Buckling analysis of functionally graded truncated conical shells under external displacement-dependent pressure

Majid Khayat,Davood Poorveis,Shapour Moradi 국제구조공학회 2017 Steel and Composite Structures, An International J Vol.23 No.1

This paper is presented to solve the buckling problem of functionally graded truncated conical shells subjected to displacement-dependent pressure which remains normal to the shell middle surface throughout the deformation process by the semi-analytical finite strip method. Material properties are assumed to be temperature dependent, and varied continuously in the thickness direction according to a simple power law distribution in terms of the volume fraction of a ceramic and metal. The governing equations are derived based on first-order shear deformation theory which accounts for through thickness shear flexibility with Sanders-type of kinematic nonlinearity. The element linear and geometric stiffness matrices are obtained using virtual work expression for functionally graded materials. The load stiffness also called pressure stiffness matrix which accounts for variation of load direction is derived for each strip and after assembling, global load stiffness matrix of the shell which may be un-symmetric is formed. The un-symmetric parts which are due to load non-uniformity and unconstrained boundaries have been separated. A detailed parametric study is carried out to quantify the effects of power-law index of functional graded material and shell geometry variations on the difference between follower and non-follower lateral buckling pressures. The results indicate that considering pressure stiffness which arises from follower action of pressure causes considerable reduction in estimating buckling pressure.

The influence of graphene platelet with different dispersions on the vibrational behavior of nanocomposite truncated conical shells

Majid Khayat,Abdolhossein Baghlani,Seyed Mehdi Dehghan,Mohammad Amir Najafgholipour 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.38 No.1

This work addresses the free vibration analysis of Functionally Graded Porous (FGP) nanocomposite truncated conical shells with Graphene PLatelet (GPL) reinforcement. In this study, three different distributions for porosity and three different dispersions for graphene platelets have been considered in the direction of the shell thickness. The Halpin–Tsai equations are used to find the effective material properties of the graphene platelet reinforced materials. The equations of motion are derived based on the higher-order shear deformation theory and Sanders’s theory. The Fourier Differential Quadrature (FDQ) technique is implemented to solve the governing equations of the problem and to obtain the natural frequencies of the truncated conical shell. The combination of FDQ with higher-order shear deformation theory allows a very accurate prediction of the natural frequencies. The precision and reliability of the proposed method are verified by the results of literature. Moreover, a wide parametric study concerning the effect of some influential parameters, such as the geometrical parameters, porosity distribution, circumferential wave numbers, GPLs dispersion as well as boundary restraint conditions on free vibration response of FGP-GPL truncated conical shell is also carried out and investigated in detail.

La perspective éthique de la didactique des langues-cultures

Hoda Khayat,Hamid Reza Shairi,Rouhollah Rahmatian,Roya Letafati 고려대학교 응용문화연구소 2014 에피스테메 Vol.0 No.12

The ethical dimension of teaching is rooted in dynamicity which in turn is in an interrelated and trans-individuality space. This dynamicity is generated by forces which reflect the ways human subjects act. Insofar as ethics opens a perspective to the other individual, the ideal and the new action, we are in a deictic orientation which gives the symbolic gestures a pragmatic dimension. Thus, the interaction ethico-didactic provides teaching-learning process with a performative and anthropological sense. So, it would be interesting to use the applied predicates which relate the educational subject with other individual. In which sense are these predicates available to create ethical-didactic activities?Our task is therefore to examine the application of predicates which would lead us to an action or a social project created by the ethical sense.

Buckling of thick deep laminated composite shell of revolution under follower forces

Majid Khayat,Davood Poorveis,Shapour Moradi,Mona Hemmati 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.58 No.1

Laminated composite shells are commonly used in various engineering applications including aerospace and marine structures. In this paper, using semi-analytical finite strip method, the buckling behavior of laminated composite deep as well as thick shells of revolution under follower forces which remain normal to the shell is investigated. The stiffness caused by pressure is calculated for the follower forces subjected to external fibers in thick shells. The shell is divided into several closed strips with alignment of their nodal lines in the circumferential direction. The governing equations are derived based on first-order shear deformation theory which accounts for through thickness-shear flexibility. Displacements and rotations in the middle surface of shell are approximated by combining polynomial functions in the meridional direction as well as truncated Fourier series with an appropriate number of harmonic terms in the circumferential direction. The load stiffness matrix which accounts for variation of loads direction will be derived for each strip of the shell. Assembling of these matrices results in global load stiffness matrix which may be un-symmetric. Upon forming linear elastic stiffness matrix called constitutive stiffness matrix, geometric stiffness matrix and load stiffness matrix, the required elements for the second step analysis which is an eigenvalue problem are provided. In this study, different parameter effects are investigated including shell geometry, material properties, and different boundary conditions. Afterwards, the outcomes are compared with other researches. By considering the results of this article, it can be concluded that the deformation-dependent pressure assumption can entail to decrease the calculated buckling load in shells. This characteristic is studied for different examples.

LA CRISE DE LA TRANSITION DEMOCRATIQUE ET LE « ONE STEP FLOW OF COMMUNICATION » DU PRESIDENT TUNISIEN

Atef KHAYAT 고려대학교 응용문화연구소 2021 에피스테메 Vol.- No.26

Through a content and semiological cross-analysis, this article aims at grasping the utterance of Tunisian president Kais Saied's statements on his official Facebook page. On July 25th, 2021 he has ended a political crisis in the country before another one was portending following the parliament freeze by him. Under the prism of a redundant speech in adequacy with the people's expectations, he starts a unique political model of its kind in the Arab-speaking world, yet more and more frequent in longtime democratic areas: populism. After coming to power through ballots, can he jeopardize a whole democratic process that is still unclear? Dans une analyse croisée sémiologique et de contenu, cet article vise à saisir les articulations des sorties du président tunisien Kais Saied sur la page officiel Facebook. Le 25 juillet 2021 il met fin à une crise politique, mais une autre s’annonce après le gel du parlement. Sous le prisme d’un discours redondant et en adéquation avec les attentes du peuple, il inaugure un modèle politique unique en son genre dans l’espace arabophone. Mais, de plus en plus fréquent dans, des aires démocratiques plus anciennes, celui du populisme. Arrivé par la voie des urnes, peut-il compromettre tout un processus démocratique encore balbutiant?

