Dynamics & Vibration Research Group

Future oil production from ultra deep-water reservoirs will require floating production units to be moored in water depths ranging from 1000m to 3000m. Mooring systems must be designed to ensure that the horizontal excursions of the vessel are not so large as to cause damage to the production risers or the sub-sea equipment. The most common type of mooring employed in shallower waters is the catenary system (wire rope or chain), which provides restoring forces through the weight of the line and its change in configuration arising from vessel motion. The required weight of line increases with increasing water depth, and eventually this places an unacceptable limitation on the working payload of the vessel. A more feasible alternative in deep water is to use taut leg fibre rope moorings, as shown in Figure 1. Fibre ropes (polyester, aramid, polyethylene etc) are lightweight and more extensible than steel, and when used in a taut-leg configuration they provide restoring forces through axial stretching rather than geometry changes. This project is concerned with the dynamic analysis of such systems.

Project Details

The aims of this research project are:

1. To study the static and dynamic behaviour of taut line moorings in ultra-deep waters, taking into account the material non-linearities and the full range of excitation forces arising from vessel motions, wave, wind and current;
2. To assess the extent to which present day mooring analysis procedures can capture the behaviour of deep water taut line moorings;
3. To consider the development of efficient numerical methods for mooring line analysis;
4. To examine the effect of the mooring lines on the surface vessel motions.
   
   An efficient 3D numerical computer program is being developed. It will include non-linear axial, bending and torsional stiffness, and allow Poisson's ratio to be different from 0.5 to allow proper modelling of the hydrostatic pressure and buoyancy effects.

Relevant/Recent Publications

• P-Y Couliard. 'Dynamics of deep water mooring lines'. First Year Report, Department of Engineering, University of Cambridge. September 1999.

Principal Investigator & Researchers

• Professor R. S. Langley
• Pierre-Yves Couliard

Funding Body

• BP Amoco Exploration UK