In the paper, we consider the problem of variable rotational speed control for a wind turbine with the pitch fixed from the view point of scheduling by wind speed. For this problem, we apply LPV (Linear Parameter Varying) technique taking the varying parameter as wind speed. Our control purposes are to extract the maximum power from wind energy in the region below the rated wind speed and then to keep the rated power in the region above the rated wind speed. The effectiveness of applying LPV technique is shown through numerical simulations, compared with the results by the conventional control which is proportional to the rotational speed squared.

View full abstract

In this paper, model experiments and numerical calculations were performed in order to clarify the behavior of the discharged water from the ocean nutrient enhancer “TAKUMI” into the sea with temperature stratifications. The results demonstrate that temperature stratification prevents the discharged water from sinking to the bottom, and the calculation in this paper can estimate the intrusion depth of the discharged water from “TAKUMI”.

View full abstract

There is a great demand for Autonomous Underwater Vehicles (AUVs) not only for wide area surveys but also for condition surveys of artificial underwater structures such as breakwater caissons, pillars, ship hulls, and installations of offshore oilfields. This paper proposes a navigation method for AUVs operating around structures, whose major configuration is given in advance. By referring to sensory data and the map of the environment where the AUV is deployed, the method enables it to localize in real-time and follow pre-given way-points without any external help as needed for conventional acoustic positioning method. Probabilistic approach called “Particle filter” utilizes multi-sensor data to realize robust and stable navigation even at harsh condition where single sensor systems might fail. This method was implemented on the AUV ”Tri-Dog 1” and experiments were carried out around breakwater caissons at the mouth of Kamaishi bay, Iwate Prefecture. The vehicle took accurate images of the surface of a caisson, foot protection blocks, and rock mound. Mosaics of the bottom and the surface of the caisson are made from these images based on the precise vehicle's position estimated at each time of the mission and their quality verifies the performance of the method. This is the first time in world that caissons have ever been observed fully autonomously by an AUV.

View full abstract

The shape and swimming method of fish vary in accordance with their environment and fish have high maneuverability in water. It is believed that studies on how fish swim can suggest a new effective propulsion method for underwater vehicles and robots, and that various types of fish type robots using new propulsion methods may contribute to ocean observations, developments and environmental protection.
This paper deals with development of a motion mechanism for fish type robot using an artificial muscle. A motion mechanism composed of a shape-memory alloy and an elastic plate is proposed for fish type robots and the characteristics of the motion mechanism are examined by model experiments. Additionally a fish type robot using the motion mechanism is developed and the swimming performance is tested in an experiment tank. The motion of the fish type robot is analyzed using motion picture taken by a digital video camera. And motion of the robot is expressed by a numerical model. The effectiveness of developed motion mechanism is examined based on the experimental results.

View full abstract

In the present study, a new fast RORO ship of pentamaran type is developed and proposed. The resistance, stability and seakeeping performances of it as well as its capability in dead weight and deck space are examined with comparison with an existing conventional RORO ferry of monohull type. The results demonstrate that the proposed pentamaran has better performances than the monohull ferry and has reasonable dead weight and larger deck space. A feasibility study of the new ship in a short route in Seto-island sea is also carried out on the basis of economical evaluation. The results show that the pentamaran can be replaced by exsisting RoRo passenger ferries in the route from economical point of view

View full abstract

The present paper proposes a Sailing Wind Farm as main energy resource with small load on an environment. It sails around EEZ of Japan seeking appropriate breezing and avoiding meeting heavy storm like Typhoon. This is a concept of main energy resource of Japan to minimize environmental load when fuel cell and hydrogen will be available for daily life. A prototype design shows feasibility of safe sailing even in case of Typhoon and structural strength in storm. If Sailing Wind Farms, 3900 units of the prototype replace coal power plants, then we can obtain 18% of total electric power generation of Japan and reduce 10% of exhausting CO₂ of the 2002 level.

View full abstract

In this study an indoor positioning system available in shipyards was developed using Bluetooth technology. As a result of the experiment in the shipyard, positioning was able to be performed in the accuracy of 1.5-3.0[m].

