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    Maximal safe set computation for pressure swing adsorption processes

    , Article Computers and Chemical Engineering ; Volume 109 , 2018 , Pages 179-190 ; 00981354 (ISSN) Fakhroleslam, M ; Fatemi, S ; Bozorgmehry Boozarjomehry, R ; De Santis, E ; Di Benedetto, M. D ; Pola, G ; Sharif University of Technology
    Elsevier Ltd  2018
    Abstract
    In this paper we propose a method towards purity control of pressure swing adsorption (PSA) processes which is based on the use of hybrid systems formalism. Hybrid systems feature both continuous and discrete-event dynamics and hence are very suited to describe in detail PSA processes. Based on mechanistic model of the processes, a local reduced-order model (LROM) is developed for PSA processes. Then the processes are represented as hybrid systems whose continuous evolution is described by the LROM. We then perform an analysis of hybrid reachability properties of the hybrid system obtained, based on which the so-called maximal safe set is computed. The analysis is performed for a two-bed,... 

    Electromagnetic Wave Propagation Analysis Using Level Set Method

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Hadi (Author) ; Shishegar, Amir Ahmad (Supervisor)
    Abstract
    Always, there has been a great interest toward electromagnetic wave propagation and new ways for simulation of the problem. Level set methods provide a powerful mathematical framework for propagating surfaces (in 3-D) or curves (in 2-D). The contours of the moving objects are viewed as the zero level sets of a function and propagated in a Eulerian point of view by means of a Hamilton–Jacobi partial differential equation expressing the conservation of the level sets under a given velocity field. Level set methods have been applied in a wide range of domains, such as physics, chemistry, fluid dynamics, combustion, image processing… In this thesis, we introduce a new numerical procedure for... 

    Level-Set Techniques for Facies Identification in Reservoir
    Modeling

    , M.Sc. Thesis Sharif University of Technology Soltani, Narges (Author) ; Razvan, Mohammad Reza (Supervisor) ; Azari, Hossein (Supervisor)
    Abstract
    The success of oil recovery depends, among other factors, on the ability to provide reliable simulations of the reservoir performance. The reservoir dynamics are usually modeled by a distributed parameter dynamic system whose parameters represent the petrophysical properties of the reservoir. A proper characterization of those reservoir properties is fundamental for an accurate reservoir simulation. The petrophysical properties are highly heterogeneous and only a limited number of measurements are available at certain locations in the reservoir. Therefor, in ordet to obtain accurate prediction of the reservoir performance, it is essential to possess reliable estimates of the petrophysical... 

    2-D Bone Structure Prediction of Proximal Femur and Dominant Joint Load Estimation using Level Set Method and Bone RemodelingTheories

    , M.Sc. Thesis Sharif University of Technology Keivan Bahari, Mahsa (Author) ; Farahmand, Farzam (Supervisor) ; Movahhedy, Mohammad Reza (Supervisor) ; Rouhi, Gholamreza (Co-Advisor)
    Abstract
    Bones adapt their form and structure to make an efficient use of their mass against the applied mechanical loads. So, it is not surprising to assume that the geometry and density distribution of a bone contains information about its loading history. The objective of this work was to develop a framework to simulate the bone remodeling procedure as a topology optimization process and then use this framework to develop a simple technique for estimating the dominant joint loads based on the bone’s density distribution.
    At first, the remodeling equation was derived from the structural optimization task of minimizing the strain energy in each time step, using the level set method. Employment... 

    Level Set Approach for Capturing Interface Position of Annular Two-Phaseflow

    , M.Sc. Thesis Sharif University of Technology Taherkhani, Morteza (Author) ; Nouri-Borujerdi, Ali (Supervisor)
    Abstract
    Numerical simulation of air-water annular two-phase flow in a tube is carried out by using level set method for determining position of interface between two phases. Governing equations include continuity, momentum and level set equations that considered for each phase. The finite difference scheme is used to discretize the differential equations. The SIMPLE algorithm is adopted to solve the discretized equations for linking continuity and momentum equation. An unequally spaced staggered grid size for flow field is adopted. The Level Set method is used to capture interface position between two phases. To increase the accuracy of solution at level set equation, 5th order finite difference and... 

