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Wave energy can be a significant factor in the progress towards a carbon-free society. This paper demonstrates the wave energy harvesting performance of a 1/2 scale cabin-suspended catamaran in regular head waves. The catamaran has a twin-seater, the length is 3.28m, and the width is 2.10m. It consists of a suspended cabin, a suspension unit, and a twin-hull. One brushed DC Motor/Generator (M/G) coupled with one gearhead is set at each of the four corners of the cabin’s deck. The shaft of the gearhead connects to a shaft of a pinion gear which meshes with a rack that is fixed on a hull through a ball joint. In this way, the vertical motion of the rack can be transferred into the rotational motion of the pinion causing the M/G generates electrical power. The power generation of the catamaran is experimentally investigated using a Maximum Power Point Tracking (MPPT) technique in a towing tank. Two control algorithms are developed: indirect MPPT and direct MPPT. It is found that the wave energy capture width ratio (CWR) obtained at the direct MPPT is approximately 11% higher than the indirect MPPT when their control parameters are having equal magnitude.

In the digital communication system, waveform distortion due to reflection of the multidrop transmission line is one of the main issues for high-speed signal transmission. Although many approaches to reducing the reflection, such as asymmetrical power splitter, stub series terminated logic, and the segmental transmission line have been used in the past, the drawbacks of amplitude loss at the receivers, or high power consumption due to excessively low impedance design are still problems. In this article, we introduce a new method, “reflection compensation line (RCL),” which is constructed in isometric length of main bus segments and stub lines. The method using the RCL intentionally generates reflections to cancel the distortion and restore the ideal waveform at the receivers. In order to reduce the waveform distortion effectively, an optimal set of transmission parameters is determined by means of evolutionary gradient search. The performance of the proposed method especially at the stub lines of both ends of the main bus line is confirmed using the SPICE simulation, and its applicability to practical systems is also discussed.

A novel concept catamaran equipped with a suspended cabin, named Wave Harmonizer Type 4 (WHzer-4), is proposed and evaluated. The mass-spring-mass system is constructed by mounting four sets of suspensions in-between the cabin and the twin-hull. Two sets of dual motor/generators (M/Gs) are attached on the center beam of the cabin's deck fore and aft. Each shaft-end of the dual M/Gs is connected to the twin-hull through a rack-pinion gear unit. In this way the vertical relative motion between the cabin and the twin-hull can be transferred into the rotational motion of the M/Gs, and vice versa. A semi-active motion control system, which contains a proportional-integral (PI) controller, is designed and applied to each of the dual M/Gs for the aim of absorbing wave energy under the condition of suppressing the local vertical velocity of the cabin as much as possible. A 1/5 scale model ship with a length of 1.6 m is built, and a forced-oscillation bench test is implemented to validate the performance of the control system. Then, a series of towing tank tests is carried out in regular head waves. The heave and pitch responses of the cabin, those of the twin-hull and the corresponding wave energy capture width ratio (CWR) at five control scenarios and two reference scenarios are investigated. Discussion on the results of the tank test shows that the motion reduction of the cabin and the wave energy harvesting can be achieved simultaneously at a few wave conditions. However, at other conditions, although noticeable amount of wave energy is harvested, motion reduction of the heave and pitch of the cabin could not be obtained at the same time. It is suggested that varying the gain settings of the PI controllers according to the location of the controllers may improve the effectiveness of the proposed control system.

In recent years, wireless power transmission (WPT) to an electric vehicle (EV) has attracted increasing attention. More than several kW is assumed for WPT, so that electromagnetic interference (EMI) is required to be considered. The WPT can also affect the control system and the automotive networks of the EV. Therefore, the noise current induced on the wire harness due to WPT cannot be ignored. The purpose of this paper is to investigate the noise current on the wire harness. As a result of the investigation, we confirmed up to several hundred μA on the wire harness.

