Sharif University of TechnologyScientia Iranica1026-309816620091201Experimental and Numerical Investigation of Marine Propeller Cavitation3131ENA. Hajilouy-BenisiDepartment of Mechanical Engineering,Sharif University of TechnologyB. FarhaniehDepartment of Mechanical Engineering,Sharif University of TechnologyR. ArazgaldiDepartment of Mechanical Engineering,Sharif University of TechnologyJournal Article20100512Cavitating
ow is investigated around marine propellers, experimentally and numerically.
Two dierent types of conventional model propellers are used for the study. The rst one is a four
bladed model propeller, so called model A, and the second one is a three bladed propeller, model B.
Model A is tested in dierent cavitation regimes in a K23 cavitation tunnel. The results are presented in
characteristic curves and related pictures. Finally, the results are discussed. Model B is investigated based
on existing experimental results. In addition, model B is used for validation of the numerical solution
prior to the testing of model A. The cavitation phenomenon is predicted numerically on a two dimensional
hydrofoil, NACA0015, as well as propeller models A and B. The cavitation prediction on a hydrofoil is
carried out in both steady and unsteady states. The results show good agreement in comparison with
available experimental data. Propeller models are simulated according to cavitation tunnel conditions and
comparisons are made with the experimental results, quantitatively and qualitatively. The results show
good agreement with experimental data under both cavitating and noncavitating conditions. Furthermore,
propeller cavitation breakdown is well reproduced in the proceeding. The overall results suggest that
the present approach is a practicable tool for predicting probable cavitation on propellers during design
processes.Sharif University of TechnologyScientia Iranica1026-309816620091201Investigations of Supersonic Flow Around a Long Axisymmetric Body3132ENM. Taeibi-RahniDepartment of Aerospace Engineering,Sharif University of TechnologyM. FarahaniDepartment of Mechanical and Aeronautical Engineering,Sharif University of TechnologyM. R. SoltaniDepartment of Aerospace Engineering,Sharif University of TechnologyM.R. HeidariDepartment of Mechanical Engineering,Sharif University of TechnologyJournal Article20100512In this work, a supersonic turbulent
ow over a long axisymmetric body was investigated,
both experimentally and computationally. The experimental study consisted of a series of wind tunnel tests
for the
ow over an ogive-cylinder body at a Mach number of 1.6 and at a Reynolds number of 8106, at
angles of attack between -2 and 6 degrees. It included the surface static pressure and the boundary layer
prole measurements. Further, the
ow around the model was visualized using a Schlieren technique. All
tests were conducted in the trisonic wind tunnel of the Qadr Research Center (QRC). Also, the same
ow
at zero angle of attack was computationally simulated using a multi-block grid (with patched method around
the block interfaces) to solve the thin layer Navier-Stokes (TLNS) equations. The numerical scheme used
was implicit Beam and Warming central dierencing, while a Baldwin-Lomax turbulence model was used
to close the Reynolds Averaged Navier-Stokes (RANS) equations. The static surface pressure results show
that the circumferential pressure at dierent nose sections varies signicantly with angle of attack (in
contrast to the circumferential pressure signatures along the cylindrical part of the body), while the total
pressure measurements in the boundary layer vary signicantly both radially and longitudinally. Two belts
with various leading edge angles were installed at dierent locations along the cylindrical portion of the
model. The computational results obtained were compared with some experimental ones (found by these
authors), showing considerably close agreements.Sharif University of TechnologyScientia Iranica1026-309816620091201Motion Equations Proper for Forward Dynamics of Robotic Manipulator with Flexible Links by Using Recursive Gibbs-Appell Formulation3133ENM. H. KorayemDepartment of Mechanical Engineering,Iran University of Science and TechnologyA. M. ShafeiDepartment of Mechanical Engineering,Iran University of Science and TechnologyJournal Article20100512In this article, a new systematic method for deriving the dynamic equations of motion
for
exible robotic manipulators is developed by using the Gibbs-Appell assumed modes method. The
proposed method can be applied to the dynamic simulation and control system design of
exible robotic
manipulators. In the proposed method, the link de
ection is described by a truncated modal expansion.