    Level Set Methods

    , M.Sc. Thesis Sharif University of Technology Tavallaee, Ali (Author) ; Fotouhi Firouzabad, Morteza (Supervisor)
    Abstract
    Level set methods (LSM) are a conceptual framework for using level sets as a tool for numerical analysis of surfaces and shapes. The advantage of the level set model is that one can perform numerical computations involving curves and surfaces on a fixed Cartesian grid without having to parameterize these objects (this is called the Eulerian approach). Also, the level set method makes it very easy to follow shapes that change topology, for example when a shape splits in two, develops holes, or the reverse of these operations. All these make the level set method a great tool for modeling time-varying objects, like inflation of an airbag, or a drop of oil floating in water  

    The Numerical Simulation of Droplet Generation and its Control Using Electrowetting Method in Microfluidic Devices

    , M.Sc. Thesis Sharif University of Technology Merdasi, Arshia (Author) ; Moosavi, Ali (Supervisor) ; Shafii, Mohammad Behshad (Supervisor)
    Abstract
    In this research, two important mechanisms were discussed including droplet generation and jumping mechanisms using electro wetting-on-dielectric. For these purposes, the finite element method (FEM) was used to solve the unsteady Naiver-Stokes equation. In addition, the level set method was applied to capture the interface between two phases. In the current study, first, droplet generation in a T-junction fluidic channel device was studied through using electro wetting actuation. The efficacy of electro wetting on the droplet generation frequency as well as droplet diameter is visible in a T-junction fluidic channel since after applying voltages, specified with non-dimensional electro... 

    A Lagrangian-extended finite-element method in modeling large-plasticity deformations and contact problems

    , Article International Journal of Mechanical Sciences ; Volume 51, Issue 5 , 2009 , Pages 384-401 ; 00207403 (ISSN) Khoei, A. R ; Biabanaki, S. O. R ; Anahid, M ; Sharif University of Technology
    2009
    Abstract
    In this paper, a Lagrangian-extended finite-element (FE) method is presented in modeling large-plasticity deformations and contact problems. The technique is used to model arbitrary interfaces in two-dimensional (2D)/three-dimensional (3D) large deformations. The material interfaces are represented independent of the FE mesh and the process is accomplished by integrating enriched elements with a larger number of Gauss points, whose positions are fixed in the element. The large elasto-plastic deformation formulation is employed within the eXtended Finite-Element Method (X-FEM) framework to simulate the nonlinear behavior of materials. The interface between two bodies is modeled by using the... 

    Electrowetting induced droplet generation in T-junctions

    , Article Journal of Heat Transfer ; Volume 143, Issue 5 , 2021 ; 00221481 (ISSN) Merdasi, A ; Moosavi, A ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2021
    Abstract
    In this study, droplet generation in a T-junction fluidic channel device was studied by using electrowetting actuation with the consideration of different droplet forming regimes. For this purpose, the finite element method (FEM) was used to solve the unsteady Naiver-Stokes equation. In addition, the level set method was applied to capture the interface between two phases. It was shown that there was a good agreement between obtained data and other work during the process of droplet generation in the absence of electrowetting actuation which results in the decrease in the size of the droplet with increasing the velocity ratios. In the shearing regime, the effectiveness of electrowetting on... 

    Molecular Diffusion in the Dynamics Brain Extracellular Space

    , Ph.D. Dissertation Sharif University of Technology Yousefnezhad, Mohsen (Author) ; Fotouhi, Morteza (Supervisor) ; Kamali Zare, Padideh (Co-Advisor) ; Vejdani, Kaveh (Co-Advisor)
    Abstract
    In the thesis , we present a universal model of brain tissue microstructure that dynamically links osmosis and diffusion with geometrical parameters of brain extracellular space (ECS) . In the first part , we investigate the biological aspects of the model , and in the second , we analysis the model in the mathematical framework . The first part : Our model robustly describes and predicts the nonlinear time dependency of tortuosity ($\lambda = \sqrt{D/{D^{*}}}$) changes with very high precision in various media with uniform and nonuniform osmolarity distribution , as demonstrated by previously published experimental data ($D$ = free diffusion coefficient , $D^{*}$ = effective... 

