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Articles 1 - 30 of 30
Full-Text Articles in Computational Engineering
Least Squares Spectral Element Method For Laminar And Turbulent Flows, –Continuous And Discontinuous Approaches–, Jaber Javanshir Hasbestan
Least Squares Spectral Element Method For Laminar And Turbulent Flows, –Continuous And Discontinuous Approaches–, Jaber Javanshir Hasbestan
Masters Theses and Doctoral Dissertations
In this research, application of a least squares spectral element method for compressible laminar and turbulent flow problems is investigated. For the turbulent Reynolds Averaged Navier-Stokes (RANS), a modified Spalart-Allmaras (SA) turbulence model is employed and integrated with the mean flow equations in a segregated fashion. Two different approaches are presented for solving the SA model using the least squares method. The first method represents a simple rearrangement of the equation. However, proper arrangement of the SAmodel is required in order to produce a stable scheme for the least squares methodology. The second approach is into divide the SA equation …
Solution Of Fully-Coupled Shallow Water Equations And Contaminant Transport Using A Primitive Variable Riemann Solver And A Semi-Discrete Supg Method, Faranak Behzadi
Solution Of Fully-Coupled Shallow Water Equations And Contaminant Transport Using A Primitive Variable Riemann Solver And A Semi-Discrete Supg Method, Faranak Behzadi
Masters Theses and Doctoral Dissertations
In the present dissertation, a finite volume and a finite element model are developed and tuned for the solution of the fully-coupled two-dimensional Shallow Water and Contaminant transport Equations with arbitrary bed topography and wetting-drying fronts. A Riemann-solver finite volume scheme, using primitive variables rather than conserved variables, and a semi-discrete Streamline Upwind Petrov-Galerkin (SUPG) method in finite element context are applied to compare the performance of these two numerical models. The Riemann-solver scheme is based on the unstructured finite volume discretization using primitive-variable Roe-flux approximation with an entropy fix. Second-order accuracy in space and time, an implicit scheme based …
A Stabilized Finite Element Dynamic Overset Method For The Navier-Stokes Equations, Chao Liu
A Stabilized Finite Element Dynamic Overset Method For The Navier-Stokes Equations, Chao Liu
Masters Theses and Doctoral Dissertations
In terms of mesh resolution requirements, higher-order finite element discretization methods offer a more economic means of obtaining accurate simulations and/or to resolve physics at scales not possible with lower-order schemes. For simulations that may have large relative motion between multiple bodies, overset grid methods have demonstrated distinct advantages over mesh movement strategies. Combining these approaches offers the ability to accurately resolve the flow phenomena and interaction that may occur during unsteady moving boundary simulations. Additionally, overset grid techniques when utilized within a finite element setting mitigate many of the difficulties encountered in finite volume implementations. This research presents the …
A Stabilized Finite Element Dynamic Overset Method For The Navier-Stokes Equations, Chao Liu
A Stabilized Finite Element Dynamic Overset Method For The Navier-Stokes Equations, Chao Liu
Masters Theses and Doctoral Dissertations
In terms of mesh resolution requirements, higher-order finite element discretization methods offer a more economic means of obtaining accurate simulations and/or to resolve physics at scales not possible with lower-order schemes. For simulations that may have large relative motion between multiple bodies, overset grid methods have demonstrated distinct advantages over mesh movement strategies. Combining these approaches offers the ability to accurately resolve the flow phenomena and interaction that may occur during unsteady moving boundary simulations. Additionally, overset grid techniques when utilized within a finite element setting mitigate many of the difficulties encountered in finite volume implementations. This research presents the …
A Parabolized Navier-Stokes Method For Wind Farm Applications, Anshul Mittal
A Parabolized Navier-Stokes Method For Wind Farm Applications, Anshul Mittal
Masters Theses and Doctoral Dissertations
Fluid flow simulations play an important role in the wind industry. With the development of large wind farms, flow simulations through an entire wind farm are becoming a necessity. These are required for designing the layout of new wind farms in the development stage and for forecasting power production from the existing ones for operational purposes. Conventional Navier-Stokes simulations (commonly referred to as CFD simulations) are computationally very expensive since they require a supercomputer with runtimes of several weeks. A Parabolized Navier-Stokes (PNS) method is developed and implemented in this study. The developed PNS method requires less stringent approximations as …
Tetrahedral Mesh Optimization And Generation Via Topological Transformations And Gradient Based Node Perturbation, Christopher B. Hilbert
Tetrahedral Mesh Optimization And Generation Via Topological Transformations And Gradient Based Node Perturbation, Christopher B. Hilbert
Masters Theses and Doctoral Dissertations
A general tetrahedral mesh optimization scheme utilizing both topological changes (i.e. flips) and gradient-based vertex optimization (i.e. smoothing) is demonstrated. This scheme is used in the optimization of tetrahedral meshes created by third-party software as well as a grid generation methodology created for this work. The particular algorithms involved are explained in detail including, an explication of the primary optimization metric, weighted condition number. In addition, a thorough literature review regarding tetrahedral mesh generation is given.
