Shahrouz Aliabadi - Academia.edu (original) (raw)

Papers by Shahrouz Aliabadi

This paper reports the development and performance of CaMEL_Aero, our truly matrix-free, parallel... more This paper reports the development and performance of CaMEL_Aero, our truly matrix-free, parallel and vectorized unstructured finite volume solver for compressible flows. The Jacobian-free GMRES method is used to solve the linear systems of equations inside each nonlinear Newton-Raphson iteration. Furthermore, the matrix-free Lower-Upper Symmetric Gauss Seidel (LUSGS) method is employed as a preconditioning technique to the GMRES solver. The solver is parallelized using mesh partitioning and Message Passing Interface (MPI) functions. The solver is also vectorized using two main vectorization techniques: the face coloring algorithm to vectorize the long loops over faces and the truncated Neumann expansions of the inverse of preconditioning matrices to vectorize the LU-SGS preconditioner, respectively. A few 2D and 3D numerical examples are presented to demonstrate the performance of the present solver.

WIT transactions on engineering sciences, 2005

In this paper we will present a new computational approach to simulate free-surface flow problems... more In this paper we will present a new computational approach to simulate free-surface flow problems efficiently. The finite element solution strategy is based on a combination approach derived from fixed-mesh and moving-mesh techniques. Here, the free-surface flow simulations are based on the Navier-Stokes equations written for two incompressible fluids where the impact of one fluid on the other one is extremely small. An interface function with two distinct values is used to locate the position of the free-surface in regions near the floating object, while mesh-moving is used to move the free-surface in regions where wave breaking is not expected. The stabilized finite element formulations are written and integrated in an arbitrary Lagrangian-Eulerian domain. In the mesh-moving scheme, we assume that the computational domain is made of elastic materials. The linear elasticity equations are solved to obtain the displacements for each computational node. The numerical example includes ...

Procedia Engineering, 2013

ABSTRACT This paper presents a gluing method for composite meshes. Different meshes are generated... more ABSTRACT This paper presents a gluing method for composite meshes. Different meshes are generated independently and are glued together using some new elements to connect them, referred to as extension elements. The resulting global mesh is non-conforming and consists of connected overlapping meshes. The method is inherently implicit, parallel and versatile, in the sense that it is PDE independent. The most cited gluing method is probably the Chimera method, used for overset grids, where patch meshes are superimposed onto a background mesh. The method employed here was originally devised for such situations and is now applied to disjoint or overlapping meshes. One of the advantages of the method is that the meshes do not have to coincide and can present a gap between them. The method is illustrated through some simple examples to demonstrate the mesh convergence. Finally, we consider the solution of the airflow in the complete respiratory system, by joining independent meshes for the large and small airways, and the simulation of the flow passing through a bypass in a stenosed artery.

Computers & Fluids, 2013

Abstract The flow fields in the small bronchial tubes are mostly laminar. However, they are quite... more Abstract The flow fields in the small bronchial tubes are mostly laminar. However, they are quite complex mainly due to the geometrical effects of the lung airways. Asymmetry, nonplanarity and multiple generations are the main attributes of the lung airway geometry. There are total 23 generations of airways in human lung. The complexity of the airflow in the lung airway increases with an increasing number of generations. Particle deposition in bronchial tubes is strongly affected by these complex flow fields. Simulation of flow and particle deposition in multi-generational bronchial tube geometries is a major challenge because of the complexity of the geometry and size of the problem. The unsteady nature of inhale–exhale breathing cycles further complicates the problem. In this study, we simulate flows and particle deposition in an idealized lung geometry consisting of a ten-generation, nonplanar, bronchial tube model using our hybrid (finite element/finite volume), matrix free, parallel CaMEL solver. Steady-state inspiratory and unsteady flows were simulated with an inlet Reynolds number of 319. In this study, the large-scale CFD simulations for ten-generation bronchial tube model were successfully demonstrated. The particle transport was simulated using our Lagrangian based particle tracking model. The impact of unsteadiness on particle deposition was investigated by employing particle deposition efficiencies in each generation and particle destination maps. Particles were released at different inhalation times to investigate the unsteady effects. The results showed different particle deposition patterns for different particle release times. Particles released later in inhalation phase resulted in comparatively more particle deposition. The particle deposition before and after inhalation peak, which had identical inflow conditions, were observed to be significantly different due to the slight differences in strength of the vortices. Also, the results showed importance of geometry in later generations in particle deposition.

