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Effect of axial deformation on flutter of cantilevered FGM cylindrical shells under axial follower forces
, Article International Journal of Civil Engineering ; Volume 13, Issue 2A , 2015 , Pages 160-170 ; 17350522 (ISSN) ; Kazemi, M. T ; Talaeitaba, S. B ; Sharif University of Technology
Iran University of Science and Technology
2015
Abstract
The effect of axial deformation of shell particles on the dynamic instability (flutter) of cantilevered cylindrical shells made of functionally graded materials (FGM) under an end axial follower force is addressed. To this end, at first, results for free vibration of FGM cylindrical shells were verified with previous outcomes and they were in very good agreement. Then, the effect of axial deformation of the shell, acting like a reducing linearly-distributed follower load, on the critical circumferential mode number and the flutter load of FGM shells was accounted for. Finally, the effect of axial deformation of the shell particles on the critical circumferential mode number and the flutter...
Stability Analysis of a Beam Subjected to Axial, Bending and Torsional Follower Loads on the Tip
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firouzabadi, Roohollah (Supervisor)
Abstract
Because the structural stability is directly related with structural damage, it is considered one of the most important issues in the industry. One of the applied cases in the stability issue discuss about the stability of the beam under follower loads. Follower loads obtained from aerodynamic pressure, rocket’s thrust, dry friction of the rotating disk, drilling and etc. Because the follower loads are always perpendicular to the beam cross section, thus with changing the angle of their location, their directions are changed. Spatial dependence makes a non-conservative and dynamic problem. So these loads causes dynamic instability that say flutter. In this study, the stability of a...
Stability of Cantilevered Beams Subjected to Random Follower Forces
, M.Sc. Thesis Sharif University of Technology ; Haddadpour, Hassan (Supervisor)
Abstract
In Mechanical systems there is always possibility of statical and dynamical following force. These forces are generated due to aerodynamic pressure, temperature gradient, and jet thrusters. In unstabel systems, if the value of this force exceeds a certaim amount the system becomes unstable. This value is called as critical force. In order to analyse these systems, fisrt of all, the governing dynamic equations are obtained by using the Galerkin-Ritz method. Then, by utilising the modal analysis, these equation are uncoupled. And then, the Ito set of equations are derived. By utilising the Lyapanov method, Ito equations are transfered to another state. and using the fokker-planc equation the...
Dynamic instability of cantilevered composite pipe conveying flow with an end nozzle
, Article 21st International Congress on Sound and Vibration 2014, ICSV 2014 ; Vol. 4, issue , 13- 17 July , 2014 , pp. 3564-3571 ; ISBN: 9781634392389 ; Abtahi, H ; Haddadpour, H ; Sharif University of Technology
Abstract
In this paper, the instability of cantilevered horizontal composite pipes is investigated. To this aim, the lateral flow forces are modelled as a distributed lateral force and the nozzle effect is modelled as a compressive axial follower force and a concentrated end mass. The coupled bending-torsional equations of motion are derived using Hamilton's principal and Galerkin method. In order to obtain the stability margin of the pipe, the standard Eigen value problem is solved. Finally, effects of elastic coupling parameter and nozzle aspect ratio are considered on the stability margin of the pipe and some conclusions are drawn
Bending-torsional instability of a viscoelastic cantilevered pipe conveying pulsating fluid with an inclined terminal nozzle
, Article Journal of Mechanical Science and Technology ; Volume 32, Issue 7 , July , 2018 , Pages 2999-3008 ; 1738494X (ISSN) ; Abtahi, H ; Firouz Abadi, R. D ; Haddadpour, H ; Dowell, E. H ; Sharif University of Technology
Korean Society of Mechanical Engineers
2018
Abstract
In the present study, dynamic stability of a viscoelastic cantilevered pipe conveying fluid which fluctuates harmonically about a mean flow velocity is considered; while the fluid flow is exhausted through an inclined end nozzle. The Euler-Bernoulli beam theory is used to model the pipe and fluid flow effects are modelled as a distributed load along the pipe which contains the inertia, Coriolis, centrifugal and induced pulsating fluid flow forces. Moreover, the end nozzle is modelled as a follower force which couples bending vibrations with torsional ones. The extended Hamilton's principle and the Galerkin method are used to derive the bending-torsional equations of motion. The coupled...
Bending-torsional stability analysis of aerodynamically covered pipes with inclined terminal nozzle and concurrent internal and external flows
, Article Journal of Fluids and Structures ; Volume 94 , 2020 ; Rahmanian, M ; Haddadpour, H ; Dehghani Firouz Abadi, R ; Sharif University of Technology
Academic Press
2020
Abstract
Stability analysis of a cantilevered pipe with an inclined terminal nozzle as well as simultaneous internal and external fluid flows is investigated in this study. The pipe is embedded in an aerodynamic cover with negligible mass and stiffness simply to streamline the external flow and avoid vortex induced vibrations. The structure of pipe is modeled as an Euler–Bernoulli beam and effects of internal fluid flow including flow-induced inertia, Coriolis and centrifugal forces and the follower force induced by the exhausting jet are taken into account. In addition, neglecting the compressibility effect and using the unsteady Wagner model, aerodynamic loading is determined as a distributed...
Dynamic Stability of Cylindrical Shells Made of Functionally-Graded Materials under Axial Follower Forces
, M.Sc. Thesis Sharif University of Technology ; Kazemi, Mohammad Taghi (Supervisor)
Abstract
Due to major problems induced by delamination in laminated composites, functionally-graded materials (FGM) have been put to growing use in recent years. In the present research, dynamic stability of FGM cylindrical shells under axial follower loads is addressed. Loading was considered in three forms: concentrated (Beck’s problem), uniformly-distributed (Leipholz’s problem), and linearly-distributed (Hauger’s problem). In order to derive the governing equations, Love’s hypotheses and First-order Shear Theory (FST) were used. To solve the equations, polynomial mode shapes were used to approximate the displacements, and the extended Galerkin method was applied. The problem was solved for mild...
Dynamic stability of cantilevered functionally graded cylindrical shells under axial follower forces
, Article Thin-Walled Structures ; Vol. 79, issue , June , 2014 , p. 138-146 ; Kazemi, M. T ; Haddadpour, H ; Mahmoudkhani, S ; Sharif University of Technology
Abstract
Flutter of cantilevered, functionally graded cylindrical shells under an end axial follower force is addressed. The material properties are assumed to be graded along the thickness direction according to a simple power law. Using the Hamilton principle, the governing equations of motion are derived based on the first-order shear deformation theory. The stability analysis is carried out using the extended Galerkin method and minimum flutter loads and corresponding circumferential mode numbers are obtained for different volume fractions, length-to-radius, and thicknesses-to-radius ratios. Two different configurations are considered for the FGM: one in which the metal phase is the outer layer...
Dynamic stability analysis of a sandwich beam with magnetorheological elastomer core subjected to a follower force
, Article Acta Mechanica ; Volume 231, Issue 9 , 2020 , Pages 3715-3727 ; Yousefi, M ; Haddadpour, H ; Sadeghmanesh, M ; Sharif University of Technology
Springer
2020
Abstract
In the present study, the effect of using magnetorheological elastomer materials and a magnetic field on the dynamic stability of a sandwich beam under a follower force has been investigated for various boundary conditions. The considered sandwich beam consists of a magnetorheological elastomer core constrained by elastic layers. The structural governing equations are derived using Hamilton’s principle and solved by the finite element method. The validity of the result is examined by comparison with those in the literature. The effects of variation in the parameters such as magnetic field intensity and the thickness of the layers on the stability of the sandwich beam are studied. Finally,...