Stabilized Finite Elements For Compressible Turbulent Navier-Stokes, Jon Taylor Erwin
Stabilized Finite Elements For Compressible Turbulent Navier-Stokes, Jon Taylor Erwin
Masters Theses and Doctoral Dissertations
In this research a stabilized finite element approach is utilized in the development of a high-order flow solver for compressible turbulent flows. The Reynolds averaged Navier-Stokes (RANS) equations and modified Spalart-Almaras (SA) turbulence model are discretized using the streamline/upwind Petrov-Galerkin (SUPG) scheme. A fully implicit methodology is used to obtain steady state solutions or to drive unsteady problems at each time step. Order of accuracy is assessed for inviscid and viscous flows in two and three dimensions via the method of manufactured solutions. Proper treatment of curved surface geometries is of vital importance in high-order methods, especially when high aspect …
Physics-Based Point Placement By Particle Dynamics Simulation, Philip Wesley Fackler
Physics-Based Point Placement By Particle Dynamics Simulation, Philip Wesley Fackler
Masters Theses and Doctoral Dissertations
A physics-based approach to point cloud distribution for mesh generation is investigated using inter-nodal attraction and repulsion forces based on the Lennard-Jones pair potential and a simplified particle dynamics simulation. This method produces smooth distributions of points which accurately correspond to desired scalar spacing fields. Resulting point distributions are triangulated using Lawson's algorithm and the quality of these resulting meshes is measured, demonstrating the effectiveness of the approach. Several features planned for future development for increasing the robustness and versatility of the proposed method are discussed.
A New Software Framework For Unstructured Mesh Representation And Manipulation, Craig R. Tanis
A New Software Framework For Unstructured Mesh Representation And Manipulation, Craig R. Tanis
Masters Theses and Doctoral Dissertations
This research presents a unique new software framework for representing and manipulating unstructured meshes in parallel, for use in modern scientific simulation codes. Due to the central nature of the unstructured mesh, this framework provides a variety of functionality, desirable throughout the lifecycle of an application, such as IO, parallel partitioning, phantom node data updates, adaptive refinement, derefinement and load balancing. What makes the framework unique is a focus on generality: like a database, the user provides a programmatic schema defining the structure of the mesh, including topological descriptions of the valid mesh entities. The system extracts adjacency information from …
Validation Of Interpolative Interfaces For Rotorcraft Applications, Adam L. Cofer
Validation Of Interpolative Interfaces For Rotorcraft Applications, Adam L. Cofer
Masters Theses and Doctoral Dissertations
The study uses computational methods to simulate fluid flow on the NASA ROBIN helicopter model and on a simplified rotor geometry previously tested at Mississippi State. The ROBIN model and the rotor are run using an unstructured grid. Results from the Tenasi flow solver are compared against both simulated and wind tunnel data. Tenasi is an unstructured, Reynolds Averaged Navier-Stokes (RANS) solver developed at the SimCenter: National Center for Computational Engineering, located at the University of Tennessee at Chattanooga. Steady-state results for the isolated ROBIN fuselage and unsteady results for both fuselage and rotor systems are computed. In the unsteady …
Higher-Order Petrov-Galerkin Methods For Analysis Of Antennas, Xueying Zhang
Higher-Order Petrov-Galerkin Methods For Analysis Of Antennas, Xueying Zhang
Masters Theses and Doctoral Dissertations
A temporally and spatially high-order accurate Petrov-Galerkin finite-element method is applied to the analysis of several antenna configurations. The method obtains numerical solutions of Maxwell's equations in the time domain using implicit time stepping and introduces energy into the domain using a Gaussian pulse to allow frequency-domain parameters to be computed over a range of frequencies with a single time-dependent solution. Verification cases for a monopole antenna and a microstrip patch antenna are used to examine the accuracy of the algorithm. Effects of varying antenna parameters on subsequent performance metrics are discussed based on the results from the simulations. Post-processing …
