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At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Applications of Phase-Based Motion Processing

Image pyramids provide useful information in determining structural response at low cost using commercially available cameras. The current effort applies previous work on the complex steerable pyramid to analyze and identify imperceptible linear motions in video. Instead of implicitly computing motion spectra through phase analysis of the complex steerable pyramid and magnifying the associated motions, instead present a visual technique and the necessary software to display the phase changes of high frequency signals within video. The present technique quickly identifies regions of largest motion within a video with a single phase visualization and without the artifacts of motion magnification, but requires use of the computationally intensive Fourier transform. While Riesz pyramids present an alternative to the computationally intensive complex steerable pyramid for motion magnification, the Riesz formulation contains significant noise, and motion magnification still presents large amounts of data that cannot be quickly assessed by the human eye. Thus, user-friendly software is presented for quickly identifying structural response through optical flow and phase visualization in both Python and MATLAB.

Branch, Nicholas A.↗
NASA NTRS1984

MTF Analysis of LANDSAT-4 Thematic Mapper

A research program to measure the LANDSAT 4 Thematic Mapper (TM) modulation transfer function (MTF) is described. Measurement of a satellite sensor's MTF requires the use of a calibrated ground target, i.e., the spatial radiance distribution of the target must be known to a resolution at least four to five times greater than that of the system under test. A small reflective mirror or a dark light linear pattern such as line or edge, and relatively high resolution underflight imagery are used to calibrate the target. A technique that utilizes an analytical model for the scene spatial frequency power spectrum will be investigated as an alternative to calibration of the scene. The test sites and analysis techniques are also described.

Schowengerdt, R.↗
NASA NTRS1989

The structural dynamics analysis of the main injector LOX inlet tee and its redesign

A ground test of a specially instrumented Space Shuttle Main Engine (SSME) revealed excessively high strains in the high pressure Liquid Oxygen (LOX) inlet line which carries LOX to the Main Injector. The inlet tee acts as a manifold which utilizes two splitter vanes to direct the flow of LOX into the main injector. When the high strains were discovered, it was thought that these splitter vanes, coupled with high energy flow was the source. This resulted not only in high strains in the LOX inlet tee, but excessive vibration at a frequency of 4000 Hz located at the gimbal bearing, and at the main injector. This was later to be known as The 4kHz Phenomenon. The dynamic analysis which was used to predict the response due to the 4kHz phenomenon and the analysis used to aid in the design modification required to the hardware to reduce or eliminate the phenomenon is examined.

Romano, E.↗
NASA NTRS1982

Preliminary investigation of effects of heavy rain on the performance of aircraft

A guideline was defined for the analysis of flight data to determine the effects of rain on the aerodynamic performance of an aircraft. It distinguishes and separates the effects of horizontal wind shears, downdrafts, gusts at the phugoid frequency, and rain based on various aerodynamic parameters. Flight data from NASA LaRC's TCV B-737 were inconclusive because precipitation rates encountered probably were not high enough. However, the guideline seemed to be valid and can be used on further flight data evaluations. Difficulties in this type of data analysis are discussed. Other indirect influences of rain on the degradation of airplane performance are also considered.

Lee, O. W. K.↗
NASA NTRS1986

Solar microwave millisecond spike at 2.84 GHz

Using the high time resolution of 1 ms, the data of solar microwave millisecond spike (MMS) event was recorded more than two hundred times at the frequency of 2.84 GHz at Beijing (Peking) Observatory since May 1981. A preliminary analysis was made. It can be seen from the data that the MMS-events have a variety of the fast activities such as the dispersed and isolated spikes, the clusters of the crowded spikes, the weak spikes superimposed on the noise background, and the phenomena of absorption. The marked differences from that observed with lower time resolution are presented. Using the data, a valuable statistical analysis was made. There are close correlations between MMS-events and hard X-ray bursts, and fast drifting bursts. The MMS events are highly dependent on the type of active regions and the magnetic field configuration. It seems to be crucial to find out the accurate positions on the active region where the MMS-events happen and to make co-operative observations at different bands during the special period when specific active regions appear on the solar disk.

