Multi-Input Multi-Output Direct Adaptive Control for a Distributed Parameter Flexible Rotating Arm
M.
Azadi
Department of Mechanical Engineering,Shiraz University
author
text
article
2008
eng
In this paper, a Multi-Input Multi-Output (MIMO) Model Reference Adaptive Control (MRAC)
scheme for a
exible rotating arm is developed. In order to construct a reference model to be
followed by this distributed parameter system, a nite element method is used to approximate
the behavior of the arm. An input error direct adaptive control algorithm is utilized as the
control approach to account for parameter uncertainty. Assuming the same approximation and
structure as the model for the actual system, the stability analysis of the proposed controller will
be straightforward. Simulation results are provided to illustrate the performance of the proposed
algorithm in the presence of disturbance and uncertainties. Also, the proposed algorithm results
are compared with those of a conventional PD controller.
Scientia Iranica
Sharif University of Technology
1026-3098
15
v.
1
no.
2008
http://scientiairanica.sharif.edu/article_2970_def23ca75768cfcb06a54bc50ddd4062.pdf
Eect of Alkali-Aggregate Reactions in Concrete Dams Using Finite Element Method
M.
Moshtagh
Department of Civil Engineering,Sharif University of Technology
author
text
article
2008
eng
The eect of Alkali-Aggregate Reactions (AAR) in concrete dams was investigated using the
nite element method. Two models have been presented to assess the eects of the AAR in
concrete dams. The stress dependency of AAR strains has been taken into account in the models
and the degradation of concrete properties during the reaction has been implemented in the nite
element program. The results of the isothermal and nonisothermal analyses of a gravity section
of a Beauharnois power plant have been presented and compared with the measured data and
the results are in close agreement. The results of the analysis demonstrate the importance of
the AAR in concrete dams. High stresses and large de
ections occur in the dam during the
reaction. Because of the stress dependency of the reaction, vertical displacements are smaller
than horizontal displacements.
Scientia Iranica
Sharif University of Technology
1026-3098
15
v.
1
no.
2008
http://scientiairanica.sharif.edu/article_2971_bfa4281390b750d4c080a97dfe9747e6.pdf
Dealing with Con ict over Water Quality and Quantity Allocation: A Case Study
M.
Karamouz
Department of Civil and Environmental Engineering,Amirkabir University of Technology
author
text
article
2008
eng
Available water resources are often not sucient or too polluted to satisfy the needs of all
water users. Therefore, con
ict over water, as a result of limitations on quantity and quality,
is a major challenge in water allocation. In this paper, a methodology for con
ict resolution
over water allocation in river-reservoir systems is presented. The proposed model includes the
genetic algorithm (GA)-based optimization and a water quantity/quality simulation model. The
objective function of the optimization model is based on the Nash bargaining theory. Nash theory
can incorporate the utility functions of the decision makers and the stakeholders, as well as their
relative authorities over the water allocation process. The WQRRS (Water Quality for River-
Reservoir Systems) model of the U.S. Hydrologic Engineering Center (HEC) and Qual2e model of
the U.S. Environmental Protection Agency (EPA) are used for simulating the Karkheh reservoir
and river water quality. In these models, the reservoir thermal stratication cycle, the reservoir
discharge quality and the water quality downstream of the reservoir are simulated. The model is
applied to the Karkheh river-reservoir system in the southern part of Iran. The utility functions
are based on the reliability of the allocated water to dierent sectors, the environmental water
demands (quality of the allocated water and in-stream
ow), water storage in the reservoir and
the quantity and quality of the return
ows. The results show that this model can be eectively
used in optimal water allocation of river-reservoir systems with con
icting objectives. In this
paper, in order to generate the policies of the Karkheh reservoir operation and the river water
quality management, the results of the optimization model are used to train the ANN model.
Scientia Iranica
Sharif University of Technology
1026-3098
15
v.
1
no.
2008
http://scientiairanica.sharif.edu/article_2972_c32fbb2f9cded30b48c44f36641bf324.pdf
Maximum Dynamic Load Carrying Capacity of a 6UPS-Stewart Platform Manipulator
M.
Shokri
Department of Mechanical Engineering,Iran University of Science and Technology
author
M. H.
Korayem
Department of Mechanical Engineering,Iran University of Science and Technology
author
text
article
2008
eng
In this paper, a computational method for obtaining the maximum Dynamic Load Carrying
Capacity (DLCC) for the 6-UPS Stewart platform manipulator is developed. In this paper, the
manipulator is assumed to be non-rigid and the joint actuator torque capacity and accuracy
of motion are considered major limiting factors in determining the maximum payload. The
maximum dynamic payload carrying capacity of the manipulator is established, while the dynamic
model of a typical hydraulic actuator system is used in the joint actuator force capacity for a given
trajectory. The
exibility of the manipulator is assumed to be eventuated from the manipulator's
joints
exibility. According to the high complexity of the dynamic equations system of the
exible
joints parallel manipulators, the eects of the
exibility of the prismatic joints are considered in
a static situation to show the considerable eects of the joint's
exibility on the motion accuracy
of the 6UPS-Stewart platform. This method can be used for determining the maximum dynamic
payload, which acts as an end-eector for the mechanical design of the manipulator and the
optimized selection of the actuator, such as machine tools, based on the hexapod mechanism.
