This paper discusses the scientific studies on aqua bio-mechanisms and those application to ocean engineering from the viewpoints of drag reduction and propulsion mechanisms of surface and underwater vehicles and sensor technology. The study of aqua bio-mechanisms, aims not only to unveil the locomotion mechanisms of the aquatic animals analyzing the external flows and the autonomous systems having various behavior forms, but also to develop machines that are tender towards their environments with locomotion function and autonomous control system making reference to the aqua bio-mechanisms. The first part deals with the biomechanics on aquatic animals, especially on pectoral fin motion, and the behavior analysis such as neuronal network and sensory biology. The second part deals with drag reduction of vehicle with an undulating body, propulsion mechanisms of vehicles and biology-inspired sensors.

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In our previous paper, effect of transom stern bottom profile form on its stern wave resistance has been studied by model tests. Discussion of the model test results has clarified that real stern end immersion at running Ir has a close correlation with the stern wave resistance at the lower ship speed range of F_<rI> < 3.1. Details of the correlation are studied in this paper. For that purpose, an analytical method to estimate the effect of Ir on the stern wave resistance is developed at first. Then, the model test results are analyzed by the method. As a result, it has been clarified that Ir relates with the stern wave resistance mainly through the resistance due to acceleration of water flow at the stern end, one of the four components of the stern wave resistance, at the lower ship speed range.

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A Wing-In-Surface-Effect-Ship (WISES) is a high speed ship which utilizes the enhanced lift/drag ratio of aerodynamic wings in the proximity to the water surface. For most of WISES's ever built are for the militaly use or for the use on calm waters, their seaworthiness is not sufficient for the economical operation on open seas. The present authors have been studying a new concept of WISES with canard configuration as the next generation of commercial WISES's. The concept is the combination of the canard configuration and the forward mounted propellers. It is expected to have better takeoff performance in rough seas than that of conventional WISES's. This paper describes the experiments of a small radio controlled self-propulsion model as a primary validation of the concept. The experiments show that the model works as designed in its takeoff operation.

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This paper concerns development of a CAD/CFD/optimizer-integrated hull-form design System. The CAD, CFD, and optimizer modules are functionally independent and basically replaceable. Main objective of the present study is system development and demonstration of the capability, which justifies use of relatively simple flow and free-surface models, static sinkage and trim, and simplified design constraints. The CAD and CFD methods used in the present study are NAPA and a Rankine-source panel method, respectively. Currently, two nonlinear optimization algorithms are implemented, i.e., the successive quadratic programming (SQP) and the genetic algorithm (GA); and results are presented for the former in the present paper. For demonstration of the present approach, the bulbous bow optimization of container ship for minimum wavemaking resistance is considered. It appeared that the present CAD-based hull form modification overcomes many issues related to unrealistic solutions often seen in the related studies, which is due to the use of insufficient hull form modification methods. In conclusion, the present system has been shown very promising and warrants further investigation for more practical design constraints and conditions.

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Using a small high-speed water tunnel (HSWT), we experimentally studied the drag reduction characteristics of microbubbles. We examined the data obtained and adjusted it to make it more reliable. Then using the adjusted data, we evaluated the amount of friction reduction obtained by using microbubbles and attempted to identify the main factor in how they reduce friction. We did this by comparing how the different conditions of the bubbles affected their skin friction. In this paper, we explain how we adjusted the data, describe how we modified the data using the wall effect, and discuss the data uncertainty. We also speculate about the main factor in friction reduction. By comparing the results of two kinds of bubble generation, porous plate injection and array hole plate injection, we estimated the quantitative relation between the void fraction near the bubble wall and the reduction in friction on the skin. We compared injection in seawater with that in tap water and found although the bubbles were smaller in seawater, there was almost no difference in friction reduction. Downstream, the bubbles were still smaller in seawater.

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Hydrodynamic shape optimization technique based on CFD calculation is becoming popular with the development of computer. Ship hull form optimization based on CFD calculation is also carried out by many researchers. However, such kind of optimization technique is not used actively in actual ship design stage. The main reason is assumed that it requires a long time to get a solution. An optimization algorism based on gradient method usually applied in hydrodynamic shape optimization takes the large part of computation time for sensitivity analysis. The finite differential method for sensitivity analysis is simple and accurate, but takes much time. On the other hand, the adjoint variable method is known as complicated but effective method for sensitivity analysis. The present study applied the adjoint variable method for sensitivity analysis of lift coefficient acting on two dimensional foil and propose an efficient computation algorism. The calculated sensitivity coefficients by present method are compared with calculated ones by finite differential method and evaluated the availability of present method.

