Showing 60 results for Oh
Behbahani H., Mohammad Elahi S.,
Volume 1, Issue 1 (September 2003)
Abstract
This Paper is the result of a research project on a pavement management system that was performed by the Transportation Division of Iran University of Science and Technology. Information used in the project was gathered from 20 zones of the Tehran Municipality. Any maintenance and repair system for roads has a number of general and coordinated activities in conjunction with programming, designing, construction, Maintenance, Evaluation, and research on road pavement. Prediction of pavement condition is one of the most important parts of, such system. Prediction models have their application at the network level as well as project level activities. At the network level it is used in predicting the condition for budget programming. While in project level it is used in economical analysis. Many factors have been used in determination of pavement condition. These factors are the design life of the pavement, loading, climatic condition, and the type of road. To be able to plan for future improvements we need to predict the future condition of the pavement. In this paper, factors affecting the prediction of pavement condition are discussed. A model is developed exclusively for Tehran based on the distress data collected.
Misaghi F., Mohammadi K., Mousavizadeh M.h.,
Volume 1, Issue 1 (September 2003)
Abstract
In the present paper, ANN is used to predict the tidal level fluctuations, which is an important parameter in maritime areas. A time lagged recurrent network (TLRN) was used to train the ANN model. In this kind of networks, the problem is representation of the information in time instead of the information among the input patterns, as in the regular ANN models. Two sets of data were used to test the proposed model. San Francisco Bay tidal levels were used to test the performance of the model as a predictive tool. The second set of data was collected in Gouatr Bay in southeast of Iran. This data set was used to show the ability of the ANN model in predicting and completing of data in a station, which has a short period of records. Different model structures were used and compared with each other. In addition, an ARMA model was used to simulate time series data to compare the results with the ANN forecasts. Results proved that ANN can be used effectively in this field and satisfactory accuracy was found for the two examples. Based on this study, an operational real time environment could be achieved when using a trained forecasting neural network.
Sabagh Yazdi S.r., Mohammad Zadeh Qomi M.,
Volume 2, Issue 2 (June 2004)
Abstract
A numerical model is introduced for solution of shallow water flow equations with negligible physical dissipations due to canal roughness and turbulence effects. Two-dimensional velocity distribution and water depth of the flow field are computed by solving the depth average equations of continuity and motion. The equations are converted to discrete form using cell vertexfinite volume method on triangular unstructured mesh. The formulation of the added numericalviscosity is chosen in such a way that preserves the accuracy of numerical results. The accuracy ofthe model is assessed by computing the challenging case of inviscid frictionless flow in a canal with a 1800 bend. The computed results are compared with analytical solution which is obtainedfrom potential flow theory. Simulation of frictionless free surface flow in a constant width meandering sinusoidal canal is considered as an application of the model. The algorithm produced encouraging results.
Mohammad T. Dastorani, Nigel G. Wright,
Volume 2, Issue 3 (September 2004)
Abstract
In this study, an artificial neural networks (ANN) was used to optimise the results
obtained from a hydrodynamic model of river flow prediction. The study area is Reynolds Creek
Experimental Watershed in southwest Idaho, USA. First a hydrodynamic model was constructed to
predict flow at the outlet using time series data from upstream gauging sites as boundary
conditions. The model, then was replaced with an ANN model using the same inputs. Finally a
hybrid model was employed in which the error of the hydrodynamic model is predicted using an
ANN model to optimise the outputs. Simulations were carried out for two different conditions (with
and without data from a recently suspended gauging site) to evaluate the effect of this suspension
in hydrodynamic, ANN and the hybrid model. Using ANN in this way, the error produced by the
hydrodynamic model was predicted and thereby, the results of the model were improved.
Soroush A., Koohi Sh.,
Volume 2, Issue 4 (December 2004)
Abstract
Lateral spreading of liquefied saturated sandy deposits happens during and shortly afterearthquakes. This paper first reviews this phenomenon by means of reviewing and comparingobservations on case histories and experimental works. Based on the results from the review andcomparison, a mechanism for describing lateral spreading will be suggested. The Finn model,adopted in the Computer code FLAC is employed to carry out numerical analyses of lateralspreading of the Wildlife Site, happened during the 1987 Superstition Hills earthquake. First themodel is calibrated by means of numerical analysis of the first centrifuge model test of theVELACS Project. For the Wildlife site, three types of analysis are carried out: a) coupledliquefaction-consolidation analysis using the coefficient of permeability (K1) of the liquefiedlayers, as reported in the literature b) analysis type (a), but with K equal to 0.1K1, and c) a fullyundrained liquefaction analysis. The analyses results, in forms of excess pore water pressures andsurface displacements, indicated that the fully undrained behavior of the liquefied layers betterrepresents the behavior and response of the site during the earthquake.
