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Das B.,American Bureau of Shipping | Weinberg M.,Abs Consulting
Safety Science | Year: 2012

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.

Chen N.-Z.,Abs Consulting | Wang G.,ABS | Guedes Soares C.,University of Lisbon
Engineering Fracture Mechanics | Year: 2011

A Palmgren-Miner's rule and fracture mechanics (FM) based approach coupled with Bayesian updating in order to establish inspection plans for marine structures is proposed. A FM formulation based upon the British Standard (BS) 7910 is calibrated by S-N curves and Palmgren-Miner's rule. A model is developed taking account of the uncertainties associated with S-N curves and Palmgren-Miner's rule to quantify the random growth of a flaw predicted by the calibrated FM formulation. The long-term stress range acting on a structural component is fitted to a two-parameter Weibull distribution, according to the rules of the American Bureau of Shipping (ABS). The reliability after inspection is updated by the Bayesian approach accounting for the probability of detection (POD) and inspection results. An inspection plan is then set up on the basis of the comparison between the updated reliability and a target reliability index. Typical fatigue-prone structural details from a tanker are utilized for demonstration of the capabilities of the approach proposed. © 2011 Elsevier Ltd.

Goodno B.J.,Georgia Institute of Technology | Gould N.C.,Abs Consulting | Caldwell P.,Schneider Electric | Gould P.L.,Washington University in St. Louis
Earthquake Spectra | Year: 2011

The focus of this survey was to collect data on the performance of mechanical and electrical systems at selected critical facilities in Haiti. First-hand observations confirmed that nonstructural elements that are well anchored and=or laterally restrained will perform well during a moderate seismic event. However, the investigation also revealed that many critical institutions in Haiti did not utilize state-of-the-art engineering design or construction practices when installing nonstructural equipment that turned out to be crucial to their post-earthquake operations. The survey team believes that absent or poorly implemented seismic anchorage of nonstructural elements hampered the ability to restore essential systems to operation after the event. © 2011, Earthquake Engineering Research Institute.

Kim S.,Abs Consulting | Lee H.-H.,Hyundai Heavy Industries
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2011

This paper presents recent efforts on the fully nonlinear seakeeping analysis using the current Computational Fluid Dynamics (CFD) technology. A key objective of this study is to implement CFD analysis procedures and methodology for the fully nonlinear seakeeping analysis of a 4500 TEU class container carrier. Numerical simulations are carried out for ship motions, nonlinear structural loads, bow slamming loads and green water on deck in extreme wave condition. The nonlinear sagging and hogging moments from the CFD analysis are successfully validated with the weakly nonlinear panel method NLOAD3D. Copyright © 2011 by the International Society of Offshore and Polar Engineers (ISOPE).

Fitzgerald G.A.,Abs Consulting
49th Annual Loss Prevention Symposium 2015, LPS 2015 - Topical Conference at the 2015 AIChE Spring Meeting and 11th Global Congress on Process Safety | Year: 2015

Consequence-based Facility Siting Studies (FSSs) typically requires the user assume a credible leak size to use in the evaluation of potential releases, which is often up to a 2" diameter leak. Many facilities tend to be less complex in comparison to large refineries or petrochemical plants, leading operators at the less complex facilities to ask why they should assume the same leak sizes as more complex facilities. Other facilities have unique processes with safety systems and factors they would like to quantify in a FSS. One solution would be to perform a Quantitative Risk Assessment (QRA) to capture the risks from all potential release locations and release sizes. However, many companies have not defined risk tolerance criteria and are resistant to do so for various reasons or do not want to invest in a QRA, which are more costly than a consequence-based study. A unique approach developed by ABS Consulting and first presented in 2011 is called the Maximum Design Leak (MDL) approach [1]. This approach calculates frequency-based leak sizes and then applies the leak size that exceeds a frequency criterion (events/year) in a consequence-based FSS instead of assuming a given leak size as credible. This avoids having to establish risk criteria in terms of fatalities/year and having to model a large number of scenarios yet takes advantage of many features in a QRA. This paper presents three case studies as examples of how the MDL has been applied and illustrates the advantages of calculating leak sizes specific to scenarios being evaluated for low complexity and low risk facilities.

Barrett A.M.,Abs Consulting | Adams P.J.,Carnegie Mellon University
Risk Analysis | Year: 2011

We develop and apply an integrated modeling system to estimate fatalities from intentional release of 17 tons of chlorine from a tank truck in a generic urban area. A public response model specifies locations and actions of the populace. A chemical source term model predicts initial characteristics of the chlorine vapor and aerosol cloud. An atmospheric dispersion model predicts cloud spreading and movement. A building air exchange model simulates movement of chlorine from outdoors into buildings at each location. A dose-response model translates chlorine exposures into predicted fatalities. Important parameters outside defender control include wind speed, atmospheric stability class, amount of chlorine released, and dose-response model parameters. Without fast and effective defense response, with 2.5 m/sec wind and stability class F, we estimate approximately 4,000 (half within ~10 minutes) to 30,000 fatalities (half within ~20 minutes), depending on dose-response model. Although we assume 7% of the population was outdoors, they represent 60-90% of fatalities. Changing weather conditions result in approximately 50-90% lower total fatalities. Measures such as sheltering in place, evacuation, and use of security barriers and cryogenic storage can reduce fatalities, sometimes by 50% or more, depending on response speed and other factors. © 2011 Society for Risk Analysis.

