Hajime Kihara

The Effect of Controlling Fins on the Motion of Resonance-Free SWATH (RFS) Platform

The speed reduction, additional resistance or slamming, which are caused by the large amplitude of ship motions, should be restricted completely for oceangoing large fast ship, because of the strict time-punctuality and high value of the cargo. In the present work, comparison of seaworthiness, such as the motion responses in head seas, is made among four types of ship hulls, i.e. Mono-hull, Ordinary SWATH, Trimaran and Resonance-Free SWATH (RFS). The last one can be regarded as a special type of catamaran. As a result of the extremely small water plane, the restoring moments are negative for RFS hull, which leads to free of resonance in the motion responses. Experiments in towing tank and theoretical calculations are carried out to examine the motion responses in waves. Calculations are generally based on potential theory modified by adding the viscous effects and including fin lifts. The results of the motion responses of RFS are compared with those of mono-hull ship, ordinary SWATH ship as well as trimaran ship. Where the motion of RFS is controlled using movable small underwater fins. The motion of ordinary SWATH is examined with and without fin control. It can be seen that the heave motion responses of RFS are very small in comparison with those of other ship hulls. Also, the pitch motion responses of RFS are much smaller than those of mono-hull or trimaran or ordinary SWATH without fin control, and are smaller than those of ordinary SWATH with fin control. Fin control actions, i.e. proportional and derivative control, are applied in the experiments and calculations. It is considered that the derivative control action is more effective on the motion responses of RFS than the proportional one as predicted. The larger the derivative gain value is, the smaller the motion response of RFS is.© 2010 ASME

Lift Characteristics of Controlling Fins of Resonance-Free SWATH

Speed reduction, additional resistance or slamming, which caused by the large ship motions, should be avoided for a high-speed oceangoing vessel, because of the delivery punctuality and high value of the cargo. A promising ship type for such the oceangoing vessel is the so-called “Resonance-Free SWATH (RFS)”. It has negative restoring moment due to the extraordinary small water plane area. As a consequence, the resonance peak is removed from the motion response. RFS is designed to cross 4,800 nautical miles of Pacific Ocean within 5 days punctually at a speed of 40 knots, with good seaworthiness such as no speed reduction or absolutely no slamming even when running in the rough sea of sea state 7 with significant wave height of 6–9 m.The attitude of RFS with negative restoring moment is adjusted by four pairs of controlling fins attached to the fore and aft ends of lower hulls. In the previous works, the quasi-steady values of lift-curve slope are usually adopted in the motion equations of frequency domain. However, when working in waves, the controlling fins are not in a steady state. The lift coefficient is no longer a constant. In addition, there exist a phase lag between the movement of attack angle and the fin-generated lift.The theoretical prediction and the experiment to analyze the phenomena of lift generation including the phase difference and the interaction among fins and lower hulls are carried out. The results show that the characteristics of fins depend on the encounter frequency. Then, the effect of lift characteristics of controlling fins on the RFS model is discussed. The results of theoretical estimation and experiment are discussed and it is observed that estimated results agree to some extent with experimental results.© 2014 ASME

On the Resonance-Motion-Free Swath (RMFS) as an oceangoing large fast platform

The speed reduction, additional resistance or slamming, which are caused by the large amplitude of ship motions, should be restricted completely for oceangoing large fast ship, because of the strict time-punctuality and high value of the cargo. In the present work, comparison of seaworthiness properties, such as no speed reduction and absolutely no slamming, is made among four types of ship hulls, i.e. mono-hull, ordinary SWATH, trimaran and Resonance-Motion-Free SWATH (RMFS). The last one can be regarded as a special type of catamaran. As a result of extremely small water plane, the restoring moments are negative for the RMFS hull, which leads to free of resonance in the motion responses. Experiments in towing tank and calculations are carried out to examine hydrodynamic forces and motion responses in waves. Calculations are generally based on potential theory modified by adding the viscous effects and including fin lifts. The results of RMFS are compared with those of mono-hull ship, ordinary SWATH ship as well as trimaran ship. The heave motion responses of RMFS are very small in comparison with those of other ship hulls. On the other hand, the pitch motion responses of RMFS are considerably small in comparison with those of mono-hull or trimaran, but are not as small as expected in comparison with those of ordinary SWATH. The reason is that a soft spring system is applied in experiments, to replace the proportional control action supplied by the fin lift. The spring system can not make use of the advantage of the negative restoring moment, which is a characteristic of RMFS. Accordingly, a new control system of ship motion by means of the lift force from fins should be developed.Copyright

Numerical Simulation of Deck Wetness for a 2D Pontoon-type Floating Structure

Numerical simulation of deck wetness for a 2D pontoon-type floating structure is carried out and the numerical results are compared with experimental ones. We use MPS(Moving Particle Semi-implicit) method which is a kind of fully Lagrangian type particle methods suitable for highly nonlinear wave-body interaction problems. In this paper, the numerical implementation of the particle method for floating body problems is explained briefly and some numerical results including comparison with experimental ones.

On the Novel Fast Ocean Platform

The mission of the large trans-ocean fast ship is to transport the high-valued and time-sensitive goods punctually at reasonable price. Accordingly, the speed reduction, additional resistance or slamming, which are caused by the large amplitude of ship motions, should be restricted completely. Some seaworthiness, such as no speed reduction and absolutely no slamming, is especially required for ships running fast in ocean waves. The final intention of the study is to compare the transport efficiency, including accuracy of time schedule and transport quality like damage of goods caused by slamming, among three types of ship hulls, i.e. mono-hull, catamaran and trimaran. As a first step, a “Resonance-Motion-Free SWATH (RMFS)” hull is considered as an example of catamaran type in the present work. As a result of very small water plane, the restoring moments are near zero for this type of hull, which leads to free of resonance in the pitch responses. Experiments in towing tank and calculations based on potential theory are carried out to examine hydrodynamic forces and motion responses in waves. The results are compared with those of typical mono-hull and trimaran ships. The predominance of RMFS regarding seaworthiness will be pointed out in the conclusion.Copyright