The present study concerns analyses of flows around downwind-sail system of an International America's Cup Class (IACC) sailing boat. The numerical method is a multi-block Navier-Stokes and Reynolds-averaged Navier-Stokes equation solver (hereafter, referred to as multi-block NS/RaNS method) recently developed by the present author. The main objectives of the present work are two folds: (1) an initial capability evaluation of the present multi-block NS/RaNS method in analyses of large-scale-separation flow; and (2) application of the present method to flow analyses around downwind-sail system of IACC sailing boat, on which very few studies have been so far reported. In the present study, the mainsail/spinnaker configuration is particularly considered, where focuses are placed on the aerodynamic interactions between the mainsail and spinnaker as well as the influences of sail trimming on flow and aerodynamic forces. The present numerical method is based on an extension of the RaNS method for ship flow analyses for applications to more general fluid dynamic problems, which was successfully demonstrated through the present work.

抄録全体を表示

The sand transport that causes the movement and deformation of a sand hill in a periodically oscillating flow is investigated in the laboratory. An experimental technique is developed to assess the variation of the state of concentration of sand particles in the process of the interaction of the particles with the fluid in motion around the sand hill as well as with the particles themselves. The method of measuring the concentration of sand particles is based on the digital image processing. It is confirmed that under the well-controlled experimental conditions of homogeneous distribution of sand particles, the decrease in brightness of the digital images of an area is determined by the concentration of the particles in the area. Taking a space average on the images with an appropriate scale to the size of sand particles to fade out the unfavorable effect of each particle makes it possible to predict inhomogeneous and continuous distribution of the concentration of sand particles from the brightness of the digital images with the limited resolution.
We make a visualization experiment of the two-dimensional flow field around a sand hill on sand bed in a flow sinusoidally oscillating in a straight channel with square section. The digital images of the unsteady flow field with suspended sand particles around the sand hill is analysed to estimate the concentration of sand particles. The results show that in the periodically oscillating flow the sand particles repeat a basic motion every half period such as sand particles running up the slope of the hill by accelerating flow, running off the hill by flow separation at the top of the hill, running down the hill as suspended in a turbidity current, and running into the roll by the rotational motion of shed vortices. It is found that these periodic motions of sand particles have particular distinguishing features of the change in the state of concentration in the process of fluidization, movement, transport, sedimentation, and accumulation.

抄録全体を表示

The structure of the head of gravity currents spreading out in all directions is investigated in the experiment and in the computation by extending the method developed in the previous paper for the two-dimensional gravity currents. A finite volume of fluid contained in a rectangular region was released instantaneously in another fluid of slightly different density in a larger region. Box models of fluid dispersion were described to elucidate the mechanisms of energy conversion in different stages of development of spreading gravity currents.
Visualization experiments were made with dye to trace the head of the spreading gravity currents. By opening the lock gate equipped obliquely in the corner of a water tank of square section, a finite volume of salt water of slightly different density in the corner of the tank was released instantaneously so as to form the gravity currents spreading over the whole area. The computation was also made in the same conditions as the experiments to study the flow structure of the head of spreading currents. The incompressible Navier-Stokes equation for an inhomogeneous fluid together with the transport equation for solute was solved by the finite volume method.
Both the experiment and the computation produce the formation and development of the gravity currents spreading in an axisymmetric manner. The results indicate that there exist different stages of development of this kind of spreading gravity currents. After the released fluid spreads at a constant speed, it slows down in the self-similar stage, and then it decelerates further in the viscous stage. It is found that the structure of the head changes according to the stages of development, which affects the mixing of fluid by spreading gravity current and that the head extending in a circle or a circular arc is subject to the three-dimensional instability to form the mountain-valley structure.

