Search

2 The most important factor in the structural design of ships and offshore structures operating in arctic region is ice load, which results from ice-structure interaction during the ice collision process. The mechanical properties of ice related to strength and failure, however, show very complicated aspect varying with temperature, volume fraction of brine, grain size, strain rate and etc. So it is nearly impossible to establish a perfect material model of ice satisfying all the mechanical characteristics completely. Therefore, in general, ice collision analysis was carried out by relatively simple material models considering only specific aspects of mechanical characteristics of ice and it would be the most significant cause of inevitable errors in the analysis. Especially, it is well-known that the most distinctive mechanical property of ice is high dependency on strain rate. Ice shows brittle attribute in higher strain rate while it becomes ductile in lower strain rate range. In this study, the simulation method of ice collision to ship hull using the nonlinear dynamic FE analysis was dealt with. To consider the strain rate effects of ice during ice-structural interaction, strain rate dependent constitutive model in which yield stress and hardening behaviors vary with strain rate was adopted. To reduce the huge amount of computing time, the modeling range of ice and ship structure were restricted to the confined region of interest. Under the various scenario of ice-ship hull collision, the structural behavior of hull panels and failure modes of ice were examined by nonlinear FE analysis technique.

함정에 사용되는 많은 탑재장비는 충격하중을 견딜 수 있도록 설계되어야 한다. 현재 우리나라 해군에서는 함정 탑재장비 및 받침대의 수중폭발에 대한 내충격 성능은 충격시험을 통하여 확 인하되, 중량과 제원 고려시 충격시험이 불가한 경우에는 이론해 석을 통하여 확인하도록 규정하고 있다. 이론해석 및 평가 방법 으로는 일반적으로 미해군의 DDAM(Dynamic Design Analysis Method)(NAVSEA)을 사용하고 있다. 그러나 DDAM은 모드중첩 법을 바탕으로 하는 선형 해석방법이기 때문에 비선형 강성특성 을 갖는 탄성마운트를 부착한 경우에는 사용할 수 없다. 따라서 최근에는 탄성마운트를 고려하기 위하여 독일의 BV043 (Federal German Army Procurement Office, 1985)에 의한 해석 방법을 사용하기도 한다. 특히 충격하의 영향이 매우 큰 탑재장비의 경우 탄성마운트를 설치하여 충격에너지를 흡수하고 함정 구조물 및 탑재장비의 안 전성을 확보할 수 있도록 설계적 조치를 취하고 있다 (Naval Sea Systems Command, 1989). Han, et al. (2011)은 함정 탑재장 비의 내충격 성능 평가를 위해 사용되는 BV043과 DDAM에 사용 되는 충격 스펙트럼을 비교 분석하였다. 탄성마운트의 개수 및 위치는 통상 많은 경험을 토대로 판단되고 배치되며, 프레임 지 지구조의 형태, 탑재장비의 중량, 중량분포의 다양성, 탄성마운 트 형태 및 적용조건에 따라 구조 응답을 고려하여 배치하여야 한다. 이러한 이유로 함정에 탑재되는 장비의 탄성마운트 배치를 위해 다양한 방법이 시도되어 왔다. Park, et al. (2001)은 확률 pISSN:1225-1143, Vol. 52, No. 4, pp. 298-304, August 2015

To ensure structural integrity of membrane type LNG tank, the rational assessment of the sloshing impact responses of tank structures should be preceded. The sloshing impact pressures acting on the insulation system of LNG tank are typical irregular loads and the resulting structural responses show very complex behaviors accompanied with fluid structure interaction. So it is not easy to estimate them accurately and immense time consuming calculation process would be necessary. In this research, a simplified method to analyse the dynamic structural responses of LNG tank insulation system under pressure time histories obtained by sloshing model test or numerical analysis was studied. The proposed technique based on the concept of linear combination of the triangular response functions which are the transient responses of structures under the unit triangular impact pressure acting on structures. The validity of suggested method was verified through the example calculations and applied to the dynamic structural response analysis of a real Mark III membrane type insulation system using the sloshing impact pressure time histories obtained by model test.

