1,316 research outputs found
Kaman 40 kW wind turbine generator - control system dynamics
The generator design incorporates an induction generator for application where a utility line is present and a synchronous generator for standalone applications. A combination of feed forward and feedback control is used to achieve synchronous speed prior to connecting the generator to the load, and to control the power level once the generator is connected. The dynamics of the drive train affect several aspects of the system operation. These were analyzed to arrive at the required shaft stiffness. The rotor parameters that affect the stability of the feedback control loop vary considerably over the wind speed range encountered. Therefore, the controller gain was made a function of wind speed in order to maintain consistent operation over the whole wind speed range. The velocity requirement for the pitch control mechanism is related to the nature of the wind gusts to be encountered, the dynamics of the system, and the acceptable power fluctuations and generator dropout rate. A model was developed that allows the probable dropout rate to be determined from a statistical model of wind gusts and the various system parameters, including the acceptable power fluctuation
High-Fidelity VLA Imaging of the Radio Structure of 3C273
3C273, the nearest bright quasar, comprises a strong nuclear core and a
bright, one-sided jet extending ~ 23 arcseconds to the SW. The source has been
the subject of imaging campaigns in all wavebands. Extensive observations of
this source have been made with the Very Large Array and other telescopes as
part of a campaign to understand the jet emission mechanisms. Partial results
from the VLA radio campaign have been published, but to date, the complete set
of VLA imaging results has not been made available. We have utilized the VLA to
determine the radio structure of 3C273 in Stokes I, Q, and U, over the widest
possible frequency and resolution range. The VLA observed the source in all
four of its configurations, and with all eight of its frequency bands, spanning
73.8 MHz to 43 GHz. The data were taken in a pseudo-spectral line mode to
minimize the VLA's correlator errors, and were fully calibrated with subsequent
self-calibration techniques to maximise image fidelity. Images in Stokes
parameters I, Q, and U, spanning a resolution range from 6 arcseconds to 88
milliarcseconds are presented. Spectral index images, showing the evolution of
the jet component are shown. Polarimetry demonstrates the direction of the
magnetic fields responsible for the emission, and rotation measure maps show
the RM to be very small with no discernible trend along or across the jet. This
paper presents a small subset of these images to demonstrate the major
characteristics of the source emission. A library of all ~500 images has been
made available for open, free access by interested parties.Comment: 9 pages, 17 figure
Design study of a feedback control system for the Multicyclic Flap System rotor (MFS)
The feasibility of automatically providing higher harmonic control to a deflectable control flap at the tip of a helicopter rotor blade through feedback of selected independent parameter was investigated. Control parameters were selected for input to the feedback system. A preliminary circuit was designed to condition the selected parameters, weigh limiting factors, and provide a proper output signal to the multi-cyclic control actuators. Results indicate that feedback control for the higher harmonic is feasible; however, design for a flight system requires an extension of the present analysis which was done for one flight condition - 120 kts, 11,500 lbs gross weight and level flight
Alien Registration- Miller, Perley R. (Millinocket, Penobscot County)
https://digitalmaine.com/alien_docs/7728/thumbnail.jp
VLA Observations of the Gravitational Lens System Q2237+0305
We report observations of the four-image gravitational lens system Q2237+0305
with the VLA at 20 cm and 3.6 cm. The quasar was detected at both frequencies
(\approx 0.7 mJy) with a flat spectrum. All four lensed images are clearly
resolved at 3.6 cm, and the agreement of the radio and optical image positions
is excellent. No radio emission is detected from the lensing galaxy, and any
fifth lensed quasar image must be fainter than \sim 20% of the A image flux
density. Since the optical quasar images are variable and susceptible to
extinction, radio flux ratios provide the best measurement of the macrolensing
magnification ratios. The radio B/A and C/A image flux ratios are consistent
with the observed range of optical variations, but the D/A ratio is
consistently higher in the radio than in the optical. The radio ratios are
consistent with magnification ratios predicted by lens models, and weaken
alternative interpretations for Q2237+0305. More accurate radio ratios can
distinguish between the models, as well as improve our understanding of both
microlensing and extinction in this system.Comment: 1 postscript file, 13 pages. To appear in AJ (1996.09), Submitted
1996.03.13, Accepted 1996.05.2
Gamma-ray Bursts, Classified Physically
From Galactic binary sources, to extragalactic magnetized neutron stars, to
long-duration GRBs without associated supernovae, the types of sources we now
believe capable of producing bursts of gamma-rays continues to grow apace. With
this emergent diversity comes the recognition that the traditional (and newly
formulated) high-energy observables used for identifying sub-classes does not
provide an adequate one-to-one mapping to progenitors. The popular
classification of some > 100 sec duration GRBs as ``short bursts'' is not only
an unpalatable retronym and syntactically oxymoronic but highlights the
difficultly of using what was once a purely phenomenological classification to
encode our understanding of the physics that gives rise to the events. Here we
propose a physically based classification scheme designed to coexist with the
phenomenological system already in place and argue for its utility and
necessity.Comment: 6 pages, 3 figures. Slightly expanded version of solicited paper to
be published in the Proceedings of ''Gamma Ray Bursts 2007,'' Santa Fe, New
Mexico, November 5-9. Edited by E. E. Fenimore, M. Galassi, D. Palme
A new technique to improve RFI suppression in radio interferometers
Radio interferometric observations are less susceptible to radio frequency
interference (RFI) than single dish observations. This is primarily due to :
(1)fringe-frequency averaging at the correlator output and (2) bandwidth
decorrelation of broadband RFI. Here, we propose a new technique to improve RFI
suppression of interferometers by replacing the fringe-frequency averaging
process with a different filtering process. In the digital implementation of
the correlator, such a filter should have cutoff frequencies times
the frequency at which the baseband signals are sampled. We show that filters
with such cutoff frequencies and attenuation 40 dB at frequencies above the
cutoff frequency can be realized using multirate filtering techniques.
Simulation of a two element interferometer system with correlator using
multirate filters shows that the RFI suppression at the output of the
correlator can be improved by 40 dB or more compared to correlators using a
simple averaging process.Comment: 12 pages, 7 figures; Invited talk given at IVS Symposium in Korea --
New Technologies in VLBI, Korea, Nov 2002; to appear in the conference
proceedings (Added answers to the questions during the discussion session
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