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A robust multi-objective optimization model for project scheduling considering risk and sustainable development criteria
, Article Environment, Development and Sustainability ; Volume 23, Issue 8 , 2021 , Pages 11494-11524 ; 1387585X (ISSN) ; Abbasianjahromi, H. R ; Sepehri, M ; Zeighami, E ; Sharif University of Technology
Springer Science and Business Media B.V
2021
Abstract
There is limited research that considers the sustainability aspect of the projects’ schedule. The present study proposes a model to cover this gap by considering sustainable development criteria. A multi-objective model with four objective functions, including minimizing cost, risk, and socio-environmental impacts, has been presented to decrease the project’s delay. Since some of the parameters are considered under conditions of uncertainty for the proximity of problems to real projects, the robust programming method is used to deal with the uncertainty, and the epsilon-constraint method was applied to solve the multi-objective model. Several scenarios are also defined to analyze the...
Modelling of queue length in freeway work zones – case study karaj-tehran freeway
, Article Promet - Traffic - Traffico ; Volume 33, Issue 1 , 2021 , Pages 49-59 ; 03535320 (ISSN) ; Sharif Ali , S ; Goodarzi, M. J ; Amini, N ; Latifi, H ; Sharif University of Technology
Faculty of Transport and Traffic Engineering
2021
Abstract
In this study, the traffic parameters were collected from three work zones in Iran in order to evaluate the queue length in the work zones. The work zones were observed at peak and non-peak hours. The results showed that abrupt changes in Freeway Free Speed (FFS) and arrival flow rate caused shockwaves and created a bot-tleneck in that section of the freeway. In addition, accel-eration reduction, abrupt change in the shockwave speed, abrupt change in the arrival flow rate and increase in the percentage of heavy vehicles have led to extreme queue lengths and delay. It has been found that using daily traffic data for scheduling the maintenance and rehabilita-tion projects could diminish the...
Numerical investigation of stability of deep excavations supported by soil-nailing method
, Article Geomechanics and Geoengineering ; Volume 16, Issue 6 , 2021 , Pages 434-451 ; 17486025 (ISSN) ; Maleki, J ; Aghakhani, N ; Yousefi, M ; Sharif University of Technology
Taylor and Francis Ltd
2021
Abstract
Deep excavation in urban areas can cause instability problems due to significant settlement at the ground surface and large movements at the excavation facing walls. One of the most popular methods used to stabilise these excavations is utilising soil-nailing method. This method has also been widely used to stabilise natural slopes and earth retaining structures. Because of the complexity involved in the mechanism of this stabilising system due to interacting effects of the soil, nails, grout and shotcrete, numerical modelling with high accuracy should be used to analyse the behaviour of the soil-nailed walls. Considering all aspects of soil-structure interaction in the present research, a...
Drilled shafts in sand: failure pattern and tip resistance using numerical and analytical approaches
, Article International Journal of Geotechnical Engineering ; 2021 ; 19386362 (ISSN) ; Ahmadi, M. M ; Sharif University of Technology
Taylor and Francis Ltd
2021
Abstract
Drilled shafts are one of the most important types of pile foundations. Several researchers have suggested different soil failure patterns for driven piles; however, for drilled shafts, this issue is inadequately addressed in the literature. In this paper, a numerical approach was pursued to obtain the location and dimensions of plastic zones around the tip of drilled shafts. The dependence of the suggested failure pattern size on the soil properties and drilled shaft dimensions was investigated. Based on several analyses, a soil jug-shaped failure pattern around the tip of drilled shafts was proposed, and its dimensions were determined using the regression-based and trial and error...
Tidal effects on groundwater dynamics in unconfined aquifers
, Article Hydrological Processes ; Volume 15, Issue 4 , 2001 , Pages 655-669 ; 08856087 (ISSN) ; Volker, R. E ; Lockington, D. A ; Sharif University of Technology
2001
Abstract
The variation of seawater level resulting from tidal fluctuations is usually neglected in regional groundwater flow studies. Although the tidal oscillation is damped near the shoreline, there is a quasi-steady-state rise in the mean water-table position, which may have an influence on regional groundwater flow. In this paper the effects of tidal fluctuations on groundwater hydraulics are investigated using a variably saturated numerical model that includes the effects of a realistic mild beach slope, seepage face and the unsaturated zone. In particular the impact of these factors on the velocity field in the aquifer is assessed. Simulations show that the tidal fluctuation has substantial...
