Showing 126 results for Li
Afshar A., Marino M.a., Jalali M.r.,
Volume 1, Issue 1 (September 2003)
Abstract
The reliable operation of spillways, in emergency as well as normal conditions, is one of the vital components in dam safety. Free or uncontrolled overflow spillways are the most reliable choice however. They usually impose higher construction cost and /or results in wasting a considerable amount of water or live capacity of the reservoirs. Employing fuse gates might be a way of reconciling dam safety with maximized storage capacity. The operation of the system can be controlled to within a few centimeters, and the entire installation is not lost for floods less than the maximum design flood. The installation offers more or less the same level of safety as ungated spillways, but avoids their inherent storage capacity loss. Optimum design of fuse gates in particular installation calls for a mathematical model. The model developed in this work includes structural, hydraulics and operational constraints while maximizing the expected cost over the useful life of the project. Accounting for the lost benefit (i.e., water lost as a result of gate tilting) has an influenced effect on the optimum design. To test the performance of the model, data from Zarineh Rud dam in Iran has been used and its result is compared with a direct search technique. The model is capable of helping the design engineer to select the best alternative considering different types of constraints.
Jalali M.r., Afshar A., Mokhtare A.r.,
Volume 2, Issue 4 (December 2004)
Abstract
It is indispensable to explore simulation techniques that not only represent complexdynamic systems in a realistic way but also allow the involvement of end users in modeldevelopment to increase their confidence in the modeling process. System dynamics as a feedbackbasedand object-oriented simulation approach is presented for reservoir operation modeling. Thequick modeling process, the trust developed in the model due to user contribution, group modelsdevelopment possibility and the effective relations of model results are the most significant strongpoints of this approach. The simple modification of model in response to changes in system andcapability to accomplish sensitivity analysis make this approach more attractive and useful ratherthan traditional reservoir operation models. In this paper system dynamics is applied to simulateoperation of a free reservoir with an Ogee spillway, a reservoir with a gated spillway and finally amulti-reservoir system with simple and gated spillways. The multi-reservoir system on Karun riverin south of Iran is modeled under flood condition as a case study in order to demonstrate thecapabilities of the developed model.
M.m. Alinia,
Volume 2, Issue 4 (December 2004)
Abstract
One main factor in design of panels subjected to axial loading is their buckling behaviour. The design of stiffeners in a metal or composite plated structure is the key factor for safety and weight reduction. This work presents a parametric study on the optimal types and geometrical properties of stiffeners in plates under in-plane axial loads. The results show that flanged type (such as T or L) longitudinal stiffeners increase the normal critical stresses by at least 28% compared to non-flanged stiffener. It is also shown that the optimum geometric properties of stiffeners correspond to the point when the buckling shape of a plate changes from the overall to local mode. Also it is illustrated that for these optimal instances, there always is a linear relationship between the cross-sectional area ratio and the rigidity ratio of the stiffeners to the plates. Finally, Sample relationships for plates having different number of stiffeners are presented.
M.h. Alipour, H. Emamifar,
Volume 3, Issue 2 (June 2005)
Abstract
Partnering is the master key element for project quality. It opens the doors to commitment
and communication between the parties and provides the mastic which turns disparate groups with
varying aims into a coherent team with common objectives (Baden-Hellard).There has been
considerable business emphasis placed upon the development of collaborative relationships across
companies in recent years. Construction is no exception. The presence of trust in the relationships
has been cited as central to successful business and project outcomes (Partnership Sourcing Ltd.
1994, Latham1994). Trust is central to the development of non- adversarial business relationships,
and hence provides fertile ground for the development of practices such as partnering, strategic
alliances and supply chain management.The paper focuses upon the partnering concept in
construction and discusses the role of trust as a key dimension for reducing adversarial relations in
project working environments.
Ali Noorzad, H.b. Poorooshasb,
Volume 3, Issue 3 (September & December 2005)
Abstract
The CANAsand constitutive law in conjunction with the ID technique is used to study the flow phenomenon in a cohesionless granular medium placed between two parallel, rough vertical walls. It is shown that the development of flow is influenced by the geometry of the case. However the main factor is the void ratio of the medium: i.e. arching will prevent the free flow of the material if its void is close to the compact state. The study is extended to cover the axisymmetric situation.
