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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 343 records · Page 19

All sources NASA NTRS DOE OSTI

NASA NTRSDate not supplied

A Methodology for Reliability Assessments of Arbitrary Satellite Constellations

The commercial success of small satellite development and multi-satellite missions has led to constellation missions being proposed in every sector of the market. This paradigm shift has the potential to enable more capable and cost-effective space science missions. However, these novel approaches to space missions have outstripped existing policy and analysis methods for assessing the reliability of multi-satellite missions. Mission designers and decisionmakers need new methods and standards for modeling how the reliability of constituent spacecraft elements affect the aggregate reliability of constellations across a wide range of concepts and application-specific requirements. The Space Mission Analysis Branch at NASA’s Langley Research Center has developed a methodology for simulating the on-orbit reliability of arbitrary spacecraft constellations. In this paper, the authors describe the methodology and provides examples of how it can be used to evaluate specific constellation designs. To demonstrate the flexibility of the approach, several different constellation configurations are considered, including both homogenous and heterogenous designs. Next, the authors demonstrate the ability to perform broad parameter sweeps to develop greater insight into the intrinsic reliability trends associated with constellation concepts. Finally, the authors provide tables and novel data graphics which enable decisionmakers to quickly discern the relationships between constellation sizes, topologies, replenishment strategies, and overall constellation reliability.

satellite↗

NASA NTRS1975

Review of aircraft noise propagation

The current state of knowledge about the propagation of aircraft noise was reviewed. The literature on the subject is surveyed and methods for predicting the most important and best understood propagation effects are presented. Available empirical data are examined and the data's general validity is assessed. The methods used to determine the loss of acoustic energy due to uniform spherical spreading, absorption in a homogeneous atmosphere, and absorption due to ground cover are presented. A procedure for determining ground induced absorption as a function of elevation angle between source and receiver is recommended. Other factors that affect propagation, such as refraction and scattering due to turbulence, which were found to be less important for predicting the propagation of aircraft noise, are also evaluated.

Putnam, T. W.↗

NASA NTRS1985

Application of the SWINT code to wing/body/tail geometries

Pressure and force calculations from the SWINT Euler code are presented and analyzed for a variety of configurations ranging from simple axisymmetric bodies to complex bodies with wings, tails, and inlets at speeds covering the supersonic Mach number range. The SWINT results are compared with both experimental data and with results from simpler computational methods to assess the increased accuracy from the Euler solution. It is shown that SWINT gives excellent results on axisymmetric bodies for attached flow; however, a better method of simulating the separation process on such bodies is needed for increased leeside accuracy. Good leeside accuracy, however, is found on a 3 to 1 elliptical body. It is shown that SWINT gives realistic downstream interference effects, resulting in good predictions of the overall aerodynamics for complex wing-body-tail geometries. The QUICK-geometry system has been coupled with SWINT code to provide a simplified geometry definition procedure for complex bodies. The QUICK method is shown to be a preferable alternative to the current method of inserting the body description directly into the code by FORTRAN statements.

Allen, J. M.↗

NASA NTRS1989

Enhanced resolution particle size distributions by multiple angle photon correlation spectroscopy

Photon correlation spectroscopy (PCS) has become a method of choice for measuring submicrometer particles. It is capable of rapid, accurate measurements of mean particle size. Since the measurements are nonperturbing, it is ideal for monitoring systems undergoing dynamic changes. Despite its widespread acceptance, the information content of PCS measurements for particle size distributions is low and provides limited resolution. A method is presented whereby PCS measurements made at several scattering angles plus the angular distribution of light scattered from the particles are combined in a single simultaneous analysis to effect an enhanced resolution particle size distribution. The efficacy of the method is assessed by recovering size distributions from computer simulated data and by comparisons of conventional PCS measurements of polystyrene spheres with those made by the new method.

