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Rahbar Ranji A,Rostami Hoseynabadi H. 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.1
Orthotropic plates form an essential part of many marine, aerospace, and automobile structures. The recent increase in the use of composite materials for plate-type structures intensified the need for solutions utilizing orthotropic plates. These structural components, in many instances, are subjected to vibration. The main purpose of this paper is to present a semi-analytical analysis of the response of orthotropic plates to forced vibrations with different combinations of boundary conditions subjected to a general distributed excitation. The solution of the partial differential equation was reduced to an iterative sequential solution of ordinary differential equations using extended Kantorovich method. The efficiency and accuracy of the proposed method were examined through comparison with available literature and was in good agreement with them.
Ultimate strength of stiffened plates with pitting corrosion
Rahbar-Ranji, Ahmad,Niamir, Nabi,Zarookian, Arvin The Society of Naval Architects of Korea 2015 International Journal of Naval Architecture and Oc Vol.7 No.3
Predicting residual strength of corroded plates is of crucial importance for service life estimation of aged structures. A series of nonlinear finite element method is employed for ultimate strength analysis of stiffened plates with pitting corrosion. Influential parameters, including plate thickness, type and size of stiffeners, pit depth and degree of pitting are varied and more than 208 finite element models are analyzed. It is found that ultimate strength is reduced by increasing pit depth to thickness ratio. Thin and intermediate plates have minimum and maximum reduction of ultimate strength with stronger stiffeners, respectively. In weak stiffener, reduction of ultimate strength in thin and intermediate plates depends on DOP. Reduction of ultimate strength in thick plates depends on thickness of plate and DOP. For intermediate plates, reduction for all stiffeners regardless of shape and size are the same.
Rahbar Ranji A,Rostami Hoseynabadi H 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.6
Cylindrical panels are structural elements widely used in engineering structures for high value of strength to weight ratio. Exact solutions of cylindrical panels are available only for a very limited number of cases. The main target of this paper is to utilize a semianalytical technique to study bending behavior of cylindrical panels with different boundary conditions under general distributed loading. The solution of the partial differential equations was reduced to an iterative sequential solution of a double set of ordinary differential equations using extended Kantorovich method. The competence and accuracy of the method is established by comparison with available results in the literature and finite element analyses which shows good agreement.
Flexural-torsional buckling analysis of angle-bar stiffened plates
Rahbar-Ranji Ahmad 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.9
The interaction of flexural-torsional buckling modes is critical for stiffened plates with asymmetric stiffeners. However, this interactionis ignored in all design rules because it is complex to characterize. In the literature, the presence of an attached plate is ignored, and stiffenedplate is treated as an ordinary asymmetric beam. In the flexural buckling mode, stiffener and the attached plate buckle together; inthe torsional buckling mode, the attached plate cannot freely rotate with stiffener. Basic equations of the flexural-torsional bucklingmodes are deduced based on hybrid beam concept and a new strain distribution assumption for sideway bending of stiffeners. Elasticbuckling stresses of different angle-bar stiffened plates are calculated and compared with those generated by the Finite element method(FEM) and those available in the literature. The present method has better agreements with FEM.
Ultimate strength of stiffened plates with pitting corrosion
Ahmad Rahbar-Ranji,Nabi Niamir,Arvin Zarookian 대한조선학회 2015 International Journal of Naval Architecture and Oc Vol.7 No.3
Predicting residual strength of corroded plates is of crucial importance for service life estimation of aged structures. A series of nonlinear finite element method is employed for ultimate strength analysis of stiffened plates with pitting corrosion. Influential parameters, including plate thickness, type and size of stiffeners, pit depth and degree of pitting are varied and more than 208 finite element models are analyzed. It is found that ultimate strength is reduced by increasing pit depth to thickness ratio. Thin and intermediate plates have minimum and maximum reduction of ultimate strength with stronger stiffeners, respectively. In weak stiffener, reduction of ultimate strength in thin and intermediate plates depends on DOP. Reduction of ultimate strength in thick plates depends on thickness of plate and DOP. For intermediate plates, reduction for all stiffeners regardless of shape and size are the same.
