Unstiffened and stiffened cylindrically curved plates are often used in ship structures. For example, they can be found on a deck with a camber, a side shell at the fore and aft parts, and the ...circular bilge part of a ship structure. It is believed that such cylindrically curved plates can be fundamentally modelled using a portion of a circular cylinder. From estimations using cylindrically curved plate models, it is known that the curvature generally increases the buckling strength compared to a flat plate under axial compression. The existence of curvature is also expected to increase both the ultimate and buckling strengths. In the present study, a series of finite element analyses were conducted on stiffened curved plates with several varying parameters such as the curvature, panel slenderness ratio, and web height and type of stiffener applied. The results of numerical calculations on stiffened and unstiffened curved plates were examined to clarify the influences of such parameters on the characteristics of their buckling/plastic collapse behavior and strength under an axial compression.
Mineral wool is an insulation material commonly used in passive fire protection (PFP) systems on offshore installations. Insulation materials have only been considered functional materials for ...thermal analysis in the conventional offshore PFP system design method. Hence, the structural performance of insulation has yet to be considered in the design of PFP systems. However, the structural elements of offshore PFP systems are often designed with excessive dimensions to satisfy structural requirements under external loads such as wind, fire and explosive pressure. To verify the structural contribution of insulation material, it was considered a structural material in this study. A series of material tensile tests was undertaken with two types of mineral wool at room temperature and at elevated temperatures for fire conditions. The mechanical properties were then verified with modified methods, and a database was constructed for application in a series of nonlinear structural and thermal finite-element analyses of an offshore bulkhead-type PFP system. Numerical analyses were performed with a conventional model without insulation and with a new suggested model with insulation. These analyses showed the structural contribution of the insulation in the structural behaviour of the PFP panel. The results suggest the need to consider the structural strength of the insulation material in PFP systems during the structural design step for offshore installations.
In this study, the development of the R–D diagram taking into account the time-dependent corrosion wastage effect is presented to identify the necessity of applying the time-dependent corrosion ...wastage on R–D diagram. The R–D (Residual strength–Damage index) diagram was proposed by Paik et al. (2012) and is an innovative method relating to safety assessment for damaged structures; its feasibility has been confirmed by a previous study concerning double hull oil tankers under grounding damage. Generally, as a result of corrosion, the structural capacity of ships and offshore structures should be decreased in parallel with the operational period. Therefore, an Aframax class double hull oil tanker that has sustained grounding damages and also corrosion with a time-dependent corrosion wastage model (13 years, 19 years and 25 years (net scantlings specified by CSR)) applied to gross (new-built) scantlings is analyzed by the ALPS/HULL progressive hull girder collapse analysis program. Based on the obtained results, the time-dependent R–D diagram is produced and compared with the original R–D diagram. Finally, for practical purposes, empirical formulas based on time-dependent R–D diagrams are proposed to evaluate the residual ultimate longitudinal strength of the corroded Aframax class double hull oil tanker under grounding damage. The proposed time-dependent R–D diagrams will be useful for assessing the first-cut safety evaluation for a ship that has sustained grounding damages under different operational periods.
•The difference between previously developed R–D diagram and other R–D diagrams is identified.•Time-dependent R–D diagram is proposed.•In case of tanker, time-dependent corrosion damage should be considered.
Subsea manifolds are widely used in the development of oil and gas fields to simplify the subsea system, minimise the number of subsea pipelines/risers and optimise the flow path in a piping system. ...The piping system is designed to satisfy the requirements for internal pressure, thermal loads, hydrostatic collapse and external operational loads under extreme environmental conditions. At present, however, there are no efficient and well-defined design procedures available that accurately predict the effects of extreme environmental conditions on pressure drop, total deformation, weight and erosion characteristics given varying design parameters considered throughout the piping system. Therefore, it is necessary to develop an new design procedure for subsea manifold piping systems with complicated shapes capable of sustaining erosion inside the piping system. The aim of this study is to develop a design procedure for subsea manifold piping systems based on a variety of parameters of influence under extreme environmental conditions, including high pressure and high temperature. A detailed numerical analysis of nonlinear finite element method and finite volume method is conducted to develop the proposed design procedure based on the results of parametric studies and generates some recommendations for the design of optimal subsea manifold piping configuration systems. The design procedure presented here will assist the design and analysis of subsea manifold piping systems.
•Proposed an efficient design procedure for subsea manifold piping systems.•Provided of a detailed numerical analysis (FEM and FVM) based parametric study.•Recommendations for the design of optimal subsea manifold piping systems.