Bott, Steven E.↗

DOE OSTI2025

Nondestructive Evaluation of Concrete: Elastic Property Imaging Through Full Waveform Inversion

Concrete is a major construction material worldwide and plays a crucial role in the nuclear industry. The elastic properties of concrete are prone to change and degrade while in service, as it is often subjected to extreme operational and environmental conditions. An accurate evaluation of concrete's elastic properties is thus essential to ensure structural integrity and safety. This is especially true for concrete in nuclear power plants, where irradiation effects significantly impact concrete mechanical properties. There are various methods to assess these properties, with ultrasound-based techniques showing high potential due to their nondestructive nature, cost-effectiveness, and safety. While several nondestructive evaluation methods exist, most rely on idealizations such as assuming homogeneous material and plane wavefronts. In this work, we address these issues by introducing an ultrasound-based nondestructive method aimed at reconstructing spatially varying images of concrete mechanical properties. By accurately modeling wave physics, including scattering and reflection, we overcome several of the aforementioned idealizations and aim to utilize the full waveform for imaging material properties through depth, resulting in more reliable images. Full waveform inversion (FWI) was first introduced by geophysicists to reconstruct subsurface elastic property images. The goal is to minimize the difference between simulated and recorded wavefield signals, often through gradient-based optimization algorithms. While FWI is primarily conducted using the acoustic approximation of the wave equation, few works focus on elastic FWI, where the goal is to reconstruct images of not only the pressure wave speed but also the shear wave speed and density (or their equivalents). This work explores the potential of using elastic FWI to predict concrete mechanical properties as an initial effort for a more accurate monitoring of concrete conditions in service. Reconstructing images of different elastic parameters enables more specificity and accurate condition diagnosis. This paper will detail this approach and provide examples demonstrating the effectiveness of elastic FWI in reconstructing comprehensive maps of concrete mechanical properties.

42 - ENGINEERING↗

NASA NTRS1993

Computational techniques for high-speed flows with viscous and chemical effects

Algorithms for solving the Euler and the Navier-Stokes equations in conjunction with chemical kinetic equations are presented. The convective flux is estimated from a quasi one dimensional interpolation procedure. Shock, contact, and expansion waves and thermochemical nonequilibrium phenomena are captured by the Lax-Friedrichs technique. Relaxation techniques were developed to enhance their effectiveness in dealing with spatial and temporal stiffness associated with the physical problems. Both explicit and implicit smoothers were implemented into the standard multigrid time stepping method. Unsteady and steady scalar problems are discussed. A perfect gas and equilibrium air shock tube problem is investigated. Numerical schemes and techniques are compared for the problems of shock and boundary layer interaction and three dimensional viscous, nonequilibrium flow encompassing an aerobrake. The results are comparable in accuracy against other high order non-oscillatory techniques. The multigrid methods are assessed using a Mach 8 flow over a complete planar body, a sphere, and a blunt delta wing at 20 deg incidence. Applying an implicit multigrid method on a nested grid of 128 by 64 nodes the reduction factor is 0.25. The central processing unit reduction factor is 2.2 after both the single and multigrid Runge-Kutta solutions converged to machine zero on a grid of 37 by 41 by 73 nodes.

Li, C. P.↗

NASA NTRS1982

A program for assessing pilot mental state in flight simulators

A program to apply proposed measures of pilot mental state in the simulator flight deck environment has been undertaken at NASA Langley Research Center. Literature survey identified a promising subset of methods for assessing workload, attention and vigilance, and task-related stress, and revealed a need for improved analytical techniques in the physiological area. An effort to apply functional modelling techniques has been initiated. A psychophysiological laboratory has been designed for simulator application. The program is designed to develop improved techniques for evaluating simulator cue fidelity and for imposing realistic workload and attentional demands on the simulator pilot.

