Effect of hull geometry on the hydrodynamic response of spar in regular waves

Abstract

The hydrodynamic response of the floating production systems, especially deep draft spars, is of major concern in the offshore industry for its influence on the selection of suitable drilling and production equipment. A number of response reduction methods are being investigated in view of better motion response and improved design methods. In the present study, experimental and numerical investigations were carried out on spar hulls with different shapes to obtain the motion response characteristics and to compare them with that of the classic spar. The spar hulls were designed for a common topside weight of 10,000 tonnes with a displacement of 65,000 tonnes. Experiments were carried out on 1:100 scaled models of spar with circular disk, enlarged base, eight-cell spars and six-cell spars for a water depth of 300 m and numerically validated using ANSYS AQWA software package. Experimental and numerical values showed good agreement especially at lower wave periods. Among the cell spars, the six-cell spar showed better motion response characteristics than the eight-cell spar, both in heave and surge, with limited difference in pitch. The spar with enlarged base was found to be more stable in pitch and less stable in heave than the spar with circular disc at keel.

Keywords:

• spar geometry
• cell spar
• RAO
• heave plate
• enlarged base
• classic spar