SEARCH · Engineering Papers

Results for “phase control”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 829 records · Page 46

All sources NASA NTRS DOE OSTI

NASA NTRS1978

Length mode piezoelectric ultrasonic transducer for inspection of solid objects

The transducer is constructed from individual transducer elements arranged in an array and configured to exhibit a predominant, longitudinal mode transversely to the array. The elements are interconnected through thin flexible sheets. Each element is individually damped, and the transducer as a whole is electrically damped through resonance with the clamped capacitance and dissipation. Electrical control permits inphase operation of all transducer elements or control with preselected phase differences.

Thompson, R. B.↗

NASA NTRS1979

Space shuttle orbital flight testing

The current plan for a flight test program to support the Skylab revisit and to accommodate changes in the schedule is presented. The stability and control aspects of the entry flight phase are discussed. The orbiter flight control effectors and their characteristics are described. The approach chosen for orbital flight testing was examined.

Hartsfield, H. W., Jr.↗

NASA NTRS1980

Gas phase hydrogen permeation in alpha titanium and carbon steels

Commercially pure titanium and heats of Armco ingot iron and steels containing from 0.008-1.23 w/oC were annealed or normalized and machined into hollow cylinders. Coefficients of diffusion for alpha-Ti and alpha-Fe were determined by the lag-time technique. Steady state permeation experiments yield first power pressure dependence for alpha-Ti and Sievert's law square root dependence for Armco iron and carbon steels. As in the case of diffusion, permeation data confirm that alpha-titanium is subject to at least partial phase boundary reaction control while the steels are purely diffusion controlled. The permeation rate in steels also decreases as the carbon content increases. As a consequence of Sievert's law, the computed hydrogen solubility decreases as the carbon content increases. This decreases in explained in terms of hydrogen trapping at carbide interfaces. Oxidizing and nitriding the surfaces of alpha-titanium membranes result in a decrease in the permeation rate for such treatment on the gas inlet surfaces but resulted in a slight increase in the rate for such treatment on the gas outlet surfaces. This is explained in terms of a discontinuous TiH2 layer.

Johnson, D. L.↗

NASA NTRS1980

The interaction of molten silicon with silicon aluminum oxynitrides

Silicon aluminum oxynitride solid solutions (sialons) based on beta-Si3N4 and Si2N2O behave differently in contact with molten silicon. The Si2N2O-based sialons convert to almost pure Si3N4, apparently through a two-step decomposition and solution-precipitation reaction, whereas the beta-Si3N4 sialons are preferentially attacked at the grain boundaries. The composition of the grain-boundary phase appears to control the rate of reaction.

Wills, R. R.↗

NASA NTRS1983

Transport Control for High-Density Digital Recorder

Tape capstan drive motor speed controlled by phase-locked loop to keep data rate off of tape compatible with demand clock rate preventing deskewbuffer overflow or underflow. Immunity to speed perturbations caused by data dropouts is obtained by switching to different data-channel reference signal whenever dropout is detected by frame synchronizer in channel currently in use. Desired tape speed is selected by changing frequency of demand rate clock and changing divisor N in programable divider.

Matlin, M. D.↗

NASA NTRS1981

Development of a digital integrated automatic landing system /DIALS/ for steep approach and landing

This paper describes the development of a three-dimensional digital integrated automatic landing system (DIALS) for a small commercial jet transport. The system uses the Microwave Landing System (MLS), body-mounted accelerometers, as well as on-board sensors usually available on commercial aircraft, but does not require inertial platforms. The system development uses modern digital control techniques. The phases of flight considered are the localizer and glideslope capture, which may be performed simultaneously or sequentially, localizer and glideslope track (hold), crab/decrab, and flare to touchdown. The system captures, tracks and flares from steep glideslopes (2.5 - 5.5 deg) selected prior to glideslope capture. The results of a nonlinear simulation are presented.