抄録全体を表示

The aerodynamic properties of a canard-configuration WISES (Wing In Surface Effect Ship) flying over calm water and/or waves are studied from experimental and theoretical points of view. A canard-configuration WISES without PAR (Power Augmented Ram) was originally proposed by Kubo and Akimotol¹⁾ and it enables easy detachment from the waves utilizing the large trim angle of the ship induced by the front wing. On the other hand, it has been suspected for the WISES that the stability is one of the serious problems against the disturbance due to the gust or waves. However the aerodynamic properties of WISES for such disturbance have not been yet made clear in detail.
In this paper, the model experiment is carried out in a towing tank imitating the WISES flying over calm water or waves, and the aerodynamic properties as well as the aerodynamic interaction effect of wings are investigated. Theoretical computations based on the BEM are also carried out and the results are compared with experiments. Through the study it is confirmed that the effect of the disturbance due to waves on the stability of WISES is scarcely to be considered, and also that the proposed theoretical method can predict aerodynamic properties of WISES in good accuracy.

抄録全体を表示

The aerodynamic properties of a canard-configuration WISES (Wing In Surface Effect Ship) flying over waves are predicted by applying the time-domain computation method based on the BEM, and the nonlinear characteristics of unsteady aerodynamic exciting forces acting on the WISES are studied through the comparison with experimental results and with linear computations reported in Part 1.
Through the study it is confirmed that the presented time-domain computation considering the nonlinearity caused by the finite amplitude of waves can predict measured results more precisely compared with the linear method shown in Part 1, especially for the phase of exciting forces. The nonlinear phenomenon due to unsteady exciting forces remarkably appears in the center-of-pressure coefficient, but the amplitude of its fluctuation itself is small and not so serious for the stable flight of WISES above waves.

抄録全体を表示

The oar blade acts as hydrofoil in stroke phase. Its angle of attack and velocity of incoming flow is not constant but transient so that the load which acts on the oar blade should be unsteady. It is absolutely necessary to estimate the load to analyze the rowing motion. But it is not appropriate to estimate with assuming steady state.
We carried a tank test using a circulating water channel. A flat plate attached to a load cell rotated in uniform flow and angle of attack varied according to the rotation of the plate. The result of this experiment indicates that the unsteady load is much larger than the steady one. And the load was properly arranged by reduced frequency. A method to estimate the unsteady load from the angle of attack and the velocity of incoming flow was established.

抄録全体を表示

We simulate the motions of a hull and of oars in order to improve rower's body motion and equipments for a faster hull speed and high efficiency. We established the simulation that solves energy equations of the hull, the rower, and the oars. It estimates the load that acts on the oar blade as unsteady force. The force that pulls the oar handle and the motion of the mass center of the rower are the input values to the simulation. The input values represent the rower's performance, that is, the rower's power and the way to move rower's body. The results of the simulation are in good agreement with the In-situ experiments, so that the simulation can be used as VPP (Velocity Prediction Program) to evaluate the improvement of rower's body motion and equipments.

抄録全体を表示

Rowing is composed of many equipments, which are a hull, a stretcher, a sliding sheet, riggers, oars and so on. There are many parameters which have influence upon hull velocity or mechanical efficiency. The simulation which calculates motions of the hull and the oar by using input of rower's motion and the force which pulls the oar handle can be used to estimate which parameter has more influence and how it should be changed for improving hull velocity and mechanical efficiency. In this study, we evaluate many parameters such as dimensions of oar or rower's motion. And it is made clear how to change parameters which have more effects than others.

抄録全体を表示

The riser for offshore oil production or drilling is a very long line like structure with a circular cross section. It is important to prevent collision of adjacent risers due to the vortex-induced vibration (VIV). In this study, the computer program code is developed for predicting the hydroelastic behaviors of the riser in current. The hydrodynamic force on a cross section of the riser is solved as two or three-dimensional flow by using the computational fluid dynamics to which the finite element method is applied. The employed FEM is based on a discretization of the spatial derivatives of the Navier-Stokes equation. Therefore, the hydrodynamic force in the transverse direction due to VIV can be considered in the prediction. The hydrodynamic forces on the several cross sections, which are divided for computing the structural response, are computed. And Moving Mesh is applied to the computer program code.
We compare the calculation results and confirm effectiveness of the Moving mesh that Moving Mesh is effective in behavior presumption of Riser.

抄録全体を表示

Hydroelastic behavior of a flexible floating structure supported by several aircushions arranged in a lattice is discussed in this paper. The modified pressure distribution method, which can consider influence of the aircushion, is applied to a prediction of the hydrodynamic forces.
A general pontoon type and four aircushion models are used for the prediction of elastic behavior. From the results, it is possible to reduce the response even if unit aircushion is a small scale. And also the aircushion type is useful to reduce the response of the structure in oblique waves.

