Sharif University of Technology
Scientia Iranica
1026-3098
2345-3605
17
1
2010
02
01
Large De ection of Functionally Graded Cantilever Flexible Beam with Geometric Non-Linearity: Analytical and Numerical Approaches
EN
A.
Davoodinik
Department of Mechanical Engineering,Tarbiat Modares University
iifumrij@scientiaunknown.non
GH.
Rahimi
Department of Mechanical Engineering,Tarbiat Modares University
lzebnaaw@scientiaunknown.non
Analytical and Adomian decomposition methods have been developed to determine the large
de
ection of a functionally graded cantilever beam under inclined end loading by fully accounting for
geometric nonlinearities, and by incorporating the physical properties of functionally graded materials,
and have also been solved. The large de
ection problem will also be solved by using an FEA solver.
Results obtained only due to end loading are validated using a developed analytical solution. The Adomian
decomposition method yields polynomial expressions for the beam conguration. The equilibrium equation
of a functionally graded cantilever beam actuated through self-balanced moments has been derived and
solved using the Adomian decomposition method and the FEA solver for which no closed form solution can
be obtained. Some of the limitations and recipes to obviate these are included. The Adomian decomposition
method will be useful toward the design of functionally graded compliant mechanisms driven by smart
actuators.
Large de ection,Functionally graded exible beams,Analytical solution,Compliant mechanism,Adomian-polynomials
http://scientiairanica.sharif.edu/article_3243.html
http://scientiairanica.sharif.edu/article_3243_76d3a761e48743914b1f1a58d90282df.pdf
Sharif University of Technology
Scientia Iranica
1026-3098
2345-3605
17
1
2010
02
01
Eects of Unsteady Friction Factor on Gaseous Cavitation Model
EN
B.
Firoozabadi
Department of Mechanical Engineering,Sharif University of Technology
email@email.com
M.
Mosharaf Dehkordi
Department of Mechanical Engineering,Sharif University of Technology
nmxxlncf@scientiaunknown.non
The condition known as a water-hammer problem is a transient condition that may occur
as a result of worst-case loadings, such as pump failures, valve closures, etc. in pipeline systems. The
pressure in the water hammer can vary in such a way that in some cases it may increase and cause
destruction to the hydraulic systems. The pressure in the water hammer can also be decreased to the
extent that it can fall under the saturation pressure, where cavitation appears. Therefore, the liquid is
vaporized, thus, making a two-phase
ow. This pressure decrease can be as dangerous as the pressure rise.
As a result of the pressure drop and vaporization of the liquid, two liquid regions are separated, which is
referred to as column separation. In almost all standard methods for simulation of column separation,
the steady friction factor was used, but in reality, the quantity of the friction factor is variable. In this
work, the unsteady friction factor has been applied in the Discrete Gas Cavity Model (DGCM), which is
a standard method of column separation prediction. Through comparisons with experimental data, results
showed that applying the unsteady friction factor can improve the magnitude of the predicted duration
shape and the timing of the pressure pulse in all of the case studies.
Water-hammer,Cavitation,Discrete gas cavity model,Unsteady friction model,Method of Characteristics
http://scientiairanica.sharif.edu/article_3244.html
http://scientiairanica.sharif.edu/article_3244_76256835a09342afa363bfd8adbbbd6d.pdf
Sharif University of Technology
Scientia Iranica
1026-3098
2345-3605
17
1
2010
02
01
Hydrodynamic Analysis of Non-Planing and Planing Hulls by BEM
EN
H.
Ghassemi
Department of Marine Technology,Amirkabir University of Technology
email@email.com
A.
Kohansal
Department of Marine Technology,Amirkabir University of Technology
uewynwum@scientiaunknown.non
A three-dimensional, potential-based Boundary Element Method (BEM) is developed for
the hydrodynamic analysis of non-planing and planing hulls in steady conditions. The method uses
constant-strength doublet and source distributions over the body surface and source distributions on the
free surface. Numerical computations are rst applied to analyze the hydrodynamic characteristics and
the free surface waves are generated by the mathematical non-planing model (Wigley hull), which is well
known in ship hydrodynamics. The second type is a planing model, namely 4666, the experimental data
of which were carried out by Clement and Blount [1]. Some numerical results of wave elevation, pressure
distribution, lift and resistance are presented. Validations show that the computed results are in good
agreement with experimental data and other numerical approaches.
Wigley hull,Planing hull,Free Surface,Pressure Distribution,Resistance and lift coecients
http://scientiairanica.sharif.edu/article_3245.html
http://scientiairanica.sharif.edu/article_3245_8281a1ed5be302555aeed8ab19fc6627.pdf
Sharif University of Technology
Scientia Iranica
1026-3098
2345-3605
17
1
2010
02
01
Maximum Allowable Dynamic Load of Flexible Manipulators Undergoing Large Deformation
EN
M. H.
Korayem
Department of Mechanical Engineering,Iran University of Science and Technology
hkorayem@iust.ac.ir
M.
