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    Sampling efficiency in Monte Carlo based uncertainty propagation strategies: Application in seawater intrusion simulations

    , Article Advances in Water Resources ; Vol. 67, issue , 2014 , pp. 46-64 Rajabi, M. M ; Ataie-Ashtiani, B ; Sharif University of Technology
    Abstract
    The implementation of Monte Carlo simulations (MCSs) for the propagation of uncertainty in real-world seawater intrusion (SWI) numerical models often becomes computationally prohibitive due to the large number of deterministic solves needed to achieve an acceptable level of accuracy. Previous studies have mostly relied on parallelization and grid computing to decrease the computational time of MCSs. However, another approach which has received less attention in the literature is to decrease the number of deterministic simulations by using more efficient sampling strategies. Sampling efficiency is a measure of the optimality of a sampling strategy. A more efficient sampling strategy requires... 

    Transient free-surface seepage in three-dimensional general anisotropic media by BEM

    , Article Engineering Analysis with Boundary Elements ; Vol. 46, issue , 2014 , p. 51-66 Rafiezadeh, K ; Ataie-Ashtiani, B ; Sharif University of Technology
    Abstract
    Kinematic boundary condition is usually used when dealing with transient free-surface flow problems in isotropic media. When dealing with anisotropic problems, a transformation can transform the anisotropic media to an equivalent isotropic media for seepage analysis, but the kinematic boundary condition cannot be used directly in the transformed media. A generalization of the kinematic boundary condition along any arbitrary direction is derived for use in the transformed domain for general three-dimensional anisotropic problems. A boundary element method for solving transient free-surface seepage problems is developed and the treatment of the proposed kinematic boundary condition in the... 

    Seepage analysis in multi-domain general anisotropic media by three-dimensional boundary elements

    , Article Engineering Analysis with Boundary Elements ; Volume 37, Issue 3 , 2013 , Pages 527-541 ; 09557997 (ISSN) Rafiezadeh, K ; Ataie Ashtiani, B ; Sharif University of Technology
    2013
    Abstract
    A three-dimensio111nal boundary element solution for the seepage analysis in multi-domain general anisotropic media has been developed based on the transformation approach. Using analytical eigenvalues and eigenvectors of the hydraulic conductivity tensor, a closed-form coordinate transformation matrix has been provided to transform the quadratic form of governing equation of seepage for the general anisotropic media to the Laplace equation. This transformation allows the analysis to be carried out using any standard BEM codes for the potential theory on the transformed space by adding small pre- and post-processing routines. With this transformation, any physical quantity like the total... 

    Three dimensional flow in anisotropic zoned porous media using boundary element method

    , Article Engineering Analysis with Boundary Elements ; Volume 36, Issue 5 , 2012 , Pages 812-824 ; 09557997 (ISSN) Rafiezadeh, K ; Ataie Ashtiani, B ; Sharif University of Technology
    2012
    Abstract
    Coupling the adjacent zones for seepage analysis in porous media needs compatibility and equilibrium equations (equality of potential on coinciding nodes and conservation of flowing mass between zones, respectively). When stretched coordinate transformation is applied to the anisotropic zones, the Dirichlet boundary conditions remain unchanged, but the Neumann boundary condition should also be transformed. Similarly in a zoned problem, for the interface between zones, compatibility equations remain unchanged during the transformation while the equilibrium equations should be transformed. In this paper, transformed Neumann boundary conditions and equilibrium equations for the interface of... 

    A rigorous finite volume model to simulate subaerial and submarine landslide-generated waves

    , Article Landslides ; 2015 , Pages 1-19 ; 1612510X (ISSN) Yavari Ramshe, S ; Ataie Ashtiani, B ; Sharif University of Technology
    Springer Verlag  2015
    Abstract
    This paper presents a new landslide-generated wave (LGW) model based on incompressible Euler equations with Savage-Hutter assumptions. A two-layer model is developed including a layer of granular-type flow beneath a layer of an inviscid fluid. Landslide is modeled as a two-phase Coulomb mixture. A well-balanced second-order finite volume formulation is applied to solve the model equations. Wet/dry transitions are treated properly using a modified non-linear method. The numerical model is validated using two sets of experimental data on subaerial and submarine LGWs. Impulsive wave characteristics and landslide deformations are estimated with a computational error less than 5 %. Then, the... 

