In this paper, we focus on a three-dimensional vortex method as a useful calculation method to estimate the maneuverability of ships. The three-dimensional vortex method which does not need the grid generation as a pre-process is a Lagrangian method. The govering equations of the three-dimensional voretex method are vorticity transport equations and continuity equations.At first, we investigate effects of arbitrary parameters in the three-dimensional vortex method. we apply the three-dimensional vortex method to estimate the force acting on cylinder and sphere in various Reynolds number.Thereafter we calculate flow fields around a VLCC in oblique motion (β = 3°, 6°, 12°) and invesitgate usefulness of the three-dimensional vortex method.
Many researches have been done about the effect of a steering motion on roll motion, as the turning motion sometimes introduces a capsizing of ship and makes serious disasters. On the contrary, the researches of the effect of a roll motion on the manoeuvrability are very few, and the mechanism is not clear. In 1970s after the construction of a high-speed container ship, it began to be pointed out that the navigation difficulty arises with such ships, and then the research on the latter was started. Eda1), Hirano2) and Sohn3)respectively proposed the mathematical models of manoeuvring motion including the roll motion, and pointed out that the course-keeping ability becomes worse and the turning radius becomes smaller when ship speed increases. This tendency becomes remarkable with lower GM. In these researches, although the turning motions were well simulated using each mathematical model,the mechanism or structure of the roll effect on the manoeuvrability has not been clarified yet.In this paper, the author introduces the rudder to yaw response equation from the simple linear mathematical model, and has clarified the following principal structure regarding to the effect of the roll motion on ship manoeuvrability. 1) The turning moment Yφφ and Nφφ induced by the roll angle become the key parameter that strongly affects the course-keeping and turning abilities of ship. This tendency becomes remarkable when roll angle becomes larger by the lower GM and higher Froude number.2) For a high-speed merchant ship whose (N'φ -Y'φl'β) becomes larger in negative due to the large bulbous bow for example, the larger negative (N'φ -Y'φl'β) makes the less stability on course and the stronger turning ability, which may make the smaller turning radius and the larger overshoot angle in Z-manoeuvre.3) On the other hand, when (N'φ -Y'φl'β) is a positive value, it becomes a phenomenon completely contrary to the above.
The power required must be determined appropriately to tow a ship, and ship performance must be predicted realistically with respect to a ship safety in the sea. Consequently, developed CFD design tools and techniques for predicting a performance are necessary in ship design stage.In our previous researches, we have developed a numerical method, i.e. Eulerian scheme with Lagrangian particles, for computing a strongly nonlinear interaction between ship and wave with breaking. Firstly, in this study, the developed model is applied to evaluate propulsion performance of a fishing boat. We also applied the model to investigate seakeeping performance of a high-speed ferry. The resistance and motions,e.g. heave and pitch, were in good agreement with experimental results and the strip theory, In addition, we also discussed pressure distribution,velocity field and free surface motions around the fishing boat and high-speed ferry in waves with breaking. We showed that the Eulerian scheme with Lagrangian particles would provide a highly accurate solution and also would be usefulness and effectiveness as a ship design tool.
In this paper, we have an aim developing the next-generation-type airship for resolving airworthiness problems especially for mooring condition. For this purpose, we propose the TORUS-TYPE AIRSHIP. The torus-type airship will have the advanced characteristics of airworthiness especially at mooring condition, and have advanced maneuverability especially for movement of any direction(forward, backward, left, right, rotation), but some instability at flight condition are considered.At first, we designed a simplified torus-type airship model, and carried out towing experiments about aerodynamic characteristics of the model in upper water space of our huge towing tank instead of carrying out experiments in a wind tunnel. By introducing torus-type airship, we will be able to minimize the mooring area, reduce the maximum mooring forces, and in the result prevent the body damage at mooring. In the second, we developed a 3D Flight-simulation program using the data from the experiment. By using the numerical simulation, we can evaluate the performance of the torus-type airship from various viewpoints including mooring.
