A Continuous Vibration Theory for Beams with a Vertical Edge Crack
A.
Meghdari
Department of Mechanical Engineering,Sharif University of Technology
author
M.
Behzad
Department of Mechanical Engineering,Sharif University of Technology
author
A.
Ebrahimi
Department of Mechanical Engineering,Sharif University of Technology
author
text
article
2010
eng
In this paper, a continuous model for
exural vibration of beams with an edge crack
perpendicular to the neutral plane has been developed. The model assumes that the displacement eld
is a superposition of the classical Euler-Bernoulli beam's displacement and of a displacement due to
the crack. The additional displacement is assumed to be a product between a function of time and an
exponential function of space. The unknown functions and parameters are determined based on the zero
stress conditions at the crack faces and the concept of J-integral from fracture mechanics. The governing
equation of motion for the beam has been obtained using the Hamilton principle and solved using a modied
Galerkin method. The results have been compared with nite element results and an excellent agreement
is observed.
Scientia Iranica
Sharif University of Technology
1026-3098
17
v.
3
no.
2010
http://scientiairanica.sharif.edu/article_3290_17c26938a9279a203cf4d5baad242ba0.pdf
Prediction of Hydraulic Efficiency of Primary Rectangular Settling Tanks Using the Non-linear k -e Turbulence Model
B.
Firoozabadi
Department of Mechanical Engineering,Sharif University of Technology
author
M.A.
Ashjari
Department of Mechanical Engineering,Sharif University of Technology
author
text
article
2010
eng
Circulation is created in some parts of settling tanks. It can increase the mixing level,
decrease the effective settling, and create a short circuiting from the inlet to the outlet. All above-mentioned
phenomena act in such a way to decrease the tank's hydraulic efficiency, which quantitatively shows how
ow within the tank is uniform and quiet. So, the main objective of the tank design process is to avoid
forming the circulation zone, which is known as the dead zone. Prediction of the
ow field and size of
the recirculation zone is the first step in the design of settling tanks. In the present paper, the non-linear
k - e " turbulence model is used for predicting the length of the reattachment point in the separated
ow of
a Karlsruhe tank. Then, the recirculation bubble size, which is out of the capability of standard turbulence
models, is determined. Also, the effect of the separation zone size on the tank's hydraulic efficiency is
investigated.
Scientia Iranica
Sharif University of Technology
1026-3098
17
v.
3
no.
2010
http://scientiairanica.sharif.edu/article_3291_a417cec42cffda001117851248400d7a.pdf
Improvements to the Mathematical Model of Acoustic Wave Scattering from Transversely Isotropic Cylinders
F.
Honarvar
Department of Mechanical Engineering,Khajeh Nasire Toosi University of Technology
author
S.
Sodagar
Department of Mechanical Engineering,Khajeh Nasire Toosi University of Technology
author
text
article
2010
eng
This paper considers the scattering of an innite plane acoustic wave from a long immersed,
solid, transversely isotropic cylinder. The mathematical model which has already been developed for this
problem does not work in the case of a normally incident wave. Modications to the mathematical model
are proposed in order to make it applicable to all incidence angles, including = 0. Numerical results are
used to demonstrate the correctness of the modied equations. Moreover, using a mathematical discussion,
it is shown that at normal incidence, the whole displacement eld is constrained within the isotropic plane
of the cylinder (cylinder cross section) and only the two elastic constants characterizing this plane appear
in the remaining equations. A perturbation study on the ve elastic constants of the transversely isotropic
cylinder conrms this result.
Scientia Iranica
Sharif University of Technology
1026-3098
17
v.
3
no.
2010
http://scientiairanica.sharif.edu/article_3292_7922b622a7575492876aed12b7627467.pdf
Synthesis of Cable Driven Robots' Dynamic Motion with Maximum Load Carrying Capacities: Iterative Linear Programming Approach
M. H.
Korayem
Department of Mechanical Engineering,Iran University of Science and Technology
author
M.
Bamdad
Department of Mechanical Engineering,Iran University of Science and Technology
author
Kh.
Najafi
Department of Mechanical Engineering,Islamic Azad University
author
text
article
2010
eng
In this paper, the general dynamic equation of motion of Cable Driven Robots (CDRs) is
obtained from Lagrangian formulation. A computational technique is developed for obtaining an optimal
trajectory to maximize the dynamic load carrying capacity for a given point-to-point task. Dynamic
equations are organized in a closed form and are formulated in the state space form. In order to nd
the Dynamic Load Carrying Capacity (DLCC) of CDRs, joint actuators torque, and robot workspace
constraints for obtaining the positive tension in cables are considered. The problem is formulated as a
trajectory optimization problem, which fundamentally is a constrained nonlinear optimization problem.
Then, the Iterative Linear Programming (ILP) method is used to solve the optimization problem. Finally,
a numerical example involving a 6 d.o.f CDR is presented and, due to validation, the results of the ILP
method are compared with the optimal control method.
