ANCHORING OF STRUCTURES IN DEEP WATER

Abstract

The oil and gas exploration industry continually discovers energy resources at greater water depths, and in many of the structures now being designed for offshore oil and gas production the anchoring system is one of the key components, having significant influence on operational characteristics as well as safety.

The best possible understanding of the problems involved in anchoring is therefore essential, and an evaluation of a design for deep-water long-term anchoring should include:

evaluation of possible excitation sources at actual site (wind, waves, current)

dynamic analysis of the structure and mooring lines

evaluation of soil properties and anchor behaviour

evaluation of fatigue strength of mooring lines

evaluation of conditions for corrosion and corrosion protection.

In this paper 'the state of the art' within these problem areas is discussed. Sample calculations of global and local dynamics of the mooring lines are compared with results from conventional quasistatic analysis to demonstrate the importance of taking into account dynamic phenomena and oscillations caused by wind, waves and current action. Areas for further research are also discussed.