2-D Cfd Design Of The Cross-Sectional Shape Of Arterial Stents, Kristen Karman
2-D Cfd Design Of The Cross-Sectional Shape Of Arterial Stents, Kristen Karman
Masters Theses and Doctoral Dissertations
An approach for desigining arterial stents to maximize wall shear stress is presented. A cost equation to maximize wall shear stress is derived and then inverted into a minimization problem for the optimizer. A 2-D mixed-element finite-volume scheme for solving the compressible Navier-Stokes equations is implemented. A paramaterization of the cross- sectional shape of the stent wire using Hicks-Henne functions is described. The strategies used in the commercial optimization software, DAKOTA, to minimize the cost equation are described. The solver is validated using well known fluid flow test cases and is shown to match other published computed results for bloodflow …
Extension Of A High-Order Petrov-Galerkin Implementation Applied To Non-Radiating And Radar Cross Section Geometries, William L. Shoemake
Extension Of A High-Order Petrov-Galerkin Implementation Applied To Non-Radiating And Radar Cross Section Geometries, William L. Shoemake
Masters Theses and Doctoral Dissertations
Capabilities of a high-order Petrov-Galerkin solver are expanded to include N-port systems. Tait-Bryan angles are employed to launch electro-magnetic waves in arbitrary directions allowing off axis ports to be driven. The transverse-electric (TE) formulation is added allowing waveguide geometries to be driven directly. A grid convergence study is performed on a coax-driven waveguide system. Physical data are matched to a hybrid-T junction (magic-T) electromagnetic waveguide structure to verify the TE driving formulation along with the Tait-Bryan angles and modified post-processing routines. A simple sphere case is used to exercise the radar cross section (RCS) routines and to examine the benefits …
Preconditioning Methods For Ideal And Multiphase Fluid Flows, Ashish Gupta
Preconditioning Methods For Ideal And Multiphase Fluid Flows, Ashish Gupta
Masters Theses and Doctoral Dissertations
The objective of this study is to develop a preconditioning method for ideal and multiphase multispecies compressible fluid flow solver using homogeneous equilibrium mixture model. The mathematical model for fluid flow going through phase change uses density and temperature in the formulation, where the density represents the multiphase mixture density. The change of phase of the fluid is then explicitly determined using the equation of state of the fluid, which only requires temperature and mixture density. The method developed is based on a finite-volume framework in which the numerical fluxes are computed using Roe’s [1] approximate Riemann solver and the …
Computational Investigation Of The Effects Of Casing Treatments On The Performance Of A Turbofan, Weiyang Lin
Computational Investigation Of The Effects Of Casing Treatments On The Performance Of A Turbofan, Weiyang Lin
Masters Theses and Doctoral Dissertations
A computational survey focused on modifications to the casing near the rotor blade tip is carried out for the purpose of enhancing the performance and increasing the stall margin of a model turbofan stage in transonic operating conditions. The study is divided into three phases. During the first phase two types of casing treatments, inward protruding rings and circumferential grooves, were tested with relatively coarse grids. In the second phase, a grid resolution study is carried out with the results from this phase influencing the choices for the third stage. In the third phase, a comprehensive study is performed to …
Computation Of Heat Transfer In Turbine Rotor Blade Cooling Channels With Angled Rib Turbulators, Guy Austin Flynt
Computation Of Heat Transfer In Turbine Rotor Blade Cooling Channels With Angled Rib Turbulators, Guy Austin Flynt
Masters Theses and Doctoral Dissertations
The effects of rotation and Reynolds number on heat transfer in rotating two-pass square and rectangular channels with smooth walls and walls with 45 degree angled and V-shaped rib turbulators were investigated numerically using an unstructured, incompressible, Reynolds-averaged Navier-Stokes flow solver. The influence of 45 degree angled ribs and channel orientation on the local Nusselt number ratios for leading and trailing surfaces in a two-pass square channel (AR=1) are compared to experimental data for Reynolds numbers from 5,000 to 25,000 and dimensionless rotation numbers from 0.0 to 0.118. The influence of V-shaped ribs and channel orientation on the local Nusselt …