It becomes increasingly important that the performance of a ship in actual seas is predicted accurately due to an increasing awareness about global warming and other environmental problems. The ship responses such as the ship motions, the stresses and the added resistances in actual seas vary with sea states and the ship speed. The onboard measurement data has this information,therefore the data is useful. However there is not an established analysis method of the onboard data because the data involves factors which are unexplained by the theoretical calculation. The ship responses which are caused by uncertainty sea states are stochastic variable. Therefore, the statistical analysis is useful in case of the prediction of ship responses with using the onboard data.The paper proposes a statistical method which estimates the correlation between sea states and ship responses for a short time as the conditional probability density function (PDF) by using the onboard measurement data. Two kinds of method are adopted to estimate the conditional PDF of ship speed loss for encounter sea states. On one hand it is parametric method, on the other it is nonparametric method. Using a time-series of sea states and ship speed loss during a one-year voyage obtained by an oceangoing simulation, the expectation and confidence interval of mean ship speed loss are estimated to validate these stochastic models based on each method. We conclude that the stochastic models are available. In particular, the stochastic model based on the nonparametric method offers an accurate prediction of the mean speed loss.
Global warming and other environmental problems are common threads in each industry. In the field of international maritime,for example, the development of low-resistance ship and energy-saving devices, the optimization of shipping schedule, and the development of new energy resources are done. It is important that the performance of a ship in actual seas is predicted accurately in those developments. The authors have proposed in the previous paper a statistical method to estimate the correlation between sea states and ship responses for a short time by using onboard measurement data. The correlation can be represented as the conditional probability density function (PDF) with Principal Component Analysis (PCA) which is one of the multi-variable analyses. We can accurately estimate the statistics of ship responses by using the conditional PDF. The onboard measurement data include various information such as nonlinearities and fluid mutual interferences. Therefore, there is a possibility that the statistical method based on the onboard measurement data will be applied to various purposes other than the estimation of ship responses.The present paper proposes two applications of the statistical method based on the onboard measurement data. The first is the application to the effective onboard measurement, the second is the application to the prediction of ship performance distribution.The ship performance distribution is defined as the probability distribution of ship responses corresponding to the voyage condition.In the first application, an attempt is made to find the onboard data with strong correlation to ship responses by analyzing the result of PCA in detail. If we can find those onboard data, the effective onboard measurement will become possible. In the second application, it is investigated whether the ship responses corresponding to the change of navigation can be estimated by using the correlation between sea states and ship responses obtained from the onboard measurement data. If we can estimate the ship responses corresponding to the change of navigation, the planning of the voyage will be made possible by using the correlation.
The present paper is aimed to illuminate the effect of bubbles in reducing frictional resistance which was confirmed by the results of full scale experiment carried out in 2008 by using the cement carrier Pacific Seagull. Obtained results from the experiment show that the resistance reduction in cases of ballast condition and full load condition were 11% and 6%,respectively. Boundary layer method of integral type is utilized in this paper with the assumption that local skin friction is reduced by the injected bubbles.Axial velocity distribution and momentum thickness are computed for with and without bubbles cases. Calculated results show that reduction rate of local skin friction has the distribution although the same constant reduction rate is applied to the local skin friction law. It means the boundary layer development is different for with and without air bubbles. It could also show the difference of velocity distribution at propeller plane which was observed in full scale experiment indirectly by thrust measurement.
Fixed type pendulum wave energy converter is a kind of movable body type wave energy converter and it was invented by Kondo with Muroran Institute of Technology in Japan. Some researches on this device were carried out experimentally and theoretically, and its high energy conversion efficiency was shown. However, this device was not practical used yet, because the initial cost is so expensive as it needs heavy construction in the sea. And also, it is difficult to keep it safety under the critical weather condition like a typhoon is another main reason. So, as a solution strategy for above problems,Furusawa proposed the uplifting type pendulum wave energy converter. Furthermore Watabe proposed the floating type pendulum wave energy converter (FPWEC) which is moored to the seabed with some lines as another solution. Changing from fixed type device to floating type device, we can expect the reduction of initial costs and emergency measures. Watabe carried out some research on FPWEC, but it is not enough to say that the design method for this device was established.In this paper, we have made a test model of FPWEC for tank test and some tests were carried out as a first step of development for this device.To estimate the performance of this device, we have measured power output and body motion in regular waves.