Computer Methods in Applied Mechanics and Engineering, 1993

The deformable-spatial-domain/stabilized-space-time (DSD/SST) formulation, introduced by Tezduyar... more The deformable-spatial-domain/stabilized-space-time (DSD/SST) formulation, introduced by Tezduyar et al. is applied to computation of viscous compressible flows involving moving boundaries and interfaces. The stabilization technique employed is a streamline-upwind/Petrov-Galerkin (SUPG) method, with a modified SUPG stabilization matrix. The stabilized finite element formulation of the governing equations is written over the space-time domain of the problem, and therefore the deformation of the spatial domain with respect to time is taken into account automatically. The frequency of remeshing is minimized to minimize the projection errors involved in remeshing and also to increase the parallelization potential of the computations. The implicit equation systems arising from the space-time finite element discretizations are solved iteratively. It is demonstrated that the combination of the SUPG stabilization and the space-time approach gives the capability of handling complicated compressible flow problems, including those with moving surfaces and shock-boundary layer interactions.

In the near future, large ram-air parachutes are expected to provide the capability of delivering... more In the near future, large ram-air parachutes are expected to provide the capability of delivering 21 ton payloads from altitudes as high as 25,000 ft. In development and test and evaluation of these parachutes the size of the parachute needed and the deployment stages involved make high-performance computing (HPC) simulations a desirable alternative to costly airdrop tests. Although computational simulations based on realistic, 3D, timedependent models will continue to be a major computational challenge, advanced finite element simulation techniques recently developed for this purpose and the execution of these techniques on "PC platforms are significant steps in the direction to meet this challenge. In this paper, two approaches for analysis of the inflation and gliding of ram-air parachutes are presented. In one of the approaches the point mass flight mechanics equations are solved with the time-varying drag and lift areas obtained from empirical data. This approach is limited to parachutes with similar configurations to those for which data are available. The other approach is 3D finite element computations based on the Navier-Stokes equations governing the airflow around the parachute canopy and Newton's law of motion governing the 3D dynamics of the canopy, with the forces acting on the canopy calculated from the simulated flow field. At the earlier stages of canopy inflation the parachute is modelled as an expanding box, whereas at the later stages, as it expands, the box transforms to a parafoil and glides. These finite element computations are carried out on the massively parallel supercomputers CRA Y T3D and Thinking Machines CM-5, typically with millions of coupled, non-linear finite elemeJIt equations solved simultaneously at every time step or pseudo-time step of the simulation. ~ 1997 by John Wiley & Sons, Ltd.

A new mixed clustered element-by-element (CEBE)/cluster companion (CC) preconditioning method for... more A new mixed clustered element-by-element (CEBE)/cluster companion (CC) preconditioning method for finite element computations is introduced. In the CEBE preconditioning, the elements are merged into clusters of elements, and the preconditioners are defined as series products of cluster level matrices. The CC preconditioning method, which is also introduced in this paper, shares a common philosophy with the multi-grid methods. The CC preconditioners are based on companion meshes associated with different levels of clustering. For each level of clustering, we construct a CEBE preconditioner and an associated CC preconditioner. Because these two preconditioners in a sen&e complement each other, when they are used in a mixed way, they can be expected to give better performance. In fact, our numerical tests, for two-and three-dimensional problems governed by the Poisson equation; demonstrate that the mixed CEBE/CC preconditioning results in convergence rates which are, in most cases, significantly better than the convergence rates obtained with the best of the CEBE and CC preconditioning methods.