抄録全体を表示

Wave-drift added mass results from non-linear interactions between waves and low-frequency oscillatory motions of a floating body, in the presence of an incident wave field. Wave-drift added mass is directly derived from a perturbation analysis with two small parameters and baced on two time scales, using the Cartesian coordinate system following the low-frequency oscillations.

抄録全体を表示

Wave-drift added mass of floating bodies is systematically measured from a slowly forced oscillation test or a free decay test in waves. The model is either a circular cylinder or an array of four circular cylinders. The experimental results are compared with calculated results.

抄録全体を表示

It is necessary for evaluation of wave-drift added mass to solve higher-order potentials. This problem is solved for a uniform circular cylinder of which draft is same as the water depth by means of the Green's theorem. Analytical solutions and calculated results of wave-drift added mass are presented. The far field conditions, radiation conditions for each order of potenials are obtained to ensure the existence of a unique solution.

抄録全体を表示

Some of solutions of velocity potentials which are necessary to evaluate wave-drift damping or wave-drift added mass have secular behaviour. As a result of the apllication of multiple scale perturbation analysis to this problem, non-secular solution is obtained. The behaviour of the non-secular solution is compared with a secular solution.

抄録全体を表示

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.

抄録全体を表示

The purpose of the fender is to protect the piers from ship collision and to reduce the damage to the ship by absorbing the energy. The resin fender that was made with the elastic resin is excellent in restoration.
In this paper authors discussed an experimental study on the crush of the bow in collision with resin fender. In this study PEL-fender and two kinds of bow models that differ with stiffness were used. And one of bow model was used for crush test. When rearranging the experimental result, the situation of bow crush was able to clarify, and the characteristics of this fender and effectiveness for actual ship collision were able to confirm. Also, we calculated bow strength by using a simplified equation. And, the calculation value almost agreed with an experimental value.

抄録全体を表示

The authors have studied the information system for structural integrity of ships by which reasonable evaluation and advanced maintenance of ship structures are achievable. 1)2)3)4)5) One of the problems to develop such an information system for practical use is the difficulty of generating analysis models for the evaluation of structural strength of ships. In this paper, a new concept for generating analysis models is proposed. Since the generation of an analysis model from the data model in the information system can be regarded as the conversion between these two data models, the mapping technique by using EXPRESS-X language is applied in this study. Based on this concept, simple beam and shell analysis models are proposed and the conversion test is carried out by using the developed mapping schema. The validity of the concept is shown with examples.

抄録全体を表示

The authors recently proposed a simplified method to estimate the ultimate strength of a continuous stiffened plate under combined thrust in stiffener direction and lateral pressure on plate side, based on a series of elastoplastic large-deflection FEA. This paper extends the method so as to consider the lateral pressure on stiffener side as well as on plate side. Since the lateral pressure on stiffener side cause compression at the stiffener top at the midspan, the so-called stiffener-induced failure takes place until it changes to the hinge-induced failure mode under a high lateral pressure. In addition, as a result of the stabilizing effect of a clamped-mode deflection caused by lateral pressure on the buckling strength of stiffeners, the ultimate compressive strength is attained after the yielding widely spreads over the stiffener's cross section at the mid-span. These FEA observations are taken into account in the formulation of the extended method. Through a comparison of the estimated ultimate strengths with the FEA results, the validity of the extended method is demonstrated.

抄録全体を表示

There are several methods to estimate the ultimate strength of hull girder, among which the method developed by Smith is widely used as a simple and practical method. In this method, the round corners such as a bilge shell part are usually considered as hard corner elements which do not undergo buckling. A series of elastoplastic large deflection analyses were performed to investigate buckling/plastic collapse behaviour of the bilge circle part subjected to uni-axial thrust. Based on the calculated results, simple formulas were derived to simulate buckling/plastic collapse behaviour of the bilge shell. The ultimate strength analyses of hull girder by Smith's method were carried out taking the buckling/plastic collapse behaviour of the bilge shell into account. Through these studies, it has been found that:
(1) A bilge structure with a conventional shape and size reaches the ultimate strength by yielding before buckling takes place. After the ultimate strength has been attained, plastic buckling takes place and the capacity decreases with the increase in deflection.
(2) The buckling/ultimate strength of the bilge circle part is dominated by design parameters such as radius/thickness ratio, yield stress and length/radius ratio of the bilge circle part.
(3) Hard corner elements could be used for bilge circle part to calculate the ultimate hull girder strength applying the Smith's method.
(4) However, the influence of buckling of the bilge circle part has to be taken into account for the accurate estimation of the load carrying capacity beyond the ultimate strength when the Smith's method is applied.

