Abstract The purpose of this study is to propose the simulation method of a small ship's motions in wash wave. Authors have proposed a reproduction method of wash wave by multi-segmented wave generators which are controlled by using computed results of CFD. Moreover, three dimensional numerical wave tank (3D-NWT) which represents a model basin and multi-segmented wave generators has been developed to simulated wash wave. In this study, ship motions in wash wave were simulated in 3D-NWT and the simulated results were compared with the experimental results which were carried out by using the reproduction method of wash wave by wave generators.

Abstract Authors continued to develop and expand new experimental methodology on tank model test with the MDES (Marine Diesel Engine Simulator) and the ATS (Auxiliary Thruster System), for making evaluation techniques on actual ship performance in waves more sophisticated. In this fourth report, the methodology is so enhanced that measured results of model test can be directly evaluated as the actual ship performance in waves. Here, the details of the newly expanded methodology are introduced, and experimental results measured from the free running model tests in waves with the expanded methodology are validated, even focusing on behaviors of ship diesel engine.

Abstract The experimental methodology for Self-Propulsion test with a MDES (Marine Diesel Engine Simulator) is expanded by a newly developed Auxiliary Thruster System. The MDES controls propeller rotational speed, by measured propeller torque and rotational speed itself as inputs, with control algorithm reflecting the marine diesel engine characteristics. Here, with auxiliary and adjustable force equaling to Skin Friction Correction on a model ship even in free running experiment, we can make propeller loading condition of model ship corresponded to that of actual ship at same Froude number. Authors developed an Auxiliary Thruster System (hereafter, ATS) whose thrust force is controllable. Then, adding the force equaling to Skin Friction Correction by the ATS, the experimental methodology with the MDES will be upgraded, because propeller torque input to the MDES are greatly approached to that corresponding in actual ship. In this study, free running model experiment in waves using the MDES and ATS were conducted, and there are significant differences between the results with and without the ATS. Furthermore, a problem on the methodology with the MDES and ATS are discussed.

ABSTRACT Controllable pitch propeller, CPP, is added to the experimental methodology for self-propulsion model test in waves with the MDES: Marine Diesel Engine Simulator. MDES is a real-time control system of propeller rotating speed reflecting the characteristics of marine diesel engine. The authors (Tanizawa, Kitagawa, Takimoto and Tsukada, 2012) introduced MDES, presented the model test results in waves and proposed the new experimental methodology to measure ship performance in waves. Using this methodology, we can measure not only ship motion responses but also the realistic dynamic responses of ship propulsion system in waves such as propeller load, rotating speed fluctuation and fuel supply rate of main engine and et cetera. As one of the additional functions of the methodology, the authors developed a model of controllable pitch propeller, CPP. This model CPP is driven by MDES and the transient response of engine to the variation of pitch angle can be reproduced. Using this model CPP and MDES, the authors conducted self-propulsion model test in waves at Actual Sea Model Basin of NMRI. This paper introduces the outline of the model CPP and result of the experiment.

ABSTRACT This paper introduces the development of marine diesel engine simulator and proposes a new experimental methodology for self-propulsion test in waves. A marine diesel engine simulator is developed for self-propulsion test of a model ship. This is composed of a servomotor, speed controller, dynamometer and PC. On the PC, marine diesel engine simulation program is installed. Based on a mathematical modeling of the engine, this program simulates fuel supply control by governor, torque generation by combustion and shafting system rotation. Inputs are rotating speed and propeller torque measured by dynamometer, and output is target speed to the speed controller of the servomotor. This is a real-time control system of propeller rotating speed, which reflects the characteristics of marine diesel engine. Using this system, the authors conducted self-propulsion test of a model ship in waves and checked system operation capabilities. We can measure not only ship motion responses but also the realistic dynamic responses of ship propulsion system in waves such as propeller load and rotating speed fluctuation, fuel supply rate and et cetera. INTRODUCTION Performance of ships is customarily evaluated in the calm sea even though ships are operated in wind and waves. This is due to the absence of practical technology to guarantee ship performance in the actual sea condition. Accordingly, contractees have no choice to accept the result of sea trial based on this business practice. This situation is hardly improved in these decades. However, to meet the recent requirement of energy saving and CO 2 emission reduction, it is craved to develop new technologies to estimate real performance of ships in the actual sea condition. Needless to say, ship performance in calm sea condition, "calm sea performance", is the base of that in actual sea condition, "actual sea performance". Now, let us briefly review the estimation method of the calm sea performance in design stage. Following procedures are commonly used.