In this article, we present our investigation and comparison of the SUPG-stabilized finite elemen... more In this article, we present our investigation and comparison of the SUPG-stabilized finite element formulations for computation of viscous compressible flows based on the conservation and entropy variables. This article is a sequel to the one on inviscid compressible flows by Le Beau et al. (1992). For the conservation variables formulation, we use the SUPG stabilization technique introduced in Aliabadi and Tezduyar (1992), which is a modified version of the one described in Le Beau et al. (1992). The formulation based on the entropy variables is same as the one introduced in Hughes et al. (1986). The two formulations are tested on three different problems: adiabatic flat plate at Mach 2.5, Reynolds number 20,000; Mach 3 compression corner at Reynolds number 16,800; and Mach 6 NACA 0012 airfoil at Reynolds number 10,000. In all cases, we show that the results obtained with the two formulations are very close. This observation is the same as the one we had in Le Beau et al. (1992) for inviscid flows.

We present the Enhanced-Discretization Interface-Capturing Technique (EDICT) for computation of u... more We present the Enhanced-Discretization Interface-Capturing Technique (EDICT) for computation of unsteady flow problems with interfaces, such as two-fluid and free-surface flows. In EDICT, we solve, over a non-moving mesh, the Navier-Stokes equations together with an advection equation governing the evolution of an interface function with two distinct values identifying the two fluids. The starting point for the spatial discretization of these equations are the stabilized finite element formulations which possess good stability and accuracy properties. To increase the accuracy in modeling the interfaces, we use finite element functions corresponding to enhanced discretization at and near the interface. These functions are designed to have multiple components, with each component coming from a different level of mesh refinement over the same computational domain. The primary component of the functions for velocity and pressure comes from the base mesh called Mesh-l. A subset of the elements in Mesh-1 are identified to be at or near the interface, and depending on where the interface is, this subset could change from one time level to another. A Mesh-2 is constructed by patching together the second-level meshes generated over this subset of elements, and the second component of the functions for velocity and pressure comes from Mesh-2. For the interface function, we have a third component coming from a Mesh-3 which is constructed by patching together the third-level meshes generated over a subset of elements in Mesh-2. With parallel computation of the test problems presented here, we demonstrate that the EDICT can be used very effectively to increase the accuracy of the base finite element formulations.

International Journal for Numerical …

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING Int. J. Numer. Meth. Engng (2010) Publ... more INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING Int. J. Numer. Meth. Engng (2010) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/nme.2886 ... Hybrid finite element/volume method for shallow water ...

Flow simulation is a computational tool for exploring science and technology involving flow appli... more Flow simulation is a computational tool for exploring science and technology involving flow applications. It can provide cost-effective alternatives or complements to laboratory experiments, field tests and prototyping. Flow simulation relies heavily on high performance computing (HPC). We view HPC as having two major components. One is advanced algorithms capable of accurately simulating complex, real-world problems. The other is advanced computer hardware and networking with sufficient power, memory and bandwidth to execute those simulations. While HPC enables flow simulation, flow simulation motivates development of novel HPC techniques. This paper focuses on demonstrating that flow simulation has come a long way and is being applied to many complex, real-world problems in different fields ofengineering and applied sciences, particularly in aerospace engineering and applied fluid mechanics. Flow simulation has come a long way because HPC has come a long way, This paper also provi...

This paper reports the development and performance of CaMEL_Aero, our truly matrix-free, parallel... more This paper reports the development and performance of CaMEL_Aero, our truly matrix-free, parallel and vectorized unstructured finite volume solver for compressible flows. The Jacobian-free GMRES method is used to solve the linear systems of equations inside each nonlinear Newton-Raphson iteration. Furthermore, the matrix-free Lower-Upper Symmetric Gauss Seidel (LU-SGS) method is employed as a preconditioning technique to the GMRES solver. The solver is parallelized using mesh partitioning and Message Passing Interface (MPI) functions. The solver is also vectorized using two main vectorization techniques: the face coloring algorithm to vectorize the long loops over faces and the truncated Neumann expansions of the inverse of preconditioning matrices to vectorize the LU-SGS preconditioner, respectively. A few 2D and 3D numerical examples are presented to demonstrate the performance of the present solver.