Here the flow of bulk solids through a circular opening at the base of a cylindrical tank is examined.
A. Afshar, H. Abbasi, M. R. Jalali,
Volume 4, Issue 1 (March 2006)
Abstract
Water conveyance systems (WCSs) are costly infrastructures in terms of materials,
construction, maintenance and energy requirements. Much attention has been given to the
application of optimization methods to minimize the costs associated with such infrastructures.
Historically, traditional optimization techniques have been used, such as linear and non-linear
programming. In this paper, application of ant colony optimization (ACO) algorithm in the design
of a water supply pipeline system is presented. Ant colony optimization algorithms, which are based
on foraging behavior of ants, is successfully applied to optimize this problem. A computer model is
developed that can receive pumping stations at any possible or predefined locations and optimize
their specifications. As any direct search method, the mothel is highly sensitive to setup parameters,
hence fine tuning of the parameters is recommended.
M.b. Javanbarg, A.r. Zarrati, M.r. Jalili, Kh. Safavi,
Volume 5, Issue 1 (March 2007)
Abstract
In the present study a quasi 2-D numerical model is developed for calculating air concentration distribution in rapid flows. The model solves air continuity equation (convection diffusion equation) in the whole flow domain. This solution is then coupled with calculations of the free surface in which air content in the flow is also considered. To verify the model, its results are compared with an analytical solution as well as a 2-D, numerical model and close agreement was achieved. The model results were also compared with experimental data. This comparison showed that the decrease in air concentration near the channel bed in an aerated flow could be well predicted by the model. The present simple numerical model could therefore be used for engineering purposes.
Ali Kheyroddin, Hosein Naderpour,
Volume 5, Issue 1 (March 2007)
Abstract
A parametric study is performed to assess the influence of the tension reinforcement
index, ( ω = ρ fy /f Bc), and the bending moment distribution (loading type) on the ultimate
deformation characteristics of reinforced concrete (RC) beams. The analytical results for 15 simply
supported beams with different amounts of tension reinforcement ratio under three different loading
conditions are presented and compared with the predictions of the various formulations and the
experimental data, where available. The plastic hinge rotation capacity increases as the loading is
changed from the concentrated load at the middle to the third-point loading, and it is a maximum
for the case of the uniformly distributed load. The effect of the loading type on the plastic rotation
capacity of the heavily reinforced beams is not as significant as that for the lightly reinforced beams.
Based on the analytical results obtained using the nonlinear finite element method, new simple
equations as a function of the tension reinforcement index, ω, and the loading type are proposed.
The analytical results indicate that the proposed equations can be used for analysis of ultimate
capacity and the associated deformations of RC beams with sufficient accuracy.
A. Yeganeh Bakhtiary, A. Ghaheri, R. Valipour,
Volume 5, Issue 1 (March 2007)
Abstract
Determination of allowable free span length plays a crucial role in design of offshore
pipelines. The seabed intervention cost and safety of an offshore pipelines project are largely
influenced by pipelines free spanning during the project life time. Different criteria are proposed by
both the current designing guidelines and researchers there is however lack of comprehensive
assessment of independent parameters affects the design length of free span. In this note, it is
intended to investigate the effects of seabed formation along with axial force on Natural Frequency
of offshore pipelines. Based on this assessment a new simple formula is proposed. Finally, to
evaluate the result of this study, the allowable free span length of Qeshem Island pipelines is
calculated as a case study and compared with those of the DNV (1998) and ABS (2001) guidelines
and the modal analysis.
S.n. Moghaddas Tafreshi, Gh. Tavakoli Mehrjardi, S.m. Moghaddas Tafreshi,
Volume 5, Issue 2 (June 2007)
Abstract
The safety of buried pipes under repeated load has been a challenging task in
geotechnical engineering. In this paper artificial neural network and regression model for
predicting the vertical deformation of high-density polyethylene (HDPE), small diameter flexible
pipes buried in reinforced trenches, which were subjected to repeated loadings to simulate the
heavy vehicle loads, are proposed.
