Loading...
Search for:
adjoints
0.007 seconds
Total 44 records
Global solution to non-self-adjoint stochastic Volterra equation
, Article Stochastics and Dynamics ; 2022 ; 02194937 (ISSN) ; Zangeneh, B. Z ; Jahanipur, R ; Sharif University of Technology
World Scientific
2022
Abstract
In this paper, we establish the existence and uniqueness of the mild solution for stochastic Volterra equation with a non-self-adjoint operator. The specific Volterra equation that we consider is a generalization of the fractional differential equation. To obtain the mild solution for the case of multiplicative problem, the resolvent property of the linear perturbation of a sectorial operator will be considered. © 2023 World Scientific Publishing Company
Neutron noise simulator based on the boundary element method (BEM)
, Article Annals of Nuclear Energy ; Volume 159 , 2021 ; 03064549 (ISSN) ; Mohamadbeygi, S ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
The purpose of the present study is to develop the neutron diffusion solver and neutron noise simulator based on the Boundary Element Method (BEM). The 2-D, 2-G neutron/adjoint diffusion equation and corresponding neutron/adjoint noise equation were solved using the mentioned method. The developed neutron static and noise simulator based on the finite element method gives accurate results when the more number of the elements is used. The motivation of the present research is to use the boundary element method to reduce the computational cost. The boundary element method attempts to use the given boundary conditions to fit boundary values into the integral equation, rather than values...
Thermal optimization of the continuous casting process using distributed parameter identification approach—controlling the curvature of solid-liquid interface
, Article International Journal of Advanced Manufacturing Technology ; Volume 94, Issue 1-4 , 2018 , Pages 1101-1118 ; 02683768 (ISSN) ; Sharif University of Technology
Springer London
2018
Abstract
Thermal optimization of the vertical continuous casting process is considered in the present study. The goal is to find the optimal distribution of the temperature and interfacial heat transfer coefficients corresponding to the primary and secondary cooling systems, in addition to the pulling speed, such that the solidification along the main axis of strand approaches to the unidirectional solidification mode. Unlike many thermal optimization of phase change problems in which the desirable (target) temperature, temperature gradient, or interface position are assumed to be a priori known, a desirable shape feature of the freezing interface (not its explicit position) is assumed to be known in...
Performance improvement of a supercritical airfoil by a multi-point optimized shock control channel
, Article Flow, Turbulence and Combustion ; Volume 100, Issue 3 , 2018 , Pages 675-703 ; 13866184 (ISSN) ; Mazaheri, K ; Sharif University of Technology
Springer Netherlands
2018
Abstract
A shock control channel (SCC) is a flow control method introduced here to control the shock wave/boundarylayer interaction (SWBLI) in order to reduce the resulting wave drag in transonic flows. An SCC transfers an appropriate amount of mass and momentum from downstream of the shock wave location to its upstream to decrease the pressure gradient across the shock wave and as a result the shock-wave strength is reduced. Here, a multi-point optimization method under a constant-lift-coefficient constraint is used to find the optimum design of the SCC. This flow control method is implemented on a RAE-2822 supercritical airfoil for a wide range of off-design transonic Mach numbers. The RANS flow...
Neutron noise simulation using ACNEM in the hexagonal geometry
, Article Annals of Nuclear Energy ; Volume 113 , 2018 , Pages 246-255 ; 03064549 (ISSN) ; Vosoughi, N ; Vosoughi, J ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
In the present study, the development of a neutron noise simulator, DYN-ACNEM, using the Average Current Nodal Expansion Method (ACNEM) in 2-G, 2-D hexagonal geometries is reported. In first stage, the static neutron calculation is performed. The neutron/adjoint flux distribution and corresponding eigen-values are calculated using the algorithm developed based on power iteration method by considering the coarse meshes. The results of the static calculation are validated against the well-known IAEA-2D benchmark problem. In the second stage, the dynamic calculation is performed in the frequency domain in which the dimension of the variable space of the noise equations is lower than the time...