The Unstructured Grid Incompressible Navier-Stokes Algorithm For Convective Heat Transfer Based On Artificial Compressibility, Jessica Elaine Kress
The Unstructured Grid Incompressible Navier-Stokes Algorithm For Convective Heat Transfer Based On Artificial Compressibility, Jessica Elaine Kress
Masters Theses and Doctoral Dissertations
The development of an explicit unstructured grid finite-volume scheme for solving the full incompressible Navier-Stokes equations along with the energy equation in a strongly coupled manner is presented. The Boussinesq approximation is utilized to account for thermal buoyancy. The method of artificial compressibilty is used to solve the resulting equations in a time marching fashion. Roe's approximate Riemann solver is used for the construction of the numerical flux. An eigensystem is derived for the flux Jacobian matrix, which is used in the evaluation of the numerical flux and the characteristic variable boundary conditions. The resulting algorithm is validated by simulating …
Mesh Generation Using A Correspondence Distance Field, Nicholas Szapiro
Mesh Generation Using A Correspondence Distance Field, Nicholas Szapiro
Masters Theses and Doctoral Dissertations
The central tool of this work is a correspondence distance field to discrete surface points embedded within a quadtree data structure. The theory, development, and implementation of the distance field tool are described, and two main applications to two-dimensional mesh generation are presented with extension to three-dimensional capabilities in mind. First is a method for surface-oriented mesh generation from a sufficiently dense set of discrete surface points without connectivity information. Contour levels of distance from the body are specified and correspondences oriented normally to the contours are created. Regions of merging fronts inside and between objects are detected in the …
Analysis And Implementation Of A High-Order Reconstruction Algorithm For An Unstructured Finite Volume Flow Solver, Shane Edmond Sawyer
Analysis And Implementation Of A High-Order Reconstruction Algorithm For An Unstructured Finite Volume Flow Solver, Shane Edmond Sawyer
Masters Theses and Doctoral Dissertations
A high-order scheme is examined an implemented in an unstructured solver. The motivation for this researcher is driven by research goals to simulate field equations, particularly those of fluid dynamics, with high fidelity. High-order schemes overcome computational limitations by computing comparable solutions on grids that are coarser than grids required by a second-order flow solver. The scheme was chosen based on two criteria. The first being that it is well documented in the literature for two-dimensional flow solvers. The second is that the scheme is extendable to the framework used in the Tenasi flow solver developed at the University of …
Generation And Optimization Of Spacing Fields, Max David Collao
Generation And Optimization Of Spacing Fields, Max David Collao
Masters Theses and Doctoral Dissertations
Meshes are used to discretize space for computational fluid dynamics (CFD) simulations. Mesh adaptation through refinement and smoothing can improve the accuracy of the CFD solution. In order to perform adaptive refinement or smoothing a spacing field is needed to define the desired edge sized in mesh. The objectives of this research are to generate spacing fields from existing CFD solutions and optimize this spacing information for efficient use by programs to perform adaptive refinement or smoothing. All work was done on 2D meshes with the intention of gaining knowledge and experience for later application to 3D meshes. The program …
Computational Design For Electromagnetic Simulations, Ryan Steven Glasby
Computational Design For Electromagnetic Simulations, Ryan Steven Glasby
Masters Theses and Doctoral Dissertations
