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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,...
On spatial filtering of flow variables in high-order finite volume methods
, Article Computers and Fluids ; Volume 132 , 2016 , Pages 19-31 ; 00457930 (ISSN) ; Farshchi, M ; Hejranfar, K ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
A new method of spatial filtering in high-order finite volume methods is presented and assessed. The base of this method is to filter face-averaged variables (fluxes) and then the recovery of cell-averaged ones. Two kinds of filtering method are proposed. The first kind is highly dissipative and appropriate for the numerical regions that need high dissipation, e.g. sponge zones. The second kind, on the other hand, is a precise method and hence is suitable for applying the high-order finite difference filters to the finite volume methods. Applying high-order finite difference filters directly to the high-order finite volume methods without using the proposed method causes stability problems...
Preconditioned characteristic boundary conditions based on artificial compressibility method for solution of incompressible flows
, Article Journal of Computational Physics ; Volume 345 , 2017 , Pages 543-564 ; 00219991 (ISSN) ; Parseh, K ; Sharif University of Technology
Abstract
The preconditioned characteristic boundary conditions based on the artificial compressibility (AC) method are implemented at artificial boundaries for the solution of two- and three-dimensional incompressible viscous flows in the generalized curvilinear coordinates. The compatibility equations and the corresponding characteristic variables (or the Riemann invariants) are mathematically derived and then applied as suitable boundary conditions in a high-order accurate incompressible flow solver. The spatial discretization of the resulting system of equations is carried out by the fourth-order compact finite-difference (FD) scheme. In the preconditioning applied here, the value of AC parameter...
The control of electron quantum trajectories on the high-order harmonic generation of CO and N2 molecules in the presence of a low frequency field
, Article Journal of Chemical Physics ; Volume 148, Issue 14 , 2018 ; 00219606 (ISSN) ; Sadighi Bonabi, R ; Mohsen Nia, M ; Irani, E ; Sharif University of Technology
American Institute of Physics Inc
2018
Abstract
In the present work, an efficient method is theoretically investigated for extending high-order harmonics and ultrashort attosecond pulse generation in N2 and CO molecules by using the time-dependent density functional theory approach. Our results show that by utilizing chirped laser field in the presence of a low frequency field, not only is the harmonic cutoff extended remarkably but also the single short quantum trajectory is selected to contribute to the harmonic spectra. When a low frequency field is added to the two-color chirped laser field, the long quantum trajectories are suppressed and only the short quantum trajectories contribute to the higher harmonic emission mechanism. As a...
Numerical study of shock-disturbances interaction in hypersonic inviscid flows with real gas effects using high-order WENO scheme
, Article Computers and Fluids ; Volume 229 , 2021 ; 00457930 (ISSN) ; Hejranfar, K ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
In the present study, the shock-disturbances interaction in hypersonic inviscid flows with real gas effects is studied by applying a high-order accurate numerical method with the shock capturing technique. To consider real gas effects, the equilibrium air model is utilized here. The strong conservative form of the unsteady compressible Euler equations in the 2D generalized curvilinear coordinates is formulated and the resulting system of equations for the equilibrium air model is discretized by using the fifth-order finite-difference WENO scheme in space and the explicit third-order TVD Runge–Kutta scheme in time to provide a highly accurate and robust equilibrium airflow solver. The...
Low-order adaptive half-sample interpolators
, Article Electronics Letters ; Volume 46, Issue 13 , June , 2010 , Pages 897-898 ; 00135194 (ISSN) ; Sharif University of Technology
2010
Abstract
Although the fractional delay filtering literature is full of design methods and implementation techniques for fractional sample interpolators, a fundamental need for the proposition of low-order efficient designs still strongly exists. Proposed is such a system for half-sample interpolation. In contrast to the typical systems studied in the literature for fractional delay filtering, the system proposed continuously adapts its interpolation kernel to the statistical variations of the input signal, and this is in fact the reason for it being needless of having a high order. Satisfactory performance of the proposed structure has been demonstrated via simulation
Free Vibration of Composite Conical Sandwich Panel with a Flexible Core
, M.Sc. Thesis Sharif University of Technology ; Kouchakzadeh, Mohammad Ali (Supervisor)
Abstract
In this thesis, free vibration of composite conical sandwich panel with a flexible is presented. Simply supported boundary condition are applied on the face’s edge only. Hamilton principle and energy method are used to derive equilibrium equations. In the mathematical formulation higher-order sandwich panel theory (HSAPT) was used. First shear deformation theory (FSDT) is used for faces.
