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At least 685 records · Page 38

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NASA NTRS1976

Random vibration of compliant wall

The paper is concerned with the realistic case of two-dimensional random motion of a membrane with bending stiffness supported on a viscoelastic spring substrate and on an elastic base plate under both subsonic and supersonic boundary layer turbulence. The cross-power spectral density of surface displacements is solved in terms of design variables of the compliant wall - such as the dimensions and material properties of the membrane (Mylar), substrate (PVC foam), and panel (aluminum) - so that a sensitivity analysis can be made to examine the influence of each design variable on the surface response statistics. Three numerical examples typical of compliant wall design are worked out and their response statistics in relation to wave drag and roughness drag are assessed. The results can serve as a guideline for experimental investigation of the drag reduction concept through the use of a compliant wall.

Yang, J.-N.↗

NASA NTRS1976

Optical technique for measurement of random water wave surfaces

An optical system using the refraction of a vertical light ray has been developed for measuring the slope of random wind-generated water waves. The basic elements of the system are photovoltaic cells which are connected to individual amplifiers so that when the refracted light beam is incident on a cell, the output of the cell is amplified and then supplied as input to a comparator. The comparator then provides a specified voltage output, independent of the incident light intensity, as long as it is above a designated background value. The comparators are designed to give output voltages comparable with standard TTL. This arrangement provides a high signal from the cell when it experiences incident light, and a low signal when there is only background light, with the high and low signals at TTL voltage levels.

Sorrell, F. Y.↗

NASA NTRS1976

Comparison of modal test results - Multipoint sine versus single-point random

The Mariner Jupiter/Saturn (MJS) spacecraft was subjected to the traditional multipoint sine dwell (MPSD) modal test using 111 accelerometer channels, and also to single-point random (SPR) testing using 26 accelerometer channels, and the two methods are compared according to cost, schedule, and technical criteria. A measure of comparison between the systems was devised in terms of the cumulative difference in the kinetic energy distribution of the common accelerometers. The SPR and MPSD method show acceptable agreement with respect to frequencies and mode damping. The merit of the SPR method is that the excitation points are minimized and the test article can be committed to other uses while data analysis is performed. The MPSD approach allows validity of the data to be determined as the test progresses. Costs are about the same for the two methods.

Leppert, E. L.↗

NASA NTRS1977

Thermal microwave emission from a random inhomogeneous layer over a homogeneous medium using the method of invariant imbedding

The paper studies thermal microwave emission from an inhomogeneous slab of a random medium, with possible nonuniform absorption, scattering, and temperature profiles, bounded by different dielectrics on both sides. The invariant imbedding method is used to cast the boundary value problem of the radiative transfer equations into an initial value problem at zero slab thickness. As a numerical example, the angular and polarization variations of brightness temperatures for ice over water are considered.

Tsang, L.↗

NASA NTRS1977

The influence of the directional energy distribution on the nonlinear dispersion relation in a random gravity wave field

The influence of the directional distribution of wave energy on the dispersion relation is calculated numerically using various directional wave spectrum models. The results indicate that the dispersion relation varies both as a function of the directional energy distribution and the direction of propagation of the wave component under consideration. Furthermore, both the mean deviation and the random scatter from the linear approximation increase as the energy spreading decreases. Limited observational data are compared with the theoretical results. The agreement is favorable.

Huang, N. E.↗

NASA NTRS1977

Control logic to track the outputs of a command generator or randomly forced target

A procedure is presented for synthesizing time-invariant control logic to cause the outputs of a linear plant to track the outputs of an unforced (or randomly forced) linear dynamic system. The control logic uses feed-forward of the reference system state variables and feedback of the plant state variables. The feed-forward gains are obtained from the solution of a linear algebraic matrix equation of the Liapunov type. The feedback gains are the usual regulator gains, determined to stabilize (or augment the stability of) the plant, possibly including integral control. The method is applied here to the design of control logic for a second-order servomechanism to follow a linearly increasing (ramp) signal, an unstable third-order system with two controls to track two separate ramp signals, and a sixth-order system with two controls to track a constant signal and an exponentially decreasing signal (aircraft landing-flare or glide-slope-capture with constant velocity).

