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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Isentropic compression of fused quartz and liquid hydrogen to several Mbar

Models of the major planets are in part based on the equations of state of very compressible materials such as hydrogen and helium. A technique of isentropically compressing soft material to several Mbar and some preliminary results on fused quartz (silicon dioxide) and liquid hydrogen is described. Quartz was found to be an electrical non-conductor up to 5 Mbar and has a volume of about 0.15 cubic centimeters per gram at that pressure. Liquid hydrogen was found to have a volume of about 1 cm3/g at a pressure of about 2 Mbar. It was not determined if it was transformed into a metal.

Hawke, R. S.↗
NASA NTRS1974

Analysis of three-point-bend test for materials with unequal tension and compression properties

An analysis capability is described for the three-point-bend test applicable to materials of linear but unequal tensile and compressive stress-strain relations. The capability consists of numerous equations of simple form and their graphical representation. Procedures are described to examine the local stress concentrations and failure modes initiation. Examples are given to illustrate the usefulness and ease of application of the capability. Comparisons are made with materials which have equal tensile and compressive properties. The results indicate possible underestimates for flexural modulus or strength ranging from 25 to 50 percent greater than values predicted when accounting for unequal properties. The capability can also be used to reduce test data from three-point-bending tests, extract material properties useful in design from these test data, select test specimen dimensions, and size structural members.

Chamis, C. C.↗
NASA NTRS1974

Numerical solution of the time-dependent compressible Navier-Stokes equations in inlet regions

The results of a study to determine the effects of compressibility on the viscous flow through channels that have straight, parallel walls are presented. Two channel configurations are considered, the flow between two semi-infinite flat plates with uniform flow prescribed at the inlet plane and a cascade of semi-infinite flat plates with uniform flow introduced upstream. The flow field is modeled by using the time dependent, compressible Navier-Stokes equations. Time dependent solutions are obtained by using an explicit finite difference technique which advances the pressure on near field subsonic boundaries such that accurate steady state solutions are obtained. Steady state results at Reynolds number 20 and 150 are presented for Mach numbers between 0.09 and 0.36 and compared with the incompressible solutions of previous studies.

Olson, L. E.↗
NASA NTRS1974

Ultrasonic velocity and adiabatic compressibility in dioxane-water mixtures

Using a method of diffraction of light on an ultrasonic beam, the velocity of ultrasounds and the adiabatic compressibility in dioxane-water mixtures were determined. The dependence of these quantities on the temperature (in the 15-50 C range) and on the concentration (0-100%) were studied. For each temperature there was found a velocity maximum and a compressibility minimum for a given value of the dioxane concentration. The different behavior of these mixtures is due to intense interactions between the molecules of the two liquids composing the mixture.

Ciupe, A.↗
NASA NTRS1973

Some design considerations for supersonic cruise mixed compression inlets

A mixed compression inlet designed for supersonic cruise has very demanding requirements for high total pressure recovery and low bleed and cowl drag. However, since the optimum inlet for supersonic cruise performance may have other undesirable characteristics, it is necessary to establish trade-offs between inlet performance and other inlet characteristics. The paper will review some of these trade-offs between the amount of internal compression, aerodynamic performance and angle-of-attack tolerance. Also some techniques in use at the Lewis Research Center for analysis of boundary layer control and subsonic diffuser flow will be discussed.

Bowditch, D. N.↗
NASA NTRS1975

Laser velocimeter measurements of high-speed compressible flows

Laser velocimeter results were compared and found to be consistent with those obtained with conventional measurement techniques and existing compressible boundary layer theory. Turbulence information at supersonic speed has been successfully obtained in compressible boundary layer with laser system.

Johnson, D. A.↗
NASA NTRS1974

Study of radar pulse compression for high resolution satellite altimetry

Pulse compression techniques are studied which are applicable to a satellite altimeter having a topographic resolution of + 10 cm. A systematic design procedure is used to determine the system parameters. The performance of an optimum, maximum likelihood processor is analysed, which provides the basis for modifying the standard split-gate tracker to achieve improved performance. Bandwidth considerations lead to the recommendation of a full deramp STRETCH pulse compression technique followed by an analog filter bank to separate range returns. The implementation of the recommended technique is examined.