Core displacement in various directions is modeled by polynomial function with indeterminate coefficient. It is assumed that the core is able to sustain shear and in-plane stresses. Temprature and humidity effects are neglected. Equations solved using generalized differential quadrature (GDQ) method....
Core displacement in various directions is modeled by polynomial function with indeterminate coefficient. It is assumed that the core is able to sustain shear and in-plane stresses. Temprature and humidity effects are neglected. Equations solved using generalized differential quadrature (GDQ) method....
Vibration and Buckling Analysis of Thick FGM Conical Shells Under Variable Thermal and Pressure Distributions, Considering Initial Geometric Imperfections Using a Higher Order TheoryVibration and Buckling Analysis of Thick FGM Conical Shells Under Variable Thermal and Pressure Distributions, Considering Initial Geometric Imperfections Using a Higher Order Theory
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firoozabadi, Rouhollah (Supervisor)
Abstract
The current study is dedicated to free vibration and buckling analysis of thick FGM conical shells conveying hot flows with the consideration of initial geometric imperfections. To this end, the higher order governing equations of motion and the corresponding boundary conditions are derived using Hamiltonian formulations. Due to the solution procedure of Frobenius series expansion, the differential form of equations is obtained by applying by part integration to the integral form of equations of motion. Radial and longitudinal temperature distributions are considered while pressure distribution and geometric imperfection variations are found to be in longitudinal direction, only. The final...
A Study on Constrained Dynamical Systems Using Fundamental Equations of Analytical Dynamics
, M.Sc. Thesis Sharif University of Technology ; Zohoor, Hassan (Supervisor) ; Sohrabpour, Saeed (Supervisor)
Abstract
Nonholonomic constraints are a vast portion of constraints that happen in variety of dynamics applications such as robotics and control. In this project we present a new form of D’Alembert’s principle and employ it to generalize classical methods of Analytical Dynamics. It results in a new formulations which can be implemented to solve constrained dynamical systems either holonomic or nonholonomic. These formulations do not have any restrictions on the order of the nonholonomic constraints and can analyze high order nonholonomic constraints (HONCs) as well as first order constraints. In addition using these formulation one can find equations of motion of nonholonomic systems without...
Opposing trends of geometrical parameters in maximisation of micro-ring resonator quality factor
, Article Electronics Letters ; Volume 47, Issue 25 , 2011 , Pages 1388-1390 ; 00135194 (ISSN) ; Rezaei, M ; Mehrany, K ; Sharif University of Technology
Abstract
Opposing trends of geometrical parameters in minimisation of bending loss and thus in maximising the quality factor are briefly discussed for micro-ring resonators. It is shown that, while the quality factor of low order modes is an oscillatory function of geometrical parameters, the quality factor of high order modes is a monotonic function. The former has discrete pairs of optimum inner and outer ring radii which maximises the quality factor. In contrast, the quality factor of the latter has no local maximum. Introduction of slight inhomogeneities does not change the overall behaviour of the quality factor but can increase its overall level when the refractive index of the ring region...
A preconditioned euler flow solver for simulation of helicopter rotor flow in hover
, Article Computational Fluid Dynamics 2010 - Proceedings of the 6th International Conference on Computational Fluid Dynamics, ICCFD 2010 ; 2011 , Pages 479-484 ; 9783642178832 (ISBN) ; Moghadam, R. K ; National Aeronautics and Space Administration; European Office for Aerospace Research and Development ; Sharif University of Technology
Abstract
In the present study, a preconditioned Euler flow solver is developed to accurately and efficiently compute the inviscid flowfield around hovering helicopter rotor. The preconditioning method proposed by Eriksson is applied. The three-dimensional preconditioned Euler equations written in a rotating coordinate frame are solved by using a cell-centered finite volume Roe's method on unstructured meshes. High-order accuracy is achieved via the reconstruction of flow variables using the MUSCL interpolation technique. Calculations are carried out for an isolated rotor in hover for different conditions and the computed surface pressure distributions are compared with the experimental data. The...
