Structural Reliability Assessment of Offshore Platforms Under Hurricane Events

2007 ◽  
Author(s):  
Liangsheng Wang ◽  
Kaisheng Chen ◽  
Justin Bucknell
Keyword(s):  
Structural Reliability ◽  
Structural Integrity ◽  
Limit State ◽  
Reliability Assessment ◽  
Assessment Method ◽  
Environmental Data ◽  
State Function ◽  
Offshore Platforms ◽  
Wave Load ◽  
Reliability Method

This paper presents a structural reliability assessment method to quantify the probability of platform failure for Trinidad offshore platforms subjected to hurricane events. Platforms are modeled as a series system composed of the topsides and jacket including foundation. The platform failure limit state function is defined in terms of environmental load and platform capacity. The platform capacity is evaluated by non-linear pushover analysis using USFOS program. A parametric relationship of wave load as a function of wave height is derived based on the offshore extreme environmental data. The first order reliability method (FORM) is used to estimate the annual failure probability. The relationship between the probability of platform failure and the reserve strength ratio (RSR) of platforms is investigated. The assessment results could be used to evaluate the level of risk associated with hurricane hazards and may be incorporated into the risk-based underwater inspection (RBUI) program as part of the structural integrity management (SIM) process.

Structural Reliability Assessment of Aging Offshore Platforms With Corrosion and Cracks

2008 ◽  
Author(s):  
Chunyan Ji ◽  
Shanshan Li
Keyword(s):  
Fatigue Crack ◽  
Structural Reliability ◽  
Structural Integrity ◽  
Fatigue Cracks ◽  
Limit State ◽  
Reliability Assessment ◽  
Shear Capacity ◽  
Offshore Platforms ◽  
Base Shear ◽  
Reliability Method

Corrosion and fatigue cracks are major threats to the structural integrity of aging offshore platforms. To rationally estimate the safety levels of the structures, a reliability assessment approach for aging offshore platform with corrosion and fatigue cracks is presented in the paper. The advanced second-order reliability method is adopted to calculate the probability index based on the limit state equation of global failure mode. The base shear capacity is taken as the ultimate strength of the platform. It is modeled as a random process that decreases with time in the presence of corrosion and fatigue crack propagating. And corrosion and fatigue crack growth rates in the main members and key nodes are modeled as random variables. A simulation method of the extreme wave loads that are applied on the structures is proposed too. Finally the reliability index of an example jacket platform is estimated in the case study.

Efficient Reliability Assessment With the Conditional Probability Method

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Rami Mansour ◽  
Mårten Olsson
Keyword(s):  
Conditional Probability ◽  
Structural Reliability ◽  
A Priori ◽  
Reliability Assessment ◽  
Probability Of Failure ◽  
Assessment Method ◽  
Probability Method ◽  
Probability Of Survival ◽  
Design Variables ◽  
Reliability Method

Reliability assessment is an important procedure in engineering design in which the probability of failure or equivalently the probability of survival is computed based on appropriate design criteria and model behavior. In this paper, a new approximate and efficient reliability assessment method is proposed: the conditional probability method (CPM). Focus is set on computational efficiency and the proposed method is applied to classical load-strength structural reliability problems. The core of the approach is in the computation of the probability of failure starting from the conditional probability of failure given the load. The number of function evaluations to compute the probability of failure is a priori known to be 3n + 2 in CPM, where n is the number of stochastic design variables excluding the strength. The necessary number of function evaluations for the reliability assessment, which may correspond to expensive computations, is therefore substantially lower in CPM than in the existing structural reliability methods such as the widely used first-order reliability method (FORM).

scholarly journals Hybrid Reliability Analysis for Spacecraft Docking Lock with Random and Interval Uncertainty

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
Jianguo Zhang ◽  
Jiwei Qiu ◽  
Pidong Wang
Keyword(s):  
Reliability Analysis ◽  
Structural Reliability ◽  
Limit State ◽  
Random Variables ◽  
Simple Problem ◽  
State Function ◽  
Limit State Function ◽  
Interval Variables ◽  
Reliability Method ◽  
Hybrid Reliability

This paper presents a novel procedure based on first-order reliability method (FORM) for structural reliability analysis with hybrid variables, that is, random and interval variables. This method can significantly improve the computational efficiency for the abovementioned hybrid reliability analysis (HRA), while generally providing sufficient precision. In the proposed procedure, the hybrid problem is reduced to standard reliability problem with the polar coordinates, where an n-dimensional limit-state function is defined only in terms of two random variables. Firstly, the linear Taylor series is used to approximate the limit-state function around the design point. Subsequently, with the approximation of the n-dimensional limit-state function, the new bidimensional limit state is established by the polar coordinate transformation. And the probability density functions (PDFs) of the two variables can be obtained by the PDFs of random variables and bounds of interval variables. Then, the interval of failure probability is efficiently calculated by the integral method. At last, one simple problem with explicit expressions and one engineering application of spacecraft docking lock are employed to demonstrate the effectiveness of the proposed methods.

