Approximation of towline influence on towed ship motions

Towing is often used when setting up offshore objects as well as for the removal of damaged ships from the crash site. For this purpose, quasi-static approach is used for approximation of towline forces acting on towed ship. So, mathematical model of towline takes into account geometric, axial and flexural stiffness while inertial and damping forces are neglected. Towed ship is modeled as a rigid body. Hydrodynamic loadings due to waves are considered along with hydrodynamic reactions i.e. added mass and radiational damping. Usually, these loadings and reactions on a ship are calculated in frequency domain. Since the properties of towline model are nonlinear, calculations should be performed in time domain. Therefore, mapping of hydrodynamic loadings and reactions from frequency to time domain is done. Obtained numerical results are compared with experimental results from available literature where ship's model is observed on regular head waves.