses.

The results were than used to develop closed form equations for use in design. The typical procedure for obtaining these equations was to start with well-established equation for a " perfect" stiffened or unstiffened plate, and modify it by a reduction factor that depends on the type and magnitude of the damage. The reduction factors were developed on the basis of the finite element results, i.e., the finite element results were used as if they were experimental data. Only well-established equations for the " perfect" structures were used, e.g., the Perry-Robertson's equation for stiffened plates and Frankland's equation for unstiffened plates.
[ top | back ]

超大型浮体構造物に過大な波浪荷重が作用した場合の全体崩壊挙動を調べることは，構造物全体としての冗長性を明らかにし，構造信頼性のさらなる向上につながる。ポンツーン型超大型浮体を対象として，このような波浪中全体崩壊挙動の簡易解析法を開発した。非線形構造解析には，防撓パネル構造の座屈・塑性崩壊挙動の効率的解析法である理想化構造要素法（Idealized Structural Unit Method, ISUM）を適用した。またISUMスーパー・エレメントの概念を新たに導入し，自由度のさらなる低減を図った。本解析法を超大型浮体の実機モデルの時間領域崩壊シミュレーションに適用した。デッキとボトムはISUMで，またガーダーおよびフロアは梁要素でモデル化した。長さ1650m x幅 495mの部分浮体モデルに関する一連の崩壊解析結果をもとに，構造崩壊が浮体波の分散関係に及ぼす影響を始めとして，崩壊挙動の基本的性質を調べた。
[ top | back ]

Although it is expected that the impact of very large floating structures (VLFS) on the natural environment is insignificant, there had been some anxious about the shading effect on marine lives due to the floating body covering sea surface. However, before the Mega-Float projects started, there was little actual data showing the extent of environmental impacts by VLFS. Therefore, investigations of environmental impacts by VLFS had been conducted under the cooperation of Technological Research Association of Mega-Float. During the Mega-Float Phase-II experiment in Tokyo Bay, continuous monitoring of vertical profiles of water temperature, salinity, dissolved oxygen and chlorophyll-a, and so on were carried out at several fixed stations below and around VLFS model. Manual samplings of seawater had been also carried out in order to investigate spatial distribution of water quality in detail. The results indicated that VLFS would hardly affect the physical environment around it as far as there exists significant current at the mooring site. However, it was found that local water quality was affected mainly by sessile animals attached on the surface of VLFS. Based on the field observation around the Mega-Float model, an ecosystem model was developed for the prediction of marine environment affected by VLFS. The model includes the effect of sessile animals on the structure and coupled with hydrodynamic model predicting physical environment in the bay. It was applied to numerical simulations with temporary varying boundary conditions in order to verify the applicability for dynamically changing real phenomena. The continuous observation data around the Mega-Float model is very useful for the verification of the results of numerical simulations. The results showed that the model could predict the dynamic change of physical environment in estuaries fairly well. By the process studies using this numerical model, it was confirmed that the influence by sessile animals on VLFS is more significant than shading effect of the floating body.
[ top | back ]

The environmental impacts of an imaginary very large floating structure (VLFS) on marine ecosystem are examined. From the previous studies, it is expected that a lot of sessile organisms adhere to the bottom surface of the VLFS, and they have some effects on their surrounding water quality. To discuss the extent of these impacts quantitatively, numerical simulation by means of coastal ecosystem model is one of the useful tools. First of all, marine ecosystem in Tokyo Bay is simulated in the case when the imaginary VLFS does not exist, and coastal ecosystem model is validated by comparison of predicted results with observed ones. Further, numerical simulations are conducted in the case when the imaginary VLFS, whose length is 5 km and width is 1 km, is moored off Oppama or off Haneda in Tokyo Bay. As a result of several computations, it is revealed that growth rate of the sessile organisms adhering to the bottom surface of the VLFS are smaller in the sea area off Haneda, where current of seawater is slow. It is because particulate organic matter (POM) and oxygen are not supplied sufficiently in the area under the VLFS. On the other hand, in the sea area off Oppama, seawater flows southward constantly at the speed of about 0.1m/s, so POM and oxygen are supplied appropriately to the sessile organisms. Hence they can grow by uptake of POM around them, and can sustain their biomass. When the VLFS is installed off Oppama, the biomass of sessile organisms per unit area is much larger than that of suspension-feeding macrobenthos, which has the same functions as the sessile organisms, in the several tidal flat estuaries in Tokyo Bay. So the sessile organisms adhering to the VLFS may have large impacts on circulation of matters such as carbon, nutrients and oxygen. Therefore, the impacts of filtering POM by the sessile organisms on carbon circulation are examined. As a result, it can be said that the sessile organisms retain POM in Tokyo Bay, which may otherwise flow out from the bay to the outer sea.
[ top | back ]