Halyo, N.↗

NASA NTRS1982

Automatic thermal control switches

Two automatic, flexible connection thermal control switches have been designed and tested in a thermal vacuum facility and in the Get Away Special (GAS) container flown on the third Shuttle flight. The switches are complementary in that one switch passes heat when the plate on which it is mounted exceeds some selected temperature and the other switch will pass heat only when the mounting plate temperature is below the selected value. Both switches are driven and controlled by phase-change capsule motors and require no other power source or thermal sensors.

Wing, L. D.↗

NASA NTRS1981

Design and fabrication of composite blades for the Mod-1 wind turbine generator

The design, tooling, fabrication, quality control, and testing phases carried out to date, as well as testing still planned are described. Differences from the 150 foot blade which were introduced for cost and manufacturing improvement purposes are discussed as well as the lightning protection system installed in the blades. Actual costs and manhours expended for Blade No. 2 are provided as a base, along with a projection of costs for the blade in production.

Batesole, W. R.↗

NASA NTRS1983

Control system for an induction motor with energy recovery

A control circuit for an induction motor powered system is disclosed in which a power factor controlled servo loop is used to control, via the phase angle of firing of a triac, the power input to the motor, as a function of load placed on the motor by machinery of the powered system. Then, upon application of torque by this machinery to the motor, which tends to overspeed the motor, the firing angle of the triac is automatically set to a fixed, and relatively short, firing angle.

Nola, F. J.↗

NASA NTRS1983

A transceiver module of the Mu radar

The transceiver (TR) module of a middle and upper atmospheric radar is described. The TR module used in the radar is mainly composed of two units: a mixer (MIX unit) and a power amplifier (PA unit). The former generates the RF wave for transmission and converts the received echo to the IF signal. A 41.5-MHz local signal fed to mixers passes through a digitally controlled 8-bit phase shifter which can change its value up to 1,000 times in a second, so that the MU radar has the ability to steer its antenna direction quickly and flexibly. The MIX unit also contains a buffer amplifier and a gate for the transmitting signal and preamplifier for the received one whose noise figure is less than 5 dB. The PA unit amplifies the RF signal supplied from the MIX unit up to 63.7 dBm (2350 W), and feeds it to the crossed Yagi antenna.

Kato, S.↗

NASA NTRS1985

Recovering Microwave Cross-Polarization Losses

Reception improved by adding normally discarded portion of signal. For signal enhancement, major and minor signals combined in slaved closedloop receiver channels. Both receiver channels served by common local oscillator controlled by phase-locked loop in main channel. 10-MHz intermediate-frequency (IF) signals of channels coherently summed. For polarization tracking, phasemeter added to measure phase difference between points A and B. With new circuit, low-level signal used at receiver to augment main signal.

Seidel, B. L.↗

NASA NTRS1984

The Effect of Matrix and Fiber Properties on Impact Resistance

The basic material properties which control impact damage are identified and testing techniques are assessed. It is demonstrated that static indentation tests can provide better information about failure processes than impact tests, and they are simpler to conduct. In thin and thick laminates, it was found that the matrix shear strength controls the onset of delamination damage and that the fiber strength controlled the penetration phase. In thin laminates, tough matrices do little to enhance impact resistance.

Elber, W.↗

NASA NTRS1985

Design and test of a pumped two-phase mounting plate

The design, fabrication, and testing of the full-scale development unit of a pumped two-phase mounting plate (TPMP) used in advanced two-phase spacecraft thermal control systems are described. The mounting plate is tested with R-11 in the evaporator mode for total heat loads of over 3000 watts and local heat fluxes over 4 W/sq cm, and in the condenser mode with condenser loads from 60 to 400 watts and inlet qualities from 8 to 94 percent. The calculated heat-transfer coefficients are between 0.66 and 1.0 W/sq cm/C and are nearly independent of the flow rate and heat load except at very low heat loads. It is shown that the TPMP can be run with inlet conditions down to 22 C subcooling without any significant gradients in the plate and that it performs well with nonuniform heat fluxes.