A series of cabin-suspended ships, named Wave Harmonizer, has been developed since 2008. The model ship consists of cabin part, hull part and conjunction part which is mounted in-between the cabin and the hull. The possibility and feasibility of introducing suspensions into small vessels are investigated. Effectiveness evaluations are made in two aspects: motion reduction of the cabin and wave energy harvesting through the oscillating cabin. According to the research results obtained in 2015 and 2016, it was found that the deck of the cabin may bear obvious inclination while weights were loading or unloading from it. Moreover, in relative long waves, the effectiveness of the motion reduction of the skyhook controller was insufficient. To solve those problems, an attitude control strategy is proposed. It is adopted as an outer-loop of the existing controller. Inclination sensors are employed to collect the rotational angle of the cabin in terms of pitch and roll. After finishing the design and construction of the double-loop control system, open loop tests are carried out in dry and wet conditions. The chain mechanism of the ship is investigated. Then a bench test is operated to validate the control concept and performance of the double-loop control system. Finally, tank tests are implemented to examine the inclination reduction of the cabin at regular head waves. In this paper, the development of the double-loop control system is described, experimental results are demonstrated with respect to the heave and pitch motion reduction of the cabin at the condition of with/without the outer control loop. It shows that the inclination reduction at the loading/unloading condition and the walking-on-deck condition are significant. However, in waves the effectiveness is not clearly verified. It suggests that the influence of the apparent gravity on the inclination measurement in waves should be investigated and solutions to accurately detect the inclination of the cabin should be sought.

The data transmission rate required for the earth observation satellites is in the order of Gbps because of the enhanced performance of the observation sensors. However, the data transmission rate is approaching to the capable limits due to the issues of increased loss caused by the connectors or wires connected. In addition, there is another issue of the transmission irruption due to the vibration during the satellite launch. The transmission technology using the non-contact connector which has high vibration tolerance against the lossy wire connection systems is proposed and this paper describes the advantages of the non-contact connector, consisting of Transmission Line Couplers (TLC). With the transmission characteristics analysis of the connector and the design concepts, analysis of actual measurement results reveal that 15 m cables transmission of 2.5Gbps and BER less than 10−12 is feasible.

To investigate the behaviour and hydrodynamic characteristics of supple nets in a wave, experiments of forced oscillation were conducted in a tank with square net panels. The four corners of the net panel were fixed to the oscillation device with a specific pretension. The hydrodynamic loads acting on the corners of the netting were measured. To simulate the experiments, a numerical model based on dynamic finite element analysis was constructed. Comparing the amplitude and phase of measured loads with the calculated results, the drag coefficient Cd and inertia coefficient Cm were determined by interpolation and iteration. The effects of various parameters on Cd and Cm were investigated. The results show that: (1) drag force is dominant at low frequency, whereas the contribution of inertia force increases with an increase of the Keulegan–Carpenter number or frequency; (2) with increasing frequency, both Cd and Cm show a decreasing trend, and the trend of Cd against the Reynolds number is similar to that in steady flow; (3) increasing oscillation amplitude makes Cd decrease, but it has no significant effect on Cm; (4) solidity generally has a positive effect on Cd and Cm.

Theoretical work of a partly porous circular cylinder is studied in the present work. The cylinder possesses a porous sidewall and an impermeable bottom. In addition, a porous plate is fixed horizontally inside the cylinder, either beneath or coincident with the water’s surface. The inner plate is to work as an obstruction to make wave dissipation more effectively. To simplify the problem, the Darcy’s fine-pore model is applied to the boundary condition on the porous body surface. Special treatment is required for the boundary condition on the inner porous plate when it is situated at the still water surface. A new boundary condition is derived at that part of the boundary based on the linear wave theory and Darcy’s law. To validate the theoretical work and computed results, a series of model tests are carried out in a wave basin. It is found that the computed results with the present method are generally in good consistence with the experimental data. The discussion on the effects of porosity and the inner plate is presented as well.

This paper discusses an innovative model test that has been carried out to know wave drift forces affecting on maneuvering of a ship relating to dynamic positioning system, as well as a theory of wave drift force including wave drift damping and wave drift added mass. Some examples of experiments done in Ocean Engineering Wave Basin, Institute of Industrial Science, University of Tokyo are shown, including Planar Motion Mechanism (PMM) tests not only in still water but also in waves. Details of PMM tests in waves are also discussed.

A new, high-speed, recreational dinghy has been developed. It is a catamaran with submerged hydrofoils, which allow the crew to control the trim and heel balances. The two hulls are allowed to rotate about a main beam. The hydrofoils, which are attached below each hull, change the angle of attack independently, and the difference between the lift forces acting on each hydrofoil makes the catamaran stable. The stability of the boat is examined by numerical calculations and one-third scale model tests.