Fu, Qi-Jun↗
NASA NTRS1985

Interdisciplinary design analysis of a precision spacecraft antenna

The Advanced Communications Technology Satellite (ACTS) will operate in the 20/30 GHz range (Ka Band), and will include a multi-beam antenna (MBA) capable of 0.3 degree scanning spot beams with very high beam-to-beam isolation. The antenna Radio Frequency (RF) performance requirements lead to stringent requirements on the antenna reflector surface shape. A prediction of RF performance of a potential flight model antenna reflector operating under space environmental conditions is made using a radiant heat input model (TRASYS), a thermal analyzer (SINDA), a structural model (NASTRAN), and RF far field pattern simulation. Interfacing software has been written to pass thermal model temperature results to the structural model, and structural model thermal deformation results to the RF far field pattern simulation. A complete analysis can be performed in a single computer run, and potential changes in design can be quickly and easily evaluated using this interdisciplinary design analysis tool.

Steinbach, R. E.↗
NASA NTRS1988

Probabilistic model for fracture mechanics service life analysis

The service longevity of complex propulsion systems, such as the Space Shuttle Main Engine (SSME), can be at risk from several competing failure modes. Conventional life assessment practice focuses upon the most severely life-limited feature of a given component, even though there may be other, less severe, potential failure locations. Primary, secondary, tertiary failure modes, as well as their associated probabilities, must also be considered. Futhermore, these probabilities are functions of accumulated service time. Thus a component may not always succumb to the most severe, or even the most probable failure mode. Propulsion system longevity must be assessed by considering simultaneously the actions of, and interactions among, life-limiting influences. These include, but are not limited to, high frequency fatigue (HFF), low cycle fatigue (LCF), and subsequent crack propagation, thermal and acoustic loadings, and the influence of less-than-ideal nondestructive evaluation (NDE). An outline is provided for a probabilistic model for service life analysis, and the progress towards its implementation is reported.

Annis, Charles↗
NASA NTRS1984

A linear aerodynamic analysis for unsteady transonic cascades

A potential flow analysis to predict unsteady airloads produced by the vibrations of turbomachinery blades operating at transonic Mach numbers is presented. The unsteady aerodynamic model includes the effects of blade geometry, finite mean pressure variation across the blade row, high frequency blade motion, and shock motion within the framework of a linearized, frequency domain formulation. The unsteady equations are solved implicit, least squares, finite difference approximation which is applicable on arbitrary grids. A numerical solution for the entire unsteady field is determined by matching a solution determined on a rectilinear type cascade mesh, which covers an extended blade passage region, to a solution determined on a detailed polar type local mesh, which covers and extends well beyond the supersonic region(s) adjacent to a blade surface. Cascades of double circular arc and flat plate blades demonstrate the unsteady analysis, and partially illustrate the effects of blade geometry, inlet Mach number, blade vibration frequency and shock motion on unsteady response.

Verdon, J. M.↗
NASA NTRS1972

Photodiodes for ten micrometer laser communication systems

The performance is discussed of 10-micron mercury-cadmiumtelluride and lead-tin-telluride photodiodes in laser heterodyne communication systems. The dependence of detector quantum efficiency, resistance, frequency response, and signal-to-noise ratio on temperature, bias, and local oscillator power are examined. Included in the discussion is an analysis of the feasibility of high temperature operation, and ability of the detector to dissipate power to a heat sink is explored. Some aspects of direct detection response are considered and figures showing flux levels from a blackbody presented.

Cohen, S. C.↗
NASA NTRS1987

Soft mounted momentum compensated pointing system for the Space Shuttle Orbiter

This paper describes a potential pointing and tracking system for the Space Shuttle with possible future application to Space Station. In order to accomplish high precision pointing and tracking (at rates up to 2 deg/s) in the expected disturbance environment, a high bandwidth gimbaled pointing system is required. A soft-mounted, momentum-compensated gimbal system is suggested for this role. A momentum-compensated system is inertially reacting, decoupling the control system dynamics from the basebody structural dynamics. This allows a soft isolation stage to be added between the basebody and the articulation stage, which attenuates high frequency disturbances. In this paper, three configurations are examined: a hard-mounted system, a passive soft-mounted system, and an active soft-mounted system. Analysis demonstrates that the soft-mounted systems have superior disturbance-rejection properties. The active soft mount allows reduction of the isolation stiffness to zero, and so obtains the highest level of performance.