Numerical Modeling of Regular Wave and Conventional Tension Leg Platform Interaction using Boundary Element Method
, M.Sc. Thesis Sharif University of Technology ; Abbaspour Tehrani fard, Madjid (Supervisor) ; Ketabdari, Mohammad Javad (Supervisor)
Abstract
Petroleum is the main source of energy in the world. So, exploration and production of this strategic matter from earth and sea has a major importance. A large amount of this black gold is hidden under deep seas floors and extraction of these sources requires knowledge of design and technology of construction of deep water offshore platforms and equipments. Convetional Tension Leg Platform (CTLP), configured as 4 cloumns and 4 pontoons, is one of deep offshore platforms moored by several pretensioned tethers. The dynamic behavior characteristics of CTLPs are extracted in this thesis by numerical modeling of CTLP and regular wave interaction. A computer program PARADISE is developed in...
Investigation of Coastal Geometry Effects on Freshwater Discharge to Saline Lakes
, M.Sc. Thesis Sharif University of Technology ; Ataie-Ashtiani, Behzad (Supervisor)
Abstract
Groundwater is the most important freshwater resource in the coastal zones. There are some factors contaminate fresh groundwaters. Sea water intrusion (SWI) is one of the most important components of groundwater salinization. Also Submarine groundwater discharge (SGD) occurs when hydraulic gradient is from landside to seaside in coastal aquifers. There are many factors intensify SWI and SGD. In this research at the first part, coastline shape effect on SWI and SGD is investigated. For to this 4 different aquifers with different coastline shapes as stepped coastline, vertical coastline, steep slope coastline, and mild slope coastline are simulated with the same hydraulic parameters and...
3D Numerical Modeling of Dynamic Instability Induced by Liquefaction in Loose Sand Deposit when Earthquake Occurs Perpendicular to the Slope
, M.Sc. Thesis Sharif University of Technology ; Pak, Ali (Supervisor)
Abstract
Soil liquefaction occurring in loose saturated sand deposits during seismic loadings is one of the most destructive earthquake-induced phenomena in the field of earthquake geotechnical engineering. Catastrophic destructions due to this phenomenon that have been observed in the earthquakes such as Kobe (1995), Chi-Chi (1999), etc. has led to extensive studies in this field. In case of soil slopes prone to liquefaction hazard, detailed analysis of this phenomenon requires considering soil-related factors (e.g. shear strength, relative density, permeability, slope geometry) on the one hand, and earthquake-related characteristics (e.g. amplitude, frequency, duration) on the other. Numerical...
Three Dimensional Numerical Simulation of Fresh Water Lens in Small Islands (Case Study: Kish Island)
, M.Sc. Thesis Sharif University of Technology ; Ataei Ashtiani, Behzad (Supervisor)
Abstract
Sensitive ecosystem and scarcity of freshwater are the main characteristics of small islands. These islands have small catchments and usually lack tangible surface water resources. As a result these islands are dependent almost entirely on groundwater. Groundwater on small islands usually occurs in the form of a freshwater lens floating on the more dense saline water. The freshwater lens is highly sensitive to various stresses such as drought, pumping, sea tide, etc. Due to the importance of freshwater lens in islands, proper and optimal use of this vital resource should be studied. Kish island`s freshwater lens was three dimensionally simulated using the numerical model SUTRA. The aim was...
An investigation of fracture geometry in hydraulic fracturing on a gas reservoir well production enhancement
, Article Petroleum Science and Technology ; Vol. 32, issue. 2 , 2014 , pp. 150-157 ; ISSN: 10916466 ; Parvazdavani, M ; Abbasi, S ; Rahnama, A. R ; Sharif University of Technology
Abstract
Utilizing improved production methods have been always challenging in upstream industries. Nowadays, hydraulic fracturing is one of the most prestigious mechanical methods. Application of this method is in wells with low productivity index. Hydraulic fracturing efficiency depends on various factors, such as fracture geometry, fluid composition, and stress distribution. But some of them would be ignored, such as fracture geometry, which is neglected due to nongravity and lack of investigation of DFN statistical population assumption. The authors develop a more comprehensive methodology based on fracture geometry and aim to model one of the gas reservoirs in Iran that is naturally fractured by...