The present paper analyzes the components of the moment and proposes an improvement of the Vertical Weight Stabilizer (VWS) invented by Hirayama 1), confirmed by Hirakawa et.al 2), Kakizoe et.al 3) and Funamizu 4). This improvement consists in modifying the guide shape from a straight line to a curved one to increase the damping effect and reduce the ship rolling. We call this as Enhanced Weight Stabilizer (EWS). Numerical simulations of VWS experiments2) were done to validate a mathematical model of the system built for this study and after that we apply it to study the effect of changing the guide shape on the damping. In this basic study, three curved shapes are analyzed and possible improvements are found.
Wing-In-Surface-Effect-Ship (WISES) is expected to be a new vehicle for transportation. WISES is very similar to so called WIG but, for WISES, there is some effect from deformable surface of water. WISES utilize ground effect, so less fuel consumption comparing with conventional aircrafts will be expected. In this paper, about the canard type WISES, the self-propulsion test is carried out in a towing tank to confirm the presence of the instability phenomenon at planing condition with a model of canard-configuration WISES. At the same time, it was examined whether the experimental results can be reproduced by using the numerical simulation. The occurrence of the instability phenomena were able to be confirmed in the experiment and a similar tendency were seen in the numerical simulation.
An unsteady wave pattern analysis proposed by Ohkusu is one of the useful methods for investigating the mechanism between hull shape and added wave resistance and also for the validation of numerical methods from the point of view of the wave pattern that indicates the pressure distribution over the free surface. In this paper, a method to improve the accuracy of the measured diffraction wave is proposed by considering the interaction effect between the steady wave field and the incident wave that have been ignored in the original method proposed by Ohkusu.Experiments using a modified Wigley model are carried out to obtain the unsteady waves and the method we propose in this paper is applied to the diffraction waves. Results are compared with those obtained by the original method and discussed. The paper also shows the hydrodynamic forces and motions obtained through the experiments comparing with several numerical methods.
An unstructured mesh method is expected to be an efficient tool for CFD analysis around complex flows, in contrast to structured mesh method. However, mesh generation around a complex geometry is still time-consuming and high-quality unstructured mesh for viscous flows is difficult to generate. A hexahedral unstructured mesh system with local refinement has merits of both structured and unstructured mesh system, and in addition, it offers an automated and robust mesh generation procedure.In this study, a hexahedral unstructured mesh was adopted for analysis of flows around twin-skeg ships. First of all, the accuracy of the computed results including grid dependence was investigated by comparing with experimental data and computed results on structured mesh. Secondly, the flows with different tunnel slope angles and horizontal skeg distances were computed and the ship resistance and propulsion performance of the twin-skeg ships were discussed.
Recently, the technique of numerical simulations and the performance of computers are rapidly improved. Therefore, the structural analysis for welding phenomena based on thermal-elastic-plastic FEM can compute with good accuracy in short time. But, if the model to be analyzed is large such as ship structure and the shape is complex, they may cause the problem that preprocessing such as mesh division process consumes much time. To overcome these problems, mesh free method such as MLPG (Meshless Local Petrov-Galerkin Method) has been developed. MLPG is one of the complete meshless methods. This means that MLPG never use the element divisions. Therefore, the connectibility information between nodes and elements is not necessary and preprocessing time expected to be reduced. Accordingly, MLPG is considered as one of the next generation computational methods which may be alternative method of FEM.Then, in order to develop structural analysis for welding problem, Meshless Local Petrov-Galerkin method (MLPG) for heat conduction analysis is applied for the moving heat source problem of welding in this study. The validity, applicability and fundamental characteristics of MLPG which is used in this study are verified through the application of bead-on-plate.Finally, the adaptive method for MLPG including generation and elimination of nodal points is proposed.
