Experiments of Hydrodynamic Forces on Vertical Bodies of Revolution Induced by Swaying and Rolling

Abstract

Floating marine structures, in many cases, employ bodies of revolution as their component members. Prediction of hydrodynamic characteristics of these bodies could be very much simplified owing to their symmetry compared with other objects of general form. This is especially the case with vertical bodies of revolution. Several methods for calculating hydrodynamic forces on vertical bodies of revolution, which utilizes theri axial symmetry, have been proposed, and each of the may be said to posess its own merits. As for results of experiments, while many examples are known of measured vertical forces due to waves and forced heaving osci11ation, very few are available for the modes of sway and roll. In view of this, we carried out forced oscillation tests and wave-excited force tests with emphasis on sway and roll, using a model of an axisymmetric column with spherical footing. We also calculated hydrodynamic forces on a few bodies including the above said model by a source distribution method which employs ring elements and is similar in principle to that developed by Fenton. For examining accuracy of this method, we first compared the values by this method for the half-immersed sphere with those presented by Kim. Then, we compared the results by this method for the above said model with those by another well known method using quadrilateral elements, and with the results of the experiments. Good agreement observed in all of these comparisons may be said to show satisfactory accuracy of this theoretical method and, at the same time, high reliability of the results of the experiments.