An automatic computational procedure has been developed to efficiently and accurately design the shape of complicated electromagnetic objects. These electromagnetic objects can be simulated for operation at high frequencies (~10 GHz), and can be comprised of dissimilar materials. The automated design procedure consists of linking together an original electromagnetic field simulation tool, an original adjoint routine for obtaining sensitivity derivatives, and an original grid-smoothing tool with an existing optimization package. The electromagnetic field simulation software employs a temporally and spatially higher-order accurate Streamline Upwind/Petrov-Galerkin finite-element method that numerically solves Maxwell’s equations in the time domain using implicit time stepping. The …
Design Optimization Using Cad Parameterization Through Capri, William Emerson Brock V
Design Optimization Using Cad Parameterization Through Capri, William Emerson Brock V
Masters Theses and Doctoral Dissertations
Design optimization is one of the many areas of Computational Engineering that is directly applicable to almost any engineering endeavor. The design cycle is a multi-step process, beginning with a Computer Aided Design (CAD) model and ending with an optimized version of that model relative to some objective function. This is accomplished by parameterizing the model, through one of many different algorithms, and finding the ideal value of those parameters with respect to the specified objective. The purpose of this research is to explore the use of a Computational Analysis PRogramming Interface (CAPRI) for utilizing CAD parameters in design optimization …
An Adaptive Hybrid Mesh Generation Method For Complex Geometries, Cameron Thomas Druyor
An Adaptive Hybrid Mesh Generation Method For Complex Geometries, Cameron Thomas Druyor
Masters Theses and Doctoral Dissertations
An adaptive hybrid mesh generation method is described to automatically provide spatial discretizations suitable for computational fluid dynamics or other 2D solver applications. This method employs a hierarchical grid generation technique to create a background mesh, an extrusion-type method for inserting boundary layers, and an unstructured triangulation to stitch between the boundary layers and background mesh. This method provides appropriate mesh resolution based on geometry segments from a file, and has the capability of adapting the background mesh based on a spacing field generated from solution data or some other arbitrary source. By combining multiple approaches to the grid generation …
Comparison Of Two Methods For Two Dimensional Unstructured Mesh Adaptation With Elliptic Smoothing, Matthew David O'Connell
Comparison Of Two Methods For Two Dimensional Unstructured Mesh Adaptation With Elliptic Smoothing, Matthew David O'Connell
Masters Theses and Doctoral Dissertations
A new mesh adaptation method for unstructured grids is presented. The technique uses virtual control volumes that are iteratively manipulated to conform the mesh to match either a Riemannianmetric tensor field or an equal distribution of scalar weights. Forcing functions similar to those used for structured grids are employed such that the resulting meshes can be compared with those generated using the new adaptation method. Several test cases using analytic functions to drive the mesh adaptation are also presented and compared with the new method. Mesh adaptation results driven by computed flow field information are also compared to those adapted …
Unstructured Grid Technologies For Hydrodynamic Applications With Bodies In Relative Motion And Mesh Deformation, Lei Ji
Masters Theses and Doctoral Dissertations
Unstructured grid technologies for hydrodynamic applications with bodies in relative motion and mesh deformation are presented. A parallel universal mesh deformation scheme is developed to manage deforming surface and volume grids for both aerodynamic and hydrodynamic applications. The approach is universal and independent of grid type. Also, it requires minimal inter-processor communication and is thus perfectly suitable to a parallel platform. The original scheme of Allen (2006) has difficulty deforming volume grids in regions near concave geometry features and for abrupt grid resolution changes. Several modifications are proposed to overcome these problems. Grid quality can be improved significantly by adding …
Winslow Elliptic Smoothing Equations Extended To Apply To General Regions Of An Unstructured Mesh, James Steven Masters
Winslow Elliptic Smoothing Equations Extended To Apply To General Regions Of An Unstructured Mesh, James Steven Masters
Masters Theses and Doctoral Dissertations