Statistical analysis of the extreme wave-induced hull girder vertical bending moments in short-term sea states is conducted. A series of time-domain numerical simulations of the wave-induced hull girder vertical bending moments are performed based on nonlinear strip method to obtain peak values of the vertical bending moments. The Peaks-Over-Threshold (POT) method is applied to detect peaks exceeding thresholds, i.e., 60%, 80%, 90%, 95%, 97.5%, 98.5% and 99.5% of percentile values, then the peaks are fitted to generalized Pareto distributions. The extreme value in N peaks is estimated by using order statistics based on the generalized Pareto distributions. The simulation results are also fitted to Weilbul distributions and the extreme value is estimated for comparisons. It is found that the POT method gives good estimations of the extreme value in general. Fitting to Weibull distribution is advantageous in a point that it contains smaller statistical uncertainties, especially when the goodness-of-fit is high. It is shown that the POT method gives better estimations on the extreme values when strong nonlinear effects such as whipping are extremely significant.
In this study, the target reliability level of ships' ultimate hull girder strength is investigated by employing risk assessment. The risk can be defined as "Risk = Failure probability x Consequence." In the present case, the failure probability corresponds to the probability of hull girder collapse in bending while the consequence to a monetary loss accompanied by the failure. First, a risk model for the hull girder collapse and the limit state function are set up. Uncertainty models for the various parameters in the limit state function for the hull girder collapse are investigated. Among them are the yielding stress, plate thickness, corrosion, wave randomness, nonlinearity of wave loads, and so on. A series of reliability analysis is performed to obtain the relation between the safety level and deck plate thickness as a risk control option. Then, the target reliability level is investigated through Cost Benefit Analysis (CBA). It is shown that the obtained target reliability level is close to the reliability level of the existing ships whose design complies with the current Common Structural Rules. Finally, a sensitivity study is conducted to investigate into the impact of the risk model parameters to the target safety levels. It is discussed how different views may affect the target safety levels.
Applications to three-dimensional fracture mechanics analyses for surface cracks in welded joints of ship structure are presented. To evaluate mechanical behaviors of ship structures, shell finite elements are often used in finite element analyses (FEA). It is difficult to solve three-dimensional crack problems such as surface cracks using the shell elements because the plate thickness is assumed in the shell element formulation. A shell-solid mixed analysis is performed to evaluate stress intensity factors (SIFs) of three-dimensional surface cracks in ship structural members. The whole analysis region is modeled by triangle or quadrilateral shell elements, and the local region near the surface crack is modeled by tetrahedral solid elements. The shell model and the solid model are connected using RBE3 (Rigid Body Element 3) connection in MSC.Nastran. In addition, a semi-auto RBE3 connection technique is developed to enhance the shell-solid mixed analysis. VCCM (Virtual Crack Closure-integral Method) using tetrahedral finite elements are adopted to calculate the SIFs of the three-dimensional surface cracks. The SIFs calculation and the evaluation of the surface cracks in the welded joints of the ship structure are demonstrated.
The characteristics of Fatigue Damage Sensors(FDS) that are in use for fatigue life estimation of monitoring structural members in ship structures are discussed in order to improve prediction accuracy of estimated fatigue life exposed to random wave loads such as storms under various loading conditions peculiar to ship structures. Coefficients affected by loading histories against constant amplitude loading and mean stress levels are introduced for the estimation procedure using FDSs and confirmed by several series of fatigue testing. This newly proposed fatigue life estimation procedure using obtained coefficients is checked by comparison results of application to a marine structure on which FDSs and strain gauges are provided simultaneously and to which random loads by varying wave are applied.
