ESTIMATION OF DAMPING COEFFICIENTS OF MOONPOOLS FOR MONOCOLUMN TYPE UNITS

The use of moonpools in offshore technology are normally related to the hull opening in drilling units with the objective to have easy installation process and protect drilling equipment
from environmental forces, and it is desirable the minimum motion of the water inside the moonpool, avoiding water impacts when lowering an equipment.

Several studies, refs. /7,10,11,12,13/, have been carried out to predict the water dynamics inside the moonpool using analytical and experimental tools, this last due to the high viscous influence in the responses, and the study of coupled dynamics of floating units with moonpools have been presented in previous works (refs. /1,2,3,8,9,17/), with especial focus on FPSO´s and Monocolumn type units.

In the present study, the objective is to verify the reliability of numerical approach in heave dynamic evaluation of monocolumns. With this approach the objective is to tune the natural period the floater and moonpool.

Two monocolumn example units were numerically calculated using WAMIT software, making possible to verify the 6 degree of freedom of the unit and the 3 of the moonpool. As the
software does not evaluate viscous forces, decay tests were performed in order to verify the external viscous damping to be considered in the numerical calculations.

The calibrated numerical model transfer functions (RAO) were compared with regular and transient wave tests, where heave and moonpool heave amplitudes could be compared.