AN EXPLORATION OF APPLICABILITY OF FUNCTIONAL MODEL TO SHIP ROLLING (TEST, NONLINEAR MOTION)

An experimental method to identify linear and nonlinear frequency response functions of ship rolling was developed. A functional polynominal of degree three was used to represent a wave-ship system. Identification procedures were designed using steady state response of the system to multi-tone inputs. The results of the roll experiments showed significant nonlinear response at the frequencies predicted by the cubic functional polynominal theory. Assuming weakly nonlinear ship rolling, an identification procedure to find the cubic frequency response function was developed using dual wave.;A series of experiments were conducted at the Davidson Laboratory wave tank using a Series 60 ship model at zero speed. The beam waves used were regular and dual waves. Software to generate dual waves by a microcomputer controlled wave maker was developed for the experiment. Characteristics of the generated dual waves were investigated by using an array of ten wave sensors. A nonlinear interaction was found between component waves at the combination frequencies. The amplitude of these wave components increased linearly with the distance from the wave maker and depends on the amplitude of the generated waves.