Microwave thermal therapy is one of the modalities for cancer treatment. There are several schemes of microwave heating. The authors have been studying thin coaxial antenna for intracavitary microwave heating aiming at the treatment of bile duct carcinoma. Up to now, the heating characteristics of the antenna are investigated by numerical simulation and experiment for finding a possibility of the treatment. In this study, in order to consider practical situations of the treatment, heating characteristics of the antenna inserted into a metallic stent is evaluated by numerical simulations. Moreover, metallic stent, which realizes effective microwave heating, is proposed.

Maneuverability in waves is important for the safety of ships and other marine vehicles. Conventionally, the maneuvering experiments are performed in still water at a constant forward velocity. In order to investigate the wave effects on ships steering, a series of towing tests with a Planer Motion Mechanism System (PMM) are carried out in waves in the present work. The ship model is forced to oscillate in horizontal plane at a low frequency when being towed forward at a small constant speed. As an extension of the previous work, the low-frequency oscillation of yaw motion is also considered. Hydrodynamic forces and the displacements of the ship model are measured throughout the tests. Then, the measured data are analyzed by the Fourier analysis to obtain components at different frequencies. By comparing the hydrodynamic forces measured in still water and that in waves, the wave effects on the maneuverability of ships are estimated. The variation of these nonlinear hydrodynamic coefficients against the wave amplitude and wavelength is examined.Copyright © 2011 by ASME

With the increasing worldwide demand of seafood and environmental problems in coastal aquaculture, offshore area has been increasingly expected to be utilized for aquaculture. An offshore aquaculture system has fewer effects on the surrounding marine environment through the rapid diffusion of organic wastes from the cultured fish than a coastal one. The offshore area then provides clean waters for cultured fish. On the other hand, the offshore aquaculture system is subject to the severe natural condition such as typhoon attack. Actually, in the current aquaculture system, the offshore sea cages are always submerged around 10m below the sea surface to avoid the effects of high waves and strong currents. However, the safety of the sea cage against the incident wave has seldom been examined, while that against the water current has been analyzed by model tests in tank and numerical simulation. We investigated the hydrodynamic force properties of a heaving sea cage in the previous work and its results proved that the deformation of net much affects on sea cage’s motion characteristics. To study the most fundamental problem, we investigated the hydrodynamic force characteristics of a rigid net as a first step and explained that these relate to its porosity and wave conditions. As a second step, in the present study, we investigate hydrodynamic force properties of an elastic net. Six square-shaped textile net models which are made of elastic strings and metallic frame are arranged. Three different porosities (0.53, 0.64 and 0.74) and two different net’s tension (10 and 50 N/m) on each porosity are employed; that is, we arranged 6 elastic net models. Forced heaving tests and diffraction tests are carried out. In addition to measuring heave force, the deformation of net surface is measured by a video image analysis system. To compare with the experimental results, we calculate hydrodynamic forces and the deformation of net using a boundary element method. The boundary condition on elastic net is that the normal velocity to the surface is not zero but proportional to the pressure difference. The deformation is also taken into consideration.Copyright © 2011 by ASME

In the present work, the diffraction of waves by an array of porous circular cylinders with or without an inner porous plate is considered in detail based on the linear wave theory. For the sake of designing more effective floating breakwaters, the transmission rate of waves propagating through the array is also calculated. Each cylinder is partly made of porous materials. Namely, it possesses a porous sidewall and an impermeable bottom. In addition, an inner porous plate is fixed horizontally inside the cylinders, which works as obstruction to make wave dissipate more effectively and eliminates the phenomenon of sloshing mode. To deal with hydrodynamic interactions among a great number of bodies, a hierarchical interaction theory, which saves computation time efficiently, is adopted to compare with the approach of Kagemoto & Yue (1986). Consequently, a series of model test of an array of porous cylinder are carried out in the basin to validate the theoretical work and the calculation results. The draft of the cylinders, the location of the inner porous plate and the spacing between adjacent cylinders are adjusted to investigate its effect on the wave dissipation.Copyright © 2010 by ASME

