The scope is to study the hydrodynamic response of the spar (39m diameter and 198.1m draft) using WAMIT. The analytical expression proposed by Tao et al., is used to estimate the viscous damping for the spar with the disc at the bottom. The disc increases the added mass and damping. The spar with single disc configuration is studied varying the disc diameter. The spar with twin disc configuration is studied varying the spacing of disc. The disc diameter and spacing is obtained for the permissible heave response of 5m and pitch of 4 degrees considering the swell (regular wave height of 2m and wave period of 25s) and sea (regular wave height of 20m and wave period of 14s) states on the east coast of India.
The results can be used to design the spar with single or twin disc. The disc diameter and spacing of the disc can be determined for the site specific swell or sea wave height and period.
The heave and pitch responses are observed to be within limits for single disc configuration with disc diameter equal to 1.4 times spar diameter and twin disc configuration with disc diameter equal to 1.3 times spar diameter and disc spacing equal to 0.4 times disc diameter.
The effect of single disc with varying diameter and twin disc with varying spacing on spar response is predicted.
The effect of viscous damping in addition to radiation damping is studied.
The effect of swell wave is found to be the significant for survival condition.