Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “COMPRESSION RATIO”

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.

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

At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Combined compressive and shear buckling analysis of hypersonic aircraft sandwich panels

The combined-load (compression and shear) buckling equations were established for orthotropic sandwich panels by using the Rayleigh-Ritz method to minimize the panel total potential energy. The resulting combined-load buckling equations were used to generate buckling interaction curves for super-plastically-formed/diffusion-bonded titanium truss-core sandwich panels and titanium honeycomb-core sandwich panels having the same specific weight. The relative combined-load buckling strengths of these two types of sandwich panels are compared with consideration of their sandwich orientations. For square and nearly square panels of both types, the combined load always induces symmetric buckling. As the panel aspect ratios increase, antisymmetric buckling will show up when the loading is shear-dominated combined loading. The square panel (either type) has the highest combined buckling strength, but the combined load buckling strength drops sharply as the panel aspect ratio increases. For square panels, the truss-core sandwich panel has higher compression-dominated load buckling strength. However, for shear dominated loading, the square honeycomb-core sandwich panel has higher shear-dominated combined load buckling strength.

Ko, William L.↗
DOE OSTI2026

Working Fluid Characterization and Performance Assessment of Subcritical Organic Rankine Cycles Based on the Lee–Kesler Approach for Energy Recovery

Here, a generalized model using the Lee–Kesler approach based on the corresponding states principle is developed to assess the performance of subcritical Organic Rankine Cycles operating with different working fluids. Each fluid is characterized by five parameters: the acentric factor, critical temperature, critical pressure, molar mass, and the ideal-gas ratio of specific heats at the critical temperature. The model was developed using the compressibility factor modified version of the Benedict–Webb–Rubin equation proposed by Lee and Kesler and the enthalpy and entropy functions to calculate thermodynamic state properties. The model was validated by comparing the results calculated with the model and working fluid thermodynamic properties obtained with the CoolProp database. This comparison was conducted for 91 working fluids, obtaining a relative error below 5% for 88 out of the 91 fluids (∼97%). A generalized parametric study was conducted to determine the influence of the pinch point and each fluid parameter on the performance of Organic Rankine Cycle (ORC) systems. It was found that efficiency increases with critical temperature, ideal-gas ratio of specific heats at the critical temperature, and acentric factor, reaching up to 13%. The developed model enables the evaluation of ORC system performance for existing working fluids. It also allows the formulation and evaluation of new fluids to enhance the performance of the ORC while retrieving energy from any kind of source; and likewise, the methodology can be applied to other power generation cycles.

24 POWER TRANSMISSION AND DISTRIBUTION↗
NASA NTRS1996

Communications and information research: Improved space link performance via concatenated forward error correction coding

With the development of new advanced instruments for remote sensing applications, sensor data will be generated at a rate that not only requires increased onboard processing and storage capability, but imposes demands on the space to ground communication link and ground data management-communication system. Data compression and error control codes provide viable means to alleviate these demands. Two types of data compression have been studied by many researchers in the area of information theory: a lossless technique that guarantees full reconstruction of the data, and a lossy technique which generally gives higher data compaction ratio but incurs some distortion in the reconstructed data. To satisfy the many science disciplines which NASA supports, lossless data compression becomes a primary focus for the technology development. While transmitting the data obtained by any lossless data compression, it is very important to use some error-control code. For a long time, convolutional codes have been widely used in satellite telecommunications. To more efficiently transform the data obtained by the Rice algorithm, it is required to meet the a posteriori probability (APP) for each decoded bit. A relevant algorithm for this purpose has been proposed which minimizes the bit error probability in the decoding linear block and convolutional codes and meets the APP for each decoded bit. However, recent results on iterative decoding of 'Turbo codes', turn conventional wisdom on its head and suggest fundamentally new techniques. During the past several months of this research, the following approaches have been developed: (1) a new lossless data compression algorithm, which is much better than the extended Rice algorithm for various types of sensor data, (2) a new approach to determine the generalized Hamming weights of the algebraic-geometric codes defined by a large class of curves in high-dimensional spaces, (3) some efficient improved geometric Goppa codes for disk memory systems and high-speed mass memory systems, and (4) a tree based approach for data compression using dynamic programming.

