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Results for “area compressibility”

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.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

An eigenvalue-based method for computing the relaxed pressure in compressible multiphase flow with N phases

The modeling of compressible multiphase flows is a decades-old area of study with many applications across various fields. Many of these application areas use stiff pressure relaxation. This process involves the solution of a nonlinear system with N + 1 equations and N + 1 unknowns, where N is the number of phases. The resolution of this system with general equations of state (EOSs) is difficult. Furthermore, nonlinear systems can admit multiple solutions, and current solution methods do not address this possibility. Very recently, a thermodynamic relaxation method was introduced, which effectively maps a relatively simple predictor equation of state onto a more complex target equation of state. In this context, the target EOSs are the chosen EOSs for the thermodynamic model. Furthermore, this thermodynamic relaxation has the benefit of simplifying the stiff pressure relaxation system of equations. In this article, we show this system reduces to a polynomial of degree N, which can be recast as an eigenvalue problem through the use of the associated companion matrix. We show that although this eigenvalue method is generally less efficient than Newton–Raphson iteration, it does not suffer from convergence issues and finds all N roots of the polynomial. Hence, the method provides a fail-safe for root-finding iterative methods and a way to address the issue of multiple solutions to the nonlinear system of equations in stiff pressure relaxation.

Eigenvalue algorithm↗
DOE OSTI2023

Advanced Ab Initio Methods for Nuclear Structure (Final Report)

Over the past decade, there has been enormous progress in the description of nuclear structure from first principles, using interactions from Chiral Effective Field Theory that are rooted in Quantum Chromodynamics, the fundamental theory of strong interactions, and many-body methods that solve the Schrödinger equation with systematically improvable approximations. Amongst those are the family of In-Medium Similarity Renormalization Group (IMSRG) framework developed by the PI and his co-workers. While these methods scale polynomially in the size N of the single-particle basis, computational efforts still grows dramatically as we increase the degrees of freedom for the nucleons by relaxing symmetries or introducing continuum couplings (see below), or as we push to improved truncations to provide precise inputs for experimental efforts, in particular in fundamental symmetry searches. In order to address this growing computational cost, one focus area of this award was the exploration of compression and factorization methods. The key to success or failure is the presence of low-rank structures within the matrix elements of NN and 3N interactions or the IMSRG evolution operator, and a means to reformulate the method that will let us exploit them.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1979

Numerical modeling of two-dimensional confined flows

A numerical model of two-dimensional confined flows is presented. The flow in the duct is partitioned into finite streams. The difference equations are then obtained by applying conservation principles directly to the individual streams. A listing of a computer code based on this approach in FORTRAN 4 language is presented. The code computes two dimensional compressible turbulent flows in ducts when the duct area along the flow is specified and the pressure gradient is unknown.

Greywall, M. S.↗
NASA NTRS1985

High resolution solutions of the Euler equations for vortex flows

Solutions of the Euler equations are presented for M = 1.5 flow past a 70-degree-swept delta wing. At an angle of attack of 10 degrees, strong leading-edge vortices are produced. Two computational approaches are taken, based upon fully three-dimensional and conical flow theory. Both methods utilize a finite-volume discretization solved by a pseudounsteady multistage scheme. Results from the two approaches are in good agreement. Computations have been done on a 16-million-word CYBER 205 using 196 x 56 x 96 and 128 x 128 cells for the two methods. A sizable data base is generated, and some of the practical aspects of manipulating it are mentioned. The results reveal many interesting physical features of the compressible vortical flow field and also suggest new areas needing research.

Murman, E. M.↗
NASA NTRS1988

Proceedings of the Mobile Satellite Conference

A satellite-based mobile communications system provides voice and data communications to mobile users over a vast geographic area. The technical and service characteristics of mobile satellite systems (MSSs) are presented and form an in-depth view of the current MSS status at the system and subsystem levels. Major emphasis is placed on developments, current and future, in the following critical MSS technology areas: vehicle antennas, networking, modulation and coding, speech compression, channel characterization, space segment technology and MSS experiments. Also, the mobile satellite communications needs of government agencies are addressed, as is the MSS potential to fulfill them.

Rafferty, William↗
NASA NTRS1935

Performance tests of a single-cylinder compression-ignition engine with a displacer piston

Engine performance was investigated using a rectangular displacer on the piston crown to cause a forced air flow in a vertical-disk combustion chamber of a single-cylinder, 4-stroke-cycle compression-ignition engine. The optimum air-flow area was determined first with the area concentrated at one end of the displacer and then with the area equally divided between two passages, one at each end of the displacer. Best performance was obtained with the two-passage air flow arranged to give a calculated maximum air-flow speed of 8 times the linear crank-pin speed. With the same fuel-spray formation as used without the air flow, the maximum clear exhaust brake mean effective pressure at 1,500 r.p.m. was increased from 90 to 115 pounds per square inch and the corresponding fuel consumption reduced from 0.46 to 0.43 pound per brake horsepower-hour. At 1,200 r.p.m., a maximum clear exhaust brake mean effective pressure of 120 pounds per square inch was obtained at a fuel consumption of 0.42 pound per brake horsepower-hour. At higher specific fuel consumption the brake mean effective pressure was still increasing rapidly.