ABSTRACT: The acceleration acting on a free-fall lifeboat (FFLB) at the water entry was numerically calculated by the MPS (Moving Particle Semiimplicit) method in three-dimensions. The MPS method has an advantage in treating the large deformation of water surface, the splash of water at the water entry, and the rigid-fluid interactions. The calculated acceleration was evaluated in the normal and the axis directions on the lifeboat. The calculated time history and the maximum value of the acceleration were close to the experiment. The effects of the skid angle and the number of passengers were investigated. As a result, it was found that the skid angle has notable effect on the acceleration in the normal direction at the fore point. It was also found that the reduction of the displacement increased the maximum acceleration; the maximum acceleration of 73% displacement in the normal direction at the fore point was higher than that of 100% displacement by 2.2 G (+26%) in our simulation. INTRODUCTION The crews are able to quickly escape from their ships by free-fall lifeboats (FFLBs) in an emergency. The FFLBs are located on the slide at the stern. Since the FFLBs are launched without boat-falls, the launching time is shorter than that for the conventional Davit-launched lifeboats, which are lowered using boat-falls. Therefore, the FFLBs are equipped with bulk carriers, which can sink quickly in case of accident. However, there are some accidents of the free-fall lifeboat at the water entry. When the lifeboat enters the water, a significant acceleration can occur and injure the occupants. Estimating the acceleration acting on a FFLB is important for the design and the safe operation. Therefore, the acceleration of FFLBs has been studied by several researchers (Boef, 1992; Arai et al., 1995 and 1996; James et al., 1996). The acceleration depends on the shape of the lifeboat and the various launching conditions. Furthermore, we need to take account of the nonlinear phenomena such as splash and large deformation of fluid at the water entry. Therefore, computational fluid dynamics approach based on particle methods, such the MPS method (Koshizuka and Oka, 1996) and the SPH method (Monaghan, 1992), are prospective for such nonlinear problems with free surface. The MPS method is a particle method for incompressible flows, and has an advantage in treating the large deformation, coalescence of fluids with free surfaces and the rigid-fluid interactions.

ABSTRACT In this study, we conducted tank experiment to measure ship responses to the Freak wave, Quasi Freak waves were generated utilizing focusing wave packet superposed on a regular wave train. Motion of the wave maker was determined in reference to wave simulations by our fully nonlinear numerical wave tank, NWT2D. An elastic model of a container ship was used to measure ship motions and whipping response. A time domain nonlinear strip method, SRSLAM, was used to simulate ship responses in the same incident waves. In this paper, the experimental and numerical results are presented and ship responses to the Freak wave are discussed. INTRODUCTION Freak wave is an extreme wave. One of the criteria of freak wave is that the maximum crest heights exceed twice the significant wave height in 20 min. time series in sea. (Soares, 2003; Dean, 1990)The mechanism of the Freak wave generation is not yet understood clearly. Recently, frequent occurrence of the Freak wave is confirmed by remote sensing and so on. The Freak wave appears unexpectedly, huge height and steepness. Therefore ships to encounter the Freak wave have serious damage at high risk. (Kjeldsen, 1997; Clauss, 2003) For safety assessment of ships, it is necessary to estimate the wave loads and ship responses by the Freak wave more accurately. A joint research project to elucidate and overcome the problem of freak wave is conducted by University of Tokyo and National Maritime Research Institute. The project is composed of two objectives. One is the observation of freak wave by remote sensing and to elucidate its mechanism. Then development of a new technique to simulate its occurrence, frequency and dimension is expected final output. The other is to elucidate the load from freak wave. Then development of avoidance system from freak wave is expected final output.

