• Journal of the Society of Naval Architects of Korea
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• v.37 no.2
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• pp.127-136
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• 2000

Welding deformations reduce the accuracy of ship hull blocks and decrease the productivity due to correction work. Preparing an error-minimizing guide at the design stage will lead to a high quality as well as high productivity. And a precise method to predict the weld deformation is an essential part of it. This paper proposes an efficient method to predict complicated weld deformations based on the inherent strain theory combined with the finite element method. The inherent strain is determined by the highest temperature and the degree of restraint. In order to calculate the inherent strain exactly, it is considered that the degree of restraint becomes different according to the fabrication stages in real structures. A simulation of a stiffened plate shows the applicability of this method to simple ship hull blocks.

• Bulletin of the Society of Naval Architects of Korea
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• v.20 no.1
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• pp.11-20
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• 1983

In this paper elastic-plastic large deflection analysis of ship structural members, plates, stiffened plates and cylindrical shallow shell, are performed by the finite element method. And for the consideration of the yielded propagation through the depth of the member, the layered element approach is employed. The present method is justified by comparing its results with those of experiment and others. As results, the nonlinear behavior and the ultimate strength curves are shown, which can be used in the design of the plates and the stiffened plates under compression, and the applicability to the shell structures is suggested. The analysis results are as followings. (1) The results of the approximate equations as well as those of buckling analysis may not guarantee precisely the safety of the structures in some cases and the optimum in other cases. Therefore they may not show the design criteria for the optimal design. (2) As the initial deflection increases, its effects on the ultimate strength of the structure generally increases, and the ultimate load, therefore, decreases. (3) This approach can be applied to the shell type structures. (4) The present method can be applied to the various structures composed of plate and beam members, for example, plates with hole and the stiffened plates with hole stiffened by spigot, doubler and/or stiffener, for the optimal design.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.6
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• pp.731-738
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• 2017

Twin-hulls frequently incur structural damage at connecting members between the hull and deck induced by pitching motions during voyages. so, reasonable reinforcement is necessary around vulnerable spots such as corner knuckle, the chine bottom and inner hull. Since guidelines for structural design are not clear, engineers often respond by reinforcing plate thickness, changing stiffener sizes and reducing frame spacing, etc. These members constitute about 85 % of the longitudinal dimensions of the ship, so it is necessary to locally reinforce certain points to minimize weight stress, and also solve construction cost problems while securing the freeboard margin. Therefore, we developed a new program by analyzing the structural design procedures for the twin car-ferries based on Korean Register of Shipping (KR) High Speed Craft Rules, identifying items that need to be added. In order to ensure the reliability of buckling estimations for procedures and design programs, we conducted a comparative study with other standards and confirmed that differences were minimal.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.4
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• pp.147-156
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• 1994

Though optimization method had been used for long time for the optimal design of ship structure, design variables in the most cases were assumed to be continuous real values or it was not easy to solve the mixed integer optimum design problems using the conventional optimization methods. Thus, it was often tried to use various initial starting points to locate the best optimum paint and to use special method such as branch and bound method to handle the discrete design variables in the optimization problems. Sometimes it had succeed, but the essential problems for dealing with the local optimum and discrete design variables was left unsolved. Hence, in this paper, Genetic Algorithms adopting the biological evolution process is applied to the ship structural design problem where the integer values for the number of stiffen design variables or the discrete values for the plate thickness variables would be more preferable in order to find out their effects on the final optimum design. Through the numerical result comparisons, it was found that Genetic Algorithm could always yield the global optimum for the discrete and mixed integer structural optimization problem cases even though it takes more time than other methods.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2005.04a
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• pp.592-600
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• 2005

Ship have cutout inner bottom and girder and floor etc. Ship's structure is used much, and structure strength must be situated, but establish new concept when high stress interacts sometimes fatally the area. There is no big problem usually by aim of weight reduction, a person and change of freight, piping etc.. Because cutout's existence grow up in this place, and elastic buckling strength by load causes large effect in ultimate strength. Therefore, stiffened perforated plate considering buckling strength and ultimate strength is one of important design criteria which must examine when decide structural concept at initial design. Therefore, md, reasonable buckling strength about stiffened perforated plate need to ultimate strength limited design . Calculated ultimate strength varied several web height and cutout's dimension, and thickness in this investigated data. Used program(ANSYS) applied F.E.A code based on finite element method

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.5
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• pp.542-550
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• 2020