Dooley, R. P.↗
NASA NTRS1975

Experimental investigation of a Mach 6 fixed-geometry inlet featuring a swept external-internal compression flow field

An investigation of a fixed-geometry, swept external-internal compression inlet was conducted at a Mach number of 6.0 and a test-section Reynolds number of 1.55 x 10 to the 7th power per meter. The test conditions was constant for all runs with stagnation pressure and temperature at 20 atmospheres and 500 K, respectively. Tests were made at angles of attack of -5 deg, 0 deg, 3 deg, and 5 deg. Measurements consisted of pitot- and static-pressure surveys in inlet throat, wall static pressures, and surface temperatures. Boundary-layer bleed was provided on the centerbody and on the cowl internal surface. The inlet performance was consistently high over the range of the angle of attack tested, with an overall average total pressure recovery of 78 percent and corresponding adiabatic kinetic-energy efficiency of 99 percent. The inlet throat flow distribution was uniform and the Mach number and pressure level were of the correct magnitude for efficient combustor design. The utilization of a swept compression field to meet the starting requirements of a fixed-geometry inlet produced neither flow instability nor a tendency to unstart.

Torrence, M. G.↗
NASA NTRS1974

An optimized buffer controlled data compression system

The digital data compression system considered uses a buffer controlled aperture algorithm which minimizes the mean-squared error between the reconstructed receiver output and transmitter input. The data compression technique selected is based on the zero-order floating aperture prediction rule. It is assumed that the statistics of the input data are initially uniformly distributed, stationary, and first-order Markov. The problem is solved for stationary data. An approach is presented for extending the results to slowly varying uniformly distributed nonstationary Markov data.

Dosik, P. H.↗
NASA NTRS1975

Analytical and experimental study of structurally efficient composite hat-stiffened panels loaded in axial compression

Structural efficiency studies were made to determine the weight-saving potential of graphite/epoxy composite structures for compression panel applications. Minimum-weight hat-stiffened and open-corrugation configurations were synthesized using a nonlinear mathematical programing technique. Selected configurations were built and tested to study local and Euler buckling characteristics. Test results for 23 panels critical in local buckling and six panels critical in Euler buckling are compared with analytical results obtained using the BUCLASP-2 branched plate buckling program. A weight efficiency comparison is made between composite and aluminum compression panels using metal test data generated by the NACA. Theoretical studies indicate that potential weight savings of up to 50% are possible for composite hat-stiffened panels when compared with similar aluminum designs. Weight savings of 32% to 42% were experimentally achieved. Experience to date suggests that most of the theoretical weight-saving potential is available if design deficiencies are eliminated and strict fabrication control is exercised.

Williams, J. G.↗
NASA NTRS1975

Design and the parametric testing of the space station prototype integrated vapor compression distillation water recovery module

Potable water for the Space Station Prototype life support system is generated by the vapor compression technique of vacuum distillation. A description of a complete three-man modular vapor compression water renovation loop that was built and tested is presented; included are all of the pumps, tankage, chemical post-treatment, instrumentation, and controls necessary to make the loop representative of an automatic, self-monitoring, null gravity system. The design rationale is given and the evolved configuration is described. Presented next are the results of an extensive parametric test during which distilled water was generated from urine and urinal flush water with concentration of solids in the evaporating liquid increasing progressively to 60 percent. Water quality, quantity and production rate are shown together with measured energy consumption rate in terms of watt-hours per kilogram of distilled water produced.

Reveley, W. F.↗
NASA NTRS1975

Finite element computation of a viscous compressible free shear flow governed by the time dependent Navier-Stokes equations

A finite element algorithm for solution of fluid flow problems characterized by the two-dimensional compressible Navier-Stokes equations was developed. The program is intended for viscous compressible high speed flow; hence, primitive variables are utilized. The physical solution was approximated by trial functions which at a fixed time are piecewise cubic on triangular elements. The Galerkin technique was employed to determine the finite-element model equations. A leapfrog time integration is used for marching asymptotically from initial to steady state, with iterated integrals evaluated by numerical quadratures. The nonsymmetric linear systems of equations governing time transition from step-to-step are solved using a rather economical block iterative triangular decomposition scheme. The concept was applied to the numerical computation of a free shear flow. Numerical results of the finite-element method are in excellent agreement with those obtained from a finite difference solution of the same problem.

