• Journal of Welding and Joining
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• 제35권3호
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• pp.82-87
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• 2017

Recent trends in shipbuilding and offshore industries are a huge increase in the ship size and the exploration and production of oil and natural gas in the arctic offshore region. High performance steel plates are required by these industrial trends. Also in IMO(International Maritime Organization) has begun to regulate of fuel of ship to environmental protection, therefore it is little bit difficult to use bunker-C oil to working ship. As the problem of environmental change such as global warming is emerged, the operation of the ship is considered to be involved in the environmental change problem, and the regulation of environmental pollution is gradually strengthened. As these environmental regulations are strengthened demand for LNG fuel ships is rapidly increasing. Currently, cryogenic steels used in LNG tanks include aluminum alloy, SUS 304, and 9%-Ni steel. Those steels are has high cost to construction of large LNG carrier. The new materials were suggested several steel mills to decrease construction cost and easy construction. The new cryogenic steel should be evaluate safety to applied real structure include LNG ship. Therefore, in this study, fracture toughness of weld joints were investigated with cryogenic steel for application of LNG tank.

• 한국해양공학회지
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• 제29권3호
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• pp.217-223
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• 2015

In order to predict the motions of a planing hull in waves, it is necessary to accurately estimate the force components acting on the hull such as the hydrodynamic force, buoyancy, and friction, as well as the wave exciting force. In particular, based on strip theory, hydrodynamic forces can be estimated by the summation of the forces acting on each cross-section of the hull. A non-linear strip method for planing hulls was mathematically developed by Zarnick, and his formula has been used to predict the vertical motions of prismatic planing hulls in regular waves. In this study, several improvements were added to Zarnick's formula to predict the vertical motions of warped planing hulls. Based on calm water model test results, the buoyancy force and moment correction coefficients were modified. Further improvements were made in the pile-up correction. Pile-up correction factors were changed according to variations of the deadrise angles using the results found in previous research. Using the same hull form, captive model tests were carried out in other recent research, and the results were compared with the present calculation results. The comparison showed reasonably good agreements between the model tests and present calculations.

• 한국해양공학회지
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• 제30권6호
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• pp.474-483
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• 2016

Accidental events such as collisions, groundings, and hydrocarbon explosions in marine structures can cause catastrophic damage. Thus, it is extremely important to predict the extent of such damage, which determines the total amount of oil spills and the residual hull girder strength. Punching fracture tests were conducted by Choung (2009b), where various sizes of indenters and circular unstiffened steel plates with different thicknesses were used to quasi-statically realize damage extents. A three-dimensional fracture strain surface was developed based on a reference (Choung et al., 2015b), where the average stress triaxiality and average normalized Lode angle were used as the parameters governing the fracture of ductile steels. In this study, new numerical analyses were performed using very fine axisymmetric elements in combination with an Abaqus user-subroutine to implement the three-dimensional fracture strain surface. Conventional numerical analyses were also conducted for the tests to identify the best fit fracture strain values by changing the fracture strains. Based on the phenomenon of the average normalized Lode angle starting out positive and then becoming slightly negative, it was inferred that the shear stress primarily dominates in determining the fractures locations, with a partial contribution from the compressive stress. It should be stated that the three-dimensional fracture surface effectively predicted at least the shear stress-dominant fracture behavior of a mild steel.

• 대한조선학회지
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• 제17권1호
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• pp.25-29
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• 1980

For the preliminary estimation of the vertical hull natural frequency, the Schlick's or Schlick-type formulae have been traditional ones and are still in common use today. Some investigators have made their efforts, based on statistical data of ships' system parameters, to extend the applicability of Schlick-type formulae to higher modes, or to utilize the Rayleigh method. For instance, the work done by Dinsenbacher et al.[5] belongs to the former and that of Nagamoto et al.[6] to the latter. In a part of his previous paper[7], the author, investigating the case of a cargo ship of medium size, suggested that provided statistically simplified curves such as trapezoid of system parameter distributions are available in hands, direct utlization of an ordinary computer program can be also an another convenient method by which we can obtain both natural frequencies and normal mode shapes. In this paper, to confirm the feasibility of the above suggestion, four high speed boats are investigated. The system parameters of them are originally given in [5]. The computer program used here is one confiled based on a calculation method derived from Myklestal-Prohl modeling of hull, transfer matrix formulation and an extended Gumbel's initial value method for solving frequency equation. The results of the investigation show that the direct calculation based on statistically oriented and reasonably assumed trapezoidal mean curves of system parameter distributions can give us natural frequencies within about 5% deviation up to several-noded modes and normal mode shapes serviceable at least up to 4- or 5-noded modes in comparision with those based on actual distributions of system parameters. For this simplified method the actual data required for input are only of ship length, displacement, total added mass, bending and shear rigidity at amidship. They are available at the early stage of design. By this method we can also easily trace variations of vibration characteristics in the course of ship design cycles.

• 대한조선학회논문집
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• 제28권2호
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• pp.293-306
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• 1991

선박은 내부에 소음원을 가지고 있을 뿐 아니라 진동의 전달 특성이 좋은 강판 구조물이기 때문에 기진원과 소음원을 포함한 구조계및 주변 음장계까지 포함한 전체계에 대한 소음 예측을 수행하여야 한다. 이러한 선내 소음 환경을 예측하기 위하여 본 연구에서는 통계적 에너지 해석법을 이용하여 고차 진동의 전달 특성, 음장과 구조물과의 상호 작용 및 음장의 투과 손실등에 대한 해석 이론을 정식화하고 이를 바탕으로 선내 소음 예측을 위한 전산 프로그램을 개발하였다. 또, 소형 연안 여객선을 대상으로 하여 이론적 소음 예측 계산을 수행하고 실선 계측 결과와 비교하여 그 타당성을 확인하였으며, 공기음과 고체음에 대한 전달 특성을 분석하여 보았다.

