SEARCH · Engineering Papers

Results for “simple”

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 703 records · Page 39

All sources NASA NTRS DOE OSTI

NASA NTRS1972

A simple second-order digital phase-locked loop.

A simple second-order digital phase-locked loop has been designed for the Viking Orbiter 1975 command system. Excluding analog-to-digital conversion, implementation of the loop requires only an adder/subtractor, two registers, and a correctable counter with control logic. The loop considers only the polarity of phase error and corrects system clocks according to a filtered sequence of this polarity. The loop is insensitive to input gain variation, and therefore offers the advantage of stable performance over long life. Predictable performance is guaranteed by extreme reliability of acquisition, yet in the steady state the loop produces only a slight degradation with respect to analog loop performance.

Tegnelia, C. R.↗

NASA NTRS1973

Fundamental equations of a mixture of gas and small spherical solid particles from simple kinetic theory.

The fundamental equations of a mixture of a gas and pseudofluid of small spherical solid particles are derived from the Boltzmann equation of two-fluid theory. The distribution function of the gas molecules is defined in the same manner as in the ordinary kinetic theory of gases, but the distribution function for the solid particles is different from that of the gas molecules, because it is necessary to take into account the different size and physical properties of solid particles. In the proposed simple kinetic theory, two additional parameters are introduced: one is the radius of the spheres and the other is the instantaneous temperature of the solid particles in the distribution of the solid particles. The Boltzmann equation for each species of the mixture is formally written, and the transfer equations of these Boltzmann equations are derived and compared to the well-known fundamental equations of the mixture of a gas and small solid particles from continuum theory. The equations obtained reveal some insight into various terms in the fundamental equations. For instance, the partial pressure of the pseudofluid of solid particles is not negligible if the volume fraction of solid particles is not negligible as in the case of lunar ash flow.

Pai, S. I.↗

NASA NTRS1973

A simple method for studying slow crack growth.

A simple, inexpensive method for studying slow crack growth is described. The method entails measurements of load relaxation at constant displacement using a double torsion specimen. It is demonstrated that the data generated using this technique are in excellent agreement with data obtained using the more complex conventional techniques, for a range of materials - steel, titanium, glass, aluminum oxide, PMMA. These encouraging initial results suggest that additional and more detailed studies using this test procedure are merited.

Williams, D. P.↗

NASA NTRS1974

Exploratory tests of a simple aero-mechanical ride comfort system for lightly loaded aircraft

Some exploratory wind tunnel and radio-controlled free-flight tests were made with a small high-wing airplane model (1.23m wing span) to study the concept of a simple aero mechanical system intended to alleviate gust loads and improve ride comfort of lightly loaded aircraft. The system consisted essentially of the outer portions of each wing being hinged in the chordwise direction and connected directly to the wing flaps using internal counter weights to provide neutral mass balance. When the wing experienced a change in velocity or angle of attack, the movable wing panels, acting as sensors and flap actuators, deflected in response to the changes in lift on the wing. The corresponding movements of the interconnected flaps tended to reduce the changes in the wing lift.

Hewes, D. E.↗

NASA NTRS1974

Normalizing parameters for the critical flow rate of simple fluids through nozzles

The two-phase critical flow rate for the simple fluids of methane, nitrogen, oxygen, and argon were normalized using the parameter G* = the square root of (rho sub c x P sub c/Z sub c). The values of G* are given and the question of how to apply this procedure to normalize the critical flow rates of the quantum fluids para-hydrogen and helium was addressed. Experimental data for p-hydrogen, reduced pressures to 4.5 and reduced temperatures from 0.87, were analyzed.

Hendricks, R. C.↗

NASA NTRS1974

A simple radiative transfer model of the high latitude mesospheric scattering layer

A simple radiative transfer model of the particle layer found at 85 km over the summer poles is presented. The effects of the layer on the global radiative temperature, the polar region temperature, and the greenhouse effect are discussed. The estimated magnitude of the global radiative temperature change is 3.5 x .001 K to 2.2 x .01 K, depending on the value of the imaginary part of the particle index of refraction. The layer is shown to have a possible secondary influence on the temperature of the polar region while the contribution which the layer makes to the greenhouse effect is shown to be negligible. The imaginary part of the particle index of refraction is shown to be important in determining the attenuation properties of the layer.