The use of high-strength aluminum alloys for ships and of shore structures has many benefits compared to carbon steels. Recently, high-strength aluminum alloys have been widely used in onshore and of shore industries, and they are widely used for the side shell structures of special-purpose ships. Their use in box girders of bridge structures and in the topside of fixed platforms is also becoming more widespread. Use of aluminum material can reduce fuel consumption by reducing the weight of the composite material through a weight composition ratio of 1/3 compared to carbon steel. The characteristics of the stress strain relationship of an aluminum structure are quite different from those of a steel structure, because of the influence of the welding[process heat affected zone (HAZ). The HAZ of aluminum is much wider than that of steel owing to its higher heat conductivity. In this study, by considering the HAZ generated by metal insert gas (MIG) welding, the buckling and final strength characteristics of an aluminum reinforcing plate against longitudinal compression loads were analyzed. MIG welding reduces both the buckling and ultimate strength, and the energy dissipation rate after initial yielding is high in the range of the HAZ being 15 mm, and then the difference is small when HAZ being 25 mm or more. Therefore, it is important to review and analyze the influence of the HAZ to estimate the structural behavior of the stiffened plate to which the aluminum alloy material is applied.

• Journal of Navigation and Port Research
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• v.31 no.10
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• pp.825-831
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• 2007

The use of high-strength aluminum alloys for ship and offshore structure generally has many benefits compared to the structural steels. These materials are used widely in a variety of fields, especially in the hull and deck of high speed craft, box-girder of bridges, deck and side plates of offshore structure. The structural weight can be reduced using these aluminum structure, which can enable high speed The characteristics of stress-strain relationship of aluminum structure are fairly different from the steel one, because of the influence of Heat Affected Zone(HAZ) by the welding processing. The HAZ of aluminum is much wider than that of steel with its high heat conductivity. In this paper, the ultimate strength characteristics of aluminum stiffened panel subjected to axial loading, such as the relationship between extent of HAZ and the behavior of buckling/ultimate strength, are investigated through the Finite Element Analysis with varying its range.

• Journal of the Society of Naval Architects of Korea
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• v.32 no.1
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• pp.25-36
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• 1995

The application of the reliability analysis is investigated as a probabilistic approach to the assessment of ship's structural strength and to the establishment of design format for longitudinal strength. Reliability analyses are carried out for 34 ships of tankers and bulk carriers built in HHI for some failure modes such as tensile yielding, compressive buckling and ultimate strength of hull girder. The safety assessment of each ship, the calculation of sensitivity factors and the derivation of target reliability index are performed. As results. the difference of reliability indices among ships is great for all modes. To provide more uniform levels of safety the establishment of new strength criteria using partial safety factors is performed. The partial safety factors for the design format are obtained according to the AFOSM method and the reliability-conditioned(RC) method. Finally, a design format using partial safety factors has been proposed. We could find out that new strength criteria can produce consistent reliability indices which are close to the target value.

• Journal of Ocean Engineering and Technology
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• v.33 no.5
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• pp.411-420
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• 2019

It is essential to design crashworthy marine structures for operations in Arctic regions, especially ice-covered waters, where the structures must have sufficient capacity to resist iceberg impact. In this study, a numerical analysis of a colliding accident between an iceberg and stiffened plates was carried out employing the commercial finite element code ABAQUS/Explicit. The ice material model developed by Liu et al. (2011) was implemented in the simulations, and its availability was verified by performing some numerical simulations. The influence of the ambient temperature on the structural resistance was evaluated while the local stress, plastic strain, and strain energy density in the structure members were addressed. The present study revealed the risk of fracture in terms of steel embrittlement induced by ambient temperature. As a result, the need to consider the possibility of brittle failure in a plate-stiffener junction during operations in Arctic regions is acknowledged. Further experimental work to understand the structural behavior in a plate-stiffener junction and HAZ is required.

• Journal of Ocean Engineering and Technology
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• v.30 no.4
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• pp.277-286
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• 2016

The first part of this study found the tendencies of the mechanical properties of two arctic structural steels (EH32 and FH32). In the second part, the crashworthiness of stiffened panels scaled down from the side frame structure of a Korean research icebreaker was determined. A procedure for designing the shapes and sizes of the stiffened panels, mass and shape of a drop striker, and a large temperature chamber, and then manufacturing these, is introduced in detail. From impact bending tests for the stiffened panels, the residual permanent deformations and deformation histories over time were captured using manual measurement and video image analyses. Numerical simulations of the impact bending tests were carried out for three different finite element models, which were mainly composed of shell elements, solid elements, and solid elements, with welding beads. It was proven from a comparison of the test results and numerical simulation results that the solid element model with the welding bead consideration approached the test results in terms of the residual deformations as long as the strain rate effect was taken into account.