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At least 703 records · Page 39

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NASA NTRS1973

A technique for increasing the accuracy of the numerical inversion of the Laplace transform with applications

A technique is introduced which extends the range of useful approximation of numerical inversion techniques to many cycles of an oscillatory function without requiring either the evaluation of the image function for many values of s or the computation of higher-order terms. The technique consists in reducing a given initial value problem defined over some interval into a sequence of initial value problems defined over a set of subintervals. Several numerical examples demonstrate the utility of the method.

Berger, B. S.↗

NASA NTRS1974

Measurement techniques for supersonic combustion testing

Measurement techniques used during nine years of intensive research in supersonic combustion are presented. The tests employed a number of combustor and injector configurations, which were directly connected to a Mach 3.2 supersonic nozzle, and both gaseous hydrogen and storable liquid fuels. Nominal plenum conditions for the arc-heated air were 3000 to 4500 R and 30 atm. Measurements included wall surface pressures, wall temperatures, heat flux, skin friction, instream cone-static and pitot pressures, and gas samples. Measurement and analysis techniques have been developed for determining total enthalpy of an airstream containing NO concentrations in excess of equilibrium using the two-throat technique, bulk combustion efficiency using steam calorimetry, radial gradients of fluid properties in the combustor exit plane using a stream tube method, and wall shear from measurements of heat transfer in a reacting supersonic flow using Reynolds analogy.

Orth, R. C.↗

NASA NTRS1974

Comparison of some classification techniques

The so-called table look-up classification procedure and a modification of it are discussed. These and several other classification techniques are evaluated and simulation results comparing some of the techniques are displayed. Indications are that the table look-up technique is quite useful in classifying large sets of data, such as in remote sensing data analysis.

Odell, P. L.↗

NASA NTRS1974

A generalized-capacity-matrix technique for computing aerodynamic flows

A numerical generalized-capacity-matrix technique is developed for application to aerodynamic flow computations. This technique allows the very fast direct (noniterative) numerical elliptic solvers to be used in problems with arbitrary internal boundaries and with a wide class of boundary conditions, including numerical application of the Kutta condition on an airfoil without iteration. Accuracy, speed, and usefulness of the technique are demonstrated with linear problems for potential flows over airfoil shapes. The method's main advantages, however, can be exploited within iterative procedures for a variety of complex flow problems governed by systems of equations not necessarily elliptic or linear.

Martin, E. D.↗

NASA NTRS1973

A novel triaxial vibration test technique

The present work examines the circumstances under which simultaneous multiaxial vibration testing may be desirable, the testing techniques and equipment required to make it feasible, and the type of results that may be obtained together with some practical limitations to the techniques. Two schemes for performing vibration testing simultaneously or sequentially along three mutually perpendicular axes are considered and the most promising, involving a 'floating' technique, is presented in some detail. Practical problems associated with jig design and system resonances, cross-coupling between the various degrees of freedom, secondary loads on shaker elements, and system drift, are considered and workable solutions proposed. A simple simulation of multiaxial testing of a 1.1-pound inertia-simulated model of an Apollo command module is presented.

Wignot, J. E.↗

NASA NTRS1974

New diagnostic technique for the study of turbulent boundary-layer separation

Description of a diagnostic technique for determining the unsteady character of turbulent boundary-layer separation. The technique uses thin platinum films mounted flush with the model surface. Voltages from these films provide measurements related to the flow character above the film. For illustration, results obtained by this technique are presented for the interaction of a hypersonic shock wave and a turbulent boundary layer, with and without separation.

Horstman, C. C.↗

NASA NTRS1974

Parametric study of STOL short-haul engine cycles and operational techniques to minimize community noise impact

The effect of aircraft operational techniques in the terminal area on community noise impact of future short-haul aircraft was investigated. These operational techniques affected altitude, flap retraction rate, thrust cutback altitude, amount of thrust cutback, and amount of turning. During landing the parameters varied were glide slope angle, change in slope angle (two segment approach), and flap extension rate. One mechanical-flap (MF) aircraft and one externally-blown-flap (EBF) aircraft were used to study by noise impact at four U.S. airports, Hanscom Field (Boston); Washington National; Midway (Chicago); and Orange County (California). With the exception of Washington National (DCA), the study showed that a reduction of approximately 40 percent in the number of people highly annoyed (as defined in the study) can be obtained by using these operational techniques. At DCA the number of people highly annoyed using the standard procedure was quite low, but it is significant that the minimumimpact case for Runway 36 reduced the number of people highly annoyed to zero using a power cutback and a turning departure path. The evaluation procedures and methodology developed in this study represents an advance in acoustical state-of-the-art and should provide an effective and useful tool for determining aircraft noise impact upon the airport community.