Study of Computation for Structural Reliability Index Based on Penalty Function Method

2014 ◽  
Vol 635-637 ◽  
pp. 443-446 ◽  
Author(s):  
Hai Tao Lu ◽  
Yu Ge Dong ◽  
Fang Ying Wu
Keyword(s):  
Unconstrained Optimization ◽  
Penalty Function ◽  
Reliability Index ◽  
Function Method ◽  
Structural Reliability ◽  
Limit State ◽  
State Function ◽  
Penalty Function Method ◽  
Design Point ◽  
Reliability Method

According to the geometric meaning of the structural reliability index, an unconstrained optimization model with structural reliability index and design point is obtained by exterior penalty function method. The Powell method, golden section method and extrapolation method are used to solve the unconstrained optimization problem. The proposed method not has to deal with the any derivative of the limited state function, and can been used to obtain structural reliability index and design point of the strong nonlinear limit state function, which first-order reliability method (FORM) may fail to converge. Three examples are given to compare penalty function method with the difference methods. The results show that the given method is simply, effective and precise enough.

A Novel Approach to Improving the Structural Reliability of a Fixed Offshore Platform Subject to Wave-in-Deck Loading Using a Holistic Structural Integrity Management (SIM) TRIAD Approach

2020 ◽  
Author(s):  
Mehrdad Kimiaei ◽  
Jalal Mirzadeh ◽  
Partha Dev ◽  
Mike Efthymiou ◽  
Riaz Khan
Keyword(s):  
Structural Reliability ◽  
Structural Model ◽  
Structural Integrity ◽  
Reliability Assessment ◽  
Offshore Structures ◽  
Offshore Platform ◽  
Offshore Platforms ◽  
Effective Manner ◽  
Integrity Management ◽  
Fixed Offshore Platform

Abstract Fixed offshore platforms subject to wave-in-deck loading have historically encountered challenges in meeting target reliability levels. This has often resulted in costly subsea remediation, impacted platform occupancy levels or premature decommissioning of critical structural assets due to safety concerns. This paper addresses the long-standing industry challenge by presenting a novel structural reliability approach that involves converging the analytical behavior of a structure to its measured dynamic response for assessment. In this approach, called the Structural Integrity Management (SIM) TRIAD method, the platform model is calibrated based on the measured in-field platform natural frequencies using a structural health monitoring (SHM) system, so that the reliability assessment can be performed on a structural model whose stiffness is simulated as close to reality as possible. The methodology demonstrates the potential of unlocking structural capacity of offshore structures by removing conservatism normally associated with traditional reliability assessment methods, thus significantly improving the ability to achieve target structural reliability levels in a cost effective manner. The SIM TRIAD method has been implemented while assessing an existing fixed offshore platform subject to wave-in-deck loads, which is located in East Malaysian waters. It has enabled the facility operator to achieve acceptable target structural reliability and has assisted in developing an optimized risk-based inspection (RBI) plan for ensuring safe operations to end of asset field life. The methodology and findings of the assessment are presented in this paper to illustrate the benefits of the SIM TRIAD method.

Most-Probable-Point-Locus Reliability Method in Standard Normal Space

1991 ◽  
Author(s):  
M. R. Khalessi ◽  
Y.-T. Wu ◽  
T. Y. Torng
Keyword(s):  
Reliability Analysis ◽  
Structural Reliability ◽  
Search Algorithm ◽  
Limit State ◽  
Iteration Procedure ◽  
Normal Space ◽  
State Function ◽  
Most Probable Point ◽  
Reliability Method ◽  
Standard Normal

Abstract This paper describes a new structural reliability analysis iteration procedure based on the concept of most probable point locus (MPPL). Using a new quadratic search algorithm, the proposed procedure examines the global behavior of the limit-state function, g, along the MPPL in the standard normal space in search of the most probable point (MPP) on the g = o surface, and identifies unusual conditions such as multiple MPPs. During the iteration procedure, the generated information is updated after each sensitivity analysis. This action helps the analyst to minimize the number of computer runs and determine the next step. By adopting two efficient convergence criteria, the proposed procedure is demonstrated to be significantly more efficient than the commonly used reliability analysis procedures, and is suitable to be integrated with existing general-purpose finite element computer programs for nondeterministic structural analysis.

The SVC Based AFOSM Method for the Structure Reliability Sensitivity Analysis

2013 ◽  
Vol 477-478 ◽  
pp. 146-149
Author(s):  
Wei Dong Chen ◽  
Ping Jia ◽  
Xian De Wu ◽  
Yan Chun Yu ◽  
Feng Chao Zhang ◽  
...  
Keyword(s):  
Reliability Analysis ◽  
Structural Reliability ◽  
Limit State ◽  
Support Vector ◽  
State Function ◽  
Structure Reliability ◽  
Reliability Sensitivity ◽  
Reliability Sensitivity Analysis ◽  
Reliability Method ◽  
First Order Second Moment

The limit state function (LSF) is implicit to many structure reliability analysis problems, which may make some classical reliability method complicated to be applied. One of the surrogate methods-support vector classification (SVC) was applied in the structural reliability analysis herein which has not been applied to structure reliability analysis until recent years. Then the advanced first order second moment method (AFOSM) can be applied. The expressions of structure system reliability sensitivity to basic variable were deduced. The flow of how to call the SVC program was presented. An example was shown to compare the SVC based method with some other classical reliability analysis methods. The results are accurately accepted and the advantages of SVC are analyzed.