View full abstract

Recently, the user-friendly and human-based thoughts have been emphasized in design and development for many kinds of products. This idea is spreading widely in the social welfare system, and “universal design” or “barrier free” is taken into the product design. On ship design, the law of “traffic barrier free” is instituted, and the application of the barrier free standard based on this has been imposed for the passenger ships of 5 gross tonnage and over. Hence, the authors have investigated the car ferries sailing in Seto Inland Sea from the viewpoint of this barrier free, and it was concluded that the physical burden was especially high for old or handicapped people when passing on the slope of a boarding bridge, especially for the helper of a wheelchair user. Since the slope may incline steeply by the tide of sea, the body burden of the wheelchair helper is anticipated to be larger. This paper carried out the biomechanical analysis using the virtual human model at that situation, and showed the body burden of a wheelchair helper in this slope of boarding bridge.

View full abstract

The scheduling of assembly process of hull blocks is very important to rationalize the total construction scheduling because the block assembly is in the middle of the manufacturing process between fabrication and erection. Hence, some researches have been made till now. There are two systems to assemble the blocks: the case done on the fixed area in a wide yard, and the case of line flow system on the conveyor. In the former case it is necessary to optimize the space where blocks are located. Though this allocation of blocks is carried out by experienced workers now, the system which supports this work has been developed recently. Since these systems are done by manual operation on the computer display, an automatic allocation system was developed by the authors here, imitating an optimal allocation of plate nesting.
The applied method is the simulated annealing (SA), which is one of the meta-heuristics approach for combinatorial optimization problems. This paper introduces the technique of the optimization of allocation and the calculation results for sample data. The results showed that this SA method is more effective to optimize the block allocation on the assembly area.

View full abstract

Influence of outrigger position of a high speed trimaran on the resistance and wave wash was investigated by the tank tests changing 9 outrigger positions of the trimaran model. The trimaran is composed of the center hull with L/B = 8.0 and B/T = 3.57 where L, B and T denote the length, breadth and draft respectively, and the outriggers with l/L = 0.375 where l denotes the outrigger length. The objective of this research is to provide a useful design data to quantify the resistance and the wave wash characteristics of the trimaran. The optimum location of the outrigger to minimize the resistance depends on ship speeds. The measured data will allow naval architects to balance hydrodynamic performance with other design considerations in the conceptual designs of high speed trimarans.

View full abstract

As a recent tendency to take high interest in the environmental problem, the time has come to reconsider the present working environment. Especially, air pollution caused by the generated metallic fume during the progress of cutting and welding in a fabrication shop is a hygienic issue for labor health. For settling this matter, it is necessary to take the pollution-control measures that are desirable to conform to the diffusing aspect of metallic fume in a fabrication shop. However, the physical property and movement characteristic of fume as minute particles have not been grasped accurately even now.
For the purpose of improving the working environment in a fabrication shop, the measurements of distributional concentration and particle size of metallic fume at N/C cutting line, sub-assembly line and cubic block manufacturing line in two shipyards were carried out. Moreover, the turbulent diffusion state of fume corresponding to measurement conditions, in which it has tendency to form those stagnant in absence of advection effect on turbulent gas flow, was numerically analyzed by using k-ε model based on SIMPLE algorithm. As the results, the prediction of fume diffusion shows considerably good agreement with the measurement data. Then, the relation between the ventilation system and the fume transportation state on the working site is investigated evidently using experimental data and calculated data, for establishing the ventilation system with efficient control of fume flow.

