Simulation of a Density Current Turbulent Flow Employing Dierent RANS Models: A Comparison Study
B.
Firoozabadi
Department of Mechanical Engineering,Sharif University of Technology
author
A.
Mehdizadeh
Department of Mechanical Engineering,Sharif University of Technology
author
text
article
2009
eng
Abstract. The accuracy of Reynolds Averaged Navier-Stokes (RANS) turbulence models to predict
the behavior of 2-D density currents has been examined. In this work, a steady density current is simulated
by the k ???? ", k ???? " RNG, two-layer k ???? " and modied 2 ???? f model, all of which are compared with the
experimental data. Density currents, with a uniform velocity and concentration, enter a channel via a
sluice gate into a lighter ambient
uid and move forward down-slope. The eddy-viscosity concept cannot
accurately simulate this
ow because of two stress production structures found within it. Results show
that all isotropic models have a weak outcome on this current, but by improving the ability of the models,
the results will improve.
Scientia Iranica
Sharif University of Technology
1026-3098
16
v.
1
no.
2009
http://scientiairanica.sharif.edu/article_2990_3bb4191f86de0faf5dd8de350d393e0b.pdf
Vibration Analysis of Moderately Thick Rectangular Plates with Internal Line Support Using the Rayleigh-Ritz Approach
Sh.
Hosseini-Hashemi
Department of Mechanical Engineering,Iran University of Science and Technology
author
H.
Payandeh
Department of Mechanical Engineering,Iran University of Science and Technology
author
K.
Khorshidi
Department of Mechanical Engineering,Iran University of Science and Technology
author
text
article
2009
eng
Abstract. In this study, the free vibration of moderately thick rectangular plates with several
internal line supports was analyzed; the plates having twenty one possible boundary conditions (a
combination of clamped, simply supported and free classical boundary conditions). The dimensionless
equations of the strain (potential) and kinetic energy were derived, based on the Mindlin plate theory,
to study the transverse vibration of moderately thick rectangular plates (in terms of the resultant stress,
with consideration of transverse shear deformation and rotatory inertia). The Rayleigh-Ritz method,
assuming two dimensional polynomial functions as admissible displacement functions, was applied.
Numerical results were presented for a wide range of aspect ratios and thickness to length ratios. The
in
uence of line support location and thickness to length ratio on the frequency parameters was shown
graphically.
Scientia Iranica
Sharif University of Technology
1026-3098
16
v.
1
no.
2009
http://scientiairanica.sharif.edu/article_2991_f58916491e374b05294e2f1870eccda9.pdf
Formulation and Numerical Solution of Robot Manipulators in Point-to-Point Motion with Maximum Load Carrying Capacity
M. H.
Korayem
Department of Mechanical Engineering,Iran University of Science and Technology
author
A.
Nikoobin
Department of Mechanical Engineering,Iran University of Science and Technology
author
text
article
2009
eng
Abstract. In this paper, a formulation is developed for obtaining the optimal trajectory of robot
manipulators to maximize the load carrying capacity for a given point-to-point task. The presented method
is based on open loop optimal control. The indirect approach is employed to derive optimality conditions
based on Pontryagin's Minimum Principle. The obtained necessary conditions for optimality lead to a
two-point boundary-value problem solved via a multiple shooting method with the BVP4C command in
MATLAB r
. Since the carrying payload is one of the system parameters, a computational algorithm is
developed, which provides the capability of calculating the maximum payload for a point-to-point task. The
main advantage of this method is obtaining various optimal trajectories with dierent maximum payloads
and path characteristics by changing the penalty matrices values. To demonstrate the eciency of the
proposed method and algorithm in obtaining the maximum payload trajectory, simulation is performed on
a two-link manipulator.
Scientia Iranica
Sharif University of Technology
1026-3098
16
v.
1
no.
2009
http://scientiairanica.sharif.edu/article_2992_ab75b7071390f9fa9c1e7fd3f11deb3d.pdf
Prediction of Stratied Charge Divided Chamber Engine Performance
A. A.
Mozafari
Department of Mechanical Engineering,Sharif University of Technology
author
M.