High-order harmonic generation of CO and N2 molecules under linearly- and bi circularly-polarized laser pulses by TD-DFT
, Article Laser Physics ; Volume 28, Issue 7 , 2018 ; 1054660X (ISSN) ; Sadighi Bonabi, R ; Mohsen Nia, M ; Irani, E ; Sharif University of Technology
Institute of Physics Publishing
2018
Abstract
We present a method for high-order harmonics generation of N2 and CO molecules under two-color circularly polarized counter-rotating laser pulses at frequencies of and 2. Pulse envelope in this investigation is sin-squared and the intensity of each laser beam is with ten-optical cycle (o.c.). We show that an isolated pulse with a pulse duration shorter than 20 attosecond from the superposition of several harmonics can be generated. Both two-color linearly- and bicircularly-polarized laser pulses are considered. Our results have also been compared with the outcomes of the previous theoretical works as well as experiment observations. It is found that for CO molecule, the...
Simulation of multi-component multi-phase fluid flow in two-dimensional anisotropic heterogeneous porous media using high-order control volume distributed methods
, Article Computers and Mathematics with Applications ; Volume 78, Issue 10 , 2019 , Pages 3303-3328 ; 08981221 (ISSN) ; Taghizadeh Manzari, M ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
In this paper, flow of multi-component two-phase fluids in highly heterogeneous anisotropic two-dimensional porous media is studied using computational methods suitable for unstructured triangular and/or quadrilateral grids. The physical model accounts for miscibility and compressibility of fluids while gravity and capillary effects are neglected. The governing equations consist of a pressure equation together with a system of mass conservation equations. For solving pressure equation, a new method called Control Volume Distributed Finite Element Method (CVDFEM) is introduced which uses Control Volume Distributed (CVD) vertex-centered grids. It is shown that the proposed method is able to...
Application of a preconditioned high-order accurate artificial compressibility-based incompressible flow solver in wide range of Reynolds numbers
, Article International Journal for Numerical Methods in Fluids ; Volume 86, Issue 1 , 2018 , Pages 46-77 ; 02712091 (ISSN) ; Parseh, K ; Sharif University of Technology
John Wiley and Sons Ltd
2018
Abstract
In the present study, the preconditioned incompressible Navier-Stokes equations with the artificial compressibility method formulated in the generalized curvilinear coordinates are numerically solved by using a high-order compact finite-difference scheme for accurately and efficiently computing the incompressible flows in a wide range of Reynolds numbers. A fourth-order compact finite-difference scheme is utilized to accurately discretize the spatial derivative terms of the governing equations, and the time integration is carried out based on the dual time-stepping method. The capability of the proposed solution methodology for the computations of the steady and unsteady incompressible...
Mathematical modeling of anisotropic hyperelastic cylindrical thick shells by incorporating thickness deformation and compressibility with application to arterial walls
, Article International Journal of Structural Stability and Dynamics ; Volume 22, Issue 13 , 2022 ; 02194554 (ISSN) ; Asghari, M ; Sharif University of Technology
World Scientific
2022
Abstract
This paper is devoted to mathematical modeling of anisotropic hyperelastic thick cylindrical shells like arteries by taking into account the volume compressibility and through-the-thickness deformation. To describe the hyperelastic behavior of this kind of shells and extract their constitutive relations, the modified anisotropic (MA) model is employed, which is able to characterize compressible behavior of hyperelastic materials like soft tissues. By considering the arterial segment as a thick cylindrical shell, the higher order thickness deformation shell theory together with nonlinear Green's strains are exploited to express its deformations and capture the thickness stretching effect. The...
