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At least 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
NASA NTRS1960

Landing Characteristics of a Reentry Capsule with a Torus-Shaped Air Bag for Load Alleviation

An experimental investigation has been made to determine the landing characteristics of a conical-shaped reentry capsule by using torus-shaped air bags for impact-load alleviation. An impact bag was attached below the large end of the capsule to absorb initial impact loads and a second bag was attached around the canister to absorb loads resulting from impact on the canister when the capsule overturned. A 1/6-scale dynamic model of the configuration was tested for nominal flight paths of 60 deg. and 90 deg. (vertical), a range of contact attitudes from -25 deg. to 30 deg., and a vertical contact velocity of 12.25 feet per second. Accelerations were measured along the X-axis (roll) and Z-axis (yaw) by accelerometers rigidly installed at the center of gravity of the model. Actual flight path, contact attitudes, and motions were determined from high-speed motion pictures. Landings were made on concrete and on water. The peak accelerations along the X-axis for landings on concrete were in the order of 3Og for a 0 deg. contact attitude. A horizontal velocity of 7 feet per second, corresponding to a flight path of 60 deg., had very little effect upon the peak accelerations obtained for landings on concrete. For contact attitudes of -25 deg. and 30 deg. the peak accelerations along the Z-axis were about +/- l5g, respectively. The peak accelerations measured for the water landings were about one-third lower than the peak accelerations measured for the landings on concrete. Assuming a rigid body, computations were made by using Newton's second law of motion and the force-stroke characteristics of the air bag to determine accelerations for a flight path of 90 deg. (vertical) and a contact attitude of 0 deg. The computed and experimental peak accelerations and strokes at peak acceleration were in good agreement for the model. The special scaling appears to be applicable for predicting full-scale time and stroke at peak acceleration for a landing on concrete from a 90 deg. flight path at a 0 deg. It appears that the full-scale approximately the same as those obtained from the model for the range of attitudes and flight paths investigated.

McGehee, John R.↗
NASA NTRS2006

Multiphysics Thermal-Fluid Design Analysis of a Non-Nuclear Tester for Hot-Hydrogen Materials and Component Development

The objective of this effort is to perform design analyses for a non-nuclear hot-hydrogen materials tester, as a first step towards developing efficient and accurate multiphysics, thermo-fluid computational methodology to predict environments for hypothetical solid-core, nuclear thermal engine thrust chamber design and analysis. The computational methodology is based on a multidimensional, finite-volume, turbulent, chemically reacting, thermally radiating, unstructured-grid, and pressure-based formulation. The multiphysics invoked in this study include hydrogen dissociation kinetics and thermodynamics, turbulent flow, convective, and thermal radiative heat transfers. The goals of the design analyses are to maintain maximum hot-hydrogen jet impingement energy and to minimize chamber wall heating. The results of analyses on three test fixture configurations and the rationale for final selection are presented. The interrogation of physics revealed that reactions of hydrogen dissociation and recombination are highly correlated with local temperature and are necessary for accurate prediction of the hot-hydrogen jet temperature.

Wang, Ten-See↗
NASA NTRS2006

A Numerical and Experimental Study of Compression-Loaded Composite Panels With Cutouts

Results from a numerical and experimental study on the effects of laminate orthotropy and circular cutout size on the response of compression-loaded composite curved panels are presented. Several 60-in-radius composite panels with four different laminate configurations were tested with cutout diameters that range from 10% to 60% of the panel width. Finite-element analyses were performed for each panel in order to identify the effects boundary conditions, measured initial geometric imperfections and thickness variations had on the nonlinear and buckling behavior of the panels. The compression-loaded panels considered herein exhibited two separate types of behavior depending on the laminate stacking sequence and cutout size. More specifically, some of the panels exhibited the classical snap-through type buckling response; however, some of the panels exhibited a monotonically increasing stable response and achieved compressive loads in excess of twice the predicted linear bifurcation buckling load. In general, the finite-element analyses were able to predict accurately the nonlinear response and buckling loads of the panels and the prebuckling and postbuckling out-of-plane deformations and strains.