    Assessment of a parallel evolutionary optimization approach for efficient management of coastal aquifers

    , Article Environmental Modelling and Software ; Volume 74 , December , 2015 , Pages 21-38 ; 13648152 (ISSN) Ketabchi, H ; Ataie Ashtiani, B ; Sharif University of Technology
    Elsevier Ltd  2015
    Abstract
    This study presents a parallel evolutionary optimization approach to determine optimal management strategies of large-scale coastal groundwater problems. The population loops of evolutionary algorithms (EA) are parallelized using shared memory parallelism to address the high computational demands of such applications. This methodology is applied to solve the management problems in an aquifer system in Kish Island, Iran using a three-dimensional density-dependent groundwater numerical model. EAs of continuous ant colony optimization (CACO), particle swarm optimization, and genetic algorithm are utilized to solve the optimization problems. By implementing the parallelization strategy, a... 

    A comparison of finite volume formulations and coupling strategies for two-phase flow in deforming porous media

    , Article Computers and Geotechnics ; Volume 67 , 2015 , Pages 17-32 ; 0266352X (ISSN) Asadi, R ; Ataie Ashtiani, B ; Sharif University of Technology
    Elsevier Ltd  2015
    Abstract
    In this paper a locally mass conservative finite volume method is employed to model the one-dimensional, two-phase immiscible flow in a poroelastic media. Since, an appropriate choice of primary variables is critical in simulating multiphase subsurface flow, depending on such a choice, the governing equations can be expressed in different forms. By implementing Picard iteration to a highly nonlinear system of equations, three numerical models including pressure form, mixed form and mixed form with a modified Picard linearization are developed in this study. These models have been evaluated in terms of stability, convergence and mass conservation in various one-dimensional test cases.... 

    Review: Coastal groundwater optimization—advances, challenges, and practical solutions

    , Article Hydrogeology Journal ; Volume 23, Issue 6 , September , 2015 , Pages 1129-1154 ; 14312174 (ISSN) Ketabchi, H ; Ataie Ashtiani, B ; Sharif University of Technology
    Springer Verlag  2015
    Abstract
    Decision models are essential tools for coastal groundwater management (CGM). A combined simulation-optimization framework is employed to develop these models. One of the main barriers in the widespread application of these models for real-world cases is their large computational burden. Recent advances in efficient computational approaches and robust optimization methods can crack this barrier. This study surveys the scientific basis of CGM to provide an overview on this subject and reviews the-state-of-the-art to clarify recent developments and to outline ideas for improving the computational performance. Key details are presented on the performance and choice of possible robust tools such... 

    Evolutionary algorithms for the optimal management of coastal groundwater: A comparative study toward future challenges

    , Article Journal of Hydrology ; Volume 520 , January , 2015 , Pages 193-213 ; 00221694 (ISSN) Ketabchi, H ; Ataie Ashtiani, B ; Sharif University of Technology
    Elsevier  2015
    Abstract
    This paper surveys the literature associated with the application of evolutionary algorithms (EAs) in coastal groundwater management problems (CGMPs). This review demonstrates that previous studies were mostly relied on the application of limited and particular EAs, mainly genetic algorithm (GA) and its variants, to a number of specific problems. The exclusive investigation of these problems is often not the representation of the variety of feasible processes may be occurred in coastal aquifers. In this study, eight EAs are evaluated for CGMPs. The considered EAs are: GA, continuous ant colony optimization (CACO), particle swarm optimization (PSO), differential evolution (DE), artificial bee... 

    Experimental study of three-dimensional flow field around a complex bridge pier

    , Article Journal of Engineering Mechanics ; Volume 136, Issue 2 , 2010 , Pages 143-154 ; 07339399 (ISSN) Beheshti, A. A ; Ataie Ashtiani, B ; Sharif University of Technology
    2010
    Abstract
    In this paper, three-dimensional turbulent flow field around a complex bridge pier placed on a rough fixed bed is experimentally investigated. The complex pier foundation consists of a column, a pile cap, and a 2×4 pile group. All of the elements are exposed to the approaching flow. An acoustic-Doppler velocimeter was used to measure instantaneously the three components of the velocities at different horizontal and vertical planes. Profiles and contours of time-averaged velocity components, turbulent intensity components, turbulent kinetic energy, and Reynolds stresses, as well as velocity vectors are presented and discussed at different vertical and horizontal planes. The approaching... 

