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NASA NTRS1983

Difference equation technique for determining the evolution of radially symmetric ultrasonic fields

A simplified difference equation technique has been developed to calculate the three-dimensional evolution of radially symmetric, complex ultrasonic fields. The parabolic approximation to the Helmholtz equation is obtained by assuming that localized changes in the magnitude of the field with respect to distance along the axis of propagation are small compared to those with respect to radial displacement. The Helmholtz equation in cylindrical coordinates may then be approximated, after separating variables, using truncated series expansions. The resulting difference equation determines complex field values at discrete locations in a plane using corresponding adjacent locations in the preceding plane. Stability criteria which determine acceptable values for various parameters are discussed. The technique has been applied to the propagation of ultrasonic fields generated by two-dimensional focusing and non-focusing, uniform and Gaussian profile, piezoelectric transducers in both profiled and non-profiled media.

Dockery, G. D.↗

NASA NTRS1985

A design technique for determining actuator gains in spacecraft vibration control

A design procedure is described which determines the gains of a diagonal damping matrix to control the vibrations of a flexible structure with application to orbiting spacecraft. The procedure is based on minimizing the energy dissipated by control actuators using nonlinear mathematical programming. Each damping gain is assumed to be an active viscous damper and the design process is formulated so that the force or torque output of the actuator does not exceed a specified value. The response of the structure at some specified time after the termination of the disturbance is constrained to be less than some prescribed value based upon spacecraft mission performance requirements. A grillage example is used to demonstrate the design process for determining gains for two representative cases. Resulting designs are verified by a finite element analysis of the structure augmented by the control actuators.

Horner, G. C.↗

NASA NTRS1985

Population mechanisms for the He(+) n = 3 levels determined from measurements of the solar 1640 A emission

The 1640 A line profile is analyzed using solar data obtained by the NRL slit spectrograph on Skylab. Data from coronal hole regions, quiet sun regions, active regions, prominence regions, and flare regions are presented. The relative densities of 3s, 3p, and 3d levels are determined from the data, and the dominant population mechanisms for these levels are inferred using a rate equation model for the He(+) ion. The relative importance of collisional excitation, radiative recombination, and photoexcitation is determined for each of the solar regions.

Seely, J. F.↗

NASA NTRS1985

Prospects for determining the cosmological helium-3 to helium-4 ratio via absorption-line studies of the local interstellar medium

The prospects for determining the interstellar (He-3)/(He-4) ratio via absorption-line studies in the extreme ultraviolet are considered. A high-resolution extreme-ultraviolet spectrometer fed by a 1-meter-class telescope similar to that discussed in the Far Ultraviolet Spectroscopic Explorer Report (1983) is assumed, and it is found that detection of He-3 may be possible with less than three days of observing time. To measure the (He-3)/(He-4) ratio with sufficient precision to determine the number of light neutrino species will require over 50 days of integration time for each object studied.

Hurwitz, M.↗

NASA NTRS1985

Ion probe determinations of the rare earth concentrations of individual meteoritic phosphate grains

A new ion probe method for quantitative measurements of the concentrations of all the REE down to the ppm level in 5-20 micron spots is presented. The first application of the method is the determination of REE abundances in meteoritic phosphates. Results are shown to be in good agreement with previous INAA and ion probe determinations. The merrillites in the St. Severin amphoterite are richer in REE than the apatites (the enrichment factors, for various REE, range from 2.3 to 14.2) in contradiction with the results of Ebihara and Honda (1983). Provided good standards for other mineral phases are found or implanted marker ion techniques are used, the method should find a wide range of applications for the study of both terrestrial and extraterrestrial crystals at the microscopic level.

Crozaz, G.↗

NASA NTRS1984

Lifetimes in Si CVD-epitaxial and other layers determined by spectral LBIC

In an effort to evaluate the minority carrier lifetimes in CVD-epitaxially grown layers in their dependence on the CVD process variables, the absolute spectral LBIC method was found to be the only available method capable of yielding both lifetime and surface recombination velocity in layers, independent of the resistivity of this layer or that of the substrate, as long as they are separated by a pn-junction. With this method, it was not only possible to determine the minority carrier lifetimes in as-grown epi-layers, but to observe their changes through the device fabrication processes. In addition, it was possible for the first time to determine the lifetimes in the alloy-regrowth p(+) layers of base high/low junction structures.

Wolf, M.↗

NASA NTRS1985

A new instrument for the determination of radio path delay due to atmospheric water vapor

A new water-vapor radiometer is being developed to determine atmospheric path-delay corrections for geodynamics applications. The radiometer has microwave channels at 20.7, 22.2, and 31.4 GHz, and includes new features which should promote radiometric precision while at the same time reduce instrument complexity. The instrument will be compact, portable, and will possess a self-diagnostic capability to ensure reliability. The performance objective is the determination of the line-of-sight path delay through the atmosphere due to water vapor with a one-sigma error less than 0.5 cm at the zenith.

