MODEL TRIALS FOR STUDYING HYDRODYNAMIC FORCE COMPONENTS IN FOLLOWING SEAS

摘要

The present paper contains results of a study of hydrodynamic forces on a semi planning monohull patrol craft in following and stern quartering seas. The study was performed at the Marine Dynamics Laboratory at SSPA Sweden, where a scale model was tested in various regular waves as well as a few irregular waves consisting of two and three components. The model was fixed in the surge, sway, roll and yaw directions but free to heave and pitch. This setup gave possibility to measure the most important forces and still having a realistic displacement, or wetted surface, for the ship model. This test methodology gives opportunity to use a relatively limited number of model trials for identifying conditions where surf riding and broaching-to are likely to occur. But the main purpose of this work is to use data for validation, or benchmarking, of numerical methods for computation of hydrodynamic forces in following and stern quartering seas. Parts of the results have also been used to evaluate the accuracy of numerical computations; this comparison has been reported by Hua et al. (2003). In the present paper it was assumed that forces, moments and waves were approximately sinusoidal so that amplitudes, frequencies and phases could be determined for the forces, moments and waves. To obtain a high accuracy, the amplitudes, encountering frequencies, phase angles and mean values have been determined using Gauss-Newtons method. This method has proven to work well as shown by figure 9. Test data have also been used to determine an equation of motion for the surge direction and some examples of numerical solutions of this equation are also shown.