Mohammad C. Pakbaz, M. Lorestani,
Volume 3, Issue 2 (June 2005)
Abstract
The main purpose of this research is evaluation of effect of chemicals on permeability of
sand- bentonite mixtures. The coefficients of permeability of sand- bentonite mixtures in water,
solutions of sodium and calcium chlorides, sodium hydroxide, acetic acid, methanol and carbon
tetrachloride were calculated using parameters obtained in 1- D consolidation test and Terzaghi’s
theory. At each void ratio permeability of samples in water is the lowest and that for carbon
tetrachloride is the highest. For all fluids the permeability index Ck is decreased as the percentage
of sand is increased. The largest Ck belongs to the samples tested in water and the smallest Ck
belongs to the samples tested in carbon tetrachloride.
B. Saghafian, A.r. Shokoohi,
Volume 4, Issue 1 (March 2006)
Abstract
Time–Area method is one of the most widely applied techniques of watershed routing, and
can be potentially used as a distributed model. In this paper, a fundamental flaw in the arrangement
of subareas in the original time-area histogram is identified for one-dimensional flow. This is
conducted on the basis of comparing time-area hydrograph with that of the kinematic wave theorem.
Accordingly, a revised time-area algorithm is developed as a substitute for the original time-area.
It is proved that in the revised approach, subareas must be reversely arranged. It is also shown that
the revised time-area hydrograph is in perfect agreement with the hydrograph derived by the
kinematics wave theory.
H. Moharrami, S.a. Alavinasab,
Volume 4, Issue 2 (June 2006)
Abstract
In this paper a general procedure for automated minimum weight design of twodimensional
steel frames under seismic loading is proposed. The proposal comprises two parts:
a) Formulation of automated design of frames under seismic loading and b) introduction of an
optimization engine and the improvement made on it for the solution of optimal design. Seismic
loading, that depends on dynamic characteristics of structure, is determined using "Equivalent
static loading" scheme. The design automation is sought via formulation of the design problem in
the form of a standard optimization problem in which the design requirements is treated as
optimization constraints.
The Optimality Criteria (OC) method has been modified/improved and used for solution of the
optimization problem. The improvement in (OC) algorithm relates to simultaneous identification of
active set of constraints and calculation of corresponding Lagrange multipliers. The modification
has resulted in rapid convergence of the algorithm, which is promising for highly nonlinear optimal
design problems. Two examples have been provided to show the procedure of automated design and
optimization of seismic-resistant frames and the performance and capability of the proposed
algorithm.
N. Naderpajouh, A. Afshar, S.a. Mirmohammadsadeghi,
Volume 4, Issue 4 (December 2006)
Abstract
The use of Value Engineering (VE) methodology in construction industry has grown
significantly, mainly in view of its extensive benefits. The main task in evaluation phase of VE
workshop is to assess alternative ideas, proposed for each function. This phase of VE, hence, could
be deemed as a Multi Criteria Decision Making (MCDM) problem. This paper presents a fuzzy
decision support system (DSS) to be employed in evaluation phase of VE. The proposed multi
alternative decision model may be recommended where alternatives’ preferences ratios are
different, and scores assigned to each alternative idea are uncertain. As use of VE has greater
payoffs at the earlier stages of the construction projects, in which most of the criteria are still vague
and not precisely defined, exploiting this DSS may result in more tangible model of decision making
process and satisfactory outlook of VE studies in construction projects. A ranking methodology in
a spreadsheet template is also provided to facilitate the ranking process. Performance of the
proposed methodology is tested using a case example in the tunneling industry.
S. Mohammadi, A. Bebamzadeh,
Volume 4, Issue 4 (December 2006)
Abstract
Explosion has always been regarded as one of the most complicated engineering
problems. As a result, many engineers have preferred rather simplified empirical approaches in
comparison to extremely complex deterministic analyses. In this paper, however, a numerical
simulation based on the combined finite/discrete element methodology is presented for analyzing the
dynamic behavior of fracturing rock masses in blasting. A finite element discretization of discrete
elements allows for complex shapes of fully deformable discrete elements with geometric and
material nonlinearities to be considered. Only a Rankine strain softening plasticity model is
employed, which is suitable for rock and other brittle materials. Creation of new lines/edges/bodies
from fracturing and fragmentation of original objects is systematically considered in the proposed
gas-solid interaction flow model. An equation of state is adopted to inexpensively calculate the
pressure of the detonation gas in closed form. The model employed for the flow of detonation gas
has resulted in a logical algorithmic procedure for the evaluation of spatial distribution of the
pressure of detonation gas, work done by the expanding gas and the total mass of the detonation gas
as functions of time indicating the ability of model to respond to changes in both the mass of
explosive charge and the size of the solid block undergoing fracture. Rock blasting and demolition
problems are amongst the engineering applications that are expected to benefit directly from the
present development. The results of this study may also be used to provide some numerical based
reliable solutions for the complex analysis of structures subjected to explosive loadings.