Pope, A. T.↗

NASA NTRS1992

Experimental results on a wall interference correction method with interface measurements

A wall interference assessment and correction method for subsonic two-dimensional wind tunnel testing is presented. This method calculates a pressure coefficient and angle of attack correction based on velocity measurements on interfaces inside of the wind tunnel. A mathematical representation of the test article is not required. An experimental verification of the suggested technique is given. A NACA 0012 airfoil is tested at a Mach number of 0.70 and at two different angles of attack. Calculated blockage corrections show reasonable agreement with results based on Hackett's method. Corrected surface pressures compare favorably to free-air flow field data if the tunnel flow field is subsonic. The present wall interference correction method can be applied to transonic tunnel flow fields with some restrictions. Errors are estimated and it is shown that the expected error in calculating the pressure coefficient correction on the model surface is in the order of the error of pressure coefficient measurement on interfaces. Necessary testing equipment in existing tunnels can easily be modified if the present method is applied.

Lo, C. F.↗

NASA NTRSDate not supplied

Community Noise Assessment of Urban Air Mobility Vehicle Operations using the FAA Aviation Environmental Design Tool

In contrast to most commercial air traffic today, vehicles serving the urban air mobility (UAM) market are anticipated to operate in communities close to the public at large. The approved model for assessing environmental impact of air traffic actions in the United States, the Federal Aviation Administration’s Aviation Environmental Design Tool (AEDT), does not support analysis of such operations due to a combined lack of a UAM aircraft performance model and aircraft noise data. This paper discusses the initial development of a method to assess the acoustic impact of UAM fleet operations on the community using AEDT and demonstrates its use for representative UAM operations. In particular, methods were developed using fixed-point flight profiles and user-supplied noise data in a manner that avoids unwanted behavior in AEDT. A set of 32 routes in the Dallas-Ft. Worth area were assessed for single and multiple (fleet) operations for two concept vehicles.

urban air mobility↗

NASA NTRSDate not supplied

Community Noise Assessment of Urban Air Mobility Vehicle Operations using the FAA Aviation Environmental Design Tool

urban air mobility↗

NASA NTRS2001

Permeability Testing of Impacted Composite Laminates for Use on Reusable Launch Vehicles

Since composite laminates are beginning to be identified for use in reusable launch vehicle propulsion systems, an understanding of their permeance is needed. A foreign object impact event can cause a localized area of permeability (leakage) in a polymer matrix composite, and it is the aim of this study to assess a method of quantifying permeability-after-impact results. A simple test apparatus is presented, and variables that could affect the measured values of permeability-after-impact were assessed. Once it was determined that valid numbers were being measured, a fiber/resin system was impacted at various impact levels and the resulting permeability measured, first with a leak check solution (qualitative) then using the new apparatus (quantitative). The results showed that as the impact level increased, so did the measured leakage. As the pressure to the specimen was increased, the leak rate was seen to increase in a nonlinear fashion for almost all the specimens tested.

Nettles, A. T.↗

NASA NTRS2001

Permeability Testing of Impacted Composite Laminates for Use on Reusable Launch Vehicles

Nettles, Alan T.↗

NASA NTRS2002

Permeability After Impact Testing of Composite Laminates

Since composite laminates are beginning to be identified for use in reusable launch vehicle propulsion systems, an understanding of their permeance is needed. A foreign object impact event can cause a localized area of permeability (leakage) in a polymer matrix composite and it is the aim of this study to assess a method of quantifying permeability-after-impact results. A simple test apparatus is presented and variables that could affect the measured values of permeability-after-impact were assessed. Once it was determined that valid numbers were being measured, a fiber/resin system was impacted at various impact levels and the resulting permeability measured, first with a leak check solution (qualitative) then using the new apparatus (quantitative). The results showed that as the impact level increased, so did the measured leakage. As the pressure to the specimen was increased, the leak rate was seen to increase in a non-linear fashion for almost all of the specimens tested.

Nettles, A.T.↗

NASA NTRS2003

Permeability After Impact Testing of Composite Laminates

Since composite laminates are beginning to be identified for use in reusable launch vehicle propulsion systems, an understanding of their permeance is needed. A foreign object impact event can cause a localized area of permeability (leakage) in a polymer matrix composite and it is the aim of this study to assess a method of quantifying permeability-after-impact results. A simple test apparatus is presented and variables that could affect the measured values of permeability-after-impact were assessed. Once it was determined that valid numbers were being measured, a fiber/resin system was impacted at various impact levels and the resulting permeability measured, first with a leak check solution (qualitative) then using the new apparatus (quantitative). The results showed that as the impact level increased, so did the measured leakage. As the pressure to the specimen was increased, the leak rate was seen to increase in a non-linear fashion for almost all of the specimens tested.

