SEARCH · Engineering Papers
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.
Increment 57 - 58 Science Symposium presentation of Advanced Colloids Experiment (ACE-T2) to RPO. The purpose of this event is for Principal Investigators to present their science objectives, testing approach, and measurement methods to agency scientists, managers, and other investigators.
The Global Climate Observing System (GCOS) has specified the need to systematically generate andvalidate Land Surface Temperature (LST) products. This document provides recommendations on goodpractices for the validation of LST products. Internationally accepted definitions of LST, emissivity andassociated quantities are provided to ensure the compatibility across products and reference data sets. Asurvey of current validation capabilities indicates that progress is being made in terms of up-scaling and insitu measurement methods, but there is insufficient standardization with respect to performing andreporting statistically robust comparisons.Four LST validation approaches are identified: (1) Ground-based validation, which involvescomparisons with LST obtained from ground-based radiance measurements; (2) Scene-based intercomparisonof current satellite LST products with a heritage LST products; (3) Radiance-based validation,which is based on radiative transfer calculations for known atmospheric profiles and land surface emissivity;(4) Time series comparisons, which are particularly useful for detecting problems that can occur during aninstrument's life, e.g. calibration drift or unrealistic outliers due to undetected clouds. Finally, the need foran open access facility for performing LST product validation as well as accessing reference LST datasets isidentified.
This paper reviews sea level contributions from land ice across the Arctic, including Greenland. We summarize ice loss measurement methods, ice loss mechanisms, and recent observations and projections, and highlight research advances over the last 3-5 years and remaining scientific challenges.
Ground reflectance was acquired at the Railroad Valley Playa calibration site in Nevada USA using different methods of collection. The data was collected near the time and date of Landsat 8 OLI and Sentinel-2 satellite overpasses so an inter-comparison could be made with the reflectance products to determine which method was more suitable for vicarious calibration. The field spectrometers and reference panels were characterized before the field campaign. A continuous acquisition method was compared to stop and measure collections. Both acquisition methods were collected along an 80 m east-west transect as well as for a series of north-south transects over an 80 x 320 m area, with the stop and measure method being performed at random sampling locations. The measurements were performed using two field spectrometers by three teams of two people to compare the repeatability. The aim of the field campaign was to determine the variability due to the operator and the method of collection.
Ground reflectance was acquired at the Railroad Valley Playa calibration site in Nevada USA using different methods of collection. The data was collected near the time and date of Landsat 8 OLI and Sentinel-2 satellite overpasses so an inter-comparison could be made with the reflectance products to determine which method was more suitable for vicarious calibration. The field spectrometers and reference panels were characterized before the field campaign. A continuous acquisition method was compared to stop and measure collections. Both acquisition methods were collected along an 80 m east-west transect as well as for a series of north-south transects over an 80 x 320 m area, with the stop and measure method being performed at random sampling locations. The measurements were performed using two field spectrometers by three teams of two people to compare the repeatability. The aim of the field campaign was to determine the variability due to the operator and the method of collection.
Tests were performed to demonstrate the feasibility of a new method of measuring surface recession of a material sample during arc-jet testing in the NASA Ames mARC subscale developmental facility. The measurement principle was inspired through tracer elements such as Ca and Na which were seen in the spectra taken during the airborne observation campaign of the Stardust re-entry and which could be clearly observed standing out against the emission spectra emitted by postshock layer and glowing surface of the re-entry capsule. The measurement principle involves seeding of the heat shield materials at a defined depth with tracer elements which show strong and characteristic emission lines in the post shock plasma. Once the material recession reaches the seeding depth, these elements get into the hot plasma and show up in the emission spectra. The methodology was successfully demonstrated during arc-jet testing of phenolic impregnated carbonablator (PICA) material which was seeded in depth with a mixture of NaCl and MgCl in powder form. In the emission spectroscopy data, the emission lines of Mg and Na showed up about 1.5 seconds after probe insertion into the arc-jet plasma and vanished after another 2.5 seconds when recessionhad consumed the seeding material. From these data, a recession rate of about 1 mm/s is estimated.The heat flux during the test was measured to be 2575 W/sq cm on a hemispherical heat flux probewhich corresponds to a heat flux of 1036 W/sq cm on the rectangular test articles. An estimate for a lower limit of the surface temperature of 2800K during the test was obtained by fitting Planck radiation to the continuum spectra emitted by the PICA sample. Typical recession rates of PICA during testing in the large arc-jet facilities at similar test conditions are reported to be on the order of 0.05 to 0.1 cm/s which agrees well with the recession rates of 0.05-0.06 cm/s estimated from the emission spectroscopy data. Further tests under better controlled conditions are suggested to quantify this measurement method. Through a different choice of seeding materials with lower melting point, an extension of the measurement principle to monitor char depth seems feasible but was not yet demonstrated. Possible applications besides ground testing are recession and possibly char depth measurements during real re-entry. Detection through emission spectroscopy could be accomplished through ground based or airborne observation as performed during the Stardust and Hayabusa re-entries, or through on-board spectrometers. A suitable mission would be the re-entryof the OSIRIS-REX mission planned for late 2023. The measured data are presented and interpreted, the results and details of future applications are discussed.
