Probabilistic Models of Uncertainties in Fatigue and Fracture Reliability Analysis

2002 ◽  
Author(s):  
W. Zhao ◽  
A. Stacey ◽  
P. Prakash
Keyword(s):  
Probabilistic Models ◽  
Reliability Assessment ◽  
Fracture Analysis ◽  
Offshore Structures ◽  
Probabilistic Methods ◽  
Probabilistic Modelling ◽  
Integrity Assessment ◽  
Growth Functions ◽  
Fatigue And Fracture ◽  
Recent Developments

Probabilistic methods enable the modelling of the uncertainties associated with the integrity assessment of structures containing defects to be taken into account. This paper presents a critical review of recent developments in the probabilistic modelling of the uncertainties associated with fatigue and fracture reliability assessment. A number of probabilistic models for the principal parameters in the S-N curve, fatigue crack growth functions and fracture analysis are presented and discussed with particular emphasis on the identification of future needs for the development of suitable code procedures for offshore structures.

Characterization of the Uncertainties in the Inspection Results of Ultrasonic Intelligent Pigs

2013 ◽  
Author(s):  
Mamdouh M. Salama ◽  
Bruce J. Nestleroth ◽  
Marc A. Maes ◽  
Chris Dash
Keyword(s):  
Probabilistic Models ◽  
Service Providers ◽  
Quantitative Risk Assessment ◽  
Life Extension ◽  
Internal Corrosion ◽  
Integrity Assessment ◽  
Diameter Pipe ◽  
Length Width ◽  
Pull Through

In-Line Inspections using magnetic flux leakage (MFL) and the Ultrasonic (UT) intelligent pigs are the most common tools used to assess the integrity of pipelines. But, both MFL and UT inspection results are subject to various sources of uncertainties which must be quantified and accounted for in the integrity assessment of the inspected pipeline. A series of pull-through tests (PTT) of seven MFL tools and two UT tools from five service providers was performed on a 12-inch diameter pipe containing pre-existing internal corrosion defects of various length, width, and depth, and located in a variety of circumferential and longitudinal positions. The results of these tests are used to quantify the detectability statistics and the sizing uncertainties of the different tools for future use in developing calibrated probabilistic models for reliability based inspection, quantitative risk assessment and life extension studies for pipelines. The results of the MFL tools were presented in 2012 OMAE conference and this paper presents the results of the two UT tools.

Comparison of Probabilistic and Possibility Theory-Based Methods for Design Against Catastrophic Failure Under Uncertainty

1999 ◽  
Author(s):  
Efstratios Nikolaidis ◽  
Harley Cudney ◽  
Sophie Chen ◽  
Raphael T. Haftka ◽  
Raluca Rosca
Keyword(s):  
Probabilistic Models ◽  
Failure Modes ◽  
Possibility Theory ◽  
Probabilistic Methods ◽  
Sufficient Information ◽  
Catastrophic Failure ◽  
Design Problems ◽  
Available Information ◽  
Theoretical Foundations ◽  
Better Than

Abstract This paper compares probabilistic and possibility-based methods for design against catastrophic failure under uncertainty. It studies the effect of the amount of information on the effectiveness of each method. The study is confined to problems where the boundary between survival and failure is sharp. First, the paper examines the theoretical foundations of probability and possibility. It also compares the two methods when they are used to assess the risk of a system. Finally, it compares the two methods on two design problems. A major difference between probability and possibility is in the axioms about the union of events. Because of this difference, probability and possibility calculi are fundamentally different and one cannot simulate possibility calculus using probabilistic models. It is shown that possibility-based methods can be less conservative than probability-based methods in systems with many failure modes. On the other hand, possibility-based methods tend to be more conservative than probability-based methods in systems that fail only if many unfavorable events occur simultaneously. Probabilistic methods are better than possibility-based methods if sufficient information is available. However, the latter can be better if little information is available. A principal reason is that it is easier to identify the most conservative possibilistic model than the most conservative probabilistic model that is consistent with the available information.

scholarly journals Adaptable legged-magnetic adhesion tracked wheel robotic platform for misaligned mooring chain climbing and inspection

2018 ◽  
Vol 45 (5) ◽  
pp. 634-646 ◽  
Author(s):  
Mahesh Dissanayake ◽  
Tariq Pervez Sattar ◽  
Shehan Lowe ◽  
Ivan Pinson ◽  
Tat-hean Gan
Keyword(s):  
Offshore Structures ◽  
Daily Basis ◽  
Robotic Platform ◽  
Destructive Testing ◽  
Content Type ◽  
Integrity Assessment ◽  
Human Operators ◽  
Chain Links ◽  
Mooring Chain ◽  
Magnetic Adhesion