Thornburgh, Robert P.↗
NASA NTRS2008

Enhanced Flight Termination System (EFTS): Flight Demonstration and Results

The Enhanced Flight Termination System (EFTS) program was initiated and propelled due to the inadvertent terminations of Global Hawk and the Strategic Target System and the NASA Inspector General's assessment letter and recommendations regarding the exploration of low-cost, lightweight space COMSEC for FTS. Additionally, the standard analog and high alphabet systems most commonly used in FTS are secure, but not encrypted. A study group was initiated to select and document a robust, affordable, reliable technology that provides encrypted FTS capability. A flight demonstration was conducted to gain experience using EFTS in an operational environment, provide confidence in the use of the EFTS components, integrate EFTS into an existing range infrastructure to demonstrate the scalability of system components, to provide a command controller that generated the EFTS waveform using an existing range infrastructure, and to provide a report documenting the results of the demonstration. The primary goal of the demonstration was to obtain operational experience with EFTS. Areas of operational experience include: mission planning, pre-flight configuration and testing, mission monitoring and recording, vehicle termination, developing mission procedures. and post mission data reduction and other post mission activities. An Advanced Medium-Range Air-to-Air Missile (AMRAAM) was selected to support the EFTS demonstration due to interest in future use of EFTS by the AMRAAM program, familiarity of EFTS by range personnel, and the availability of existing operational environment to support EFTS testing with available program funding. For demonstration purposes, the AMRAAM was successfully terminated using an EFTS receiver and successfully demonstrating EFTS. The EFTS monitoring software with spectrum analyzer and digital graphical display of aircraft, missile, and target were also demonstrated.

Tow, David↗
NASA NTRS2005

Selecting Data from a Star Catalog

MCDUMP is a computer program that selects data from the SKYMAP SKY2000 Master Star Catalog a database about 150 MB in size, stored on a computer hard drive. The database describes about 300,000 stars, each by means of a 500-byte entry. MCDUMP reads all 300,000 entries, then generates an output file that comprises a subset of entries selected according to one or more criteria entered by the user. Examples of criteria that could be entered include: location in a selected portion of the sky; constancy or a specified degree of variability of brightness; absence of nearby, bright companion stars; a particular surface temperature; and brightness sufficient to enable detection by a specified astronomical instrument. The output of MCDUMP can be in the form of either a single 520-column file or multiple files that contain fewer columns to facilitate printing. MCDUMP has been configured and tested for use under the HP-UX 10.20 operating system (a Hewlett-Packard version of the UNIX operating system). It should also be possible to adapt MCDUMP to other versions of UNIX.

Tracewell, David A.↗
NASA NTRS2010

Effect of the Machining Processes on Low Cycle Fatigue Behavior of a Powder Metallurgy Disk

A study has been performed to investigate the effect of various machining processes on fatigue life of configured low cycle fatigue specimens machined out of a NASA developed LSHR P/M nickel based disk alloy. Two types of configured specimen geometries were employed in the study. To evaluate a broach machining processes a double notch geometry was used with both notches machined using broach tooling. EDM machined notched specimens of the same configuration were tested for comparison purposes. Honing finishing process was evaluated by using a center hole specimen geometry. Comparison testing was again done using EDM machined specimens of the same geometry. The effect of these machining processes on the resulting surface roughness, residual stress distribution and microstructural damage were characterized and used in attempt to explain the low cycle fatigue results.

Telesman, J.↗
NASA NTRS2013

Analysis of the Effects of Streamwise Lift Distribution on Sonic Boom Signature

Investigation of sonic boom has been one of the major areas of study in aeronautics due to the benefits a low-boom aircraft has in both civilian and military applications. This work conducts a numerical analysis of the effects of streamwise lift distribution on the shock coalescence characteristics. A simple wing-canard-stabilator body model is used in the numerical simulation. The streamwise lift distribution is varied by fixing the canard at a deflection angle while trimming the aircraft with the wing and the stabilator at the desired lift coefficient. The lift and the pitching moment coefficients are computed using the Missile DATCOM v. 707. The flow field around the wing-canard- stabilator body model is resolved using the OVERFLOW-2 flow solver. Overset/ chimera grid topology is used to simplify the grid generation of various configurations representing different streamwise lift distributions. The numerical simulations are performed without viscosity unless it is required for numerical stability. All configurations are simulated at Mach 1.4, angle-of-attack of 1.50, lift coefficient of 0.05, and pitching moment coefficient of approximately 0. Four streamwise lift distribution configurations were tested.

