Yassin Hassan
Texas A&M University, Nuclear Engineering, Faculty Member
- Yassin Hassan is University Distinguished Professor, Regents Professor and the L.F. Peterson '36 Chair II in Engineer... moreYassin Hassan is University Distinguished Professor, Regents Professor and the L.F. Peterson '36 Chair II in Engineering. He is professor in the Department of Nuclear Engineering and the J. Mike Walker ’66 Department of Mechanical Engineering, Texas Aedit
For moving boundary problems, previous body-conformal grid methods require frequent re-meshing as the boundary moves, thus increasing computational cost. An immersed boundary method (IBM) is an attractive method to resolve the problem... more
For moving boundary problems, previous body-conformal grid methods require frequent re-meshing as the boundary moves, thus increasing computational cost. An immersed boundary method (IBM) is an attractive method to resolve the problem since it is based on the fixed, non-body-conformal grids. In the IBM, force density terms are used so that no-slip boundary condition is satisfied on the boundary. On the other hand, lattice Boltzmann methods (LBMs) have been used as an alternative of Navier-Stokes equation method due to their efficiency to parallelize and simplicity to implement. The common feature of the IBM and the LBM of using non-body-conformal grids motivated the use of the IBM in the lattice Boltzmann method frame, which is usually called an immersed boundary-lattice Boltzmann method (IB-LBM). Besides, a split-forcing property in the LBM, due to its kinetic nature, facilitates the use of direct-forcing IBM. For the evaluation of boundary force density term, we need to adopt an interpolation scheme because the boundary, in general, does not match computational nodes. The interpolation schemes can be classified into diffuse and sharp interface schemes. The former usually uses the discrete delta function to evaluate the boundary force on the prescribed boundary points, while the latter uses interpolation from neighboring fluid nodes to evaluate the boundary force on the computation node either inside or outside closest to the boundary. In the diffuse scheme, the boundary force density terms evaluated on the boundary points should be distributed onto neighboring computational nodes using the discrete delta functions so that the boundary effect may exert on computational process. The objective of this study is to compare two interface schemes simultaneously for a moving boundary problem under the IB-LBM and to understand advantages and disadvantages of each scheme. We considered a problem of flow induced by inline oscillation of a circular cylinder since both experimental and body-conformal grid method results are available for this problem. Velocity results from both schemes showed overall good agreement with experimental data. However, the sharp interface scheme showed spurious oscillations in the surface force coefficient and pressure fields, although after filtering or smoothing, the force coefficients showed good agreement with the body-fitted results. In contrast, the diffuse interface scheme produced smooth variations in the surface force coefficient but over-predicted the absolute values especially at phase angles with the high magnitude of accelerations. These results can be attributed to the use of discrete delta functions. We could reduce the over-prediction by considering the effect of the diffuse area.
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21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS; PRIMARY COOLANT CIRCUITS; FLUID MECHANICS; HEAT TRANSFER; HYDRAULICS; PWR TYPE REACTORS; COMPUTER CODES; COOLANTS; DATA COVARIANCES; FINITE ...
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The Energy Citations Database (ECD) provides access to historical and current research (1948 to the present) from the Department of Energy (DOE) and predecessor agencies.