In this work, a method for the measurement of surface tension using continuous periodic forcing is presented. To reduce gravitational effects, samples are electrostatically levitated prior to forcing. The method, called Faraday forcing, is particularly well suited for fluids that require high temperature measurements such as liquid metals where conventional surface tension measurement methods are not possible. It offers distinct advantages over the conventional pulse-decay analysis method when the sample viscosity is high or the levitation feedback control system is noisy. In the current method, levitated drops are continuously translated about a mean position at a small, constant forcing amplitude over a range of frequencies. At a particular frequency in this range, the drop suddenly enters a state of resonance, which is confirmed by large executions of prolate/oblate deformations about the mean spherical shape. The arrival at this resonant condition is a signature that the parametric forcing frequency is equal to the drop’s natural frequency, the latter being a known function of surface tension. A description of the experimental procedure is presented. A proof of concept is given using pure Zr and a Ti(sub 39.5)Zr(sub 39.5)Ni(sub 21) alloy as examples. The results compare favorably with accepted literature values obtained using the pulse-decay method.
Increment 59-60 Science Symposium presentation of Advanced Colloids Experiment (ACE-T11, Khusid - NJIT (New Jersey Inst. of Technology)) to RPO (Research Program Office). The purpose of this event is for Principal Investigators to present their science objectives, testing approach, and measurement methods to agency scientists, managers, and other investigators. It is often assumed that time-average weightlessness simulated in a clinostat can reduce the effect of gravity on samples. Why not use it for colloids? Low-gravity parabolic flight tests on a non-buoyancy matched suspension demonstrated that time-average weightlessness in a clinostat does not eliminate gravity effect on patterns in colloids formed by an electric field. The long-term microgravity ISS (International Space Station) experiment provides a unique opportunity to reveal the relationship between external forces on the scale of individual particles and the colloid dynamics on the macroscopic scale.
Increment 57-58 Science Symposium presentation of Advanced Colloids Experiment (ACE-T12) to RPO. The purpose of this event is for Principal Investigators to present their science objectives, testing approach, and measurement methods to agency scientists, managers, and other investigators. This flight experiment was added after the Science Symposium, so these charts for more for reference, than presentation.
Increment 59-60 Science Symposium presentation of Advanced Colloids Experiment (ACE-T10) (by GRC (Glenn Research Center) to the RPO-JSC (Research Planning Office-Johnson Space Center), via WebEx. The purpose of this event is for Principal Investigators to present their science objectives, testing approach, and measurement methods to agency scientists, managers, and other investigators.
Increment 59-60 Science Symposium presentation of Advanced Colloids Experiment (ACE-T10) (by GRC (Glenn Research Center) to the RPO-JSC (Research Planning Office-Johnson Space Center), via WebEx. The purpose of this event is for Principal Investigators to present their science objectives, testing approach, and measurement methods to agency scientists, managers, and other investigators.
This presentation describes experimental and computational approaches to measuring pressure gain in the various devices currently under investigation wherein the working fluid undergoes a pressure gain combustion (PGC) process. Pressure gain is essentially a measure of the fluid availability for work or thrust production. The devices covered are Resonant Pulse Combustors, Internal Combustion Wave Rotors, Pulse Detonation Engines, and Rotating Detonation Engines. The approaches to pressure gain measurement differ in each device. However, all of the approaches attempt to address the fundamental challenges of PGC system measurement: the extremely harsh environment which makes instrumentation difficult, and the temporal and spatial non-uniformity associated with the exhausting flow which makes assigning a single value to the total pressure difficult. As part of the two-day 2019 International Constant Volume and Detonative Combustion Workshop, held in conjunction with the 2019 AIAA Propulsion and Energy Forum, this presentation is intended to foster discussion and eventual consensus on acceptable measurement methods.