Simulating dynamic plastic continuous neural networks by finite elements
, Article IEEE Transactions on Neural Networks and Learning Systems ; Volume 25, Issue 8 , August , 2014 , Pages 1583-1587 ; ISSN: 2162237X ; Torghabehi, O. O ; Sharif University of Technology
Abstract
We introduce dynamic plastic continuous neural network (DPCNN), which is comprised of neurons distributed in a nonlinear plastic medium where wire-like connections of neural networks are replaced with the continuous medium. We use finite element method to model the dynamic phenomenon of information processing within the DPCNNs. During the training, instead of weights, the properties of the continuous material at its different locations and some properties of neurons are modified. Input and output can be vectors and/or continuous functions over lines and/or areas. Delay and feedback from neurons to themselves and from outputs occur in the DPCNNs. We model a simple form of the DPCNN where the...
Lattice Boltzmann method for simulating impulsive water waves generated by landslides
, Article Scientia Iranica ; Vol. 21, issue. 2 , 2014 , p. 318-328 ; 1026-3098 ; Sarfaraz, M ; Sharif University of Technology
Abstract
Impulsive water waves generated by landslides impose severe damage on coastal areas. Very large mass ows in the ocean can generate catastrophic tsunamis. Preventing damage to dams and coastal structures, and saving the lives of local people against landslide-generated waves, has become an increasingly important issue in recent years. Numerical modeling of landslide-generated waves is a challenging subject in CFD. The reason lies in the difficulty of determining the interaction between the moving solids and sea water, which causes complicated turbulent regimes around the moving mass and at the water surface. Submarine or aerial types of landslide can further complicate the problem. Up to now,...
The effect of step on the hydraulic characteristics of the subcritical free surface flow in conveyance tunnel
, Article Tunnelling and Underground Space Technology ; Volume 28, Issue 1 , 2012 , Pages 212-217 ; 08867798 (ISSN) ; Nabipour, M ; Sharif University of Technology
Abstract
Due to the water scarcity and uneven distribution of water resources, conveyance systems are designed to carry water through basins. For this purpose conveyance tunnels which carry supper/subcritical flows are commonly constructed. The occurrence of steps in the tunnels created by segment off-sets during the TBM operations would cause significant local head losses. As a result, the flow discharge may reduce. In this study subcritical free surface flow in conveyance tunnel is simulated using the one-dimensional HEC-RAS model. Impact of the invert segment off-set on the discharge rate is then estimated. Similarly a two-dimensional numerical model based on the Volume of Fluid (VOF) scheme is...
Free fall and controlled gravity drainage processes in fractured porous media: Laboratory and modelling investigation
, Article Canadian Journal of Chemical Engineering ; Volume 93, Issue 12 , October , 2015 , Pages 2286-2297 ; 00084034 (ISSN) ; Ayatollahi, S ; Masihi, M ; Sharif University of Technology
Wiley-Liss Inc
2015
Abstract
Gravity drainage is known to be one of the most effective methods for oil recovery in fractured reservoirs. In this study, both free fall and controlled gravity drainage processes were studied using a transparent fractured experimental model, followed by modelling using commercial CFD software. The governing equations were employed based on the Darcy and mass conservation laws and partial pressure formulation. Comprehensive examination was done on variables such as fluid saturation, velocity, and pressure distribution in the matrix and fracture, as well as fluid front level and production rate. Additionally, effects of the model parameters on the gravity drainage performance were...