Dynamic simulation of the ultra-fast-rotating sandwich cantilever disk via finite element and semi-numerical methods
, Article Engineering with Computers ; Volume 38 , 2022 , Pages 4127-4143 ; 01770667 (ISSN) ; Habibi, M ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2022
Abstract
In the presented research, vibrational, and amplitude behaviors of a sandwich spinning disk made of two laminated layers and graphene nanoplatelets reinforced composite (GPLRC) core has been reported. The Coriolis and centrifugal impacts have been taken into account due to its rotational feature. The stresses and strains have been obtained through the high-order shear deformable theory (HSDT). The structure’s boundary conditions (BCs) are determined using laminated rotating disk’s governing equations employing energy methods and ultimately have been solved via a computational approach called generalized differential quadrature method (GDQM). The rotational disk’s vibrations with different...
Higher-Order quantified boolean satisfiability
, Article 47th International Symposium on Mathematical Foundations of Computer Science, MFCS 2022, 22 August 2022 through 26 August 2022 ; Volume 241 , 2022 ; 18688969 (ISSN); 9783959772563 (ISBN) ; Haase, C ; Hadizadeh, Z ; Mansutti, A ; Sharif University of Technology
Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing
2022
Abstract
The Boolean satisfiability problem plays a central role in computational complexity and is often used as a starting point for showing NP lower bounds. Generalisations such as Succinct SAT, where a Boolean formula is succinctly represented as a Boolean circuit, have been studied in the literature in order to lift the Boolean satisfiability problem to higher complexity classes such as NEXP. While, in theory, iterating this approach yields complete problems for k-NEXP for all k > 0, using such iterations of Succinct SAT is at best tedious when it comes to proving lower bounds. The main contribution of this paper is to show that the Boolean satisfiability problem has another canonical...
High Order Approximate Linearization to Control Glucose Levelin Patients with Type I Diabetes
, M.Sc. Thesis Sharif University of Technology ; Bozorgmehri Boozarjomehry, Ramin (Supervisor)
Abstract
Three different feedback linearization control methods are applied to nonlinear control of type I diabetes mellitus model. One is exact FBL and the two others are approximate manners based on approximations of the nonlinear system and its duality one-form, utilizing uniform approximation and a homotopy operator, respectively. An extended luenberger observer is also employed to observe the required states of designed compensators. The nonlinear compensators are designed based on a minimal model and applied to the minimal model, as well as Sorensen’s physiological model. In addition to the mentioned close-loop control strategies, a discrete control strategy based on an optimization problem is...
Damage Map for a Light-Weight Sandwich Beam under Low Velocity Impact Loading
, M.Sc. Thesis Sharif University of Technology ; Kouchakzadeh, Mohammad Ali (Supervisor)
Abstract
The main purpose of this study is the analysis of low velocity impact on the light weight sandwich beams. Some parameters such as weight, failure mode, and impact energy absorption capability are very essential in the design of sandwich beams. The failure mode map is a technique to design sandwich structures, in which no single component is over-designed with respect to other components. In this study, the failure mode map of foam core sandwich beams composed of E-glass/Epoxy and PVC foam is drawn and investigated by an analytical method. For this purpose, displacement relations for bending of a sandwich beam are written using higher order theory. In addition, the sandwich beam is modeled...
Neutron Noise Calculation Using High order Nodal Expansion Method
, M.Sc. Thesis Sharif University of Technology ; Vosoughi, Naser (Supervisor)
Abstract
This study consists of two parts: steady state calculations and neutron noise calculations in the frequency domain for two rectangular and hexagonal geometries. In the steady state calculation, the neutron diffusion and its adjoint equations are approximated by two-dimensional coordinates in two-group energy and are solved using the average current nodal expansion method. Then, by considering the node size in the dimensions of a fuel assembly, different orders of flux expansion are investigated. For verification purposes, the calculations have been performed by power iteration method for two test problems of BIBLIS-2D and IAEA-2D. For rectangular geometry with increasing flux expansion order...