A numerical model to simulate the water quality around a Mega-Float in Tokyo Bay is presented. The model consists of two parts, a hydrodynamic model and a marine ecosystem model. Tidal currents, water temperature, salinity and water density are calculated in a bay with/without a Mega-Float in the hydrodynamic model. A marine ecosystem model including the floating matters such as nutrients, phytoplankton, zooplankton and organic matters are extended to include not only the effects of marine mussels attaching on the bottom of the Mega-Float but also the benthic effects with the mussels fallen down to the sea bottom. The marine mussel is modeled as a macro benthos similar to an ecosystem model for a tidal flat estuary. The variation of water quality in the case of with/without a Mega-Float of 5 km length, 2 km breadth and 1 m draft are given in graphics. The environmental impact on marine environment at each location is evaluated with two evaluation functions that are newly proposed to evaluate the changes of the water quality of the bay due to the installation of the Mega-Float.
[ top | back ]

地球環境問題を考慮に入れて海洋空間を調査するには，経時変化を捉えるために定期的な観測が必要であり，かつ，広範囲にわたって調査をおこなう必要があるために，テザーケーブルの拘束を受けずに自由に水中を泳ぎ回ることができる自律型水中ロボットを用いて観測をおこなうことが有利である．あらかじめ決められた航路を辿る類の単純なミッションに限定すれば，今日既に自律型水中ロボットの実用化が世界的に進められる時代に入ってきたといえる．今後このような実用化が進むにつれて，自律型水中ロボットの自律機能は，さらに高度に発展することを求められるようになるであろう．本講演では，東京大学生産技術研究所でこれまで開発をおこなってきた水中ロボットについて，高度な機能により水中構造物を自動観測する技術，および今後の展開について紹介する．
[ top | back ]

CO₂を貯留した海底盆地からは、物質拡散と、海流に伴って誘起される移流とが同時に起き、海洋内のCO₂拡散を生じる。著者は海盆内におよそ半載貯留された液体CO₂からのこれらの拡散現象を研究した｡海底と海盆の地形についたは2次元或いは3次元の幾つかの形状によって近似し、今回新たに、実海底を近似できる境界適合座標系での流動と拡散の微分方程式、および数値解のための差分方程式を導いた。海洋内のCO₂特有の特性や挙動については、界面のCO₂水和物を通しての物質移動、CO₂溶解による海水膨張、溶解熱および海底境界層内の拡散係数を考慮した。さらに数値解を差分法によって求め、流速、CO₂濃度、pH分布、海盆内濃度貯留およびから海洋へのCO₂流束を示し、これらに基づいて海底地形と半載貯留法の特性について述べた。
[ top | back ]

低温高圧の環境下で二酸化炭素をハイドレート化し、海底や地層中に固定する試みに加えて、メタンハイドレートの採掘にCO₂ ハイドレートを利用するといったコンセプトが提案されている。本論文では、ガスハイドレートの生成・分解に関する基礎的な特性について述べるとともに、CO₂ ハイドレートを用いた生産システムやメタンハイドレートからの置換回収の可能性について論じた。
[ top | back ]

Methane hydrates occur in offshore Japan with possibly large quantities. In order to promote its utilization as an energy resource, the Japan's Methane Hydrate Exploitation Program (MH21 program) was plotted out under the lead of the Ministry of Economy, Trade and Industry (METI) and initiated by the MH21 Research Consortium in FY 2001. The MH21 program is a 16-year-project and includes the study of offshore development system to enable economically and technically feasible production of methane gas from methane hydrates. This paper describes the outline of the MH21 program and the R&D plan of methane hydrate development system as part of the program.
[ top | back ]

浮体構造物は海岸の有効利用のために開発されてきた。その構造は大別してポンツーン型と半潜水型に区分することができる。巨大規模の浮体構造物はしばしばメガフロートと呼ばれ、海上空港・埠頭・石油備蓄基地・工業又は住宅用スペースとして利用することが検討されている。浮体構造物はその構造的特性から、浅い海水面を利用するための、最も経済的な方法の一つと考えられている。また、浮体構造物は埋立工法などと比較して、周辺環境に対するマイナスの影響が少ないという特徴を有する。さらに地震に対して安全なうえ、一つの場所から他の場所に容易に移動させることも可能である。1995年の阪神淡路地震では海上交通が、食料や物資の輸送に最も有効であったことが証明された。地震により道路や鉄道システムが深刻な被害を受けたことにより、陸上交通による復旧事業は極めて困難であった。浮体式防災拠点は浮体構造技術を応用した施設・システムであり、震災場所に海上から容易に近づくことが可能である。また、この施設は平常時に駐車場・釣りのための公園・緊急時の食料・物資の貯蔵基地などの有効利用を図れるよう計画されている。このような都市の機能を果たすことにより、維持管理費の一部を軽減することを狙っている。震災時には、移動式防災拠点は被災地にタグボートにより曳航され、復旧活動に最も便利な海岸に係留され、船舶からの緊急物資を積み卸し、被災地に供給する中継基地の役割を果たす。さらに拠点は緊急のヘリポート・情報センター・医療基地・備蓄基地などの機能を併せ持つことができる。2000年に、政府は防災対策の一環として東京・名古屋・大阪に３つの浮体式防災拠点を建設した。これらの拠点は、将来の地震による災害からの復旧活動のうえで、大きな役割を果たすことが期待されている。
[ top | back ]