抄録全体を表示

In this paper distinct element method is developed for the collapse analysis of sea ice ridge. Rotation of the rigid body is described using quarternion to prevent the accumulation of numerical error, and interactions between rigid bodies are expressed using impulsive forces. Fusions between elements are expressed by the springs eletween centers of masses. The ridge is assumed to be the assemble of rectangular body, and by falling the bricks on the cover the ice model was generated. The analysis of the collision of the ridge model with offshore structure is analyzed and compared with the experimental data, as well as several empirical formulae.

抄録全体を表示

Fatigue cracks may initiate and propagate due to repeated wave exciting pressure in marine structures. Propagation of fatigue cracks may cause losses of serviceability such as those due to the oil and/or water tightness of a critical compartment boundary. To maintain the fitness for purpose of a structure, the prediction of fatigue crack path may play a very important role, so that we have developed an accurate and efficient system in predicting fatigue crack paths, which can make use of the FEM model for structural design. To investigate applicability of the system, the predicted crack paths are compared with experimental results of fatigue test specimen of 3-D welded structural components. It has been verified that the present results are in good agreement with experimental results.

抄録全体を表示

It is clear that detection of fatigue crack initiation in complex welded structures like hulls is quite difficult, and that the crack length at recognition is mostly long compared to that in mechanical parts. From these facts, not only stress reduction at critical area by design improvement, but also newly developed steels excellent for fatigue crack propagation resistance are desirable for structural integrity. Newly developed structural steel FCA, in which fatigue crack propagation resistance was controlled by metallic microstructures, was introduced in the part one within a series of our research. Various fatigue properties of FCA in air and in synthetic sea water were reported in the part two. As the continuous research after these two papers, fatigue properties of various welded joints with FCA are compared with those with conventional steel. From these experimental results, it can be clarified that the fatigue life extension effect by FCA is observed also in welded joint specimens and welded structural models as the same as FAC itself.

抄録全体を表示

This study investigated the simplified crack growth analysis method for side-shell-plate to annular-bottom-plate welded joints in cylindrical tank under cyclic large deformation. Under cyclic large deformation, gross plasticity behavior is occurred in crack section with high crack growth rate of ultra low cycle fatigue fracture mode. For the crack located in shell-annular welded joints, there are not sufficient solutions to calculate nonlinear fracture mechanics parameters to estimate this high crack growth rate, such as J-integral, crack mouth opening displacement and load point displacement. Predicted equations using fully plastic solutions determined by series FE-analyses have been developed to simplify crack growth analyses. And ultra low cycle fatigue crack growth tests have been conducted with structural model of L-type shell-annular welded joints. It has been concluded that simplified crack growth analysis method has good predictability for fracture behavior of the structural model.

抄録全体を表示

This paper deals with precautions needed for an accurate numerical analysis of welding residual stress and deformation. By comparison of numerical results with experimental data, the precautions of the thermal-elastic-plastic FEM are investigated. The butt joint made by one pass and one layer welding was selected as the object of study, because the feature of butt joint is to be made one jointed plate from two separated plates by the welding. Then the boundary conditions change by the moving of the deposited metal melted by heat souce. The obtained precautions are as follows: The element division is determined by the size of melting point of mother material on the welding direction and the size of inherent strain area calculated by the fix-bar model on perpendicular to the welding direction. The boundary condition of butt joint is expressed by the method that the perpendicular restraint to the welding direction along weld center line does not exit before the melting metal being not deposited and exits after being deposited.