In many steel plate stockyards, steel plates are piled up on the yard for a restriction of the yard's site area,and the steel plates must be moved from the top op the pile one by one. Therefore, we must turn over the many steel plates to pick up objective plates for the sorting. Workloads of turning over the steel plates are relevant to an order of pick up the steel plates. So, planning to determine the order can reduce costs for delivering the steel plates.This planning problem is a large scale multi-decision problem including hierarchical decisions. For this reasons, it is difficult to optimize the problem using usual optimization techniques such as Taboo search and Genetic algorithm. In this paper, the planning problems are modeled as Markov decision processes, and optimum planning is achieved by Hierarchical reinforcement learning. The proposed method is demonstrated through several numerical experiments to compare a method using a simple heuristics. The results off the numerical experiments show that the proposed method can save the costs about more than 10% compared to the method using the heuristics.
Empty container allocation problems arise due to imbalance on trades. Imbalanced trade is a common fact in the liner shipping,creating the necessity of repositioning empty containers from import-dominant ports to export-dominant ports in an economic and efficient way. The present work configures a liner shipping network, by performing the routes assignment and their integration to maximize the profit for a liner shipping company. The empty container repositioning problem is expressly taken into account in whole process. By considering the empty container repositioning problem in the network design, the choice of routes will be also influenced by the empty container flow, resulting in an optimum network, both for loaded and empty cargo. The Liner Shipping Network Design Program (LS-NET program) will define the best set of routes among a set of candidate routes, the best composition of the fleet for the network and configure the empty container repositioning network. Further, a network of Asian ports was studied and the results obtained show that considering the empty container allocation problem in the designing process can influence the final configuration of the network.
Tramper cargo handling at port is done on a first-come and first-served basis in most cases. A tramper has to voyage at high velocity to the port for early turn of cargo handling and after arrival waits for a long time for her turn to come. The act is inefficient and leads to severe increase of CO2 emission. Port reservation system can mitigate the problem. If ships can get the rights of loading at a future date, the ships can voyage to the destination port at slower speed. In this paper tramper transportation simulator is developed which can re-create demurrage distribution and estimate CO2 emission generated by ship. Firstly, basic port reservation system based on auction is estimated and that the reservation system favors smaller ships over bigger ships is revealed. Secondly, a modification of the reservation rule is introduced and it is shown that its effect is enough to mitigate the potential problem.
Enterprises are likely to make a decision based on only a few likely combinations of various possibilities of internal and external business situations. Because the future from present standpoint is aggregate of various possibilities, it is appropriate to make a decision based on the analysis which considers all the necessary scenarios probabilistically. Our former paper applies a PSA (Probabilistic Safety Assessment) concept to a decision making problem in maritime transportation system and shows that probabilistic approach can be highly useful not only for safety but also for enterprise decision making with some modifications. But the above procedure accompanies a lot of analyst's subjective judgments, man hour and computational time to execute. This paper proposes a dynamic event tree generation method by feedback system to mitigate these difficulties and applies it to a realistic decision making problem in maritime transportation system to demonstrate its applicability and usefulness.
An underwater vehicle for virtual mooring was constructed at the Research Institute for Applied Mechanics (RIAM), Kyushu University. The disk type vehicle that houses various pieces of observation equipment glides back and forth between the sea surface and the seabed collecting ocean data. If the position is outside the sea area of virtual mooring because of currents etc., the vehicle is controlled so that it returns the previous area during its next dive. Horizontal movement of the vehicle is done with gliding and without thrusters. The gliding ratio and the course of the vehicle are controlled by moving the position of the built-in weight.This paper presents the developed test-bed vehicle and its field experiment.
Nowadays, risers and pipelines are widely used by the Offshore Industry. Such pipes are deployed mainly as a connection element for the stream of hydrocarbon or other service fluid during the offshore well drilling or the hydrocarbon production. The pipes that connect the platform at the sea surface down to the wellhead is named riser by the Industry. Several researches have been carried out about the risers' mechanical behavior focusing mainly on the interaction among the pipe's structure, floating platform's motion, external hydrodynamic forces, and soil contact.However up till now, most of such investigations have neglected the effect of the internal flow on the pipe's structure.Thus this work is focused on this gap: the interaction between the pipe's structure and the forces and other effects caused by its internal flow. An Experiment was carried out at the Deep Sea Basin of the National Maritime Research Institute (Japan) using as a model, a silicon made tube of 10m length. During the experiment, fresh water was pumped into the model in order to verify the effects of the internal flow. In addition, comments about the numerical simulation of the pipe's mechanical behavior in the time domain are included.