    Impulse waves effects on coastlines and onshore industrial structures

    , Article Proceedings of the 5th International Conference on Asian and Pacific Coasts, APAC 2009, 13 October 2009 through 16 October 2009 ; Volume 4 , 2010 , Pages 29-36 ; 9789814466561 (ISBN) Najafi Jilani, A ; Ataie Ashtiani, B ; Sharif University of Technology
    Abstract
    Laboratory investigations have been performed on impulse wave's effects near the coastlines such as shoaling effects and run-up. Wave run-up over on smooth impermeable slope are studied in over than 100 experimental tests. The influences of the bed slope angle, incident impulse wave height and still water depth are investigated. The available empirical equations for impulsive wave run-up have been examined by comparison with the collected experimental data. A new equation has been presented for run-up estimation based on the laboratory measurements. It has been compared with others empirical equations and the differences have been discussed. The shoaling effects on the impulse wave feature... 

    Numerical modeling of subaerial and submarine landslide-generated tsunami waves—recent advances and future challenges

    , Article Landslides ; Volume 13, Issue 6 , 2016 , Pages 1325-1368 ; 1612510X (ISSN) Yavari Ramshe, S ; Ataie Ashtiani, B ; Sharif University of University
    Springer Verlag 
    Abstract
    Landslide-generated waves (LGWs) are among natural hazards that have stimulated attentions and concerns of engineers and researchers during the past decades. At the same period, the application of numerical modeling has been progressively increased to assess, control, and manage the risks of such hazards. This paper represents an overview of numerical studies on LGWs to explore associated recent advances and future challenges. In this review, the main landslide events followed by an LGW hazard are scrutinized. The uncertainty regarding landslide characteristics and the lack of data concerning generated tsunami properties highlights the necessity of probabilistic analysis and numerical... 

    Numerical modeling of subsidence in saturated porous media: A mass conservative method

    , Article Journal of Hydrology ; Volume 542 , 2016 , Pages 423-436 ; 00221694 (ISSN) Asadi, R ; Ataie Ashtiani, B ; Sharif University of Technology
    Elsevier B.V  2016
    Abstract
    In this paper, a second order accurate cell-centered finite volume method (FVM) is coupled with a finite element method (FEM) to solve the deformation of a saturated porous layer based on Biot's consolidation model. The proposed numerical technique is applied to the fully unstructured triangular grids to simulate actual geological formations. To reconstruct the pressure gradient at control volume faces, the diamond scheme is implemented as a multipoint flux approximation method. Also the least square algorithm is used to interpolate pressure at the vertices from the cell-center values. The stability of this numerical model is studied in comparison to the different FEMs through various... 

    Scour hole influence on turbulent flow field around complex bridge piers

    , Article Flow, Turbulence and Combustion ; Volume 97, Issue 2 , 2016 , Pages 451-474 ; 13866184 (ISSN) Beheshti, A. A ; Ataie Ashtiani, B ; Sharif University of Technology
    Springer Netherlands 
    Abstract
    Experimental results of detailed flow measurements using an Acoustic-Doppler Velocimeter (ADV) around a complex bridge pier (CBP) are presented. The pier consists of a column, a pile cap (PC) and a 2×4 pile group. The time-averaged velocities, turbulence intensities, and Reynolds stresses are studied and presented at different horizontal and vertical planes. Streamlines obtained from the velocity fields are used to show the complexity of the flow around the pier. It is shown that the main feature of the flow responsible for the entrainment of the bed sediments is a contracted (pressurized) flow below the PC toward the piles. A deflected flow around the PC and a strong down-flow along its... 

    Discussion of “Neuro-fuzzy GMDH systems based evolutionary algorithms to predict scour pile groups in clear water conditions” by M. Najafzadeh

    , Article Ocean Engineering ; Volume 123 , 2016 , Pages 249-252 ; 00298018 (ISSN) Beheshti, A. A ; Ataie Ashtiani, B ; Sharif University of Technology
    Elsevier Ltd 
    Abstract
    The author utilized neuro-fuzzy based group method of data handling (NF-GMDH) to predict the local scour depth around pile groups under clear-water conditions. They collected the datasets from literature. To predict the local scour by using NF-GMDH, nine dimensional parameters were considered to define a functional relationship between input and output variables. The results of NF- GMDH networks were compared with that of the empirical equations. However, the collected datasets for pile group scouring, the method of implementing the empirical formula to calculate scour depth, and using the equation of Sheppard et al. (2004) suggested for single pier to predict local scouring around pile... 