Grote, M. G.↗

NASA NTRS1985

Modeling the radiant transfers of sparse vegetation canopies

The scattering dynamics of sparse vegetation canopies were studied within the framework of the three-dimensional radiative transfer model of Kimes (1984). The model was upgraded by including an algorithm for the anisotropic scattering of a soil boundary. Validation of the model was carried out using measured directional reflectance data for two canopies exhibiting typical scattering behavior with low and intermediate vegetation density. The canopies were: an orchard grass canopy; and a hard wheat canopy. A number of factors were found contributing to the final reflectance distribution of the canopies, including: (1) the strong anisotropic scattering properties of the soil; (2) the geometric effect of the vegetation probability gap function on the soil anisotropy and solar irradiance; and (3) the anisotropic scattering of vegetation which is controlled by the phase function and the layering of leaves. The application of the theoretical results to the development of earth-observing sensor systems is discussed.

Kimes, D. S.↗

NASA NTRS1985

Oxides of Nitrogen Emissions from the Combustion of Monodisperse Liquid Fuel Sprays

A study of NO sub x formation in a one dimensional monodisperse spray combustion system, which allowed independent droplet size variation, was conducted. Temperature, NO and NO sub x concentrations were measured in the transition region, encompassing a 26 to 74 micron droplet size range. Emission measurements of hydrocarbons, carbon monoxide, carbon dioxide and oxygen were also made. The equivalence ratio was varied between 0.8 and 1.2 for the fuels used, including methanol, isopropanaol, n-heptane and n-octane. Pyridine and pyrrole were added to n-heptane as nitrogen-containing additives in order to simulate synthetic fuels. Results obtained from the postflame regions using the pure fuels indicate an optimum droplet size in the range of 43 to 58 microns for minimizing NO sub x production. For the fuels examined, the maximum NO sub x reductions relative to the small droplet size limit were about 10 to 20% for lean and 20 to 30% for stoichiometric and rich mixtures. This behavior is attributed to droplet interactions and the transition from diffusive to premixed type of burning. Preflame vaporization controls the gas phase stoichiometry which has a significant effect on the volume of the hot gases surrounding a fuel droplet, where NO sub x is formed.

Sarv, H.↗

NASA NTRS1986

Effect of volume fraction and size of fine-gamma prime particles on raising the creep strength of a DS nickel-base superalloy

The creep behavior of a directionally solidifified nickel-base superalloy, DKS3, has been investigated as a function of the volume fraction and size of the gamma-prime phase at 760 and 950 C. The dislocation structure and morphology of gamma-prime was examined by transmission electron microscopy at the primary, secondary and tertiary creep stages at 73.8 kgf/sq mm. Experimental results are described in terms of a high temperature creep model in the range of temperatures and applied stresses where shearing of the gamma-prime phase does not control the straining process.

Lin, D. L.↗

NASA NTRS1985

Analysis of the effects of fuel spray characteristics on NO(x) formation

Results from experimental and analytical studies on NO(x) formation in a one-dimensional monodisperse spray combustion system are reported. In a previous investigation, an optimum droplet diameter was reported for minimizing NO(x) emissions. In this paper, the effects of enhanced prevaporization and droplet interactions in addition to droplet size effects on NO(x) formation are investigated by air preheating experiments. These phenomena have been incorporated into an analytical model which predicts NO(x) formed from the combustion of monodisperse fuel sprays. Both, experimental and computed results indicate the importance of the extent of prevaporization and droplet interactions on NO(x) production. Preflame vaporization controls the gas phase stoichiometry which has a significant effect on the volume of the hot gases surrounding a fuel droplet where NO(x) is formed. On the other hand, the release of fuel vapor from the droplet to the reaction zone is influenced by droplet interactions which reduce the volume of the hot gases and NO(x) production by bringing the flame closer to the droplet surface.

Sarv, H.↗

NASA NTRS1986

Phased-array design for MST and ST radars

All of the existing radar systems fully dedicated to clear-air radar studies use some type of phased-array antennas. The effects of beam-steering techniques including feed networks and phase shifters; sidelobe control; ground-clutter suppression; low altitude coverage; arrays with integrated radiating elements and feed networks; analysis of coaxial-collinear antennas; use of arrays with multiple beams; and array testing and measure on structural design of the antenna are discussed.

Ecklund, W. L.↗