The rapid proliferation of oil/gas drilling and wind turbine installations with jack-up rig-formed structures increases structural safety requirements, due to the greater risks of operational ...collisions during use of these structures. Therefore, current industrial practices and regulations have tended to increase the required accidental collision design loads (impact energies) for jack-up rigs. However, the existing simplified design approach tends to be limited to the design and prediction of local members due to the difficulty in applying the increased uniform impact energy to a brace member without regard for the member’s position. It is therefore necessary to define accidental load estimation in terms of a reasonable collision scenario and its application to the structural response analysis. We found by a collision probabilistic approach that the kinetic energy ranged from a minimum of 9 MJ to a maximum 1049 MJ. Only 6% of these values are less than the 35 MJ recommendation of DNV-GL (2013). This study assumed and applied a representative design load of 196.2 MN for an impact load of 20,000 tons. Based on this design load, the detailed design of a leg structure was numerically verified via an FE analysis comprising three categories: linear analysis, buckling analysis and progressive collapse analysis. Based on the numerical results from this analysis, it was possible to predict the collapse mode and position of each member in relation to the collision load. This study provided a collision strength assessment between attendant vessels and a jack-up rig based on probabilistic collision scenarios and nonlinear structural analysis. The numerical results of this study also afforded reasonable evaluation criteria and specific evaluation procedures.
Ships, ship-shaped offshore structures, land-based structures and aerospace structures typically consist of various curved plate components. It is difficult to simulate the buckling and post-buckling ...of curved thin and/or thick plates that have characteristics of nonlinear structural mechanics, such as nonlinear behaviour when loading is applied. The elastic post-buckling behaviour of a curved plate is very complex, and accompanied by mode changes due to the occurrence of secondary buckling behaviour. Therefore, it is very important to clarify the elastic post-buckling behaviour when subjected to axial loading. The aim of this study was to derive an analytical calculation based on the formulation of the total potential energy, and a mathematical solution to simulate the elastic buckling and post-buckling behaviour of cylindrically curved plates under axial compression. The accuracy of the proposed method with the aforementioned modelling techniques was verified through comparison with finite element analyses of various curved plate configurations.
The present paper is Part III of a series of three papers on the methods useful for ultimate limit state assessment of ships and ship-shaped offshore structures. It is focused on the methods for the ...progressive collapse analysis of hull girders under bending moments, in contrast to the previous two papers (Parts I and II), respectively, dealing with methods for the ultimate limit state assessment of unstiffened plates and stiffened panels. An AFRAMAX-class hypothetical double hull oil tanker structure designed by IACS common structural rules (CSR) method is studied as an illustrative example. The ultimate vertical bending moment capacity of the hull structure is then analyzed by ANSYS FEA, ALPS/HULL, and IACS CSR methods, and their resulting computations are compared.
Aluminium outfitting is widely used in offshore platforms owing to its anti-corrosion ability and its light weight. However, various standards exist (ISO, NORSOK and EN) for the design of handrails ...used in offshore platforms, and different suppliers have different criteria. This causes great confusion for designers. Moreover, the design load required by the standards is not clearly defined or is uncertain. Thus, many offshore projects reference previous project details or are conservatively designed without additional clarification. In this study, all of the codes and standards were reviewed and analysed through prior studies, and data on variable factors that directly and indirectly affect the handrails applied to offshore platforms were analysed. A total of 50 handrail design load scenarios were proposed through deterministic and probabilistic approaches. To verify the proposed new handrail design load selection scenario, structural analysis was performed using SACS (offshore structural analysis software). This new proposal through deterministic and probabilistic approaches is expected to improve safety by clarifying the purpose of the handrails. Furthermore, the acceptance criteria for probabilistic scenarios for handrails suggest considering the frequency of handrail use and the design life of offshore platforms to prevent excessive design. This study is expected to prevent trial and error in handrail design while maintaining overall worker safety by applying a loading scenario suitable for the project environment to enable optimal handrail design.
Welding often results in welding distortion during the assembly process. The welding distortion of thin-plate structures such as the living quarters of ships and offshore installations is a more ...significant problem than in the case of thick-plate structures. Pre-stressing/heating and fairing, which are additional works to mitigate and control welding distortion, are inevitable, and the construction planning is accordingly delayed. In order to prevent welding distortion and minimize the additional work during the assembly process, increasing the plate thickness and/or the number of stiffeners may be a simple solution, but it may give rise to problems related to cost and weight. In this study, the welding distortion control effect of the type of stiffeners on the door openings of various living quarter structures was investigated using an experimental method and a finite element method. The results showed the feasibility of mitigating and controlling the welding distortion, and the optimum selection of the type of stiffeners was confirmed.
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