Rarefied gas flows typically encountered in MEMS systems are numerically investigated in this stu... more Rarefied gas flows typically encountered in MEMS systems are numerically investigated in this study. Fluid flow and heat transfer in rectangular and circular microchannels in the slip flow regime are studied in detail by our recently developed implicit, incompressible, hybrid (finite volume/finite element) flow solver. The hybrid flow solver methodology is based on the pressure correction or projection method, which involves a fractional step approach to obtain an intermediate velocity field by solving the original momentum equations with the matrix-free, implicit, cellcentered finite volume method. The poisson equation resulting from the fractional step approach is then solved by node based Galerkin finite element method for an auxiliary variable which is closely related to pressure and is used to update the velocity field and pressure field. The hybrid flow solver has been extended for applications in MEMS by incorporating first order slip flow boundary conditions. Extended inlet boundary conditions are used for rectangular microchannels, whereas classical inlet boundary conditions are used for circular microchannels to emphasize on the entrance region singularity. In this study, rarefaction effects characterized by Knudsen number (Kn) in the range of 0 ≤ Kn ≤ 0.1 are numerically investigated for rectangular and circular microchannels with constant wall temperature. Extensive validations of our hybrid code are performed with available analytical solutions and experimental data for fully developed velocity profiles, friction factors, and Nusselt numbers. The influence of rarefaction on rectangular microchannels with aspect ratios between 0 and 1 is thoroughly investigated. Friction coefficients are found to be decreasing with increasing Knudsen number for both rectangular and circular microchannels. The reduction in the friction coefficients is more pronounced for rectangular microchannels with smaller aspect ratios. Effects of rarefaction and gas-wall surface interaction parameter on heat transfer are analyzed for rectangular and circular microchannels. For most engineering applications heat transfer is decreased with rarefaction. However for fluids with very large Prandtl numbers velocity slip dominates the temperature jump resulting in an increase in heat transfer with rarefaction. Depending on the gas-wall surface interaction properties extreme reductions in the Nusselt number can occur. Present results confirm the existence of a transition point below and above which heat transfer enhancement and reduction can occur.

Journal of Aerospace Computing, Information, and Communication, 2004

ABSTRACT

Proceedings of the 2nd International Conference on Computing for Geospatial Research & Applications - COM.Geo '11, 2011

... Full Text: PDF PDF. Authors: Marvin D. Watts, Jackson State University, Jackson, MS. Elizah S... more ... Full Text: PDF PDF. Authors: Marvin D. Watts, Jackson State University, Jackson, MS. Elizah S. Dasari, Jackson State University, Jackson, MS. ... top of page AUTHORS. Search for Marvin D. Watts Search for Elizah S. Dasari Search for Shahrouz K. Aliabadi. ...

Proceedings 15th International Parallel and Distributed Processing Symposium. IPDPS 2001, 2001

Parallel computation of unsteady, free-surface flow applications are performed using stabilized f... more Parallel computation of unsteady, free-surface flow applications are performed using stabilized finite element method. The finite element formulations are written for fix meshes and are based on the Navier-Stokes equations and an advection equation governing the motion of the interface function. To increase the accuracy of the method, an interface-sharpening/mass conservation algorithm is designed. The method has been implemented on

This paper addresses one aspect of an on-going project at Jackson State University regarding home... more This paper addresses one aspect of an on-going project at Jackson State University regarding homeland security in the state of Mississippi. The project proposes an integrated tool for multi- scale storm surge and flood forecast, as well as evaluation of the flood damage on coastal infrastructure including transportation systems in the three counties in Mississippi state. Specifically, this paper describes the storm surge and wave models used for hurricane forecast and simulation, and the methodology that we use to integrate the results from flood modeling into geographical information systems for visualization, analysis and decision-making. The simulation and prediction of storm surges and waves are intrinsically complex due to the interaction of a wide range of fluid motions, ranging from large-scale tide and wave to small- scale street level turbulence. Multi-scale flood simulation becomes a reality due to the rapid development of computer technology, the maturity of computational...

