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).

METAMODEL-BASED PROBABILISTIC DESIGN OPTIMIZATION OF STATIC SYSTEMS WITH AN EXTENSION TO DYNAMIC SYSTEMS

2011 ◽  
Vol 18 (04) ◽  
pp. 305-326 ◽  
Author(s):  
TURUNA S. SEECHARAN ◽  
GORDON J. SAVAGE
Keyword(s):  
Structural Reliability ◽  
Mechanistic Model ◽  
Complex Form ◽  
Probability Of Failure ◽  
Performance Measure ◽  
Surface Model ◽  
Probabilistic Design ◽  
Design Variables ◽  
Reliability Method ◽  
Distribution Parameters

In design, much research deals with cases where design variables are deterministic thus ignoring possible uncertainties present in manufacturing or environmental conditions. When uncertainty is considered, the design variables follow a particular distribution whose parameters are defined. Probabilistic design aims to reduce the probability of failure of a system by moving the distribution parameters of the design variables. The most popular method to estimate the probability of failure is a Monte Carlo Simulation where, using the distribution parameters, many runs are generated and the number of times the system does not meet specifications is counted. This method, however, can become time-consuming as the mechanistic model developed to model a physical system becomes increasingly complex. From structural reliability theory, the First Order Reliability Method (FORM) is an efficient method to estimate probability and efficiently moves the parameters to reduce failure probability. However, if the mechanistic model is too complex FORM becomes difficult to use. This paper presents a methodology to use approximating functions, called 'metamodels', with FORM to search for a design that minimizes the probability of failure. The method will be applied to three examples and the accuracy and speed of this metamodel-based probabilistic design method will be discussed. The speed and accuracy of three popular metamodels, the response surface model, the Radial Basis Function and the Kriging model are compared. Later, some theory will be presented on how the method can be applied to systems with a dynamic performance measure where the response lifetime is required to computer another performance measure.

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.

scholarly journals A Practical Nonprobabilistic Reliability Assessment Method on Key Strata Shear Failure in Longwall Mining

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Hebing Luan ◽  
Jiachen Wang ◽  
Guowei Ma ◽  
Ke Zhang
Keyword(s):  
Structural Reliability ◽  
Shear Failure ◽  
Longwall Mining ◽  
Reliability Assessment ◽  
Friction Angle ◽  
Assessment Method ◽  
Mechanical Tests ◽  
Potential Hazard ◽  
Support Design ◽  
Key Strata

Roof cutting has long been a potential hazard factor in longwall panels in some diggings in China. Meanwhile, the key strata structural reliability, which provides an assessment on the stability of overlying roof strata, may be a significant reference for support design in underground coal mines. This paper aims to investigate a practical nonprobabilistic reliability assessment method on key strata. The mechanical tests and the hollow inclusion triaxial strain tests were conducted to measure relevant mechanical parameters and in situ stress. Furthermore, against the typical failure features in Datong Diggings, China, a shear failure mechanical model of key strata is proposed. Then, an allowable-safety-factor based nonprobabilistic stability probability assessment method is given. The sensitivity of geometrical dimensions and uncertainty levels of friction angle and cohesion are further studied. It is found that thickness and span of key strata have more dominative effect on key strata’s stability compared with the other factor and the increase of uncertainty levels results in decrease of stability probability.

Simplified Strength Reliability and Integrity Analysis of TTRs

2014 ◽  
Author(s):  
Mir Emad Mousavi ◽  
Sanjeev Upadhye ◽  
Kevin Haverty
Keyword(s):  
Extreme Events ◽  
Structural Reliability ◽  
Probability Distributions ◽  
Probabilistic Approach ◽  
Reliability Assessment ◽  
Cost Effective ◽  
Probability Of Failure ◽  
Annual Probability ◽  
Reliability Methods ◽  
Integrity Analysis

The design of riser systems can be improved if structural reliability methods are used to assess their safety and integrity and confirm that such design meets a target annual probability of failure. TTRs are typically multi–bore assemblies involving several sub-assemblies. The failure of any of the components of a TTR under extreme or service environmental conditions can lead to an immediate failure of the entire assembly and impose a direct risk of damaging the wellheads, conductors, casing and tubing hangers, or other subsea equipment, because they are installed directly on top of the wellhead. However, the actual strength safety of the TTR cannot be examined unless after it is installed and examined under extreme events. Because of the numerous uncertainties associated with the design of TTRs, a probabilistic approach based on structural reliability methods can account for many of those uncertainties and serve as a basis for their reliable and cost-effective design. In turn, a comprehensive reliability assessment of a TTR requires extensive analysis that is considerably more complex and time consuming compared to a conventional deterministic-based analysis. This paper presents a probabilistic-based simplified methodology for the strength reliability assessment of TTR systems. In this method, marginal values on some uncertain model inputs are considered similar to the conventional analysis methods but, some key random variables related to environmental demands and component capacities are considered with their associated probability distributions. As a result, this method can be used to estimate the minimum level of safety of the TTR under extreme events. Additionally, results of the proposed method are discussed for integrity analysis and integrity-based optimal design of the TTR system, which compare the safety of the TTR components and estimate the component Optimality Factors for improving the design integrity and meeting a target minimum annual probability of failure.

