• Journal of the Society of Naval Architects of Korea
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• v.48 no.2
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• pp.178-182
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• 2011

Generally in order to reduce the steel weight of stiffened plate, stiffener spaces tend to be narrow and the plate gets thin. However, it will involve more fabrication cost because it can lead to the increase of welding length and the number of structural members. In the yard, the design which is able to reduce the total fabrication cost is needed, although it requires more steel weight. The purpose of this study is to find optimum stiffener spaces to minimize the fabrication cost for the cargo tank of LPG Carriers. Global optimization methods such as ES(Evolution Strategy) and GA(Genetic Algorithm) are introduced to find a global optimum solution and the sum of steel material cost and labor cost is selected as main objective function. Convergence degree of both methods in according to the size of searching population is examined and an efficient size is investigated. In order to verify the necessity of the optimum design based on the cost, minimum weight design and minimum cost design are carried out.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.3
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• pp.279-289
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• 2009

For a Product Oil Carrier, longitudinal bulkhead as well as transverse one is corrugated shape in general and intersection part of bulkheads is utilized for a pipe trunk. Since lower and upper stools are to be connected with all of longitudinal and transverse bulkheads, they have a uniform height respectively. The purpose of this study is the development of design system for the minimization of total weight of longitudinal and transverse bulkheads at the initial design stage. In this study, the beam element models for longitudinal and transverse corrugated bulkheads are established and they are applied to the structural analysis. For the practical design, the selection and the position of an additional pipe trunk are considered in this study. In addition the required minimum distance between the bracket installed along the web of corrugation at lower stool and the diaphragm is taken into consideration during optimization process. Evolution strategy(ES) is adopted as an optimization technique.

• Strategy21
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• s.44
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• pp.213-253
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• 2018

The Russo-Japanese War(1904-1905) in the early 20th century greatly influenced the international politics in Northeast Asia and the destiny of both countries. There are many studies on the cause of the outbreak and its effect on the Korean peninsula. The victory and defeat of the battle of Tsushima also the subject of research by renowned scholars and navy officers. Many previous studies have analyzed the process of engagement. However, There was a lack of research that analyzed at the tactical level of naval commanders. Therefore, this study tries to review the battle of Tsushima in terms of tactical level, that is formation, maneuvering, damage control. Naval operations at sea with many variables are not always done as planned. The intuitive judgement and readiness have had a decisive impact on victory and defeat. The analysis of the naval warfare on the basis of formation, maneuvering, and damage control makes the cause of the win more clearly. The conclusion of the this study can be summarized in five ways. First, victory would be achieved through the suppression of the beginning. The destiny of the Tsushima battle was determined by an 1 hour after first firing. The Japanese fleet caught fire by paralyzing the command and control capabilities of the Russian fleet. Second, the Japanese fleet's power was superior to the Russian fleet. In general, Japan and Russia had similar powers, and Admiral Togo's "T crossing tactics" decisively contributed the victory. However, when compared to the weapon system level, formation and maneuvering, Japan was much more dominant. Third, people realized that one side to be annihilated in the battle between similar powers after the Tsushima battle. The common perception before the Battle of Tsushima was that the battle ship would not sunken, and that the result of wiping out was difficult. However, there is s time for one sided victory and defeat depending on the early suppression nad the destruction of the command and control ability. Fourth, it is the importance of damage control ability. The main cause of the Russian fleet's loss of command and control ability was thick smoke from fire, and maneuverability was greatly deteriorated due to coal overload. In this way, importance is still valid after more than 100 tears. Fifth, the area of uncertainty. In the navy battles, one or two shots of clear firing in the beginning and small misconception and minor mistakes decide win or loss. Ultimately, this area of fortune can be linked to mindset of the commander. I hope this research will be help to naval researchers and naval commanders at the sea.

• International Journal of Naval Architecture and Ocean Engineering
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• v.2 no.3
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• pp.139-145
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• 2010

In the present study, we conducted resistance test, propeller open water test and self-propulsion test for a ship's resistance and propulsion performance, using computational fluid dynamics techniques, where a Reynolds-averaged Navier-Stokes equations solver was employed. For convenience of mesh generation, unstructured meshes were used in the bow and stern region of a ship, where the hull shape is formed of delicate curved surfaces. On the other hand, structured meshes were generated for the middle part of the hull and the rest of the domain, i.e., the region of relatively simple geometry. To facilitate the rotating propeller for propeller open water test and self-propulsion test, a sliding mesh technique was adopted. Free-surface effects were included by employing the volume of fluid method for multi-phase flows. The computational results were validated by comparing with the existing experimental data.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.6
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• pp.598-612
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• 2017

The recently developed Harmonic Polynomial Cell (HPC) method has been proved to be a promising choice for solving potential-flow Boundary Value Problem (BVP). In this paper, a flux method is proposed to consistently deal with the Neumann boundary condition of the original HPC method and enhance the accuracy. Moreover, fixed mesh algorithm with free surface immersed is developed to improve the computational efficiency. Finally, a two dimensional (2D) multi-block strategy coupling boundary-fitted mesh and fixed mesh is proposed. It limits the computational costs and preserves the accuracy. A fully nonlinear 2D numerical wave tank is developed using the improved HPC method as a verification.