This paper reports the development and performance of CaMEL_Aero, our truly matrix-free, parallel... more This paper reports the development and performance of CaMEL_Aero, our truly matrix-free, parallel and vectorized unstructured finite volume solver for compressible flows. The Jacobian-free GMRES method is used to solve the linear systems of equations inside each nonlinear Newton-Raphson iteration. Furthermore, the matrix-free Lower-Upper Symmetric Gauss Seidel (LUSGS) method is employed as a preconditioning technique to the GMRES solver. The solver is parallelized using mesh partitioning and Message Passing Interface (MPI) functions. The solver is also vectorized using two main vectorization techniques: the face coloring algorithm to vectorize the long loops over faces and the truncated Neumann expansions of the inverse of preconditioning matrices to vectorize the LU-SGS preconditioner, respectively. A few 2D and 3D numerical examples are presented to demonstrate the performance of the present solver.

WIT transactions on engineering sciences, 2005

In this paper we will present a new computational approach to simulate free-surface flow problems... more In this paper we will present a new computational approach to simulate free-surface flow problems efficiently. The finite element solution strategy is based on a combination approach derived from fixed-mesh and moving-mesh techniques. Here, the free-surface flow simulations are based on the Navier-Stokes equations written for two incompressible fluids where the impact of one fluid on the other one is extremely small. An interface function with two distinct values is used to locate the position of the free-surface in regions near the floating object, while mesh-moving is used to move the free-surface in regions where wave breaking is not expected. The stabilized finite element formulations are written and integrated in an arbitrary Lagrangian-Eulerian domain. In the mesh-moving scheme, we assume that the computational domain is made of elastic materials. The linear elasticity equations are solved to obtain the displacements for each computational node. The numerical example includes ...

Procedia Engineering, 2013

ABSTRACT This paper presents a gluing method for composite meshes. Different meshes are generated... more ABSTRACT This paper presents a gluing method for composite meshes. Different meshes are generated independently and are glued together using some new elements to connect them, referred to as extension elements. The resulting global mesh is non-conforming and consists of connected overlapping meshes. The method is inherently implicit, parallel and versatile, in the sense that it is PDE independent. The most cited gluing method is probably the Chimera method, used for overset grids, where patch meshes are superimposed onto a background mesh. The method employed here was originally devised for such situations and is now applied to disjoint or overlapping meshes. One of the advantages of the method is that the meshes do not have to coincide and can present a gap between them. The method is illustrated through some simple examples to demonstrate the mesh convergence. Finally, we consider the solution of the airflow in the complete respiratory system, by joining independent meshes for the large and small airways, and the simulation of the flow passing through a bypass in a stenosed artery.

Computers & Fluids, 2013

Abstract The flow fields in the small bronchial tubes are mostly laminar. However, they are quite... more Abstract The flow fields in the small bronchial tubes are mostly laminar. However, they are quite complex mainly due to the geometrical effects of the lung airways. Asymmetry, nonplanarity and multiple generations are the main attributes of the lung airway geometry. There are total 23 generations of airways in human lung. The complexity of the airflow in the lung airway increases with an increasing number of generations. Particle deposition in bronchial tubes is strongly affected by these complex flow fields. Simulation of flow and particle deposition in multi-generational bronchial tube geometries is a major challenge because of the complexity of the geometry and size of the problem. The unsteady nature of inhale–exhale breathing cycles further complicates the problem. In this study, we simulate flows and particle deposition in an idealized lung geometry consisting of a ten-generation, nonplanar, bronchial tube model using our hybrid (finite element/finite volume), matrix free, parallel CaMEL solver. Steady-state inspiratory and unsteady flows were simulated with an inlet Reynolds number of 319. In this study, the large-scale CFD simulations for ten-generation bronchial tube model were successfully demonstrated. The particle transport was simulated using our Lagrangian based particle tracking model. The impact of unsteadiness on particle deposition was investigated by employing particle deposition efficiencies in each generation and particle destination maps. Particles were released at different inhalation times to investigate the unsteady effects. The results showed different particle deposition patterns for different particle release times. Particles released later in inhalation phase resulted in comparatively more particle deposition. The particle deposition before and after inhalation peak, which had identical inflow conditions, were observed to be significantly different due to the slight differences in strength of the vortices. Also, the results showed importance of geometry in later generations in particle deposition.