Cooke, C. H.↗
NASA NTRS1976

Analytical and experimental study of structurally efficient composite hat-stiffened panels loaded in axial compression

Structural efficiency studies were made to determine the weight saving potential of graphite/epoxy composite structures for compression panel applications. Minimum weight hat-stiffened and open corrugation configurations were synthesized using a nonlinear mathematical programming technique. Selected configurations were built and tested to study local and Euler buckling characteristics. Test results for 23 panels critical in local buckling and six panels critical in Euler buckling are compared with analytical results obtained using the BUCLASP-2 branched plate buckling program. A weight efficiency comparison is made between composite and aluminum compression panels using metal test data generated by the NACA. Theoretical studies indicate that potential weight savings of up to 50% are possible for composite hat-stiffened panels when compared with similar aluminum designs. Weight savings of 32% to 42% were experimentally achieved. Experience suggests that most of the theoretical weight saving potential is available if design deficiencies are eliminated and strict fabrication control is exercised.

Williams, J. G.↗
NASA NTRS1975

Joint Classification and Data Compression of multidimensional information sources - Application to ERTS

This paper describes a concept of Joint Classification and Data Compression of multidimensional information sources in the context of applications to Earth Resources Technology Satellites. The concept is used to define an Information Extraction System intended to remove data redundancy early in the sensor to user link in both classification and film interpretation applications. The approach uses cascaded partially supervised clustering to extract spectral intensity features from spatially local sources. Data compression is then used to efficiently represent spatial features within the spectral intensity feature map.

Hilbert, E. E.↗
NASA NTRS1976

Buckling behavior and structural efficiency of open-section stiffened composite compression panels

Several experiments with J- and blade-stiffened graphite/epoxy panels were conducted to obtain insight into how well experimental data could be correlated with analysis for the buckling behavior of open-section stiffened composite compression panels. Although some nonlinear behavior was observed during the experiments, adequate correlation with analysis was obtained to justify the use of linear, thin-plate buckling analysis in a minimum-weight design synthesis program for J- and blade-configurations. Results from two design studies using this program are presented. In the first study the minimum weights of Jand blade-configurations for two different material systems (graphite/epoxy and aluminum) are determined subject to buckling and strength constraints for a wide range of the compressive load index. In the second study the minimum weights required for graphite/epoxy blade-stiffened panels to satisfy additional stiffness constraints typical of medium-size commercial aircraft wing structures are determined. Both minimum-weight studies indicate that graphite/epoxy open-section stiffened panels can be designed so that weight savings of 30 to 50% are possible compared with the most efficient aluminum designs.

Williams, J. G.↗
NASA NTRS1975

Advances in data compression

A rigorous real-variables treatment of general data compression and encoding problems, centered on formulation and proof of relevant existence theorems and a unified formulation of source coding (both noiseless and with a fidelity criterion) in inaccurately or incompletely specified statistical environments. Difficulties in modeling of sources with unknown or imperfectly known statistical descriptions are analyzed and source codes (SC) are classified (variable-rate noiseless SC, fixed-rate noiseless SC) and analyzed, along with types of code sequences (weighted-universal, maximin-universal, strongly or weakly minimax-universal). Universal coding on video data, variable-rate coding with distortion, and distortion-rate functions are discussed. Design strategies for universal coding algorithms are suggested, but the article is not oriented to specific methods of synthesizing data compression systems.

Davisson, L. D.↗
NASA NTRS1976

Data compression for satellite images

An efficient data compression system is presented for satellite pictures and two grey level pictures derived from satellite pictures. The compression techniques take advantages of the correlation between adjacent picture elements. Several source coding methods are investigated. Double delta coding is presented and shown to be the most efficient. Both predictive differential quantizing technique and double delta coding can be significantly improved by applying a background skipping technique. An extension code is constructed. This code requires very little storage space and operates efficiently. Simulation results are presented for various coding schemes and source codes.

Chen, P. H.↗