Accuracy evaluation system for curved shell plates was developed. This system compares the plate design data with the point cloud data of the actual curved shell plate. Point cloud data is generated by a laser scanner with references based on the edge of the actual shell plates. Displacement errors which refer to the distances from each point in the point cloud data to the desired design surface are evaluated and visualized by color map and histogram. This developed system enables users to understand the errors on the whole surface of curved shell plates quantitatively. This accuracy evaluation system was tested on actual curved shell plates, and correlations between the distribution of the errors and the making process are illustrated in this paper.
Decision of principal particulars is the first stage of ship design. This stage is an important stage where essential information of the ship is decided and the influence on the cost and performance is extremely larger. However, various analyses which contain the error margin are used because detailed information on the ship is not available. Therefore a higher degree of uncertainty is involved in the early design stage. On the other hand, product information is expressed as a fixed value in the present design support system and the systems can not deal with the uncertainties involved in the design information and design process. The purpose of this study is to propose the new design support system considering uncertainties in the product information.The characteristics of the proposed method are following points.1) In order to express product information as unfixed ones, adjustment parameters are used in the new design support system. Fixed product information in a design solution can assume only a single numerical value. On the other hand unfixed product information can be changed to improve the feasibility or optimality because it can assume more than one numerical value. 2) A optimization method named Wildcard GA is newly introduced. In order to express product information as unfixed ones, "*" (asterisk) is used in the Wildcard GA. "*" means both "0" and "1". By using this feature, plural design proposal are made from one gene.Some examples using the proposed method are shown in the paper and these are compared with the solution of present technique. As a result, the possibility of the improvement of the design is shown.
Dynamic-scale model tests of a ship anchor chain were conducted to investigate the oscillation of the anchor chain in a chain locker during anchoring. In the tests, the pay-out velocity of the chain was kept constant for a range of speeds 1.0m/s to 2.5m/s. The lateral oscillation and the tension of the ascending chain were measured. The statistical analysis of test data was carried out. Then,resonance phenomena of the chain caused by increasing the pay-out velocity are discussed theoretically. In addition, the effect of the chain pipe length and the upper room height of the chain locker are also described for the purpose of reducing the oscillation. As the results, it is found that the pay-out velocity of the anchor chain, the breadth of the chain locker, the chain pipe length and the upper room height of the chain locker affect lateral oscillation of a chain in a chain locker.
This paper describes the concept of the buoyancy-control type ballast-free ship proposed by Yokohama National University and the result of various studies carried out to examine its performance. In this study, we carried out model experiments in a water circulating channel to measure the ability of the system to exchange seawater in the buoyancy control tanks. We also confirmed by numerical analysis that the increase of the ship resistance by the appendage, i.e., intake and exit vents, is less than 1 percent of the total ship resistance. One of the aims of this concept is to alter existing ships to ballast-free ones by leaving the structures of the existing ships almost as they are, i.e., ballast tanks of conventional ships are to be used as buoyancy control tanks necessary for the proposed system with slight modifications. In order to realize retrofitting of conventional ships to ballast-free ships easily, we propose a simple method by inserting intake and exit units into the space between longitudinal stiffeners on the ship bottom.Furthermore, structural analysis by using a finite element method was performed and we confirmed that no serious problem occurs by the buoyancy control operation. The proposed ballast-free ship concept is a favorable option to solve the ship's ballast water problem.
Shipping market shows higher volatility than real economy in financial movements. Although shipping and shipbuilding companies have their own methods for the decision-making in the unstable market,they will not reveal their specific approaches.The present paper proposes methods of evaluating operation strategies,extracting consensus outlook of market participants from price differences in secondhand ships.The paper also demonstrates the comparison of best strategies at a sharp decline of the market. The proposed methods of evaluating portfolio of fleet and its management will provide basis for the future analysis of volatile shipping market.