Moriandini, C., and Wong, J., (2007). Paper number ISOPE-2007-JSC515 published in proceedings of 21st International Offshore and Polar Engineering (ISOPE) Conference, Lisbon, Portugal, 1-6 July 2007.

Abstract

In recent years, thanks to access to consistent environmental databases and powerful numerical tools, heading analysis for single point mooring systems have been the forefront step of tackling numerous issues such as green water, offloading availability, refine hull scantling, life extension study, extreme and fatigue resistance of mooring and riser system, sloshing in tanks, accelerations at process support point and devices, etc.

During the design phases, one of the basic problems raised by Single Point Mooring system is the estimation of the maximum beam waves. In one hand, the designer is happy to impose the maximum design wave all around the floater, e.g. the 100-Year return period wave will hit the F(P)SO from head sea to beam sea. But such assumption may lead to overly designed floating unit, therefore having financial and schedule consequences, especially for unit in rather harsh environments. In the other hand, there is the need to properly assess the wave height distribution around the floater using available tools and weather information for the specific site. This paper presents the details and the necessary requirement for performing such analysis.

A tentative methodology is proposed together with the expected outcomes for the various fields of expertise. Heading analysis basically provides relative wave/swell/wind/current heading distribution over a period of time and therefore requires the following family of data to be assessed: Environmental data combining both amplitude and direction of wind sea, swell(s) (if any), wind and current over a significant period of time.

Accurate modelling of the floating structure towards wind, wave and current excitations, and to a lesser extent its mooring system. Response of the unit to each environmental condition using mooring analysis software, Finally tentative ways of validating the results against field measurement or others, will be proposed and some examples are given. 

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