Computer Methods in Applied Mechanics and Engineering, 1993

The deformable-spatial-domain/stabilized-space-time (DSD/SST) formulation, introduced by Tezduyar... more The deformable-spatial-domain/stabilized-space-time (DSD/SST) formulation, introduced by Tezduyar et al. is applied to computation of viscous compressible flows involving moving boundaries and interfaces. The stabilization technique employed is a streamline-upwind/Petrov-Galerkin (SUPG) method, with a modified SUPG stabilization matrix. The stabilized finite element formulation of the governing equations is written over the space-time domain of the problem, and therefore the deformation of the spatial domain with respect to time is taken into account automatically. The frequency of remeshing is minimized to minimize the projection errors involved in remeshing and also to increase the parallelization potential of the computations. The implicit equation systems arising from the space-time finite element discretizations are solved iteratively. It is demonstrated that the combination of the SUPG stabilization and the space-time approach gives the capability of handling complicated compressible flow problems, including those with moving surfaces and shock-boundary layer interactions.

In the near future, large ram-air parachutes are expected to provide the capability of delivering... more In the near future, large ram-air parachutes are expected to provide the capability of delivering 21 ton payloads from altitudes as high as 25,000 ft. In development and test and evaluation of these parachutes the size of the parachute needed and the deployment stages involved make high-performance computing (HPC) simulations a desirable alternative to costly airdrop tests. Although computational simulations based on realistic, 3D, timedependent models will continue to be a major computational challenge, advanced finite element simulation techniques recently developed for this purpose and the execution of these techniques on "PC platforms are significant steps in the direction to meet this challenge. In this paper, two approaches for analysis of the inflation and gliding of ram-air parachutes are presented. In one of the approaches the point mass flight mechanics equations are solved with the time-varying drag and lift areas obtained from empirical data. This approach is limited to parachutes with similar configurations to those for which data are available. The other approach is 3D finite element computations based on the Navier-Stokes equations governing the airflow around the parachute canopy and Newton's law of motion governing the 3D dynamics of the canopy, with the forces acting on the canopy calculated from the simulated flow field. At the earlier stages of canopy inflation the parachute is modelled as an expanding box, whereas at the later stages, as it expands, the box transforms to a parafoil and glides. These finite element computations are carried out on the massively parallel supercomputers CRA Y T3D and Thinking Machines CM-5, typically with millions of coupled, non-linear finite elemeJIt equations solved simultaneously at every time step or pseudo-time step of the simulation. ~ 1997 by John Wiley & Sons, Ltd.

A new mixed clustered element-by-element (CEBE)/cluster companion (CC) preconditioning method for... more A new mixed clustered element-by-element (CEBE)/cluster companion (CC) preconditioning method for finite element computations is introduced. In the CEBE preconditioning, the elements are merged into clusters of elements, and the preconditioners are defined as series products of cluster level matrices. The CC preconditioning method, which is also introduced in this paper, shares a common philosophy with the multi-grid methods. The CC preconditioners are based on companion meshes associated with different levels of clustering. For each level of clustering, we construct a CEBE preconditioner and an associated CC preconditioner. Because these two preconditioners in a sen&e complement each other, when they are used in a mixed way, they can be expected to give better performance. In fact, our numerical tests, for two-and three-dimensional problems governed by the Poisson equation; demonstrate that the mixed CEBE/CC preconditioning results in convergence rates which are, in most cases, significantly better than the convergence rates obtained with the best of the CEBE and CC preconditioning methods.