As communicated at various forums, a multilateral, web-based symposium, featuring ISS Increments 61 and 62 investigations will be held on September 17, 18 and 19, 2019 beginning at 0600 CDT. The purpose of this event is for Principal Investigators to present their science objectives, testing approach, and measurement methods to agency scientists, managers, and other investigators. Participation is encouraged to gather a global picture of the science planned to be performed on ISS during Increments 61 and 62.
In order to understand the risk posed to astronauts by electric arc-generated particles, high-speed, high-resolution, quantitative thermal imaging was needed. The measurement requirements appeared to be beyond the capabilities of commercial thermal imaging systems, but the particles were known to have a significant amount of emission in the visible spectrum. This led to the use of commercially available, high-speed video cameras as imaging radiometers. Measured particle temperatures were consistent with predictions and other measurement data. The optical temperature measurement method, results, and conclusions are presented, along with recommendations for further work.
AN Air Mobility (UAM) is an opportunity for aviation to improve transportation systems across the world. Representative UAM vehicle attributes include electrical vertical takeoff and landing (eVTOL) vehicles that can accommodate up to 6 passengers (or equivalent cargo), are possibly autonomous, perform missions of up to 100 nautical miles at altitudes up to 3000 ft. above ground level, have flight speeds up to 200 knots, and weigh between 800 and 8000 pounds. Along with the many anticipated benefits, there will be noise issues that need to be addressed. In 2018, NASA formed an Urban Air Mobility Noise Working Group (UNWG) to assemble noise experts from industry, universities and government agencies to identify, discuss, and address UAM noise issues. This oral presentation summarizes technology gaps and goals associated with four areas of interest: Tools & Technologies, Ground & Flight Testing, Human Response & Metrics, and Regulation & Policy, and is drawn from a draft white paper [1] by the same title. Tools & Technologies include noise prediction tools and noise reduction technologies that have been developed for conventional rotorcraft and fixed-wing vehicles that may be applicable or need to be modified for UAM. Prediction tools need to be able to account for variable speed rotors and other temporal variation effects that impact community noise. A reprioritization of noise sources needs to be done since UAM vehicles include multiple rotors/propellers, often in proximity to one another and/or the airframe, with dynamic transition, and new noise sources such as electric motors or hybrid-electric propulsion. Scattering and propagation methods need to be developed that include the vehicle components and surfaces near a receiver such as buildings and vertiports. Validation databases are needed to quantify prediction uncertainties. Prediction tools used to evaluate community noise will need source models appropriate for a wide range of UAM vehicles. Existing noise reduction technologies need to be evaluated and new noise reduction technologies should be developed in anticipation of future noise requirements. Although the prediction and treatment of interior cabin noise is a secondary goal, it is recognized that new tools and methods may be needed due to the uniqueness of the vehicle design and the presence of both acoustic and structure-borne loads. Ground & Flight Testing has been a critical part of validating noise reduction technologies and verifying that an air vehicle is ready for certification. UAM vehicles introduce new challenges for test procedures such as different source noise directivity, unsteady sources due to maneuvers, and a variety of takeoff and approach trajectories. The operating environment will be more complex than current aircraft with the introduction of vertiports in populated areas with “urban canyons” making reflections an important part of noise prediction and annoyance. It is expected that new test procedures and measurement methods will be necessary. Consideration will need to be given for both piloted and autonomous operations. Human Response & Metrics may be very different for UAM noise compared to current experience with airport noise. Current metrics used to certify rotorcraft and fixed-wing aircraft may not be as useful for evaluating UAM noise. Operations at lower altitudes may influence annoyance. Psychoacoustic and community testing will be needed to quantify annoyance and assess appropriate metrics. In addition to conventional noise level metrics, considerations such as audibility and temporal variation of the sound may be required. Differences between indoor or outdoor exposure will have an impact with dependence on urban and residential flight paths. Aircraft noise is currently regulated at a national level and typically involves partnerships with the industry to establish regulations. Regulators realize that current policies and procedures may not be appropriate for some of the emerging air vehicles and new procedures may be needed to address UAM noise. Development of new policies and procedures are needed so that local communities do not hastily attempt to establish their own restrictions that will both limit growth of the market and create an inconsistent and confusing regulatory environment. To expedite this development, it is crucial early measurement data are shared through partnership arrangements to support both noise certification and noise modeling/noise assessment. At the same time, an effective engagement strategy should be developed to address local community noise issues associated with UAM vehicles and flight operations as they arise.