Moore, C S↗
NASA NTRS1943

Tests of Aluminum-alloy Stiffened-sheet Specimens Cut from an Airplane Wing

The specimens used in the present tests were cut from an actual airplane wing of the stressed-skin type. The specimens thus obtained were not representative of the usual type of laboratory specimens because the stiffeners were not exactly parallel nor evenly spaced and, in one case, the skin consisted of pieces of sheet of different thicknesses. The test data obtained indicate that the buckling strain of stiffened curved sheet can be computed with reasonable accuracy by the equation given by Wenzek. The ultimate loads of the specimens when tested as flat sheet were within +/-11 percent of the product of the compressive yield strength and the cross-sectional area of the stiffeners. A rivet spacing equal to 98 times the sheet thickness was a source of weakness, and rivet spacings up to 36 times the sheet thickness appeared satisfactory.

Holt, Marshall↗
DOE OSTI2024

THM: the MOOSE thermal hydraulics module

The MOOSE Thermal Hydraulics Module (THM) is designed to facilitate the development of thermal hydraulic system models. It provides the capability to assemble networks of coupled components such as pipes, junctions, valves, turbomachinery, and heat exchangers. Its library of components supports a single-phase, compressible flow model based on a variable-area formulation of the Euler equations of gas dynamics and discretized using a finite volume scheme. THM offers a flexible system for specifying closures such as friction factors or heat transfer coefficients, allowing the user to choose from built-in correlations or define their own in the input file. A control logic system can be used to control input parameters, necessary for implementing transient scenarios and mirroring real control systems in thermal hydraulic systems. THM can be coupled with other MOOSE-based applications for multiphysics calculations. This talk will give an introduction to the capabilities of THM and provide some examples of its usage and validation.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2025

MOOSE Thermal-Hydraulics Module - MOOSE workshop

The MOOSE Thermal Hydraulics Module (THM) is designed to facilitate the development of thermal hydraulic system models. It provides the capability to assemble networks of coupled components such as pipes, junctions, valves, turbomachinery, and heat exchangers. Its library of components supports a single-phase, compressible flow model based on a variable-area formulation of the Euler equations of gas dynamics and discretized using a finite volume scheme. THM offers a flexible system for specifying closures such as friction factors or heat transfer coefficients, allowing the user to choose from built-in correlations or define their own in the input file. A control logic system can be used to control input parameters, necessary for implementing transient scenarios and mirroring real control systems in thermal hydraulic systems. THM can be coupled with other MOOSE-based applications for multiphysics calculations. This training will give an introduction to the capabilities of THM and provide some examples of its usage and validation.

97 - MATHEMATICS AND COMPUTING↗
DOE OSTI2022

A review on nearly isothermal compression technology

Compressors can be described as the heart of a vapor compression refrigeration system, circulating the working fluid in the system. Significant benefits can be gained from improving its efficiency since energy consumption is responsible for almost the entire system's power input. An effort has been made to achieve isothermal compression through liquid refrigerant injection or inter-stage cooling in refrigeration systems. In recent years, much effort has been invested into isothermal compression technology for air compressors or compressed air energy storage systems with the rise of renewable energy. Here, this work has explored the advancements made in this area and categorized them to discuss the benefits, limitations, and tradeoffs. Evidently, increasing heat transfer area is a significant aid in improving heat transfer, resulting in better isothermal compression. However, liquid pistons open more avenues for this to be pursued, and therefore, are limited to air compression applications. In addition, water injection proved to be the most effective among the methods. Finally, there is a need for more experimental research on refrigeration applications and the field is still in its infancy.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2025

Initial assessment of alternative carbon fiber geometries for design of cost-effective compressive performance: Size effect studies

Carbon fiber provides opportunity to reduce weight in structural composites, including wind turbine blades, due to the material's superior specific stiffness and specific strength compared to alternatives. Despite these advantages, cost and compressive performance are considered weaknesses for carbon fiber products available today. Studies to produce low-cost carbon fiber alternatives, including the use of textile-derived precursor systems, have shown progress and merit through the DOE/ORNL low-cost carbon fiber initiatives. Here, this work focuses on enabling increases in compressive strength through design of the carbon fiber geometry, applicable to both textile and conventional precursor systems, while also providing opportunities to reduce carbon fiber processing costs. Fiber-resin interface and fiber alignment are among the most frequently cited factors controlling composite compressive performance. However, it is believed that there is opportunity in traditionally unexplored routes to increasing compressive strength through alteration of the carbon fiber geometry by increasing the fiber area moment of inertia and/or the fiber perimeter and interfacial area. This paper presents initial results from manufacturing carbon fiber materials to assess the impacts of carbon fiber size on tested composite compressive performance with projected neutral or even beneficial impact on fiber and composite manufacturing economics. Carbon fiber systems with increasing size illustrate a favorable correlation for compressive performance greater than predicted from a micromechanical failure model. The manufacturing and mechanical test results support the hypothesis of this work that alterations to fiber geometry can be used to produce improvements of the compressive strength of carbon fiber reinforced polymers and provide incentive for related work in designing alternative shapes to further enhance compressive performance.