With the increasing world demand for seafood and environmental problems in coastal aquaculture, offshore area has been increasingly expected to be utilized for aquaculture. The offshore aquaculture system has fewer effects on the surrounding marine environment through the rapid diffusion of organic wastes from the cultured fish than the coastal one. The offshore area then provides clean waters for cultured fish. On the other hand, the offshore aquaculture system is subject to the severe natural condition such as typhoon attack. Actually, in the current aquaculture system, the offshore sea cages are always submerged around 10m below the sea surface to avoid the effects of high waves and strong currents. However, the safety of the sea cage against the incident wave has seldom been examined, while that against the water current has been analyzed by model tests in tank and numerical simulation. We investigated the hydrodynamic force properties of a heaving sea cage in the previous work and its results proved that the deformation of net much affects on sea cage’s motion characteristics. To study the most fundamental problem, we investigated the hydrodynamic force properties of an undeformable net in the present study. Nine net models are arranged. These models have square-shaped frame and its inner dimensions are 216 × 216 mm. In these net models, three different twine diameters and three different twine intervals are arranged. The porosities of these models are in the range of 0.39 to 0.91. In addition, an impermeable plate model is also arranged. Forced heaving tests and wave exciting force tests are carried out on each net and plate model. Added mass and damping coefficients, as obtained by forced heaving tests, differ according to porosity of net and oscillation frequency and amplitude. Wave exciting forces, as obtained by wave exciting force tests, also differ according to porosity of net and wave slope and the forces increase with wave amplitude in higher order than one. To compare with experimental results, we theoretically calculate the hydrodynamic forces from a linearized potential flow approach supplementing the effect of porosity. In the boundary condition on the net surface, the vertical velocity to the surface is not equal to zero, but determined by the permeate coefficient of the surface.

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 © 2009 by ASME

With the increasing world demand for seafood and environmental problems in coastal aquaculture, offshore area has been increasingly expected to be utilized for aquaculture. The offshore aquaculture system has fewer effects on the surrounding marine environment through the rapid diffusion of organic wastes from the cultured fish than the coastal one. The offshore area then provides clean waters for cultured fish. On the other hand, the offshore aquaculture system is subject to the severe natural condition such as typhoon attack. Actually, in the current aquaculture system, the offshore fish cages are always submerged around 10m below the sea surface to avoid the effects of high waves and strong currents. However, the safety of the sea cage against the incident wave has seldom been examined, while that against the water current has been analyzed by model tests in tank and numerical simulation. In the present study, therefore, we investigated hydrodynamic property of a heaving sea cage as the first step. Forced oscillation tests and wave exciting force tests have been carried out, and numerical modeling have also been made to estimate hydrodynamic characteristics theoretically and to estimate the drag and mass coefficients. Results of the forced oscillation tests show that the added mass and damping coefficient of sea cage models depend on forced oscillation amplitude. This dependence may be mainly attributed to the deformation of net, and we successfully reduce the dependence on the forced oscillation amplitude in the result of reanalysis which takes into account the deformation of net. Results of measured wave exciting force show that wave exciting forces are not linear in wave amplitude. This may be due to the viscous drag effects as well as the deformation of net. On the other hand, we calculated the flow around a sea cage. This is based on velocity potential and supplemented the effect of viscosity by equivalent linearization. In the boundary condition on the sea cage surface, the vertical velocity to the surface is not equal to zero, but determined by the permeate coefficient of the surface. This permeate coefficient is a function of wave amplitude, wave period and porosity of the net. In the future works, deformation of net should be also taken into account in this calculation.Copyright © 2009 by ASME

With the increasing world demand for seafood and environmental problems in coastal aquaculture, offshore area has been increasingly expected to be utilized for aquaculture. The offshore aquaculture system has fewer effects on the surrounding marine environment through the rapid diffusion of organic wastes from the cultured fish than the coastal one. The offshore area then provides clean waters for cultured fish. On the other hand, the offshore aquaculture system is subject to the harsh natural condition such as typhoon attack. Actually, in the current aquaculture system, the offshore fish cages are submerged every time around 10m below the sea surface to escape from high waves and strong currents. However, the safety of the sea cage against the incident wave has not been examined, while that against the water current has been analyzed by tank model test and numerical simulation. In the present study, therefore, the hydrodynamic forces on the submerged sea cage from the incident wave were investigated by the tank model test, and the motion of the submerged sea cage was observed. As a result of the forced oscillation test, the numerical values of the added mass and damping coefficient of the sea cage scatter according to the wave amplitude for the same frequency of the forced oscillation. The difference in the added mass may be attributed to the effects of ladder and the bending of the net. The current analysis is focused on modeling of the bending of the net. Then the difference was also found in the damping coefficient at the same frequency of the forced oscillation. The damping coefficient based on viscosity was separated by the equivalent linearization using the equation of Morison’s drag force. As a result, the scattering of the damping coefficient was reduced, adjusting the drag coefficient. It is a future study to examine the relationship between each mode of the motion of the sea cage and the adjusted drag coefficient. As for the experiment of the mooring system, the larger mooring force worked on the rope between the cushion float and anchor than that between the cushion float and frame rope of the sea cage. The motion of the submerged sea cage was suppressed so that the mooring force between the cushion float and frame rope was reduced. However, the mooring force depends on the initial tension of the mooring rope, therefore the relationship between the initial tension and the mooring force should be examined as future studies.Copyright © 2008 by ASME