Fatigue Reliability Assessment of Coupled Spar-Mooring System

2011 ◽  
Author(s):  
Mohammed Jameel ◽  
Suhail Ahmad
Keyword(s):  
Limit State ◽  
Reliability Assessment ◽  
Coupled Analysis ◽  
State Function ◽  
Mooring System ◽  
Limit State Function ◽  
Mooring Lines ◽  
Reliability Indices ◽  
Current Limit ◽  
Reliability Method

Spar platform is a compliant floating structure used for exploration of oil and gas from deep sea. To ensure safe operations, reliability against mooring line failure is a major concern in design. Furthermore, the mooring lines have high investment costs and are normally not accessible for in-service inspection. The common approach for solving the dynamics of Spar system is to employ a decoupled quasi-static approach which ignores the platform and mooring lines interaction. Coupled analysis, used presently, considers the mooring lines and platform in an integrated single model. Hence, it effectively captures the damping effect due to Spar and mooring lines coupling. Finite element code ABAQUS is used to obtain the response of Spar-mooring system under long crested random sea with current. Limit state function is derived based on failure due to fatigue for probabilistic reliability assessment. Random variables, participating actively in the limit state function are identified and statistically modeled. The most probable points or the design points are found to be an effective parameter for estimating partial factors of safety for load and resistance variables. First Order Reliability Method (FORM) is used to calculate probability of failure and reliability indices. The results are later checked against Monte carlo simulation. Reliabilities of segmental length of mooring and of full length are determined as they may significantly differ if the mooring properties change along the length. Reliability indices of annual and life time sea states are calculated.

scholarly journals An Improved Structural Reliability Analysis Method Based on Local Approximation and Parallelization

Mathematics ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 209
Author(s):  
Bolin Liu ◽  
Liyang Xie
Keyword(s):  
Reliability Analysis ◽  
Failure Probability ◽  
Structural Reliability ◽  
Limit State ◽  
Local Approximation ◽  
State Function ◽  
Limit State Function ◽  
Enrichment Technique ◽  
Reliability Method ◽  
Multiple Sample

The Kriging-based reliability method with a sequential design of experiments (DoE) has been developed in recent years for implicit limit state functions. Such methods include the efficient global reliability analysis, the active learning reliability method combining Kriging and MCS Simulations. In this research, a novel local approximation method based on the most probable failure point (MPFP) is proposed to improve such methods. In this method, the MPFP calculated in the last iteration is the center of the next sampling region. The size of the local region depends on the reliability index obtained by the First Order Reliability Method (FORM) and the deviation distance of the standard deviation. The proposed algorithm, which approximates the limit state function accurately near MPFP rather than in the whole design space, can avoid selecting samples in regions that have negligible effects on the reliability analysis results. In addition, a multi-point enrichment technique is also introduced to select multiple sample points in each iteration. After the high-quality approximation of limit state function is obtained, the failure probability is calculated by the Monte Carlo method. Four numerical examples are used to validate the accuracy and efficiency of the proposed method. Results show that the proposed method is very effective for an accurate evaluation of the failure probability.

An improved first order reliability method based on modified Armijo rule and interpolation-based backtracking scheme

2020 ◽  
pp. 1748006X2095989
Author(s):  
Sheng-Tong Zhou ◽  
Di Wang ◽  
Qian Xiao ◽  
Jian-min Zhou ◽  
Hong-Guang Li ◽  
...  
Keyword(s):  
Structural Reliability ◽  
Limit State ◽  
Initial Step ◽  
State Function ◽  
Computationally Efficient ◽  
Step Size ◽  
First Order Reliability Method ◽  
First Order ◽  
Reliability Method ◽  
Initial Step Size

Hasofer-Lind and Rackwtiz-Fiessler (HLRF) method is an efficient iterative algorithm for locating the most probable failure point and calculating the first order reliability index in structural reliability analysis. However, this method may encounter numerical instability problems for high nonlinear limit state function (LSF). In this paper, an improved HLRF-based first order reliability method is developed based on a modified Armijo line search rule and an interpolation-based step size backtracking scheme to improve the robustness and efficiency of the original HLRF method. Compared with other improved HLRF-based methods, the proposed method can not only guarantee the global convergence but also adaptively estimate some sensitive algorithm parameters, such as initial step size, step-size reduction coefficient, using the current known iterative information. Ten selected examples with high nonlinear LSFs are used to compare the robustness and efficiency of the proposed method with the original HLRF method and the improved HLRF (iHLRF) method. Results indicate that the proposed method is not only more computationally efficient but also less sensitive to the remaining user-defined algorithm parameters than the iHLRF method.

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