Rao, T. R. N.↗
NASA NTRS1946

Some Effects of Compressibility on the Flow Through Fans and Turbines

The laws of conservation of mass, momentum, and energy are applied to the compressible flow through a two-dimensional cascade of airfoils. A fundamental relation between the ultimate upstream and downstream flow angles, the inlet Mach number, and the pressure ratio across the cascade is derived. Comparison with the corresponding relation for incompressible flow shows large differences. The fundamental relation reveals two ranges of flow angles and inlet Mach numbers, for which no ideal pressure ratio exists. One of these nonideal operating ranges is analogous to a similar type in incompressible flow. The other is characteristic only of compressible flow. The effect of variable axial-flow area is treated. Some implications of the basic conservation laws in the case of nonideal flow through cascades are discussed.

Perl, W.↗
DOE OSTI2018

Joint Sparsity Pattern Recovery With 1-b Compressive Sensing in Distributed Sensor Networks

In this paper, we study the problem of joint sparse support recovery with 1-b quantized compressive measurements in a distributed sensor network. Multiple nodes in the network are assumed to observe sparse signals having the same but unknown sparse support. Each node quantizes its measurement vector element-wise to 1 b. First, we consider that all the quantized measurements are available at a central fusion center. We derive performance bounds for sparsity pattern recovery using 1-bit quantized measurements from multiple sensors when the maximum likelihood decoder is employed. We further develop two computationally tractable algorithms for joint sparse support recovery in the centralized setting. One algorithm minimizes a cost function defined as the sum of the likelihood function and the l-∝ quasi-norm, while the other algorithm extends the binary iterative hard thresholding algorithm to the multiple measurement vector case. Second, we consider a decentralized setting where each node transmits 1-b measurements to its one-hop neighbors. The basic idea behind the algorithms developed in the decentralized setting is to embed collaboration among nodes and fusion strategies. We show that even with noisy 1-b compressed measurements, joint support recovery can be carried out accurately in both centralized and decentralized settings. Additionally, we further show that the performance of the proposed 1-bit compressive sensing-based algorithms is very close to that of their real-valued counterparts except when the signal-to-noise ratio is very small.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Elastic Properties across the y→α Volume Collapse in Cerium versus Pressure and Temperature

Here, the longitudinal and transverse sound speeds, c L and c T , of polycrystalline cerium were measured isothermally vs pressure up to the critical temperature across the iso-structural γ-α volume collapse (VC) phase transition. We deduce values for the adiabatic bulk modulus BS, the shear modulus G = ρc T 2 , the Poisson’s ratio ν and the Debye temperature, θ D (p). We find that the elastic constant C 12 is solely responsible for the decrease of B S with pressure towards the VC at RT. With increasing temperature, the lattice contribution ΔS vib (γ→α) to the total entropy change across the VC decreases more rapidly to zero than the total entropy itself suggesting that another mechanism, possibly disorder, assists in stabilizing the γ-phase entropically against the α-phase. Also, with increasing temperature, the Poisson’s ratio becomes negative near the VC transition, meaning that cerium metal takes on auxetic characteristics over a small pressure range. At the critical point the Poisson’s ratio ought to be -1, since the isothermal bulk modulus vanishes and the shear modulus remains nonzero.