Yoo, Paul↗
NASA NTRS2013

Effect of Boundary-Layer Bleed Hole Inclination Angle and Scaling on Flow Coefficient Behavior

Phase II data results of the Fundamental Inlet Bleed Experiments study at NASA Glenn Research Center are presented which include flow coefficient behavior for 21 bleed hole configurations. The bleed configurations are all round holes with hole diameters ranging from 0.795 to 6.35 mm, hole inclination angles from 20deg to 90deg, and thickness-to-diameter ratios from 0.25 to 2.0. All configurations were tested at a unit Reynolds number of 2.46 10(exp 7)/m and at discrete local Mach numbers of 1.33, 1.62, 1.98, 2.46, and 2.92. Interactions between the design parameters of hole diameter, hole inclination angle, and thickness-to-diameter as well as the interactions between the flow parameters of pressure ratio and Mach number upon the flow coefficient are examined, and a preliminary statistical model is proposed. An existing correlation is also examined with respect to this data.

Eichorn, Michael B.↗
NASA NTRS2013

Designing for Virtual Windows in a Deep Space Habitat

This paper discusses configurations and test analogs toward the design of a virtual window capability in a Deep Space Habitat. Long-duration space missions will require crews to remain in the confines of a spacecraft for extended periods of time, with possible harmful effects if a crewmember cannot cope with the small habitable volume. Virtual windows expand perceived volume using a minimal amount of image projection equipment and computing resources, and allow a limited immersion in remote environments. Uses for the virtual window include: live or augmented reality views of the external environment; flight deck, piloting, observation, or other participation in remote missions through live transmission of cameras mounted to remote vehicles; pre-recorded background views of nature areas, seasonal occurrences, or cultural events; and pre-recorded events such as birthdays, anniversaries, and other meaningful events prepared by ground support and families of the crewmembers.

habitation↗
NASA NTRS2009

Space Communications and Navigation (SCaN) Network Simulation Tool Development and Its Use Cases

In this work, we focus on the development of a simulation tool to assist in analysis of current and future (proposed) network architectures for NASA. Specifically, the Space Communications and Navigation (SCaN) Network is being architected as an integrated set of new assets and a federation of upgraded legacy systems. The SCaN architecture for the initial missions for returning humans to the moon and beyond will include the Space Network (SN) and the Near-Earth Network (NEN). In addition to SCaN, the initial mission scenario involves a Crew Exploration Vehicle (CEV), the International Space Station (ISS) and NASA Integrated Services Network (NISN). We call the tool being developed the SCaN Network Integration and Engineering (SCaN NI&E) Simulator. The intended uses of such a simulator are: (1) to characterize performance of particular protocols and configurations in mission planning phases; (2) to optimize system configurations by testing a larger parameter space than may be feasible in either production networks or an emulated environment; (3) to test solutions in order to find issues/risks before committing more significant resources needed to produce real hardware or flight software systems. We describe two use cases of the tool: (1) standalone simulation of CEV to ISS baseline scenario to determine network performance, (2) participation in Distributed Simulation Integration Laboratory (DSIL) tests to perform function testing and verify interface and interoperability of geographically dispersed simulations/emulations.