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 © 2008 by ASME

With the increasing world demand for seafood and environmental problems in coastal aquaculture, offshore area has been increasingly expected to be utilized for aquaculture. The present study proposed the concept of an offshore aquaculture system with an automated feeding platform. The offshore aquaculture system has fewer effects on the surrounding marine environment through the rapid diffusion of organic wastes than the coastal one. The offshore area then provides clean waters for cultured fish. On the other hand, the offshore aquaculture system is subject to the severe natural condition such as typhoon attack. Actually, in the current aquaculture system, the cultured fish is starved during a few days before and after typhoon attack since the feeding ship is not able to approach the offshore sea cages, which is submerged every time around 10m below the sea surface to escape from high waves and strong currents. The automated feeding system should be therefore developed to enable the cultured fish to grow faster under the severe natural condition. The proposed system consists of several submerged fish cages and a feeding platform, which includes fuel tanks, feed storage silos, and an automated feeding machine. The feeding platform was designed by numerical analysis and tank model test in order to suppress its motion as small as possible. The motion of the feeding platform was first predicted by numerical analysis. The unmoved point was formed at each period of the incident wave. It moves upward as the period of the incident wave increases. Consequently, the point at 8m below the sea surface (3m above the bottom of the feeding platform) is the best one to attach the feeding hose. As a result of tank model test, pitch and heave motions of the feeding platform were dominant in the waves with short (1.5 seconds) and long (3.1 seconds) periods, respectively. An unmoved point was observed on the surface of the feeding platform as predicted by the numerical model, while the top of the feeding platform moved more largely. The unmoved point for the feeding hose was specified at above the bottom of the feeding platform.Copyright © 2008 by ASME

The dynamic positioning system of floating ocean structures requires hydrodynamic force derivatives to construct an accurate maneuvering model. In a severe sea state, the effects of ambient wave field on the maneuvering properties are not negligible. To investigate wave drift forces affecting on maneuvering of a ship relating to dynamic positioning system, an innovative model test, i.e. the Planer Motion Mechanism (PMM) test in waves is discussed in the present paper. Meanwhile, a theory to evaluate wave drift force including wave drift damping and wave drift added mass is summarized. Some examples of experiments done in Ocean Engineering Wave Basin of Institute of Industrial Science, University of Tokyo are presented and compared with calculated results based on the above theory.Copyright © 2008 by ASME

Recently, much attention has been paid on the maneuvering characters of ships in waves. Apparently, ships steering in waves are subjected to linear wave loads at the encountering frequency. Nevertheless, the maneuvering characters of ships are more affected by the nonlinear wave drift forces at low frequencies. In the present work, to examine the wave effects on the ship maneuverability, a serial of towing tests with a Planer Motion Mechanism system (PMM) is carried out in waves. Forces and horizontal displacements of the model are measured throughout the tests. The measured data are analyzed by the Fourier analysis to obtain components at different frequencies. Discussion on the importance of the force components is made.Copyright © 2007 by ASME

An experimental expression of the restoring force of a tire compressed by a flat plate and a dull edge is derived. Using this expression, equations of motion of a light truck that runs over a low bar-like projection placed normal to the direction of the motion of the truck are set up. These equations are solved by a numerical method in the situation that the left-hand wheels of the truck run over the projection. Based on the solution, the force applied to the road by the truck in this situation is calculated. Experiments are made to measure the force applied. A force-measuring device equipped with a force-receiving flat top plate is settled in the road with the top plate flush with the road surface, and a bar-like projection is attached to the top plate. The force is measured when the left-hand wheels of the truck run over the device. It is concluded that the results of calculation show good agreement with those of experiment.