Two-dimensional free convection heat transfer below a horizontal hot isothermal flat strip
, Article Journal of Heat Transfer ; Volume 137, Issue 5 , May , 2015 ; 00221481 (ISSN) ; Nouri Gheimassi, A ; Salari, A ; Behshad Shafii, M ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2015
Abstract
Convection heat transfer below a horizontal, hot, and isothermal strip of infinite length and width of 2L embedded in fluids with different Prandtl number (Pr) and Nusselt number (Nu) is analyzed with the aid of integral method. A new concept is utilized to determine the boundary layer thickness at the strip's edge, which is based on matching the flow rate of the boundary layer below the strip at its edge and the flow rate of the plume, which forms after the heated fluid detaches from the strip's edge. In addition to these novelties, a numerical model is developed to verify the analytical framework, and an excellent agreement is observed between the analytical and numerical models
Thermo-mechanical modeling of friction stir welding
, Article International Journal of Materials Research ; Volume 101, Issue 3 , 2010 , Pages 390-397 ; 18625282 (ISSN) ; Serajzadeh, S ; Sharif University of Technology
2010
Abstract
In this paper an integrated model has been utilized to predict thermo-mechanical behavior during friction stir welding of an aluminum alloy. A finite element code, ABAQUS, is employed to solve the governing equations of heat conduction and plastic deformation, while a rigid - viscoplastic material behavior is utilized and effects of different thermal and mechanical boundary conditions are considered in the simulation. To assess the accuracy of the model, predicted results have been compared with experimental data and good agreement has been observed
An integrated SPH-polyhedral DEM algorithm to investigate hydraulic stability of rock and concrete blocks: application to cubic armours in breakwaters
, Article Engineering Analysis with Boundary Elements ; Volume 84 , 2017 , Pages 1-18 ; 09557997 (ISSN) ; Pak, A ; Sharif University of Technology
Abstract
In this paper, a combination of the Lagrangian meshfree method of SPH and Polyhedral DEM is presented to simulate the interaction between the free surface of water and solid objects possessing sharp edges and flat surfaces, such as armour units of breakwaters. Both SPH and DEM schemes are validated successfully against experimental data. The numerical scheme is utilized to inspect the stability of concrete cubic armours in rubble-mound breakwaters through systematic analyses with various geometrical parameters and environmental conditions. The numerical results regarding the required dimensions of the cubic blocks for providing stability of the armour units under the wave attack are compared...
Enhancement of surface adsorption-desorption rates in microarrays invoking surface charge heterogeneity
, Article Sensors and Actuators, B: Chemical ; Volume 242 , 2017 , Pages 956-964 ; 09254005 (ISSN) ; Saidi, M. S ; Sadeghi, A ; Sharif University of Technology
Elsevier B.V
2017
Abstract
This investigation is devoted to the influences of non-uniform wall characteristics on the surface adsorption-desorption rates in an electrokinetic microarray. Utilizing already explored electroosmotic and electrophoretic velocities, the species transport equations are solved by a finite-volume-based numerical approach. Uniform, sinusoidal, and pulse-like distributions of the zeta potential are considered in the analysis. The developed model is validated by comparing the results with those of two analytical solutions that are derived for limiting conditions. The results reveal that, in some cases, the surface charge heterogeneity can reduce the saturation time by more than 60%. The efficacy...
Numerical study on a heeled one-stepped boat moving forward in planing regime
, Article Applied Ocean Research ; Volume 96 , 2020 ; Tavakoli, S ; Kohansal, A ; Khosravani, R ; Ghassemzadeh, A ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Stepped planing hulls have the potential to reach high-speeds in the sea. The step on the bottom of these vessels influence the pressure distribution and thus stability of the vessel, especially in transverse plane. Understanding the behavior of these vessels in a non-zero heel condition is fundamental in the early stage design. In the current paper, numerical simulation of the viscous flow field around a heeled one-stepped planing hull is performed to evaluate influences of the asymmetric planing on the performance of the vessel. The numerical model is validated in two steps. At the first step, performance of a heeled stepless planing hull operating in calm water is simulated using the...
A numerical approach on side resistance of drilled shafts embedded in sandy soils
, Article International Journal of Geotechnical Engineering ; Volume 14, Issue 6 , 2020 , Pages 644-652 ; Ahmadi, M. M ; Sharif University of Technology
Taylor and Francis Ltd
2020
Abstract
This study numerically investigates the side resistance of drilled shafts (bored piles) in sand using FLAC2D computer program. The results of the equations available in the literature are compared with the results of the present numerical study. A series of analyses is also conducted to assess the effects of various soil and pile parameters on the magnitude of side resistance of bored piles embedded in sand. Furthermore, the coupling (combined) effect of coefficient of lateral earth pressure with friction angle, and the coefficient of lateral earth pressure with a unit weight of soil on side resistance are investigated. The results show that the maximum effect of K0 on side resistance occurs...