Free vibration analysis of functionally graded cylindrical shells with different shell theories using semi-analytical method

Majid Khayat,Seyed Mehdi Dehghan,Mohammad Amir Najafgholipour,Abdolhossein Baghlani 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.28 No.6

In this study, the semi-analytical finite strip method is adopted to examine the free vibration of cylindrical shells made up of functionally graded material. The properties of functionally graded shells are assumed to be temperature-dependent and vary continuously in the thickness direction according to a simple power law distribution in terms of the volume fraction of ceramic and metal. The material properties of the shells and stiffeners are assumed to be continuously graded in the thickness direction. Theoretical formulations based on the smeared stiffeners technique and the classical shell theory with first-order shear deformation theory which accounts for through thickness shear flexibility are employed. The finite strip method is applied to five different shell theories, namely, Donnell, Reissner, Sanders, Novozhilov, and Teng. The approximate procedure is compared favorably with three-dimensional finite elements. Finally, a detailed numerical study is carried out to bring out the effects of power-law index of the functional graded material, stiffeners, and geometry of the shells on the difference between various shell theories. Finally, the importance of choosing the shell theory in simulating the functionally graded cylindrical shells is addressed.

Persistent elevation of aminotransferases in liver transplant in association with chronic norovirus infection

Ammar Abdulaziz Khayat,Grzegorz W Telega 대한간학회 2019 Clinical and Molecular Hepatology(대한간학회지) Vol.25 No.4

Causes of Delay in Khuzestan Steel Company Construction Projects

Saeb, Sajjad,Khayat, Navid,Telvari, Abdulrasoul Korean Institute of Industrial Engineers 2016 Industrial Engineeering & Management Systems Vol.15 No.4

Construction project is a competitive business with high risk especially in developing countries like Iran which faces with many problems such as delay and time and costs increases. Thus, the first priority here is to determine the causes of prolongation of construction projects and to evaluate their importance. Khuzestan Steel Company (KSC) has made important contribution to the projects in Iran and in turn is required to finish them on time. In this study, an attempt was made to investigate the causes of delay in implementation of construction projects held by this company. Data was collected through questionnaire distributed among the sample including 10 owners, 10 consultants and 15 con-tractors. Accordingly, participants rated the causes in the questionnaire so the most important priorities of each area were specified using TOPSIS method. The results showed that according to the employers, consultants and contractors' viewpoints, the most important reason for delays in construction projects of KSC is related to the financial matters. Hence, according to the results obtained, causes for delays in the company's projects are largely related to the drilling permits and long administrative cycle to renew them. Besides, continuous production of steel in this company is another reason to delays of construction projects.

The Effectiveness of the Use of Distance-Evaluation Tools and Methods among Students with Learning-Difficulties from the Teachers' Point of View

Almaleki, Deyab A.,Khayat, Wejdan W.,Yally, Taghreed F.,Al-hajjaji, Aysha A. International Journal of Computer ScienceNetwork S 2021 International journal of computer science and netw Vol.21 No.5

This study aimed to identify the effectiveness of the use of distance-evaluation tools and methods among students with learning difficulties from the teachers' point of view, to achieve this goal. A scale was built, and the psychometric characteristics were validated. It consisted, in its final form, of 17 items distributed on four axes, in addition to three open questions. It was applied to a random sample of (149) teachers of students with learning difficulties in Makkah Region. The results showed that teachers' keenness to encourage students with learning difficulties, so that they would not feel frustrated with the distance learning process. It was also evident that teachers did not use achievement portfolios in the evaluation process. In connection with the appropriate evaluation methods, the majority indicated the use of work sheets and visual evaluation methods that rely on audio and visual skills, such as presenting videos, pictures, audio and games, and applying short objective tests. Among the proposals to improve evaluation methods and tools: Individual evaluation, attention to individual treatment, obligating personal attendance of students to school, splitting the required tasks, and not increasing the skills required to be mastered. As for the obstacles that teachers face: Lack of time, difficulty in communicating with students with distance learning difficulties and problems related to the Internet such as interruption, weakness, or lack of availability.

Numerical simulation of dynamic segregation of self-consolidating concrete (SCC) in T-box set-up

Masoud Hosseinpoor,Kamal H. Khayat,Ammar Yahia 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.20 No.3

A CFD software was used to simulate free surface flow of SCC in the T-Box test. In total, seven simulations were developed to study the effect of rheological parameters on the non-restricted flow performance of SCC in both horizontal and vertical directions. Different suspending fluids having five plastic viscosity values between 10 and 50 Pa.s, three yield stress values between 14 and 75 Pa, one density of 2500 kg/m3, and one shear elasticity modulus of 100 Pa were considered for suspension of 178 spherical particles of 20-mm diameter and 2500 kg/m3 density. The results of the simulations are found to correlate well to changes in rheological parameters of the suspending fluid. Plastic viscosity was shown to be the most dominant parameter affecting flowability and dynamic stability compared to the yield stress. A new approach was proposed to evaluate performability of SCC based on a trade-off between flowability and dynamic stability.