A Probabilistic Approach to Fatigue Safety and Integrity of TTRs

2014 ◽  
Author(s):  
Mir Emad Mousavi ◽  
Sanjeev Upadhye ◽  
Vishnu Vijayaraghavan ◽  
Kevin Haverty
Keyword(s):  
Fatigue Damage ◽  
Probabilistic Method ◽  
Probabilistic Approach ◽  
Probabilistic Methods ◽  
Fatigue Reliability ◽  
Fatigue Design ◽  
Integrity Index ◽  
Biased Estimators ◽  
Integrity Analysis

Probabilistic methods can improve the reliability of fatigue damage evaluation in top tensioned (production) risers because they tend to provide less biased estimators on their safety, which can be used for more reliable decision making concerning their design. Such methods consider the collective impact of uncertainties in the riser system, which is not accurately assessed in conventional fatigue analysis. The large factors of safety that are commonly used in deterministic-based fatigue damage assessment tend to assure the high safety of the design, still they are generic factors that do not take advantage of available data for accurate quantification of system safety. This paper presents a probabilistic method toward fatigue reliability and integrity analysis of TTR systems. By using rules of probability, a simplified method is developed to estimate the probability of failure of the TTR system in its lifetime, considering the uncertainties with the Palmgren-Miner rule, the cyclic loads, and the fatigue strength of the components, and other analysis approximations. The method is then used for a comparative assessment on the fatigue reliability of the TTR components and calculating its fatigue Integrity Index. The method is illustrated in a case study and is used to provide recommendations that could possibly improve the TTR fatigue design by reducing its cost, increasing its safety, and maximizing its integrity.

Fatigue Safety Factors for Deepwater Risers

2002 ◽  
Author(s):  
B. Stahl ◽  
H. Banon
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Safety Factor ◽  
Damage Index ◽  
Rational Approach ◽  
Fatigue Reliability ◽  
Safety Factors ◽  
Fatigue Design ◽  
Uncertainty Parameters ◽  
Deepwater Risers

Fatigue life is governed by a number of variables that are highly uncertain. The safety factor on fatigue life is used in a deterministic way to account for the estimated fatigue damage uncertainty. High uncertainties lead to high fatigue safety factors, and vice versa. Evaluation of the uncertainties in the variables governing fatigue design provides a grip on what the safety factor should be. This paper addresses riser fatigue using a fatigue reliability model that is relatively simple but still captures the important elements of the fatigue problem. The bias and uncertainty of stress range are extremely important parameters in design against fatigue. This is due not only to the fact that these parameters are highly uncertain, but also to the fact that they are greatly amplified in the fatigue damage equation by the ‘slope’ m of the S-N curve. The Palmgren-Miner fatigue damage index and the intercept value of the S-N curve are additional important variables in fatigue design. A model for combining wave-induced and vortex-induced vibration (VIV) is introduced together with the best available data and reference to industry work in this technology area. A recently completed joint industry project on riser reliability provides good calibration points for the critical fatigue reliability variables. Reliability and sensitivity studies are performed to demonstrate the effect of the uncertainty parameters. An approach to selecting deterministic fatigue design factors that yield specified reliability targets is developed and illustrated. The study provides a rational approach to selecting safety factors for design of deepwater risers, taking into account both wave and VIV-induced fatigue damage.

scholarly journals Fatigue damage and reliability assessment of subway train bogie frames under operating conditions

2020 ◽  
Vol 12 (1) ◽  
pp. 168781402090359
Author(s):  
Binjie Wang ◽  
Shouguang Sun ◽  
Shuang Ma ◽  
Xi Wang
Keyword(s):  
Fatigue Damage ◽  
Fatigue Cracks ◽  
Probabilistic Approach ◽  
Reliability Assessment ◽  
Elastic Vibration ◽  
Assessment Method ◽  
Operating Conditions ◽  
Fatigue Reliability ◽  
Rail Corrugation ◽  
Subway Train

Fatigue cracks developed on subway train bogie frames before reaching the designed lifetime, which poses great challenges to operational safety. This article presents a structural fatigue reliability assessment method combining both the in-service measurement of dynamic stress and probabilistic approach for lifetime prediction. It was found that curved interval with rail corrugation can induce the elastic vibration and the modal stress on the frame, which caused the accelerated accumulation of the fatigue damage. The predicted failure mileage for the welding joint with 99% reliability was only 340,000 km, which agreed well with the real operation situation.