Sirlin, Samuel W.↗
NASA NTRS1987

Implementation of optimal trajectory control of series resonant converter

Due to the presence of a high-frequency LC tank circuit, the dynamics of a resonant converter are unpredictable. There is often a large surge of tank energy during transients. Using state-plane analysis technique, an optimal trajectory control utilizing the desired solution trajectory as the control law was previously proposed for the series resonant converters. The method predicts the fastest response possible with minimum energy surge in the resonant tank. The principle of the control and its experimental implementation are described here. The dynamics of the converter are shown to be close to time-optimal.

Oruganti, Ramesh↗
NASA NTRS1988

Performance of lightweight manipulators under joint variable feedback control - Analytical study of limitations

The performance limitations of joint-variable-feedback-controlled manipulators due to manipulator flexibility are studied in fine and gross motions. A finite-dimensional time-domain manipulator model is used in the study. Fine-motion analysis results agree very well with the previously reported results of infinite-dimensional frequency-domain models. The limitations of a class of adaptive controllers in high-speed gross motion control are studied. Manipulation speeds are quantified as low, medium, or high with reference to the arm flexibility and dynamic nonlinearities.

Cetinkunt, Sabri↗
NASA NTRS1989

Modal coupling and acoustic intensity measurements

Acoustic-intensity measurement techniques for highly resonant coupled structural-acoustic systems are discussed. Frequency-averaging effects are shown to cause inaccurate results in such systems, and it is recommended that the analysis bandwidth be selected carefully to account for the response modal density and Q factor. The applicability of these findings to the analysis of reverberation chambers is indicated.

Silcox, R. J.↗
NASA NTRS1990

An introduction to chaos theory in CFD

The popular subject 'chaos theory' has captured the imagination of a wide variety of scientists and engineers. CFD has always been faced with nonlinear systems and it is natural to assume that nonlinear dynamics will play a role at sometime in such work. This paper will attempt to introduce some of the concepts and analysis procedures associated with nonlinear dynamics theory. In particular, results from computations of an airfoil at high angle of attack which exhibits a sequence of bifurcations for single frequency unsteady shedding through period doublings cascading into low dimensional chaos are used to present and demonstrate various aspects of nonlinear dynamics in CFD.

Pulliam, Thomas H.↗
NASA NTRS2012

Spacecraft-to-Earth Communications for Juno and Mars Science Laboratory Critical Events

Deep Space communications typically utilize closed loop receivers and Binary Phase Shift Keying (BPSK) or Quadrature Phase Shift Keying (QPSK). Critical spacecraft events include orbit insertion and entry, descent, and landing.---Low gain antennas--> low signal -to-noise-ratio.---High dynamics such as parachute deployment or spin --> Doppler shift. During critical events, open loop receivers and Multiple Frequency Shift Keying (MFSK) used. Entry, Descent, Landing (EDL) Data Analysis (EDA) system detects tones in real-time.

radio science↗
NASA NTRS1995

Some features of the small-scale solar wind fluctuations

We have investigated small-scale variations of the solar wind ion flux measured with Faraday cups onboard the Prognoz-8 satellite. These measurements have a high time resolution of 1.24 seconds for intervals with a duration of several hours and as high as 0.02 seconds for some periods of about 1 hour duration. The main goal of this work is the determination of the quantitative features of fast ion flux fluctuations using mainly spectral analysis but also other methods. We also identify their association with interplanetary plasma parameters. Particularly, it is shown that the slope of the power spectra in the frequency range from 1E-4 to 6E-2 Hz is close to the classical Kolmogorov (-5/3) law. We also discuss some intervals with a very high level of the relative amplitude of flux fluctuations (10-20 percent) which were observed near the Earth's bow shock in the foreshock region. The use of the wavelet method for the long time series allows us to study the temporal evolution of power spectra.

Zastenker, G.↗
NASA NTRS1988

A cascaded Schwarz converter for high frequency power distribution

It is shown that two Schwarz converters in cascade provide a very reliable 20-kHz source that features zero current commutation, constant frequency, and fault-tolerant operation, meeting requirements for spacecraft applications. A steady-state analysis of the converter is presented, and equations for the steady-state performance are derived. Fault-current limiting is discussed. Experimental results are presented for a 900-W version, which has been successfully tested under no-load, full-load, and short-circut conditions.

Ray, Biswajit↗