ABSTRACT The estimation of the mooring tension of moored vessels in the harbor and port is important for keeping its position especially in wind and waves during loading or unloading of the dangerous cargo such as oil and chemical. The oil tankers are usually moored by the dolphin mooring. The model experiment of the moored tanker by the dolphin mooring was carried out in wind and waves. The mooring system mainly consists of 4 mooring lines and 2 fenders. 4 mooring lines consist of bow line, stern line and 2 spring lines. The mooring system of 6 mooring lines was compared with that of 4 mooring lines. The effect of the number of mooring lines, mooring line material, wind and wave direction on the mooring tension was investigated. The experimental results were compared with the numerical calculation. INTRODUCTION When the ship is moored, the mooring system is dependent on the type of wharf such as a quay and dolphin. The kinds of quay are vertical quay and permeable at the lower part the quay. The tanker is generally moored by the dolphin system. The quay runs out with some distance and the wave transmits because it is supported by the pillars. When tanker is loaded or unloaded, the valve on the deck is connected to the loading arm installed on the exclusive quay for it. This loading arm is allowed to move due to the external disturbances such as wave, wind and current in a certain limitation. It is rare that the incoming wave from outer sea does not directly reach the moored ship in the port and harbor, however the ship should be maintained in a suitable position and the mooring tension should also be in an allowable range within the breakage strength.

ABSTRACT Visualization of three-dimensional shipping water flow on running ship foredeck was conducted at the wave basin of NMRI. Two high speed video cameras, a mirror and synchronous stroboscopic sheet light were mounted on starboard deck and the shipping water on portside deck was observed through the transparent current plate attached along the centerline of the model ship. In this paper, the experimental technique for flow visualization is briefed. High speed video images are presented to show three dimensional features of shipping water motions. And the results of their PIV and PTV analysis are presented together with measured time history of incident waves, model ship motions and impact pressure on the deck. INTRODUCTION Impact load due to green water shipping is one of the most severe hydrodynamic load acting on ships. Shipping water often damages containers, hatch cover, equipment and superstructure on the deck. In the extreme case, severe green water hits and breaks the bridge windows, floods electronics and disables all functions of the ship for navigation. In this manner, green water shipping is dangerous for ships. However, number of past studies concerning the shipping water is not so much and understanding of the phenomenon is insufficient even now. In Japan, Tasaki (1961) is known as a pioneer of shipping water study. He conducted a series of model experiment and measured the impact pressure on deck together with the shipping water volume. In his detailed report, he presented measured data and discussed the influence of various items such as freeboard, swell up of free surface due to forwarding speed of ship and relative water level at the stem. Following this work, Goda and Miyamoto (1976) studied shipping water impact pressure using a one-dimensional dam breaking model. Mizoguchi (1988) conducted an experiment of shipping water and analyzed its motions numerically.

ABSTRACT It is important to establish the preventing technique of disabled ships from drifting under the rough weather and towing technique as soon as possible. In the PC system the drift motion, towline tension, unstable motion of towed vessels and effective horse power have been estimated. This towing support tool is called Optimum Towing Support System (OTSS). This system provides the support for towing operation. It also includes the drift motion such as drift speed and direction with different ship types. The paper describes the flow of the system and also elaborates on the wave drift force and ship motion with a variety of ship status. INTRODUCTION The 5 year research project from the fiscal year of 1998 to 2002 named ‘Drift prevention of disabled ships in rough seas’ sponsored by the Ministry of Land, Infrastructure and Transport finished March in 2003. The purpose of this project is to establish the technology to prevent disabled ships caused by the engine trouble and on. From drifting and to tow them to the safety area, and thus the secondary disasters would be prevented from occurring. The optimum towing support system called OTSS using the personal computer has been developed (Hara, 2000, 2001, 2002). It can provide the operators with the information of prediction such as drift motion, towline tension, maneuvering and needed horse power of tow boats. This report describes the outline of the system and the simulation results using the graphical display of the results of OTSS. OUTLINE OF OTSS OTSS is the computer program which can predict the drift motion, towline tension, unstable motion of towed ships and towing trajectory using the personal computer. The function of the system is by Fig.1. (1) Similar ship production function