The application of suction and blowing in performance improvement of transonic airfoils with shock control bump
, Article Scientia Iranica ; Volume 24, Issue 1 , 2017 , Pages 274-292 ; 10263098 (ISSN) ; Nejati, A ; Charlang Kiani, K. C ; Sharif University of Technology
Sharif University of Technology
2017
Abstract
Shock Control Bump (SCB) reduces the wave drag in transonic ight. To control the boundary layer separation and to reduce the wave drag for two transonic airfoils, RAE-2822 and NACA-64A010, we investigate the application of two flow control methods, i.e. suction and blowing, to add them to the SCB. An adjoint gradient-based optimization algorithm is used to find the optimum shape and location of SCB. The performance of both Hybrid Suction/SCB (HSS) and Hybrid Blowing/SCB (HBS) is a function of the sucked or injected mass flow rate and their position. A parametric study is performed to find the near optimum values of the aerodynamic coefficients and efficiency. A RANS solver is validated and...
On cylindrical graph construction and its applications
, Article Electronic Journal of Combinatorics ; Volume 23, Issue 1 , 2016 ; 10778926 (ISSN) ; Hejrati, M ; Madani, M ; Sharif University of Technology
Australian National University
2016
Abstract
In this article we introduce the cylindrical construction, as an edge-replacement procedure admitting twists on both ends of the hyperedges, generalizing the concepts of lifts and Pultr templates at the same time. We prove a tensor-hom duality for this construction and we show that not only a large number of well-known graph constructions are cylindrical but also the construction and its dual give rise to some new graph constructions, applications and results. To show the applicability of the main duality we introduce generalized Grötzsch, generalized Petersen-like and Coxeter-like graphs and we prove some coloring properties of these graphs
A coupled adjoint formulation for non-cooled and internally cooled turbine blade optimization
, Article Applied Thermal Engineering ; Volume 105 , 2016 , Pages 327-335 ; 13594311 (ISSN) ; Mazaheri, K ; Chaharlang Kiani, K ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
Most researches on the application of the adjoint method in turbine blade design are concentrated on the aerodynamic shape optimization without considering the heat transfer to/from the blade material. In this study, the adjoint method is extended to the conjugate heat transfer problems in which the viscous flow field is coupled to heat transfer in the solid region. Introducing a new adjoint variable in the solid domain, a heat adjoint equation is derived which is coupled with the energy adjoint equation in the fluid zone at the fluid/solid interface. The detailed mathematical description associated with the derivation of the heat adjoint equation with corresponding boundary conditions are...
Enhanced finite difference scheme for the neutron diffusion equation using the importance function
, Article Annals of Nuclear Energy ; Volume 96 , 2016 , Pages 412-421 ; 03064549 (ISSN) ; Vosoughi, N ; Gharib, M ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
Mesh point positions in Finite Difference Method (FDM) of discretization for the neutron diffusion equation can remarkably affect the averaged neutron fluxes as well as the effective multiplication factor. In this study, by aid of improving the mesh point positions, an enhanced finite difference scheme for the neutron diffusion equation is proposed based on the neutron importance function. In order to determine the neutron importance function, the adjoint (backward) neutron diffusion calculations are performed in the same procedure as for the forward calculations. Considering the neutron importance function, the mesh points can be improved through the entire reactor core. Accordingly, in...
Optimal design of multiphase composites under elastodynamic loading
, Article Computer Methods in Applied Mechanics and Engineering ; Volume 300 , 2016 , Pages 265-293 ; 00457825 (ISSN) ; Sharif University of Technology
Elsevier
2016
Abstract
An algorithm is proposed to optimize the performance of multiphase structures (composites) under elastodynamic loading conditions. The goal is to determine the distribution of material in the structure such that the time-averaged total stored energy of structure is minimized. A penalization strategy is suggested to avoid the checkerboard instability, simultaneously to generate near 0-1 topologies. As a result of this strategy, the solutions of presented algorithm are sufficiently smooth and possess the regularity of H1 function space. A simple method for the continuum adjoint sensitivity analysis of the corresponding PDE-constrained optimization problem is presented. It is general and can be...