Mohammad Reza Kavian Pour, H.r. Masoumi ,
Volume 6, Issue 3 (September 2008)
Abstract
Hydraulics of stepped spillway is a very complicated phenomenon, as it consists of a two phase flow passing through a set of designed steps. The steps increase the rate of energy dissipation taking place on the spillway face. Turbulence, flow aeration and energy dissipation are the main tasks in the design of such structures. This study consists of the experimental investigation to determine the energy dissipation over stepped spillways. Experiments conducted at Water Research Institute on two physical models of the Siyah Bisheh stepped spillways in Iran. To develop a more generalized expression, the results of previous investigations were also considered in our study. Therefore, a wide range of variables were taken into account to estimate the energy dissipation along the non-uniform flow regime. Assuming the energy dissipation along the uniform flow regime to be equal to the vertical displacement of the jet, the total energy lost was calculated. A comparison of the results with those of measurements showed a regression of 0.92 for the total energy dissipation, which is one of the features of the present method for estimating of the energy dissipation, compared with the previous investigation.
Amir Hamidi, S. Mohsen Haeri,
Volume 6, Issue 3 (September 2008)
Abstract
The deformation and stiffness characteristics of a cemented gravely sand was investigated using
triaxial equipment. The triaxial tests were conducted in both dry and saturated undrained conditions.
Artificially cemented samples are prepared using gypsum plaster as the cementing agent. The plaster was
mixed with the base soil at the weight percentages of 1.5, 3, 4.5 and 6. The applied confining pressure varied
between 25 to 500 kPa in triaxial tests. The process of yielding of the soil was investigated for the considered
soil and the bond and final yield points were identified for the cemented soil with different cement contents.
The variations of deformation and stiffness parameters with cement content and confining stress were studied
as well. Some of the parameters were determined for both drained and undrained conditions to investigate the
effect of drainage condition on the stiffness and yield characteristics of the tested cemented gravely sand.
According to the results, the difference between drained and undrained tangent stiffness decreases with
increase in confining stress. Finally the effect of cement type was investigated as an important parameter
affecting the stiffness at bond yield. The rate of increase in tangent stiffness at bond yield changes with cement
content for different cementing agents.
S.h. Ebrahimi, S. Mohammadi, A. Asadpoure,
Volume 6, Issue 3 (September 2008)
Abstract
A new approach is proposed to model a crack in orthotropic composite media using the extended
finite element method (XFEM). The XFEM uses the concept of partition of unity in addition to meshless basic
idea of approximating a field variable by its values at a set of surrounding nodes. As a result, higher order
approximations can be designed with the same total number of degrees of freedom. In this procedure, by using
meshless based ideas, elements containing a crack are not required to conform to crack edges. Therefore mesh
generating is performed without any consideration of crack conformations for elements and the method has
the ability of extending the crack without any remeshing. Furthermore, the type of elements around the cracktip
is the same as other parts of the finite element model and the number of nodes and consequently degrees
of freedom are reduced considerably in comparison to the classical finite element method. Developed
orthotropic enrichment functions are further modified to enable modeling isotropic problems.
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.
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.
M.h. Vahidnia, A.a. Alesheikh, A. Alimohammadi, F. Hosseinali,
Volume 7, Issue 3 (Sept. 2009)
Abstract
Landslides are major natural hazards which not only result in the loss of human life but also cause economic
burden on the society. Therefore, it is essential to develop suitable models to evaluate the susceptibility of slope failures
and their zonations. This paper scientifically assesses various methods of landslide susceptibility zonation in GIS
environment. A comparative study of Weights of Evidence (WOE), Analytical Hierarchy Process (AHP), Artificial
Neural Network (ANN), and Generalized Linear Regression (GLR) procedures for landslide susceptibility zonation is
presented. Controlling factors such as lithology, landuse, slope angle, slope aspect, curvature, distance to fault, and
distance to drainage were considered as explanatory variables. Data of 151 sample points of observed landslides in
Mazandaran Province, Iran, were used to train and test the approaches. Small scale maps (1:1,000,000) were used in
this study. The estimated accuracy ranges from 80 to 88 percent. It is then inferred that the application of WOE in
rating maps’ categories and ANN to weight effective factors result in the maximum accuracy.