ABSTRACT A numerical wave tank (NWT) was applied to the simulation of coupled motions of ship and anti-rolling tank (ART) in beam seas. NWT is a time domain fully nonlinear simulation program based on potential theory. Solving both velocity and acceleration fields, the coupled motions among wave field, floating body and internal fluid motion of ART were simulated. For the successful simulation, artificial damping is introduced to the ART. Particularly in the resonant case, artificial damping is indispensable to stabilize the simulation. Also in the actual ART, dampers are attached inside to avoid severe sloshing. The dampers reduce internal fluid motion, at the same time reduce efficiency of ART. In this article, outline of the tank experiment is reported first. Then, theoretical study of ART is reviewed to understand the basics of ship roll response with ART. Next, the formulation of NWT for coupled ship and ART problem is outlined and the simulated result is presented. Analytical solution and the results of the simulation are compared together with the experimental result and validity of theory and NWT results are discussed. INTRODUCTION In IMO, the argument of damage stability is moving to intact stability related problems as the next topic. Current IS-Code was configurated approximately 40 years ago and was used so far. However, it has become difficult to apply it to recent ships such as the large-size container ship, passenger ship, PCC and so on. Thus, the revision of IS-Code is required. Stability of ships in wind and waves are the object of the argument. For this argument, ship specific stability is the basis. However, when the various anti-rolling devices are equipped, we should discuss the stability including effects of these devices. Anti-rolling devices in the passenger ship is used to reduce the roll amplitude and provide maximum riding comfort.

ABSTRACT A series of model tests in waves were conducted to measure the shipping water loads that act on deck and hatch covers due to deck wetness. A model of bulk carrier was used. The tests were carried out in irregular waves of which significant height is 10.6 meters and peak period is 14 seconds. In order to discuss the effects of wave heading and ship forward speed on the shipping water loads, the model tests were made in several combinations of wave heading and ship speed conditions. It was confirmed that the deck wetness and shipping water loads will be reduced considerably if the wave heading is altered to the quarter or beam seas or the ship speed is reduced. In order to verify the results of experiment quantitatively, shipping water loads on fore deck and hatch cover were estimated by improving estimation methods that were developed by the author (Ogawa, 1997). Measured shipping water loads were also compared with present rule and requirement for hatch cover. Although it is difficult to directly correlate measured values with the rule and requirement, mean values of measured results tend to be larger than the ones of the rule. It is also found that the shipping water loads defined in the requirement is ranked to somewhere between l/l0 and 113 significant values in relation to the measured results. INTRODUCTION A Revision work of International Convention on Load Lines (ICLL66) is carrying out in the International Maritime Organization (IMO) in recent years. Rational revision is needed by the use of the seakeeping theory, which has been progressed after the establishment of ICLL66. Revision work is carrying out gradually. At the present time, revision of regulation especially about minimum bow height and hatch cover is carrying out. (Watanabe et. al., 2000)

ABSTRACT In this paper, wave drift speed of a floating body is discussed. Measurements of wave drift speed were conducted on both twodimensional floating body and three-dimensional floating body. Then, an estimation method of wave drift speed was derived from the analysis of measurement results. The mechanism of wave drift speed varies with wavelength. In short wave range, wave drift force due to wave scattering pushes the floating body. Therefore, drift speed is decided by the equilibrium of wave drift force and fluid drag and it is proportional to the wave slope. In long wave range, on the other hand, wave drift force hardly acts on the floating body, because wave almost transmits the floating body. Therefore, the drift speed is decided by the wave-current speed and it is proportional to the square of the wave slope. Taking these wave drift mechanisms into consideration, an estimation method of wave drift speed, which covers entire wave range, is proposed. INTRODUCTION A joint research project named "On the drifting prevention of disabled ships in rough waves" is conducted by National Maritime Research Institute, the Maritime Safety Agency of Japan, Osaka University, Kyushu University, rope manufactures and a salvage company. In this project, development of towing support system for rescue ships and accuracy improvement of drift course prediction system are expected as final output. The authors are in charge of the latter system. The drift course prediction system was developed by the Maritime Safety Agency of Japan and had been put into practice. Accurate estimation of the drift speed is the key technology for the drift course prediction. In the total drift speed, the ocean current speed and tidal current speed are leading terms and drift speed due to wind and waves are correction terms.