Optimization of neutron energy-group structure in thermal lattices using ultrafine bilinear adjoint function
, Article Progress in Nuclear Energy ; Volume 85 , 2015 , Pages 648-658 ; 01491970 (ISSN) ; Salehi, A. A ; Vosoughi, N ; Akbari, M ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
To solve neutron transport equation in multigroup approach, in addition to weighting function and number of energy groups, proper selection of the group boundaries have high importance for the accuracy of the calculations. In the current paper, the bilinear combination of forward and adjoint neutron spectra is used for the optimization of 69 energy group structure of WIMSD5 lattice physics code. To remedy the energy self-shielding effect, homogeneous adjoint and forward BN equations on an ultrafine energy group structure have been solved to obtain the ultrafine forward and adjoint spectra. The coarse group intervals are selected to have equal values of bilinear function in each...
The application of the gradient-based adjoint multi-point optimization of single and double shock control bumps for transonic airfoils
, Article Shock Waves ; 2015 ; 09381287 (ISSN) ; Nejati, A ; Chaharlang Kiani, K ; Taheri, R ; Sharif University of Technology
Springer New York LLC
2015
Abstract
A shock control bump (SCB) is a flow control method which uses local small deformations in a flexible wing surface to considerably reduce the strength of shock waves and the resulting wave drag in transonic flows. Most of the reported research is devoted to optimization in a single flow condition. Here, we have used a multi-point adjoint optimization scheme to optimize shape and location of the SCB. Practically, this introduces transonic airfoils equipped with the SCB which are simultaneously optimized for different off-design transonic flight conditions. Here, we use this optimization algorithm to enhance and optimize the performance of SCBs in two benchmark airfoils, i.e., RAE-2822 and...
Galerkin and Generalized Least Squares finite element: A comparative study for multi-group diffusion solvers
, Article Progress in Nuclear Energy ; Volume 85 , 2015 , Pages 473-490 ; 01491970 (ISSN) ; Saadatian Derakhshandeh, F ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
Abstract In this paper, the solution of multi-group neutron/adjoint equation using Finite Element Method (FEM) for hexagonal and rectangular reactor cores is reported. The spatial discretization of the neutron diffusion equation is performed based on two different Finite Element Methods (FEMs) using unstructured triangular elements generated by Gambit software. Calculations are performed using Galerkin and Generalized Least Squares FEMs; based on which results are compared. Using the power iteration method for the neutron and adjoint calculations, the neutron and adjoint flux distributions with the corresponding eigenvalues are obtained. The results are then validated against the valid...
Propagation noise calculations in VVER-type reactor core
, Article Progress in Nuclear Energy ; Volume 78 , January , 2015 , Pages 10-18 ; 01491970 (ISSN) ; Vosoughi, N ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
Neutron noise induced by propagating disturbances in VVER-type reactor core is addressed in this paper. The spatial discretization of the governing equations is based on the box-scheme finite difference method for triangular-z geometry. Using the derived equations, a 3-D 2-group neutron noise simulator (called TRIDYN-3) is developed for hexagonal-structured reactor core, by which the discrete form of both the forward and adjoint reactor dynamic transfer functions (in the frequency domain) can be calculated. In addition, both types of noise sources, namely point-like and traveling perturbations, can be modeled by TRIDYN-3. The results are then benchmarked in different cases. Considering the...
Development of two-dimensional, multigroup neutron diffusion computer code based on GFEM with unstructured triangle elements
, Article Annals of Nuclear Energy ; Volume 51 , 2013 , Pages 213-226 ; 03064549 (ISSN) ; Vosoughi, N ; Sharif University of Technology
2013
Abstract
Various methods for solving the forward/adjoint equation in hexagonal and rectangular geometries are known in the literatures. In this paper, the solution of multigroup forward/adjoint equation using Finite Element Method (FEM) for hexagonal and rectangular reactor cores is reported. The spatial discretization of equations is based on Galerkin FEM (GFEM) using unstructured triangle elements. Calculations are performed for both linear and quadratic approximations of the shape function; based on which results are compared. Using power iteration method for the forward and adjoint calculations, the forward and adjoint fluxes with the corresponding eigenvalues are obtained. The results are then...