In any engineering endeavor, it is important to have the ability to efficiently and intelligently break up a region of interest in order to explore and investigate the interesting and dynamic aspects of the system enclosed in the region. In the field of fluid mechanics - and, in particular, computational fluid dynamics - this region breakup (known as discretization) has traditionally been done using structured meshes but, because of their flexibility with capturing real-world geometry, unstructured meshes are being increasingly utilized. Not surprisingly, techniques that have traditionally been reserved for structured meshes are migrating to the world of unstructured meshing …
Fully Anisotropic Split-Tree Adaptive Refinement Mesh Generation Using Tetrahedral Mesh Stitching, Vincent Charles Betro
Fully Anisotropic Split-Tree Adaptive Refinement Mesh Generation Using Tetrahedral Mesh Stitching, Vincent Charles Betro
Masters Theses and Doctoral Dissertations
Due to the myriad of geometric topologies that modern computational fluid dynamicists desire to mesh and run solutions on, the need for a robust Cartesian Mesh Generation algorithm is paramount. Not only do Cartesian meshes require less elements and often help resolve flow features but they also allow the grid generator to have a great deal of control in so far as element aspect ratio, size, and gradation. Fully Anisotropic Split-Tree Adaptive Refinement (FASTAR) is a code that allows the user to exert a great deal of control and ultimately generate a valid, geometry conforming mesh. Due to the split-tree …
A Hybrid Method For Flows In Local Chemical Equilibrium And Nonequilibrium, Nicholas G. Currier
A Hybrid Method For Flows In Local Chemical Equilibrium And Nonequilibrium, Nicholas G. Currier
Masters Theses and Doctoral Dissertations
The primary objective of this work is to develop a more efficient chemically active compressible Euler equation solver. Currently, a choice between the physical accuracy of a finite-rate solver or the computational efficiency of an equilibrium flow solver must be made. The number of species modeled continues to increase with available computational resources. A method of further leveraging the increase in computational power is desired. The hybrid chemistry scheme proposed here attempts to maintain the accuracy of finite-rate schemes while retaining some of the cost savings associated with equilibrium chemistry solvers. The method given uses a full finite-rate flux in …
A Numerical Investigation Of S-Duct Flows With Boundary-Layer Ingestion, Benjamin C. Johnson
A Numerical Investigation Of S-Duct Flows With Boundary-Layer Ingestion, Benjamin C. Johnson
Masters Theses and Doctoral Dissertations
The essence of this paper is to report the computational research conducted to further NASA's study of active flow control systems for a flush-mounted inlet with significant boundary-layer ingestion (BLI). In conjunction with a NASA-sponsored research grant, the aim is to further accumulate knowledge and insight on the effectiveness of flow control devices in reducing circumferential distortion. Using Computational Fluid Dynamics (CFD), this study seeks to validate wind tunnel results recorded by the NASA Langley Research Center. After numerically reproducing experimental data, the future goal is use CFD to simulate the interaction between the inlet and turbofan stage. This study …
Sonic Boom Prediction Methods Using Feature-Based Adaptation Of Unstructured Meshes, Jacob Chackasseril Varghese
Sonic Boom Prediction Methods Using Feature-Based Adaptation Of Unstructured Meshes, Jacob Chackasseril Varghese
Masters Theses and Doctoral Dissertations
This study examines the improvement of near-field sonic boom prediction of an inviscid supersonic configuration using two grid generation refinement procedures. The first method uses P_HUGG, a parallel hierarchical Cartesian mesh generation algorithm to generate a volume mesh, with the solution-based mesh adaptation capability of P_HUGG being exploited. The mesh quality was improved using P_OPT, a parallel optimization-based mesh-smoothing program. In the second method, the commercially-available software POINTWISE™ is used for volume mesh generation. Then, P_REFINE, a parallel subdivision refinement code, is used t o adaptively refine the mesh. The effectiveness of capturing far field shocks was examined using TENASI, …