36 MATERIALS SCIENCE↗
NASA NTRS1991

Detonation duct gas generator demonstration program

The feasibility of the generation of detonation waves moving periodically across high speed channel flow is experimentally demonstrated. Such waves are essential to the concept of compressing requirements and increasing the engine pressure compressor with the objective of reducing conventional compressor requirements and increasing the engine thermodynamic efficiency through isochoric energy addition. By generating transient transverse waves, rather than standing waves, shock wave losses are reduced by an order of magnitude. The ultimate objective is to use such detonation ducts downstream of a low pressure gas turbine compressor to produce a high overall pressure ratio thermodynamic cycle. A 4 foot long, 1 inch x 12 inch cross-section, detonation duct was operated in a blow-down mode using compressed air reservoirs. Liquid or vapor propane was injected through injectors or solenoid valves located in the plenum or the duct itself. Detonation waves were generated when the mixture was ignited by a row of spark plugs in the duct wall. Problems with fuel injection and mixing limited the air speeds to about Mach 0.5, frequencies to below 10 Hz, and measured pressure ratios of about 5 to 6. The feasibility of the gas dynamic compression was demonstrated and the critical problem areas were identified.

Wortman, Andrew↗
NASA NTRS1947

Calculation of Compressible Flows past Aerodynamic Shapes by Use of the Streamline Curvature

A simple approximate method is given for the calculation of isentropic irrotational flows past symmetrical airfoils, including mixed subsonic-supersonic flows. The method is based on the choice of suitable values for the streamline curvature in the flow field and the subsequent integration of the equations of motion. The method yields limiting solutions for potential flow. The effect of circulation is considered. A comparison of derived velocity distributions with existing results that are based on calculation to the third order in the thickness ratio indicated satisfactory agreement. The results are also presented in the form of a set of compressibility correction rules that lie between the Prandtl-Glauert rule and the von Karman-Tsien rule (approximately). The different rules correspond to different values of the local shape parameter square root sign YC sub a, in which Y is the ordinate and C sub a is the curvature at a point on an airfoil. Bodies of revolution, completely supersonic flows, and the significance of the limiting solutions for potential flow are also briefly discussed.

Perl, W↗
DOE OSTI2019

Magnetic resonance cholangiopancreatography using optimized integrated combination with parallel imaging and compressed sensing technique

Purpose: To assess the combined parallel imaging (PI) and optimized integrated compressed sensing technique (prototype Compressed SENSE) for magnetic resonance cholangiopancreatography (MRCP) compared with conventional MRCP. Methods: This prospective study was approved by our Institutional Review Board, and all patients provided written informed consent. A total of 56 consecutive patients (27 men and 29 women; mean age 67.2 years) underwent breath-hold three-dimensional (3D) MRCP with PI alone (BH-MRCP; acquisition time, 23 s), respiratory-triggered 3D MRCP with PI alone (RT-MRCP; 201 s) and respiratory-triggered 3D MRCP with Compressed SENSE (RT-MRCPcs; 45 s). Relative duct-to-periductal contrast ratios (RCs) of the pancreaticobiliary ducts were calculated for quantitative image analyses. Two radiologists graded the visibility of the pancreaticobiliary ducts, pancreatic cystic lesion, motion artifact, and overall image quality using a five-point rating scale for qualitative image analyses. Theses qualitative and quantitative measurements were then compared among the three sequences. Results: RCs of the common bile duct, right hepatic duct (RHD), left hepatic duct (LHD), and main pancreatic duct at the pancreatic head, body, and tail segments, were significantly higher RT-MRCP, followed by RT-MRCPcs and BH-MRCP (P < 0.001). The visibility of the peripheral RHD and LHD was slightly better in RT-MRCP than in RT-MRCPcs and BH-MRCP (P < 0.001). The visibility of other pancreaticobiliary ducts, pancreatic cystic lesion, motion artifact, and overall image quality were almost comparable among three sequences. Conclusion: The acquisition time was markedly reduced in RT-MRCPcs compared with conventional RT-MRCP while there were significant differences in both quantitative and qualitative analyses, the differences were small enough that the reduced acquisition time makes up for it.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Phase assemblage of composite cements