Jennings, Esther↗
NASA NTRS2015

The Effect of Backward-Facing Step Height on Instability Growth and Breakdown in Swept Wing Boundary-Layer Transition

A low-speed experiment was performed on a swept at plate model with an imposed pressure gradient to determine the effect of a backward-facing step on transition in a stationary-cross flow dominated flow. Detailed hot-wire boundary-layer measurements were performed for three backward-facing step heights of approximately 36, 45, and 49% of the boundary-layer thickness at the step. These step heights correspond to a subcritical, nearly-critical, and critical case. Three leading-edge roughness configurations were tested to determine the effect of stationary-cross flow amplitude on transition. The step caused a local increase in amplitude of the stationary cross flow for the two larger step height cases, but farther downstream the amplitude decreased and remained below the baseline amplitude. The smallest step caused a slight local decrease in amplitude of the primary stationary cross flow mode, but the amplitude collapsed back to the baseline case far downstream of the step. The effect of the step on the amplitude of the primary cross flow mode increased with step height, however, the stationary cross flow amplitudes remained low and thus, stationary cross flow was not solely responsible for transition. Unsteady disturbances were present downstream of the step for all three step heights, and the amplitudes increased with increasing step height. The only exception is that the lower frequency (traveling crossflow-like) disturbance was not present in the lowest step height case. Positive and negative spikes in instantaneous velocity began to occur for the two larger step height cases and then grew in number and amplitude downstream of reattachment, eventually leading to transition. The number and amplitude of spikes varied depending on the step height and cross flow amplitude. Despite the low amplitude of the disturbances in the intermediate step height case, breakdown began to occur intermittently and the flow underwent a long transition region.

Eppink, Jenna L.↗
NASA NTRS2016

Model Predictions and Observed Performance of JWST's Cryogenic Position Metrology System

The James Webb Space Telescope cryogenic testing requires measurement systems that both obtain a very high degree of accuracy and can function in that environment. Close-range photogrammetry was identified as meeting those criteria. Testing the capability of a close-range photogrammetric system prior to its existence is a challenging problem. Computer simulation was chosen over building a scaled mock-up to allow for increased flexibility in testing various configurations. Extensive validation work was done to ensure that the actual as-built system meet accuracy and repeatability requirements. The simulated image data predicted the uncertainty in measurement to be within specification and this prediction was borne out experimentally. Uncertainty at all levels was verified experimentally to be less than 0.1 millimeters.

Lunt, Sharon R.↗
NASA NTRS2016

Model Predictions and Observed Performance of JWST's Cryogenic Position Metrology System

The James Webb Space Telescope cryogenic testing requires measurement systems that both obtain a very high degree of accuracy and can function in that environment. Close-range photogrammetry was identified as meeting those criteria. Testing the capability of a close-range photogrammetric system prior to its existence is a challenging problem. Computer simulation was chosen over building a scaled mock-up to allow for increased flexibility in testing various configurations. Extensive validation work was done to ensure that the actual as-built system meet accuracy and repeatability requirements. The simulated image data predicted the uncertainty in measurement to be within specification and this prediction was borne out experimentally. Uncertainty at all levels was verified experimentally to be less than 0.1 millimeters.

Lunt, Sharon R.↗
NASA NTRS2018

Applications of Parallel-Element, Embedded Mesh-Cap Acoustic Liner Concepts

This study explores progress achieved with 2DOF, 3DOF, and MDOF acoustic liners constructed with mesh caps embedded within a honeycomb core. These liner configurations offer potential for broadband noise reduction, and are suitable for conventional aircraft implementation. Samples for each configuration are tested in the NASA normal incidence tube and grazing flow impedance tube, with and without a wire mesh facesheet. Impedances based on these measured data compare favorably with those predicted using a transmission line impedance prediction model. Predicted impedances are then used as input for an aeroacoustic propagation code to compute axial acoustic pressure distributions in the grazing flow tube. These predicted distributions compare favorably with the corresponding measured distributions at frequencies away from the frequency of peak attenuation, but suffer slight degradation for frequencies very near the peak attenuation frequency, where the predicted results are sensitive to input impedance changes. As expected, the noise reduction frequency range increases as more degrees of freedom are included. Although the specific results achieved herein may differ from those that would be achieved with other 2DOF, 3DOF, and MDOF liners, this comparison highlights some of the key features that can be exploited in the design of parallel-element, embedded mesh-cap liners.