• 대한조선학회논문집
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• 제29권4호
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• pp.45-57
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• 1992

선박과 같은 복잡한 대상물을 설계하거나 생산하는데 사용되는 소프트웨어 시스템들간의 상호 정보교환을 위한 표현방법을 구체화하는 제품모델(Product Model)의 표준화 동향을 살펴보았으며, 이를 근거로 제품모델을 기초로 한 선박모델을 정의하기 위한 새로운 표현방법을 정립하여 제안하였다. 제안된 선박모델의 표현방법론을 통해 응용측면에서 제품모델링 기술과 시스템 구현측면에서의 객체지향시스템 기술을 고찰하였다. 본 논문을 통해 제안한 표현방법론의 적합성을 검증하기 위해 선박구획배치 모델링을 프로토타입 모델링 대상으로 하여 객체지향 선박구획배치 프로그램("OO_COMDEF"라 함)을 작성하였고 이를 구획배치 모델링에 적용하여 보았다. 본 표현방법론은 조선 전용 CAD/CAM 시스템의 국내 개발을 위한 Framework의 첫단계로서 제시하고자 한다.

• 대한조선학회논문집
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• 제36권4호
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• pp.95-104
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• 1999

강 구조물의 대형화에 기인하여 대형 해양구조물, 선박, 교량 및 고층 구조물에서의 극후판의 사용이 지속적으로 증가하고 있으며, 이런 경향은 앞으로도 계속될 것으로 생각된다. 그러나, 극후판을 사용하여 구조물을 시공할 때, 층상균열의 발생이 보고되고 있으며 이것은 극후판의 두께방향 중심부를 따라 분포하는 황, 인등의 불순 개재물 및 용접에 기인하여 발생하는 구속 잔류응력에 의하여 발생하는 것으로 알려져 있다. 연속 주조공법에 의하여 제조되는 극후판의 제조공정의 특성상, 층상균열의 발생은 회피하기가 현실적으로 어려우며, 따라서, 본 논문에서는 강구조물의 층상균열 발생의 감소 방안으로서, 금속학적 측면보다는 용접강도 측면에서 유한요소법에 기초한 전산 프로그램을 사용하여 최적 개선부형상 및 용접순서를 선정하고자 한다.

• 대한조선학회논문집
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• 제34권1호
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• pp.68-76
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• 1997

본 논문에서는 선박 및 해양 구조물을 구성하는 용접 판구조물의 변형 및 잔류응력 등 용접 초기 결함을 효율적으로 평가할 수 있는 열탄소성 해석방법을 정립하였다. 또한 평판의 선상가열공법(line heating process)을 열탄소성 시뮬레이션함으로써 작업의 고능률화 및 자동화를 위한 기초연구를 수행하였다. 판구조물에 대한 열전도 해석을 수행하기 위하여 해석적인 방법과 수치적인 방법을 병행하였다. 판구조물의 열탄소성 해석방법에 있어서는 초기변형도법에 근거한 유한요소법을 사용하였으며, 증분 구간중 소성 구역에서는 응력 증분 및 항복응력 중분의 2 차항까지 고려해서 시간 증분을 최적 제어함으로써 해석 불능에 빠지는 문제를 극복하였다. 특히 응력 중분에 탄성계수의 온도에 따른 증분을 2 차항까지 포함시켰다. 평판의 두께와 입열량을 변화시키면서 일련의 용접 열탄소성 실험을 수행하였는 바, 온도 및 용접 변형을 계측하여 수치 계산 결과와 비교하여 상호 부합성이 양호함을 확인하였다.

• 대한조선학회논문집
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• 제56권6호
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• pp.507-514
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• 2019

Computational studies of accelerating flow around 2D Circular Cylinder was performed to investigate characteristics of wake field and drag forces. Previous studies had revealed that drag on the cylindrical body in accelerating flow is much greater than that in the flow with constant velocity; however, the underlying physics on the drag increase has not been clearly investigated. In order to investigate the drag increase and its relationship with wake development, this study employed a finite-volume based CFD code, Fluent 13.0 with k-ω SST model for turbulence effects. Inflows are modeled with varied accelerations from 0.4905 to 9.81m/s². The drag computed in the present study is in good agreement with previous studies, and clearly shows the increase compared to the drag on the body in the flow with constant velocity. The results also show that drag crisis observed at high Reynolds number in the case of the flow with constant velocity is also found in the case of accelerating flow. The analysis for wake and recirculation length shows that conventional vortex shedding does not occur even at high Reynolds number and the drag increase is larger at higher acceleration.

• 한국해양공학회지
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• 제31권4호
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• pp.288-298
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• 2017

A study of the damage evolution laws for ductile materials was carried out to predict the ductile fracture behavior of a marine structural steel (EH36). We conducted proportional and non-proportional stress tests in the experiments. The existing 3-D fracture strain surface was newly calibrated using two fracture parameters: the average stress triaxiality and average normalized load angle taken from the proportional tests. Linear and non-linear damage evolution models were taken into account in this study. A damage exponent of 3.0 for the non-linear damage model was determined based on a simple optimization technique, for which proportional and non-proportional stress tests were simultaneously used. We verified the validity of the three fracture models: the newly calibrated fracture strain model, linear damage evolution model, and non-linear damage evolution model for the tensile tests of the asymmetric notch specimens. Because the stress evolution pattern for the verification tests remained at mode I in terms of the linear elastic fracture mechanics, the three models did not show significant differences in their fracture initiation predictions.