The phase assemblage of binary Portland cements with 45 wt% replacement by calcareous fly ash and slag has been investigated by experiment, mass balance and thermodynamic simulations. The input for these calculations was based on clinker reaction measured by XRD-Rietveld refinement, on SCM reaction measured by SEM-EDS full element mapping and on C-S-H composition by SEM-EDS point analyses. A sensitivity analysis estimates the uncertainty of determination of phase volume as at best ± 2 cm{sup 3}/100 cm{sup 3}, and thus of rather semi-quantitative character. The differences between experiment and calculations regarding AFt/AFm, C-S-H and portlandite were assessed. Gel/space ratios computed using the volumes of all hydrates showed a clear correlation to compressive strength, which was unaffected by the mix composition. This suggests that the type of hydrates formed has little or no influence on the compressive strength and that the key factor is the space filling.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Linear and nonlinear dust ion acoustic solitary waves in a quantum dusty electron-positron-ion plasma

The behavior of linear and nonlinear dust ion acoustic (DIA) solitary waves in an unmagnetized quantum dusty plasma, including inertialess electrons and positrons, ions, and mobile negative dust grains, are studied. Reductive perturbation and Sagdeev pseudopotential methods are employed for small and large amplitude DIA solitary waves, respectively. A minimum value of the Mach number obtained for the existence of solitary waves using the analytical expression of the Sagdeev potential. It is observed that the variation on the values of the plasma parameters such as different values of Mach number M, ion to electron Fermi temperature ratio σ, and quantum diffraction parameter H can lead to the creation of compressive solitary waves.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Investigation of Ion-Acoustic Solitons in Magnetosphere and Tokamak Warm Plasma with Two-Temperature Electrons

The properties of oblique propagation of small amplitude ion-acoustic soliton are investigated in a plasma containing weakly relativistic ions and two-temperature electrons (cold and hot electrons). The reductive perturbation method is used to derive the Korteweg−de Vries equation for the present plasma model. It is found that the parameters determining the nature of soliton are different for compressive or rarefactive structures. Moreover, the effects of weakly relativistic ions, the temperature ratio, and the density ratio of hot-to-cold electron species on soliton characters are studied. The theory is applied on the case of relativistic ions observed in the magnetosphere and in the case of nonrelativistic ions observed in tokamaks.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

DME-Propane Autoignition Measurements inside a Shock Tube

Dimethyl ether (DME) is a biofuel that has the potential to replace diesel in heavy-duty engines. A blend of propane (C3H8) and DME could reduce emissions when compared to diesel at heavy-duty compression engine-relevant conditions. Testing a potential new mixture in a compression engine requires a high-fidelity chemical kinetics model that accurately predicts autoignition delay times, which is especially necessary for a compression engine. In this work, autoignition data has been gathered at an equivalence ratio of 2.0 for pressures of 60 and 80 bar. DME and propane were combusted in synthetic air while excited hydroxyl (OH*) chemiluminescence was used to gather ignition delay times. Data was compared to recent chemical kinetic mechanisms for the two different pressures. Using the mechanism with the best fit of autoignition data, a sensitivity analysis was conducted to analyze the chemical kinetics of the DME/C3H8 combustion at elevated pressures.

Mohammed, Zuhayr Pasha↗
NASA NTRS1985

Anatomy of a cosmic-ray neutrino source and the Cygnus X-3 system

The effects of an intense beam of ultra-high energy cosmic rays from a compact object in the Cygnus X-3 binary system hitting the companion star, and of the subsequent production of secondary neutrinos, are examined. A maximum allowable beam luminosity of about 10 to the 42nd erg/s is found for a system containing a 1-10 solar mass main sequence target star. The proton beam must heat a relatively small area of the target star to satisfy observational constraints on the resulting stellar wind. With such a model, the neutrino to gamma-ray flux ratio of about 1000 can result from a combination of gamma-ray absorption and a large neutrino to gamma-ray duty cycle ratio. It is found that the high density of the atmosphere resulting from compression by the beam leads to pion cascading and a neutrino spectrum peaking at 1-10 GeV energies.