Probabilistic Assessment of Low-Cycle Fatigue Behavior of Structural Welds

1976 ◽  
Vol 98 (1) ◽  
pp. 26-32 ◽  
Author(s):  
B. R. Ellingwood
Keyword(s):  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Probabilistic Methods ◽  
Cycle Fatigue ◽  
Loading History ◽  
Fatigue Reliability ◽  
Small Probability ◽  
Fatigue Design ◽  
Uncertainty In Design ◽  
Selection Of

Low-cycle fatigue behavior of structural welds is dependent on material characteristics, geometry at fatigue-critical locations, loading history including residual stresses, and environment. Since these factors may occur randomly and contribute significantly to the uncertainty in design, probabilistic methods are required for their analysis and for the development of appropriate fatigue design criteria. The analysis and prediction of low-cycle fatigue behavior of structural welds is discussed in terms of the foregoing factors. Consideration of statistical uncertainties in the various parameters enables prediction and interpretation of variability in fatigue response, and permits selection of design allowables which correspond to a small probability of unacceptable fatigue performance. These techniques are shown to provide a systematic basis for assessing fatigue reliability of structural welds.

Fatigue Variation in Ships due to the Variability of Environmental Loads

2012 ◽  
Author(s):  
Wengang Mao ◽  
Zhiyuan Li ◽  
Jonas W. Ringsberg ◽  
Igor Rychlik
Keyword(s):  
Fatigue Damage ◽  
Structural Integrity ◽  
Structural Strength ◽  
Fatigue Cracks ◽  
Maritime Industry ◽  
Fatigue Design ◽  
Routing Design ◽  
Potential Use

The design and analysis of structural strength against fatigue failure always includes large uncertainties. It is crucial to understand and identify the most important uncertainties that affect the performance, functionality and service life of an engineering structure — in particular when it comes to the safety aspect, which may involve the risk of loss of human lives. In maritime industry, it is known that due to various sources of uncertainties in ship fatigue design, some ships may survive (the occurrence of fatigue cracks which may endanger the structural integrity) much longer than their designed life, while other ships develop fatigue cracks far too early. The current investigation presents some of the most important uncertainties and their effects on the accuracy of fatigue assessments in a container vessel. The study emphasizes the analysis of the fatigue damage variation when the ship is sailing on different routings between two ports. A fatigue model developed by the authors for ship fatigue routing application is employed to estimate the long term fatigue damage. In this model, only a few parameters, i.e. the encountered significant wave height and operational profiles, are needed. The procedure of using this model for a ship fatigue routing design is described in detail. Its potential use and benefits are demonstrated in a case study by a 2,800 TEU container ship using both full-scale measurements and hindcast wave data. It is shown that awareness and careful fatigue routing design can reduce fatigue damage significantly by up to 50%!

Probabilistic Failure Analysis of Steel Structures Exposed to Fatigue

2013 ◽  
Vol 577-578 ◽  
pp. 101-104 ◽  
Author(s):  
Martin Krejsa
Keyword(s):  
Failure Analysis ◽  
Fatigue Damage ◽  
Fatigue Cracks ◽  
Probabilistic Method ◽  
Reliability Assessment ◽  
Steel Structures ◽  
Probabilistic Methods ◽  
Cyclic Loads ◽  
Structural Details ◽  
Probabilistic Failure Analysis

The paper is focuses on one of probabilistic methods which can be used for failure analysis and reliability assessment of steel structures which are subject to cyclic loads and exposed to fatigue. A particular attention is paid to creation and propagation of fatigue cracks from edges and surface. On the basis of the reliability assessment, a system of inspections is proposed for structural details which tend to be sensitive to fatigue damage. A new probabilistic method which is still under development - Direct Optimized Probabilistic Calculation (DOProC) was used for this probabilistic task. This method is the basis of the FCProbCalc code.