Scientia Iranica
Sharif University of Technology
1026-3098
15
v.
1
no.
2008
http://scientiairanica.sharif.edu/article_2973_42ad2933e8951909f36a4b470b072be9.pdf
Interpretation of Tensile Softening in Concrete, Using Fractal Geometry
H.
Khezrzadeh
Department of Civil Engineering,Sharif University of Technology
author
M.
Mofid
Department of Civil Engineering,Sharif University of Technology
author
text
article
2008
eng
Concrete is a heterogeneous material with a wide variety of usage in structural design. Concrete
under tension exhibits strain softening, i.e., a negative slope in the stress{deformation diagrams.
Dierent softening curves have been proposed in the literature to interpret this phenomenon.
In current research, a new softening curve for concrete has been proposed by using the newly
introduced concept of fractal geometry. This new softening curve is denominated a 'Quasi-fractal'
softening curve and consists of two parts, a linear portion at the beginning and an exponential
portion in the rest of the curve. A comparison of a \Quasi-fractal" softening curve with a set of
proposed experimental softening curves has been performed, which reveals good agreement.
Scientia Iranica
Sharif University of Technology
1026-3098
15
v.
1
no.
2008
http://scientiairanica.sharif.edu/article_2974_01aff1279f00c1840e0fac2406d37852.pdf
Enhancement of Natural Convection in Circular and Triangular Ducts Using Corona Discharge in Air and Nitrogen
M.
Molki
Department of Mechanical and Industrial Engineering,Southern Illinois University at Edwardsville
author
T.
Harirchian
Department of Mechanical and Industrial Engineering,Southern Illinois University at Edwardsville
author
text
article
2008
eng
A computational eort is undertaken to investigate the eect of corona discharge in air and
nitrogen gas on the enhancement of heat transfer. A corona is a visible luminous emission that
occurs in the vicinity of sharp edges where the electric eld is intense. This phenomenon is
associated with gas ionization and acceleration of ions in strong electric elds, dragging the
gas particles and generating a secondary
ow, known as corona wind. Corona wind may be
employed as an active enhancement technique for heat transfer. Here, corona wind is used to
enhance natural convection inside circular tubes and triangular ducts. The paper describes, not
only the enhancement of heat transfer, but also, the shortcoming and challenges encountered
in the computational modeling of corona discharge. It is shown that the solution of the electric
charge density suers from some degree of irregularity and asymmetry, while an azimuthally
symmetric solution is expected. If this deciency is not rectied, the resulting electric body force
and the predicted
ow eld are not accurate. Two remedies are recommended to improve the
solution, namely, articial viscosity and structured grids. Moreover, the present computations
indicate that, for the Rayleigh number of 3737 and the applied voltage of 8.25-9.5 kV, the corona
discharge enhances heat transfer by 17.9-106.9.
Scientia Iranica
Sharif University of Technology
1026-3098
15
v.
1
no.
2008
http://scientiairanica.sharif.edu/article_2975_499c395288c8ffac1322f4c609e0913c.pdf
Turbulent Heat Transfer in a Channel with a Built-in Square Cylinder: The Eect of Reynolds Number
M.
Farhadi
Department of Mechanical Engineering,Shahid Bahonar University of Kerman
author
text
article
2008
eng
Turbulent heat transfer, in a three dimensional channel
ow, in the presence of a square cylinder,
was investigated numerically. The existence of a square cylinder in a channel, compared to a plain
one, changes the heat transfer rate from the walls of the channel. A Large Eddy Simulation (LES)
of a turbulent
ow was performed to simulate
ow behavior in a channel for Reynolds numbers
in the range of 1000 to 15000. The results obtained for the Nusselt number distribution along
the wall of the channel, at Re = 3000, followed those of experimental data with good accuracy.
It was observed that the existence of a square cylinder makes the attached wall boundary layer
separate, with a subsequent recirculation zone downstream of the cylinder. The Nusselt number
distribution along the wall of the channel shows an increase, with a relative maximum, slightly
downstream of the reattachment point. Heat transfer from the wall of the channel increases
with increasing Reynolds number. A correlation was obtained for the variation of the mean total
Nusselt number with the Reynolds number.
Scientia Iranica
Sharif University of Technology
1026-3098
15
v.
1
no.
2008
http://scientiairanica.sharif.edu/article_2976_a45900b5d64ca81c3c7d7d0e35f4c2c1.pdf
Modeling and Intelligent Control of a Robotic Gas Metal Arc Welding System
H.
