1) 고 망간 강관 용접의 최종 잔류 응력 예측을 위해 Goldak’s double ellipsoidal 열원을 이용한 3차원 열-탄소성 해석을 적용하였다. 실험적인 잔류 응력 측정은 수행한 해석모델의 유효성을 확인하기 위해 HDM을 적용하여 계측되었다. 해석과 계측값의 정량적/정성적 결과가 유사하게 관찰되었다. 그 결과 제안된 잔류 응력 예측 방법의 타당성을 확인할 수 있었다.

In the mobile jack-up unit, the leg supporting the hull is a very important structure, and it is important to closely examine the changes in accident load, environmental load, and seabed ground during jack-up operation. Generally, jack-up rigs are three-legged structures with a triangular hull that comprises several movable legs used to raise the hull above the sea surface. They can be operated in shallow water at less than 120 m, while large jack-up rigs, which have a structure that can withstand severe environmental loads, can be employed at depths ranging from 150 m to 200 m. However, a complex process is required to finalize the structural design of a jack-up rig, and the influence of various parameters must be comprehensively considered. In other words, the rig will encounter variable environmental conditions with variations in parameters such as wave height, wave period, wind speed, air gap, and so on. A unified procedure is proposed to review the structural strength of legs, hulls, and cantilevers, and different models and analyses can be configured so that it can be solved within a unit flow-chart. Through this process, we can expect that engineering time and cost can be reduced. From survey results, it was possible to determine the inputs to examine the effects of variables, and a large jack-up rig operating under extreme environmental conditions was modeled. In the present study, the jack-up rig was operating in the North Sea, and leg length and water depth were 160 m and 100 m, respectively. The basic environmental characteristics included wave height (20 m), wave period (10 s), wind speed (30 m/s), and air gap (22 m). A parametric sensitivity analysis was performed with varying environmental parameters. Through sensitivity analysis of environmental characteristics, the significance and sensitivity of the effect of each environmental parameter on leg strength was clarified. It is expected that this will be very useful guidance about the effect of parameters during the conceptual design stage of jack-up rigs.

During welding of structure, non-uniform thermal distribution is occurred by local heating and conduction in copula. This process causes non-uniform thermal deformation and that occurs thermal stress. Especially, pipe is used in shipbuilding and laying pipe is essential. As well pipe material is applied with STS 316L (Stainless Steel) and STS Duplex(Stainless Steel Duplex) in LNG carrier ship. So welding property of that material is studied in order to predict welding deformation and thermal stress. First of all each material is made a experiment to know thermal distribution and shrinkage deformation. Through this experiment, it was possible to obtain differences in welding shrinkage due to the mechanical and thermal properties of the two materials. As a result, basic data on welding shrinkage for each material were obtained, and it will be used to develop a prediction equation through additional research in the future.

An important trend in recent ships and offshore structures is that they require high strength as well as light weight. Due to this trend, various materials are being used to replace existing carbon steel, with aluminum alloys being used frequently. In particular, this trend is conspicuous in outfitting rather than in traditional structural strength members. As a typical example, the use of aluminum alloys is increasing in helideck structures and handrails, which are tertiary components. In order to make the example structures above, welding is absolutely necessary. There are various welding methods used for aluminum alloy, with gas metal arc welding (GMAW) the most widely used. It is very important to be able to simulate welding and to predict various physical quantities of this welding technique in the production of aluminum alloy structures. In particular, welding-induced residual stresses are always generated in a structure that has been welded, and can greatly influence structural stability. Therefore, this paper proposes a method to simulate the welding phenomenon using a precise welding heat source for various aluminum alloys. Additionally, the validity of the proposed finite element (FE) analysis method is verified by measuring the residual stress of the representative aluminum alloy.