The Fuzzy (PI+D)2 Sliding Mode Scheme to Motor Vibration Control
Saman Rahbar,Farzin Piltan,Ehsan Pouladi,Hossein Davarpanah,Somayeh Jowkar 보안공학연구지원센터(IJUNESST) 2015 International Journal of u- and e- Service, Scienc Vol.8 No.1
This paper proposes new fuzzy type sliding mode controller for multi-DOF joints to reduce/eliminate motor vibration. The fuzzy (PI+D)2 single-input single-output (SISO) fuzzy system is applied to modify each element of the control in a sliding mode controller. The proposed method is designed based on the Lyapunov method. Mathematical proof for the stability and the convergence of the system is presented. Various operation situations such as the set point control and the trajectory control are simulated. The simulation results demonstrate that the chattering and the steady state errors, which usually occur in the classical sliding mode control, are eliminated and satisfactory trajectory tracking is achieved.
Eigenvalue Analysis of Flexural-torsional Buckling of Angle-bar Stiffened Plates
Ahmad Rahbar-Ranji 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.3
Equilibrium method is employed to analyze interaction of flexural and torsional buckling of angle-bar stiffened plates. The cross sectional areas of the angle-bar stiffened plate for these two modes are different (hybrid beam). In flexural buckling mode, angle-bar and attached plate buckle together, however in torsional buckling mode only angle-bar would be buckled. Basic equations of equilibrium for flexural and torsional buckling modes of angle-bar stiffened plates are deduced based on hybrid beam concept and new strain distribution assumption for sideway bending of stiffeners. Elastic buckling stress of different angle-bar stiffened plates are calculated and compared with finite element method and those available in the literature. It is shown that present method has very good agreements with finite element method for isolated rigid angle-bar and isolated rigid angle-bar with rigid attached plate. For isolated rigid angle-bar with pin connected to rigid attached plates it has better agreement than previously proposed method.
Elastic tripping analysis of corroded stiffeners in stiffened plate with irregular surfaces
Ahmad Rahbar-Ranji 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.9
Tripping of stiffeners is one of the buckling modes of stiffened panels which could rapidly lead to its catastrophic failure. Loss ofthickness in the web and flange of stiffeners due to corrosion reduces elastic buckling strength. It is common practice to assume a uniformthickness reduction for corroded surfaces. To estimate the remaining strength of a corroded structure, a much higher level of accuracyis required since corroded surfaces are irregular. Finite element method is employed to analyze elastic tripping stress of corrodedstiffeners with irregular surfaces. Comparing the results with elastic tripping stress of un-corroded stiffener, a reduction factor is introduced. It is found that for flat-bars and angle-bars the reduction factor increases by increasing corrosion loss; however, for tee-bars remainsalmost unchanged. Surface roughness has no significant effect on reduction of tripping Euler stress of angle-bars and flat-bars;however, it has an effect on reduction of tripping Euler stress of small flat-bars. For high values of corrosion loss, reduction of trippingEuler stress is higher in flat-bars than angle-bars. Corrosion at the mid-length or ends of flat-bars is more detrimental than full length. Corrosion at the ends of angle-bars is more detrimental than full length and mid-length.
The Effects of Resveratrol on Silica-Induced Lung Oxidative Stress and Inflammation in Rat
Esfahani Maryam,Rahbar Amir Hossein,Asl Sara Soleimani,Bashirian Saed,Mir Moeini Effat Sadat,Mehri Fereshteh 한국산업안전보건공단 산업안전보건연구원 2023 Safety and health at work Vol.14 No.1
Background: Chronic exposure to silica is related with the provocation of an inflammatory response and oxidative stress mechanism. Vitamin D has multiple benefits in biological activities particularly respiratory system disease. Method: In this research, 20 male Wistar rats were randomly allocated into four groups (5 rats /group) as follow:Group1 received saline as (negative control) group. The group 2 received a single IT instillation of silica (positive control) group; the group 3was co-administratedwith single ITsilica and Vitamin D (20mg/kg/day) daily for a period of 90 days. The rats of group 4 received Vitamin D daily for a period of 90 days. Results: Silica significantly increased serum and lung total Oxidant Status (TOS). Meanwhile, silica reduced serum and lung total antioxidant capacity (TAC), GSH and tumor necrosis factor-a (TNF-a). Vitamin D treatment meaningfully reversed oxidative stress, antioxidants status and inflammatory response. Also, Vitamin D improved histopathological changes caused by silica. Conclusion: These findings indicate that Vitamin D exerts protective effects against silica-induced lung injury. It seems that Vitamin D has potential use as a therapeutic object for silica induced lung injure.