    Simulation of incompressible two-phase flows with large density differences employing lattice Boltzmann and level set methods

    , Article Computer Methods in Applied Mechanics and Engineering ; Volume 198, Issue 2 , December , 2008 , Pages 223-233 ; 00457825 (ISSN) Mehravaran, M ; Hannani, S. K ; Sharif University of Technology
    2008
    Abstract
    A hybrid lattice Boltzmann and level set method (LBLSM) for two-phase immiscible fluids with large density differences is proposed. The lattice Boltzmann method is used for calculating the velocities, the interface is captured by the level set function and the surface tension force is replaced by an equivalent force field. The method can be applied to simulate two-phase fluid flows with the density ratio up to 1000. In case of zero or known pressure gradient the method is completely explicit. In order to validate the method, several examples are solved and the results are in agreement with analytical or experimental results. © 2008 Elsevier B.V. All rights reserved  

    Arbitrary Discontinuities in Transient Dynamic Finite Element Modeling Using the Level Set and X-FEM Techniques

    , M.Sc. Thesis Sharif University of Technology Khaleghi, Maryam (Author) ; Khoei, Amir Reza (Supervisor) ; Mofid, Masoud (Supervisor)
    Abstract
    In computational mechanic, paying attention to new methods of problem solving is very important. These approaches can offer more desirable results than the standard finite element method. The extended finite element method (X-FEM) is one of them, which is applied in modeling of discontinuities, singularities, crack propagation and etc. In this method, we do not need to align the element edge with the boundary of discontinuity. It means that the elements can be cut by interface (enriched elements) in the discontinuity boundary. One of the difficulties in (X-FEM) is blending elements, which happens in elements that are blended to enriched element that can decrease the convergence rate. The... 

    Shape and Topology Optimization for Elliptic Boundery Value Problems using a Piecewise Constant Level Set Method

    , M.Sc. Thesis Sharif University of Technology hadadi, Alireza (Author) ; Fotouhi Firouzabad, Morteza (Supervisor)
    Abstract
    The aim of this thesis is describes the method a variational piecewise constant level set method for solving elliptic shape and topology optimization problems. The original model is approximated by a two-phase optimal shape design problem by the ersatz material approach. Under the piecewise constant level set framework, we first reformulate the two-phase design problem to be a new constrained optimization problem with respect to the piecewise constant level set function. Then we solve it by the projection Lagrangian method. A gradient-type iterative algorithm is presented. Comparisons between our numerical results and those obtained by level set approaches show the effectiveness, accuracy... 

    A polygonal finite element method for modeling arbitrary interfaces in large deformation problems

    , Article Computational Mechanics ; Volume 50, Issue 1 , 2012 , Pages 19-33 ; 01787675 (ISSN) Biabanaki, S. O. R ; Khoei, A. R ; Sharif University of Technology
    2012
    Abstract
    In this paper, a polygonal-FEM technique is presented in modeling of arbitrary interfaces in large deformations. The method is used to model the internal interfaces and arbitrary geometries using a uniform non-conformal mesh. The technique is applied to capture discontinuous deformations in the non-conformal elements, which are cut by the interface in a uniform regular mesh. In this approach, a uniform non-conformal mesh is decomposed into sub-elements that conform to the internal interfaces. The geometry of interface is used to produce various triangular, quadrilateral and pentagonal elements at the intersection of interface with regular FE mesh, in which the extra degrees-of-freedom are... 

    Integration of spatial fuzzy clustering with level set for segmentation of 2-D angiogram

    , Article IECBES 2014, Conference Proceedings - 2014 IEEE Conference on Biomedical Engineering and Sciences: "Miri, Where Engineering in Medicine and Biology and Humanity Meet", 8 December 2014 through 10 December 2014 ; December , 2015 , Pages 309-314 ; 9781479940844 (ISBN) Ghalehnovi, M ; Zahedi, E ; Fatemizadeh, E ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    Abstract
    Coronary angiography is a vital instrument to detect the prevailing of vascular diseases, and accurate vascular segmentation acts a crucial role for proper quantitative analysis of the vascular tree morphological features. Level set methods are popular for segmenting the coronary arteries, but their performance is related to suitable start-up and optimum setting of regulating parameters, essentially done manually. This research presents a novel fuzzy level set procedure with the objective of segmentation of the coronary artery tree in 2-D X-ray angiography as automatically. It is clever to clearly develop from the early segmentation with spatial fuzzy grouping. The adjusting parameters of... 