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In this study, we assess several interface schemes for stationary complex boundary flows under the direct‐forcing immersed boundary‐lattice Boltzmann methods (IB‐LBM) based on a split‐forcing lattice Boltzmann equation (LBE). Our strategy... more
In this study, we assess several interface schemes for stationary complex boundary flows under the direct‐forcing immersed boundary‐lattice Boltzmann methods (IB‐LBM) based on a split‐forcing lattice Boltzmann equation (LBE). Our strategy is to couple various interface schemes, which were adopted in the previous direct‐forcing immersed boundary methods (IBM), with the split‐forcing LBE, which enables us to directly use the direct‐forcing concept in the lattice Boltzmann calculation algorithm with a second‐order accuracy without involving the Navier–Stokes equation. In this study, we investigate not only common diffuse interface schemes but also a sharp interface scheme. For the diffuse interface scheme, we consider explicit and implicit interface schemes. In the calculation of velocity interpolation and force distribution, we use the 2‐ and 4‐point discrete delta functions, which give the second‐order approximation. For the sharp interface scheme, we deal with the exterior sharp interface scheme, where we impose the force density on exterior (solid) nodes nearest to the boundary. All tested schemes show a second‐order overall accuracy when the simulation results of the Taylor–Green decaying vortex are compared with the analytical solutions. It is also confirmed that for stationary complex boundary flows, the sharper the interface scheme, the more accurate the results are. In the simulation of flows past a circular cylinder, the results from each interface scheme are comparable to those from other corresponding numerical schemes. Copyright © 2010 John Wiley & Sons, Ltd.
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The prediction of multidimensional heat transfer and fluid flow problems requires the solution of Navier-Stokes equations. Although the use of upwind approximation for the convection terms removes the potential of nonphysical spatial... more
The prediction of multidimensional heat transfer and fluid flow problems requires the solution of Navier-Stokes equations. Although the use of upwind approximation for the convection terms removes the potential of nonphysical spatial oscillations, such a procedure is burdened with excessive numerical diffusion. Recently published work by Smith and Hutton presented results for some 20 different candidate methods to estimate the convection terms. The overall conclusion was that none of the methods was totally successful. The more accurate methods exhibited nonphysical spatial oscillations. More recently, a procedure was proposed that alleviates the problem of false diffusion. The purpose of this paper is to present several challenging cases, with various flow orientation, to show that the proposed procedure always circumvents the negative coefficients in the discretization equation such that the influence coefficients cannot become negative. The Smith and Hutton test case has been examined to illustrate the merit of this technique. The results are competitive with a large majority of those examined by Smith and Hutton.
Research Interests: Mathematics, Applied Mathematics, Convection, Mass Transfer, Fluid Mechanics, and 11 moreHeat Transfer, Discretization, Oscillations, PARTIAL DIFFERENTIAL EQUATION, Fluid flow, Mathematical Model, Numerical Stability, Energy Transfer, Differential equation, Convection Diffusion Equation, and Upwind Scheme
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Research Interests: Physics, Mechanics, Fluid Mechanics, Two Phase Flow, Heat Transfer, and 11 morePARTIAL DIFFERENTIAL EQUATION, Fluid flow, Mathematical Model, Nuclear Science and engineering, Thermal Shock, Three Dimensional, Interdisciplinary Engineering, Energy Transfer, Differential equation, Flow Rate, and Experimental Data
Abstract A new simple stable approach to the numerical solution of problems in fluid flow and heat transfer has been developed. The new approach avoids the stability problems of the skew upwind difference scheme while reducing the... more
Abstract A new simple stable approach to the numerical solution of problems in fluid flow and heat transfer has been developed. The new approach avoids the stability problems of the skew upwind difference scheme while reducing the inaccuracies of numerical diffusion ...
Research Interests: Mechanical Engineering, Civil Engineering, Mathematics, Applied Mathematics, Heat Transfer, and 11 moreNumerical Analysis, Computation, Fluid flow, Numerical Stability, Numerical computation, Numerical Solution, Numerical Diffusion, Numerical Modelling of Heat Transfer Systems, Skew, Upwind Scheme, and Difference Scheme
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22 GENERAL STUDIES OF NUCLEAR REACTORS; 21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS; PRESSURE VESSELS; STRESS ANALYSIS; THERMAL SHOCK; PWR TYPE REACTORS; REACTOR ACCIDENTS; ANL; C CODES; ...