Jones, M. G.↗
NASA NTRS2016

Comparison of RTA Vibratory Loading in the 40- by 80-Foot Wind Tunnel and 80- by 120-Foot Wind Tunnel at the National Full-Scale Aerodynamics Complex

This paper presents data taken in the 80- by 120-Foot Wind Tunnel in 1992 to data taken in the 40- by 80-Foot Wind Tunnel in 2016 at the NFAC. In both sets of data, the RTA was equipped with an identical set of S-76 helicopter blades. These data sets were compared to determine the repeatability of the RTA as a testing device, and to quantify differences in 40- by 80-Foot Wind Tunnel vs. 80- by 120-Foot Wind Tunnel results. The contents include an overview of the RTA and test facility, as well as a discussion of the methodology used. Vibratory load data is presented for a variety of wind and RPM conditions in various test section configurations. Data presented in this report quantifies the repeatability of the RTA.

NFAC↗
NASA NTRS2020

Vertical Climb Testing of a Full-Scale Proprotor on the Tiltrotor Test Rig

The Tiltrotor Test Rig (TTR) is a new NASA facility for testing full-scale proprotors. The first test campaign in the National Full-Scale Aerodynamics Facility (NFAC) concluded in November 2018. The wind-tunnel test included vertical climb conditions; that is, axial flow at low airspeeds (true hover is not possible in the NFAC). The rotor tested was the Bell Model 699, a 609 rotor modified specifically for wind-tunnel testing. The rotor was tested under a variety of NFAC configurations, some unprecedented and unique to vertical climb. Researchers must understand the differences in configuration if they are to make proper use of the data. This paper presents results for several different test configurations, including assessments of data quality. Comparisons with earlier tests of a similar rotor, the 0.656- scale Joint Vertical Experimental (JVX) rotor, are included to provide additional insights into rotor and wind tunnel behavior.

Acree, C. W.↗
NASA NTRS2019

Assimilation of Sentinel 1 and SMAP – Based Satellite Soil Moisture Retrievals into SWAT Hydrological Model: the Impact of Satellite Revisit Time and Product Spatial Resolution on Flood Simulations in Small Basins

In runoff generation process, soil moisture plays an important role as it controls the magnitude of the flood events to the rainfall inputs. In this study, we investigated the ability of a new era of satellite soil moisture retrievals to improve the Soil & Water Assessment Tool (SWAT) daily discharge simulations via soil moisture data assimilation for two small (< 500 km2) and hydrologically different catchments located in Central Italy. We ingested 1) the Soil Moisture Active and Passive (SMAP) Enhanced L3 Radiometer Global Daily 9 km EASE-Grid soil moisture, 2) the Advanced SCATterometer (ASCAT) H113 soil moisture product released within the EUMETSAT Satellite Application Facility on Support to Operational Hydrology and Water Management (H-SAF) which has a nearly daily temporal resolution and sampling of 12.5 km, and 3) a fused ASCAT/Sentinel-1 (S1) satellite soil moisture product named SCATSAR-SWI with temporal and spatial sampling of 1 day and 1 km, respectively into SWAT hydrological model via Ensemble Kalman Filter (EnKF). Different configurations were tested with the aim of exploring the effect of the hydrological regime, the land use conditions, the spatial sampling and the revisit time of the products (which controls the amount of available data to be potentially ingested). Results show a general improvement of SWAT discharge simulations for all products in terms of error and Nash Sutcliffe efficiency index. In particular, we found a relatively good behavior of both the active and the passive products in terms of low flows improvement especially for the catchment characterized by a higher baseflow component. The benefit of the higher spatial resolution of SCATSAR obtained via S1 over ASCAT was small likely due to very challenging areas for S1 retrieval. Eventually, better performances were obtained for the passive product in the more forested catchment. With the aim of exploring the benefit of having more frequent satellite soil moisture observations to be ingested, we tested the performance of the ASCAT product with a reduced temporal sampling obtained by temporally matching ASCAT observations to that of SMAP. The results show a significant reduction of the performance of ASCAT, suggesting that the correction frequency (due to the higher number of observations available) for small catchments is an important aspect for improving flood forecasting as it helps to adjust more frequently the soil moisture pre-storm conditions.

Small basins↗