Haghpanahi
Department of Mechanical Engineering,Iran University of Science and Technology
yspnfoap@scientiaunknown.non
H. R.
Heidari
Department of Mechanical Engineering,Iran University of Science and Technology
xhhbhjcm@scientiaunknown.non
In this paper, a general formula for nding the Maximum Allowable Dynamic Load
(MADL) of geometrically nonlinear
exible link manipulators is presented. The dynamic model for
links in most mechanisms is often based on the small de
ection theory but for applications like lightweight
links, high-precision elements or high speed it is necessary to capture the de
ection caused by
nonlinear terms. First, the equations of motion are derived, taking into account the nonlinear straindisplacement
relationship using Finite Element Method (FEM) approaches. The maximum allowable
loads that can be achieved by a mobile manipulator during a given trajectory are limited by a number
of factors. Therefore, a method for determination of the dynamic load carrying capacity for a given
trajectory is explained, subject to the accuracy, actuator and amplitude of residual vibration constraints
and by imposing a maximum stress limitation as a new constraint. In order to verify the eectiveness of
the presented algorithm, two simulation studies considering a
exible two-link planar manipulator mounted
on a mobile base are presented and the results are discussed. The simulation results indicate that the eect
of introducing geometric elastic nonlinearities and inertia nonlinearities on the maximum allowable loads
of a manipulator.
Flexible link,Finite Element,Large Deformation,Load,Residual vibration
http://scientiairanica.sharif.edu/article_3246.html
http://scientiairanica.sharif.edu/article_3246_b4be3aba979e251aaaad13a0db9fc265.pdf
Sharif University of Technology
Scientia Iranica
1026-3098
2345-3605
17
1
2010
02
01
On Fatigue Striations
EN
Arthur J.
McEvily
Department of Materials Engineering,University of Dhaka
kctjqwle@scientiaunknown.non
Hisao
Matsunaga
Department of Materials Engineering,University of Essex
kkqbjuzv@scientiaunknown.non
This paper provides a review of the research that has led to our current understanding
of the process of fatigue striation formation. An important question addressed is whether or not at low
stress intensity values, fatigue cracks can propagate intermittently in steels and aluminum alloys. It is
concluded that there is no valid evidence for propagation on other than a cycle-by-cycle basis.
Fatigue striations,Fatigue crack growth,Fatigue fractography,Fatigue mechanism
http://scientiairanica.sharif.edu/article_3247.html
http://scientiairanica.sharif.edu/article_3247_8427aed77ecafd7f3e84580aefae68ec.pdf
Sharif University of Technology
Scientia Iranica
1026-3098
2345-3605
17
1
2010
02
01
Application of Screens and Trips in Enhancement of Flow Characteristics in Subsonic Wind Tunnels
EN
K.
Ghorbanian
Department of Aerospace Engineering,Sharif University of Technology
email@email.com
M. R.
Soltani
Department of Aerospace Engineering,Sharif University of Technology
jzufniwp@scientiaunknown.non
M. D
Manshadi
Department of Aerospace Engineering,Sharif University of Technology
fslmciwb@scientiaunknown.non
Subsonic wind tunnel experiments were conducted to study the turbulence level in the test
section. Measurements were performed by introducing trip strip and/or damping screens on the
ow
eld. The results indicated that the introduction of trip strips not only reduced the turbulence intensity
compared to cases without it, but also
attened the variations. Further, the experiments which investigated
the impact of the damping screens indicated a similar reduction in turbulence intensity; the pattern,
however, remained the same. Furthermore, the results for cases wherein both trip strips as well as damping
screens were placed on the contraction and in the settling chamber, respectively, showed that turbulence
intensity was even more reduced than in previous cases. It is believed that the combination of several
damping screens with the trip strip could be a sound method for turbulence reduction in subsonic wind
tunnels.
wind tunnel,Turbulence reduction,Trip strip,Screen
http://scientiairanica.sharif.edu/article_3248.html
http://scientiairanica.sharif.edu/article_3248_d9fc27268ba6c25892ece973717a5816.pdf
Sharif University of Technology
Scientia Iranica
1026-3098
2345-3605
17
1
2010
02
01
Computational Simulation of Current Forces on Floating Production Storage and Ooading in Irregular Waves
EN
M. R.
Islam
Department of Geomatics Engineering,Farab Co.
pbcvnvvp@scientiaunknown.non
Omar Bin
Yaakob
Department of Marine Technology,Bangladesh University of Engineering & Technology, BUET
szixtidh@scientiaunknown.non
Adi Maimun bin
Abdul Malik
Department of Marine Technology,Bangladesh University of Engineering & Technology, BUET
tiszkvsf@scientiaunknown.non
M. Yusof bin
M. Kamal
Department of Marine Technology,Bangladesh University of Engineering & Technology, BUET
unqhycmp@scientiaunknown.non
This paper presents the eect of current forces on the motion of forces on Floating
Production Storage and Ooading (FPSO) in irregular waves. The objective of this research is to compute
the motion of FPSO in irregular waves by time domain simulation including the eect of current forces.
A study is made on the slowly varying oscillations of a moored single body system in a current and waves.
Linear potential theory is used to describe the
uid motion, and three-dimensional source distribution
techniques are applied to obtain the hydrodynamic forces and transfer function of the wave exciting forces.
OCIMF (1994) data are used for estimation of the current forces. The non-linear time domain simulations
have been carried out in irregular waves. Based on it, slowly varying motion responses are examined
including the eect of the current forces. Several environmental conditions, such as the current angle
of attack, current velocity, signicant wave height and mean wave period are considered, which may
signicantly aect FPSO motion in surge, sway and yaw moments. It is found that the eect of current
forces is quite signicant when the current velocity is increased. In this simulation, while the current
velocity is increased to 3.0 meter/seconds, the impact on FPSO motion is quite signicant, which should
be taken into consideration from the point of view of safety, failure of mooring systems, operating responses
and the dynamic positioning of the FPSO.
FPSO,Current forces,Irregular waves,Motion,Seakeeping
http://scientiairanica.sharif.edu/article_3249.html
http://scientiairanica.sharif.edu/article_3249_3f8d9fb1c523b7191159e2362bb90506.pdf