2,629 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
Statement of James Perley and Mary Burgan Before the Commission on the Future of Worker-Management Relations
Testimony_Perley_and_Burgan_081094.pdf: 197 downloads, before Oct. 1, 2020
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
The EVLA: Prospects for HI
To continue the unparalleled success of the Very Large Array (VLA) for radio
astronomy, the facility is currently being converted to become the 'Expanded
VLA' (EVLA). The EVLA will radically improve the VLA in order to cover the full
0.93-50 GHz radio wavelength range without gaps, provide up to an order of
magnitude better sensitivity, and to allow observations at much larger
bandwidths and spectral resolution as currently possible. For observations of
the 21 cm line of atomic neutral hydrogen (HI), the EVLA offers thousands of
km/s velocity coverage at sub-km/s resolution for targeted observations as well
as an improved spectral baseline stability. In addition, every L-band (21 cm)
continuum or targeted HI observation can be set-up to simultaneously observe a
full z=0-0.53 HI redshift survey at a velocity resolution of a few km/s. In
turn, every HI observation will also yield deep radio continuum images of the
field. These synergies will deliver a wealth of data which opens up a wide
'discovery space' to study the details of galaxy evolution and cosmology.Comment: to appear in the proceedings to the conference: "The Evolution of
Galaxies through the Neutral Hydrogen Window", Arecibo, PR, US
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
Burst of the Century? A Case Study of the Afterglow of Nearby Ultra-Bright GRB 130427A
GRB 130427A is the brightest gamma-ray burst observed by any satellite in almost
30 years and one of the most thoroughly observed. I will present a summary of the
worldwide campaign to monitor the afterglow of this event from GHz to TeV energies
and from seconds to years after the explosion. Remarkably, the entire data set can be
described to good agreement using standard synchrotron afterglow theory, providing
strong support for the validity the basic model in describing the evolution of this event
and for GRB afterglows generally. Distinct forward and reverse shock components are
resolved in both the SED and multifrequency light curves; the late-time high-energy
emission seen by LAT is produced by the forward shock. We also infer a tenuous,
wind-stratified medium surrounding this burst, suggesting a massive, low-metallicity
progenitor. While GRB 130427A was an incredibly rare and fortuitous event its
properties are probably not intrinsically unusual, and it provides lessons for what
might be routinely achieved in the future with faster and deeper multiwavelength
follow-up of gamma-ray bursts
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