The experimental data from tests show that the vertical diametric strain (VDS) of pipe embedded
in reinforced sand depends on relative density of sand, number of reinforced layers and height of
embedment depth of pipe significantly. Therefore in this investigation, the value of VDS is related
to above pointed parameters.
A database of 72 experiments from laboratory tests were utilized to train, validate and test the
developed neural network and regression model. The results show that the predicted of the vertical
diametric strain (VDS) using the trained neural network and regression model are in good
agreement with the experimental results but the predictions obtained from the neural network are
better than regression model as the maximum percentage of error for training data is less than
1.56% and 27.4%, for neural network and regression model, respectively. Also the additional set
of 24 data was used for validation of the model as 90% of predicted results have less than 7% and
21.5% error for neural network and regression model, respectively. A parametric study has been
conducted using the trained neural network to study the important parameters on the vertical
diametric strain.
Hon.m. Asce, M.r. Jalali, A. Afshar, M.a. Mariño,
Volume 5, Issue 4 (December 2007)
Abstract
Through a collection of cooperative agents called ants, the near optimal solution to the
multi-reservoir operation problem may be effectively achieved employing Ant Colony Optimization
Algorithms (ACOAs). The problem is approached by considering a finite operating horizon,
classifying the possible releases from the reservoir(s) into pre-determined intervals, and projecting
the problem on a graph. By defining an optimality criterion, the combination of desirable releases
from the reservoirs or operating policy is determined. To minimize the possibility of premature
convergence to a local optimum, a combination of Pheromone Re-Initiation (PRI) and Partial Path
Replacement (PPR) mechanisms are presented and their effects have been tested in a benchmark,
nonlinear, and multimodal mathematical function. The finalized model is then applied to develop an
optimum operating policy for a single reservoir and a benchmark four-reservoir operation problem.
Integration of these mechanisms improves the final result, as well as initial and final rate of
convergence. In the benchmark Ackley function minimization problem, after 410 iterations, PRI
mechanism improved the final solution by 97 percent and the combination of PRI and PPR
mechanisms reduced final result to global optimum. As expected in the single-reservoir problem,
with a continuous search space, a nonlinear programming (NLP) approach performed better than
ACOAs employing a discretized search space on the decision variable (reservoir release). As the
complexity of the system increases, the definition of an appropriate heuristic function becomes more
and more difficult this may provide wrong initial sight or vision to the ants. By assigning a
minimum weight to the exploitation term in a transition rule, the best result is obtained. In a
benchmark 4-reservoir problem, a very low standard deviation is achieved for 10 different runs and
it is considered as an indication of low diversity of the results. In 2 out of 10 runs, the global optimal
solution is obtained, where in the other 8 runs results are as close as 99.8 percent of the global
solution. Results and execution time compare well with those of well developed genetic algorithms
(GAs).
A. Foroughi-Asl, S. Dilmaghani, H. Famili,
Volume 6, Issue 1 (March 2008)
Abstract
Self-Compacting Concrete (SCC) is a highly fluid yet stable concrete that can flow consistently under
its own weight, pass between bars, and fill in formwork without the need of compaction. The application of
SCC effectively resolves the difficulties of concreting in situations with complicated formwork and congested
reinforcements. In this paper, the bond between SCC and steel reinforcement was investigated. The bonding
strengths of reinforcing bars were measured using cubic specimens of SCC and of normal concrete. The SCC
specimens were cast without applying compaction, whereas the specimens of normal concrete were cast by
conventional practice with substantial compaction and vibration. The results showed that SCC specimens
generated higher bond to reinforcing bars than normal concrete specimens and the correlation between bond
strength and compressive strength of NC is more consistent.