H.m. Noh, Y.o. Cho,
Volume 8, Issue 1 (3-2010)
Abstract
In this paper, the processes which are currently under development in South Korea, concerning railway
safety management system are introduced. Railway safety management system in South Korea is briefly presented,
making particular attentions to Systems Engineering Management Plan (SEMP). To make huge national R&D projects
successful, systematic management process is essential. In this respect, detailed applying SEMP on railway safety
management system of South Korea is discussed including Systems Engineering process and Verification and
Validation procedures. Furthermore, a computer-aided systems engineering tool (Cradle) is used in order to make the
management process more easily controllable.
S.m. Mir Mohammad Hosseini, A.a. Hajimohammadi, A. R. Hajimohammadi,
Volume 8, Issue 2 (6-2010)
Abstract
Seismic piezocone device (SCPTu) together with Resonant Column and Cyclic Triaxial test apparatus are
employed to measure small strain shear modulus (G0) of carbonate sandy and clayey soils of southern coasts of Iran.
A large area of southern regions of Iran is formed from clay, silt and sand. In this study, maximum shear modulus that
is derived from both field (by seismic piezocone) and laboratory (by Resonant Column and Cyclic Triaxial) tests on
soil samples from the southern region, indicated a meaningful effect of sample disturbance. Results show that in
laboratory tests, loose samples tend to become denser and therefore exhibit greater stiffness whereas dense samples
tend to become looser, showing a reduction in stiffness. According to the results of the present study, there are narrow
limits of soils shear moduli for which the laboratory tests and the field measurements yield approximately the same
amounts. This limit of shear moduli is about 30-50(MPa) for clay deposits and 70-100 (MPa) for sandy deposits. Since
the shear moduli of soils in small strains can also be computed from the shear wave velocity, also correlations based
on parameters derived from SCPTu test for shear wave velocity determination of sandy and clayey soils of the studied
area are presented. This study shows that shear wave velocity can be related to both corrected tip resistance and total
normal stress. The measurements of the damping ratio and shear module, because of a great disturbance of stiff
deposits during the sampling process and also due to considerable differences between the laboratory and field
results, by the laboratory approaches are not reliable and advised.
P. Alimohammadi, N. Shariatmadari, M.a. Abdoli, H. Ghiasinejad, A. Mansouri,
Volume 8, Issue 2 (6-2010)
Abstract
Hydrologic Evaluation of Landfill Performance (HELP) model is one of the most accepted tools to simulate
the hydrological attributes of landfills. Although some major deviations from real values has been reported about the
calculated results for leachate generation by HELP model but other researchers and/or engineers in practice have
used it in some places to estimate amount of leachate produced in the landfills. On the Other hand this model is
elaborated and mainly used in developed countries with the waste having low moisture content and also in climatic
conditions with high precipitation. This research investigated the applicability of the model in arid areas, by
construction of two 30m× 50m (effective horizontal length) test cells in Kahrizak landfill (longitude=51°, 20',
latitude= 35° 27' degrees), and monitoring the real leachate generation from each one. A set of field capacity and
saturated water conductivity tests were also performed to determine basic hydrologic properties of municipal waste
landfilled. A comparison was made between values calculated by HELP model and recorded values, shows that a
prediction of leachate on annual basis can be done by HELP model with acceptable accuracy but when the infiltration
of water to waste body increases due to leachate production, the model intents to underestimate water storage capacity
of the landfill, which lead to deviation of calculated values from real ones.
Khelifa Harichane, Mohamed Ghrici, Said Kenai,
Volume 9, Issue 2 (June 2011)
Abstract
When geotechnical engineers are faced with cohesive clayey soils, the engineering properties of those soils may need to be
improved to make them suitable for construction. The aim of this paper is to study the effect of using lime, natural pozzolana or
a combination of both on the geotechnical characteristics of two cohesive soils. Lime or natural pozzolana were added to these
soils at ranges of 0-8% and 0-20%, respectively. In addition, combinations of lime-natural pozzolana were added at the same
ranges. Test specimens were subjected to compaction tests and shear tests. Specimens were cured for 1, 7, 28 and 90 days after
which they were tested for shear strength tests. Based on the experimental results, it was concluded that the combination limenatural
pozzolana showed an appreciable improvement of the cohesion and internal friction angle with curing period and
particularly at later ages for both soils.