View full abstract

As a recent tendency to take high interest in the environmental problem, the time has come to reconsider the present working conditions. The thermal environment at an exposed working place in a hot season with skylight should keep within the thermal limitation of human body, considering the metabolic heat and radiation heat. Otherwise, the storage of body heat accumulating during an operation has an effect on deteriorating the work efficiency and the deficit of attention. In case of severe conditions beyond the criterion of thermal environment, some countermeasures such as the use of sunshade or cooling fan need to be taken adequately. Then, the relation between the heat storage of body during work and the environmental factors has to be clarified reliably corresponding to the magnitude of working load.
In order to grasp this relation, the formula of heat storage of human body considering the effect of sunshine is established, and the experiment in the exercise using an ergo-meter is carried out with measuring the temperature of body skin under sunshine environment. Moreover, the working conditions on the upper deck of a building ship are measured to investigate the actual situation of working environment. And it attempts to examine the thermal criterion of working environment by merging these results.

View full abstract

Recently, free-fall lifeboats have been widely adopted as efficient and safety life saving apparatuses for large merchant ships such as bulk carriers and tankers. However, because the increase of the size of mother ships leads to increases in fall heights, dangerous behaviours such as the occurrence of boat motion towards the mother ship after water entry and/or intensive acceleration to the occupants in the boat when it enters the water surface must be anticipated.
In past studies, water entry performance has mainly been examined in terms of the launching conditions of free-fall lifeboats; the effect of hull shape has not generally been investigated. In this study, therefore, model experiments and numerical simulations were carried out, and a free-fall lifeboat system to be used for large merchant ships with 25 meter fall heights was examined. Improvement of the hull shape and optimization of the launching parameters were then conducted based on the issues found from the investigation.

View full abstract

Effects of sway motion on roll reduction performance of a U-tube-type anti-rolling tank are experimentally investigated. Forced rolling and swaying tests of an anti-rolling tank model show that the water in the tank violently moves in different frequencies in roll and sway modes, respectively. A forced motion test in roll and sway coupling mode of the anti-rolling tank model demonstrates that sway motion significantly affects on its roll reduction performance. In larger frequency region, sway motion reduces the roll damping generated by an anti-rolling tank, and in smaller frequency region, sway motion increases it.

View full abstract

A wave maker for a circulating water channel is newly designed and constructed and its wave making properties are reported. The characteristics obtained experimentally for the cases of 5 velocities and 4 frequencies are good for unsteady model test in head sea. Some following problems are pointed out. The amplitudes of the generated waves increase near the side walls and the distortion factors of the waves are large in some cases. Model test for a planning boat is also performed in regular head waves caused in the circulating water channel and the obtained results for the increase of resistance and the motions in waves are shown to be good. Some results are different with that for displacement type of ships, for example the added resistance may be in proportion to the amplitude of incident wave at high speeds. The unsteady wave pattern analysis can be performed more easily and in a shorter time compared with in a long tow tank.

View full abstract

In this study, two different scaled models of a Large Passenger Ship (110,000 gross tonnage), which has three decks in water tight compartments, were developed. And the damaged ship's behaviors in intermediate stages of flooding were experimentally investigated. In some cases, large heel angle was measured for both of the models. However, the times to reach to the maximum heel angle for these ships have significantly different from the safety point of view. It was confirmed that the difference is caused by the difference of flooding velocity from damaged opening affected by the size of the opening and air compression in the damaged water tight compartments.

View full abstract

The authors have developed an evaluation method of facial expression for evaluating ride quality of vehicles. They demonstrated that facial expression can be quantitatively characterised by introducing the concept of the Fourier Descriptor (FD) and that the relationship between one's each individual facial factor such as eyes or a mouth and his/her psychological situation can be sufficiently expressed by the optimised discriminant analysis model. The present paper deals with overall evaluation of facial expression by other people using the FDs of both eyes and mouth. The subjects were asked to exhibit the six fundamental emotions investigated in the field of psychology: happiness, surprise, fear, anger, disgust and sadness. The fuzzy measure theory was here introduced to represent human ambiguous judgement. The process of estimating one's emotion from his/her overall facial expression was modelled by means of the fuzzy integral. The contributions of each individual factor of average of both eyes' shapes, mouth's shape and difference of both eyes' shapes to the evaluation were then identified quantitatively as fuzzy measures.

