Search for: adjoints
Total 42 records
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
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 B
N 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...
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
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
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
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
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
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...
Development of galerkin finite element method three-dimensional computational code for the multigroup neutron diffusion equation with unstructured tetrahedron elements, Article Nuclear Engineering and Technology ; Volume 48, Issue 1 , 2016 , Pages 43-54 ; 17385733 (ISSN) ; Sharif University of Technology
Korean Nuclear Society
In the present paper, development of the three-dimensional (3D) computational code based on Galerkin finite element method (GFEM) for solving the multigroup forward/adjoint diffusion equation in both rectangular and hexagonal geometries is reported. Linear approximation of shape functions in the GFEM with unstructured tetrahedron elements is used in the calculation. Both criticality and fixed source calculations may be performed using the developed GFEM-3D computational code. An acceptable level of accuracy at a low computational cost is the main advantage of applying the unstructured tetrahedron elements. The unstructured tetrahedron elements generated with Gambit software are used in the...
The application of the gradient-based adjoint multi-point optimization of single and double shock control bumps for transonic airfoils, Article Shock Waves ; Volume 26, Issue 4 , 2016 , Pages 491-511 ; 09381287 (ISSN) ; Nejati, A ; Chaharlang Kiani, K ; Taheri, R ; Sharif University of Technology
Springer New York LLC
A shock control bump (SCB) is a flow control method that 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 that 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...
Effective point kinetic parameters calculation in Tehran research reactor using deterministic and probabilistic methods, Article Nuclear Science and Techniques ; Volume 28, Issue 12 , 2017 ; 10018042 (ISSN) ; Abbaspour, A ; Sharif University of Technology
The exact calculation of point kinetic parameters is very important in nuclear reactor safety assessment, and most sophisticated safety codes such as RELAP5, PARCS, DYN3D, and PARET are using these parameters in their dynamic models. These parameters include effective delayed neutron fractions as well as mean generation time. These parameters are adjoint-weighted, and adjoint flux is employed as a weighting function in their evaluation. Adjoint flux calculation is an easy task for most of deterministic codes, but its evaluation is cumbersome for Monte Carlo codes. However, in recent years, some sophisticated techniques have been proposed for Monte Carlo-based point kinetic parameters...
Article Annals of Nuclear Energy ; Vol. 63 , 2014 , pp. 205-208 ; ISSN: 03064549 ; Vosoughi, N ; Sharif University of Technology
To quantify the core barrel motion (CBM) in a pressurized water reactor, a scaling factor can be calculated to convert the Root Mean Square (RMS) value of the ex-core signals (%) to the core barrel motion amplitude (mil) (Thompson et al., 1980). In the current paper, a scaling factor is calculated using the direct and adjoint methods for a typical VVER-1000 reactor. The scaling factor is calculated using the perturbed parameters that result from CBM. The results show that the calculated scaling factors are not the same in one and two-dimensional modeling, and strongly depend on the ex-core detector location. The linearity assumption of relative detector response versus the small displacement...
Article Applied Thermal Engineering ; Volume 105 , 2016 , Pages 327-335 ; 13594311 (ISSN) ; Mazaheri, K ; Chaharlang Kiani, K ; Sharif University of Technology
Elsevier Ltd 2016
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...
Article Engineering Optimization ; Volume 48, Issue 2 , 2016 , Pages 213-230 ; 0305215X (ISSN) ; Mazaheri, K ; Sharif University of Technology
Taylor and Francis Ltd
A complete continuous adjoint formulation is presented here for the optimization of the turbulent flow entropy generation rate through a turbine cascade. The adjoint method allows one to have many design variables, but still afford to compute the objective function gradient. The new adjoint system can be applied to different structured and unstructured grids as well as mixed subsonic and supersonic flows. For turbulent flow simulation, the k-ω shear-stress transport turbulence model and Roe's flux function are used. To ensure all possible shape models, a mesh-point method is used for design parameters, and an implicit smoothing function is implemented to avoid the generation of non-smoothed...
A sensitivity analysis of thermal lattices kinetic parameters with respect to the spectral weighting function using ultrafine BN method, Article Progress in Nuclear Energy ; Volume 88 , 2016 , Pages 310-320 ; 01491970 (ISSN) ; Salehi, A. A ; Vosoughi, N ; Ayyoubzadeh, S. M ; Sharif University of Technology
Accurate calculation of kinetic parameters is of utmost importance in the safety analysis of a nuclear reactor. In the current paper, two approaches are investigated to evaluate these parameters in energy phase space. In the first approach, these parameters are derived from an energy-continuous form of the forward and adjoint transport equations and then integrals with respect to the energy variable are replaced by weighted summations over the energy groups, while in the second approach these parameters are extracted from the multi-group forward equation and its associate adjoint equation in which their multigroup constants are weighted by forward spectrum. The difference of weighting...