양용식 1 ·강중규 2 ·이장현 1,† ·김성찬 3 ·황세윤 1 3 Abstractinevitably introduces the residual stresses which affect the fatigue strength of the joint structure. The mitigation of fatigue strength depends on the residual stress magnitude and distribution. Stress relief analyses are of practical interest for all cyclic loaded welded structures, such as ships and offshore structures. In order to estimate the effects of relaxation of residual stresses in the welded structure, this paper presents a finite element analysis procedure and experimental results for the welded structure. Cruciform specimens joint by MAG welding have been tested to measure the released stress. Relieved welding residual stresses obtained by finite element analysis are compared with those measured by experiment.

Ship structure is composed of the welded mixture members which are plate and stiffeners. Ship structure is also influenced by variable loadings such as wave and inertia load. There have been several fatigue damage problems on the co nnection between longitudinal and transverse web due to wide usage of high tensi le steel and adoption of wide web space to improve shipbuilding productivity. It is impo ssible to estimate the fatigue lives for all connection details through refined fatigue analys is. It is necessary to use the simplified approach for the fatigue life estimation of the conn ection details. PLUS analysis, which is suggested by the classification society, is one of the simplified approaches and is widely adopted to get fatigue lives for the connection details along whole cargo hold area. However, ship building yards still have difficulties to get fat igue lives due to large amount of calculation and time even if this approach reduce the time and amount of calculation. This paper treats the computing system developed to reduce effo rts of estimating the fatigue lives. The influence factors of mean shear stress and local dynamic pressure are easily calculated and fatigue lives for all hot spots can be es timated automatically by the developed computing system. It is possible to reduce computing time and efforts to get the fatigue lives for the connection details between longitudinals and transverse webs along the ship. This system was applied to get fatigue lives on the connection details of a VLCC and verified the availability.

This paper presents a simple and fast approach to plan the arrangement of supports and to do a ship docking analysis. The unpredicted structural damages often happen from a docking works as the size of ships are getting larger and larger. In docking a ship, excessive reaction forces from supports are primary causes of the structural damage. The grillage analysis method is employed to simply calculate only the reaction forces at supports. The grillage modeling strategies are proposed to improve the accuracy. In this paper, the results obtained by the proposed approach are compared with those of the current whole-ship FEA for typical types of ships. Comparison shows that the results from the present grillage approaches are reasonably in a good agreement with the 3-D full F.E one. Finally, an integrated program developed for the ship docking analysis is described.

There are a lot of openings, holes and slots in ship structural members. It is not easy to solve the troubles around the openings adequately at the detail design stage, because there are a lot of concerning locations. There are not also clear design rules of classification societies and it is not possible to apply direct calculation for all the concerning members. Therefore, it is necessary to set up simpli fied approach such as a standard or guidance in order to decide the opening design quic kly. For this study, guidance and regulations of each classification and several companies were surveyed. Grillage analysis and the refined mesh method were used to eval uate the strength around hole considering boundary condition and more detailed member arrangement. As a result, the standard for opening design was established and verified. ※Keywords: Hole design(개구부 설계), Opening design(개구부 설계), Standard(표준), Guidance(기준), Stress Concentration factor(응력집중계수) 접수일: 2007년 10월 22일, 승인일: 2007년10월 24일 g교신저자: schankim@inhatc.ac.kr, 032-870-2171

*** Abstract A ship is composed of many grillage structures especially the deck which is consists of primary girders, transverse and longitudinal members. Several holes are arranged on these primary members for pipes, vents , etc. which cause stress conce ntration due to the discontinuity of the member. It is not easy to get the stress values around all these holes because of the huge amount of time necessary for computations. In this paper, a simple method to compute for the stress around the holes is suggested. This method is composed of two steps which are grillage analysis for primary m embers and detailed stress analysis using the results of the grillage analysis. This method is made for the design of the primary members with openings supporting the deck structure.

The present study investigates the fire development characteristics on a Ro-Ro ferry vehicle using the modified FDS code considering droplet break-up. Numerical simulations are compared with model-scale tests for validation of field model. The predicted results such as smoke layer temperature and oxygen concentration are in good agreement with model-scale tests. Also, it is shown that water spray systems are very effective to control the fire development on a vehicle deck. These numerical simulations using a field model may be helpful in accomplishing the fire safety for marine vehicle.