抄録全体を表示

In order to build a ship efficiently, a master schedule is to be planned in advance, and must take into account the overall works including the assembly, outfitting, and painting of hull blocks. In the planning, it is important to reduce the variation in the daily workload at each stage in construction, otherwise the control of the work forces becomes difficult and futile work expenses are incurred. Hence, this paper has picked up the scheduling problem concerning the assembly work, outfitting work, and painting work of hull blocks before the erection stage, and an optimal system has been developed so that the deviation of the site work might be kept to a minimum; the object function is the standard deviation of scattering of daily work for each procedure in a week, and the constraint is the number of waiting blocks put temporarily in the stock yards. The method adopted for this optimization is the tabu search algorithm, while the branch•and•bound method is also considered for comparison. The tabu search method is one of the meta•heuristic techniques recently developed widely, which improves the local search method. As a result of comparing this technique with the branch•and•bound method, the tabu searching method proved that a solution near the optimal value could be obtained in a short computation time in case of many combinations.

抄録全体を表示

The combinatorial optimization of the sequence for pipe assembly was studied in order to mass produce the pipe units efficiently using the branch-and-bound method in the previous report by the authors. As a result of the simulation, shortening of the total working hours and a reduction in the middle stock were achieved. However, two problems remained; it was difficult to get an optimization solution in the case of many combinations, and only the average value of each working process was taken. For the former problem, the tabu search algorithm has been introduced in addition to the branch-and-bound method, and the revised process of the production has been proposed as a simulation using this algorithm. For the latter problem, the technique of fuzzy scheduling has been adopted to take into account the variation in working time for each process and in the resulting delivery time. The period for each work has been formalized using the fuzziness, and the reliability of the completion period has been calculated for the current process and the improved process mentioned above. As a result, the proposed process that was calculated by the optimization program has been evaluated as having high reliability compared to the current process. According to this study, it is considered that these optimization techniques and the evaluation method of reliability using the fuzzy scheduling technique are quite effective.

抄録全体を表示

In recent years, ballast water has been blamed for a variety of marine pollution problems, particularly for transporting harmful aquatic organisms from one part of the world to another and damaging the ecosystem of the new areas. A relatively simple mechanism to control this problem is to exchange ballast water on the high seas between ports in order to remove invasive species before the ship reaches its destination. However, some issues regarding ballast exchange on the open sea need to be addressed before this operation is introduced. One of them is the sloshing of the sea water in the ballast tank. In this paper, ballast water exchange on the open sea by means of the Sequential exchange method is simulated. Irregular seaways are generated from the ISSC spectrum, and the sloshing response of the ballast water due to the roll motion of the ship is numerically computed. Ballast tanks of Panamax and Cape-size bulk carriers are examined. The result of the numerical simulation shows the occurrence of a severe sloshing at the lower part of the bottom-surface of top-side tank of the Cape-size bulk carrier. It is also proved that the danger of sloshing decreases remarkably if the course of the ship in waves is changed.

抄録全体を表示

Microwave remote sensing is effective technique for sea surface measurement. For example, it enables us to know the wind vector on global scale. In order to develop more advanced measurement, it is necessary to understand the mechanism of microwave scattering at sea surface. This phenomenon consists of two physical processes. One is the formation of sea surface by the composite action of wind, waves and currents, and the other is microwave scattering at that surface. Because these processes are so complicated, appropriate models are not established. In this paper, the relation between sea surface condition and microwave scattering is investigated. Microwave scattering from wind wave surfaces is measured in the experimental tank and the results are analyzed by scattering coefficients and Doppler spectra. In order to connect these values with water surface parameters, surface condition is investigated minutely. The energy of high frequency waves is expressed by the friction velocity, and so it is presumed that there is the universal law between friction velocity and scattering coefficient. Since wind-generated current exist, the usual dispersion relation is not available. Furthermore, very high frequency components move at the phase velocity of components near the spectral peak. The results of Doppler spectra agree with that phenomenon.

