Challenges for a Total System Analysis on Deepwater Floating Systems

In the design of floating systems, three major system components need special attention: the floater, the moor- ing system, and the riser system. This paper will focus on one the most unique areas in the structural design of these com- ponents, namely, the fluid-induced effects on floating structure systems and the associated structural response. Due to the rapid growth in the offshore field, particularly in deep waters, this analysis is seeing a phenomenological growth, and con- siderable research is ongoing in this area, with steady advancement in the design procedure. The state-of-the-art in the treatment of the individual components of the floating structure, namely, the floater, the mooring system, and the riser system will be briefly described. The importance of their interactive coupling effects with fluid is the special subject that will be emphasized. In particular, the 'Total System Analysis' of the floating system consisting of all three of its dynamic components will be laid out. A possible systematic approach for the complete system and various simplifications available for an efficient practical solution will be elaborated. The paper will conclude with a discussion of the present-day deep water design challenges that remain and the research that is needed to meet these challenges. INTRODUCTION OF OFFSHORE STRUCTURES The design life span of offshore structures ranges from a few years to as many as 25 years based on their applications. Often their useful life extends beyond their design life, and they remain operational longer. In most instances, the float- ing offshore structures are required to stay in position in all weather conditions. Offshore structures (1) are defined by either their function or their configuration. The functions of an offshore structure may be one of the following (even though multiple functions may be possible for a structure):  Exploratory Drilling Structures: A Mobile Offshore Drilling Unit (MODU) configuration is largely deter- mined by the variable deck payload and transit speed re- quirements.