Tiourad
Department of Mechanical Engineering,Sharif University of Technology
author
text
article
2009
eng
Abstract. Certain stratied charge divided chamber engines have a very small pre-chamber, equipped
with a spark plug and a main chamber connected to the pre-chamber through nozzles. A theoretical model
is presented in this research to predict ignition delay and initiation of combustion in the pre-chamber. It
considers
ame progress in the pre-chamber up to the point where the
ame penetrates the main chamber
through the connecting nozzles. Step by step calculations then continue in the main chamber and the
mass fraction burned and the energy release rate are calculated. The process continues to the point
where all the fuel is burned. At each step, due to a one degree rotation of the crank shaft, there is
a change in the cylinder volume, due to the movement of the piston and, also, a change in the mole
fraction burned, due to the burning of a fraction of the mixture. Considering heat transfer from the
cylinder contents to its surrounding area, some important operating parameters, such as indicated power,
indicated thermal eciency, indicated specic fuel consumption, indicated mean eective pressure and
volumetric eciency, are predicted. Stepwise calculations also provide in-cylinder pressure-volume and
pressure-crank angle diagrams, as well as the in-cylinder contents temperature variation with the crank
position and concentration of species existing in the combustion products. Predicted values obtained by the
present model are compared with corresponding experimental values available in the literature to evaluate
the accuracy of the model. The comparison shows reasonable agreement between theoretical and measured
values.
Scientia Iranica
Sharif University of Technology
1026-3098
16
v.
1
no.
2009
http://scientiairanica.sharif.edu/article_2993_85be02c0d9f27aa32cade55a3a08087d.pdf
Generalized Curvilinear Coordinate Interface Tracking in the Computational Domain
A.H.
Nikseresht
Department of Mechanical Engineering,Shiraz University
author
text
article
2009
eng
Abstract. Volume Of Fluid (VOF) is one of the most powerful methods to resolve free surface
ows.
In this study, a new algorithm is developed in a curvilinear coordinate system, which implements an
implicit pressure based method (SIMPLE) with a staggered grid and a Lagrangian propagation of the
interface, using the VOF method in the computational domain. Based on this algorithm, a computer code
is generated and two test cases of dam-breaking problems, both in curvilinear and Cartesian grid systems,
are examined and, then, two applications of this method, including
ow through a curved gate under a
dam and the impact problem of a circular cylinder, are presented. The results show good agreement with
experimental and other computational results.
Scientia Iranica
Sharif University of Technology
1026-3098
16
v.
1
no.
2009
http://scientiairanica.sharif.edu/article_2994_488f4b714132ae35f970c7c354791c6e.pdf
Eects of Rotary Inertia and Gyroscopic Momentum on the Flexural Vibration of Rotating Shafts Using Hybrid Modeling
S.
Soheili
Department of Mechanical Engineering,Ferdowsi University of Mashhad
author
A.
Farshidianfar
Department of Mechanical Engineering,Ferdowsi University of Mashhad
author
text
article
2009
eng
Abstract. In this paper, the eect of shaft rotation on its natural frequency is investigated.
Considering rotary inertia and gyroscopic momentum, the fourth order dierential equation representing
the
exural vibration of the shaft is solved by the new analytical method. The Distributed Lumped Modeling
Technique (DLMT) is applied to obtain the transfer matrix for the distributed elements using the proposed
method and for the lumped elements consisting of rotary inertia and gyroscopic eects. The results
obtained by this method are compared and veried with the results of two other methods. The eects of
shaft diameter, shaft length and disk inertia on the natural frequency are discussed for various speeds. It
is shown that, while the new method brings highly accurate results, its simplicity and accuracy provide
proper application for use in industrial systems.
Scientia Iranica
Sharif University of Technology
1026-3098
16
v.
1
no.
2009
http://scientiairanica.sharif.edu/article_2995_3c629471dbc3f5c9f2b3725ed311d84e.pdf
Eect of Reduced Frequency on the Aerodynamic Behavior of an Airfoil Oscillating in a Plunging Motion
M.R.
Soltani
Department of Aerospace Engineering,Sharif University of Technology
author
F.
Rasi Marzabadi
Department of Mechanical Engineering,Sharif University of Technology
author
text
article
2009
eng
Abstract. A series of low speed wind tunnel tests were conducted to study the unsteady aerodynamic
behavior of an airfoil sinusoidally oscillating in plunge. The experiments included measuring the surface
pressure distribution over a range of reduced frequencies, k = 0:03 ???? 0:06. In addition, steady state data
were acquired and were used to furnish a baseline for further analysis and comparison. The model was
oscillated with amplitude of 15 cm and at three dierent mean angles of attack of 0, 10 and 18. The
unsteady aerodynamic loads were calculated from the surface pressure measurements, 64 ports, along the
chord for both upper and lower surfaces. The plunging displacements were transformed into the equivalent
angle of attack. Variations of the pressure coecients and aerodynamic loads with the equivalent angle
of attack showed strong sensitivity to the reduced frequency and mean angles of attack.
Scientia Iranica
Sharif University of Technology
1026-3098
16
v.
1
no.
2009
http://scientiairanica.sharif.edu/article_2996_30e57879c82d9a0fc3aa18548ac1a6a8.pdf
A Phenomenological Model of Nanocrystalline Coating Production Using the Plasma Electrolytic Saturation (PES) Technique
P.