In this article, we present our investigation and comparison of the SUPG-stabilized finite elemen... more In this article, we present our investigation and comparison of the SUPG-stabilized finite element formulations for computation of viscous compressible flows based on the conservation and entropy variables. This article is a sequel to the one on inviscid compressible flows by Le Beau et al. (1992). For the conservation variables formulation, we use the SUPG stabilization technique introduced in Aliabadi and Tezduyar (1992), which is a modified version of the one described in Le Beau et al. (1992). The formulation based on the entropy variables is same as the one introduced in Hughes et al. (1986). The two formulations are tested on three different problems: adiabatic flat plate at Mach 2.5, Reynolds number 20,000; Mach 3 compression corner at Reynolds number 16,800; and Mach 6 NACA 0012 airfoil at Reynolds number 10,000. In all cases, we show that the results obtained with the two formulations are very close. This observation is the same as the one we had in Le Beau et al. (1992) for inviscid flows.

We present the Enhanced-Discretization Interface-Capturing Technique (EDICT) for computation of u... more We present the Enhanced-Discretization Interface-Capturing Technique (EDICT) for computation of unsteady flow problems with interfaces, such as two-fluid and free-surface flows. In EDICT, we solve, over a non-moving mesh, the Navier-Stokes equations together with an advection equation governing the evolution of an interface function with two distinct values identifying the two fluids. The starting point for the spatial discretization of these equations are the stabilized finite element formulations which possess good stability and accuracy properties. To increase the accuracy in modeling the interfaces, we use finite element functions corresponding to enhanced discretization at and near the interface. These functions are designed to have multiple components, with each component coming from a different level of mesh refinement over the same computational domain. The primary component of the functions for velocity and pressure comes from the base mesh called Mesh-l. A subset of the elements in Mesh-1 are identified to be at or near the interface, and depending on where the interface is, this subset could change from one time level to another. A Mesh-2 is constructed by patching together the second-level meshes generated over this subset of elements, and the second component of the functions for velocity and pressure comes from Mesh-2. For the interface function, we have a third component coming from a Mesh-3 which is constructed by patching together the third-level meshes generated over a subset of elements in Mesh-2. With parallel computation of the test problems presented here, we demonstrate that the EDICT can be used very effectively to increase the accuracy of the base finite element formulations.

International Journal for Numerical …

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING Int. J. Numer. Meth. Engng (2010) Publ... more INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING Int. J. Numer. Meth. Engng (2010) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/nme.2886 ... Hybrid finite element/volume method for shallow water ...

Flow simulation is a computational tool for exploring science and technology involving flow appli... more Flow simulation is a computational tool for exploring science and technology involving flow applications. It can provide cost-effective alternatives or complements to laboratory experiments, field tests and prototyping. Flow simulation relies heavily on high performance computing (HPC). We view HPC as having two major components. One is advanced algorithms capable of accurately simulating complex, real-world problems. The other is advanced computer hardware and networking with sufficient power, memory and bandwidth to execute those simulations. While HPC enables flow simulation, flow simulation motivates development of novel HPC techniques. This paper focuses on demonstrating that flow simulation has come a long way and is being applied to many complex, real-world problems in different fields ofengineering and applied sciences, particularly in aerospace engineering and applied fluid mechanics. Flow simulation has come a long way because HPC has come a long way, This paper also provi...

This paper reports the development and performance of CaMEL_Aero, our truly matrix-free, parallel... more This paper reports the development and performance of CaMEL_Aero, our truly matrix-free, parallel and vectorized unstructured finite volume solver for compressible flows. The Jacobian-free GMRES method is used to solve the linear systems of equations inside each nonlinear Newton-Raphson iteration. Furthermore, the matrix-free Lower-Upper Symmetric Gauss Seidel (LU-SGS) method is employed as a preconditioning technique to the GMRES solver. The solver is parallelized using mesh partitioning and Message Passing Interface (MPI) functions. The solver is also vectorized using two main vectorization techniques: the face coloring algorithm to vectorize the long loops over faces and the truncated Neumann expansions of the inverse of preconditioning matrices to vectorize the LU-SGS preconditioner, respectively. A few 2D and 3D numerical examples are presented to demonstrate the performance of the present solver.