42 ENGINEERING↗
NASA NTRS1991

Enhancement of the no-vent fill process

This paper presents an analytical and experimental evaluation of an enhanced techniques for no-vent fill. The method entails injecting liquid through the top of the receiver vessel, thereby increasing surface area and agitation of the ullage/liquid interface. Both of these factors promote condensation induced ullage collapse, and reduce compressive impedance to the incoming liquid. The enhanced process was analyzed by modifying the surface area algorithm of an existing tank thermodynamic code to model a downward-pointing, conical jet impringing on a steadily rising liquid surface. Transient pressure and temperature measurements from several tests with Freon-114 were input into the revised model to calculate condensation rate as a function of fill level. By expressing these rates in dimensionless form (i.e., in terms of Stanton number and Prandtl number), an empirical correlation similar to the submerged jet model of Brown and Sonin (1989) was derived. This provided a basis for developing an expression which relates top fill to bottom fill performance.

Vaughan, David A.↗
NASA NTRS1990

Some optical and electron microscope comparative studies of excimer laser-assisted and nonassisted molecular-beam epitaxically grown thin GaAs films on Si

The quality of GaAs thin films grown via MBE under pulsed excimer laser irradiation on Si substrates is examined in both laser-irradiated and nonirradiated areas using Raman scattering, Rayleigh scattering, and by photoluminescence (PL), as a function of temperature, and by TEM. The temperature dependence of the PL and Raman peak positions indicates the presence of compressive stress in the thin GaAs films in both laser-irradiated and nonirradiated areas. This indicates incomplete homogeneous strain relaxation by dislocations at the growth temperature. The residual compressive strain at the growth temperature is large enough such that even with the introduction of tensile strain arising from the difference in thermal expansion coefficients of GaAs and Si, a compressive strain is still present at room temperature for these thin GaAs/Si films.

Lao, Pudong↗
NASA NTRS2005

Compression Techniques for Improved Algorithm Computational Performance

Analysis of thermal data requires the processing of large amounts of temporal image data. The processing of the data for quantitative information can be time intensive especially out in the field where large areas are inspected resulting in numerous data sets. By applying a temporal compression technique, improved algorithm performance can be obtained. In this study, analysis techniques are applied to compressed and non-compressed thermal data. A comparison is made based on computational speed and defect signal to noise.

Zalameda, Joseph N.↗
NASA NTRS1967

Double copper sheath multiconductor instrumentation cable is durable and easily installed in high thermal or nuclear radiation area

Multiconductor instrumentation cable in which the conducting wires are routed through two concentric copper tube sheaths, employing a compressed insulator between the conductors and between the inner and outer sheaths, is durable and easily installed in high thermal or nuclear radiation area. The double sheath is a barrier against moisture, abrasion, and vibration.

Mc Crae, A. W., Jr.↗
DOE OSTI2022

A lightweight, user-configurable detector ASIC digital architecture with on-chip data compression for MHz X-ray coherent diffraction imaging

Today, most X-ray pixel detectors used at light sources transmit raw pixel data off the detector ASIC. With the availability of more advanced ASIC technology nodes for scientific application, more digital functionalities from the computing domains (e.g., compression) can be integrated directly into a detector ASIC to increase data velocity. In this paper, we describe a lightweight, user-configurable detector ASIC digital architecture with on-chip compression which can be implemented in 130 nm technologies in a reasonable area on the ASIC periphery. In addition, we present a design to efficiently handle the variable data from the stream of parallel compressors. The architecture includes user-selectable lossy and lossless compression blocks. The impact of lossy compression algorithms is evaluated on simulated and experimental X-ray ptychography datasets. This architecture is a practical approach to increase pixel detector frame rates towards the continuous 1 MHz regime for not only coherent imaging techniques such as ptychography, but also for other diffraction techniques at X-ray light sources.

47 OTHER INSTRUMENTATION↗
NASA NTRS1994

Learning random networks for compression of still and moving images

Image compression for both still and moving images is an extremely important area of investigation, with numerous applications to videoconferencing, interactive education, home entertainment, and potential applications to earth observations, medical imaging, digital libraries, and many other areas. We describe work on a neural network methodology to compress/decompress still and moving images. We use the 'point-process' type neural network model which is closer to biophysical reality than standard models, and yet is mathematically much more tractable. We currently achieve compression ratios of the order of 120:1 for moving grey-level images, based on a combination of motion detection and compression. The observed signal-to-noise ratio varies from values above 25 to more than 35. The method is computationally fast so that compression and decompression can be carried out in real-time. It uses the adaptive capabilities of a set of neural networks so as to select varying compression ratios in real-time as a function of quality achieved. It also uses a motion detector which will avoid retransmitting portions of the image which have varied little from the previous frame. Further improvements can be achieved by using on-line learning during compression, and by appropriate compensation of nonlinearities in the compression/decompression scheme. We expect to go well beyond the 250:1 compression level for color images with good quality levels.

Gelenbe, Erol↗