Taheri
Faculty of Engineering,University of Tehran
author
C.
Dehghanian
Department of Chemical Engineering,Isfahan University of Technology
author
text
article
2009
eng
Abstract. The Plasma Electrolytic Saturation (PES) technique is a relatively new process, which
uses a high DC voltage power supply with a related organic electrolyte. Within the phenomenological
model, the mechanism of the nanocrystalline coating formation processes has been developed to clarify the
controlling variations of the procedure. Within the informative model, a feedback parameter for the formed
surface state estimation was established. This parameter is the power spectral density of the current. The
voltage versus current characteristics of the treatment within the plasma region depend on the main
electrolysis conditions, such as current density, electrolyte concentration and agitation rate. Application
of the control algorithm of the parameters could increase the eciency of the plasma electrolytic saturation
and nanocrystalline coating formation. In this process, the electric eld strength, E", within the surface
region reached a value of between 106 and 108 V/m, which was sucient for initiation of ionization
processes in the vapor envelope. The ionization phenomena initially appeared as a quick sparking in
scattered gaseous bubbles and then transformed into a uniform glow distributed throughout the vapor
plasma envelope. Because of the hydrodynamic stabilization of the vapor envelope in the region of 180-
210 V, the current dropped and the glow discharge transformed into intensive arcing, accompanied by a
characteristic low-frequency acoustic emission.
Scientia Iranica
Sharif University of Technology
1026-3098
16
v.
1
no.
2009
http://scientiairanica.sharif.edu/article_2997_28928ef4abf2d13106b4a9498c5bc153.pdf
The Eect of Heavy Fermion or F-Semiconductor Systems on Gd-Intermetallic Systems
A.
Yazdani
Department of Physics,Tarbiat Modares University
author
text
article
2009
eng
Abstract. Based on the instability of magnetic behavior through the concept of local exchange and
hybridization, a new class of heavy fermion is constructed with a stable local magnetic ion, \Gd". The
lattice constant, DC/AC- magnetic susceptibility, (T), and electrical resistivity, (T), measurement
in the magnetic unstable intermetallic compounds of Gd2AxB1????x, show that (I) The hidden magnetic
internal energy is manifested by shape and eld dependence is strongly at x = 0:4, (II) The lattice
parameter of a crystal and magnetic structure, as well as high transition temperature, \Tc", strongly
depends on the conductive electron concentration. Both the functional change of the lattice parameter
(non-Vegard behavior) and magnetic character with electron concentration suggest that the free electrons
are not completely free and are somehow participating in the band functions and magnetic character, and
that (III) There is a coexistence of Kondo behavior and magnetic ordering \re-entrant antiferromagnet"
for x = 0:4 in the range of temperature 30 < Tk < 90 K with TN = Tmax = 30 K, so that (IV) Finally, the
metal insulator-like behavior with a complete quench of magnetic ordering occurs antiferromagnetically,
named superparamagnet, at a certain conductive electron, \x = 0:3", where the sample is eld dependent
(on which , it it is suggested, P"ijJij = 0).
Keyword: Possibility of Kondo eect on \Gd".
Scientia Iranica
Sharif University of Technology
1026-3098
16
v.
1
no.
2009
http://scientiairanica.sharif.edu/article_2998_d454f00c7fd14e2a726872ac3bdf93f1.pdf
On the Kinematic Analysis of a Spatial Six-Degree-of-Freedom Parallel Manipulator
H.
Zohoor
Department of Mechanical Engineering,Sharif University of Technology
author
M.
Vakil
Department of Mechanical Engineering,Sharif University of Technology
author
H.
Pendar
Department of Mechanical Engineering,Sharif University of Technology
author
text
article
2009
eng
Abstract. In this paper, a novel spatial six-degree-of freedom parallel manipulator actuated by three
base-mounted partial spherical actuators is studied. This new parallel manipulator consists of a base
platform and a moving platform, which are connected by three legs. Each leg of the manipulator is
composed of a spherical joint, prismatic joint and universal joint. The base-mounted partial spherical
actuators can only specify the direction of their corresponding legs. In other words, the spin of each leg is
a passive degree-of-freedom. The inverse pose and forward pose of the new mechanism are described. In
the inverse pose kinematics, active joint variables are calculated with no need for evaluation of the passive
joint variables. To solve the forward pose problem, a much simpler method compared to the traditional
method is introduced. Closed form relations for the inverse and forward rate kinematics are proposed.
Finally, two sets of singular conguration of the newly introduced manipulator with dierent natures are
obtained.
Scientia Iranica
Sharif University of Technology
1026-3098
16
v.
1
no.
2009
http://scientiairanica.sharif.edu/article_2999_2d6c6fed2b01426f358385c8b22fdaef.pdf