Reliability Assessment and Useful Life of Turbine Blades Using Probabilistic Methods

2011 ◽  
Author(s):  
J. A. Rodri´guez ◽  
J. C. Garci´a ◽  
G. Urquiza ◽  
M. Basurto ◽  
F. Sierra
Keyword(s):  
Probabilistic Method ◽  
Turbine Blades ◽  
Probabilistic Approach ◽  
Repeated Measurements ◽  
Probabilistic Methods ◽  
Economic Losses ◽  
Steam Turbines ◽  
Good Judgment ◽  
Stable Conditions ◽  
Useful Life

Steam turbines have numerous applications in various sectors of industry and it is known by experience that blade failures are the most common origin of breakdown in these machines, causing significant economic losses in turbomachinery industry. The turbines are designed to work in stable conditions of operation; nevertheless, failure in blades could appear after a short time of work. Failures are attributed to resonance of the blades to certain excitation frequencies. The vibration stresses reached by resonance conditions and the combination of other random variables could determine the useful life of the blades. In the deterministic design of turbines, the failure possibility is reduced in acceptable small levels by means of safety factors based on the good judgment. However, the possibility of failure could be reduced by using probabilistic methods. In the probabilistic approach, the variability in the properties of the material, tolerances in manufacture and uncertainties in the load are considered with statistical methods. The probabilistic method allows to evaluate the uncertainty or randomness present in some variables which translates in a high level of reliability in the results and a better operation analysis of the turbines. There are a lot of variables in the operation of the turbomachineries, in its design and construction. These variables are conceived under a certain degree of uncertainty, that is to say, these cannot be totally controlled. Generally, repeated measurements of mechanical phenomena generate a lot of input variables each one with certain instability in their magnitude that contributes to increase the probability of failure before the estimated time. In this work the reliability and useful life of blade steam turbines of 110 MW of the L-0 stage are analyzed using deterministic numerical methods and a probabilistic approach. Curves of the useful life for both cases are obtained. The probabilistic approach shows that failure occurs when a combination of variables and the presence of failure are combined.

scholarly journals Probabilistic Approach to Precipitation-Runoff Relation in a Mountain Catchment: A Case Study of the Kłodzka Valley in Poland

Water ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1229
Author(s):  
Adam Perz ◽  
Leszek Sobkowiak ◽  
Dariusz Wrzesiński
Keyword(s):  
Water Resources ◽  
Probabilistic Approach ◽  
Geological Structure ◽  
Probabilistic Methods ◽  
Copula Functions ◽  
Zonal Distribution ◽  
North West ◽  
Total Runoff ◽  
Mountain Catchment

On the basis of daily precipitation and discharges recorded in 1974–2013 relations between precipitation and runoff in the Kłodzka Valley (KV) in south-western Poland were analyzed. The degree of synchronicity between them was determined using the bivariate Archimedean copulas. This study aims at identifying and then describe in a probabilistic way the precipitation and runoff relations in the area playing an important role in the formation of water resources, but also particularly exposed to flooding. It was found that isolines of the synchronous occurrence of precipitation and total runoff in the Nysa Kłodzka catchment controlled by gauge Kłodzko had a zonal distribution, with the synchronicity values decreasing from south-east to north-west of the study area. This proves that its eastern part is more hydrologically active, compared to the western part, and as such it determines the amount of water resources of the study area. The decrease in synchronicity is influenced by the type and spatial distribution of precipitation, the structure of water supply, and the geological structure of the study area. Moreover, probabilistic methods applied in this research differ from those used in previous research on the hydrology of KV, as we propose using the copula functions. The method presented can be used to evaluate the availability of water resources in areas playing a key role in their formation on different scales.

scholarly journals Conception and Evolution of the Probabilistic Methods for Ship Damage Stability and Flooding Risk Assessment

2021 ◽  
Vol 9 (6) ◽  
pp. 667
Author(s):  
Dracos Vassalos ◽  
M. P. Mujeeb-Ahmed
Keyword(s):  
Risk Assessment ◽  
Probabilistic Method ◽  
Probabilistic Methods ◽  
Full Description ◽  
Safety Level ◽  
Probability Of Survival ◽  
Damage Stability ◽  
Passenger Ships ◽  
Flooding Hazards ◽  
Flooding Risk

