2019 年 85 巻 875 号 p. 19-00109
Recently, wave-powered electrical generators, using double-cones moving on circular rails, have been proposed. Rotational motion of the generator’s hull, induced by waves, is changed into the rotational and translational movement of either a rigid magnetized double-cone, rolling on divergent-convergent circular rails, or a double-cone geared motor-generator, rolling on concentric circular rails. However, if such generator is not directly floating on the water waves of random direction, period and height, but it is placed inside of the hull of a ship, the movement of the double-cone is one-directional and dictated by the rolling period and amplitude of the ship’s hull. In such case, divergent-convergent straight rails resembling an O letter might be more efficient than the circular rails. In this work, the optimal design conditions of such a mechanism are examined. Concretely, the O-rails are fixed on the hull of a ship, which is excited to roll along its longitudinal axis, by using a pendulum. Movies of the double-cone moving on the O-rails were shot, and the total travelling time was determined through the slow motion processing of the movies, for various values of the inclination angle of the hull, and energies introduced into the system by the pendulum. Optimal geometry of the O-rails was decided in order to maximize the kinetic energy of translation of the double-cone. Apparent spring constants and damping ratio for the oscillatory movement of the double-cone were experimentally found and validated by a theoretical model. Experimentally observed optimal length of the pendulum arm, to maximize the total traveling time of the double-cone, was justified by a two degree of freedom vibration model of the test rig.