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A robust dual source level set method for three-dimensional echocardiography image segmentation
, Article Journal of Theoretical and Applied Information Technology ; Volume 95, Issue 21 , 2017 , Pages 5701-5710 ; 19928645 (ISSN) ; Fatemizadeh, E ; Behnam, H ; Sharif University of Technology
Abstract
Echocardiography as a common place device has been widely used for diagnosis. Segmentation of left ventricle just using the standard level set formulation based on the magnitude of intensity cannot restrict the contour evolution completely due to the lack of sharp edges. This paper aims to introduce a robust method for segmentation of three-dimensional echocardiography images based on two boundary maps namely distance map and probabilistic map as stopping criteria of contour evolution which are extracted using two different approaches. The distance map is extracted by applying Free Form Deformation (FFD) method on manually determined landmarks of initial spherical volume to register the...
Stress-constrained topology optimization: A topological level-set approach
, Article Structural and Multidisciplinary Optimization ; Volume 48, Issue 2 , August , 2013 , Pages 295-309 ; 1615147X (ISSN) ; Takalloozadeh, M ; Sharif University of Technology
2013
Abstract
The objective of this paper is to introduce and demonstrate an algorithm for stress-constrained topology optimization. The algorithm relies on tracking a level-set defined via the topological derivative. The primary advantages of the proposed method are: (1) the stresses are well-defined at all points within the evolving topology, (2) the finite-element stiffness matrices are well-conditioned, making the analysis robust and efficient, (3) the level-set is tracked through a simple iterative process, and (4) the stress constraint is precisely satisfied at termination. The proposed algorithm is illustrated through numerical experiments in 2D and 3D
Level Set Methods
, M.Sc. Thesis Sharif University of Technology ; 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
Upwind compact implicit and explicit high-order finite difference schemes for level set technique
, Article International Journal of Computational Methods in Engineering Science and Mechanics ; Volume 13, Issue 4 , 2012 , Pages 308-318 ; 15502287 (ISSN) ; Kebriaee, A ; Sharif University of Technology
2012
Abstract
This paper investigates implementation of upwind compact implicit and explicit high-order finite difference schemes for solution of the level set equation. The upwind compact implicit and explicit high-order finite difference schemes are well-known techniques to descritize spatial derivatives for convection term in hyperbolic equations. Applying of upwind high-order schemes on the level set equation leads to less error and CPU time reduction compared to essential non-oscillatory (ENO), weighted essential non-oscillatory schemes (WENO), and even different particle level set methods. The results indicate the error based on area loss decreases drastically with applying high-order upwind,...
Maximal safe set computation for pressure swing adsorption processes
, Article Computers and Chemical Engineering ; Volume 109 , 2018 , Pages 179-190 ; 00981354 (ISSN) ; 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,...
Modeling the R-curve effects in laminate composites using the interface thick level set method
, Article Theoretical and Applied Fracture Mechanics ; Volume 108 , August , 2020 ; Kouchakzadeh, M. A ; Sharif University of Technology
Elsevier B. V
2020
Abstract
This paper presents a new model for simulating delamination growth in composites in presence of the resistance curve (R-curve) effects. This model is extended from the interface thick level set (ITLS) method which is developed recently. In this approach the common definition of damage in the constitutive relationship of the interface elements is replaced with a new damage definition based on the thick level set (TLS) method. This new damage definition provides a direct link between fracture and damage mechanics that allows use of interface elements without a predefined cohesive law. In this paper the ITLS method is adopted to incorporate the R-curve effects caused by extended bridging, in...
Electromagnetic Wave Propagation Analysis Using Level Set Method
, M.Sc. Thesis Sharif University of Technology ; 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
;
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...
A hybrid segmentation framework for computer-assisted dental procedures
, Article IEICE Transactions on Information and Systems ; Volume E92-D, Issue 10 , 2009 , Pages 2137-2151 ; 09168532 (ISSN) ; Aghaeizadeh Zoroofi, R ; Abbaspour Tehrani Fard, A ; Shirani, G ; Asharif, M. R ; Sharif University of Technology
Abstract
Teeth segmentation in computed tomography (CT) images is a major and challenging task for various computer assisted procedures. In this paper, we introduced a hybrid method for quantification of teeth in CT volumetric dataset inspired by our previous experiences and anatomical knowledge of teeth and jaws. In this regard, we propose a novel segmentation technique using an adaptive thresholding, morphological operations, panoramic re-sampling and variational level set algorithm. The proposed method consists of several steps as follows: first, we determine the operation region in CT slices. Second, the bony tissues are separated from other tissues by utilizing an adaptive thresholding technique...
Counting cells of order-k voronoi tessellations in ℝ3 with morse theory
, Article 37th International Symposium on Computational Geometry, SoCG 2021, 7 June 2021 through 11 June 2021 ; Volume 189 , 2021 ; 18688969 (ISSN) ; 9783959771849 (ISBN) ; di Montesano, S. C ; Edelsbrunner, H ; Saghafian, M ; Sharif University of Technology
Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing
2021
Abstract
Generalizing Lee's inductive argument for counting the cells of higher order Voronoi tessellations in ℝ2 to ℝ3, we get precise relations in terms of Morse theoretic quantities for piecewise constant functions on planar arrangements. Specifically, we prove that for a generic set of n ≥ 5 points in ℝ3, the number of regions in the order-k Voronoi tessellation is Nk−1 − (k/2)n + n, for 1 ≤ k ≤ n − 1, in which Nk−1 is the sum of Euler characteristics of these function's first k − 1 sublevel sets. We get similar expressions for the vertices, edges, and polygons of the order-k Voronoi tessellation. © Ranita Biswas, Sebastiano Cultrera di Montesano, Herbert Edelsbrunner, and Morteza Saghafian;...
