Hydrodynamic coefficients of generic subsea modules in forced oscillation tests – importance of structural elements

A systematic study of hydrodynamic coefficients for simplified subsea modules has been performed to support the estimation of the coefficients needed for planning of subsea installation operations. The coefficients are assessed for a nearly two-dimensional test setup. The tests are performed as forced oscillations at various amplitudes and periods, representing the forces on the module lowered through the water column. The importance of each of the main components of the subsea modules – mudmat, protection roof and process equipment of different shapes inside the modules are studied at fully submerged condition. Results for the module elements, generic contents and different combinations of these elements are presented. For the tested modules, damping is generally the dominating hydrodynamic force. However, the presence of the content inside the modules will generally increase the importance of added mass. Estimation of the hydrodynamic coefficients by summation of the coefficients for the individual structure elements generally overestimates the damping, compared to the coefficients measured for the complete modules. For added mass, estimation based on summation gives generally good results.