Shigeo Mita

Increasing ship roll stability by using anti-rolling tanks

This paper shows a study on anti-rolling tank and its effects on ship roll motion. A flexible passive anti-rolling tank that consists of two fixed reservoirs, a set of three connected ducts and a set of five connected air pipes is designed for carrying out experiments. Experiments were conducted in regular sinusoidal waves of small amplitude and in irregular waves. First step, experiments are conducted in regular waves. Second step, experiments are conducted in irregular waves. For regular wave, experiments were conducted in constant wave heights and constant wave slopes. For irregular wave, experiments were conducted in two idealized wave spectrum. Those spectrum are ITTC (International Towing Tank Conference) idealized spectrum and JONSWAP (Joint North Sea Wave Project) idealized spectrum. After carrying out experiments and analysis, a view of the effects of the designed anti-rolling tank on roll motion of the model ship is shown in this paper. Both theoretical and experimental results show that when the model ship using the anti-rolling tank, the roll stability of the model ship is increased. It is recognized that the highest effects of anti-rolling tank on roll motion of the model ship in experiments with both regular waves and irregular waves are obtained when the model ship is experimented with a wave frequency nearby its natural roll frequency. At this level of the water, the natural frequency of the anti-rolling tank is also nearby the natural roll frequency of the model ship.

Responses of Roll Damping on Anti-rolling Tank Devices

This paper shows a study on roll damping of anti-rolling tank (ART). A flexible passive ART that consists of two fixed reservoirs, a set of three connected ducts and a set of five connected air pipes is designed for carrying out experiments. Experiments were conducted in regular sinusoidal waves of small amplitude. A view of the effect of designed ART on roll damping is shown in this research. To estimate roll damping coefficients of the model ship, several serials of experiments have been conducted. Experiments had been conducted with various diameters of the ducts and various numbers of opened valves of the connected air pipes. By changing the diameter of the ducts and controlling the number of opened valves of the connected air pipes, the volumes of moving water and air flows between two reservoirs will be changed. Consequently, the roll damping coefficients and the stabilizing moments of the ART are changed, too. Some graphs that show the responses of roll damping of the ART are drawn. The influence of the ART on roll damping of the model ship is compared in theory and in experiments. Both theoretical and experimental results show that when the model ship using ART, a stabilizing moment is created. This stabilizing moment will make the magnitude of roll motion of the model ship reduced. It is recognized that the highest effect of ART to roll motion of the model ship is obtained when the model ship is experimented with a wave frequency near its natural frequency.

On the Characteristic of the New Material Fender for Ship Collision

The new material fender that was made with TPE (Thermo Plastic Elastomer) is excellent in restoration, and it has good compression characteristic for energy absorber. We are doing the research that checks the characteristic of the new material fender for ship collision by the model test and numerical analysis. This report studied the characteristic of the new material fender for ships head-on collision by using the PEL-fender and urethane foam as the model. When rearranging the results, (1) When the entrance angle of the bow becomes large, the slope of a reaction force-bow penetration curve becomes steep. At this time, the change rate of the slope becomes steep with the increase of the entrance angle. Although reaction force differs as for PEL-fender and urethane foam, these trends resemble. (2) The reaction force of the dynamic test is bigger than the reaction force of the static test. (3) Absorbing effciency and energy absorbing factor do not change by the bow measure.

Influence of the Bow Collision Condition on the Characteristic of the New Material Fender with Bridge Piers

The new material fender is made from thermoplastic elastomer, and shape of the cross section is honeycomb. Honeycomb and foam are the two major classes of cellular solid, and commonly be used to absorb energy. Authors are performing the research that checks the characteristic of the new material fender to ship collision by the model test and numerical analysis. This report studies the influence of the bow collision condition by using the urethane form as the model. When rearranging the results, ( 1 ) Reaction force-bow penetration curve shows that the reaction force increases linearly with increase of bow penetration to a certain distance. Then, reaction force rapidly increases with little increase in the penetration distance. ( 2 ) When location of the penetration approaches the end of fender, the slope of the reaction force-bow penetration curve becomes moderate. In the case, the slope of the curve at the same penetration distance increases with the increase of the width of the fender, although this increase saturate to a certain value when the width/ depth ratio exceeds 6.

Influence of the Bow Measure on the Characteristic of the Resin Fender in Head-on Collision

The resin fender that was made with the elastic resin has a good compression characteristic for energy absorber. We are doing the research that checks the characteristic of the resin fender by the model test and numerical analysis and used urethane foam and PEL-fender as a model. In the present paper, we report about the research result of the model test in the time that the ship that is different bow measure collided dynamically. When rearranging the results, (1) When the entrance angle of the bow becomes large, the slope of a reaction force-bow penetration curve become steep. At this time, the change rate of the slope becomes steep with the increase of the entrance angle. These characteristics agree with the result of a static test. However, reaction force bigger than a static test. (2) Absorbing efficiency and energy absorbing factor do not change by the bow measure.