All the mathematical operations are done by only 33 and 31 matrices. Also, all dynamic expressions
of a link are expressed in the same link local coordinate system. Based on the developed formulation, an
algorithm is proposed that recursively and systematically derives the equation of motion, then this method
is compared with the recursive Lagrangian method. As shown, this method is computationally simpler
and more ecient and it reduces a large amount of computational complexity. Finally, a computational
simulation for a manipulator with two elastic links is presented to verify the proposed method.Sharif University of TechnologyScientia Iranica1026-309816620091201Computational Simulation of Marangoni Convection Under Microgravity Condition3134ENM.H. SaidiDepartment of Mechanical Engineering,Sharif University of TechnologyB. AsadiDepartment of Mechanical Engineering,Sharif University of TechnologyG. AhmadiDepartment of Mechanical Engineering,Clarkson UniversityJournal Article20100512In this work, the rising of a single bubble in a quiescent liquid under microgravity condition
was simulated. In addition to general studies of microgravity eects, the initiation of hydrodynamic
convection, solely due to the variations of interface curvature (surface tension force) and thus the
generation of shearing forces at the interfaces, was also studied. Then, the variation of surface tension
due to the temperature gradient (Marangoni convection), which can initiate the onset of convection even
in the absence of buoyancy, was studied. The related unsteady incompressible full Navier-Stokes equations
were solved using a nite dierence method with a structured staggered grid. The interface was tracked
explicitly by connected marker points via a hybrid front capturing and tracking method. A one eld
approximation was used where one set of governing equations is only solved in the entire domain and
dierent phases are treated as one
uid with variable physical properties, while the interfacial eects are
accounted for by adding appropriate source terms to the governing equations. Also, a Multi-grid technique,
in the context of the projection method, improved convergences and computational stiness. The results
show that the bubble moves in a straight path under microgravity condition, compared to the zigzag motion
of bubbles in the presence of gravity. Also, in the absence of gravity, the variation of surface tension force
due to interface curvature or temperature gradient can still cause the upward motion of the bubble. This
phenomenon was explicitly shown in the results of this paper.Sharif University of TechnologyScientia Iranica1026-309816620091201New Dynamics Model for Rail Vehicles and Optimizing Air Suspension Parameters Using GA3135ENH. SayyaadiDepartment of Mechanical Engineering,Sharif University of TechnologyN. ShokouhiDepartment of Mechanical Engineering,Sharif University of TechnologyJournal Article20100512In this paper, a complete four axle rail vehicle model with 70 Degrees Of Freedom (DOFs)
is addressed, which includes; a carbody, two bogies and four axles. In order to include track irregularity
eects on vehicle behavior, a simplied track model for a straight line is proposed. As the performance
of the suspension components, especially for air springs, has signicant eects on rail-vehicle dynamics
and the ride comfort of passengers, a complete nonlinear thermo-dynamical air spring model which is
a combination of two dierent models is introduced and then implemented in the complete rail-vehicle
dynamics. By implementing the Presthus formulation [1], the thermo-dynamical parameters of an air
spring are estimated and then tuned, based on the experimental data. Eects of air reservoir volume and
connecting pipe length and diameter on system performances are investigated. For improving passenger
comfort during their trips, air suspension parameters of the modeled rail vehicle are tuned to minimize the
Sperling ride comfort index. Results showed that by modication of air suspension parameters, passenger
comfort is improved and the ride comfort index is reduced by about 10%. The Genetic Algorithm (GA)
optimization method is also used to optimize air suspension parameters. Results showed that improved
air suspension congurations are more practical, compared to optimized ones.Sharif University of TechnologyScientia Iranica1026-309816620091201Natural Convection over a Non-Isothermal Vertical Flat Plate in Supercritical Fluids3136ENA.R. TeymourtashDepartment of Mechanical Engineering,Ferdowsi University of MashhadM. Ebrahimi WarkianiDepartment of Engineering,Ferdowsi University of MashhadJournal Article20100512In many applications, convection heat transfer is coupled with conduction and radiation
heat transfer, which generate temperature gradients along the walls and may greatly aect natural
convection heat transfer. The main objective of this study is to calculate the heat-transfer characteristics
for natural convection from a non-isothermal vertical
at plate into a supercritical
uid. The in
uence
of the non-uniformity of wall temperature on the heat transfer by natural convection along a vertical
plate, having a linearly distributed temperature (characterized by the slope S) is also investigated.
The thermal expansion coecient is considered as a function of the temperature, the pressure, the
van der Waals constants and the compressibility factor. The trends of the curves obtained with this
equation and with values from tables of thermodynamic properties were similar and diverged at a critical
point. These features conrmed the validity of this equation. Then, the governing systems of partial
dierential equations are solved numerically using the nite dierence method. The local Nusselt number
was then calculated and plotted as a function of the local Rayleigh number. It was observed that a
positive slope of temperature distribution increases the heat transfer rate and a negative slope decreases
it.Sharif University of TechnologyScientia Iranica1026-309816620091201Backlash Nonlinearity Modeling and Adaptive Controller Design for an Electromechanical Power Transmission System3137ENM. Saadat FoomaniDepartment of Mechanical Engineering,Sharif University of TechnologyR. KalantariDepartment of Electrical & Computer Engineering,Semnan UniversityJournal Article20101025Nonlinearity characteristics, such as backlash, in various mechanisms, limit the performance
of feedback systems by causing delays, undesired oscillations and inaccuracy. Backlash in
uence
analysis and modeling is necessary to design a precision controller for this nonlinearity. Backlash between
meshing gears in an electromechanical system is modeled by the use of dierential equations and a
nonlinear spring-damper. According to this model, the paper shows that oscillations and delays cannot
be compensated by a state feedback controller. Therefore, an adaptive algorithm is designed, based on
dierent regions of the system angular position error. Since this controller needs an estimation of the
backlash value, it is estimated by a learning unit in the adaptive controller. Simulations show that the
presented adaptive controller can eliminate backlash oscillations properly, in accordance with previous
works.