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The complex behavior of thermal fluids in nuclear reactors require the usage of computational fluid dynamics (CFD) codes for design and analysis. In order to use CFD codes, they require regular benchmark problems to ensure the predictions... more
The complex behavior of thermal fluids in nuclear reactors require the usage of computational fluid dynamics (CFD) codes for design and analysis. In order to use CFD codes, they require regular benchmark problems to ensure the predictions are reasonable representations of reality. The twin jet water facility (TJWF) designed and built at the University of Tennessee, Knoxville was created for this purpose. The facility features twin planar-like turbulent free shear jets injecting fluid into a transparent tank to study a variety of flow behavior. The experimental work using this facility by Texas A&M University was used for the benchmarking activities. This work was conducted using a steady Reynolds-averaged Navier–Stokes formulation to simulate the flow behavior. It was determined that the standard k–ε and elliptic blending Reynolds stress model (EBRSM) turbulence models can be used to simulate the twin jet behavior with reasonable success for design and analysis activities.
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This study used an artificial neural network (ANN) regression model in wire-wrapped fuel assemblies to estimate the transition-to-turbulence flow regime boundary (RebT) and friction factor. The ANN models were trained and validated using... more
This study used an artificial neural network (ANN) regression model in wire-wrapped fuel assemblies to estimate the transition-to-turbulence flow regime boundary (RebT) and friction factor. The ANN models were trained and validated using existing experimental datasets. The bundle dataset comprised several design parameters, such as the number of rods, rod diameter, wire diameter, lattice pitch, edge pitch, and wire helical pitch. The log–log scale Reynolds number and linearity characteristics of the friction coefficient were used to over-sample the friction factor in the laminar and turbulent regimes for resolving the data imbalance. Three-quarters of the entire dataset was used for training, while the remainder was used for validation. The Levenberg–Marquardt approach with the Gauss–Newton approximation for the Hessian of the training cost function was used for training the model. The number of hidden layers for RebT was selected based on the minimum validation error. The pin numbe...
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Recent interest for the development of high-temperature gas reactors has increased the need for more advanced understanding of flow characteristics in randomly packed pebble beds. A proper understanding of these flow characteristics can... more
Recent interest for the development of high-temperature gas reactors has increased the need for more advanced understanding of flow characteristics in randomly packed pebble beds. A proper understanding of these flow characteristics can provide a better idea of the cooling capabilities of the system in both normal operation and accident scenarios. In order to enhance the accuracy of computationally efficient, intermediate fidelity modeling, high-fidelity simulation may be used to generate correlative data. For this research, NekRS, a GPU-enabled spectral-element computational fluid dynamics code, was used in order to produce the high-fidelity flow data for beds of 1,568 and 45,000 pebbles. Idaho National Lab’s Pronghorn porous media code was used as the intermediate fidelity code. The results of the high-fidelity model were separated into multiple concentric regions in order to extract porosity and velocity averages in each region. The porosity values were input into the Pronghorn m...
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An analysis of the simplified boiling water reactor (SBWR) is carried out using the reactor analysis computer program ROMONA-4B in an operational transient scenario, a turbine trip with failure of all the bypass valves. The SBWR model... more
An analysis of the simplified boiling water reactor (SBWR) is carried out using the reactor analysis computer program ROMONA-4B in an operational transient scenario, a turbine trip with failure of all the bypass valves. The SBWR model represents the vessel`s internal components, such as flow areas, diameters, and volumes. The one-quarter-core neutron parameters are calculated with the CASMO-3 transport theory
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Thermal mixing in a representative model of a main feedwater line that carries feedwater to the steam generator and auxiliary feedwater injector is investigated using the TEM-PEST Version L Mod 4 computer code; a single-phase,... more
Thermal mixing in a representative model of a main feedwater line that carries feedwater to the steam generator and auxiliary feedwater injector is investigated using the TEM-PEST Version L Mod 4 computer code; a single-phase, three-dimensional, time-dependent, hydrothermal analysis code. Transient simulation was performed and the resultant temperature histories were examined in order to assess the degree of thermal mixing and its possible implications concerning pressurized thermal shock and thermal fatigue cracking phenomena. Under certain auxiliary feedwater injector flow rates, thermal stratification was predicted.
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