• Journal of the Society of Naval Architects of Korea
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• v.48 no.6
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• pp.569-574
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• 2011

In research vessels or naval ships, airborne noise from machineries such as diesel engine is the major source of underwater noise at low speed. In this paper, effect of engine noise on underwater noise is studied by considering two paths; sound radiation from hull plate and direct airborne noise transmission through hull plate. SEA (Statistical energy analysis) is used to predict hull plate vibration induced by engine noise, where SEA model consists of only two subsystems; engine room air space and hull plate. The pressure level in water is calculated from sound radiation by plate. Engine noise transmission through hull plate is obtained by assuming plane wave propagation in air-limp plate-water system. Two effects are combined and compared to the measurement, where speaker is used as a source in engine room and sound pressure levels in engine room and water are measured. The hydrophone is located 1 m away from the hull plate. It is found below 1000 Hz, prediction overestimates underwater sound pressure level by 5 to 12 dB.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.6
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• pp.675-687
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• 2009

In general, the forming process of the curved hull plates consists of sub tasks, such as roll bending, line heating, and triangle heating. In order to complement the automated curved hull forming system, it is necessary to develop an algorithm to classify the curved hull plates of a ship into standard shapes with respect to the techniques of forming task, such as the roll bending, the line heating, and the triangle heating. In this paper, the curved hull plates are classified by four standard shapes and the combination of them, or saddle, convex, flat, cylindrical shape, and the combination of them, that are related to the forming tasks necessary to form the shapes. In preprocessing, the Gaussian curvature and the mean curvature at the mid-point of a mesh of modeling surface by Coon's patch are calculated. Then the nearest neighbor method to classify the input plate type is applied. Tests to verify the developed algorithm with sample plates of a real ship data have been performed.

• Journal of Power System Engineering
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• v.9 no.4
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• pp.220-224
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• 2005

The thermal elasto-plastic analysis for the prediction of welding distortion of a 3 dimensional large-scaled ship structure is a very time-consuming work since the analysis is a nonlinear problem, and a lot of finite elements are needed to simulate the large ship hull block. Generally, 3-D finite elements have been used in the 3-D welding distortion problem to assess precisely the temperature gradient through the thickness direction of the welding plate. As a result of the adoption of 3-D element, degrees of freedom are rapidly increased in the problem to be solved. In this study, to improve the time efficiency of welding thermal elasto-plastic analysis, a layered shell element was proposed to simulate 3-D temperature gradient, and the results were compared with the experiment. The experiments were carried out for the type of bead-on-plate welding, and we found the measured data have a good agreement with the FEA results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.06a
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• pp.23-24
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• 2008

• Bulletin of the Society of Naval Architects of Korea
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• v.3 no.1
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• pp.33-45
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• 1966

The effect of thermal stress on a ship's hull is not considered to be serious by most naval architects. Frequently, however, cracking of hulls has been reported which occurred at sea while there were no external forces except the heat from the sun. Detailed investigations have been made of these reports and it has been reliably determined that the damage was initiated by solar heating. The author is not interested in all steel ship or in the applicability and validity of the formular itself, as it has already been proven by the experiments such as S.S. Boulder Victory. The author therefore proceeds directly to calculate the stress distribution on he hull and superstructure of the prototype model ship. These calculations are based on the experimental nonsymetrical temperature gradient data taken earlier on the Boulder Victory. The calculations were made principally to determine the extent of stresses which occurred on an all-steel ship in one case and secondly, those that occurred on a ship with a steel hull and an aluminum superstructure. From the calculations, the author expected the stress distribution of the two case would show distinctly different aspects, but the acquired results were very similar. Generally, at the point of junction of the steel hull and aluminum superstructure sharp peak stresses appeared. At the juncture of the superstructure and the main deck the ship with the aluminum superstructure registered almost 1000 psi more stress than did the ship with the all-steel construction. In the view of these findings, the author recommends to ship designers that pay particular attention to the point of junction of steel and aluminum plate. The author has proven that it is extremely important that a greater safety factor be used at the aluminum-steel junction point than at any other point. Although thermal effects cause high juncture-point stresses in all-steel ships, they are not nearly as critical as in ship constructed of two or more metals.