Source record↗

NASA NTRS1974

One way Doppler extractor. Volume 1: Vernier technique

A feasibility analysis, trade-offs, and implementation for a One Way Doppler Extraction system are discussed. A Doppler error analysis shows that quantization error is a primary source of Doppler measurement error. Several competing extraction techniques are compared and a Vernier technique is developed which obtains high Doppler resolution with low speed logic. Parameter trade-offs and sensitivities for the Vernier technique are analyzed, leading to a hardware design configuration. A detailed design, operation, and performance evaluation of the resulting breadboard model is presented which verifies the theoretical performance predictions. Performance tests have verified that the breadboard is capable of extracting Doppler, on an S-band signal, to an accuracy of less than 0.02 Hertz for a one second averaging period. This corresponds to a range rate error of no more than 3 millimeters per second.

Blasco, R. W.↗

NASA NTRS1974

Adaptations of advanced safety and reliability techniques to petroleum and other industries

The underlying philosophy of the general approach to failure reduction and control is presented. Safety and reliability management techniques developed in the industries which have participated in the U.S. space and defense programs are described along with adaptations to nonaerospace activities. The examples given illustrate the scope of applicability of these techniques. It is indicated that any activity treated as a 'system' is a potential user of aerospace safety and reliability management techniques.

Purser, P. E.↗

NASA NTRS1974

One way Doppler Extractor. Volume 2: Digital VCO technique

A feasibility analysis and trade-offs for a one-way Doppler extractor using digital VCO techniques is presented. The method of Doppler measurement involves the use of a digital phase lock loop; once this loop is locked to the incoming signal, the precise frequency and hence the Doppler component can be determined directly from the contents of the digital control register. The only serious error source is due to internally generated noise. Techniques are presented for minimizing this error source and achieving an accuracy of 0.01 Hz in a one second averaging period. A number of digitally controlled oscillators were analyzed from a performance and complexity point of view. The most promising technique uses an arithmetic synthesizer as a digital waveform generator.

Nossen, E. J.↗

NASA NTRS1975

Ionospheric direct measurement techniques

The most important physical parameters of the ionosphere which have been studied extensively over the years are: (1) the temperature, density, chemical composition, and directed motion (wind) of the ionized and neutral gas particles; and (2) the electric and magnetic fields. This review will discuss direct in situ techniques used on sounding rockets and satellites to measure these physical parameters. The techniques reviewed are restricted to those which are applicable to altitudes above about 100 km, where the mean free path is greater than the characteristic dimension of the instruments. Direct in situ instrumentation is defined as an experiment which measures the parameters in the immediate vicinity of the vehicle carrying the instrument; remote sensing techniques will not be discussed here.

Bauer, S. J.↗

NASA NTRS1974

Techniques for evaluating long periodic orbit variations

A method of analyzing long periodic variations of orbits from osculating elements is presented. A precision of 0.03 arc sec in inclination has been achieved with this technique for the GEOS 1 and 2 orbits. A combined numerical-analytical technique for computing mean elements is also described. This method has given mean elements with a precision of 0.1 arc sec in inclination and 10 cm in semimajor axis for the GEOS satellites. Application of these techniques to the determination of earth tidal parameters is also discussed.

Douglas, B. C.↗

NASA NTRS1974

Digital vibration control techniques

Analog vibration control techniques are reviewed and are compared with digital techniques. The advantages of the digital methods over the analog methods are demonstrated. The following topics are covered: (1) methods of computer-controlled random vibration and reverberation acoustic testing; (2) methods of computer-controlled sinewave vibration testing; and (3) methods of computer-controlled shock testing. Basic concepts are stressed rather than specific techniques or equipment. General algorithms are described in the form of block diagrams and flow diagrams. Specific problems and potential problems are discussed. The material is computer sciences oriented but is kept at a level that facilitates an understanding of the basic concepts of computer-controlled induced environmental test systems.

Chapman, P.↗

NASA NTRS1975

A flight investigation of oscillating air forces: Equipment and technique

The equipment and techniques are described which are to be used in a project aimed at measuring oscillating air forces and dynamic aeroelastic response of a swept wing airplane at high subsonic speeds. Electro-hydraulic inertia type shakers installed in the wing tips will excite various elastic airplane modes while the related oscillating chordwise pressures at two spanwise wing stations and the wing mode shapes are recorded on magnetic tape. The data reduction technique, following the principle of a wattmeter harmonic analyzer employed by Bratt, Wight, and Tilly, utilizes magnetic tape and high speed electronic multipliers to record directly the real and imaginary components of oscillatory data signals relative to a simple harmonic reference signal. Through an extension of this technique an automatic flight-flutter-test data analyzer is suggested in which vector plots of mechanical admittance or impedance would be plotted during the flight test.