System Reliability of Existing Jacket Platform in Malaysian Water (Failure Path and System Reliability Index)

2014 ◽  
Vol 567 ◽  
pp. 307-312 ◽  
Author(s):  
V. John Kurian ◽  
Mohamed Mubarak Abdul Wahab ◽  
T.S. Kheang ◽  
Mohd Shahir Liew
Keyword(s):  
System Reliability ◽  
Reliability Index ◽  
Structural Reliability ◽  
Pushover Analysis ◽  
Probability Of Failure ◽  
Jacket Platform ◽  
First Order ◽  
Failure Path ◽  
Reliability Method ◽  
Two Parameters

The objective of this work is to determine the structural reliability of an existing jacket platform in Malaysia, by determining the system probability of failure and its corresponding reliability index. These two parameters are important indicators for assessing the integrity and reliability of the platform, and will point out whether the platform is suitable for continued operation. In this study, pushover analysis is used to determine possible failure paths of the structure, while First Order Reliability Method (FORM) and Simple Bound Formula are used to determine the failure probability and reliability index. Three failure paths of the platform are established. The reliability index of these paths is found with the highest Reliability Indexto be 18.82 from the 315-degree path, while the system reliability index is 9.23. This illustrates that the platform is robust and the chances of collapse is very small.

Performance of In-Line Inspection Tools and Their Influence on the Structural Reliability of Corroded Pipeline

2006 ◽  
Author(s):  
Jose´ de Jesu´s Leal Carvajalino ◽  
Fa´bio de Castro Marangone ◽  
Jose´ Luiz de Franc¸a Freire
Keyword(s):  
Sequential Analysis ◽  
Structural Reliability ◽  
Field Measurements ◽  
Visual Basic ◽  
Probability Of Failure ◽  
First Order ◽  
Reliability Method ◽  
Minimum Number ◽  
Corrosion Defects ◽  
Reference Tool

This paper presents: i) the assessment of in-line inspection (ILI) tools’ performance in the measurement of defects caused by corrosion; ii) different methods for calculating the probability of failure (POF) of corroded pipeline based on the ILI report. The ILI report is compared to the geometry of defects measured by a reference tool (field measurements) and the errors associated with each measurement system are analyzed and assessed through different statistical methods. The minimum number of field measurements necessary to verify the performance of the ILI in sizing the corrosion defects is determined by implementing a test based on sequential analysis. The POF of a pipeline is calculated using two methods: i) first order reliability method (FORM) and ii) propagation of uncertainties. The comparison between calculated and acceptable POF enables the determining of the next reinspection period. When the calculated POF exceeds the acceptable POF before completing the amount of time desired for the next inspection, the developed procedure enables determining the number of repairs that must be made to reach the desired time when the next ILI will be performed. Finally, a software in Visual Basic® language was developed to implement this work.

Computational Models to Predict the Structural Reliability of Aerospace Systems

2013 ◽  
Author(s):  
Robert G. Tryon ◽  
Animesh Dey ◽  
Richard A. Holmes ◽  
Ganapathi Krishnan
Keyword(s):  
Structural Reliability ◽  
Computational Models ◽  
Probability Of Failure ◽  
Performance Function ◽  
Auxiliary Power Unit ◽  
Auxiliary Power ◽  
Statistical Variation ◽  
Commercial Airline ◽  
Reliability Method ◽  
Turbine Disks

Three case studies are presented in which computational-based methodologies have been used to assess structural reliability in the aerospace industry. The studies involve hot section turbine disks of a helicopter engine, fan blades of a commercial airline engine and bearings in an auxiliary power unit. In all cases, the results of the computational models were used to support the certification process for design and application changes. The statistical variation in design and usage parameters including geometry, materials, speed, temperature and other environmental factors are considered. The response surface approach was used to construct a durability performance function. This performance function is used with the first order reliability method (FORM) to determine the probability of failure and the sensitivity of the failure to the design and usage parameters. A hybrid combination of perturbation analysis and Monte Carlo simulation is used to incorporate time dependent random variables. System reliability is used to determine the system probability of failure, and the sensitivity of the system durability to the design and usage parameters.

