123 research outputs found
sBOOM Propagation for the Third AIAA Sonic Boom Prediction Workshop
No abstract availabl
A Domain-Decomposed Multilevel Method for Adaptively Refined Cartesian Grids with Embedded Boundaries
Preliminary verification and validation of an efficient Euler solver for adaptively refined Cartesian meshes with embedded boundaries is presented. The parallel, multilevel method makes use of a new on-the-fly parallel domain decomposition strategy based upon the use of space-filling curves, and automatically generates a sequence of coarse meshes for processing by the multigrid smoother. The coarse mesh generation algorithm produces grids which completely cover the computational domain at every level in the mesh hierarchy. A series of examples on realistically complex three-dimensional configurations demonstrate that this new coarsening algorithm reliably achieves mesh coarsening ratios in excess of 7 on adaptively refined meshes. Numerical investigations of the scheme's local truncation error demonstrate an achieved order of accuracy between 1.82 and 1.88. Convergence results for the multigrid scheme are presented for both subsonic and transonic test cases and demonstrate W-cycle multigrid convergence rates between 0.84 and 0.94. Preliminary parallel scalability tests on both simple wing and complex complete aircraft geometries shows a computational speedup of 52 on 64 processors using the run-time mesh partitioner
Cartesian Mesh Simulations and Farfield Propagation Results
No abstract availabl
Cartesian Mesh Simulations for the 3rd AIAA Sonic Boom Prediction Workshop
No abstract availabl
Simulation-Based Height of Burst Map for Asteroid Airburst Damage Prediction
Entry and breakup models predict that airburst in the Earth's atmosphere is likely for asteroids up to approximately 200 meters in diameter. Objects of this size can deposit over 250 megatons of energy into the atmosphere. Fast-running ground damage prediction codes for such events rely heavily upon methods developed from nuclear weapons research to estimate the damage potential for an airburst at altitude. (Collins, 2005; Mathias, 2017; Hills and Goda, 1993). In particular, these tools rely upon the powerful yield scaling laws developed for point-source blasts that are used in conjunction with a Height of Burst (HOB) map to predict ground damage for an airburst of a specific energy at a given altitude. While this approach works extremely well for yields as large as tens of megatons, it becomes less accurate as yields increase to the hundreds of megatons potentially released by larger airburst events. This study revisits the assumptions underlying this approach and shows how atmospheric buoyancy becomes important as yield increases beyond a few megatons. We then use large-scale three-dimensional simulations to construct numerically generated height of burst maps that are appropriate at the higher energy levels associated with the entry of asteroids with diameters of hundreds of meters. These numerically generated HOB maps can then be incorporated into engineering methods for damage prediction, significantly improving their accuracy for asteroids with diameters greater than 80-100 m
Characterization of Space Shuttle Ascent Debris Aerodynamics Using CFD Methods
An automated Computational Fluid Dynamics process for determining the aerodynamic Characteristics of debris shedding from the Space Shuttle Launch Vehicle during ascent is presented. This process uses Cartesian fully-coupled, six-degree-of-freedom simulations of isolated debris pieces in a Monte Carlo fashion to produce models for the drag and crossrange behavior over a range of debris shapes and shedding scenarios. A validation of the Cartesian methods against ballistic range data for insulating foam debris shapes at flight conditions, as well as validation of the resulting models, are both contained. These models are integrated with the existing shuttle debris transport analysis software to provide an accurate and efficient engineering tool for analyzing debris sources and their potential for damage
Design of Rail Instrumentation for Wind Tunnel Sonic Boom Measurements and Computational-Experimental Comparisons
An innovative pressure rail concept for wind tunnel sonic boom testing of modern aircraft configurations with very low overpressures was designed with an adjoint-based solution-adapted Cartesian grid method. The computational method requires accurate free-air calculations of a test article as well as solutions modeling the influence of rail and tunnel walls. Specialized grids for accurate Euler and Navier-Stokes sonic boom computations were used on several test articles including complete aircraft models with flow-through nacelles. The computed pressure signatures are compared with recent results from the NASA 9- x 7-foot Supersonic Wind Tunnel using the advanced rail design
Three-Dimensional Adaptive Grid Computation with Conservative, Marker-Based Tracking for Interfacial Fluid Dynamics
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76614/1/AIAA-2006-1523-676.pd
MgB2 superconducting thin films with a transition temperature of 39 Kelvin
We report the growth of high-quality c-axis-oriented epitaxial MgB2 thin
films by using a pulsed laser deposition technique. The thin films grown on
(1`1 0 2) Al2O3 substrates show a Tc of 39 K. The critical current density in
zero field is ~ 6 x 10^6 A/cm2 at 5 K and ~ 3 x 10^5 A/cm^2 at 35 K, suggesting
that this compound has great potential for electronic device applications, such
as microwave devices and superconducting quantum interference devices. For the
films deposited on Al2O3, X-ray diffraction patterns indicate a highly
c-axis-oriented crystal structure perpendicular to the substrate surface.Comment: 3 pages and 3 figure
Second Order Accurate Schemes for Magnetohydrodynamics With Divergence-Free Reconstruction
In this paper we study the problem of divergence-free numerical MHD and show
that the work done so far still has four key unresolved issues. We resolve
those issues in this paper. The problem of reconstructing MHD flow variables
with spatially second order accuracy is also studied. The other goal of this
paper is to show that the same well-designed second order accurate schemes can
be formulated for more complex geometries such as cylindrical and spherical
geometry. Being able to do divergence-free reconstruction in those geometries
also resolves the problem of doing AMR in those geometries. The resulting MHD
scheme has been implemented in Balsara's RIEMANN framework for parallel,
self-adaptive computational astrophysics. The present work also shows that
divergence-free reconstruction and the divergence-free time-update can be done
for numerical MHD on unstructured meshes. All the schemes designed here are
shown to be second order accurate. Several stringent test problems are
presented to show that the methods work, including problems involving high
velocity flows in low plasma-b magnetospheric environments.Comment: 85 pages, 6 figure
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