This work reports the results of a numerical investigation aiming at assessing the structural safety of an actual offshore topside steel structure exposed to accidental localised fire conditions. ...Particularly, the paper explores the nonlinear thermomechanical and ultimate strength behaviours obtained by means of two fire approaches: sophisticated CFD (Computational Fluid Dynamics) and “LF-ESF” (Localised Fire with Ellipsoidal Solid Flame), previously developed and validated by the authors. CFD-based approaches, which typically solve nearly compressible flow with input energy given by a combustion model, allow accurate evaluation of a fluid-thermo response for the entire duration of the simulated accident. However, the analysis complexity, massive amount of produced data, excessive computational and time-consuming make CFD approaches unsuitable for the current applied design usage. On the other hand, the proposed LF-ESF approach displays quite accurate estimates in comparison to CFD counterparts. Moreover, the LF-ESF can be directly modelled in FE-based commercial software and used to obtain the steel temperature variation and thermomechanical behaviour. The obtained results indicate that the LF-ESF approach combined with FE-based models can provide reliable fire-safety analyses, ensuring that the main safety (load-bearing) functions of the offshore steel structures are not impaired during accidental fire conditions.
•One-way coupling localized fire simulations through CFD-FEM and Localised Fire with Ellipsoidal Solid Flame approaches.•Thermomechanical analyses of localized fires scenarios in offshore topside steel structures through sophisticated models.•The failure mechanisms with and without fire scenarios were investigated.•Unlike conventional methods based on the uniform heating assumption, the LF-ESF method considers the thermal gradient.
•Three-dimensional reconstruction of imperfect experimental specimens is presented.•The implementation of a light longitudinal stiffener in corroded panels to recover the load capacity is ...investigated.•The performance of the corroded and repaired panel is compared for different loading conditions.
Hull plating thickness reduction due to corrosion generates a significant decrease in the structure ultimate load capacity, which may compromise the vessel’s integrity. In offshore oil and gas production units demobilization to a shipyard is unfeasible, so reparation must be performed locally and efficiently. This article presents an experimental - numerical investigation to assess the performance of an alternative in situ repair methodology for FPSO mid-ship corroded side panels subjected to common types of loads. The repair technique consists in the inclusion, with a single-pass welding, of an intermediate light longitudinal steel stiffener on the plating exposed to considerable thickness reduction, to reestablish the load carrying capacity, thus extending its operational life. A set of nine mid-ship panels of a VLCC (very large crude carrier) converted into an FPSO (floating production storage and offloading) platform, on a scale of 1:3.5, are fabricated and subjected to uniaxial compression. The panels portray the corrosion free intact condition, two levels of thickness reduction (25% and two with 58%) and two repair light stiffener profile dimensions for each level of thickness loss. A finite element model (FEM) is developed and firstly employed to compare and validate the experimental results for uniaxial compression. The FEM is subsequently employed to evaluate other typical loading combinations encountered in hull structures, including lateral pressure, uniaxial compression and shear stresses. The results show that the inclusion of an intermediate light longitudinal steel stiffener may satisfactorily restore the plate and consequently the panel load carrying capacity, allowing additional hull plating thickness reduction.
This paper presents a numerical - experimental research to evaluate the effect of corrosion in panels subjected to uniaxial compression and subsequent repair. The effects of corrosion are ...approximated by a uniform reduction in the plating's thickness. Currently, repairing a corroded offshore structure involves the change of the hull plating, which is excessively expensive and, therefore, other alternatives should be investigated in order to extend its useful life. The experimental study considers a set of five panels with an average scale of 1:3.5, representing a typical intact panel of a VLCC (Very large Crude Oil Carrier) converted into a FPSO (Floating Production Storage and Offloading) platform and two different plating reduction thickness levels. These experiments are reproduced through a numerical model that considers geometric and material nonlinearities. The geometrical imperfections in the surfaces of plates and stiffeners are reconstructed from measurements using techniques of laser scanning and optical capture. Thickness distributions are measured with an ultrasonic sensor in several predetermined panel sections points. True stress vs true strain curves for all panel's elements are obtained by tensile tests and employed in the numerical model. Once the numerical model is validated, the effect of the axial load eccentricity, the supported element load redistribution due to changes in the thickness, and the effects of the inclusion of intermediate repair on the plate are studied. The results show that the inclusion of an intermediate light stiffener allows recovering the panel load capacity and prolonging the useful life of offshore platforms. Likewise, it is concluded that the selection of the repair should be based on the local strength recovery of the plate, which is most affected.
