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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Computational simulation of high-temperature metal matrix composites cyclic behavior

A procedure was developed and is described that can be used to computationally simulate the cyclic behavior of high-temperature metal matrix composites (HTMMC) and its degradation effects on the structural response. This procedure consists of HTMMC mechanics coupled with a multifactor-interaction constituent material relationship and with an incremental iterative nonlinear analysis. The procedure is implemented in a computer code that can be used to computationally simulate the thermomechanical behavior of HTMMC starting from the fabrication process and proceeding through thermomechanical cycling, accounting for the interface/interphase region. Results show that combined thermal/mechanical cycling, the interphase, and in situ matrix properties have significant effects on the structural integrity of HTMMC.

Chamis, Christos C.↗
DOE OSTI2014

Communication: Minimum in the thermal conductivity of supercooled water: A computer simulation study

We report the results of a computer simulation study of the thermodynamic properties and the thermal conductivity of supercooled water as a function of pressure and temperature using the TIP4P-2005 water model. The thermodynamic properties can be represented by a two-structure equation of state consistent with the presence of a liquid-liquid critical point in the supercooled region. Our simulations confirm the presence of a minimum in the thermal conductivity, not only at atmospheric pressure, as previously found for the TIP5P water model, but also at elevated pressures. This anomalous behavior of the thermal conductivity of supercooled water appears to be related to the maximum of the isothermal compressibility or the minimum of the speed of sound. However, the magnitudes of the simulated thermal conductivities are sensitive to the water model adopted and appear to be significantly larger than the experimental thermal conductivities of real water at low temperatures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1974

Computer simulation of a fringe type laser velocimeter

A computer simulation of a fringe type laser velocimeter has been written to determine the theoretical characteristics of the laser velocimeter when applied to a given flow field. The program includes the effect of particle size and composition on particle lag, light scattering characteristics and signal contrast. The model of the laser velocimeter includes the laser, optical system, photomultiplier, and counter type data processing electronics. The LV particle size analyzer is also modeled and incorporated in the program. An example application of the program to a Mach 5 wind tunnel using a backscatter laser velocimeter is presented.

Meyers, J. F.↗
NASA NTRS1980

KU-Band rendezvous radar performance computer simulation model

The preparation of a real time computer simulation model of the KU band rendezvous radar to be integrated into the shuttle mission simulator (SMS), the shuttle engineering simulator (SES), and the shuttle avionics integration laboratory (SAIL) simulator is described. To meet crew training requirements a radar tracking performance model, and a target modeling method were developed. The parent simulation/radar simulation interface requirements, and the method selected to model target scattering properties, including an application of this method to the SPAS spacecraft are described. The radar search and acquisition mode performance model and the radar track mode signal processor model are examined and analyzed. The angle, angle rate, range, and range rate tracking loops are also discussed.

Griffin, J. W.↗
NASA NTRS1982

Water immersion and its computer simulation as analogs of weightlessness

Experimental studies and computer simulations of water immersion are summarized and discussed with regard to their utility as analogs of weightlessness. Emphasis is placed on describing and interpreting the renal, endocrine, fluid, and circulatory changes that take place during immersion. A mathematical model, based on concepts of fluid volume regulation, is shown to be well suited to simulate the dynamic responses to water immersion. Further, it is shown that such a model provides a means to study specific mechanisms and pathways involved in the immersion response. A number of hypotheses are evaluated with the model related to the effects of dehydration, venous pressure disturbances, the control of ADH, and changes in plasma-interstitial volume. By inference, it is suggested that most of the model's responses to water immersion are plausible predictions of the acute changes expected, but not yet measured, during space flight. One important prediction of the model is that previous attempts to measure a diuresis during space flight failed because astronauts may have been dehydrated and urine samples were pooled over 24-hour periods.

Leonard, J. I.↗
NASA NTRS1990

Computer Simulation Of Cyclic Oxidation

Computer model developed to simulate cyclic oxidation of metals. With relatively few input parameters, kinetics of cyclic oxidation simulated for wide variety of temperatures, durations of cycles, and total numbers of cycles. Program written in BASICA and run on any IBM-compatible microcomputer. Used in variety of ways to aid experimental research. In minutes, effects of duration of cycle and/or number of cycles on oxidation kinetics of material surveyed.

Probst, H. B.↗
NASA NTRS2004

Computational Simulation of Composite Structural Fatigue

Progressive damage and fracture of composite structures subjected to monotonically increasing static, tension-tension cyclic, pressurization, and flexural cyclic loading are evaluated via computational simulation. Constituent material properties, stress and strain limits are scaled up to the structure level to evaluate the overall damage and fracture propagation for composites. Damage initiation, growth, accumulation, and propagation to fracture due to monotonically increasing static and cyclic loads are included in the simulations. Results show the number of cycles to failure at different temperatures and the damage progression sequence during different degradation stages. A procedure is outlined for use of computational simulation data in the assessment of damage tolerance, determination of sensitive parameters affecting fracture, and interpretation of results with insight for design decisions.