Abbas Afshar, S. Ali Zahraei, M. A. Marino,
Volume 6, Issue 1 (March 2008)
Abstract
In a large scale cyclic storage system ,as the number of rule parameters and/or number of operating
period increase, general purpose gradient-based NLP solvers and/or genetic algorithms may loose their
merits in finding optimally feasible solution to the problem. In these cases hybrid GA which decomposes the
main problem into two manageable sub-problems with an iterative scheme between GA and LP solvers may
be considered as a sound alternative This research develops a hybrid GA-LP algorithm to optimally design
and operate a nonlinear, non-convex, and large scale lumped cyclic storage system. For optimal operation of
the system a set of operating rules are derived for joint utilization of surface and groundwater storage
capacities to meet a predefined demand with minimal construction and operation cost over a 20 seasonal
planning period. Performance of the proposed model is compared with a non-cyclic storage system. The
management model minimizes the present value of the design and operation cost of the cyclic and non-cyclic
systems under specified and governing constraints, employing the developed GA-LP hybrid model. Results
show that cyclic storage dominates non-cyclic storage system both in cost and operation flexibility.
Kourosh Shahverdiani, Ali Reza Rahai, Faramarz Khoshnoudian,
Volume 6, Issue 2 (June 2008)
Abstract
Large capacity cylindrical tanks are used to store a variety of liquids. Their Satisfactory
performance during earthquake is crucial for modern facilities. In present paper, the behavior of cylindrical
concrete tanks under harmonic excitation is studied using the finite element method. Liquid sloshing, liquid
viscosity and wall flexibility are considered and additionally excitation frequency, liquid level and tank
geometry is investigated. The results show a value for wall thickness to tank diameter ratio which may be used
as a guide in the consideration of wall flexibility effects.
Saeed Ghaffarpour Jahromi, Ali Khodaii,
Volume 6, Issue 4 (December 2008)
Abstract
In this study an empirical model which can be used to predict the rutting parameter (G*/sinδ) for neat and powder rubber modified bitumen describes. The model was developed using 36 unique powder rubber modified bitumen combinations, rubber concentrations were varied at 5% intervals between 5 and 20%. The effects of powder rubber particle size on model accuracy were also studied ultimately a model was produced with the capability of predicting rutting parameter values over a range of temperatures and rubber concentrations. By definition, the upper limit of the performance grade is dependent on the rutting parameter value therefore, the relationship was also considered in terms of high end failure temperature. The Rubber Coefficient for rutting parameter (Rcg) was identified as an important parameter in the estimation of rutting parameter (G*/sinδ) with the addition of powder rubber. This term is a quantitative representation of the increase typically witnessed in rutting parameter values with the addition of powder rubber. Ambient ground powder rubber exhibited higher Rcg values than cryogenically ground particles. Additionally, 95% confidence intervals were generated for the predictive model thus providing a range of accuracy for the model. The resulting confidence intervals were approximately +/-1300 Pa these confidence intervals were seen to capture 92.6% of the 462 data points used. Findings from this research suggest that the differences between cryogenic and ambient powder rubber bitumen are accurately described using the Rcg, furthermore bitumen properties may be predicted using an empirical equation.
Mahmood R. Abdi, Ali Parsapajouh, Mohammad A. Arjomand,
Volume 6, Issue 4 (December 2008)
Abstract
Clay soils and their related abnormal behavior such as excessive shrinkage, swelling, consolidation settlement and cracking on drying has been the subject of many investigations. Previous studies mainly evaluated the effects of additives such as lime, cement and sand on these characteristics. Initial results indicated that the soil characteristics were improved. However, reportedly in many cases, these additives resulted in a decrease in plasticity and increase in hydraulic conductivity. As a result, there has been a growing interest in soil/fiber reinforcement. The present investigation has focused on the impact of short random fiber inclusion on consolidation settlement, swelling, hydraulic conductivity, shrinkage limit and the development of desiccation cracks in compacted clays. To examine the possible improvements in the soil characteristics, samples consisting of 75% kaolinite and 25% montmorillonite were reinforced with 1, 2, 4 and 8 percent fibers as dry weight of soil with 5, 10 and 15mm lengths. Results indicated that consolidation settlements and swelling of fiber reinforced samples reduced substantially whereas hydraulic conductivities increased slightly by increasing fiber content and length. Shrinkage limits also showed an increase with increasing fiber content and length. This meant that samples experienced much less volumetric changes due to desiccation, and the extent of crack formation was significantly reduced.