The paper provides a full description and explanation of the probabilistic method for ship damage stability assessment from its conception to date with focus on the probability of survival (s-factor), explaining pertinent assumptions and limitations and describing its evolution for specific application to passenger ships, using contemporary numerical and experimental tools and data. It also provides comparisons in results between statistical and direct approaches and makes recommendations on how these can be reconciled with better understanding of the implicit assumptions in the approach for use in ship design and operation. Evolution over the latter years to support pertinent regulatory developments relating to flooding risk (safety level) assessment as well as research in this direction with a focus on passenger ships, have created a new focus that combines all flooding hazards (collision, bottom and side groundings) to assess potential loss of life as a means of guiding further research and developments on damage stability for this ship type. The paper concludes by providing recommendations on the way forward for ship damage stability and flooding risk assessment.

Effect of Manufacturing Variability on Turbine Engine Performance: A Probabilistic Study

2013 ◽  
Author(s):  
Michael Gorelik ◽  
Jacob Obayomi ◽  
Jack Slovisky ◽  
Dan Frias ◽  
Howie Swanson ◽  
...  
Keyword(s):  
Performance Metrics ◽  
Model Development ◽  
Engine Performance ◽  
Performance Model ◽  
Probabilistic Methods ◽  
System Level ◽  
Turbine Engine ◽  
Probabilistic Study ◽  
Blade Geometry

While turbine engine Original Equipment Manufacturers (OEMs) accumulated significant experience in the application of probabilistic methods (PM) and uncertainty quantification (UQ) methods to specific technical disciplines and engine components, experience with system-level PM applications has been limited. To demonstrate the feasibility and benefits of an integrated PM-based system, a numerical case study has been developed around the Honeywell turbine engine application. The case study uses experimental observations of engine performance such as horsepower and fuel flow from a population of engines. Due to manufacturing variability, there are unit-to-unit and supplier-to-supplier variations in compressor blade geometry. Blade inspection data are available for the characterization of these geometric variations, and CFD analysis can be linked to the engine performance model, so that the effect of blade geometry variation on system-level performance characteristics can be quantified. Other elements of the case study included the use of engine performance and blade geometry data to perform Bayesian updating of the model inputs, such as efficiency adders and turbine tip clearances. A probabilistic engine performance model was developed, system-level sensitivity analysis performed, and the predicted distribution of engine performance metrics was calibrated against the observed distributions. This paper describes the model development approach and key simulation results. The benefits of using PM and UQ methods in the system-level framework are discussed. This case study was developed under Defense Advanced Research Projects Agency (DARPA) funding which is gratefully acknowledged.

scholarly journals Statistical Downscaling of Daily Wind Speed Variations

2014 ◽  
Vol 53 (3) ◽  
pp. 660-675 ◽  
Author(s):  
Megan C. Kirchmeier ◽  
David J. Lorenz ◽  
Daniel J. Vimont
Keyword(s):  
Wind Speed ◽  
Gamma Distribution ◽  
Large Scale ◽  
Probabilistic Method ◽  
Probabilistic Approach ◽  
Local Scale ◽  
Scale Parameters ◽  
Wind Speeds ◽  
Distribution Shape ◽  
Realistic Information

AbstractThis study presents the development of a method to statistically downscale daily wind speed variations in an extended Great Lakes region. A probabilistic approach is used, predicting a daily-varying probability density function (PDF) of local-scale daily wind speed conditioned on large-scale daily wind speed predictors. Advantages of a probabilistic method are that it provides realistic information on the variance and extremes in addition to information on the mean, it allows the autocorrelation of downscaled realizations to be tuned to match the autocorrelation of local-scale observations, and it allows flexibility in the use of the final downscaled product. Much attention is given to fitting the proper functional form of the PDF by investigating the observed local-scale wind speed distribution (predictand) as a function of the decile of the large-scale wind (predictor). It is found that the local-scale standard deviation and the local-scale shape parameter (from a gamma distribution) are nonconstant functions of the large-scale predictor. As such, a vector generalized linear model is developed to relate the large-scale and local-scale wind speeds. Maximum likelihood and cross validation are used to fit local-scale gamma distribution shape and scale parameters to the large-scale wind speed. The result is a daily-varying probability distribution of local-scale wind speed, conditioned on the large-scale wind speed.

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