Minnetyan, Levon↗
NASA NTRS2005

Computational Simulation of Composite Structural Fatigue

Progressive damage and fracture of composite structures subjected to monotonically increasing static, tension-tension cyclic, pressurization, and flexural cyclic loading are evaluated via computational simulation. Constituent material properties, stress and strain limits are scaled up to the structure level to evaluate the overall damage and fracture propagation for composites. Damage initiation, growth, accumulation, and propagation to fracture due to monotonically increasing static and cyclic loads are included in the simulations. Results show the number of cycles to failure at different temperatures and the damage progression sequence during different degradation stages. A procedure is outlined for use of computational simulation data in the assessment of damage tolerance, determination of sensitive parameters affecting fracture, and interpretation of results with insight for design decisions.

Minnetyan, Levon↗
DOE OSTI2017

Atomistic Computer Simulations of Water Interactions and Dissolution of Inorganic Glasses

Computational simulations at the atomistic level play an increasing important role in understanding the structures, behaviors, and the structure-property relationships of glass and amorphous materials. In this paper, we reviewed atomistic simulation methods ranging from first principles calculations and ab initio molecular dynamics (AIMD), to classical molecular dynamics (MD) and meso-scale kinetic Monte Carlo (KMC) simulations and their applications to glass-water interactions and glass dissolutions. Particularly, the use of these simulation methods in understanding the reaction mechanisms of water with oxide glasses, water-glass interfaces, hydrated porous silica gels formation, the structure and properties of multicomponent glasses, and microstructure evolution are reviewed. Here, the advantages and disadvantageous of these methods are discussed and the current challenges and future direction of atomistic simulations in glass dissolution are presented.

36 MATERIALS SCIENCE↗
NASA NTRS1994

Self contamination effects in the TAUVEX UV Telescope: Ground testing and computer simulation

The contamination effects due to outgassing from construction materials of the TAUVEX (Tel Aviv University UV Telescope) were evaluated using a combination of ground testing and computer simulations. Tests were performed from the material level of the system level including: (1) High sensitivity CVCM(10(exp -3 percent) measurements of critical materials. (2) Optical degradation measurements of samples specially contaminated by outgassing products at different contamination levels. (3) FTIR studies of chemical composition of outgassed products on above samples. (4) High resolution AFM studies of surface morphology of contaminated surfaces. The expected degradation of TAUVEX performance in mission was evaluated applying a computer simulation code using input parameters determined experimentally in the above tests. The results have served as guidelines for the proper selection of materials, cleanliness requirements, determination of the thermal conditions of the system and bakeout processes.

Lifshitz, Y.↗
NASA NTRS1978

Reference manual for the Langley Research Center flight simulation computing system

The researchers at the Langley Research Center Flight Simulation Computing System are provided with an advanced real-time digital simulation capability. This capability is controlled at the user interface level by the Real Time Simulation Supervisor. The Supervisor is a group of subprograms loaded with a simulation application program. The Supervisor provides the interface between the application program and the operating system, and coordinates input and output to and from the simulation hardware. The Supervisor also performs various utility functions as required by a simulation application program.

Cleveland, J. I., II↗
NASA NTRS1977

Signal-to-noise ratio estimation in digital computer simulation of lowpass and bandpass systems with applications to analog and digital communications, volume 3

Techniques are developed to estimate power gain, delay, signal-to-noise ratio, and mean square error in digital computer simulations of lowpass and bandpass systems. The techniques are applied to analog and digital communications. The signal-to-noise ratio estimates are shown to be maximum likelihood estimates in additive white Gaussian noise. The methods are seen to be especially useful for digital communication systems where the mapping from the signal-to-noise ratio to the error probability can be obtained. Simulation results show the techniques developed to be accurate and quite versatile in evaluating the performance of many systems through digital computer simulation.

Tranter, W. H.↗
NASA NTRS2002

Opportunities for Breakthroughs in Large-Scale Computational Simulation and Design

Opportunities for breakthroughs in the large-scale computational simulation and design of aerospace vehicles are presented. Computational fluid dynamics tools to be used within multidisciplinary analysis and design methods are emphasized. The opportunities stem from speedups and robustness improvements in the underlying unit operations associated with simulation (geometry modeling, grid generation, physical modeling, analysis, etc.). Further, an improved programming environment can synergistically integrate these unit operations to leverage the gains. The speedups result from reducing the problem setup time through geometry modeling and grid generation operations, and reducing the solution time through the operation counts associated with solving the discretized equations to a sufficient accuracy. The opportunities are addressed only at a general level here, but an extensive list of references containing further details is included. The opportunities discussed are being addressed through the Fast Adaptive Aerospace Tools (FAAST) element of the Advanced Systems Concept to Test (ASCoT) and the third Generation Reusable Launch Vehicles (RLV) projects at NASA Langley Research Center. The overall goal is to enable greater inroads into the design process with large-scale simulations.

Alexandrov, Natalia↗