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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

System identification and controller design using experimental frequency response data

Recent findings from modeling and controller design for the NASA-Marshall Single Structure Control Facility have raised questions regarding the ability of modern control design techniques and modern modeling techniques to deal effectively with the stringent modeling and control design requirements of Large Space Structure Control. A brief and general discussion is presented of the results of studies into the modeling and control issues performed under sponsorship of the NASA/ASEE Summer Faculty Fellowship Program. Several issues are addressed. The first is a study of a modeling technique based on least squares identification of individual transfer functions from measured frequency response data. The second is a study of multiobjective optimization techniques applied to the modeling, or system identification, problem. The third issue is a study into the question of whether multiobjective optimization approaches can be effectively used for control system design using only frequency response data, thereby bypassing the difficult modeling problem. The last issue studied involves the resolution of seeming discrepancies between predicted and measured control computer time delays in the Single Structure Control Facility.

Irwin, R. Dennis↗
NASA NTRS1981

Frequency response of the vestibulo-ocular reflex /VOR/ in the monkey

The frequency response of the vestibulo-ocular reflex has been investigated in the alert monkey during sinusoidal rotation about a vertical axis in a frequency range of 0.001-0.5 Hz. Phase and gain of nystagmus slow phase velocity was determined. In the frequency range above 0.1 Hz, nystagmus slow phase velocity was in phase with (compensated for) head velocity. At lower frequencies, an increasing phase lead was present which could reach more than 90 deg. Gain fell off correspondingly at low frequencies. Calculated time constants were 10-40 s in different monkeys. Animals which had been exposed to numerous previous rotary stimuli in the laboratory showed much shorter time constants than did 'native' monkeys.

Buettner, U. W.↗
NASA NTRS1981

Pitfalls and guidelines for the numerical evaluation of moderate-order system frequency response

The design and evaluation of a feedback control system via frequency response methods relies heavily upon numerical methods. In application, one can usually develop low order simulation models which for the most part are devoid of numerical problems. However, when complex feedback interactions, for example, between instrument control systems and their flexible mounting structure, must be evaluated, simulation models become moderate to large order and numerical problems become common. A large body of relevant numerical error analysis literature is summarized in a large language understandable to nonspecialists. The intent is to provide engineers using simulation models with an engineering feel for potential numerical problems without getting intertwined in the complexities of the associated mathematical theory. Guidelines are also provided by suggesting alternate state of the art methods which have good numerical evaluation characteristics.

Frisch, H. P.↗
NASA NTRS1985

Frequency response of a jet engine test facility air supply system

The frequency response of a laboratory scale model of a portion of the air supply system of an engine test facility is obtained both experimentally and using one-dimensional, small-signal, distributed parameter theory. The effects of line terminations and mean flow are considered. Good agreement between experiment and theory is obtained. Predictions are extended to a full scale test facility air supply system operating under several possible test conditions.

Franke, M. E.↗
NASA NTRS1980

Frequency response fo multiple-sampling rate systems

Analytical procedure simplifies prediction of frequency response of multirate digital control systems. Although developed for Space Shuttle flightcontrol system, procedure is applicable to any multirate system describable by linear, constant-coefficient differential equations of difference equations.

Scharmack, D. K.↗
NASA NTRS1980

Extending the operating temperature, wavelength and frequency response of HgCdTe heterodyne detectors

Near ideal optical heterodyne performance was obtained at GHz IF frequencies in the 10 micrometer wavelength region with liquid nitrogen cooled HgCdTe photodiodes. Heterodyne NEP's as low as 2.7 x 10 to the minus 20th power W/Hz at 100MHz, 5.4 x 10 to the minus 20th power W/Hz at 1.5 GHz, and 9.4 x 19 to the minus 20th power W/Hz at 3 GHz were achieved. Various physical phenomena which occur within a photodiode and affect heterodyne operation were examined in order to assess the feasibility of extending the operating temperature, wavelength, and frequency response of these HgCdTe photomixers.

Spears, D. L.↗
NASA NTRS1975

Effect of varying differentiator frequency response on recorded peak dP/dt

Dogs were used to study the effects of varying the differentiator cutoff frequency on the recorded peak first derivative of left ventricular pressure with respect to time (dP/dt), using high-precision solid-state pressure transducers and recording equipment. In canine hearts with a basic periodicity of 1 to 3 Hz, the differentiator frequency response required to record an accurate peak dP/dt is found to be influenced by the value of peak dP/dt. At peak dP/dt ranging from 1500 to 9000 mm Hg/sec (200 and 1200 kPa/sec), a differentiator cutoff frequency of at least 90 Hz was required to record accurately peak dP/dt.

Barry, W. H.↗
NASA NTRS1986

Real-time open-loop frequency response analysis of flight test data

A technique has been developed to compare the open-loop frequency response of a flight test aircraft real time with linear analysis predictions. The result is direct feedback to the flight control systems engineer on the validity of predictions and adds confidence for proceeding with envelope expansion. Further, gain and phase margins can be tracked for trends in a manner similar to the techniques used by structural dynamics engineers in tracking structural modal damping.

Bosworth, J. T.↗