Trankle, T. L.↗

NASA NTRS1977

A study of key features of random atmospheric disturbance models for the approach flight phase

An analysis and brief simulator experiment were performed to identify and classify important features of random turbulence for the landing approach flight phase. The analysis of various wind models was carried out within the context of the longitudinal closed-loop pilot/vehicle system. The analysis demonstrated the relative importance of atmospheric disturbance scale lengths, horizontal versus vertical gust components, decreasing altitude, and spectral forms of disturbances versus the pilot/vehicle system. Among certain competing wind models, the analysis predicted no significant difference in pilot performance. This was confirmed by a moving base simulator experiment which evaluated the two most extreme models. A number of conclusions were reached: attitude constrained equations do provide a simple but effective approach to describing the closed-loop pilot/vehicle. At low altitudes the horizontal gust component dominates pilot/vehicle performance.

Heffley, R. K.↗

NASA NTRS1978

Random sampling adaptively focusing synthetic aperture radar

A high resolution narrow angle of view imaging radar system is considered that employs an airborne synthetic aperture of 600 meters operating at X-band to produce a beamwidth of approximately 0.05 mr. This system differs from a conventional SAR in that only a smaller number of wavefront samples, spaced randomly over the aperture are processed, and adaptive beamforming with open loop scanning is used. As a result, the processing requirements are reduced to within the capability of present day small computer technology, and the tolerance on flight stability is loosened by about 100:1. The system is described and initial analysis and evaluation results are presented.

Powers, E. N.↗

NASA NTRS1978

Impedance measurement using a two-microphone, random-excitation method

The feasibility of using a two-microphone, random-excitation technique for the measurement of acoustic impedance was studied. Equations were developed, including the effect of mean flow, which show that acoustic impedance is related to the pressure ratio and phase difference between two points in a duct carrying plane waves only. The impedances of a honeycomb ceramic specimen and a Helmholtz resonator were measured and compared with impedances obtained using the conventional standing-wave method. Agreement between the two methods was generally good. A sensitivity analysis was performed to pinpoint possible error sources and recommendations were made for future study. The two-microphone approach evaluated in this study appears to have some advantages over other impedance measuring techniques.

Seybert, A. F.↗

NASA NTRS1978

Are quasar redshifts randomly distributed

A statistical analysis of possible clumping (not periodicity) of emission line redshifts of QSO's shows the available data to be compatible with random fluctuations of a smooth, non-clumped distribution. This result is demonstrated with Monte Carlo simulations as well as with the Kolmogorov-Smirnov test. It is in complete disagreement with the analysis by Varshni, which is shown to be incorrect.

Weymann, R. J.↗

NASA NTRS1978

Radiative transfer theory for active remote sensing of half-space random media

In active remote sensing of low-loss and scattering-dominant areas, the effect of volume scattering can be modeled as a half-space random medium with lateral and vertical fluctuations. Correlation functions are assumed to be Gaussian laterally and exponential vertically. A radiative transfer theory is developed in this paper to calculate backscattering cross sections. An iteration process is used. When calculated to first order in albedo, the result gives the single-scattering effects and confirms previous work. Calculated to second order, it is found that the backscattered power exhibits depolarization effects. This important consequence is studied numerically by illustrating the backscattering cross sections as a function of incidence angles and frequencies.

Tsang, L.↗

NASA NTRS1979

Scattering by randomly oriented ellipsoids: Application to aerosol and cloud problems

A program was developed for computing the scattering and absorption by arbitrarily oriented and randomly oriented prolate and oblate spheroids. This permits examination of the effect of particle shape for cases ranging from needles through spheres to platelets. Applications of this capability to aerosol and cloud problems are discussed. Initial results suggest that the effect of nonspherical particle shape on transfer of radiation through aerosol layers and cirrus clouds, as required for many climate studies, can be readily accounted for by defining an appropriate effective spherical particle radius.

