An advanced procedure for the quantitative risk assessment of offshore installations in explosions

Hydrocarbon explosion and fire are typical accidents in the offshore oil and gas industry, sometimes with catastrophic consequences such as casualties, property damage and pollution. Successful engineering and design should meet both functional requirements associated with operability in normal conditions and health, safety, environmental and ergonomics (HSE&E) requirements associated with accidental and extreme conditions. A risk-based approach is best for successful design and engineering to meet HSE&E requirements. This study aimed to develop an advanced procedure for assessing the quantitative risk of offshore installations in explosions. Unlike existing industry practices based on prescriptive rules or qualitative approaches, the proposed procedure uses an entirely probabilistic approach. The procedure starts with probabilistic selection of accident scenarios. As the defining components of risk, both the frequency and consequences associated with selected accident scenarios are computed using the most refined technologies. Probabilistic technology is then applied to establish the relationship between the probability of exceedance and the physical values of the accident. Acceptance risk criteria can be applied to define the nominal values of design and/or level of risk. To validate and demonstrate the applicability of the proposed procedure, an example of its application to topside structures of an FPSO unit subjected to hydrocarbon explosions is detailed. The conclusions and insights obtained are documented

Nonlinear structural behaviour of membrane-type LNG carrier cargo containment systems under impact pressure loads at −163 °C

This paper is a sequel to the paper dealing with quasi-static responses previously studied by the authors. The structural failure of membrane-type liquefied natural gas carrier (LNGC) cargo tank is an important issue in the construction of ultra-large an LNG carrier. However, quasi-static analysis to investigate the structural failure is difficult and tends to give conservative results. To compensate the weak points of the quasi-static analysis, a procedure for the dynamic analysis was developed to assess the structural failure using nonlinear finite element method. A nonlinear finite element method is employed to model metal membrane, insulation and surface contacts. Various element formulations are tested at different points along a corrugated surface to optimise the accuracy of the model with respect to computation time. Material properties used in the model are calibrated based on experimentally measured values at cryogenic conditions (−163 °C). The model is used to predict the structural failure under different impact pressure loads and loading patterns. It is concluded that the structural damage is less likely to occur under 30 bar

Strength assessment of stiffened blast walls in offshore installations under explosions

Offshore installations are exposed to hydrocarbon explosions and/or fire accidents. Especially, explosions lead to serious damages to human, safety, and environment. To minimise and prevent the damage from explosions, blast walls are generally installed in oil and gas production structures. Typical blast walls are classified into flat, corrugated, and stiffened types. Among them, corrugated blast walls are frequently used for reasons such as construction, cost, and energy absorption. However, it has been known that a corrugated type of blast wall buckles between the web and flange under the explosion loads, and loses its stiffness. It means that the buckling phenomenon of a blast wall is closely related to the structural strength. This study investigates on the structural characteristics of a blast wall under quasi-static and dynamic (explosion) loads with or without a flat-plated stiffener. Finally, it can be concluded that the flat type of stiffeners are located at the buckling region to delay the buckling and improve the strength of blast walls

Long-term stochastic heave-induced dynamic buckling of a top-tensioned riser and its influence on the ultimate limit state reliability

A top-tensioned riser is a slender pipe that conveys fluids between a floater and a subsea system. High top-tension keeps its straight configuration and helps to prevent compressive loads. Because of the floater's heave motion, the tension on the riser fluctuates giving rise to dynamic buckling. This paper examines the dynamic buckling characteristics of a top-tensioned riser analyzing the governing equation with nonlinear damping. The equation is discretized in space by the finite difference method and then is numerically integrated by the Runge-Kutta method. As main objective, an ultimate limit state function for risers is used to investigate its reliability during parametric excitation. While the short-term stationary Gaussian random motion of a floater can be described by a response spectrum, the uncertainties of a long-term response are considered by Monte Carlo simulation. In view of an applied example, it is found that the dynamic buckling would occur often, and although the probability of failure is acceptable, it can cause serious failure when axial excitation is of significance in harsher sea states. This study aims to contribute in clarifying the role of parametric vibrations (dynamic buckling) in the reliability of risers for ultimate limit state

A practical method to determine the dynamic fracture strain for the nonlinear finite element analysis of structural crashworthiness in ship–ship collisions

Ship–ship collisions continue to occur regardless of efforts to prevent them. The collisions involve highly nonlinear characteristics associated with structural crashworthiness, including crushing and fracture as well as buckling and plastic collapse. When applying nonlinear finite element analysis (NLFEA) to solve these problems, a reliable critical fracture strain accounting for strain-rate effects due to collision speed must be implemented. This study proposes a practical method to estimate the dynamic fracture strain to be used for the structural crashworthiness analysis associated with the collisions. For this purpose, the strain-rate characteristics in struck ship were investigated by NLFEA, in which the striking vessel was assigned various velocities in the range of practical ship speeds. Based on computations, an empirical formula was developed to calculate the strain rate at a given collision speed, allowing for a practical estimation of the dynamic fracture strain. The formula is validated by a comparison with experiment

A life-cycle cost model for the reliability-based design of disconnectable FPSO mooring lines