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This paper presents a method of grid generation that reduced the error of the numerical calculation. Generally, solution adaptive grid method is known as a method for reducing the error of the numerical calculation. However, the weight function for solution adaptive grid method is an expedient thing like gradients of the solution, etc.. It seems to be able to generate grid that reduces the error, if the error defined as a difference between true solution of the equation and numerical solution is used for the weight function for solution adaptive grid method. Such error could not be defined, however, because true solution of the equation is impossible to obtain. Recently, the numerical calculation method that guaranteed existence and error bound of the solution for the problem mathematically was developed in the field of applied mathematics. And this method is called numerical methods with guaranteed accuracy. In this study, by using error bound obtained from numerical methods with guaranteed accuracy as weight generation was applied to numerical calculation of the comparatively simple ordinary differential equation. On the nonlinear equation called Emden's equation, the result showed that the error was reduced in comparison with numerical solution on regularly-interval grid. But, it was found that the error of numerical solution increased on the linear Burgurs' equation.

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Self-adjoint variational principle on the integral equation of wing theory was found without distinction of 2D wing, 3D wing and propeller. It was based on the fact that the solution of the adjoint integral equation is related directory to the solution of the original integral equation expressed by the strength density of bound vortex, if the adjoint camber line is chosen symmetric of the original in flow direction. The self-adjoint functional described by quadratic form has symmetric kernel. The accompanying homogeneous integral equation of 2D wing theory becomes an eigenvalue problem of a polar type of which weight function is the solution for a flat plate. The eigenfunctions were utilized for obtaining canonical form of the functional so that the solution was expanded by the eigenfunctions . Symmetry of 3D wing contour which cancels the irreversibility that the vortex flows out rear is required for existence of the exact self-adjoint variational principle. However, in the case of high-aspect-ratio airfoil or propeller, the self-adjoint variational principle exists without asking the symmetry of wing contour.

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Numerical simulation of maneuvering of "Naniwa-maru" was performed to clarify the maneuver characteristics in particular with wearing operation. "Naniwa-maru" belongs to a type called Higaki-kaisen, and the Higaki- kaisen is a type of the more generic class of vessels named "Bezai-ship." Bezai-ship are typical Japanese sailing traders in the 18th to the mid-19th century which have different appearance and construction from those of Western tall ships. The present paper shows the numerical simulation of her wearing operation, and the results compared with the measured data. The equations of motion dealt with coupled ship motions of surge, sway, roll and yaw with co-ordinate system using horizontal body axes. The numerical simulation indicates ship response according to the measured time history of rudder angle, and shows the ship trajectory and the sailing state parameters such as heading angle, leeway angle, heel angle and velocity. The calculated results indicated the ship performance very well.

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When a large disaster like Tsunami or earthquake occurs, Mega-Float can be considered to be a stronghold for disaster prevention. It is quite important to tow the Mega-Float unit to the devastated site safely and swiftly in this concept. In some cases the floating unit might be combined each other on site for constructing a large scale platform. The wave bending moment, elastic motion, added resistance increase clue to waves and towline tension were calculated with a variety of rigidity of the floating unit in order to evaluate the critical towing operation. The calculation for the floating units was mainly divided into 8 cases from 50m to 400m with 3 kind of rigidity. The depth was varied with only 300m length floating unit. Using those results the needed horse power and critical wave height on the towing operation were shown. The approximate and simple method obtaining the critical wave height in short crested waves for emergency towing operation was presented compared with that in regular waves. The probability of possible towing operation was also shown in the classified sea area around Japan considering the wave height and wave period distribution table.

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A captive model test of oblique towing and circular motion to obtain the stationary hydrodynamic forces in ship maneuvering motion, requires a large number of runnings of a towing carriage. In this paper, PMM tests with low frequency are adopted instead of the troublesome captive model tests mentioned above in order to obtain the stationary hydrodynamic forces, and a component type mathematical model developed by the authors is applied to the hydrodynamic forces in order to estimate the forces enough beyond the conventional drift angles in maneuvering motion. As the result, it is found that the stationary hydrodynamic forces extracted from PMM test are agree well with the forces from oblique towing test(O.T.T.) and circular motion test(CMT), that the good estimation of hydrodynamic force beyond the range of motion conducted in PMM test is possible, and that the combination of the component type mathematical model and PMM tests with three modes is effective to predict a ship hull hydrodynamic forces by easy procedure.

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Sharper bow waterline shape can reduce the wave added resistance at sea more than that for conventional blunt bow. Ax-Bow is an example based on such principle. The bow with sharp waterline at all waterline heights can reduce the resistance further, but the effect of the bulbous-bow is expected to become deteriorated. According to the model test results on a low speed full ship, such bow shape with all sharpen waterlines show the same performance in still water, and better performance in waves in comparison with a conventional blunt bow.

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The effectiveness of the MPS (Moving Particle Semi-implicit) method on strongly nonlinear free surface problems has been presented in the past studies. But to handle practical wave problems by the method we need very long computation time and enormous memory. Therefore we propose a method to simulate a large wave field with a restricted small calculation domain. Two effective methods to handle wave problems are presented. First one is a wave absorption with the side-wall of calculation domain. Second one is an actuated bottom to simulate the infinite depth of water. Additionally wave damping problems caused by numerical factor is considered.

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Much effort has been spent for the development of the hull shape or energy saving devices. These efforts have been focused on the low resistance and high propulsive performance of the ship sailing in still water. In a view of actual voyage, the ship always runs under wind and wave. The wind and wave cause the speed loss or increasing the fuel consumption. Therefore, the reduction of external forces, such as wind and wave, acting on a ship is very important for the ship's performance in actual sea. In this paper, the authors study the reduction method of wind forces acting on the accommodation and the hull of ships. Square corner cut on an accommodation structure and/or a ship hull can reduce wind forces. The effect of this method is confirmed by wind tunnel tests. The test result for its application to the accommodation structure of Bulk Carrier shows the wind resistance reduction by the ratio of about 10%. The square corner cut on the side line of upper deck of the hull structure of PCC (Pure Car Carrier) gives the reduction of side wind force and yaw moment by about 20% according to the wind tunnel test. The reduction of side wind force can also reduce the drift angle of the sailing PCC in wind, and accordingly can reduce the ship resistance and speed loss. The total reduction of horsepower for PCC in such case is estimated to be about 6%.

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This report deals with an approximate calculation of hydrodynamic forces generated by interactions between two ships which are moving along parallel courses at the same velocity. With the assumption of the rigid free-surface and infinite water depth, the calculation method is based on the linearized thin-wing theory, using sources distributed over the center plane to represent thickness effects of two ship bodies. In the previous report, it was assumed that trailing vortices having uniform strength extend along the infinite down stream. In this report, the author improved the vortex shedding model described above, considering decay of the trailing vortices. In general, the magnitude of the decay coefficient has a significant effect on the interaction hydrodynamic force. There is good agreement between the present calculations and experimental results for the lateral force acting on the after body of the two ships. In addition, it is clarified that influence of the vortex decay on the lateral force is remarkable compared with that on the yaw moment.

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An experimental study on the drift resistance acting on an oscillating ship is carried out. A scale model of a container ship is forced to make sway or roll motion in steady flow, and the lateral forces acting on it is measured by a load-cell. The experimental results demonstrate that the drift resistance coefficient is not constant, but depends on the amplitude of the oscillating motions and reduced velocity. A new drift resistance coefficient is deduced based on an assumption that strength of shedding vortices depends on relative velocity of the hull to flow, which consists of steady drift velocity and oscillating velocity due to sway or roll motion. It is found that the new coefficients for sway or roll motion can be expressed by functions of only Keulegan-Carpenter number. Using the simple coefficients, the drift coefficient of a ship can be predicted.

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We measured heave and pitch motions of Wigley model with a forward velocity in the circular compact wave basin (AMOEBA, diameter=1.6m) having absorbing wave makers around it. It was observed that the measurement results in the AMOEBA are the same as that in the large basin. This indicates that we can carry out the experiments of ship motions with the good accuracy in the AMOEBA instead of the large basin. This wave basin can easily generate the directional regular waves. By using it's performance, we show an advance technique to get the directional characteristics of ship motions with forward velocity. To confirm it, experiments of ship motions in bi-directional regular waves were performed.

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Ship berthing is one of the most difficult ship operations. In the previous works, the artificial neural network (ANN) is verified to make it automatically. However, there are still many obstacles before it will be practically used. One of the problems is neither sea trial nor model ship experiment was done before. We have conducted model ship experiments based on ANN, and discuss for the availability in various conditions, especially for the method how to provide suitable teaching data. Combining model ship experiments and simulation, we have concluded that ANN can be practically applicable for automatic ship berthing. Secondary, we have discussed on the structure design of ANN for this purpose and propose a new ANN structure rationally.

