• Title/Summary/Keyword: Accidental limit state

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Risk Based Accidental Limit State Evaluation on Explosion Accident at Shale Shaker Room of Semi-Submersible Drilling Rig (반잠수식 시추선의 Shale Shaker Room 폭발 사고에 대한 위험도 기반 사고한계상태 평가)

  • Yoo, Seung-Jae;Kim, Han-Byul;Park, Jin-Hoo;Won, Sun-Il;Choi, Byung-Ki
    • Special Issue of the Society of Naval Architects of Korea
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    • 2015.09a
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    • pp.69-73
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    • 2015
  • An evaluation of the accidental limit state (ALS) for design of a semi-submersible drilling rig is one of the essential design requirements as well as ultimate limit state (ULS) and fatigue limit state (FLS). This paper describes the ALS evaluation on the explosion accident at shale shaker room of semi-submersible drilling rig. There are three steps for the ALS evaluation such as structural analysis at concept design, risk based safety design and structural analysis at detailed design. For the ALS evaluation at concept design, conceptual explosion overpressure from the Rule guided by the classification society was used in the structural analysis that was carried out using LS-DYNA. To set up the design accidental load (DAL), explosion analysis was carried out using FLACS taking safety barriers into consideration. Then, the structural analysis was carried out applying DAL for the ALS evaluation at detailed design. Through the ALS evaluation on the explosion at shale shaker room, the importance of the risk based safety design was described.

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Role of accidental torsion in seismic reliability assessment for steel buildings

  • Chang, Heui-Yung;Lin, Chu-Chieh Jay;Lin, Ker-Chun;Chen, Jung-Yu
    • Steel and Composite Structures
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    • v.9 no.5
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    • pp.457-471
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    • 2009
  • This study investigates the role of accidental torsion in seismic reliability assessment. The analyzed structures are regular 6-story and 20-story steel office buildings. The eccentricity in a floor plan was simulated by shifting the mass from the centroid by 5% of the dimension normal to earthquake shaking. The eccentricity along building heights was replicated by Latin hypercube sampling. The fragilities for immediate occupancy and life safety were evaluated using 0.7% and 2.5% inter-story drift limits. Two limit-state probabilities and the corresponding earthquake intensities were compared. The effect of ignoring accidental torsion and the use of code accidental eccentricity were also assessed. The results show that accidental torsion may influence differently the structural reliability and limit-state PGAs. In terms of structural reliability, significant differences in the probability of failure are obtained depending on whether accidental torsion is considered or not. In terms of limit-state PGAs, accidental torsion does not have a significant effect. In detail, ignoring accidental torsion leads to underestimates in low-rise buildings and at small drift limits. On the other hand, the use of code accidental eccentricity gives conservative estimates, especially in high-rise buildings at small drift limits.

Reliability Assessments and Design Load Factors for Reinforced Concrete Containment Structures of Nuclear Power Plant

  • Han, Bong-Koo
    • Nuclear Engineering and Technology
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    • v.29 no.6
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    • pp.444-450
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    • 1997
  • The current ASME code for reinforced concrete containment structures are not based on probability concepts. The stochastic nature of natural hazard or accidental loads and the variations of material properties require a probabilistic approach for a rational assessment of structural safety and performance. The paper develops design load factors for the serviceability limit state of reinforced concrete containment structures. The target limit state probability is determined and the load factors are calculated by the numerical analysis. Design load factors are proposed and carried out the reliability assessments.

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A Study on the Design Concept and Simplified Analysis Method in Dropped Object Accidents by Lifting Crane (크레인 중량물 낙하사고에 대응한 설계개념과 간이 해석법에 대한 연구)

  • Kim, Ul-Nyeon;Kim, Han-Byul
    • Journal of the Society of Naval Architects of Korea
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    • v.56 no.3
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    • pp.251-262
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    • 2019
  • This paper is about design concept and simplified analysis method against dropped object events. The ships and offshore structures are exposed to various types of dropped object accidents such as laydown area struck by drill collar and topside deck hit by food container during their lifetime. Mitigation can be accomplished by proper facility layout and designing structures to safely absorb energy from accidental loads. It shall be designed to avoid loss of life, environmental pollution and loss of assets. Impact loads can lead to structural global collapse of the main structure or punching of a local barrier type structure with potential to escalate directly or indirectly to a global collapse of the structure. This study provides the background information on the issue of dropped object of the shipyard and also focuses on structural assessment of the local individual component such as deck plate, stiffener and web/girder by using simplified analysis method. The results of the simplified analysis method were compared with numerical results using non-linear finite element simulation.

On the structural behavior of ship's shell structures due to impact loading

  • Lim, Hyung Kyun;Lee, Joo-Sung
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.10 no.1
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    • pp.103-118
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    • 2018
  • When collision accident between ships or between ship and offshore platform occurs, a common phenomenon that occurs in structures is the plastic deformation accompanied by a large strain such as fracture. In this study, for the rational design against accidental limit state, the plastic material constants of steel plate which is heated by line heating and steel plate formed by cold bending procedure have been defined through the numerical simulation for the high speed tension test. The usefulness of the material constants included in Cowper-Symonds model and Johnson-Cook model and the assumption that strain rate can be neglected when strain rate is less than the intermediate speed are verified through free drop test as well as comparing with numerical results in several references. This paper ends with describing the future study.

