On The Hydrodynamic Forces Acting on Box Type Vessels and Their Motions : (2nd Report) On Three-Dimensiona Model Tests and Theoretical Calculations

Abstract

In regard to a box type floating vessel as one of the fundamental configurations of a floating ocean structure, this study has been proceeded with to establish an estimating method of its motion in waves with high accuracy. The authours have carried out forced oscillation tests and wave exciting force tests in beam seas by use of a box type vessel of low length-to-beam ratio (L/B=1) which is supposed to have three-dimensional effects, and made two-dimensional and three-dimensional theoretical calculations, and then compared the test results with the calculation results, with the following conclusion brought about. 1) The added mass for heave and amplitude of wave excited heaving force agree well with those obtained by a three-dimensional calculation, but not by a two-dimensional calculation. Three-dimensional effects especially appear in the added mass for heave and the amplitude of wave excited heaving force, and this tendency is more remarkable in shallow water. Therefore, a three-dimensional calculation is very useful. 2) The damping force for sway, added moment of inertia for roll, coupling inertia of roll into sway, and amplitude and phase lag of wave excited swaying force are in agreement with those obtained by a two-dimensional calculation, as well as a three-dimensional calculation. 3) In heave and roll, the damping terms obtained from tests cannot be fully explained only by the wave damping, without viscous damping. The estimation methods of them backed up by experiment are necessary. 4) Shallow water effects appear in the heave, roll, heaving force, rolling moment, and the sway and swaying force in a range small in ξ_b (=ω^2B/(2g)), that is, in a range of long wave length.