39,718 research outputs found
Whirl and Stall Flutter Simulation Using CFD
This paper presents recent research on numerical methods for whirl and stall flutter using computational
fluid dynamics. The method involves coupling of the HMB3 CFD solver of the University of
Glasgow and a NASTRAN derived structural model. Based upon a literature survey, a significant amount
of research has been conducted on the numerical investigation of tiltrotors, with a focus on the XV-15
and V-22 aircraft. Within this paper, the coupling procedure is presented along with a steady CFD computation
to highlight the accuracy of the high-fidelity method. In addition to this, a simple method is used
to investigate the whirl flutter boundary of a standard propeller and the XV-15 blade
Simple pressure gauge for uranium hexafluoride
A sensitive detector and pressure gauge for uranium hexafluoride in high‐vacuum systems is described. Negative surface ionization of UF_6 occurs on ribbon filaments operated at temperatures too low for electron emission to be significant. The ion current measured on a cylindrical collector surrounding the filament assembly varies regularly with UF_6 pressure below 10^(−3) Torr. Different filament materials are considered, including rhenium, thoriated tungsten, and platinum. Rhenium is found to be the most satisfactory material for operation of diode emitters as a pressure gauge. Gauge constants (in A Torr^(−1)) are derived from comparing negative surface ionization currents with the response of a capacitance manometer and are shown to be independent of temperature within a reasonable operating range. The effects of exposing the rhenium filament to various gases is considered, and it is shown that brief exposure to acetylene substantially improves the operating characteristics of the gauge
Autonomous integrated GPS/INS navigation experiment for OMV. Phase 1: Feasibility study
The phase 1 research focused on the experiment definition. A tightly integrated Global Positioning System/Inertial Navigation System (GPS/INS) navigation filter design was analyzed and was shown, via detailed computer simulation, to provide precise position, velocity, and attitude (alignment) data to support navigation and attitude control requirements of future NASA missions. The application of the integrated filter was also shown to provide the opportunity to calibrate inertial instrument errors which is particularly useful in reducing INS error growth during times of GPS outages. While the Orbital Maneuvering Vehicle (OMV) provides a good target platform for demonstration and for possible flight implementation to provide improved capability, a successful proof-of-concept ground demonstration can be obtained using any simulated mission scenario data, such as Space Transfer Vehicle, Shuttle-C, Space Station
Parallel Performance for a Real Time Lattice Boltzmann Code
The paper will present the details of a Lattice Boltzmann solver running in real time for unsteady
wake computations. In addition to algorithmic implementation, computational results, single
core and parallel optimization of the methods are also discussed
Multichannel calculation of excited vector resonances and the
A multichannel calculation of excited states is
carried out within a generalization of the Resonance-Spectrum Expansion, which
may shed light on the classification of the resonance, discovered
by BABAR and originally denoted X(2175). In this framework, a complete spectrum
of bare states is coupled to those OZI-allowed decay channels that
should be most relevant for the considered energy range. The included - and
-wave two-meson channels comprise the lowest pseudoscalar, vector, scalar,
and axial-vector mesons, while in the sector both the and
states are coupled. The only two free parameters are tuned so as to
reproduce mass and width of the , but come out reasonably close to
previously used values. Among the model's -matrix poles, there are good
candidates for observed resonances, as well other ones that should exist
according to the quark model. Besides the expected resonances as unitarized
confinement states, a dynamical resonance pole is found at MeV.
The huge width makes its interpretation as the somewhat dubious,
but further improvements of the model may change this conclusion.Comment: 6 pages, 5 figures, RevTex4; v2: very recent experimental result,
some extra discussion, and 2 references added; v3: 3 new figures, 2 new
equations, and some rephrasing; version accepted for publication in Phys.
Rev.
Nuclear Magnetohydrodynamic EMP, Solar Storms, and Substorms
In addition to a fast electromagnetic pulse (EMP), a high altitude nuclear
burst produces a relatively slow magnetohydrodynarnic EMP (MHD EMP), whose
effects are like those from solar storm geomagnetically induced currents (SS
GIC). The MHD EMP electric field E < 10^-1 V/m and lasts < 10^2 sec, whereas
for solar storms E > 10^-2 V/m and lasts >10^3 sec. Although the solar storm
electric field is lower than MHD EMP, the solar storm effects are generally
greater due to their much longer duration. Substorms produce much smaller
effects than SS GIC, but occur much more frequently. This paper describes the
physics of such geomagnetic disturbances and analyzes their effects.Comment: 29 pages, 14 figures, 5 table
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