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This paper describes the effect of compressibility of fluid outside the vibrating ship hulls on the inertia and damping forces as the fluid-structure interaction. In conventional analysis of hull vibrations, fluid has been assumed to be incompressible although the effect of compressibility has not been fully understood. It is known that the compressibility is essentially important in the fields of underwater explosions, seaquake responses and sound propagation in water. In this investigation 3-D finite element analysis is carried out to calculate the pressure fields around the uniform beam vibrating vertically with sinusoidal natural modes. Added mass and damping coefficients can be expressed as functions of frequency and nodal distances. It is found that the added mass coefficient may increase up to 5 % for the hull girder vibration of typical VLCC and bulk carriers if the compressibility is considered. It is also revealed that the sound wave radiation is not likely as far as the frequency band is within the ordinary range of observed hull girder vibrations.

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Elastic buckling stresses of rectangular plates subjected to in-plane loads are generally calculated as eigenvalue problems to get their accurate solutions. The elastic buckling stresses have to be evaluated when thin-walled structures such as ships and offshore structures are designed. Since it is difficult for structural designers to frequently use numerical methods to get the accurate values, they usually use simple equations or charts generated from the numerical way. However the buckling stresses obtained from the equations and charts are sometimes inaccurate. This paper describes a method that the designers can remotely use the numerical way through Internet technology. The designer can know accurate buckling stress values using the system developed in this study. For example, they can immediately get elastic buckling^stresses of the rectangular plates on Internet web browsers after they input minimum number of parameters.

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In this paper, the hydro-elastic response of a submerged floating structure with tension legs in waves is investigated as a part of basic studies on marine tunnel structures. The analytical method is applied to the submerged floating structure. Then, the hydro-elastic characteristics of a floating structure model with a submerged plate and tension legs in regular long waves are investigated numerically. Next, in order to demonstrate the validity of theoretical results an experimental study is carried out for a basic model in regular waves. It was found that experimental results for the frequency response amplitude are in good correspondence to theoretical results in the low frequency range. Finally, characteristics of hydro-elastic responses of a 1,000m-class submerged floating structure under trial design are also investigated applying the above method.

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Wave statistics are important for the evaluation of a service performance of a ship. In general, wave statistics are given as a scattering table of significant wave height and mean wave period based on observation results. To make it easy to treat the table, researchers have proposed analytical distribution of wave statistics. The lognormal or Weibull distribution is often applied to the distribution of wave statistics. However, theoretical grounds of the lognormal and Weibull distribution are not so clear. Authors propose new stochastic models of wave statistics based on the regression to equilibrium condition. The models are expressed by stochastic differential equation with Gaussian process, and the distribution of wave statistics are obtained theoretically. The validity of the distribution is evaluated by the observation results of significant wave height and mean wave period. In addition, the time series simulations of significant wave height and mean wave period are shown.

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In recent years, some ocean yacht races have experienced disasters in which several entries suffered capsizing and results in the loss of lives. From this reality, it is pointed out now that there is a possibility of overlooking survivability of latest sailing yachts. The aim of this research is to ascertain whether such drawback is common to the latest yacht design or not. For this purpose, the authors attempt to develop a database of principal dimensions of yacht hulls, sails and rigging since 1930s. The total number of yachts used here is more than 700. This database clearly indicates an obvious tendency in transition of yacht design from safer to faster.

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In order to evaluate the environmental impact of marine development in the enclosed sea, numerical simulations of the tidal current and eco-system became very important. The tidal current is influenced by various parameters, namely, wind, river water, air temperature, solar radiation and etc as well as the bay shape and the depth, but systematic parameter studies are not made so much. In this paper, in order to confirm the applicability of the tidal current simulation by multi level model, following items are discussed. 1) Tidal current simulations of the supposed rectangular bay and comparisons with the liner long wave theory 2) Tidal current simulations of the Ariake sea and comparisons with the Ariake project data, considering the effects of wind and river flow 3) Nutrient salt transport and sediment transport from the sea bottom layer by upwelling, considering settling velocity, from viewpoint of ocean nourishment and transportation

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In order to clarify the oceans role in the overall geochemical cycle of CO_2, getting to know a vertical concentration of phytoplankton is very important. The authors measured the vertical distribution of chlorophyll a in the western pacific equatorial ocean during the R/V MIRAI cruse (MR01-K05, MR02-K06), and analyzed a number of data which measured on the ship. The results show that the phytoplankton distribution has strong correlation with mixed layer depth and compensation depth, and the chlorophyll maximum depth vary according to the mixed layer depth.

