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Hahn, H.

Publications and source records attributed to Hahn, H..

6 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Simulation of a spatial, servo-hydraulic test facility for space structures

In this paper different control concepts for servo-hydraulic test facilities are derived using exact linearization techniques. Based on different linear and nonlinear models of the test table and the actuator dynamics several nonlinear controllers of different complexity are derived. The closed loop system performance of the controlled servo-hydraulic test facility is tested in various computer simulations using both, standard test signals and large test signals as system inputs. The simulation results turn out, that in case of standard input signals the test facility controller must include a linear test table mechanics model and a nonlinear servo-hydraulic actuator model. Additional simulations demonstrate the robustness of the control concept selected for standard test signals with respect to variations of plant parameters.

Leimbach, K.-D.↗
NASA NTRS1975

Sustained small oscillations in nonlinear control systems

Some results of bifurcation theory were used to study the existence of small-amplitude periodic behavior in launch vehicle dynamics, assuming that nonlinearity exists as a cubic term in the rudder response. The analysis follows closely Sattinger's (1973) approach to the theory of periodic bifurcations. The conditions under which a bifurcating branch of orbitally stable periodic solutions will exist are determined. It is shown that in more complicated cases, the conditions under which the system matrix has a pair of simple purely imaginary eigenvalues can be determined with the aid of linear stability techniques.

George, J. H.↗
NASA NTRS1972

Field dependence of gaseous-ion mobility - Theoretical tests of approximate formulas.

The approximate formulas considered include relations based on the Wannier free-flight theory, the Kihara medium-field expansion, and the Frost-Patterson interpolation formulas. A few accurate theoretical results are available for testing the foregoing formulas. Cases concerning high fields, intermediate fields, and resonant charge transfer are examined. It is found that of the formulas tested, the one based on the Wannier free-flight theory is the most flexible, since it can be used for all fields and all ion-neutral force laws and mass ratios.

Hahn, H.↗
NASA NTRS1972

Field dependence of gaseous ion mobility: Test of approximate formulas

The accuracies of three approximate formulas were tested by comparison with special cases for which accurate results could be found. The Wannier free flight theory was found to be superior, and can be extended to yield a formula without further adjustable constants that gives an exact result at low electric fields and good results at medium and high fields. It is applicable for any ion neutral force law and mass ratio.

Hahn, H.↗