A. Hamidi, M. Alizadeh, S.m. Soleimani,
Volume 7, Issue 1 (March 2009)
Abstract
There are limitations in experimental studies on sand-gravel mixtures due to the small size of testing
specimens. Due to this problem, many researchers have worked on prediction of the shear strength of mixture by testing
the sandy fraction of soil alone and developed empirical relationships. Most of the previous relationships have been
determined for low surcharge pressures in which particle breakage does not affect the shear strength parameters.
However, the particle breakage affects the relationships in higher confinements. At the present study, the results of
large scale direct shear tests on sand and sand-gravel mixtures was used to investigate the shear behavior and
dilatancy characteristics in a wider range of surcharge pressures. The gravel content, relative density, surcharge
pressure and gravel grain size were considered as variables in testing program. The relationships between shear
strength characteristics of sand and sand-gravel mixtures were determined considering dilation characteristics of the
soil. In this regard, the minimum void ratio was found as a useful indirect index that relates uniquely to the critical
state friction angle independent of soil gradation. The relations between critical state or peak friction angles of the
mixture with minimum void ratio were determined as a function of surcharge pressure. The correlations could be useful
for determination of the strength parameters of sand-gravel composites by testing sandy fraction of mixture.
Shahriar Afandizadeh, Jalil Kianfar,
Volume 7, Issue 1 (March 2009)
Abstract
This paper presents a hybrid approach to developing a short-term traffic flow prediction model. In this
approach a primary model is synthesized based on Neural Networks and then the model structure is optimized through
Genetic Algorithm. The proposed approach is applied to a rural highway, Ghazvin-Rasht Road in Iran. The obtained
results are acceptable and indicate that the proposed approach can improve model accuracy while reducing model
structure complexity. Minimum achieved prediction r2 is 0.73 and number of connection links at least reduced 20%
as a result of optimization.
Mohammad Naisipour, Mohammad Hadi Afshar, Behrooz Hassani, Ali Rahmani Firoozjaee,
Volume 7, Issue 1 (March 2009)
Abstract
A meshless approach, collocation discrete least square (CDLS) method, is extended in this paper, for solving
elasticity problems. In the present CDLS method, the problem domain is discretized by distributed field nodes. The field
nodes are used to construct the trial functions. The moving least-squares interpolant is employed to construct the trial
functions. Some collocation points that are independent of the field nodes are used to form the total residuals of the
problem. The least-squares technique is used to obtain the solution of the problem by minimizing the summation of the
residuals for the collocation points. The final stiffness matrix is symmetric and therefore can be solved via efficient
solvers. The boundary conditions are easily enforced by the penalty method. The present method does not require any
mesh so it is a truly meshless method. Numerical examples are studied in detail, which show that the present method
is stable and possesses good accuracy, high convergence rate and high efficiency.
Alireza Mortezaei, Ali Kheyroddin,
Volume 7, Issue 1 (March 2009)
Abstract
The work presented in this paper investigates the causes of size effects in structural-concrete members. It is
based on the use of a finite-element model found to yield realistic predictions of structural-concrete behavior in all
cases investigated to date. In fact, the previous use of this model in investigations of size effects in reinforced-concrete
beams indicated that such effects reflect the dependence of load-carrying capacity on small unintended eccentricities
of the applied load and/or load-induced anisotropy, rather than, as widely considered, on fracture-mechanics
characteristics. The present work extends the scope of the above investigation so as to include the case of reinforced
concrete flanged shear walls, the behavior of which is already established experimentally. It is found that, unlike the
flanged shear walls with a height-to-length ratio larger than 2, the shear walls investigated in the present work, in
contrast with the interpretation given to recently published experimental findings, are size-effect independent.