Wakefield D.J.,Abs Consulting
International Conference on Nuclear Engineering, Proceedings, ICONE | Year: 2012

The American Nuclear Society in cooperation with the American Society of Mechanical Engineers through a Joint Committee on Nuclear Risk management (JCNRM) is developing a standard titled "Low Power and Shutdown PRA Methodology, ANSI/ANS-58.22". This LPSD Standard sets forth requirements for low power and shutdown probabilistic risk assessments (PRAs) and also requirements for shutdown qualitative risk assessment (QLRA) that can be used to support risk-informed decisions for commercial nuclear power plants. This Standard also prescribes a method for applying these requirements for specific applications. The PRA requirements in this Standard are intended to be used together with other PRA standards that cover different aspects of PRA scope. Specifically, they are intended to be used directly with the PRA Standard developed by the American Society of Mechanical Engineers (ASME) and the American Nuclear Society (ANS) ("Standard for Level 1/Large Early Release Frequency Probabilistic Risk Assessment for Nuclear Power Plant Applications," ASME-RA-Sa-2009 [1]). The ASME/ANS Combined Standard covers PRAs for both internal hazard events and external hazard events for a commercial nuclear power plant operating at full power. The PRA scope covered by the Low Power and Shutdown (LPSD) PRA Methodology Standard is limited to analyzing accident sequences initiated by "internal hazard events" or "external hazard events", excluding only internal fire hazards. Therefore, this Standard covers all potential accident initiators arising at low power and shutdown conditions, except for internal fires. The only other initiators explicitly excluded are accidents resulting from purposeful human-induced security threats (e.g., sabotage). This Standard's PRA technical requirements are presented in support of a quantitative PRA for annual average risk. For applications involving a specific outage, modifications to the technical requirements are noted. The quantitative PRA requirements in this Standard are further restricted to requirements for: (a) a full Level 1 analysis of the core damage frequency (CDF), and (b) a limited Level 2 analysis sufficient to evaluate the large early release frequency (LERF). The scope is also limited to analyzing accident sequences involving fuel while it is in the reactor vessel. Events involving fuel while it is in the spent fuel pool are not covered. All comments received on earlier drafts of the LPSD standard have been responded to and the standard adjusted accordingly. At present, these responses and revisions are being reviewed by those who offered comments. In April, 2012 the LPSD PRA Methodology Standard is being submitted to the JCNRM to determine its readiness for a formal ballot. A subcommittee of the JCNRM, consisting of persons not involved in the LPSD writing group, will perform the readiness review. The schedule for the next re-ballot will be determined in part by the outcome of this readiness review and is expected to take place later 2012. Copyright © 2012 by ASME.

Bardetsky A.,Abs Consulting
Collision and Grounding of Ships and Offshore Structures - Proceedings of the 6th International Conference on Collision and Grounding of Ships and Offshore Structures, ICCGS 2013 | Year: 2013

It is of primary importance in the aftermath of an accident to be able to assess the possibility of progressive structural failure of the damaged ship. The progressive structural failure caused by cracks emanating from the damaged area leads to a gradual reduction of the ship's residual strength, eventually leading up to the point of total hull girder collapse. This paper presents a procedure for predicting the crack propagation under sea wave loading using the fracture mechanics approach, the spectral fatigue approach and an equivalent stress intensity factor (SIF) range concept. The SIF is obtained from the finite element model of a damaged ship subjected to sea wave dynamic loading. The validity of the SIF obtained from the finite element modeling is confirmed by the independent weight function method widely used in fracture mechanics. The procedure for estimation of the crack propagation is proposed and implemented for a typical modern 170,000DWT bulk carrier in full load condition. The results of this research work can be used to support informed decision-making on the transit voyage from the accident location to the repair facility. © 2013 Taylor & Francis Group.

Kim S.,Abs Consulting
International Journal of Naval Architecture and Ocean Engineering | Year: 2011

Seakeeping analysis has progressed from the linear frequency-domain 2D strip method to the nonlinear time-domain 3D panel method. Nevertheless, the violent free surface flows such as slamming and green water on deck are beyond the scope of traditional panel methods based on potential theory. Recently, Computational Fluid Dynamics (CFD) has become an attractive numerical tool that can effectively deal with the violent free surface flows. ABS, as a classification society, is putting forth a significant amount of effort to implement the CFD technology to the advanced strength assessment of modern commercial ships and high-speed naval craft. The main objective of this study is to validate the CFD technology as a seakeeping tool for ship design considering fully nonlinear three-dimensional slamming and green water on deck. The structural loads on a large container carrier were successfully calculated from the CFD analysis and validated with segmented model test measurements. © SNAK, 2011.

Chavez J.W.,Abs Consulting
Bulletin of the International Institute of Seismology and Earthquake Engineering | Year: 2012

This paper presents an overview of the current (2011) seismic codes in Central and South America. The main aspects of the various seismic provisions of the local model building codes used in the region are presented, and briefly discussed. The issues presented include code development, site characterization, building classification, design response spectra, seismic forces and reduction factor, design considerations, construction practice and code enforcement.

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