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Houston, TX, United States

The American Bureau of Shipping is a classification society, with a mission to promote the security of life, property and the natural environment, primarily through the development and verification of standards for the design, construction and operational maintenance of marine-related facilities. At the end of 2012, ABS was the second largest class society with a classed fleet of nearly 12,000 commercial vessels and offshore facilities.ABS' core service is the provision of classification services through the development of standards called ABS Rules. These Rules form the basis for assessing the design and construction of new vessels and the integrity of existing vessels and marine structures. Wikipedia.

Gaspar B.,University of Lisbon | Teixeira A.P.,University of Lisbon | Guedes Soares C.,University of Lisbon | Wang G.,American Bureau of Shipping
Marine Structures

The present study aims at applying structural reliability methods to assess the implicit safety levels of the buckling strength requirements for longitudinal stiffened panels implemented in the IACS Common Structural Rules (CSR) for double hull oil tankers. The buckling strength requirements considered are used in the initial stage of the hull girder scantlings' design to control the buckling capacity of longitudinal stiffened panels subjected to the compressive loads induced by the hull girder vertical bending. The following buckling collapse failure modes are explicitly considered in the design formulation: uniaxial buckling of the plating between stiffeners, column buckling of stiffeners with attached plating and lateral-torsional buckling or tripping of stiffeners.The paper presents the procedure used to assess the implicit safety levels of the strength requirements for the three buckling collapse failure modes above mentioned, which includes the optimization of the scantlings of the plate panels and longitudinal stiffeners in order to reflect the minimum strength required by the formulation. A first order reliability formulation is adopted, and stochastic models proposed in the literature are used to quantify the uncertainty in the relevant design variables. A sample of five oil tankers representative of the range of application of the IACS-CSR design rules is considered. The effect of corrosion in the implicit safety levels is quantified based on the three corrosion levels of the Net Thickness Approach (NTA) adopted in the design rules. Sensitivity analyses are also performed to quantify the relative contribution or importance of each design random variable to the implicit safety levels. © 2011 Elsevier Ltd. Source

Ivanov L.D.,American Bureau of Shipping
Marine Technology and Engineering

The procedure in class rules for control of ship's hull girder strength is followed but all parameters are presented in probabilistic format. The effect of corrosion wear on hull girder geometric properties is considered in probabilistic terms. A procedure is then proposed for the probabilistic presentation of the still water and wave-induced hull girder hogging and sagging loads as a single phenomenon. Lastly, the rules of the composition law of the constituent variables are used to build the probabilistic distribution of the total hull girder load and the corresponding total hull girder bending stresses. Thus, it becomes possible to calculate the probability of exceeding any given limit of the total hull girder stresses. © 2011 Taylor & Francis Group, London. Source

Lokshin A.Z.,Saint Petersburg State University | Ivanov L.D.,American Bureau of Shipping | Mishkevich V.,StreamLine
Ships and Offshore Structures

An analytical method for control of the strength of a grillage (gross panel) under unidirectional in-plane axial load is proposed. It allows us to solve the following tasks: (i) calculation of the critical stiffness of transverse girders, (ii) calculation of the maximum unidirectional in-plane compression load when the structure's scantlings are known (iii) and calculation of the required structure's scantlings when the unidirectional in-plane compression load is given. The proposed procedure is helpful in the application of probabilistic methods without employing specialised computer programmes, which is an advantage when fast (although approximate) evaluation is needed for the grillage critical buckling strength (e.g. ship's deck structure) before applying the finite-element method (FEM) analysis. Results of analytical approach are compared and confirmed using FEM data. A probabilistic method for control of the strength of ship's deck structure under unidirectional in-plane axial load is proposed. It allows us to assess the effect of deterioration due to corrosion on the deck's buckling strength while avoiding the use of specialised computer programmes. © 2013 Taylor & Francis. Source

Ivanov L.D.,American Bureau of Shipping
Ships and Offshore Structures

The paper presents a study on an approximate semi-probabilistic approach for assessment of any given requirement for minimum hull girder section modulus (HGSM). It consists of calculating the HGSM using as input data the reduced (due to corrosion) plates' thicknesses and longitudinals' cross-sections with exactly the same probability of exceedance. Its accuracy is checked against results obtained by the complete probabilistic approach developed by the author. In this paper, the requirement for minimum HGSM is based on the IMO (International Maritime Organization)-formulated permissible reduction by 10% of the as-built HGSM. A numerical example is given for a bulk carrier of 25,000 deadweight ton (25K DWT). A comparison between the results obtained by the complete probabilistic method and those obtained by the semi-probabilistic method showed that the accuracy of the semi-probabilistic method is around +8% when the 95th percentile of the corrosion wastage of plates and longitudinals is used, and around -2% when the 99th percentile of the corrosion wastage of plates and longitudinals is used. The semi-probabilistic approach is simpler than the complete probabilistic approach but has relatively high accuracy, especially for higher-order percentiles, and thus is recommended for practical use. © 2013 Copyright Taylor and Francis Group, LLC. Source

Das B.,American Bureau of Shipping | Weinberg M.,Abs Consulting
Safety Science

Presence of congestion and confinement in offshore modules due to limited availability of space make Vapor Cloud Explosions (VCEs) a significant contributor to risk. There are several methods available for quantifying the blast overpressure generated over distances and time. The approaches range from one-dimensional analysis using correlation models to 3-D analysis using Computational Fluid Dynamics (CFDs). The correlation models are easy to use and well-suited for assessing a number of credible VCE scenarios. However, the overpressure results predicted by correlation models depend on a good estimate of flammable mass. This paper proposes a method to improve the estimation of flammable mass. The UKOOA Ignition model developed by the Energy Institute London is used to estimate the flammable mass; and is modified to account for the effect of mitigation measures on release rate. A directional probability for wind is also added to the model. The proposed model takes into consideration the platform geometry and offshore conditions for each scenario, release location and direction, and wind direction. An offshore production platform with three deck levels is presented as an example case. The flammable mass is also computed using CFD and the results are compared to that of the proposed and the conventional methods. The results show that the flammable masses for selected scenarios are better estimated by the proposed method, being much lower than estimated by the conventional method, though larger than the CFD results. This paper presents an interim result of a project undertaken to improve QRA studies for VCE events. © 2012 Elsevier Ltd. Source

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