Janssen, M. A.↗

NASA NTRS1985

A method for determining acoustic-liner admittance in ducts with sheared flow in two-cross-sectional directions

A method is developed for determining the acoustic admittance of a test liner installed in the wall of a grazing flow impedance tube. The mean flow is permitted flow gradients in both cross-sectional directions of the tube. The unknown admittance value is obtained by solving an eigenvalue problem. This eigenvalue problem results from the application of the finite-element method to the partial differential equation and boundary conditions governing the acoustic field. The credibility of the method is established by comparing results with exact solutions obtained for a constant mean-flow profile and with previous results for cases involving shear in only one cross-sectional direction. Excellent comparisons are obtained in both cases. The analysis is used in conjunction with a limited amount of experimental data and shows that the flow must be accurately modeled in order to determine the acoustic-liner properties.

Watson, W. R.↗

NASA NTRS1983

A pyroloysis technique for determining microamounts of hydrogen in lunar soil using the helium ionization detector

A method has been developed which will determine hydrogen in sub-milligram samples of lunar soil. It consists of heating the sample in a pyroprobe followed by the gas chromatographic determination of hydrogen using the helium ionization detector. Using a 7 foot, 1/8 OD stainless steel column packed with Carbosieve S, 120/140 mesh, hydrogen was well-separated from the other gases released from lunar soil. Standards of hydrogen in helium were used for calibration. The limit to detection under the conditions used was about 2 ng. The method was linear from 2 ng to 270 ng. The method was checked using some actual lunar samples. Results were typical of those obtained for lunar soils using other methods.

Bustin, R.↗

NASA NTRS1983

Determination of neutron flux distribution by using ANISN, a one-dimensional discrete S sub n ordinates transport code with anisotropic scattering

The purpose of this project was to use a one-dimensional discrete coordinates transport code called ANISN in order to determine the energy-angle-spatial distribution of neutrons in a 6-feet cube rock box which houses a D-T neutron generator at its center. The project was two-fold. The first phase of the project involved adaptation of the ANISN code written for an IBM 360/75/91 computer to the UNIVAC system at JSC. The second phase of the project was to use the code with proper geometry, source function and rock material composition in order to determine the neutron flux distribution around the rock box when a 14.1 MeV neutron generator placed at its center is activated.

Ghorai, S. K.↗

NASA NTRS1985

Determination of corrections to flow direction sensor measurements over an angle-of-attack range from 0 degree to 85 degrees

An investigation was conducted into the nature of corrections for angle-of-attack and angle-of-sideslip measurements obtained with sensors mounted in front of each wingtip of a general aviation airplane. These flow corrections have been obtained from both wind-tunnel and flight tests over an angle-of-attack range from 0 to 85 deg. Both the angle-of-attack and angle-of-sideslip flow corrections were found to be substantial. The corrections were a function of the angle of attack and angle of sideslip and were fairly insensitive to configuration changes and rotational effects. The angle-of-attack flow correction determined from the static wind-tunnel tests agreed reasonably well with the correction determined from flight tests.

Moul, T. M.↗

NASA NTRS1986

STEP and STEPSPL: Computer programs for aerodynamic model structure determination and parameter estimation

The successful parametric modeling of the aerodynamics for an airplane operating at high angles of attack or sideslip is performed in two phases. First the aerodynamic model structure must be determined and second the associated aerodynamic parameters (stability and control derivatives) must be estimated for that model. The purpose of this paper is to document two versions of a stepwise regression computer program which were developed for the determination of airplane aerodynamic model structure and to provide two examples of their use on computer generated data. References are provided for the application of the programs to real flight data. The two computer programs that are the subject of this report, STEP and STEPSPL, are written in FORTRAN IV (ANSI l966) compatible with a CDC FTN4 compiler. Both programs are adaptations of a standard forward stepwise regression algorithm. The purpose of the adaptation is to facilitate the selection of a adequate mathematical model of the aerodynamic force and moment coefficients of an airplane from flight test data. The major difference between STEP and STEPSPL is in the basis for the model. The basis for the model in STEP is the standard polynomial Taylor's series expansion of the aerodynamic function about some steady-state trim condition. Program STEPSPL utilizes a set of spline basis functions.

Batterson, J. G.↗

NASA NTRS1986

Effects of wing modification on an aircraft's aerodynamic parameters as determined from flight data

A study of the effects of four wing-leading-edge modifications on a general aviation aircraft's stability and control parameters is presented. Flight data from the basic aircraft configuration and configurations with wing modifications are analyzed to determine each wing geometry's stability and control parameters. The parameter estimates and aerodynamic model forms are obtained using the stepwise regression and maximum likelihood techniques. The resulting parameter estimates and aerodynamic models are verified using vortex-lattice theory and by analysis of each model's ability to predict aircraft behavior. Comparisons of the stability and control derivative estimates from the basic wing and the four leading-edge modifications are accomplished so that the effects of each modification on aircraft stability and control derivatives can be determined.