•Three-dimensional reconstruction of imperfect experimental specimens through two different methodologies is presented.•The plating thickness reduction on the ultimate load of stiffened panels is evaluated.•A light longitudinal stiffener is introduced to recover the panel's strength.•The load supported by each panel component (plating and stiffeners) is individually presented.
This paper presents a model to evaluate the thermal energy transfer between a localized fire and the surfaces exposed to it, without the flame impinging the ceiling of the semi-open compartment. ...Although this type of fire may not have significant consequences for the structure as a whole, it is capable of triggering other disasters such as explosions and larger fires, which is why its study becomes increasingly important. Currently, this accident is analyzed using either sophisticated or semi-empirical numerical models available in the literature. The former uses computational fluid dynamics (CFD), which acceptably reproduces the fire, although with high computational cost. In turn, the semi-empirical models generally present conservative results. The proposed model presents variants in classic simple models available in the literature with the aim of being a tool that allows designers to estimate the thermal fields resulting from this type of fires at the preliminary structure design stage. In this model, the thermal analysis is performed using a finite element program, considering relevant parameters that characterize the fire such as: heat release rate, location and equivalent diameter of the fire source, among others. Through subroutines, the finite element model considers (a) a modification of hot gases temperature field based in a classic simple model and (b) proposition of a new geometry of the flame. The estimated radiative heat flux employs a solid ellipsoidal flame whose height changes according to the heat release rate. The convective heat flux is evaluated using a model for localized fire. Efficiency and accuracy of the methodology are checked by comparing the simulation results with those obtained by sophisticated models developed in fire dynamic simulator (FDS). The cases studied consider: (a) the replication of the experimental test conducted at Luleå University and (b) an offshore platform deck under localized fire action. The results of the first case confirm that the FDS replicates the experimental measurements with high accuracy. Finally, the results show that the proposed model allows to realistically represent the temperature fields generated by the fire, with relatively low computational cost compared to the CFD models for cases (a) and (b), therefore it is possible to use it to develop preliminary analyses in other fire scenarios.
This article presents a comparative study to predict the thermal behavior of an offshore topside structure under localized fire using different fire models. Thermal fields are estimated using models ...with different approaches. Sophisticated fire models based on computational fluid dynamics (CFD) are often used in the analysis of this type of accident. However, their high complexity and calculation time make it difficult to use in the design stage of the structure. Simple models usually offer lower temperatures than those estimated by the CFD-FEM model, with limited use in structures with complex geometries. Localized fire with ellipsoidal solid flame (LF-ESF) model was developed as an alternative to previous models that are excessively complex (CFD based) or estimate lower temperatures (Simple). LF-ESF model can evaluate in the design stage the thermal behavior of steel structures under localized fires with the appropriate accuracy in acceptable computation time. The thermal analysis is developed with the aid of commercial software of finite elements. Three case studies are analyzed considering localized fire due to the burning of hydrocarbons. The first two develop the thermal analysis in simple structures and show the main differences between each fire model considered. The last case study evaluated the thermal behavior of an offshore topside structure. The results obtained allow to conclude that the LF-ESF model realistically represents the temperature fields generated by the fire with a relatively low computational cost as compared to the CFD models.
This paper introduces a numerical model to assess the thermomechanical behavior of offshore structures subjected to pool fires. The aim of this model is to improve the representation of fires in ...comparison with other existing models (e.g., nominal fire curves or zone modeling). The method proposed combines two-zone model—2ZM and a modified solid flame model—MSFM for calculating the convection and radiation portions of the heat transfer process between the fire and the structure. Thermal and mechanical analyses are performed sequentially using the commercial Finite Element Analysis software ABAQUS
®
. To assess the structure’s behavior , the transient temperature field resulting from the preceding thermal analysis is used together with pre-existing operating loads for the mechanical analysis. A pool fire in a tank barge is presented as a case study. Comparison of temperature and strain fields obtained with the method proposed to the results of other methods for assessment of the casualty indicates that the new model allows more realistic estimation of the temperature fields produced by the fire with relatively low computational costs.