Reliability Analysis Method for Concrete Containment Structures (콘크리트 차폐(遮蔽) 구조물(構造物)의 신뢰성(信賴性) 해석방법(解析方法))

  • Han, Bong Koo;Chang, Sung Pil
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.10 no.1
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    • pp.9-16
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    • 1990
  • The safety of concrete nuclear containment structures should be secured against all kinds of loading due to various natural disasters or extraordinary accidental loads. The current design criteria of concrete containment structures are not based on the reliabillty-based design concept but rely on the conventional design concept. In this paper, a probabillty-based reliability analysis were proposed based on a FEM-based random vibration analysis and serviceability limit state of structures. The limit state model defined for the study is a serviceability limit state in terms of the more realistic crack failure that might cause the emission of radioactive materials, and the results are compared with those of the strength limit state. More accurate reliability analyses under various dynamic loads such as earthquake loads were made possible by incorporation the FEM and random vibration theory, which is different from the conventional reliability analysis method. The uncertainties in loads and resistance available in Korea and the refernces were adapted to the situation of Korea, and especially in the case of earthquake, the design earthquake was assessed based on the available re ports on probabilistic description of earthquake ground acceleration in the Korea peninsula.

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Collision-Damage Analysis of a Floating Offshore Wind Turbine Considering Ship-Collision Risk

  • Young-Jae Yu;Sang-Hyun Park;Sang-Rai Cho
    • Journal of Ocean Engineering and Technology
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    • v.38 no.3
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    • pp.124-136
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    • 2024
  • As the number of offshore wind-power installations increases, collision accidents with vessels occur more frequently. This study investigates the risk of collision damage with operating vessels that may occur during the operation of an offshore wind turbine. The floater used in the collision study is a 15 MW UMaine VolturnUS-S (semi-submersible type), and the colliding ships are selected as multi-purpose vessels, service operation vessels, or anchor-handling tug ships based on their operational purpose. Collision analysis is performed using ABAQUS and substantiation is performed via a drop impact test. The collision analyses are conducted by varying the ship velocity, displacement, collision angle, and ship shape. By applying this numerical model, the extent of damage and deformation of the collision area is confirmed. The analysis results show that a vessel with a bulbous bow can cause flooding, depending on the collision conditions. For damage caused by collision, various collision angles must be considered based on the internal stiffener arrangement. Additionally, the floater can be flooded with relatively small collision energy when the colliding vessel has a bulbous bow.

On the Derivation of Material Constants Associated with Dynamic Behavior of Heat Formed Plates (열성형 판 부재의 동적거동에 관련된 재료상수 산출에 관한 연구)

  • Lee, Joo-Sung;Lim, Hyung-Kyun
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.29 no.2
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    • pp.105-114
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    • 2016
  • When impact load is applied to a plate structure, a common phenomenon that occurs in structures is plastic deformation accompanied by a large strain and eventually it will experience a fracture accordingly. In this study, for the rational design against accidental limit state, the plastic material constants of steel plate which is formed by line heating and by cold bending procedure have been defined through the numerical simulation for the high speed tension test. The usefulness of the material constants included in Cowper-Symonds model and Johnson-Cook model with the assumption that strain rate can be neglected when strain rate is less than the intermediate speed is verified through comparing the present numerical results with those in references. This paper ends with describing the future study.

Comparison Study of the Impact Response Characteristics of Fixed Cylindrical Offshore Structures Considering Seawater Fluid Region (해수유체영역을 고려한 고정식 실린더형 해양구조물의 충격응답특성 비교연구)

  • Lee, Kangsu;Hong, Keyyong
    • Journal of Advanced Marine Engineering and Technology
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    • v.39 no.4
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    • pp.489-494
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    • 2015
  • This research focused on minimizing the response of fixed cylindrical offshore structures to a ship impact considering the seawater fluid part. A collision between a ship and offshore structure is generally a complex problem and it is often impractical to perform rigorous finite element analyses to include all the effects and sequences during the collision. The structural behavior of a fixed cylindrical type offshore substructure with a seawater fluid part has a simpler response and small deformation due to the dissipation of impact energy. Upon applying the impact force of a ship to the cylindrical structure, the maximum acceleration, internal energy, and plastic strain are calculated for each load cases using Ls-dyna finite element software. In the maximum cases 2.0 m/s velocity, the response result for the structure was carried out to compare between having a fluid region and no fluid region. Fluid-structure interaction analysis was performed using the ALE method, which make it possible to apply a fluid region on the impact problem. The case of a fixed cylindrical type offshore structure without a seawater fluid part can be a more conservative design.