Assessment of Uncertainty Sources in Fatigue Usage in Relation to Deterministic Margins, and Sensitivity Analysis

2017 ◽  
Author(s):  
Y. S. Garud ◽  
David A. Steininger
Keyword(s):  
Sensitivity Analysis ◽  
Safety Factor ◽  
Environmental Effects ◽  
Design Criterion ◽  
Safety Factors ◽  
Uncertainty Sources ◽  
Sensitivity Assessment ◽  
Asme Code ◽  
Taylor Series Method ◽  
The Impact

Considerations of environmental effects in fatigue have resulted in proposals to augment the original basis and deterministic methods of fatigue assessment, such as in the ASME Code Subarticles NB-3200 and NB-3600. This process of deterministically combining various elements, each with its own set of safety factors, of the CUF-based assessment has the potential to be overly conservative and restrictive in practice. Furthermore, as in the commonly used deterministic design approaches, fixed safety factors are subjectively assigned; as a result the approach does not provide a logical basis to account for uncertainties or variability, and the resulting level of reliability cannot be assessed quantitatively. Therefore, it is useful and desirable to complement the simplicity of deterministic approach by relating the safety factor to target reliability (or probability of meeting the design criterion) so that an appropriately adequate conservatism can be utilized. The feasibility of such an inter-relation and its underlying probabilistic basis were demonstrated in our recent paper that provided a rational basis to account for the significant uncertainties in assessing the CUF-based fatigue including environmental effects. The objective of this paper is to provide further assessment of the above basis for uncertainty quantification and its linkage to deterministic safety factor approach, with additional focus on the quantitative sensitivity analysis of varied sources of uncertainty in the CUF estimation. Results of the case studies implementing the proposed approach combining these uncertainties are presented. New expressions for sensitivity assessment are developed. Results of sensitivity analysis are presented with the goal of demonstrating the sensitivity/ranking of significant contributors to the final CUF uncertainty and the resulting deterministic margins in relation to the target (specified) reliability. The overall approach, also summarized in the paper, utilizes the generally accepted concept of propagation of input uncertainties based on the Taylor series method and the framework of the stress-strength interference technique. The utility and limitations of the approach are discussed in defining the acceptable deterministic margins and in quantifying the impact of various elements of conservatism in the current CUF based fatigue evaluations.

An Approach for a Statistical Evaluation of Uncertainty in Assessing Fatigue Usage Including Environmental Effects

2014 ◽  
Author(s):  
Y. S. Garud ◽  
David A. Steininger ◽  
Ken Wolfe
Keyword(s):  
Environmental Effects ◽  
Critical Issue ◽  
Performance Criterion ◽  
Fatigue Performance ◽  
Statistical Characteristics ◽  
Original Design ◽  
Uncertainty Distribution ◽  
Asme Code ◽  
Input Variables ◽  
The Impact

The assessment for adequacy in managing the effects of fatigue in the ASME Code Class-1 (pressure boundary) components is based on a calculated measure of the projected fatigue damage. This measure is the highest cumulative usage factor (CUF) in a given component under a specified set of cyclic loadings and their expected number of repetitions. The Code-based calculation of CUF and its adjustments for potential environmentally-assisted fatigue (EAF) damage accumulation utilize a multitude of inputs, and conservative assumptions and applied margins. To support the extended service life beyond the original design, or longer life of new designs, changes in inputs and/or conservative assumptions used in these deterministically calculated CUFs are often made to meet a deterministic performance criterion. This makes the impact of uncertainty in the inputs and/or changes in the conservative adjustments difficult to assess. This paper presents a generic, engineering approach for estimation of the uncertainty distribution of CUF based on the expected statistical characteristics of input variables used in the calculation of EAF-based CUF. The approach does not involve Monte Carlo sampling. The proposed statistical approach analytically combines variances of the inputs leading to an acceptable estimation of the total variance of the CUF. The approach does not require specification of full probability distribution(s) for the input variables, nor is the dependence between variables a critical issue from the analytical point of view. Feasibility and limitations of the approach are discussed in relation to the NB-3200 and NB-3600 procedures of the ASME Code and the current Fen-based augmentation for environmental effects. This approach is further examined in the framework of stress–strength interference methodology to account for the uncertainty in the fatigue performance criterion, that can lead to a rational deterministic safety factor interpretation and its relation to a quantifiable measure of the probability of exceeding the fatigue performance criterion.

An Approach for a Statistical Evaluation of Uncertainty in Assessing Fatigue Usage Including Environmental Effects

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Yogendra S. Garud ◽  
David A. Steininger ◽  
Ken Wolfe
Keyword(s):  
Environmental Effects ◽  
Critical Issue ◽  
Performance Criterion ◽  
Fatigue Performance ◽  
Statistical Characteristics ◽  
Original Design ◽  
Uncertainty Distribution ◽  
Asme Code ◽  
Input Variables ◽  
The Impact

The assessment for adequacy in managing the effects of fatigue in the ASME Code Class-1 (pressure boundary) components is based on a calculated measure of the projected fatigue damage. This measure is the highest cumulative usage factor (CUF) in a given component under a specified set of cyclic loadings and their expected number of repetitions. The Code based calculation of CUF and its adjustments for potential environmentally assisted fatigue (EAF) damage accumulation utilize a multitude of inputs, and conservative assumptions and applied margins. To support the extended service life beyond the original design, or longer life of new designs, changes in inputs and/or conservative assumptions used in these deterministically calculated CUFs are often made to meet a deterministic performance criterion. This makes the impact of uncertainty in the inputs and/or changes in the conservative adjustments difficult to assess. This paper presents a generic, engineering approach for estimation of the uncertainty distribution of CUF based on the expected statistical characteristics of input variables used in the calculation of EAF-based CUF. The approach does not involve Monte Carlo sampling. The proposed statistical approach analytically combines variances of the inputs leading to an acceptable estimation of the total variance of the CUF. The approach does not require specification of full probability distribution(s) for the input variables, nor is the dependence between variables a critical issue from the analytical point of view. Feasibility and limitations of the approach are discussed in relation to the NB-3200 and NB-3600 procedures of the ASME Code and the current Fen-based augmentation for environmental effects. This approach is further examined in the framework of stress–strength interference methodology to account for the uncertainty in the fatigue performance criterion which can lead to a rational deterministic safety factor interpretation and its relation to a quantifiable measure of the probability of exceeding the fatigue performance criterion.

Elastoplastic Collapse of Tubes Under External Pressure

1970 ◽  
Vol 92 (4) ◽  
pp. 735-742 ◽  
Author(s):  
O. Heise ◽  
E. P. Esztergar
Keyword(s):  
Safety Factor ◽  
External Pressure ◽  
Code Design ◽  
Test Results ◽  
Plastic Range ◽  
Safety Factors ◽  
Characteristic Ratio ◽  
Collapse Pressure ◽  
Asme Code ◽  
Current Design

The specific objective of this paper is to develop external pressure design safety factors that are consistent with theory, test results, and service experience for application in pressure vessel codes. The standard methods of collapse pressure predictions for the buckling of tubes in the elastic and the plastic ranges are briefly reviewed. Test results on tubes made of various materials were collected from the literature and are compared with the corresponding predictions. For thin tubes which buckle in the elastic range, the correlation between the theory and experimentally measured collapse pressure is shown to be poor, justifying the large safety factors used in current design practice. For intermediate and thick tubes which buckle in the plastic range, it is demonstrated that the correlation of test results and theory improves significantly with decreasing radius-to-thickness ratio of the tubes. The range of improved correlation is identified by a material dependent “characteristic ratio” of tube radius and wall thickness. Based on the experimental evidence, a variable safety factor is proposed for inclusion in the ASME Code design charts. A simple formula for the conversion of the present plastic range allowable pressure into the new increased allowable pressure is presented. The consequences of the variable safety factor are discussed with respect to the resulting actual margin of safety, the economic advantages, and the requirements for the development of design rules for the creep range.

Evaluation of Hydraulic Fracturing Models and Their Limitations to Predict No-Drill Zones for Horizontal Directional Drilling

2018 ◽  
Author(s):  
Saeed Delara ◽  
Kendra MacKay
Keyword(s):  
Hydraulic Fracturing ◽  
Safety Factor ◽  
Standard Procedure ◽  
Accurate Determination ◽  
Strength Properties ◽  
Analytical Models ◽  
Alternative Methods ◽  
Directional Drilling ◽  
Horizontal Directional Drilling ◽  
The Impact

Horizontal directional drilling (HDD) has become the preferred method for trenchless pipeline installations. Drilling pressures must be limited and a “no-drill zone” determined to avoid exceeding the strength of surrounding soil and rock. The currently accepted industry method of calculating hydraulic fracturing limiting pressure with application of an arbitrary safety factor contains several assumptions that are often not applicable to specific ground conditions. There is also no standard procedure for safety factor determination, resulting in detrimental impacts on drilling operations. This paper provides an analysis of the standard methods and proposes two alternative analytical models to more accurately determine the hydraulic fracture point and acceptable drilling pressure. These alternative methods provide greater understanding of the interaction between the drilling pressures and the surrounding ground strength properties. This allows for more accurate determination of horizontal directional drilling limitations. A comparison is presented to determine the differences in characteristics and assumptions for each model. The impact of specific soil properties and factors is investigated by means of a sensitivity analysis to determine the most critical soil information for each model.

scholarly journals Robust Inferences from a Before-and-After Study with Multiple Unaffected Control Groups

2013 ◽  
Vol 1 (2) ◽  
pp. 209-234 ◽  
Author(s):  
Pengyuan Wang ◽  
Mikhail Traskin ◽  
Dylan S. Small
Keyword(s):  
Sensitivity Analysis ◽  
Control Groups ◽  
Two Stage ◽  
Time Effects ◽  
Unaffected Control ◽  
Group Time ◽  
Before And After ◽  
Group Variation ◽  
The Impact ◽  
Before And After Study

AbstractThe before-and-after study with multiple unaffected control groups is widely applied to study treatment effects. The current methods usually assume that the control groups’ differences between the before and after periods, i.e. the group time effects, follow a normal distribution. However, there is usually no strong a priori evidence for the normality assumption, and there are not enough control groups to check the assumption. We propose to use a flexible skew-t distribution family to model group time effects, and consider a range of plausible skew-t distributions. Based on the skew-t distribution assumption, we propose a robust-t method to guarantee nominal significance level under a wide range of skew-t distributions, and hence make the inference robust to misspecification of the distribution of group time effects. We also propose a two-stage approach, which has lower power compared to the robust-t method, but provides an opportunity to conduct sensitivity analysis. Hence, the overall method of analysis is to use the robust-t method to test for the overall hypothesized range of shapes of group variation; if the test fails to reject, use the two-stage method to conduct a sensitivity analysis to see if there is a subset of group variation parameters for which we can be confident that there is a treatment effect. We apply the proposed methods to two datasets. One dataset is from the Current Population Survey (CPS) to study the impact of the Mariel Boatlift on Miami unemployment rates between 1979 and 1982.The other dataset contains the student enrollment and grade repeating data in West Germany in the 1960s with which we study the impact of the short school year in 1966–1967 on grade repeating rates.

scholarly journals A Model for the Thermal Behaviour of an Offshore Cable Installed in a J-Tube

Proceedings ◽  
2020 ◽  
Vol 58 (1) ◽  
pp. 31
Author(s):  
Jeremy Arancio ◽  
Ahmed Ould El Moctar ◽  
Minh Nguyen Tuan ◽  
Faradj Tayat ◽  
Jean-Philippe Roques
Keyword(s):  
Sensitivity Analysis ◽  
Numerical Model ◽  
Thermal Behaviour ◽  
Energy Production ◽  
Power Transmission ◽  
Temperature Fields ◽  
Sobol Indices ◽  
Lumped Element ◽  
Thermal Phenomena ◽  
The Impact

In the race for energy production, supplier companies are concerned by the thermal rating of offshore cables installed in a J-tube, not covered by IEC 60287 standards, and are now looking for solutions to optimize this type of system. This paper presents a numerical model capable of calculating temperature fields of a power transmission cable installed in a J-tube, based on the lumped element method. This model is validated against the existing literature. A sensitivity analysis performed using Sobol indices is then presented in order to understand the impact of the different parameters involved in the heating of the cable. This analysis provides an understanding of the thermal phenomena in the J-tube and paves the way for potential technical and economic solutions to increase the ampacity of offshore cables installed in a J-tube.

scholarly journals Assessing Genotypic and Environmental Effects on Endophyte Communities of Fraxinus (Ash) Using Culture Dependent and Independent DNA Sequencing

2021 ◽  
Vol 7 (7) ◽  
pp. 565
Author(s):  
Anindita Lahiri ◽  
Brian R. Murphy ◽  
Trevor R. Hodkinson
Keyword(s):  
Community Composition ◽  
Environmental Effects ◽  
High Throughput Sequencing ◽  
Fungal Community Composition ◽  
Species Identity ◽  
Ash Dieback ◽  
Hymenoscyphus Fraxineus ◽  
Culture Independent ◽  
The Impact ◽  
Culture Dependent

Fraxinus excelsior populations are in decline due to the ash dieback disease Hymenoscyphus fraxineus. It is important to understand genotypic and environmental effects on its fungal microbiome to develop disease management strategies. To do this, we used culture dependent and culture independent approaches to characterize endophyte material from contrasting ash provenances, environments, and tissues (leaves, roots, seeds). Endophytes were isolated and identified using nrITS, LSU, or tef DNA loci in the culture dependent assessments, which were mostly Ascomycota and assigned to 37 families. Few taxa were shared between roots and leaves. The culture independent approach used high throughput sequencing (HTS) of nrITS amplicons directly from plant DNA and detected 35 families. Large differences were found in OTU diversity and community composition estimated by the contrasting approaches and these data need to be combined for estimations of the core endophyte communities. Species richness and Shannon index values were highest for the leaf material and the French population. Few species were shared between seed and leaf tissue. PCoA and NMDS of the HTS data showed that seed and leaf microbiome communities were highly distinct and that there was a strong influence of Fraxinus species identity on their fungal community composition. The results will facilitate a better understanding of ash fungal ecology and are a step toward identifying microbial biocontrol systems to minimize the impact of the disease.

scholarly journals Addition of Flucytosine to Fluconazole for the Treatment of Cryptococcal Meningitis in Africa: A Multicountry Cost-effectiveness Analysis

2019 ◽  
Vol 70 (1) ◽  
pp. 26-29 ◽  
Author(s):  
Tinevimbo Shiri ◽  
Angela Loyse ◽  
Lawrence Mwenge ◽  
Tao Chen ◽  
Shabir Lakhi ◽  
...  
Keyword(s):  
Sensitivity Analysis ◽  
Cost Effectiveness ◽  
Cryptococcal Meningitis ◽  
Cost Effective ◽  
Immunodeficiency Virus ◽  
The Mean ◽  
The Cost ◽  
The Impact ◽  
Costing Analysis ◽  
Very High

Abstract Background Mortality from cryptococcal meningitis remains very high in Africa. In the Advancing Cryptococcal Meningitis Treatment for Africa (ACTA) trial, 2 weeks of fluconazole (FLU) plus flucytosine (5FC) was as effective and less costly than 2 weeks of amphotericin-based regimens. However, many African settings treat with FLU monotherapy, and the cost-effectiveness of adding 5FC to FLU is uncertain. Methods The effectiveness and costs of FLU+5FC were taken from ACTA, which included a costing analysis at the Zambian site. The effectiveness of FLU was derived from cohorts of consecutively enrolled patients, managed in respects other than drug therapy, as were participants in ACTA. FLU costs were derived from costs of FLU+5FC in ACTA, by subtracting 5FC drug and monitoring costs. The cost-effectiveness of FLU+5FC vs FLU alone was measured as the incremental cost-effectiveness ratio (ICER). A probabilistic sensitivity analysis assessed uncertainties and a bivariate deterministic sensitivity analysis examined the impact of varying mortality and 5FC drug costs on the ICER. Results The mean costs per patient were US $847 (95% confidence interval [CI] $776–927) for FLU+5FC, and US $628 (95% CI $557–709) for FLU. The 10-week mortality rate was 35.1% (95% CI 28.9–41.7%) with FLU+5FC and 53.8% (95% CI 43.1–64.1%) with FLU. At the current 5FC price of US $1.30 per 500 mg tablet, the ICER of 5FC+FLU versus FLU alone was US $65 (95% CI $28–208) per life-year saved. Reducing the 5FC cost to between US $0.80 and US $0.40 per 500 mg resulted in an ICER between US $44 and US $28 per life-year saved. Conclusions The addition of 5FC to FLU is cost-effective for cryptococcal meningitis treatment in Africa and, if made available widely, could substantially reduce mortality rates among human immunodeficiency virus–infected persons in Africa.

Impacts of high-speed railway on the industrial pollution emissions in China

Kybernetes ◽  
2020 ◽  
Vol 49 (11) ◽  
pp. 2713-2735 ◽  
Author(s):  
Xiaomin Fan ◽  
Yingzhi Xu ◽  
Yongqing Nan ◽  
Baoli Li ◽  
Haiya Cai
Keyword(s):  
Environmental Effects ◽  
Industrial Pollution ◽  
High Speed ◽  
Assessment Method ◽  
Economic Effects ◽  
High Speed Railway ◽  
Central Cities ◽  
Content Type ◽  
Pollution Emissions ◽  
The Impact

Purpose The purpose of this paper is to analyse the impact of high-speed railway (HSR) on industrial pollution emissions using the data for 285 prefecture-level cities in China from 2004 to 2016. Design/methodology/approach The research method used in this paper is the multi-period difference-in-differences (DID) model, which is an effective policy effect assessment method. To further address the issue of endogeneity, the DID integrated with the propensity score matching (PSM-DID) approach is employed to eliminate the potential self-selection bias. Findings The results show that the HSR has significantly reduced industrial pollution emissions, which is validated by several robustness tests. Compared with peripheral cities, HSR exerts a greater impact on industrial pollution emissions in central cities. In addition, the mechanism test reveals that the optimised allocation of inter-city industries is an important channel for HSR to mitigate industrial pollution emissions, and this is closely related to the location of HSR stations. Originality/value Previous studies have paid more attention to evaluating the economic effects of HSR, however, most of these studies overlook its environmental effects. Consequently, the impact of HSR on industrial pollution emissions is led by using multi-period DID models in this paper, in which the environmental effects are measured. The results of this paper can provide a reference for the pollution reduction policies and also the coordinated development of economic growth and environmental quality.

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