Summary
Inhibitors are a rare but serious complication of treatment of patients with haemophilia. Phase III clinical trials enrol too few patients to adequately assess new product inhibitor risk. ...This project explores the feasibility of using a public health surveillance system to conduct national surveillance for inhibitors. Staff at 17 U.S. haemophilia treatment centres (HTC) enrolled patients with haemophilia A and B into this prospective study. HTC staff provided detailed historic data on product use and inhibitors at baseline, and postenrolment patients provided monthly detailed infusion logs. A central laboratory performed inhibitor tests on blood specimens that were collected at baseline, annually, prior to any planned product switch or when clinically indicated. The central laboratory also performed genotyping of all enrolled patients. From January 2006 through June 2012, 1163 patients were enrolled and followed up for 3329 person‐years. A total of 3048 inhibitor tests were performed and 23 new factor VIII inhibitors were identified, 61% of which were not clinically apparent. Infusion logs were submitted for 113 205 exposure days. Genotyping revealed 431 distinct mutations causing haemophilia, 151 of which had not previously been reported elsewhere in the world. This study provided critical information about the practical issues that must be addressed to successfully implement national inhibitor surveillance. Centralized testing with routine monitoring and confirmation of locally identified inhibitors will provide valid and representative data with which to evaluate inhibitor incidence and prevalence, monitor trends in occurrence rates and identify potential inhibitor outbreaks associated with products.
Summary
Background
Hemophilia A (HA) is an X‐linked bleeding disorder caused by a deficiency in factor VIII (FVIII). von Willebrand disease (VWD) is characterized by a quantitative or qualitative ...defect in von Willebrand factor (VWF). Patients with VWD with severely low VWF or VWD Type 2N (VWD2N), a VWD subtype distinguished by defective VWF binding to FVIII, may have reduced FVIII levels secondary to their VWD. These patients superficially resemble patients with HA and pose a potential for misdiagnosis.
Objectives
To investigate the unexplained cause of bleeding in HA patients without known FVIII mutations by assessing plasma VWF antigen (VWF:Ag), FVIII binding capacities and VWF genotypes.
Patients/Methods
Thirty‐seven of 1027 patients with HA studied as part of the Hemophilia Inhibitor Research Study lacked identifiable F8 mutations. These patients (cases) and 73 patients with identified F8 mutations (controls) were evaluated for VWF:Ag, a patient's VWF capacity to bind FVIII (VWF:FVIIIB) and VWF sequence.
Results
Four cases had VWF:Ag < 3 IU dL−1 and VWF mutations consistent with Type 3 VWD. Six cases and one control were heterozygous for mutations previously reported to cause Type 1 VWD (VWD1) (n = five cases and one control) or predicted to be deleterious by Polyphen2 and SIFT prediction tools (n = 1 case). One control had VWF:Ag < 30 IU dL−1 and seven patients (four cases and three controls), including two cases who were heterozygous for a known VWD2N mutation, had reduced VWF:FVIIIB.
Conclusions
These data emphasize that some patients diagnosed with HA require VWF assessments in order to achieve a comprehensive diagnosis and an optimal treatment strategy.
Department for Coagulation Disorders University Hospital SE-205 02 Malmo, Sweden. Jan.astermark@medforsk.mas.lu.se
BACKGROUND AND OBJECTIVES: The strongest risk factor identified for inhibitor ...development in people with severe hemophilia A is the type of factor VIII gene mutation. The objective of this study was to evaluate the mutation type dependent concordance rate of inhibitor formation in siblings. DESIGN AND METHODS: The gene defect, treatment and inhibitor history were evaluated in 113 families in which two or more siblings had severe hemophilia A. RESULTS: Seventy-nine of the families (69.9%) were concordant in that either all or none of the siblings had a history of inhibitors. The concordance in 59 families with inhibitors was 42.4%. The corresponding figures for the 74 families with intron 22 inversion were 63.5% and 40.0%, respectively, and the overall concordance within 14 families with nonsense mutations was 78.6%. The siblings in two families with large gene deletions had no inhibitor history. A small proportion of the families with missense mutations, small deletions/insertions and splice site mutations developed inhibitors, but in four of the families two or more siblings developed high-responding inhibitors. In 18 of the 25 concordant families (72.0%) with inhibitors, the inhibitor was also of the same type (high-responding). INTERPRETATION AND CONCLUSIONS: This is the first study of the association between inhibitor formation and the causative factor VIII gene mutation in siblings. The data show that the type of mutation provides, to some extent, the basis for this relationship, but the mutation itself is not enough to predict the risk for therapy-induced inhibitor formation.
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