Numerical Simulations for the Prediction of Wave Forces on Underwater Vehicle using 3D Panel Method Code

Abstract

This study describes a method useful for predicting the hydrodynamic forces on fully appended underwater vehicle when operating beneath the free surface waves. The hydrodynamic forces acting on the underwater vehicle due to waves are sum of the incident wave force, diffraction force and radiation forces. Ansys AQWA which is based on Panel Method is selected to compute wave forces both in frequency domain and time domain. Series of numerical simulations are performed considering the 2nd order Stokes wave theory and head seas conditions. The water depth is assumed infinite hence the interference effect on vertical boundaries and horizontal bottom can be neglected. The simulation procedure requires generating panels on the vehicle's surface, defining the mass properties and providing the desired the sea wave condition. In frequency domain analyses, wave forces and moments are determined at different submergence depths and wave frequencies. These analyses reveal that magnitude of surge force, heave force and pitch moment are the most dominant as compared to other forces and moments. Numerical results in the time domain are also collected in order to investigate the effect of various factors such as wave amplitude, frequency, vehicle depth, orientation, etc., on these forces and moment. The results are then used to derive analytical formulations for wave forces and moment by curve fitting approach. The accuracy of the formulations is ensured by verifying the results with real time simulations using two test conditions in which the different values of parameters are selected. The proposed method brings great convenience to assess the maneuverability characteristics of underwater vehicles operating near sea waves.