• Strategy21
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• s.36
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• pp.180-214
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• 2015

The Republic of Korea navy challenged from the unexpected surprise attacks by the North Korea navy, albeit, the developments of up-to-date naval forces' technology, and the ceaseless efforts for war preparedness. My study divided into two categories. Qualitative methods used for literature review of international relations theory related to the war onset and for investigating events occurred on the Peninsula and its surrounding seas from 1968 to 2007. Quantitative method used such as the analyses of national power index of the two Koreas, the United States, and China, the uses of equation model to calculate power index of alliance, COPDAB(Conflict and Peace Data Bank) index analysis. Like Choi's study on East Asia maritime conflict, as a conclusion, considering both AT theory and maritime national power as a tool for predicting maritime conflict in the Peninsula proved significant. Based on the study, ROK navy need to prepare for the maritime conflict because the results showed North Korea would initiate maritime disputes sooner or later using fatal asymmetric forces and methods. As a policy suggestion, we are required to maintain a concrete ROK-US alliance ties and to construct naval forces due to the deterring functions of maritime national power.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.5
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• pp.353-361
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• 2016

Recently, the small shipyard companies have difficulties that causes by depression of shipbuilding industry. The small shipyard companies need some strategies to overcome the slump in shipbuilding industry field. In this paper, we conduct the survey for present condition diagnosis of small shipyard companies, and analyze the production process based on Information Strategy Planning(ISP) method. When analyze based on ISP, we apply IDEF0 and LOVC technique to analyze the production process of small shipyard companies. Also we conduct the gap analysis between the analyzed present condition and the requirements of improvement. Therefore, the most important result of the analysis is to establish a system for enterprise planning and management, which customized for small shipyard companies, with satisfying economic feasibility and usability.

• Strategy21
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• s.34
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• pp.178-206
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• 2014

The battlefield environment in the maritime has been changed by advanced IT technology, variation of naval warfare condition, and developed military science and technology. In addition, state-of-the-art surface combatants has become to multi-purpose battleship that is heavily armed in order to meet actively in composed future sea battlefield condition and perform multi-purpose missions as well as having capability of strategic strike. To maximize the combat strength and survivability of ship, it is not only possible for Zumwalt(DDG-1000) class combatant to conduct multi-purpose mission with advanced weapon system installation, innovative hull form and upper structure such as deckhouse, shipboard high-powered sensor, total ship computing environment, and integrated power control but it was designed so that can be installed with energy based weapon systems in immediate future. Zumwalt class combatant has been set a high value with enormous threatening surface battleship in the present, it seems to be expected that this ship will be restraint means during operation in the littoral. The advent of Zumwalt class battleship in the US Navy can be constructed as a powerful intention of naval strength building for preparing future warfare. It is required surface ship that can be perform multi-purpose mission when the trend of constructed surface combatants was analyzed. In addition, shipboard system has been continuously modernized to keep the optimized ship and maximize the survivability with high-powered detection and surveillance sensor as well as modularity of combat system to efficient operation.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.2
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• pp.180-187
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• 2018

Corrugated bulkhead has been adopted for cargo tank bulkheads of commercial vessels such as bulk carriers, product oil carriers and chemical tankers. It is considered that corrugated bulkhead is a preferred structural solution, compared to the flat stiffened bulkhead, due to several advantages such as lower mass, easier maintenance and smaller corrosion problems. Many researches to find the optimum shape of corrugated bulkhead have been mostly carried out for bulk carriers. Compared to corrugated bulkheads of bulk carriers, ones of chemical tankers are more complicated since they are composed of transverse and longitudinal bulkheads, and they are made of higher priced materials. The purpose of this study is the development of minimum weight design method for corrugated bulkhead of chemical tankers. Evolution strategy is applied as an optimization technique. It has been verified from many researches that evolution strategy searches global optimum point prominently by using multi-individual searching technique. Multi-individual searching methods need excessive time if they connect to 3-D finite element model for repetitive structural analyses. In order to resolve this issue, 2-D beam element connected to deck and lower stool is substituted for a corrugated structure in this study. To verify the reliability of the structural responses by idealized 2-D beam model, they have been compared with ones by 3-D finite element model. In this study, optimum design for corrugated bulkhead of 30 K chemical tanker has been carried out, and the results by developed optimum design program have been compared with design data of existing ship. It is found out that optimum design is about 9% lighter than one of existing ship.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.606-623
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• 2019

The path following problem of a ship sailing in restricted waters under wind effect is investigated based on Robust $H_{\infty}$ Guaranteed Cost Control (RHGCC). To design the controller, the ship maneuvering motion is modeled as a linear uncertain system with norm-bounded time-varying parametric uncertainty. To counteract the bank and wind effects, the integral of path error is augmented to the original system. Based on the extended linear uncertain system, sufficient conditions for existence of the RHGCC are given. To obtain an optimal robust $H_{\infty}$ guaranteed cost control law, a convex optimization problem with Linear Matrix Inequality (LMI) constraints is formulated, which minimizes the guaranteed cost of the close-loop system and mitigates the effect of external disturbance on the performance output. Numerical simulations have confirmed the effectiveness and robustness of the proposed control strategy for the path following goal of a ship sailing in restricted waters under wind effect.