ABSTRACT A linear and a fully nonlinear numerical wave tanks (NWTs) were applied to study wave drift force acts on a two-dimensional Lewis form body in finite depth wave flume. These NWTs are based on potential theory and the fluid and floating body motions are directly simulated in time domain. Boundary value problems both on the velocity potential ф and its time derivative ∂ ф /∂t are solved at each time step. The coupling condition between fluid and floating body is imposed as the implicit boundary condition of O ф /Ot on wetted body surface. The radiation condition at both tank ends are satisfied by artificial damping technique. Using these NWTs, effects of the floor step of the flume on wave drift force were studied. Measurement of wave drift force was also conducted in our two dimensional wave flume. In this second report, the resuits of simulations and measurements are presented and the effect of the floor step on wave drift force is discussed. INTRODUCTION A joint research project named "On the drifting prevention of disabled ships in rough waves" is conducted by Ship Research Institute, Maritime Safety Agency, Osaka University, Kyushu University, rope manufactures and a salvage company. In this project, a prototype onboard towing support system for rescue ships is expected to be developed as a final output. As a part of this project, the authors are studying wave drift force and drift motion of a freely floating body under various conditions. Shape of the sea floor is one of the important condition. When a disabled ship is drifting to coast and be in danger of running aground, accurate estimation of required power for rescue ships as well as estimation of drifting speed and course is very important to avoid disaster.

INTRODUCTION Introduction of NWT group and its brief history The Numerical Wave Tank (NWT) group of the International Society of Offshore and Polar Engineers was established at the 5th ISOPE conference in The Hague (1995) by Prof. C.H. Kim (Texas A & M University). This group is open freely to everybody interested in this topic. It is aimed at developing links between active researchers in the field of the numerical simulation of free surface waves, their generation and their interaction with solid bodies. The activities of the group will tend to: Prompt the concept of numerical wave tank in the scientific community, Exchange experience between participants in a friendly spirit, exempt from competition attitude, Build and maintain a free access data bank on selected benchmarks. At the 6th ISOPE conference in Los Angeles (1996), A.H. C16ment was elected by the participants as the group leader. It was also decided that the mandate of group leader is two years. During the NWT group meeting at the 7th conference in Honolulu (1997), the concept of Numerical Wave Tank was clarified by the participants. Numerical Wave Tanks are computer codes whose final goal is to reproduce physical wave basins as closely as possible. They must present at least the following features : free surface flow dominated by gravity in a bounded domain, fully non-linear boundary conditions (free-surface, floating body) simulation in the time-domain physical wave generation (moving wall or varying pressure) finite constant depth Extra properties may possibly be accounted for as for instance: viscosity, surface tension, sediment transport, wave breaking, current, uneven bottom, sloping beaches, fixed bodies, floating bodies, other modes of generation.