Stecker, F. W.↗
NASA NTRS1992

The influence of chromium on structure and mechanical properties of B2 nickel aluminide alloys

Major obstacles to the use of NiAl-based alloys and composites are low ductility and toughness. These shortcomings result in part from a lack of sufficient slip systems to accommodate plastic deformation of polycrystalline material (von Mises Criterion). It has been reported that minor additions of chromium to polycrystalline NiAl cause the predominant slip system to shift from the usual. If true, then a major step toward increasing ductility in this compound may be realized. The purpose of the present study was to verify this phenomenon, characterize it with respect to chromium level and Ni to Al ratio, and correlate any change in slip system with microstructure and mechanical properties. Compression and tensile specimens were prepared from alloys containing 0 to 5 percent chromium and 45 to 55 percent aluminum. Following about one percent strain, transmission electron microscopy foils were produced and the slip systems determined using the g x b = 0 invisibility criterion. Contrary to previous results, chromium was found to have no effect on the preferred slip system of any of the alloys studied. Possible reasons for the inconsistency of the current results with previous work are considered. Composition-structure-property relationships are discerned for the alloys, and good correlation are demonstrated in terms of conventional strengthening models for metallic systems.

Cotton, James Dean↗
NASA NTRS1992

Failure mechanisms of uni-ply composite plates with a circular hole under static compressive loading

The objective of the study was to identify and study the failure mechanisms associated with compressive-loaded uniply graphite/epoxy square plates with a central circular hole. It is found that the type of compressive failure depends on the hole size. For large holes with the diameter/width ratio exceeding 0.062, fiber buckling/kinking initiated at the hole is found to be the dominant failure mechanism. In plates with smaller hole sizes, failure initiates away from the hole edge or complete global failure occurs. Critical buckle wavelengths at failure are presented as a function of the normalized hole diameter.

Khamseh, A. R.↗
NASA NTRS1993

Shear and compression buckling analysis for anisotropic panels with centrally located elliptical cutouts

An approximate analysis for buckling of biaxial- and shear-loaded anisotropic panels with centrally located elliptical cutouts is presented in the present paper. The analysis is composed of two parts, a prebuckling analysis and a buckling analysis. The prebuckling solution is determined using Lekhnitskii's complex variable equations of plane elastostatics combined with a Laurent series approximation and a boundary collocation method. The buckling solution is obtained using the principle of minimum potential energy. A by-product of the minimum potential energy equation is an integral equation which is solved using Gaussian quadrature. Comparisons with documented experimental results and finite element analyses indicate that the approximate analysis accurately predicts the buckling loads of square biaxial- and shear-loaded panels having elliptical cutouts with major axes up to sixty percent of the panel width. Results of a parametric study are presented for shear- and compression-loaded rectangular anisotropic panels with elliptical cutouts. The effects of panel aspect ratio, cutout shape, cutout size, cutout orientation, laminate anisotropy, and combined loading on the buckling load are examined.

Britt, V. O.↗
NASA NTRS2006

High-Strain-Rate Compression Testing of Ice

In the present study a modified split Hopkinson pressure bar (SHPB) was employed to study the effect of strain rate on the dynamic material response of ice. Disk-shaped ice specimens with flat, parallel end faces were either provided by Dartmouth College (Hanover, NH) or grown at Case Western Reserve University (Cleveland, OH). The SHPB was adapted to perform tests at high strain rates in the range 60 to 1400/s at test temperatures of -10 and -30 C. Experimental results showed that the strength of ice increases with increasing strain rates and this occurs over a change in strain rate of five orders of magnitude. Under these strain rate conditions the ice microstructure has a slight influence on the strength, but it is much less than the influence it has under quasi-static loading conditions. End constraint and frictional effects do not influence the compression tests like they do at slower strain rates, and therefore the diameter/thickness ratio of the samples is not as critical. The strength of ice at high strain rates was found to increase with decreasing test temperatures. Ice has been identified as a potential source of debris to impact the shuttle; data presented in this report can be used to validate and/or develop material models for ice impact analyses for shuttle Return to Flight efforts.

Shazly, Mostafa↗