Sayyaadi
Department of Mechanical Engineering,Sharif University of Technology
author
text
article
2008
eng
Welding is an important manufacturing process that can be automated and optimized. This
paper focuses on the development of a robotic arc welding system, wherein a three-degreeof-
freedom Selective Compliance Assembly Robot Arm (SCARA) is interfaced to a Gas Metal
Arc Welding (GMAW) process. The entire system is composed of a robot linked to a GMAW
system. Set points are derived using the desired mass and heat input, along with the weld speed.
The stick-out and the current of the welding process are controlled using an Adaptive Neural
Network Controller (ANNC). The trajectory of the robot or the weld prole is also controlled by
implementing a Mixed Fuzzy-GA Controller (MFGAC) on a three-axis SCARA robot. The system
is, then, analyzed and the results show adequate improvement in the eciency and performance
of the proposed controller in welding a curvilinear weld prole.
Scientia Iranica
Sharif University of Technology
1026-3098
15
v.
1
no.
2008
http://scientiairanica.sharif.edu/article_2977_9772a87d23a3b04e9f5a78639076a379.pdf
Behaviour of Plate Girders Subjected to Combined Bending and Shear Loading
F.
Shahabian
School of Engineering,Ferdowsi University of Mashhad
author
text
article
2008
eng
Theoretical predictions regarding the ultimate resistance of slender plate girders to applied shear
loading, based on existing theories and formulas, show close correlation with the test data
presented. When a plate girder is subjected to a bending moment in addition to shear, the
determination of the ultimate resistance becomes more complex. Herein, an interaction formula
for the ultimate resistance of slender plate girders to combined bending and shear loading is
proposed, which shows satisfactory correlation with the available theories and which is acceptable
for practical purposes. The proposed interaction equation covers web panel aspect ratios, bw=dw,
from 1 to 2 and slender ratios, dw=tw, from 150 to 300.
Scientia Iranica
Sharif University of Technology
1026-3098
15
v.
1
no.
2008
http://scientiairanica.sharif.edu/article_2978_bc78d394d2c838c58eb4747a8378e051.pdf
Seismic Performance of TMDs in Improving the Response of MRF Buildings
S.M.
Zahrai
Department of Civil Engineering,University of Tehran
author
text
article
2008
eng
In this paper, the eectiveness of Tuned Mass Dampers (TMDs) in controlling building structures
under earthquake excitations is studied through investigating the practical considerations and
vibration control eciency of tuned mass dampers for 5-, 8-, 10- and 15-story buildings utilizing
a structural system with special Moment-Resisting Frames (MRFs) in both directions. Assuming
its frequency to be near the 1st natural frequency of buildings, it is designed to control the
largest response of the buildings. The eect of detuning, on some TMD parameters, on the
seismic performance is studied through time-history analysis using the El Centro and Tabas
earthquake records. In addition, the results of time-history analysis are compared with those of
a response spectrum analysis for the structures with and without TMD, in order to judge its
eectiveness. Under earthquake excitation, the performance of structures having TMDs greatly
depends on the characteristics of the ground motion. When the rst mode of a MDOF structure
dominates the structural response, a seismic response reduction can be easily achieved. While
the rst mode response of a structure with TMD is proved to be substantially reduced, the
higher mode response, in fact, increases as the number of stories increases. It is observed that
TMD is eective in reducing maximum displacement in MRF buildings by as much as 32.2%
in the Tabas earthquake and 45.3% in the El Centro earthquake. The maximum displacement
results of a response spectrum analysis for the uncontrolled and controlled case in the El Centro
earthquake, in an 8-story structure, are 25.70 cm and 14.59 cm, respectively, whereas the
maximum displacement using time-history analysis, in the uncontrolled and controlled cases,
are 27.54 cm and 15.14 cm, respectively.
Scientia Iranica
Sharif University of Technology
1026-3098
15
v.
1
no.
2008
http://scientiairanica.sharif.edu/article_2979_6d8a8cfd751f7c24eb11113da3682197.pdf
A Transformation Technique in Designing Multi-Attributes C Control Charts
S.T.
Akhavan Niaki
Department of Industrial Engineering,Sharif University of Technology
author
B.
Abbasi
Department of Industrial Engineering,Sharif University of Technology
author
text
article
2008
eng
In a production process, when the quality of a product depends on more than one characteristic, multivariate quality control techniques are used. Although multivariate statistical process control is receiving increased attention in the literature, little work has been done to deal with multi-attribute processes. In this paper, we develop a new methodology to monitor multi-attribute processes in which the defects counts are important and different types of defects are dependent random variables. In order to do this, based on the symmetric square root transformation concept, first we transform multi-attribute data such that the correlation between variables either vanishes or becomes very small. Then, by simulation and bisection method, we find the symmetric control limits and form a symmetric rectangular region for control. In simulation studies, we present some numerical examples to illustrate the proposed method and to evaluate and compare its performance to the ones of the existing method.
Key words
Multivariate C control charts, process monitoring, optimal control limits, symmetric control charts, symmetric square root
Scientia Iranica
Sharif University of Technology
1026-3098
15
v.
1
no.
2008
http://scientiairanica.sharif.edu/article_2980_d41d8cd98f00b204e9800998ecf8427e.pdf