45,975 research outputs found
Prediction of the flow-field interference induced by the long-range laser velocimeter in the Ames 40- by 80-foot and the 80- by 120-foot wind tunnels
The predicted flow disturbances induced in the test sections of the Ames 40- by 80-Foot Wind Tunnels by the presence of the Long-Range Laser Velocimeter (LRLV) are presented. The predictions were made using a potential-flow paneling code to model the test section and the LRLV, and a calculation of the resulting flow field was made. The flow velocity and angularity were calculated at numerous locations in the flow field relative to the LRLV, and the results are presented
Iron line profiles including emission from within the innermost stable orbit of a black hole accretion disc
Reynolds & Begelman (1997) have recently proposed a model in which the broad
and extremely redshifted iron line seen during a deep minimum of the light
curve of the Seyfert 1 galaxy MCG-6-30-15 originates from matter spiralling
into a Schwarzschild black hole, contrary to previous claims that the black
hole may be spinning rapidly (Iwasawa et al 1996; Dabrowski et al 1997). Here
we calculate in detail the X-ray spectrum produced by their model using the
full reflected continuum emission, including absorption features. This
calculation takes into account the doppler and relativistic effects. For the
range of parameters we consider, we find that the spectrum should show a large
photoelectric absorption edge of iron, which is not seen in the data. The
absorption edge is a consequence of the line emitting matter within the
innermost stable orbit being highly ionized, and is largely independent of the
parameters chosen for their model. If we restrict our attention to the 3-10 keV
band we may effectively remove this absorption edge by fitting a steeper power
law, but this results in a significant underprediction of the 0.4-0.5 keV flux.
We conclude that the data on MCG-6-30-15 are more consistent with the Kerr than
the Schwarzschild model.Comment: 5 pages with 5 postscript figures. Accepted for publication in MNRA
A numerical simulation of the NFAC (National Full-scale Aerodynamics Complex) open-return wind tunnel inlet flow
The flow into an open return wind tunnel inlet was simulated using Euler equations. An explicit predictor-corrector method was employed to solve the system. The calculation is time-accurate and was performed to achieve a steady-state solution. The predictions are in reasonable agreement with the experimental data. Wall pressures are accurately predicted except in a region of recirculating flow. Flow-field surveys agree qualitatively with laser velocimeter measurements. The method can be used in the design process for open return wind tunnels
Motion of buoyant particles and coarsening of solid-liquid mixtures in a random acceleration field
Flow induced by a random acceleration field (g-jitter) is considered in two
related situations that are of interest for microgravity fluid experiments: the
random motion of an isolated buoyant particle and coarsening of a solid-liquid
mixture. We start by analyzing in detail actual accelerometer data gathered
during a recent microgravity mission, and obtain the values of the parameters
defining a previously introduced stochastic model of this acceleration field.
We then study the motion of a solid particle suspended in an incompressible
fluid that is subjected to such random accelerations. The displacement of the
particle is shown to have a diffusive component if the correlation time of the
stochastic acceleration is finite or zero, and mean squared velocities and
effective diffusion coefficients are obtained explicitly. Finally, the effect
of g-jitter on coarsening of a solid-liquid mixture is considered. Corrections
due to the induced fluid motion are calculated, and estimates are given for
coarsening of Sn-rich particles in a Sn-Pb eutectic fluid, experiment to be
conducted in microgravity in the near future.Comment: 25 pages, 4 figures (included). Also at
http://www.scri.fsu.edu/~vinals/ross2.p
Fast Mesh Refinement in Pseudospectral Optimal Control
Mesh refinement in pseudospectral (PS) optimal control is embarrassingly easy
--- simply increase the order of the Lagrange interpolating polynomial and
the mathematics of convergence automates the distribution of the grid points.
Unfortunately, as increases, the condition number of the resulting linear
algebra increases as ; hence, spectral efficiency and accuracy are lost in
practice. In this paper, we advance Birkhoff interpolation concepts over an
arbitrary grid to generate well-conditioned PS optimal control discretizations.
We show that the condition number increases only as in general, but
is independent of for the special case of one of the boundary points being
fixed. Hence, spectral accuracy and efficiency are maintained as increases.
The effectiveness of the resulting fast mesh refinement strategy is
demonstrated by using \underline{polynomials of over a thousandth order} to
solve a low-thrust, long-duration orbit transfer problem.Comment: 27 pages, 12 figures, JGCD April 201
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