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In the present paper, the authors study about the possibility of obtaining characteristics of ocean wave systems using echo signals from a marine radar system. They solve the radar equation to simulate A-SCOPE, original echo signals from marine radar system, after generating 2-dimensional wave field having prescribed wave characteristics including 2-dimensional wave spectra. The A-SCOPE signals are converted from 2-dimensional wave field expressed in a rectangular coordinate system to a polar coordinate system. Provided the A-SCOPE signals, they analyses the signals by means of spectral analysis methods of already developed to discuss about the accuracy and error infusions during the data processing. After analyzed simulated radar echo of long-crested regular waves and short-crested irregular wave systems, they point out several defects contained in the existing analysis methods. They finally propose a method that will make it possible to obtain characteristics of wave systems propagating to different directions.

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From the viewpoint of an environmental conservation, it is often required to eliminate air bubbles in cooling seawater discharged from process plants to sea area. The air bubbles are generated due to a nappe from a weir in a seawater discharge basin. A de-aeration chamber is one of technology to eliminate the air bubbles in seawater. For the design of de-aeration chamber, a volume and size distribution of air bubbles in seawater are essential engineering information, however, few quantitative investigations are carried out. Therefore, the volume and size distribution of air bubbles generated due to the nappe were measured for seawater and tap water, and it was found that the size of air bubbles in seawater became smaller than that in tap water, etc.

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The main purpose of this paper is put on realizing high accuracy tracking and berthing maneuvering using Brysonn-Ho's discrete varying gain controller (DTVLQC). The authors adopt the discrete model in order to represent ship's maneuvering motion, because of the easiness in model fitting technique and effectiveness of the fitted model. The ship's motions are adaptively identified using a RLS method and the optimal variable gains under the quadratic evaluation index are calculated. Lastly in order to verify the effectiveness of these methods, we report and discuss about the results of the actual onboard experiments.

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It has been considered that the Environmental database system in coastal area is necessary to be established. For modeling a marine ecosystem of coastal sea area many kind of environmental parameters are necessary. Especially parameters determined from actual sea/marine environments are usually exclusive to the sea area concerned. In Osaka bay sea area, there have been being carried out systematic observations on seawater qualities including some environmental characteristics for more than half a century, by fisheries and environmental departments of local governments. The authors obtained those observation results and have been carrying out fundamental studies for developing an environmental database system using those results. In the present paper, they propose a method for explaining the temporal transition of environmental characteristics introducing methods of Auto-Regress ional Analysis model (AR-model) and Vector AR-model. They applied the long-term environmental data to these models and obtained successful results that explain the transition of environmental characteristics in time. They also obtained agreeable results that show interaction between environmental items.

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It is very important to clarify some objective indices, which can demonstrate one's physical condition of motion sickness. The authors proposed an analysis method using the fluctuation of heartbeat for this purpose. The CGSA (Coarse Graining Spectral Analysis) method was developed in the field of medicine, and it is reported that this method is effective to distinguish fractal component from wideband signal. The CGSA method was applied to one's heartbeat fluctuation through the stages of motion sickness incidence in this paper. Some physiological indices of the relative stress, the relaxation rate, and the percent fractal are introduced to compare them with the subject's psychological changes. The authors showed that the CGSA method is also thought to be useful to understand the subjects' physiological and psychological condition objectively, but more subjects' results are necessary to clarify the relationship between subject's motion-sickness degree and some indices of mental stresses and/or relaxation.

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The authors have been analysing physiological responses to low-frequency oscillations, such as electroencephalogram (EEG), electrocardiogram (ECG), respiration, perspiration, electrogastrogram (EGG), facial expression. There were some difficulties in estimating physiological changes through stages of motion sickness incidence. And therefore, establishment of some physiological indices of motion sickness and/or human errors has been desired for a long time so as to obtain objective evaluation and clarify the mechanism of motion sickness and human errors. In this paper, some time-frequency-analysis methods are examined in detail which can quantify the electroencephalogram change in the time domain as well as in the frequency domain. The Gabor transform was applied to subjects' encephalogram during exposure to low-frequency oscillations in a ship-motion simulator. Measurement of some students of a university of mercantile marine was also conducted at the navigation bridge on board a training ship. The authors concluded that the proposed method could demonstrate EEG changes quantitatively and it helps well in evaluating one's motion sickness incidence and/or human error occurrence.

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