3,826 research outputs found
Averaged initial Cartesian coordinates for long lifetime satellite studies
A set of initial Cartesian coordinates, which are free of ambiguities and resonance singularities, is developed to study satellite mission requirements and dispersions over long lifetimes. The method outlined herein possesses two distinct advantages over most other averaging procedures. First, the averaging is carried out numerically using Gaussian quadratures, thus avoiding tedious expansions and the resulting resonances for critical inclinations, etc. Secondly, by using the initial rectangular Cartesian coordinates, conventional, existing acceleration perturbation routines can be absorbed into the program without further modifications, thus making the method easily adaptable to the addition of new perturbation effects. The averaged nonlinear differential equations are integrated by means of a Runge Kutta method. A typical step size of several orbits permits rapid integration of long lifetime orbits in a short computing time
Optimal hybrid propulsion systems thrust trajectories in a patched-conic N-body force field
Euler-Lagrange equations for approximating optimal thrust trajectories for limited hybrid propulsion system in N-body dynamic environmen
An influence coefficient method for the application of the modal technique to wing flutter suppression of the DAST ARW-1 wing
The methods used to compute the mass, structural stiffness, and aerodynamic forces in the form of influence coefficient matrices as applied to a flutter analysis of the Drones for Aerodynamic and Structural Testing (DAST) Aeroelastic Research Wing. The DAST wing was chosen because wind tunnel flutter test data and zero speed vibration data of the modes and frequencies exist and are available for comparison. A derivation of the equations of motion that can be used to apply the modal method for flutter suppression is included. A comparison of the open loop flutter predictions with both wind tunnel data and other analytical methods is presented
Requirements for Kalman filtering on the GE-701 whole word computer
The results of a study to determine scaling, storage, and word length requirements for programming the Kalman filter on the GE-701 Whole Word Computer are reported. Simulation tests are presented which indicate that the Kalman filter, using a square root formulation with process noise added, utilizing MLS, radar altimeters, and airspeed as navigation aids, may be programmed for the GE-701 computer to successfully navigate and control the Boeing B737-100 during landing approach, landing rollout, and turnoff. The report contains flow charts, equations, computer storage, scaling, and word length recommendations for the Kalman filter on the GE-701 Whole Word computer
Research in orbit determination optimization for space trajectories
Research data covering orbit determination, optimization techniques, and trajectory design for manned space flights are summarized
A study of the optimization method used in the NAVY/NASA gas turbine engine computer code
Sources of numerical noise affecting the convergence properties of the Powell's Principal Axis Method of Optimization in the NAVY/NASA gas turbine engine computer code were investigated. The principal noise source discovered resulted from loose input tolerances used in terminating iterations performed in subroutine CALCFX to satisfy specified control functions. A minor source of noise was found to be introduced by an insufficient number of digits in stored coefficients used by subroutine THERM in polynomial expressions of thermodynamic properties. Tabular results of several computer runs are presented to show the effects on program performance of selective corrective actions taken to reduce noise
Density and spin response function of a normal Fermi gas at unitarity
Using Landau theory of Fermi liquids we calculate the dynamic response of
both a polarized and unpolarized normal Fermi gas at zero temperature in the
strongly interacting regime of large scattering length. We show that at small
excitation energies the {\it in phase} (density) response is enhanced with
respect to the ideal gas prediction due to the increased compressibility.
Viceversa, the {\it out of phase} (spin) response is quenched as a consequence
of the tendency of the system to pair opposite spins. The long wavelength
behavior of the static structure factor is explicitly calculated. The results
are compared with the predictions in the collisional and superfluid regimes.
The emergence of a spin zero sound solution in the unpolarized normal phase is
explicitly discussed.Comment: 4 pages, 2 figure
Automated landing, rollout, and turnoff using MLS and magnetic cable sensors
A description of the simulation program used to study the landing approach, rollout and turnoff of the B737-100 aircraft utilizing MLS and a buried magnetic leader cable as navigation aids is presented. Simulation results are given and show the concept to be both feasible and practical for commercial type aircraft terminal area control
Self-consistent calculation of particle-hole diagrams on the Matsubara frequency: FLEX approximation
We implement the numerical method of summing Green function diagrams on the
Matsubara frequency axis for the fluctuation exchange (FLEX) approximation. Our
method has previously been applied to the attractive Hubbard model for low
density. Here we apply our numerical algorithm to the Hubbard model close to
half filling (), and for , in order to study the
dynamics of one- and two-particle Green functions. For the values of the chosen
parameters we see the formation of three branches which we associate with the a
two-peak structure in the imaginary part of the self-energy. From the imaginary
part of the self-energy we conclude that our system is a Fermi liquid (for the
temperature investigated here), since Im
around the chemical potential. We have compared our fully self-consistent FLEX
solutions with a lower order approximation where the internal Green functions
are approximated by free Green functions. These two approches, i.e., the fully
selfconsistent and the non-selfconsistent ones give different results for the
parameters considered here. However, they have similar global results for small
densities.Comment: seven pages, nine figures as ps files. Accepted in Int. J. Modern
Phys. C (1997
Low thrust interplanetary trajectory open loop error analysis, volume 1 Final report
Computer program for open-loop error analysis of low thrust interplanetary trajectorie
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