Nettles, Alan T.↗

NASA NTRS2011

Humidity Steady State Low Voltage Testing of MLCCs (Based on NESC Technical Assessment Report)

Review of the low voltage reduced Insulation Resistance (IR) failure phenomenon in Multilayer ceramic capacitors (MLCCs)and NASA approaches to contend with this risk. 1. Analyze published materials on root cause mechanisms. 2. Investigate suitability of current test methods to assess MLCC lots for susceptibility. 3. Review current NASA parts selection and application guidelines in consideration of benefits vs. disadvantages.

Sampson, Mike↗

NASA NTRS1994

Generation of Particles and Seeding

One of the most important elements in laser velocimetry, yet the most neglected, is the small particle embedded in the flow field that scatters the light necessary to make velocity measurements. The characteristics of this small particle are often ignored in the effort to obtain data. This seems strange since it is the primary cause of measurement error. If the particle is too large, it will not follow the flow resulting in an inaccurate representation of the fluid velocity. If the particle is too small, it will not scatter sufficient light to provide the signal-to-noise necessary to minimize measurement uncertainty in the signal processing electronics. This lecture will attempt to remove the confusion in choosing a seeding method by assessing many of the techniques currently used. It will outline their characteristics and typical limitations imposed by various applications. The lecture will then focus on the ramifications of these methods on measurement accuracy.

Meyers, James F.↗

NASA NTRS1992

The structures, binding energies and vibrational frequencies of Ca3 and Ca4: An application of the CCSD(T) method

The Ca3 and Ca4 metallic clusters have been investigated using state-of-the-art ab initio quantum mechanical methods. Large atomic natural orbital basis sets have been used in conjunction with the singles and doubles coupled-cluster (CCSD) method, a coupled-cluster method that includes a perturbational estimate of connected triple excitations, denoted CCSD(T), and the multireference configuration interaction (MRCI) method. The equilibrium geometries, binding energies and harmonic vibrational frequencies have been determined with each of the methods so that the accuracy of the coupled-cluster methods may be assessed. Since the CCSD(T) method reproduces the MRCI results very well, cubic and quartic force fields of Ca3 and Ca4 have been determined using this approach and used to evaluate the fundamental vibrational frequencies. The infrared intensities of both the e' mode of Ca3 and the t2 mode of Ca4 are found to be small. The results obtained in this study are compared and contrasted with those from our earlier studies on small Be and Mg clusters.

Lee, Timothy J.↗

NASA NTRSDate not supplied

Comparison of Inlet Broadband Acoustic Liner Predictions to Quiet Technology Demonstrator 3 Flight Data

Companion acoustic liner attenuation predictions and flight data representative of certification conditions are analyzed to determine the validation quality and gain an understanding of current prediction shortcomings. These comparisons are limited to the inlet broadband component of fan noise. Two prediction methods are assessed: a traditional, semiempirical model, and a computational approach with a parabolic duct propagation code coupled with a Ffowcs Williams-Hawkings solver for free-field propagation. The semiempirical method is widely used for aircraft system noise predictions, but does not explicitly account for several physical parameters important for sound attenuation. The computational approach includes these effects, but requires a significant increase in cycle time. For the three-degree-of-freedom (3DOF) liner tested, both methods have a bias error less than 0.5 dB for cutback and takeoff power settings, and a much larger 3–4 dB bias for approach power setting. The standard deviation of each method varies between 1–2 dB for different conditions. The similar performance of both approaches illustrates that, in this instance, the additional complexity of the computational approach does not provide a clear improvement over the semiempirical method. Planned improvements to the numerical grid and source assumptions may result in reevaluation of this conclusion in later work.

aircraft system noise↗