Turbine blade aerodynamic optimization on unstructured grids using a continuous adjoint method
, Article ASME 2012 International Mechanical Engineering Congress and Exposition, IMECE 2012, Houston, TX, 9 November 2012 through 15 November 2012 ; Volume 1 , 2012 , Pages 425-431 ; 9780791845172 (ISBN) ; Mazaheri, K ; Irannejad, A ; Sharif University of Technology
2012
Abstract
A gradient based optimization using the continuous adjoint method for inverse design of a turbine blade cascade is presented. The advantage of the adjoint method is that the objective function gradients can be evaluated by solving the adjoint equations with coefficients depending on the flow variables. This method is particularly suitable for aerodynamic design optimization for which the number of design variables is large. Bezier polynomials are used to parameterize suction side of the turbine blade. The numerical convective fluxes of both flow and adjoint equations are computed by using a Roe-type approximate Riemann solver. An approximate linearization is applied to simplify the...
Neutron noise simulation by GFEM and unstructured triangle elements
, Article Nuclear Engineering and Design ; Volume 253 , 2012 , Pages 238-258 ; 00295493 (ISSN) ; Vosoughi, N ; Sharif University of Technology
2012
Abstract
In the present study, the neutron noise, i.e. The stationary fluctuation of the neutron flux around its mean value, is calculated in 2-group forward and adjoint diffusion theory for both hexagonal and rectangular reactor cores. To this end, the static neutron calculation is performed at the first stage. The spatial discretization of equations is based on linear approximation of Galerkin Finite Element Method (GFEM) using unstructured triangle elements. Using power iteration method, forward and adjoint fluxes with the corresponding eigenvalues are obtained. The results are then benchmarked against the valid results for BIBLIS-2D and IAEA-2D benchmark problems and DONJON computer code. The...
Optimization of the direct discrete method using the solution of the adjoint equation and its application in the multi-group neutron diffusion equation
, Article AIP Conference Proceedings ; Volume 1389 , 2011 , Pages 1777-1781 ; 0094243X (ISSN) ; 9780735409569 (ISBN) ; Vosoughi, N ; Sharif University of Technology
2011
Abstract
Obtaining the set of algebraic equations that directly correspond to a physical phenomenon has been viable in the recent direct discrete method (DDM). Although this method may find its roots in physical and geometrical considerations, there are still some degrees of freedom that one may suspect optimize-able. Here we have used the information embedded in the corresponding adjoint equation to form a local functional, which in turn by its minimization, yield suitable dual mesh positioning
Localization of a noise source in VVER-1000 reactor core using neutron noise analysis methods
, Article International Conference on Nuclear Engineering, Proceedings, ICONE, 17 May 2010 through 21 May 2010 ; Volume 2 , May , 2010 ; 9780791849309 (ISBN) ; Vosoughi, N ; Zahedinejad, E ; Nuclear Engineering Division ; Sharif University of Technology
2010
Abstract
In this paper, localization of a noise source from limited neutron detectors sparsely distributed throughout the core of a typical VVER-1000 reactor is investigated. For this purpose, developing a 2-D neutron noise simulator for hexagonal geometries based on the 2-group diffusion approximation, the reactor dynamic transfer function is calculated. The boxscheme finite difference method is first developed for hexagonal geometries, to be used for spatial discretisation of both 2-D 2-group static and noise diffusion equations. The dynamic state is assumed in the frequency domain which leads to discarding of the time disrcetisation. The developed 2-D 2- group neutron noise simulator calculates...
Aerodynamic shape optimization using a morphing-body optimization method
, Article 13th AIAA/ISSMO Multidisciplinary Analysis and Optimization Conference 2010, 13 September 2010 through 15 September 2010, Ft. Worth, TX ; 2010 ; 9781600869549 (ISBN) ; Mazaheri, K ; Sharif University of Technology
2010
Abstract
A morphing-body optimization method is introduced to accelerate adjoint-based shape optimization techniques. The optimization process solves the flow and adjoint equations around a continuously deforming body whose shape is controlled by the cost function. Effect of various parameters on the efficiency of the scheme is studied. It is found that, for the best performance of the algorithm, the morphing rate of the airfoil should be restricted, since larger rates foster oscillations and lower values are not computationally feasible. Moreover, the iterative procedure in the adjoint solver should be adapted to the iteration scheme in the flow solver and to the morphing rate