For large ships and offshore vessels, structural safety is verified through whole-ship analysis using commercial software. In the case of general oil tankers, classification rules for structural ...strength evaluation are uniformly applied. Structural strength evaluation is mainly divided into the cargo hold, fore-end, and aft-end parts. For the structural design of a cargo ship, it is important to calculate the design load and determine the thickness and size of the structural member. Structural FEA (Finite Element Analysis) is performed on only the cargo hold range as recommended by the CSR (Common Structure Rule). There is no FE analysis recommendation for either the aft- or the fore-end area. Therefore, structural safety is carried out based on existing design experience and engineer judgment. With previous approaches, it is difficult to clarify the safety of the aft-end part according to external loads such as hull girder load and local pressure. Recently, local buckling damage cases have investigated the aft-end of the shuttle tanker. Although this is a good example, it can be recognized that it is necessary to improve the accuracy of prediction when estimating the structural safety at the aft-end part. In this study, a novel FE-based evaluation methodology about buckling damage is proposed. In order to conduct a structural strength verification based on FE analysis modeling, reasonable solutions for load conditions, boundary conditions, modeling methods, and evaluation criteria are presented. This result is expected to be helpful in examining the structural strength of the aft-end part of similar carriers in the future.
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.
As the demand for eco-friendly energy increases, the offshore wind power generation sector is showing rapid growth. As offshore wind turbines become larger, the need for specialized installation ...vessels is becoming a more crucial issue. Wind turbine installation vessels (WTIV) require a necessary pre-loading process where the legs and spudcans are penetrated into the seabed to secure stability during installation. Due to these operational characteristics, the installation work can be completed safely when safe pre-loading is finished. Analyzing previous structural collapse accidents investigated by HSE, 53% of them were punch-through problems related to the seabed, which occurred with a high frequency. Therefore, these lead to major accidents, which is a very high-risk problem. In this study, we investigated and analyzed the punch-through accident cases, and a WTIV model with six legs was applied to numerically examine the maximum vertical reaction force variation when punch through occurs for each leg. The maximum vertical reaction force takes place in leg number three when a punch through occurs in leg number five and maximum stress exceeds the allowable criteria in both hull and legs. This requires proper structural reinforcement such as an increase in the thickness and change in the high-yield stress. The key results of this investigation can be used to determine the basic specifications of wind turbine installation vessels, and the reaction force distribution pattern can be used as fundamental data for leg and hull structural design.
•Interreader agreement for presence of ILA based on the Fleischner society guideline was substantial (κ, 0.74).•Interreader agreement for the subtype of ILA was only fair (κ, 0.38).•The deep ...learning-based quantitative system for ILA was able to identify ILA despite the use of various CT protocols.•Automated quantification tool dedicated for ILA in routine clinical practice may aid in objectively identifying ILA by accurately quantifying the extent of ILA per zonal volume.
We aimed to evaluate the performance of a fully automated quantitative software in detecting interstitial lung abnormalities (ILA) according to the Fleischner Society guidelines on routine chest CT compared with radiologists’ visual analysis.
This retrospective single-centre study included participants with ILA findings and 1:2 matched controls who underwent routine chest CT using various CT protocols for health screening. Two thoracic radiologists independently reviewed the CT images using the Fleischner Society guidelines. We developed a fully automated quantitative tool for detecting ILA by modifying deep learning-based quantification of interstitial lung disease and evaluated its performance using the radiologists’ consensus for ILA as a reference standard.
A total of 336 participants (mean age, 70.5 ± 6.1 years; M:F = 282:54) were included. Inter-reader agreements were substantial for the presence of ILA (weighted κ, 0.74) and fair for its subtypes (weighted κ, 0.38). The quantification system for identifying ILA using a threshold of 5 % in at least one zone showed 67.6 % sensitivity, 93.3 % specificity, and 90.5 % accuracy. Eight of 20 (40 %) false positives identified by the system were underestimated by readers for ILA extent. Contrast-enhancement in a certain vendor and suboptimal inspiration caused a true false-positive on the system (all P < 0.05). The best cut-off value of abnormality extent detecting ILA on the system was 3.6 % (sensitivity, 84.8 %; specificity 92.4 %).
Inter-reader agreement was substantial for ILA but only fair for its subtypes. Applying an automated quantification system in routine clinical practice may aid the objective identification of ILA.
As interest in eco-friendly energy development continues to rise, the offshore wind turbine market is growing at a high rate of increase every year. In line with this, the demand for installation ...vessels with large capacity is also increasing rapidly. WTIVs (Wind Turbine Installation Vessels) employ spudcans in the seabed for the installation of wind turbines. Currently, the assessment of spudcans is an important issue in ensuring structural safety in the entire structure system. This study examines the current procedure suggested by classification societies and a new procedure that accounts for the new loading scenarios based on realistic operating conditions. This new procedure is further validated through an FEA (Finite Element Analysis). The current procedure yields maximum stress values below the allowable criteria because it does not consider the effect of the seabed slope, the leg bending moment, and the spudcan shape. However, the results of some load conditions as defined in the new procedure confirm the need for reinforcement under actual preload conditions. Therefore, the new procedure considers a broader range of real-world operating conditions, and the possible problems were verified through a detailed FEA.
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.
Recently, shipyards have been booming in the product carrier (PC) market of the global shipbuilding industry. Due to the rising market conditions, orders for large container vessels and PCs are also ...steadily increasing. According to the industry, freight rates for LR tankers (70K) and MR tankers (50K) in the shipbuilding industry have rose to the highest level during the previous year. In order to secure the competitiveness of PCs, various core items are required, and Korean shipbuilders have been leading the market for a long time based on their knowledge of the design and production of low-fuel ships. In recent years, there have been frequent cases of coating cracks in the cargo hold after sea trial. All relevant rules presented by the classification so far are structural design, safety evaluation, and inspection standards, and coating cracks are considered a problem for coating makers. In other words, they must establish a standard coating measure agreed upon by all parties (owner, shipbuilder, and coating maker); therefore, solutions have been proposed by each shipping company. In this study, the causes of coating cracks occurring in the cargo hold of PCs during tank tests in sea trials were analyzed and measures to prevent them were studied. The main point of this study is assumed that coating crack are caused by mechanical load induced by structural behavior, and the numerical analysis methodology is newly introduced. Based on the results of the numerical analysis, it was confirmed that there is a high probability of coating cracks in the critical area where high stress occurs in the cargo hold. Therefore, the results obtained in this study will be useful to prevent coating cracks in future PC designs.
In recent years, oil and gas pipes and risers in deep sea reservoirs are required to have high resistance to collapse. This paper reports the comprehensive investigation of the residual stress ...distributions in a recently developed seam-welded offshore gas transmission riser of high-strength steel. Experimental hole drilling methods are applied to understand the residual stress distribution in the real scaled riser. Then, FE modelling on double-V groove is performed for a systematic parametric residual stress analysis of the riser components with consideration of parameters including the ratio of component radius to wall thickness (r/t), joint preparation, pass size, and heat input. Through the use of a residual stress decomposition technique, the thickness-through-thickness residual stress is partitioned into membrane and bending stresses. According to the results of the parametric study, a method for prediction of residual stress in circumferential direction is developed based on simplified empirical formulas for existing riser configurations with varying welding conditions.
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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