169,536 research outputs found
Applications of inverse simulation to a nonlinear model of an underwater vehicle
Inverse simulation provides an important alternative
to conventional simulation and to more formal
mathematical techniques of model inversion. The
application of inverse simulation methods to a nonlinear
dynamic model of an unmanned underwater vehicle with
actuator limits is found to give rise to a number of
challenging problems. It is shown that this particular
problem requires, in common with other applications that
include hard nonlinearities in the model or discontinuities
in the required trajectory, can best be approached using a
search-based optimization algorithm for inverse
simulation in place of the more conventional Newton-
Raphson approach. Results show that meaningful inverse
simulation results can be obtained but that multi-solution
responses exist. Although the inverse solutions are not
unique they are shown to generate the required
trajectories when tested using conventional forward
simulation methods
The MSFC/J70 orbital atmosphere model and the data bases for the MSFC solar activity prediction technique
The MSFC/J70 Orbital Atmospheric Density Model, a modified version of the Smithsonian Astrophysical Observatory Jacchia 1970 model is explained. The algorithms describing the MSFC/J70 model are included as well as listing of the computer program. The 13-month smoothed values of solar flux (F sub 10.7) and geomagnetic index (S sub p), which are required as inputs for the MSFC/J70 model, are also included and discussed
Rocket observations of electron-density irregularities in the equatorial ionosphere below 200 km
Nike Apache rockets carring instrumentation to measure electron density and its fine structure in the equatorial ionosphere were launched from Chilca, Peru in May and June 1975. The fine structure experiment and the data reduction system are described. Results obtained from this system are presented and compared with those obtained by VHF radar and from other rocket studies. A description of the equatorial ionosphere and its features is also presented
Transonic transport study: Economics
An economic analysis was performed to evaluate the impact of advanced materials, increased aerodynamic and structural efficiencies, and cruise speed on advanced transport aircraft designed for cruise Mach numbers of .90, .98, and 1.15. A detailed weight statement was generated by an aircraft synthesis computer program called TRANSYN-TST; these weights were used to estimate the cost to develop and manufacture a fleet of aircraft of each configuration. The direct and indirect operating costs were estimated for each aircraft, and an average return on investment was calculated for various operating conditions. There was very little difference between the operating economics of the aircraft designed for Mach numbers .90 and .98. The Mach number 1.15 aircraft was economically marginal in comparison but showed significant improvements with the application of carbon/epoxy structural material. However, the Mach .90 and Mach .98 aircraft are the most economically attractive vehicles in the study
Sensitivity analysis of the space shuttle to ascent wind profiles
A parametric sensitivity analysis of the space shuttle ascent flight to the wind profile is presented. Engineering systems parameters are obtained by flight simulations using wind profile models and samples of detailed (Jimsphere) wind profile measurements. The wind models used are the synthetic vector wind model, with and without the design gust, and a model of the vector wind change with respect to time. From these comparison analyses an insight is gained on the contribution of winds to ascent subsystems flight parameters
What can we learn from Dijet suppression at RHIC?
We present a systematic study of the dijet suppression at RHIC using the
VNI/BMS parton cascade. We examine the modification of the dijet asymmetry A_j
and the within-cone transverse energy distribution (jet-shape) along with
partonic fragmentation distributions z and j_t in terms of: qhat; the path
length of leading and sub-leading jets; cuts on the jet energy distributions;
jet cone angle and the jet-medium interaction mechanism. We find that A_j is
most sensitive to qhat and relatively insensitive to the nature of the
jet-medium interaction mechanism. The jet profile is dominated by qhat and the
nature of the interaction mechanism. The partonic fragmentation distributions
clearly show the jet modification and differentiate between elastic and
radiative+elastic modes
Design, fabrication and acoustic tests of a 36 inch (0.914 meter) statorless turbotip fan
The LF336/E is a 36 inch (0.914 meter) diameter fan designed to operate in a rotor-alone configuration. Design features required for modification of the existing LF336/A rotor-stator fan into the LF336/E statorless fan configuration are discussed. Tests of the statorless fan identified an aerodynamic performance deficiency due to inaccurate accounting of the fan exit swirl during the aerodynamic design. This performance deficiency, related to fan exit static pressure levels, produced about a 20 percent thrust loss. A study was then conducted for further evaluation of the fan exit flow fields typical of statorless fan systems. This study showed that through proper selection of fan design variables such as pressure ratio, radius ratio, and swirl distributions, performance of a statorless fan configuration could be improved with levels of thrust approaching the conventional rotor-stator fan system. Acoustic measurements were taken for the statorless fan system at both GE and NASA, and when compared to other lift fan systems, showed noise levels comparable to the quietest lift fan configuration which included rotor-stator spacing and acoustic treatment. The statorless fan system was also used to determine effects of rotor leading edge serrations on noise generations. A cascade test program identified the serration geometry based on minimum pressure losses, wake turbulence levels and noise generations
Quadruplex digital flight control system assessment
Described are the development and validation of a double fail-operational digital flight control system architecture for critical pitch axis functions. Architectural tradeoffs are assessed, system simulator modifications are described, and demonstration testing results are critiqued. Assessment tools and their application are also illustrated. Ultimately, the vital role of system simulation, tailored to digital mechanization attributes, is shown to be essential to validating the airworthiness of full-time critical functions such as augmented fly-by-wire systems for relaxed static stability airplanes
Precision orbit computations for an operational environment
Taking advantage of the improvements to the Earth's gravitation field and tracking station coordinates, an orbital computational consistency of the order of 5 meters was achieved for total position differences between orbital solutions for the Seasat and GEOS-3. The main source of error in these solutions was in the mathematical models that are required to generate these results, i.e., gravitation, atmospheric drag, etc. Different Earth gravitation fields and tracking coordinates were analyzed and evaluated in obtaining these computational results. Comparisons and evaluations of the Seasat results were obtained in terms of different solution types such as the Doppler only, Laser only, Doppler and Laser, etc. Other investigation using the Seasat data were made in order to determine their effect on the computational results at this particular level of consistency
- …