    Efficient fuzzy Bayesian inference algorithms for incorporating expert knowledge in parameter estimation

    , Article Journal of Hydrology ; Volume 536 , 2016 , Pages 255-272 ; 00221694 (ISSN) Rajabi, M. M ; Ataie Ashtiani, B ; Sharif University of Technology
    Elsevier 
    Abstract
    Bayesian inference has traditionally been conceived as the proper framework for the formal incorporation of expert knowledge in parameter estimation of groundwater models. However, conventional Bayesian inference is incapable of taking into account the imprecision essentially embedded in expert provided information. In order to solve this problem, a number of extensions to conventional Bayesian inference have been introduced in recent years. One of these extensions is 'fuzzy Bayesian inference' which is the result of integrating fuzzy techniques into Bayesian statistics. Fuzzy Bayesian inference has a number of desirable features which makes it an attractive approach for incorporating expert... 

    Develop of a fully nonlinear and highly dispersive water wave equation set; analysis of wave interacting with varying bathymetry

    , Article Prediction and Simulation Methods for Geohazard Mitigation - Proceedings of the International Symposium on Prediction and Simulation Methods for Geohazard Mitigation, IS-KYOTO 2009, 25 May 2009 through 27 May 2009, Kyoto ; 2009 , Pages 213-218 ; 9780415804820 (ISBN) Najafi Jilani, A ; Ataie Ashtiani, B ; Sharif University of Technology
    Abstract
    Extended Boussinesq-type water wave equations are derived in two horizontal dimensions to capture the nonlinearity effects and frequency dispersion of wave in a high accuracy order. A multi-parameter perturbation analysis is applied in several steps to extend the previous second order Boussinesq-type equations in to 6th order for frequency dispersion and consequential order for nonlinearity terms. The presented high-order Boussinesq-type equation is applied in a numerical model to simulate the wave field transformation due to physical processes such as shoaling, refraction and diffraction. The models results are compared with available experimental data which obtained in a laboratory wave... 

    Simulation of wave generated by landslides in Maku dam reservoir

    , Article Prediction and Simulation Methods for Geohazard Mitigation - Proceedings of the International Symposium on Prediction and Simulation Methods for Geohazard Mitigation, IS-KYOTO 2009, 25 May 2009 through 27 May 2009 ; 2009 , Pages 91-96 ; 9780415804820 (ISBN) Yavari Ramshe, S ; Ataie Ashtiani, B ; Sharif University of Technology
    Abstract
    In this work, impulsive wave generation and propagation generated by landslides are studied numerically for a real case. Maku dam reservoir, in the northwestern of Iran is considered as the case study. Generated wave heights, wave run-up, maximum wave height above the dam crest and the probable overtopping volume have been evaluated, using a two-dimensional numerical model (LS3D). This model is validated using available three-dimensional experimental data for simulating impulsive wave caused by sub-aerial landslides. Based on the results, the generated wave height for first and second scenarios are 12 m and 18 m respectively. The wave height of 8 m is observed close to dam body. Because of... 

    Modification of compressible smooth particles hydrodynamics for angular momentum in simulation of impulsive wave problems

    , Article Prediction and Simulation Methods for Geohazard Mitigation - Proceedings of the International Symposium on Prediction and Simulation Methods for Geohazard Mitigation, IS-KYOTO 2009, 25 May 2009 through 27 May 2009 ; 2009 , Pages 201-206 ; 9780415804820 (ISBN) Mansour Rezaei, S ; Ataie Ashtiani, B ; Sharif University of Technology
    Abstract
    In this work, Compressible Smooth Particles Hydrodynamics (C-SPH) is applied for numerical simulation of impulsive wave. Properties of linear and angular momentum in SPH formulation are studied. Kernel gradient of viscous term in momentum equation is corrected to ensure preservation of angular momentum. Corrected SPH method is used to simulate solitary Scott Russell wave and applied to simulate impulsive wave generated by two-dimensional under water landslide. In each of test cases, results of corrected SPH are compared with experimental results. The results of the numerical simulations and experimental works are matched and a satisfactory agreement is observed. Furthermore, vorticity... 

    Conceptualization of karstic aquifer with multiple outlets using a dual porosity model

    , Article Groundwater ; Volume 55, Issue 4 , 2017 , Pages 558-564 ; 0017467X (ISSN) Hosseini, S. M ; Ataie Ashtiani, B ; Sharif University of Technology
    Abstract
    In this study, two conceptual models, the classic reservoir (CR) model and exchange reservoirs model embedded by dual porosity approach (DPR) are developed for simulation of karst aquifer functioning drained by multiple outlets. The performances of two developed models are demonstrated at a less developed karstic aquifer with three spring outlets located in Zagros Mountain in the south-west of Iran using 22-years of daily data. During the surface recharge, a production function based on water mass balance is implemented for computing the time series of surface recharge to the karst formations. The efficiency of both models has been assessed for simulation of daily spring discharge during the...