ABSTRACT: A fully nonlinear numerical wave tank (NWT) is applied to estimation of the wave drift force acting on two-dimensional fixed and floating bodies. This is a time domain simulation program which solves simultaneous equations of ideal fluid motion and floating body motion. Using this NWT, the diffraction problem and the radiation-diffraction problem of a two-dimensional Lewis form body in regular waves are simulated and the wave drift force is calculated both from transmitted wave and from direct pressure integral on the wetted body surface. To examine the accuracy of NWT, the first harmonic components of simulated hydrodynamic forces, body motions, wave reflection and transmission coefficients and wave drift force are compared with linear theory and experimental data of Nojiri (1975). The first harmonic components of the nonlinear simulation are confirmed to be in good agreement with linear theory. INTRODUCTION Recently, forecasting of the course and speed of drifting wrecked ship is one of the urgent topics. When a ship is in distress in rough seas, the coastal guard has to keep tracking of the ship and send rescue boats in minimum delay. If the location of the ship is lost, accurate forecasting systems are indispensable for rescue team to save the human lives and properties. In particular, in the case of wrecked oil carrier, it will be disaster unless rescued swiftly. As a part of development of the forecasting system, the authors study the wave drift force acting on floating body with arbitrary shape in large amplitude waves. Evaluation of the wave drift force is important also for the power evaluation of towing boats. For this purpose, we should consider the effect of forward velocity on the drift force. If the towed ship is in shallow area, the shape of sea bottom may also affect the drift force.

ABSTRACT A numerical wave tank is applied to the study on chaotic roll motions of two-dimensional floating body. This numerical wave tank is constructed by time domain fully nonlinear simulation method based on potential theory. In this simulation method, boundary value problems both on the velocity potential ф and its time derivative δ ф /δ t are solved. The coupling condition between wave and floating body is imposed as the implicit boundary condition of δ ф /δ t on wetted body surface. The radiation condition at the tank ends are satisfied by artificial damping technique. Using this numerical wave tank, chaotic motions of a two dimensional unstable floating body with small negative GM are simulated in time domain taking fully nonlinear fluid-body interaction into account. Simulated time history, phase plot and Poincare section of roll motions are presented and the dependency of the motion to wave height is discussed. INTRODUCTION Responses of floating bodies such as ships or ocean structures to incident waves are one of the main concern in ocean engineering. The responses are usually treated as harmonic assuming small amplitude wave an body motions. Under the assumption, the frequency responses have been investigated by linear or perturbation theories. However, the body motions are not always harmonic in real ocean. When amplitude of wave and body motions are large in rough seas. Nonlinear effects are dominant. Capsizing in a plunging breaker is an extreme example. Even if wave amplitudes are small, nonlinearities due to body shape, restoring force, mooring force, free water on the deck etc. affect to the body motions and parametric or chaotic motions may be resulted. In this paper, chaotic roll motions of two dimensional unstable floating body with small negative GM are investigated numerically.

ABSTRACT Parametric roll motion of a two-dimensional floating body is studied numerically, theoretically and experimentally. For numerical study, a fully nonlinear numerical wave tank is applied. This is a time domain simulation program which solves simultaneous equations of ideal fluid motion and floating body motions. To satisfy the radiation condition at the tank ends, an artificial damping technique is applied. Using this numerical wave tank, motions of a floating body in regular waves are simulated and the critical wave height, which excite the parametric roll oscillation, is estimated. Theoretical estimation of this criteria is also given from the stability analysis of coupled Mathieu type equation of heave and roll motions. To validate these numerical and theoretical results, an experiment is performed. Comparison among numerical, theoretical and experimental results" show that the simulated motions well agree with the measured motions in both harmonic and parametric oscillations, and as a result, the criteria estimated by the numerical Simulations agrees with the measured criteria qualitatively and quantitatively, meanwhile the theoretical criteria agrees qualitatively. INTRODUCTION Responses of floating bodies such as ships or ocean structures to incident waves are one of the main concern in ocean engineering. The responses are usually treated as harmonic assuming small amplitude wave and body motions. Under the assumption, the frequency responses have been investigated by linear or perturbation theories. But, the body motions are not always harmonic in real ocean. When amplitude of wave and body motions are large in rough seas, nonlinear effects become dominant. Capsizing in the plunging breaker is the extreme example. Even if the amplitudes are small, nonlinearity due to body shape, mooring force, free water on the deck etc. affect t6 the body motions and chaotic or parametric motions may be resulted.