On the applicability of Morison equation to force estimation induced by internal solitary wave on circular cylinder

The current field induced by internal solitary wave can be quite large and it can cause destruction to marine structures. In recent years the forces induced by internal solitary wave on circular cylinder have been studied extensively, and Morison equation is commonly used to estimate the forces. However, the applicability of Morison equation to force estimation induced by internal solitary wave has not been validated. Two sets of numerical simulations are used to check the validity of Morison equation in predicting forces induced by internal solitary wave, one for directly calculating the forces on the cylinder, another for deriving the velocity field at the cylinder location, which is required by the Morison equation. The comparison of directly calculated forces and those estimated from the Morison equation reveals that the Morison equation fails to predict the temporal evolution of the forces. A modified Morison equation incorporating the total derivative is put forward and it proves to predict the forces reasonably well with appropriately determined inertial and drag coefficients. Further experiments and numerical simulations are necessary to determine the dependence of the inertial and drag coefficients on the cylinder configuration and wave parameters.