Joint estimation of facies boundaries and petrophysical properties in multi-facies channelized reservoirs through ensemble-based Kalman filter and level set parametrization
, Article Journal of Petroleum Science and Engineering ; Volume 167 , 2018 , Pages 752-773 ; 09204105 (ISSN) ; Pishvaie, M. R ; Boozarjomehry, R. B ; Sharif University of Technology
Elsevier B.V
2018
Abstract
Ensemble-based assimilation methods are the most promising tools for dynamic characterization of reservoir models. However, because of inherent assumption of Gaussianity, these methods are not directly applicable to channelized reservoirs wherein the distribution of petrophysical properties is multimodal. Transformation of facies field to level set functions have been proposed to alleviate the problem of multimodality. Level set representation ensures that the estimated fields are facies realizations as well as no modification of the assimilation method is required. Moreover, due to the complexity of the history matching problem in the channelized reservoirs, most researchers conventionally...
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) ; 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
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 ; 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...
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 ; 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...
Determination of the Degree of Occlusion of Coronary Arteries by Processing Angiography Images
, M.Sc. Thesis Sharif University of Technology ; Zahedi, Edmond (Supervisor) ; Fatemizade, Emadeddin (Supervisor)
Abstract
Cardiovascular disease is considered as the most important cause of death in the world. The coronary vessels, with three main arteries, has quite important. Coronary angiography is still the most common modality for physicians to assess the severity of vessel narrowing or stenosis during percutaneous coronary intervention procedure. For this procedure, a thin, flexible tube called a catheter is put into a blood vessel in your arm, groin (upper thigh), or neck. The tube is threaded into your coronary arteries, and the dye is released into your bloodstream. X-ray pictures are taken while the dye is flowing through the coronary arteries. Physicians evaluate angiographic images visually with...
The Numerical Simulation of Droplet Generation and its Control Using Electrowetting Method in Microfluidic Devices
, M.Sc. Thesis Sharif University of Technology ; 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...
Displacement and stress constrained topology optimization
, Article Proceedings of the ASME Design Engineering Technical Conference, Portland, OR ; Volume 2 A , August , 2013 ; 9780791855850 (ISBN) ; Suresh, K ; Sharif University of Technology
American Society of Mechanical Engineers
2013
Abstract
The objective of this paper is to demonstrate a topology optimization method subject to displacement and stress constraints. The method does not rely on pseudo-densities; instead it exploits the concept of topological level-set where 'partial' elements are avoided. Consequently: (1) the stresses are well-defined at all points within the evolving topology, and (2) the finite-element analysis is robust and efficient. Further, in the proposed method, a series of topologies of decreasing volume fractions are generated in a single optimization run. The method is illustrated through numerical experiments in 2D
A sampling theorem for convex shapes with algebraic boundaries
, Article 2017 12th International Conference on Sampling Theory and Applications, SampTA 2017, 3 July 2017 through 7 July 2017 ; 2017 , Pages 499-503 ; 9781538615652 (ISBN) ; Amini, A ; Sharif University of Technology
Abstract
In this paper we present a sampling result about continuous-domain black and white images that form a convex shape. In particular, we will study shapes whose boundaries belong to the zero-level sets (roots) of bivariate polynomials. In [1] it was shown that generalized 2D moments of the image can lead to annihilation equations for the coefficients of the bivariate polynomial that determine the boundary of the shape. More precisely, when the bivariate polynomial is of degree n (which has n(n+3)/2 non-trivial coefficients), the results in [1] indicate that for invertibility of the linear annihilation equations, 2D moments of up to degree 3n-1 (overall equation moments) are required. In this...
An X-FEM implementation of hydro-fracture growth in naturally fractured saturated porous media
, Article Poromechanics 2017 - Proceedings of the 6th Biot Conference on Poromechanics, 9 July 2017 through 13 July 2017 ; 2017 , Pages 2027-2034 ; 9780784480779 (ISBN) ; Khoei, A. R ; Khalili, N ; Sharif University of Technology
Abstract
In this paper, a coupled hydro-mechanical formulation is developed for the simulation of interaction between hydraulic fractures and natural discontinuities within saturated porous media. The momentum balance equation of the bulk together with the momentum balance and continuity equations of the fluid phase are employed to obtain the fully coupled set of governing equations. The hydro-fracture is modeled for fluid flow using the Darcy law. The natural discontinuity on the other hand is modeled for both opening and closing modes which induce fluid flow and/or contact behavior along the crack edges. The discontinuity in the displacement field is incorporated by using the Heaviside enrichment...
Scaling of clusters and winding-angle statistics of isoheight lines in two-dimensional Kardar-Parisi-Zhang surfaces
, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 79, Issue 3 , 2009 ; 15393755 (ISSN) ; Rouhani, S ; Sharif University of Technology
2009
Abstract
We investigate the statistics of isoheight lines of (2+1) -dimensional Kardar-Parisi-Zhang model at different level sets around the mean height in the saturation regime. We find that the exponent describing the distribution of the height-cluster size behaves differently for level cuts above and below the mean height, while the fractal dimensions of the height-clusters and their perimeters remain unchanged. The statistics of the winding angle confirms the previous observation that these contour lines are in the same universality class as self-avoiding random walks. © 2009 The American Physical Society