Rarefied gas flows typically encountered in MEMS systems are numerically investigated in this stu... more Rarefied gas flows typically encountered in MEMS systems are numerically investigated in this study. Fluid flow and heat transfer in rectangular and circular microchannels in the slip flow regime are studied in detail by our recently developed implicit, incompressible, hybrid (finite volume/finite element) flow solver. The hybrid flow solver methodology is based on the pressure correction or projection method, which involves a fractional step approach to obtain an intermediate velocity field by solving the original momentum equations with the matrix-free, implicit, cellcentered finite volume method. The poisson equation resulting from the fractional step approach is then solved by node based Galerkin finite element method for an auxiliary variable which is closely related to pressure and is used to update the velocity field and pressure field. The hybrid flow solver has been extended for applications in MEMS by incorporating first order slip flow boundary conditions. Extended inlet boundary conditions are used for rectangular microchannels, whereas classical inlet boundary conditions are used for circular microchannels to emphasize on the entrance region singularity. In this study, rarefaction effects characterized by Knudsen number (Kn) in the range of 0 ≤ Kn ≤ 0.1 are numerically investigated for rectangular and circular microchannels with constant wall temperature. Extensive validations of our hybrid code are performed with available analytical solutions and experimental data for fully developed velocity profiles, friction factors, and Nusselt numbers. The influence of rarefaction on rectangular microchannels with aspect ratios between 0 and 1 is thoroughly investigated. Friction coefficients are found to be decreasing with increasing Knudsen number for both rectangular and circular microchannels. The reduction in the friction coefficients is more pronounced for rectangular microchannels with smaller aspect ratios. Effects of rarefaction and gas-wall surface interaction parameter on heat transfer are analyzed for rectangular and circular microchannels. For most engineering applications heat transfer is decreased with rarefaction. However for fluids with very large Prandtl numbers velocity slip dominates the temperature jump resulting in an increase in heat transfer with rarefaction. Depending on the gas-wall surface interaction properties extreme reductions in the Nusselt number can occur. Present results confirm the existence of a transition point below and above which heat transfer enhancement and reduction can occur.

Journal of Aerospace Computing, Information, and Communication, 2004

ABSTRACT

Proceedings of the 2nd International Conference on Computing for Geospatial Research & Applications - COM.Geo '11, 2011

... Full Text: PDF PDF. Authors: Marvin D. Watts, Jackson State University, Jackson, MS. Elizah S... more ... Full Text: PDF PDF. Authors: Marvin D. Watts, Jackson State University, Jackson, MS. Elizah S. Dasari, Jackson State University, Jackson, MS. ... top of page AUTHORS. Search for Marvin D. Watts Search for Elizah S. Dasari Search for Shahrouz K. Aliabadi. ...

Proceedings 15th International Parallel and Distributed Processing Symposium. IPDPS 2001, 2001

Parallel computation of unsteady, free-surface flow applications are performed using stabilized f... more Parallel computation of unsteady, free-surface flow applications are performed using stabilized finite element method. The finite element formulations are written for fix meshes and are based on the Navier-Stokes equations and an advection equation governing the motion of the interface function. To increase the accuracy of the method, an interface-sharpening/mass conservation algorithm is designed. The method has been implemented on

This paper addresses one aspect of an on-going project at Jackson State University regarding home... more This paper addresses one aspect of an on-going project at Jackson State University regarding homeland security in the state of Mississippi. The project proposes an integrated tool for multi- scale storm surge and flood forecast, as well as evaluation of the flood damage on coastal infrastructure including transportation systems in the three counties in Mississippi state. Specifically, this paper describes the storm surge and wave models used for hurricane forecast and simulation, and the methodology that we use to integrate the results from flood modeling into geographical information systems for visualization, analysis and decision-making. The simulation and prediction of storm surges and waves are intrinsically complex due to the interaction of a wide range of fluid motions, ranging from large-scale tide and wave to small- scale street level turbulence. Multi-scale flood simulation becomes a reality due to the rapid development of computer technology, the maturity of computational...