Technological Research Association of Mega-Float (hereinafter referred to as "TRAM") was established in April 1995 and has carried out "Research and Development of an Ultra Large Floating Structure" for a six-year program. This research was successfully completed in March 2001 with sufficient results regarding technical possibility of large floating airport. TRAM　was terminated and the technologies are succeeded to Shipbuilding Research Centre of Japan(Referred to as SRCJ). Meanwhile, recently Haneda Airport along Tokyo Bay is planned by Japanese government to have an additional runway in near future. Regarding construction method of a runway, 3 methods are nominated as candidates, namely Floating Structure Type as called mega-float, conventional reclamation method and pile system with upper structure. This article introduces outline of result of mega-float research and also a floating runway for Haneda airport proposed by The Shipbuilding Association of Japan developing results of mega-float research project. Details of subject are as follows.

• Layout of floating airport for research and a new runway for Haneda
• Design conditions in both cases
• Outline of runway structure for both cases
• Hydro-elastic motion by waves in both cases
• Mooring system for both cases

本研究は、不規則な風・波を同時にうける浮体橋の動的応答予測のためのコンピュータープログラムの開発に関するものである。本論文では、分離ポンツーン型浮体橋を対象とする。それぞれのポンツーン基礎は６自由度を有する剛体としてモデル化され、ポンツーン基礎を接続する上部工は、弾性体としてモデル化される。係留系は、非線形復元力特性を有するバネとしてモデル化される。発散波の周波数依存性を時間領域で厳密に考慮するため、メモリー効果を考慮している。本解析プログラムの方法論を示すため、典型的な浮体橋の例について、数値解析例を示す。さらにワークショップでのプレゼンテーションでは、本プログラムの検証として行った水槽内に浮かべた浮体橋モデルに対する風洞実験のビデオ紹介等もあわせておこなう。
[ top | back ]

回転水槽に設置された水理模型及び海洋流動モデルによる数値計算法を用いることにより、水質浄化装置に関する数値計算と実験を行ったので、その結果を報告する。
[ top | back ]

沿岸域において藻場が衰退し，荒地のようになる現象は，「磯焼け」と呼ばれており，全国各地で問題となっている．磯焼けの原因については種々の説があるが，複合的な要因で起こること，海域によって現象が異なることなどから，完全な解明には至っていない．高知県室戸岬周辺では，高温・貧栄養である黒潮の接岸が磯焼けの主因と考えられているが，高知県海洋深層水研究所により，低温・富栄養である海洋深層水の放水口付近で藻場が回復していることが報告されている．

本研究では，海洋深層水による藻場修復のメカニズムを解明することを目的としており，室戸岬周辺における海藻および藻食性動物（ウニならびに藻食魚類）の現存量調査，これら藻食性動物の摂餌速度を求める水槽実験，藻食性動物の摂餌圧を考慮した生態系モデルの構築等を行っている．その結果，磯焼け状態から藻場が回復する過程において藻食性魚類の摂餌圧が重要な役割を果たしており，その摂餌圧が放流された海洋深層水の濃度に大きく依存することがわかった．
[ top | back ]

インド政府は、21世紀の環境問題とエネルギー問題を解決する有効な手段の一つとして海洋温度差発電に期待している。インド国立海洋技術研究所は、インド洋における世界最大の1000ｋW実証プロジェクトを推進するために佐賀大学と1997年に研究協力協定を締結し、プロジェクトを進めている。1000ｋWのプラントと取水管は、完成し、現在、取水管の設置を行っている。実証サイトは、インド南東部のTamilnadu沖、３５kmの付近で、フローティングタイプである。

今回の実証プロジェクトの目的は、１MWフローティングタイプの海洋温度差発電の設計、製造、性能、発電について明らかにすることである。さらに、アンモニアループやタービンの性能や様々な技術について明らかにする。たとえば、(1)コンパクト熱交換器の設計、製造、評価、(2)熱交換器内の汚れの制御及び評価、(3)内径１ｍ、長さ1000ｍの取水管の構造解析及びバージとの連携、などある。

本論文では、本実証プロジェクトの全容の詳細と現状及び今後の展望について述べる。
[ top | back ]