Hess, R. A.↗

NASA NTRS1985

Determination of nitrogen monoxide in high purity nitrogen gas with an atmospheric pressure ionization mass spectrometer

An atmospheric pressure ionization mass spectrometric (API-MS) method was studied for the determination of residual NO in high purity N2 gas. The API-MS is very sensitive to NO, but the presence of O2 interferes with the NO measurement. Nitrogen gas in cylinders as sample gas was mixed with NO standard gas and/or O2 standard gas, and then introduced into the API-MS. The calibration curves of NO and O2 has linearity in the region of 0 - 2 ppm, but the slopes changed with every cylinder. The effect of O2 on NO+ peak was additive and proportional to O2 concentration in the range of 0 - 0.5 ppm. The increase in NO+ intensity due to O2 was (0.07 - 0.13)%/O2, 1 ppm. Determination of NO and O2 was carried out by the standard addition method to eliminate the influence of variation of slopes. The interference due to O2 was estimated from the product of the O2 concentration and the ratio of slope A to Slope B. Slope A is the change in the NO+ intensity with the O2 concentration. Slope B is the intensity with O2 concentration.

Kato, K.↗

NASA NTRS1986

Analytical determination of propeller performance degradation due to ice accretion

A computer code has been developed which is capable of computing propeller performance for clean, glaze, or rime iced propeller configurations, thereby providing a mechanism for determining the degree of performance degradation which results from a given icing encounter. The inviscid, incompressible flow field at each specified propeller radial location is first computed using the Theodorsen transformation method of conformal mapping. A droplet trajectory computation then calculates droplet impingement points and airfoil collection efficiency for each radial location, at which point several user-selectable empirical correlations are available for determining the aerodynamic penalities which arise due to the ice accretion. Propeller performance is finally computed using strip analysis for either the clean or iced propeller. In the iced mode, the differential thrust and torque coefficient equations are modified by the drag and lift coefficient increments due to ice to obtain the appropriate iced values. Comparison with available experimental propeller icing data shows good agreement in several cases. The code's capability to properly predict iced thrust coefficient, power coefficient, and propeller efficiency is shown to be dependent on the choice of empirical correlation employed as well as proper specification of radial icing extent.

Miller, T. L.↗

NASA NTRS1986

Determination of solid mass fraction in partially frozen hydrocarbon fuels

Filtration procedures alone are insufficient to determine the amounts of crystalline solid in a partially frozen hydrocarbon distillate fraction. This is due to the nature of the solidification process by which a large amount of liquid becomes entrapped within an interconnected crystalline structure. A technique has been developed to supplement filtration methods with an independent determination of the amount of liquid in the precipitate thereby revealing the actual value of mass percent crystalline solid, %S. A non-crystallizing dye is injected into the fuel and used as a tracer during the filtration. The relative concentrations of the dye in the filtrate and precipitate fractions is subsequently detected by a spectrophotometric comparison. The filtration apparatus was assembled so that the temperature of the sample is recorded immediately above the filter. Also, a second method of calculation has been established which allows significant reduction in test time while retaining acceptable accuracy of results. Data have been obtained for eight different kerosene range hydrocarbon fuels.

Cotterell, E. M.↗

NASA NTRS1984

Goddard Laboratory for Atmospheric Sciences physical retrieval system for remote determination of weather and climate parameter from HIRS2 and MSU observations

At the Goddard Laboratory for Atmospheric Sciences (GLAS) a physically based satellite temperature sounding retrieval system, involving the simultaneous analysis of HIRS2 and MSU sounding data, was developed for determining atmospheric and surface conditions which are consistent with the observed radiances. In addition to determining accurate atmospheric temperature profiles even in the presence of cloud contamination, the system provides global estimates of day and night sea or land surface temperatures, snow and ice cover, and parameters related to cloud cover. Details of the system are described elsewhere. A brief overview of the system is presented, as well as recent improvements and previously unpublished results, relating to the sea-surface intercomparison workshop, the diurnal variation of ground temperatures, and forecast impact tests.

Susskind, J.↗

NASA NTRS1986

Precision attitude determination and control using gyros and earth sensor

A novel scheme to estimate the biases present in the gyros and the attitude of three-axis stabilized earth pointing spacecraft using the outputs of gyros and earth sensor is presented. The earth sensor pitch output is averaged every orbit to provide pitch gyro bias correction. Roll and yaw gyro biases are determined by averaging the earth sensor roll output every quarter orbit and suitably combining the four quarter orbit averages obtained in each orbit. Yaw attitude information is also required once every orbit. Simulation studies including error sources due to earth sensor, gyros, yaw sensor and horizon radiance uncertainty in the winter poles showed that attitude determination accuracy of 0.01-0.03 deg (3 sigma) can be achieved about all the axes.

Rajaram, S.↗