Optimal Control of Performance Risk for Large Potentially Dangerous Systems (LPDS)

2002 ◽  
Author(s):  
Sviatoslav A. Timashev
Keyword(s):  
Optimal Control ◽  
Risk Analysis ◽  
Conditional Probability ◽  
Structural Reliability ◽  
Process Analysis ◽  
Probability Of Failure ◽  
Simultaneous Optimization ◽  
Normal Operation ◽  
Residual Lifetime ◽  
Parameter Problem

The paper considers the safety problem for large potentially dangerous systems (LPDS). Disruption of their normal operations may lead to casualties, ecological and property damage. Solution to the above problem is sought in the framework of risk control of LPDS during their normal operation, based on the principle of preventive actions. Risk is described as the product of conditional probability of failure and the overall consequences of such failure. Methods of brining down risk analysis problems to reliability problems are presented. They are based on the following: assessments of “cost of life” (as economic equivalent of casualty); simultaneous optimization of the LPDS and its safety subsystem (expansion of the object of optimization). Such an approach allows unification and merging of structural reliability theory and probabilistic risk analysis. A quantitative method of damage size (the first component of risk) assessment is described, based on computer modeling of a full group of scenarios of a structural failure developing into a full blown LPDS catastrophe. As a result of modeling, the destruction zones and the character, size and probabilities of all kinds of damage (casualties, ecological damage, loss of property) are assessed. It is proposed, as the main method of securing LPDS integrity and safety, to equip each LPDS with suitable monitoring/inspection/maintenance systems, designed as an instrument for controlling the second component of risk (conditional probability of failure), on the basis of a three-level (warning-alarm-failure) control policy. In the outlined format maintenance/repair is considered as optimal control of random degradation and renewal functions, interaction of which forms a certain regeneration process. Analysis of this process allows defining the optimal triggering levels of deterioration parameters or risk that minimize total expenditures of LPDS performance while ensuring its safety. The problem formulated above naturally embodies all existing maintenance methods (based on admissible performance time, rate of failure and on actual and prognosed system condition). Further, the problem of optimal cessation of performance is solved. It allows convoluting a multi-parameter problem into a one-parameter problem and defining the ultimate permissible level of conditional probability of failure. The described methods of risk analysis and control were used in residual lifetime monitoring systems for oil pumping aggregates and for main oil pipe line segments repair prioritization.

A New Approach for the Evaluation of Structural Failure by Credibility Distribution

2020 ◽  
Vol 14 (1) ◽  
pp. 217-227
Author(s):  
Palash Dutta ◽  
Nisha Gohain
Keyword(s):  
Structural Reliability ◽  
Reliability Assessment ◽  
Assessment Method ◽  
Present Approach ◽  
Structural Failure ◽  
New Approach ◽  
Failure Assessment ◽  
Probabilistic Nature ◽  
Assessment Problems ◽  
Failure Evaluation

Aim: To devise an effective structural failure analysis approach under uncertainty. Background: In reliability evaluation, plenty of factors are uncertain, or sometimes, spontaneously represented via linguistic expressions, and as a consequence, the traditionalist appraisal methods cannot capably handle the ambiguity and vagueness that occurs in reliability assessment components. Subsequently, this leads to the problem of tremendous computationally multifaceted and scanty correctness. Objective: To overcome the limitations and to develop efficiency as well as accuracy in structural failure evaluation techniques, an attempt has been made to devise a novel structural reliability assessment method via credibility distribution. Methods: To get rid of the problems of massive computationally difficult and inadequate precision, an algorithm has been devised using credibility sampling. To exhibit the novelty, validity, and applicability of the present approach, some structural failure assessment problems are solved along with a comparison with the existing approach. Results: The proposed method was verified by four examples and applied in structural analysis. It was observed that the present approach is technically sound and efficient; it can overcome all the drawbacks of the existing approach. Moreover, the approach can be executed in any uncertain situation. Conclusion: After evaluation of failure assessment, it is experienced that the increase in the number of simulations leads to better precision. Furthermore, it is encountered that when hybridization problems i.e., representation of imprecise components in the problem of structural failure, are both fuzzy and probabilistic nature, then the failure assessment is attained to be maximum.

scholarly journals DEVELOPED PROBABILISTIC REDUCTION FACTORS FOR LOPHIRA ALATA (EKKI) TIMBER JOISTS SUBJECTED TO CREEP-RUPTURE

2016 ◽  
Vol 36 (1) ◽  
pp. 39-44
Author(s):  
JM Kaura ◽  
A Lawan ◽  
AA Salihu
Keyword(s):  
Reliability Analysis ◽  
Structural Reliability ◽  
Significant Loss ◽  
Creep Rupture ◽  
Time Dependent ◽  
Load Duration ◽  
Design Variables ◽  
Reliability Method ◽  
Load Carrying ◽  
Strength And Stiffness

Wood experiences a significant loss of strength and stiffness when loaded over period of time. This phenomenon is known as creep-rupture. Several models were developed for the estimation of the reduction of load carrying capacity of timber with time. In this paper, the results of time dependent structural reliability analysis of timber joist produced with Lophiraalata (Ekki) timber specie was presented. Three load duration models were considered in the study, namely: The Model proposed by Wood, Gerhards model, and Nielsen. The timber joist was designed in accordance with the Eurocode 5. The uncertainties in all the basic design variables were fully accommodated in the time dependent reliability analysis. The entire process was implemented using a developed MATLAB program employing First Order Reliability Method (FORM). Time dependent mathematical models for modification of safety index to account for the effect of load duration were proposed. The use of both Gerhards and Nielsen model, for the design of Lophiraalata timber members was recommended.  http://dx.doi.org/10.4314/njt.v36i1.6

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