Hummel, J. R.↗

NASA NTRS1974

Behaviour of ion velocity distributions for a simple collision model

Calculation of the ion velocity distributions for a weakly ionized plasma subjected to crossed electric and magnetic fields. An exact solution to Boltzmann's equation has been obtained by replacing the Boltzmann collision integral with a simple relaxation model. At altitudes above about 150 km, where the ion collision frequency is much less than the ion cyclotron frequency, the ion distribution takes the shape of a torus in velocity space for electric fields greater than 40 mV/m. This shape persists for one to two hours after application of the electric field. At altitudes where the ion collision and cyclotron frequencies are approximately equal (about 120 km), the ion velocity distribution is shaped like a bean for large electric field strengths. This bean-shaped distribution persists throughout the lifetime of ionospheric electric fields. These highly non-Maxwellian ion velocity distributions may have an appreciable affect on the interpretation of ion temperature measurements.

St-Maurice, J.-P.↗

NASA NTRS1974

A simple formulation of oxygen absorption at centimeter wavelengths

Carefully performed experiments by a number of investigators have supported the Van Vleck line shape theory for oxygen absorption in the lower-frequency wing (0-50 GHz). In view of the frequent need to compute oxygen absorption at centimeter wavelengths and lower a computationally simple four-line absorption model based on the Van Vleck theory is offered. The approximation yields computational accuracy better than 1% over the entire range of atmospheric pressures and temperatures for frequencies less than 30 GHz when it is compared with the Van Vleck 45-line expression. The versatility of the model in adapting to various line-broadening expressions is also shown. Instead of refining the present theories, this communication is mainly intended to propose a more convenient formulation to compute oxygen absorption.

Claassen, J. P.↗

NASA NTRS1974

Ground-state energies of simple metals

A structural expansion for the static ground-state energy of a simple metal is derived. Two methods are presented, one an approach based on single-particle band structure which treats the electron gas as a nonlinear dielectric, the other a more general many-particle analysis using finite-temperature perturbation theory. The two methods are compared, and it is shown in detail how band-structure effects, Fermi-surface distortions, and chemical-potential shifts affect the total energy. These are of special interest in corrections to the total energy beyond third order in the electron-ion interaction and hence to systems where differences in energies for various crystal structures are exceptionally small. Preliminary calculations using these methods for the zero-temperature thermodynamic functions of atomic hydrogen are reported.

Hammerberg, J.↗

NASA NTRS1975

Simple and effective method to lock buoy position to ocean currents

Window-shade drogue, used with drifting buoys to keep them moving with current at speed as close to that of current as possible, has drag coefficient of 1.93 compared to maximum of 1.52 for previous drogues. It is remarkably simple to construct, use, and store.

Vachon, W. A.↗

NASA NTRS1974

A simple method of calculating power-law velocity profile exponents from experimental data

Analytical expressions for the effects of compressibility and heat transfer on laminar and turbulent shape factors H have been developed. Solving the turbulent equation for the power law velocity profile exponent N has resulted in a simple technique by which the N values of experimental turbulent profiles can be calculated directly from the integral parameters. Thus the data plotting, curve fitting, and slope measuring, which is the normal technique of obtaining experimental N values, is eliminated. The N values obtained by this method should be within the accuracy with which they could be measured.

Allen, J. M.↗

NASA NTRS1974

A simple method for the generation of organ and vessel contours from roentgenographic or fluoroscopic images

A simple method for outlining or contouring any area defined by a change in film density or fluoroscopic screen intensity is described. The entire process, except for the positioning of an electronic window, is accomplished using a small computer having appropriate softwave. The electronic window is operator positioned over the area to be processed. The only requirement is that the window be large enough to encompass the total area to be considered.