• Proceedings of the KWS Conference
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• 2002.05a
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• pp.149-151
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• 2002

In this study, a formula for thermal processing induced plate deformations, in terms of process parameters such as heat input and plate thickness, is developed analytically using an infinite laminated plate theory to consider cuboidal inclusion with an eigenstrains. When a plate has arbitrary heating lines, complex deformed shape of plate was calculated by the method estimating plate deformation proposed by this study. To make a curved surface of the ship hull, the line heating method is mainly used. Application in automatization of line heating was deliberate by using proposed method.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.3
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• pp.53-60
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• 1997

Generally, a safety estimation based on the buckling strength is carried out to evaluate the strength of plate members in the design process of ship hull structures and more accurate and efficient tool for the buckling strength estimation of enormous plate members of ship structure is naturally demended for saving design process. While, in the reason that the design codes of classification societies do not consider the various effects or include some effects roughly, considerate safe side results are suggested occasionally. In this study, advanced buckling strength estimation system prepared various classification buckling evaluation codes and new evaluation code considering the effects of in-plane tension, plate boundary condition, lateral load & residual stress is developed using the window management system of engineering workstation. Additionally maximum deflection estimation formula is equipped for the increase of fabrication reliability of thin plate ship structure. From this evaluation system, more reliable buckling safety of plate panel will be guaranteed in the ship hull design stage. In order to expand the use of this system pc version system will be developed sooner or later.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.158-161
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• 2008

In the line array roll set (LARS) process, the initial plate is progressed into the final shape in a stepwise or pathwise manner according to the basic principle of the incremental forming process. The deformation proceeds simultaneously in the longitudinal and transverse directions. It was found that the curvature level of the formed plates in the previous study was well over the curvature required in shipyards. This fact shows that the LARS method has considerable potential for shipbuilding applications. In this study, several experiments with the LARS system is carried out fur manufacturing of plates with large curvatures. The bulbs at a stem and stern among ship hull plates correspond to these plates. Furthermore, the qualities of formed plates are evaluated according to the types of roll arrangements through experimental and numerical analyses.

• Korean Journal of Computational Design and Engineering
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• v.17 no.3
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• pp.188-197
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• 2012

Recently, aluminum ships are constructed more than ever because of the environmental pollution generated by FRP (Fiber Reinforced Plastic) ships. In particular, FRP ships have been replaced by the Aluminum ships. The forming process of the curved aluminum plate has been performed only by labor works without systematic technique. Therefore, it is difficult to construct the aluminum ship that the design satisfies both required propulsion performance and hull design. Present study introduces a MPSF (Multi Point Stretching Forming) that is a flexible manufacturing technique to form large sheet panels of doubly curvature. The hull pieces are stretch-formed over the MPSD (multi-point stretching die) generated by the punch element matrix. In this study, MPSF is applied to deform the doubly curved surfaces of aluminum ship. The forming system including FEA (finite element analysis) of the processes for stretching the plate were carried out by static implicit analysis is suggested. Residual deformation of the surface is modeled by an elasto-plastic contact phenomena while the forming process is simulated by FEA. Finally, the proposed system is also validated, comparing the deformed shape by MPSF with that of object surfaces.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.289-292
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• 2009

The line array roll set process, as one of many kinds of incremental forming processes, is a continuous process in which a flat metal plate is formed into a singly or doubly curved plate through successive passes of forming rolls. It was found that the curvature level of the formed plates in the previous study was well over the curvature required in shipyards. This fact shows that the LARS method has considerable potential for shipbuilding applications. In a shipbuilding yard, hull forming is an important fabrication process in which flat plates are deformed into singly or doubly curved plates. The major purpose of the present study is to estimate experimentally the general applicability of the line array roll set process for the manufacture of ship hull plates. In this study, the target shapes are selected through investigation of the shape classification of ship hull plates that comprise a certain vessel. Forming processes for twisted shapes are analyzed with the finite element method (FEM). Finally, the results of experimental work for two types of target shapes are presented.