Floating production, storage, and offloading units (FPSOs) are widely used to develop offshore oil fields from shallow to ultra-deep waters, and some possess fast disconnection systems to avoid harsh environmental conditions. According to a literature survey, the current industry practice is based on the perceptions and experiences of operators to judge the disconnection of these units during cyclonic storms. However, systematic criteria should be established to judge whether disconnection is needed, and the downtime costs and safety issues associated with life-cycle costs should be considered. In this paper, a life-cycle cost model is proposed to optimize (1) the disconnection criteria of FPSOs and (2) the design of their mooring system. Relevant ultimate limit states and reliabilities are considered in association with hull collapse, mooring system failure, and green water impact failure. Effects of downtime costs (deferred production costs), mobilization, and other failure costs are considered. Disconnection criteria are then formulated in terms of the significant wave height and wind speed limits. Because a permanent mooring system may exhibit excessive resistance, it is possible to further optimize the life-cycle cost by reducing the system’s resistance until an optimum reliability is obtained, minimizing the costs for non-permanent service. An FPSO in the Gulf of Mexico is selected as an example to illustrate the application of the developed model. The results of this study show that important savings for an overall FPSO project can be achieved by implementing the proposed optimizations

On design criteria for a disconnectable FPSO mooring system associated with expected lifecycle cost

Some floating production, storage and offloading units (FPSOs) possess disconnectable systems to avoid harsh environments. According to a literature survey, the practice is based on perceptions and experiences of operators to judge disconnection; however, this paper offers a rational approach. A life-cycle cost model is proposed to optimise (1) the disconnection criteria and (2) the design of mooring lines under reliability format. Relevant ultimate limit states are considered in association with hull, moorings and green water failure. Effects of future failure costs are considered (downtime, environmental damage, reputation, etc.). Disconnection criteria are then formulated in terms of significant wave height and wind speed limits. Because a permanent mooring system may exhibit excessive resistance, it is possible to reduce the lines’ thickness until the cost is optimised for non-permanent service. Results for an example in the Gulf of Mexico show that important savings can be achieved by implementing the proposed optimisations

Benefits of biomarker selection and clinico-pathological covariate inclusion in breast cancer prognostic models

Introduction: Multi-marker molecular assays have impacted management of early stage breast cancer, facilitating adjuvant chemotherapy decisions. We generated prognostic models that incorporate protein-based molecular markers and clinico-pathological variables to improve survival prediction. Methods: We used a quantitative immunofluorescence method to study protein expression of 14 markers included in the Oncotype DX™ assay on a 638 breast cancer patient cohort with 15-year follow-up. We performed cross-validation analyses to assess performance of multivariate Cox models consisting of these markers and standard clinico-pathological covariates, using an average time-dependent Area Under the Receiver Operating Characteristic curves and compared it to nested Cox models obtained by robust backward selection procedures. Results: A prognostic index derived from of a multivariate Cox regression model incorporating molecular and clinico-pathological covariates (nodal status, tumor size, nuclear grade, and age) is superior to models based on molecular studies alone or clinico-pathological covariates alone. Performance of this composite model can be further improved using feature selection techniques to prune variables. When stratifying patients by Nottingham Prognostic Index (NPI), the most prognostic markers in high and low NPI groups differed. Similarly, for the node-negative, hormone receptor-positive sub-population, we derived a compact model with three clinico-pathological variables and two protein markers that was superior to the full model. Conclusions: Prognostic models that include both molecular and clinico-pathological covariates can be more accurate than models based on either set of features alone. Furthermore, feature selection can decrease the number of molecular variables needed to predict outcome, potentially resulting in less expensive assays.This work was supported by a grant from the Susan G Komen Foundation (to YK)

Stabilizing entanglement autonomously between two superconducting qubits

Quantum error-correction codes would protect an arbitrary state of a multi-qubit register against decoherence-induced errors, but their implementation is an outstanding challenge for the development of large-scale quantum computers. A first step is to stabilize a non-equilibrium state of a simple quantum system such as a qubit or a cavity mode in the presence of decoherence. Several groups have recently accomplished this goal using measurement-based feedback schemes. A next step is to prepare and stabilize a state of a composite system. Here we demonstrate the stabilization of an entangled Bell state of a quantum register of two superconducting qubits for an arbitrary time. Our result is achieved by an autonomous feedback scheme which combines continuous drives along with a specifically engineered coupling between the two-qubit register and a dissipative reservoir. Similar autonomous feedback techniques have recently been used for qubit reset and the stabilization of a single qubit state, as well as for creating and stabilizing states of multipartite quantum systems. Unlike conventional, measurement-based schemes, an autonomous approach counter-intuitively uses engineered dissipation to fight decoherence, obviating the need for a complicated external feedback loop to correct errors, simplifying implementation. Instead the feedback loop is built into the Hamiltonian such that the steady state of the system in the presence of drives and dissipation is a Bell state, an essential building-block state for quantum information processing. Such autonomous schemes, broadly applicable to a variety of physical systems as demonstrated by a concurrent publication with trapped ion qubits, will be an essential tool for the implementation of quantum-error correction.Comment: 39 pages, 7 figure

ER and HER2 expression are positively correlated in HER2 non-overexpressing breast cancer

PMCID: PMC3446380This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited