Time-dependent creep analysis and life assessment of 304 L austenitic stainless steel thick pressurized truncated conical shells

Mosayeb Davoudi Kashkoli,Mohammad Zamani Nejad 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.28 No.3

This paper presents a semi-analytical solution for the creep analysis and life assessment of 304L austenitic stainless steel thick truncated conical shells using multilayered method based on the first order shear deformation theory (FSDT). The cone is subjected to the non-uniform internal pressure and temperature gradient. Damages are obtained in thick truncated conical shell using Robinson's linear life fraction damage rule, and time to rupture and remaining life assessment is determined by Larson-Miller Parameter (LMP). The creep response of the material is described by Norton's law. In the multilayer method, the truncated cone is divided into <i>n</i> homogeneous disks, and <i>n</i> sets of differential equations with constant coefficients. This set of equations is solved analytically by applying boundary and continuity conditions between the layers. The results obtained analytically have been compared with the numerical results of the finite element method. The results show that the multilayered method based on FSDT has an acceptable amount of accuracy when one wants to obtain radial displacement, radial, circumferential and shear stresses. It is shown that non-uniform pressure has significant influences on the creep damages and remaining life of the truncated cone.

Creep damage and life assessment of thick cylindrical pressure vessels with variable thickness made of 304L austenitic stainless steel

Mosayeb Davoudi Kashkoli,Khosro Naderan Tahan,Mohammad Zamani Nejad 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.32 No.6

Using firstfirst-order shear deformation theory (FSDT), a semi semi-analytical solution is employed to analyze creep damage and remaining life assessment of 304L austenitic stainless steel thick (304L ASS) cylindrical pressure vessels with variable thickness subjected to the temperature gradient and internal non non-uniform pressure. Damages are obtained in thick cylinder using RobinsonRobinson’s linear life fraction damage rule, and time to rupture and remaining life assessment is determined by Larson Larson-Miller Parameter (LMP). The thermo-elastic creep response of the material is described by Norton Norton’s law. The novelty of the present work is that it seeks to investigate creep damage and life assessment of the vessels with variable thickness made of 304L ASS using LMP based on first first-order shear deformation theory. A numerical solution using finite element method (FEM) is also presented and good agreement is found. It is shown that temperature gradient and non non-uniform pressure have significant influences on the creep damages and remaining li fe of the vessel vessel.

Multiple Structural Breaks in Korea's Macroeconomic Data

Mosayeb Pahlavani,Charles Harvie 한국경제연구학회 2008 Korea and the World Economy Vol.9 No.3

The Korean economy has undergone rapid economic growth and structural change since the early 1960s. Over this period of time it has been one of the fastest growing economies in Asia, but, more recently, has been vulnerable to external shocks which have contributed to major volatility in the economy. This paper employs quarterly time series data to endogenously determine the timing of major structural breaks for various macroeconomic variables in the Korean economy. The ADF (Augmented Dickey and Fuller) test and the LP (Lumsdaine and Papell, 1997) test are used to examine the time series properties of the data. The ADF test results provide no evidence against the unit root null hypothesis in all major macroeconomic variables under study. After accounting for the two most significant structural breaks in the data impacting on both the intercept and trend (model CC), results from the LP test indicate that the null of at least one unit root is rejected for some of the variables under investigation at the 10% level or better. The paper also goes further to shed some light on the implications of the Asian financial crisis on the Korean economy, as this is considered to be the most severe external shock to affect the economy in the recent past. Our preliminary empirical findings verify this, indicating that the dates of structural breaks in most cases point to the Asian financial crisis. However, using the LP approach it is shown that a second structural break can be identified, the timing of which depends on key policy changes or other factors contributing to economic turbulence in the Korean economy. The estimated two structural breaks were found to be statistically significant for all of the variables under investigation.

A comparison between the dynamic and static stiffness of ballasted track: A field study

Mosayeb, Seyed-Ali,Zakeri, Jabbar-Ali,Esmaeili, Morteza Techno-Press 2016 Geomechanics & engineering Vol.11 No.6

Rail support modulus is an important parameter for analysis and design of ballasted railway tracks. One of the challenges in track stiffness assessment is its dynamic nature under the moving trains which differs it from the case of standing trains. So the present study is allocated to establish a relation between the dynamic and static stiffness of ballasted tracks via field measurements. In this regard, two different sites of ballasted tracks with wooden and concrete sleepers were selected and the static and dynamic stiffness were measured based on Talbot - Wasiutynski method. In this matter, the selected tracks were loaded by two heavy and light car bodies for standing and moving conditions and consequently the deflection basins were evaluated in both sites. Knowing the deflection basins respect to light and heavy loading conditions, both of static and dynamic stiffness values were extracted. Finally two definite relations were obtained for ballasted tracks with wooded and concrete sleepers.

Families of Distributions Arising from Distributions of Ordered Data

Ahmadi, Mosayeb,Razmkhah, M.,Mohtashami Borzadaran, G.R. The Korean Statistical Society 2015 Communications for statistical applications and me Vol.22 No.2

A large family of distributions arising from distributions of ordered data is proposed which contains other models studied in the literature. This extension subsume many cases of weighted random variables such as order statistics, records, k-records and many others in variety. Such a distribution can be used for modeling data which are not identical in distribution. Some properties of the theoretical model such as moment, mean deviation, entropy criteria, symmetry and unimodality are derived. The proposed model also studies the problem of parameter estimation and derives maximum likelihood estimators in a weighted gamma distribution. Finally, it will be shown that the proposed model is the best among the previously introduced distributions for modeling a real data set.

Testing for Structural Breaks in the Korean Economy 1980-2005: An application of the Innovational outlier and additive outlier models

Charles Harvie,Mosayeb Pahlavani 한국경제연구학회 2006 Korea and the World Economy Vol.7 No.2

Sources of Economic Growth in South Korea

Charles Harvie,Mosayeb Pahlavani 한국경제연구학회 2007 Korea and the World Economy Vol.8 No.2

The primary objective of this paper is to examine the major determinants of GDP growth in South Korea, emphasizing the importance of investment, trade and human capital using quarterly time series data covering the period 1980Q1 to 2005Q3. The time series properties of the data are, first, analyzed using the Zivot-Andrews (1992) model. The empirical results derived indicate that there is insufficient evidence against the null hypothesis of unit roots for all of the variables under investigation. Second, the Gregory-Hansen (1996) co integration technique, allowing for the presence of potential structural breaks in the data, is applied, and is found to reject the null hypothesis of no co integration relationship in favour of the existence of at least one cointegration relation in the presence of single structural breaks in the system. By applying these methodologies we find that most of the endogenously determined structural breaks coincide with the gradual effects of the Asian crisis on the Korean economy. Taking into account the resulting endogenously determined structural breaks the error correction version of the ARDL procedure is then employed, to specify the short- and long-term determinants of economic growth in the presence of structural breaks. Based on the preliminary empirical findings obtained we conclude that, in the long-term, policies aimed at promoting various types of physical and human capital, and trade openness, have improved Korea’s economic growth. More specifically, the empirical results show that while the effects of physical and human capital as well as exports are highly significant, as expected, total imports were found to be non significant, and this could be due to compositional changes away from the importation of capital goods to consumer goods as Korean standards of living have improved. It was also found that the speed of adjustment in the estimated models is relatively high and had the expected significant and negative sign.

Irritable bowel syndrome is concentrated in people with higher educations in Iran: an inequality analysis

Asieh Mansouri,Mostafa Amini Rarani,Mosayeb FallahiIman Alvandi 한국역학회 2017 Epidemiology and Health Vol.39 No.-

OBJECTIVES: Like any other health-related disorder, irritable bowel syndrome (IBS) has a differential distribution with respect to socioeconomic factors. This study aimed to estimate and decompose educational inequalities in the prevalence of IBS. METHODS: Sampling was performed using a multi-stage random cluster sampling approach. The data of 1,850 residents of Kish Island aged 15 years or older were included, and the determinants of IBS were identified using a generalized estimating equation regression model. The concentration index of educational inequality in cases of IBS was estimated and decomposed as the specific inequality index. RESULTS: The prevalence of IBS in this study was 21.57% (95% confidence interval [CI], 19.69 to 23.44%). The concentration index of IBS was 0.20 (95% CI, 0.14 to 0.26). A multivariable regression model revealed that age, sex, level of education, marital status, anxiety, and poor general health were significant determinants of IBS. In the decomposition analysis, level of education (89.91%), age (−11.99%), and marital status (9.11%) were the three main contributors to IBS inequality. Anxiety and poor general health were the next two contributors to IBS inequality, and were responsible for more than 12% of the total observed inequality. CONCLUSIONS: The main contributors of IBS inequality were education level, age, and marital status. Given the high percentage of anxious individuals among highly educated, young, single, and divorced people, we can conclude that all contributors to IBS inequality may be partially influenced by psychological factors. Therefore, programs that promote the development of mental health to alleviate the abovementioned inequality in this population are highly warranted.