Article Annals of Nuclear Energy ; Volume 113 , 2018 , Pages 246-255 ; 03064549 (ISSN) ; Vosoughi, N ; Vosoughi, J ; Sharif University of Technology
Elsevier Ltd 2018
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...
Article Annals of Nuclear Energy ; Volume 37, Issue 8 , 2010 , Pages 1089-1100 ; 03064549 (ISSN) ; Vosoughi, N ; Zahedinejad, E ; Sharif University of Technology
In this paper, the development of a neutron noise simulator for hexagonal-structured reactor cores using both the forward and the adjoint methods is reported. The spatial discretisation of both 2-D 2-group static and dynamic equations is based on a developed box-scheme finite difference method for hexagonal mesh boxes. Using the power iteration method for the static calculations, the 2-group neutron flux and its adjoint with the corresponding eigenvalues are obtained by the developed static simulator. The results are then benchmarked against the well-known CITATION computer code. The dynamic calculations are performed in the frequency domain which leads to discarding of the time...
M.Sc. Thesis Sharif University of Technology ; Mazaheri, Karim
This study develops an aerodynamic shape optimization code using parallel processing capability based on a gradient-based adjoint method. Calculation of the gradient of the objective function with respect to design variables is the most costly part of the gradient-based optimization algorithms. Applying adjoint methods, gradients can be calculated with solving some additional equations known as the "adjoint equations", instead of direct calculation. In this study, the blade shape optimization is performed by inverse design method and using steepest descent optimization algorithm. The objective function of inverse design problem is the desired blade surface pressure distribution. In each...
M.Sc. Thesis Sharif University of Technology ; Hosseini, Aboulfazl
The present M.Sc. thesis consists of two sections including static calculation and neutron noise calculations in rectangular and hexagonal geometries. The multi-group, two dimensional neutron diffusion equations and corresponding adjoint equations are solved in the static calculation. The spatial discretization of equation is based on Boundary Element Method (BEM). The result are benchmarked against the valid results for BIBLIS-2D and IAEA -2D benchmark problem. In the second section, neutron noise calculation are performed for two types of noise sources, i.e. absorber of variable strength and Inadvertent Loading and Operation of a Fuel Assembly in an Improper Position (ILOFAIP). The...
M.Sc. Thesis Sharif University of Technology ; Mazaheri, Karim
In this study, aerodynamic shape optimization of axial compressors is considered. In order to optimization, one of the gradient based optimization algorithms, namely Adjoint method, is used. Recently, Adjoint method has been emerged as one of the reliable gradient based optimization algorithms in turbomahineries applications. Because this method is a gradient method of optimization, similar to the other entire gradient based algorithms, adjoint method also has a better convergence than non-gradient based optimization algorithms. In this work, aerodynamic shape optimization of two-dimensional cross section through a transonic axial compressor is studied. The process is considered for midspan...
M.Sc. Thesis Sharif University of Technology ; Mazaheri, Karim
Adjoint-based aerodynamic optimization has drawn much attention, recently. It is based on gradient optimization procedures and requires the sensitivities of the design variables to find the optimized shape. The advantage of this method is that it estimates the sensitivities by solving an “adjoint equation”, instead of calculating them directly. In this thesis, the method is used to design airfoil shapes both in inviscid and viscous flows. In this regard, a flow solver and an adjoint solver have been developed. First, the validity of the flow solver is tested according to credited data form papers and softwares. Then, the optimizing program is tested using some inverse design problems....
Article Annals of Nuclear Energy ; Volume 97 , 2016 , Pages 132-141 ; 03064549 (ISSN) ; Vosoughi, N ; Sharif University of Technology
In the present study, the neutron noise, i.e. the stationary fluctuation of the neutron flux around its mean value is calculated based on the 2G, 3D neutron diffusion theory. To this end, the static neutron calculation is performed at the first stage. The spatial discretization of the neutron diffusion equation is performed based on linear approximation of Galerkin Finite Element Method (GFEM) using unstructured tetrahedron elements. Using power iteration method, neutron flux and corresponding eigen-value are obtained. The results are then benchmarked against the valid results for VVER-1000 (3D) benchmark problem. In the second stage, the neutron noise equation is solved using GFEM and...
Article Electronic Journal of Combinatorics ; Volume 23, Issue 1 , 2016 ; 10778926 (ISSN) ; Hejrati, M ; Madani, M ; Sharif University of Technology
Australian National University 2016
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
Article Computer Methods in Applied Mechanics and Engineering ; Volume 300 , 2016 , Pages 265-293 ; 00457825 (ISSN) ; Sharif University of Technology
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...