Evolution Of Arctic Marine Structural Forms

ABSTRACT Over the last quarter century, the evolution of structural forms for offshore structures in the North American Arctic has been closely tied to developments in our understanding of ice structure interactions. The architecture of offshore structures is one of pure function: to support an operation and to survive. Once the socio-economic and environmental issues are resolved, islands, bottom founded structures, floating structures, and active devices, the principal categories, derive their form almost exclusively from the designer's understanding of the ice, environmental and operational forces to which they are expected to be subjected. The evolution of their forms reflects development of ice mechanical knowledge. Islands were initially designed as simple gravel mounds with a flat top, and have evolved to incorporate slope protection, freezing, ice barriers, and for deeper water, caisson containment walls. The gravity based structure has taken a multitude of forms on the drawing board, resulting in several different realizations including the Concrete Island Drilling System (CIDS) and the Single Steel Drilling Caisson (SSDC). Monopods, monotones, the Hibernia star structure, and various storage and platform combinations are designed to passively resist the full spectrum of ice forces to which they are likely to be subjected. Active structures, which in some way actively destroy or avoid ice features capable of causing damage to References, nomenclature, and figures at end of paper. them, have led to fantastic and sometimes bizarre designs. Floating structures, a more conventional variation of active structures include ice vaning ships, the round Kulluk and various forms of stationary icebreakers. The paper follows the evolution of the forms in each of the principal classes within the context of associated ice mechanical developments. Possible evolutionary directions for the future are considered, including use of new materials and technologies such as space alloys, composite construction, and underwater habitats. The designs, prototypes, and structures presented in the paper are based on those developed in the industry. INTRODUCTION AND BACKGROUND The development of structures to resist static or dynamic ice forces has been a major pursuit for naval architects and marine or civil engineers for several decades. Products of their endeavors merit mention as some of the most notable works of engineering ever produced [19]. A good deal of insight into the fundamentals of the generation of ice forces on structures was shown in the classical works by the Russians, Zubov [22] and Korzhavin [15]. The latter correctly identified and applied the concepts of shape and contact coefficients, attributing to structural a significant effect, on the magnitude of ice loads and effective pressures. Similarly, a great deal of empirical knowledge of the variation in intensity of dynamic ice loads with different ship hull forms has been generated from the design and development of ice breakers, However, precise engineering characterization of the load spectrum likely to occur when ice encounters a specific structural form could not be developed solely on the basis of these classical works, and remained to be developed during the focus on Arctic oil and gas exploration in the 1970s and early 1980s.