Newell, J. D.↗

NASA NTRS1975

Experimental investigation of a simple distortion index utilizing steady-state and dynamic distortions in a Mach 2.5 mixed-compression inlet and turbofan engine

A wind tunnel investigation was conducted to determine the amplitude and spatial distribution of steady-state and dynamic distortion produced in an inlet with 45 percent of the overall supersonic area contraction occurring internally. It was found that the inlet support strut location and/or the overboard bypass flow rate has a significant effect on the spatial distribution of distortion. Because of this effect the majority of the stall points exhibited four-per-revolution patterns of distortion. Data from this test were used to formulate a simple index that combines steady-state and dynamic distortions. Distortion results obtained with this index correlated well with exhaust nozzle area. It is shown that the exhaust nozzle area of a TF30-P-3, as modified for use in this test, can be controlled in a scheme to avoid engine stall. A considerable increase in engine distortion tolerance can be achieved by opening the 7th-stage bleed. The engine exhibited higher tolerance to distortion for multiple patterns of distortion per-revolution than for a one-per-revolution pattern of distortion.

Costakis, W. G.↗

NASA NTRS1975

Turbulence processes and simple closure schemes

The closure problem in turbulence is reviewed, and some simple closure schemes are introduced. Processes occurring in turbulent flow are discussed on the basis of solutions for some elementary flows such as homogeneous turbulence with and without uniform shear. Closure by specification of initial conditions, and finally practical closure schemes for more complicated flows are considered. The latter include Reynolds stress, eddy viscosity, and mixing-length closures.

Deissler, R. G.↗

NASA NTRS1975

Catalogue of geoidal variations for simple seafloor topographic features

A catalogue is presented of theoretical geoidal variations for three types of structural features common to the earth's surface: seamounts, submarine ridges, and submarine trenches. These structures were simulated by simple geometric shapes modeled in three-dimensions. A computer program calculated the potential and gravitational variations over the models. Profile plots of geoidal variations and free-air gravity anomalies are presented over cross-sections of the structures. A ready reference information set is provided for comparison with satellite altimeter data for ocean areas.

Bowin, C.↗

NASA NTRS1975

A simple reaction-rate model for turbulent diffusion flames

A simple reaction rate model is proposed for turbulent diffusion flames in which the reaction rate is proportional to the turbulence mixing rate. The reaction rate is also dependent on the mean mass fraction and the mean square fluctuation of mass fraction of each reactant. Calculations are compared with experimental data and are generally successful in predicting the measured quantities.

Bangert, L. H.↗

NASA NTRS1974

Steady simple shear flow past a circular cylinder at moderate Reynolds numbers - A numerical solution

The two-dimensional steady flow of an incompressible viscous fluid past a circular cylinder, placed symmetrically in a simple shear field, has been studied for both the stationary and the freely rotating case by solving numerically the Navier-Stokes equations for values of the Reynolds number R in the range from 0.047 to 70. At R = 0.047, the results obtained are in substantial agreement with the analytic small-R perturbation solution given by Robertson and Acrivos (1970). Inertia effects were found, however, to play a significant role even at R = 1, and hence the calculated flow pattern for R greater than or equal to 1 differs significantly from that of the creeping-flow solution. Specifically, for the freely rotating case, the region of closed streamlines decreases rapidly in extent with increasing R, two symmetrically placed wakes are formed on either side of the cylinder, and the dimensionless rotational speed of the freely suspended cylinder decreases as the reciprocal of the square root of R.

Kossack, C. A.↗

NASA NTRS1975

Turbulence processes and simple closure schemes

The closure problem in turbulence is briefly reviewed, and some simple closure schemes are introduced. Processes occurring in turbulent flow are discussed on the basis of solutions for some elementary flows such as homogeneous turbulence with and without uniform shear. Closure by specification of initial conditions, and finally practical closure schemes for more complicated flows (e.g., pipe flows) are considered briefly. The latter include Reynolds stress, eddy viscosity, and mixing-length closures.

Deissler, R. G.↗