View full abstract

Navigational safety is highly demanded in order to prevent marine accidents. However the reduction of personnel expenses is enforced recently to reduce total transportation cost and it means that the securement of crew who have an excellent skill becomes difficult. So the increase of sea disaster accident originated with the degradation of skill of sailors is concerned in the future and the introduction of an automatic navigation device is the one of the solution of such a problem.
In this paper, the improved algorithm to avoid colliding with a stopping ship is proposed. The effect of parameters on evasion navigation is examined by numerical simulation. Furthermore, model experiments were carried out using Real-time Kinematic GPS (RTK-GPS) at pond to verify the effectiveness of the algorithm for automatic collision avoidance. It is shown that the collision avoidance system functions well both on numerical simulation and model experiments.

View full abstract

The aim of this study is to investigate the effect of pitting corrosion on local strength of hold frames of bulk carriers. In the present study, a series of 3-point bend tests with small structural models which consist of web, shell and face plates has been conducted. Artificial pitting was made on the web plate. In these tests, a concentrated load has been applied at the center of simply supported models so that shear load would act on the web plate. In this testing condition, load increased even after shear buckling occurred. When there is artificial pitting, fracture of web occurs. While no fracture is observed when there is no pitting. It has been revealed that shear buckling load and ultimate load decreases gradually and maximum vertical deflection decreases drastically with the increase of area ratio of pitting. As a result of non-linear FE-analyses, shear buckling load of the structural models where pitting prevailed uniformly on the web plates was found to be almost the same as that of the structural models where the web plates have uniform corrosion corresponding to the average thickness loss.

View full abstract

Pitting corrosion is typical corrosion observed on coated hold frames of bulk carriers which exclusively carry coal and iron ore. In order to secure the safety of these types of bulk carriers, it is important to understand the effect of pitting corrosion on local strength of hold frames.
In order to investigate this effect, a series of non-linear FE-analyses has been performed with pitted rectangular plates under compressive and shear loading conditions. It has been revealed that ultimate compressive and shear strength of pitted plates is smaller than that of uniformly corroded plates in terms of average thickness loss and that prediction results of ultimate strength using average thickness loss at the minimum cross section would be on the safe side. It has been also found that reduction of tensile strength due to pitting corrosion is larger than that of ultimate compressive and shear strength.

View full abstract

The effect of inclined angle on static strength of fillet welded joint for inclined hold frame at forward and afterward hold is studied. In this study normal shear strength of the inclined fillet welded joint and inclined partial penetrated welded joint are mainly considered with experimental results and FEM analysis results. And the parallel shear strength of the inclined welded joint is also discussed.
The effect of gap depth of the fillet welded joint is quantitatively discussed and is considered about equivalency of the effect of grooving corrosion of the fillet welded joint for the parallel shear strength of fillet welded joint.

View full abstract

An application of the Idealized Structural Unit Method (ISUM) to analyze the progressive collapse behavior of ship's hull girder in longitudinal bending is developed. A new ISUM stiffened plate model that can cope with local panel buckling, overall stiffener buckling and localization of plastic deformation in local plate panel is employed. Stiffeners and panels are modeled individually by beam-column elements and ISUM plate elements with consideration of their interaction effect. A lateral shape function for plate panels based on their collapse mode is assumed. In the present paper, the effects of welding residual stresses are considered both in plate and in stiffeners. The progressive collapse analyses of a 1/3-scale welded steel frigate model and a single-hull VLCC are performed. High computational efficiency and sufficient accuracy of ISUM are demonstrated through a comparison with test results and large-scale nonlinear FEA.

View full abstract

A new technique for surface strain distribution measurement has been developed by the use of piezoelectric material and sensor array. A piezoelectric element (PVDF film) is mounted onto the structure surface, and then electrical charge induced by the surface deformation is measured by sensor array at the multi point simultaneously. In this research, total system to measure strain distribution has been developed, which consists of the following parts; array sensor and signal processing circuit to measure a strain distribution of surface of material, circuit to transfer the measured data to personal computer, and software to process the measured results. The validity and accuracy of proposed technique is given by performing experiment using fatigue testing machine and then compare the result to the FEM analysis.

View full abstract