Asano, S.↗

NASA NTRS1979

Electrical Evaluation of RCA MWS5001D Random Access Memory, Volume 1

Electrical characterization and qualification tests were performed on the RCA MWS5001D, 1024 by 1-bit, CMOS, random access memory. Characterization tests were performed on five devices. The tests included functional tests, AC parametric worst case pattern selection test, determination of worst-case transition for setup and hold times and a series of schmoo plots. The qualification tests were performed on 32 devices and included a 2000 hour burn in with electrical tests performed at 0 hours and after 168, 1000, and 2000 hours of burn in. The tests performed included functional tests and AC and DC parametric tests. All of the tests in the characterization phase, with the exception of the worst-case transition test, were performed at ambient temperatures of 25, -55 and 125 C. The worst-case transition test was performed at 25 C. The preburn in electrical tests were performed at 25, -55, and 125 C. All burn in endpoint tests were performed at 25, -40, -55, 85, and 125 C.

Klute, A.↗

NASA NTRS1979

Electrical Evaluation of RCA MWS5501D Random Access Memory, Volume 2, Appendix a

The electrical characterization and qualification test results are presented for the RCA MWS5001D random access memory. The tests included functional tests, AC and DC parametric tests, AC parametric worst-case pattern selection test, determination of worst-case transition for setup and hold times, and a series of schmoo plots. The address access time, address readout time, the data hold time, and the data setup time are some of the results surveyed.

Klute, A.↗

NASA NTRS1979

Electrical Evaluation of RCA MWS5001D Random Access Memory, Volume 3, Appendix B

The electrical characterization and qualification test results are presented for the RCA MWS5001D random access memory. The tests included functional tests, AC and DC parametric tests, AC parametric worst-case pattern selection test, determination of worst-case transition for setup and hold times, and a series of schmoo plots. The test values for the output voltage, average input current, the supply current and the leakage current are presented.

Klute, A.↗

NASA NTRS1979

Electrical Evaluation of RCA MWS5001D Random Access Memory, Volume 4, Appendix C

The electrical characterization and qualification test results are presented for the RCA MWS5001D random access memory. The tests included functional tests, AC and DC parametric tests, AC parametric worst-case pattern selection test, determination of worst-case transition for setup and hold times, and a series of schmoo plots. Statistical analysis data is supplied along with write pulse width, read cycle time, write cycle time, and chip enable time data.

Klute, A.↗

NASA NTRS1979

Electrical Evaluation of RCA MWS5001D Random Access Memory, Volume 5, Appendix D

The electrical characterization and qualification test results are presented for the RCA MWS 5001D random access memory. The tests included functional tests, AC and DC parametric tests, AC parametric worst-case pattern selection test, determination of worst-case transition for setup and hold times, and a series of schmoo plots. Average input high current, worst case input high current, output low current, and data setup time are some of the results presented.

Klute, A.↗

NASA NTRS1979

Electrical Characterization of the RCA CDP1822SD Random Access Memory, Volume 1, Appendix a

Electrical characteristization tests were performed on 35 RCA CDP1822SD, 256-by-4-bit, CMOS, random access memories. The tests included three functional tests, AC and DC parametric tests, a series of schmoo plots, rise/fall time screening, and a data retention test. All tests were performed on an automated IC test system with temperatures controlled by a thermal airstream unit. All the functional tests, the data retention test, and the AC and DC parametric tests were performed at ambient temperatures of 25 C, -20 C, -55 C, 85 C, and 125 C. The schmoo plots were performed at ambient temperatures of 25 C, -55 C, and 125 C. The data retention test was performed at 25 C. Five devices failed one or more functional tests and four of these devices failed to meet the expected limits of a number of AC parametric tests. Some of the schmoo plots indicated a small degree of interaction between parameters.

Klute, A.↗