Purpose Mooring chains used to stabilise offshore floating platforms are often subjected to harsh environmental conditions on a daily basis, i.e. high tidal waves, storms, etc. Therefore, the integrity assessment of chain links is vital, and regular inspection is mandatory for offshore structures. The development of chain climbing robots is still in its infancy due to the complicated climbing structure presented by mooring chains. The purpose of this paper is to establish an automated climbing technique for mooring chain inspection. Design/methodology/approach This paper presents a Cartesian legged tracked-wheel crawler robot developed for mooring chain inspection. The proposed robot addresses the misalignment condition of the mooring chains which is commonly evident in in situ conditions. Findings The mooring chain link misalignment is investigated mathematically and used as a design parameter for the proposed robot. The robot is validated with laboratory-based climbing experiments. Practical implications Chain breaking can lead to vessel drift and serious damage such as riser rupture, production shutdown and hydrocarbon release. Currently, structural health monitoring of chain links is conducted using either remotely operated vehicles which come at a high cost or by manual means which increase the danger to human operators. The robot can be used as a platform to convey equipment, i.e. tools for non-destructive testing/evaluation applications. Originality/value This study has upgraded a previously designed magnetic adhesion tracked-wheel mooring chain climbing robot to address the misalignment issues of operational mooring chains. As a result of this study, the idea of an orthogonally placed Cartesian legged-magnetic adhesion tracked wheel robotic platform which can eliminate concerns related to the misaligned mooring chain climbing has been established.

Scale Effect in Ice Flexural Strength

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Mohamed Aly ◽  
Rocky Taylor ◽  
Eleanor Bailey Dudley ◽  
Ian Turnbull
Keyword(s):  
Flexural Strength ◽  
Sea Ice ◽  
Probabilistic Models ◽  
Scale Effects ◽  
Offshore Structures ◽  
Bridge Piers ◽  
Freshwater Ice ◽  
Flexural Failure ◽  
Ice Loads ◽  
Ice Strength

Ice flexural strength is an important parameter in the assessment of ice loads on the hulls of ice-class ships, sloped offshore structures, and sloped bridge piers. While scale effects in compressive ice strength are well known, there has been debate as to the extent of scale effects in ice flexural strength. To investigate scale effects during flexural failure of both freshwater and saline ice, a comprehensive up-to-date database of beam flexural strength measurements has been compiled. The database includes 2073 freshwater ice beam tests with beam volumes between 0.00016 and 2.197 m3, and 2843 sea ice beam tests with volumes between 0.00048 and 59.87 m3. The data show a considerable decrease in flexural strength as the specimen size increases, when examined over a large range of scales. Empirical models of freshwater ice flexural strength as a function of beam volume, and of saline ice as function of beam and brine volumes have been developed using regression analysis. For freshwater ice, the scale-dependent flexural strength is given as: σf=839(V/V1)−0.13 For sea ice, the dependence of flexural strength has been modeled as: σ=1324(V/V1)−0.054e−4.969vb. Probabilistic models based on the empirical data were developed based on an analysis of the residuals, and can be used to enhance probabilistic analysis of ice loads where ice flexural strength is an input.

Statistical Uncertainties in Wave Heights and Combined Loads on Offshore Structures

1991 ◽  
Vol 113 (2) ◽  
pp. 156-161
Author(s):  
S. R. Winterstein ◽  
S. Haver
Keyword(s):  
Environmental Variables ◽  
Probabilistic Models ◽  
Offshore Structures ◽  
Annual Maximum ◽  
Storm Events ◽  
Base Shear ◽  
Combined Loads ◽  
Wave Heights ◽  
Gumbel Model ◽  
Non Gaussian

Probabilistic models of combined environmental variables are shown, and their effect on the probability distribution of annual maximum base shear is estimated. A new “generalized Gumbel” model is introduced for the critical wave height parameter. By preserving higher statistical moments, this model better follows extreme storm events. Uncertainty in this model is included through statistical uncertainty in these moments. Corresponding reliability confidence intervals are also shown as a function of the sample size of hindcast data. Finally, models of the non-Gaussian crest and the drag parameter are found to be of similar importance in predicting the 100-yr base shear.

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