Realistic estimation of roll damping coefficients in waves based on model tests and numerical simulations

Roll damping is one of the most important parameters in the assessment of the behavior of floating systems in waves, but its prediction is still an open issue. Despite the greater improvements achieved with the advent of computational fluid dynamics, the estimation of roll damping is still highly dependent on experiments. A typical approach is to perform decay tests and use the damping coefficients as direct inputs in numerical simulations of motions in waves. The present study shows that roll damping is significantly affected by the incident wave and proposes a hybrid approach to estimate roll damping coefficients in waves combining experimental results from model tests in waves with numerical simulations. To illustrate the proposed procedure the experimental data of a typical ship-shaped FPSO in regular and irregular waves have been used. These results have been compared with those from typical decay tests in calm-water. A time-domain nonlinear potential model has also been used to benchmark the results of the hybrid approach. It was found that the damping coefficients obtained from the hybrid approach provide a more realistic representation of the roll dynamics than those from typical decay tests.