Scientia Iranica
Sharif University of Technology
1026-3098
17
v.
3
no.
2010
http://scientiairanica.sharif.edu/article_3293_4973f602225f42b1b8de18d5c598f69c.pdf
Robust Control of Non-linear Flexible Spacecraft
M.
Malekzadeh
Department of Civil Engineering,Amirkabir University of Technology
author
A.
Naghash
Department of Aerospace Engineering,Amirkabir University of Technology
author
H.A.
Talebi
Department of Electronical Engineering,Amirkabir University of Technology
author
text
article
2010
eng
In this paper, the problem of attitude control of a 1D non-linear
exible spacecraft is
investigated. Three controllers are presented. The rst is a non-linear dynamic inversion, the second is
a linear -synthesis and the third is a composition of dynamic inversion and a -synthesis controller. It
is assumed only one reaction wheel is used. Actuator saturation is considered in the design of controllers.
The performances of the proposed controllers are compared in terms of nominal performance, robustness to
uncertainties, vibration suppression of panels, sensitivity to measurement noise, environment disturbance
and non-linearity in large maneuvers. To evaluate the performance of the proposed controllers, an
extensive number of simulations on a non-linear model of the spacecraft are performed. Simulation results
show the ability of the proposed controller in tracking the attitude trajectory and damping panel vibration.
It is also veried that the perturbations, environment disturbance and measurement errors have only slight
eects on the tracking and damping responses.
Scientia Iranica
Sharif University of Technology
1026-3098
17
v.
3
no.
2010
http://scientiairanica.sharif.edu/article_3294_bd787dfda14210b9b0653832f18ec622.pdf
Duct Design in Subsonic and Supersonic Flow Regimes with and without Normal Shock Waves Using Flexible String Algorithm
A.
Hajilouy-Benisi
Department of Mechanical Engineering,Sharif University of Technology
author
M.
Nili-Ahmadabadi
Department of Mechanical Engineering,Sharif University of Technology
author
M.
Durali
Department of Mechanical Engineering,Sharif University of Technology
author
F.
Ghadak
Department of Aerospace Engineering,I.P.M.
author
text
article
2010
eng
In this investigation, the Flexible String Algorithm (FSA) used before for the inverse design
of 2D subsonic ducts is developed and applied for the inverse design of subsonic and supersonic ducts with
and without normal shock waves. In this method, the duct wall shape is changed under a novel algorithm
based on the deformation of a virtual
exible string in a
ow. Deformation of the string due to the local
ow conditions resulting from changes in the wall geometry is performed until the target shape satisfying
the prescribed walls pressure distribution is achieved. The
ow eld at each shape modication step is
analyzed using an Euler equation solution by the AUSM method. Some validation test cases and design
examples in subsonic and supersonic regimes are presented here, which show the robustness and
exibility
of the method in handling the complex geometries in various
ow regimes. In the case of unsymmetrical
ducts with two unknown walls, the FSA is modied to increase the convergence rate signicantly. Also, the
eect of duct inlet and outlet boundary conditions on the convergence of the FSA is investigated. The FSA
is a physical and quick converging approach and can eciently utilize
ow analysis codes as a black box.
Scientia Iranica
Sharif University of Technology
1026-3098
17
v.
3
no.
2010
http://scientiairanica.sharif.edu/article_3295_fe1681d530b1812cdc016698897255cc.pdf
Geometrically Non-linear Analysis of Unsymmetrical Fiber-Reinforced Laminated Annular Sector Composite Plates
M.
Salehi
Department of Mechanical Engineering,Amirkabir University of Technology
author
S.R.
Falahatgar
Department of Mechanical Engineering,Guilan University
author
text
article
2010
eng
The geometrically non-linear behavior of unsymmetrical, ber-reinforced, laminated,
annular sector composite plates is studied. The rst order shear deformation theory is applied to the
von Karman type non-linear behavior of unsymmetrically, laminated, annular sector composite plates.
Five equilibrium equations, ve stress-displacement relations, three curvature-displacement relationships,
together with eight stress resultants, stress couples and shear force relationships are solved. The nonlinear
nature of the problem prohibits the application of a closed form solution method. Consequently,
the Dynamic Relaxation (DR) numerical method is chosen for solving the system of 21 simultaneous
equations. The in-plane and out-of-plane displacements are reported for dierent congurations of annular
sector plates. Dierent sector angles, ber orientations and plate thicknesses are considered. For better
observation of the numerical methods, they are illustrated graphically. The correlations of the present
results and the corresponding nite element generated results are very satisfactory.
Scientia Iranica
Sharif University of Technology
1026-3098
17
v.
3
no.
2010
http://scientiairanica.sharif.edu/article_3296_157cbd4637f93ac110ccd6c8086276b2.pdf