Reed, W. H., III↗

NASA NTRS1975

Metabolic rate control during extravehicular activity simulations and measurement techniques during actual EVAS

A description of the methods used to control and measure metabolic rate during ground simulations is given. Work levels attained at the Space Environment Simulation Laboratory are presented. The techniques and data acquired during ground simulations are described and compared with inflight procedures. Data from both the Skylab and Apollo Program were utilized and emphasis is given to the methodology, both in simulation and during flight. The basic techniques of work rate assessment are described. They include oxygen consumption, which was useful for averages over long time periods, heart rate correlations based on laboratory calibrations, and liquid cooling garment temperature changes. The relative accuracy of these methods as well as the methods of real-time monitoring at the Mission Control Center are discussed. The advantages and disadvantages of each of the metabolic measurement techniques are discussed. Particular emphasis is given to the problem of utilizing oxygen decrement for short time periods and heart rate at low work levels. A summary is given of the effectiveness of work rate control and measurements; and current plans for future EVA monitoring are discussed.

David J. Horrigan↗

NASA NTRS1974

An interdisciplinary analysis of Colorado Rocky Mountain environments using ADP techniques

The author has identified the following significant results. Good ecological, classification accuracy (90-95%) can be achieved in areas of rugged relief on a regional basis for Level 1 cover types (coniferous forest, deciduous forest, grassland, cropland, bare rock and soil, and water) using computer-aided analysis techniques on ERTS/MSS data. Cost comparisons showed that a Level 1 cover type map and a table of areal estimates could be obtained for the 443,000 hectare San Juan Mt. test site for less than 0.1 cent per acre, whereas photointerpretation techniques would cost more than 0.4 cent per acre. Results of snow cover mapping have conclusively proven that the areal extent of snow in mountainous terrain can be rapidly and economically mapped by using ERTS/MSS data and computer-aided analysis techniques. A distinct relationship between elevation and time of freeze or thaw was observed, during mountain lake mapping. Basic lithologic units such as igneous, sedimentary, and unconsolidated rock materials were successfully identified. Geomorphic form, which is exhibited through spatial and textual data, can only be inferred from ERTS data. Data collection platform systems can be utilized to produce satisfactory data from extremely inaccessible locations that encounter very adverse weather conditions, as indicated by results obtained from a DCP located at 3,536 meters elevation that encountered minimum temperatures of -25.5 C and wind speeds of up to 40.9m/sec (91 mph), but which still performed very reliably.

Hoffer, R. M.↗

NASA NTRS1975

A preliminary study of air-pollution measurement by active remote-sensing techniques

Air pollutants are identified, and the needs for their measurement from satellites and aircraft are discussed. An assessment is made of the properties of these pollutants and of the normal atmosphere, including interactions with light of various wavelengths and the resulting effects on transmission and scattering of optical signals. The possible methods for active remote measurement are described; the relative performance capabilities of double-ended and single-ended systems are compared qualitatively; and the capabilities of the several single-ended or backscattering techniques are compared quantitatively. The differential-absorption lidar (DIAL) technique is shown to be superior to the other backscattering techniques. The lidar system parameters and their relationships to the environmental factors and the properties of pollutants are examined in detail. A computer program that models both the atmosphere (including pollutants) and the lidar system is described. The performance capabilities of present and future lidar components are assessed, and projections are made of prospective measurement capabilities for future lidar systems. Following a discussion of some important operational factors that affect both the design and measurement capabilities of airborne and satellite-based lidar systems, the extensive analytical results obtained through more than 1000 individual cases analyzed with the aid of the computer program are summarized and discussed. The conclusions are presented. Recommendations are also made for additional studies to investigate cases that could not be explored adequately during this study.

Wright, M. L.↗

NASA NTRS1975

Remote sensing techniques for prediction of watershed runoff

Hydrologic parameters of watersheds for use in mathematical models and as design criteria for flood detention structures are sometimes difficult to quantify using conventional measuring systems. The advent of remote sensing devices developed in the past decade offers the possibility that watershed characteristics such as vegetative cover, soils, soil moisture, etc., may be quantified rapidly and economically. Experiments with visible and near infrared data from the LANDSAT-1 multispectral scanner indicate a simple technique for calibration of runoff equation coefficients is feasible. The technique was tested on 10 watersheds in the Chickasha area and test results show more accurate runoff coefficients were obtained than with conventional methods. The technique worked equally as well using a dry fall scene. The runoff equation coefficients were then predicted for 22 subwatersheds with flood detention structures. Predicted values were again more accurate than coefficients produced by conventional methods.

Blanchard, B. J.↗