    A multiphysics model for analysis of droplet formation in electrohydrodynamic 3D printing process

    , Article Journal of Aerosol Science ; Volume 135 , 2019 , Pages 72-85 ; 00218502 (ISSN) Mohammadi, K ; Movahhedy, M. R ; Khodaygan, S ; Sharif University of Technology
    Elsevier Ltd  2019
    Abstract
    Electrohydrodynamic (EHD) printing is a novel technology used for fabricating high-resolution part features from a wide range of materials. Due to the multiphysics dynamics and the multiphase nature of the microdroplet formation in the EHD printers, modeling of this phenomenon is complicated. In this paper, the formation of a droplet in an EHD printer—under a pulsed electrical field—is simulated using a new numerical model which couples the fluid flow, the electric field distribution and the movement of the electric charges under dynamic and transient conditions. The level-set method is applied to the entire multiphysics domain in order to study the formation of the droplet. The presented... 

    Investigation of Flow Inside the Pressure Swirl Atomizer

    , Ph.D. Dissertation Sharif University of Technology Kebriaee, Azadeh (Author) ; Nouri Boroujerdi, Ali (Supervisor)
    Abstract
    In the present work, the behavior of flow inside the pressure-swirl atomizers (PSA) is studied by the numerical simulation. The pressure-swirl atomizer is widely used in many industrial applications such as fuel injection in gas turbine, internal combustion engine and liquid-fuel rocket, spray drying, spray in firing and agricultural nozzles.
    The flow simulation inside the injector (PSA) deals with many complicated considerations due to air core formation in the axial zone of the injector as well as high tangential and axial velocities in the swirl chamber. The two phase flow is modeled by level set methods in the pressure swirl atomizer. Moreover, the explicit algebraic Reynolds stress... 

    A generalized finite element method for modeling arbitrary interfaces in large deformation problems

    , Article Computational Plasticity XI - Fundamentals and Applications, COMPLAS XI, 7 September 2011 through 9 September 2011 ; September , 2011 , Pages 1306-1317 ; 9788489925731 (ISBN) Biabanaki, S. O. R ; Khoei, A. R ; Sharif University of Technology
    Abstract
    In this paper, a generalized-FEM technique is presented in modeling of arbitrary interfaces in large deformations. The method is used to model the internal interfaces and arbitrary geometries using a uniform non-conformal mesh. The technique is applied to capture independent deformations at both sides of separated element cut by the interface in a uniform regular mesh. In this approach, a uniform non-conformal mesh is decomposed into subelements that conform to the internal interfaces. The geometry of interface is used to produce various triangular, quadrilateral and pentagonal elements at the intersection of interface with regular FE mesh, in which the extra degrees-of-freedom are defined... 

    Simulation of buoyant bubble motion in viscous flows employing lattice Boltzmann and level set methods

    , Article Scientia Iranica ; Volume 18, Issue 2 B , 2011 , Pages 231-240 ; 10263098 (ISSN) Mehravaran, M ; Hannani, S. K ; Sharif University of Technology
    2011
    Abstract
    Recently, a hybrid Lattice Boltzmann Level Set Method (LBLSM) for two-phase incompressible fluids with large density differences, in cases of negligible or a priori known pressure gradients, has been proposed. In the present work, the mentioned LBLSM method is extended to take into account pressure gradient effects. The lattice Boltzmann method is used for calculating velocities, the interface is captured by the level set function, and the surface tension is replaced by an equivalent body force. The method can be applied to simulate two-phase fluid flows with density ratios up to 1000 and viscosity ratios up to 100. In order to validate the method, the evolution and merging of rising bubbles... 

    The level set modeling of droplet dynamic in fluid-fluid interaction

    , Article 39th AIAA Fluid Dynamics Conference, 22 June 2009 through 25 June 2009, San Antonio, TX ; 2009 ; 9781563479755 (ISBN) Darbandi, M ; Mazaheri, I ; Dehkordi, A. M ; Schneider, G. E ; Sharif University of Technology
    Abstract
    In this work, we present a level set method to simulate steady and unsteady mass transfer from a single droplet moving in a second phase fluid under buoyant force. We initially use level set to determine the interface between the two phases, where the shape of drop forms. Next, we extend this method to solve a unique mass transfer equation for the entire solution domain without considering the discontinuity appeared at the interface. We use a finite element method incorporated with the characteristic-based split (CBS) algorithm to implement axi-symmetric mass transfer equations on a stationary Eulerian grid. Of course, the convection-diffusion modeling of mass transfer is different from the...