The buckling responses of certain cylindrical shell structures are extremely sensitive to geometric imperfections. The NASA Engineering and Safety Center (NESC) Shell Buckling Knockdown Factor Project (SBKF) is conducting research to develop analysis-based buckling design recommendations. Experiments are used to verify the analysis-based factors, but the sensitivity of the test articles to geometric imperfections requires implementing as-manufactured imperfections into high-fidelity finite element method (FEM) models. Geometry measurement methods such as structured light scanning are used for all geometric surface data used in this work. Common preprocessing and visualization steps used in SBKF are discussed, and steps of how surface scans are prepared for implementation into a finite element model is described. The Python Tool for Implementing Geometric Imperfections in Reduced Structures (Py_TIGIRS), written specifically for the use with SBKF, is briefly described and uses eight functions to extract, modify, and write geometric imperfections into Abaqus input files. Results of the preprocessing methods and results from Py_TIGIRS are provided and compared for Composite Test Articles (CTA) 8.2, 8.2B, and 8.3. Excellent agreement between the visualized scan data and the FEM-extracted geometry is demonstrated. A brief example of why geometric surface imperfections are significant in nonlinear numerical analyses for thin cylinders in axial compression is provided as motivation to use tools such as Py_TIGIRS. Future developments of Py_TIGIRS including expansion to structures of arbitrary geometry is planned.
The buckling responses of certain cylindrical shell structures are extremely sensitive to geometric imperfections. The NASA Engineering and Safety Center (NESC) Shell Buckling Knockdown Factor Project (SBKF) is conducting research to develop analysis-based buckling design recommendations. Experiments are used to verify the analysis-based factors, but the sensitivity of the test articles to geometric imperfections requires implementing as-manufactured imperfections into high-fidelity finite element method (FEM) models. Geometry measurement methods such as structured light scanning are used for all geometric surface data used in this work. Common preprocessing and visualization steps used in SBKF are discussed, and steps of how surface scans are prepared for implementation into a finite element model is described. The Python Tool for Implementing Geometric Imperfections in Reduced Structures (Py_TIGIRS), written specifically for the use with SBKF, is briefly described and uses eight functions to extract, modify, and write geometric imperfections into Abaqus input files. Results of the preprocessing methods and results from Py_TIGIRS are provided and compared for Composite Test Articles (CTA) 8.2, 8.2B, and 8.3. Excellent agreement between the visualized scan data and the FEM-extracted geometry is demonstrated. A brief example of why geometric surface imperfections are significant in nonlinear numerical analyses for thin cylinders in axial compression is provided as motivation to use tools such as Py_TIGIRS. Future developments of Py_TIGIRS including expansion to structures of arbitrary geometry is planned.
Pedotransfer functions (PTFs) provide point predictions of soil hydraulic properties from more readily measured soil characteristics, yet uncertainties and biases in measurement methods, sampling distributions, and boundary conditions can limit accuracy when estimating near-saturated hydraulic conductivity (K(n)). These limitations may be particularly problematic in understudied urban landscapes that often contain altered hydraulic properties. To better treat deficiencies in PTF performance, we addressed three objectives, which were to: 1) develop PTFs to predict urban K(n), 2) assess bulk density and coarse fragments as explanatory variables; and 3) evaluate the predictive capability of these PTFs by comparing their output to measured hydraulic conductivity values from three other studies of urban soil hydraulics. We used artificial neural networks (ANN) and random forest (RF) approaches to predict urban K(n), with the training dataset including 307 tension infiltrometer tests and other measurements drawn from urban soil assessments in 11 U.S. cities. The PTFs utilized a hierarchy of inputs, starting with percentage sand, silt, clay, and then adding percentage coarse fragments and bulk density. The ANN models performed similar to the RF models, and all models exhibited similar or better predictive performance as models results collected from published articles. The inclusion of bulk density or coarse fragments did not improve accuracy over soil texture alone. Possible reasons for this result include low correlation between K(n) and bulk density and the exclusion of large voids during flow measurements with tension infiltrometers. The models have been made available as an open-source software package to encourage adoption by users working in urban systems.