抄録全体を表示

For converting renewable energy into electricity, it is not only important to raise energy conversion efficiency, but also to flat-and-smooth of generating electricity considering demand-and-supply balance and system cooperation. Although there are accumulation of electricity and a proposal of storing energy with a flywheel etc., as this measure, equipment different from power generation is needed, and it becomes the factor which raises cost.
Generally, when it is fine, a wave is small, and when a wave is high, it is bad weather. For this reason, it is thought that photovoltaics and wave power generation can complement each other fault, and can perform flat-and-smoothization of the amount of power generation.
This paper describes verification of the possibility of hybridizing of solar and wave energy and application to the system from an experiment of the combined cycle power generation system of the photovoltaics and wave power generation which were performed with the Offshore Wave Power Device “Mighty Whale”.

抄録全体を表示

At recent regular sessions of IMO (International Maritime Organization) /MSC (Maritime Safety Committee) several safety regulations have been discussed by FSA (Formal Safety Assessment) procedures. In the discussion the problems based on statistical uncertainty were arisen. Since member governments of IMO have a tendency to treat the problems arbitrarily, there exist differences among states of the IMO member governments
In this paper scientific treatment methods of problems based on statistical uncertainties are presented and applied to two actual problems which were arisen during the process of discussion in the continuous session of IMO/MSC.
The one is the treatment of unknown caused accidents, the other is related to validity of the indication based on risk reduction by introduction of new regulation. The former is resolved by application of Bayesian statistics, the latter should be treated by reliability analysis. The methods presented in this paper will be the tool for formation of mutual agreement among stakeholders who have opposite interests.

抄録全体を表示

Recently, the present working environment tends to be reconsidered with high interest in the environmental problem. Especially, air pollution by generating metallic fume during the progress of cutting and welling is the unavoidable issue for labor health. For settling this matter, it is necessary to design the suitable ventilation system that is desirable to be generally composed of large scaled equipments with high efficiency due to big capacity of a fabrication shop. However, the physical property and movement characteristic of fume as minute particles have not been grasped accurately even now.
In this paper, with a view to establishing the ventilation system with perfect control of fume flow, the transportation phenomena on fume, that are assumed minute particles to be gas-phase in turbulent flow by driving vent fans, would be clarified using experimental means and numerical calculation. The experimental simulations of fume diffusion using smoke generator in the three dimensional models of fabrication shop are executed with the appropriate similarity law. And the experimental result of fume flow shows considerably good agreement with the calculated data using two-layers Zone model on the diffusion state of heat and fume. Furthermore, the relation between the ventilation system and the fume transportation state in a fabrication shop is investigated evidently using experimental data.

抄録全体を表示

A market system for shipbuilding industry is designed to establish normal competitive conditions against injurious price war. The OECD council on shipbuilding seeks a new agreement to deal with government subsidies, pricing and other practices that distort the shipbuilding market. Our alternative solution of the problem is to create a centralized market trading shipbuilding-options. The shipbuilding-option is a right, but not an obligation, to order shipbuilding at specified shipyard within a certain time period. The shipbuilding-option does not specify the ship price, which is determined by negotiations. It is probable that the shipbuilding-option market will weaken price war in shipbuilding market by giving premiums to leading shipyards. In order to investigate the utility of the shipbuilding-option market we introduce a methodology in experimental economics. Simulative market game is produced, and the game experiment by real human players is carried out. The proposed market system has a damping effect on dumping. Shipbuilding-options contribute to reliable relationships between shipbuilders and shipowners.

抄録全体を表示

In the fire safety design for a ship, the engine room fire due to flammable oils is a very important issue and has received much attention in recent years. However, the nature of the engine room fire is still not well understood due to its extreme complexity of the physical and chemical mechanisms. A series researches have been carried out by the authors to investigate the engine room fire, and the emphasis of the present study is placed on the emission and the movement of the smoke during oil burning, which is very important phenomenon for a successful fire safe design such as setting up escape routes and installing fire detectors.
In the present work, at first an oil burning experiment in a box-typed compartment, which is a simplified engine room fire model, is conducted on oxygen rich conditions to investigate the distinctive features of the smoke emission and the smoke movement for such type of engineer room fires. From the experiments, several types of quantitative relation between the oil burning rate and the smoke generating rate are obtained. Then a three-dimensional numerical analysis using k-ε based CFD model is performed to investigate the detailed turbulent heat and smoke diffusion phenomena for the experimental model. Both experimental and numerical results are believed to be useful in designing more effective evacuation systems and more reasonable smoke sensor arrangement.

抄録全体を表示