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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Interplanetary stream magnetism: Kinematic effects

The particle density, and the magnetic field intensity and direction are calculated in corotating streams of the solar wind, assuming that the solar wind velocity is constant and radial and that its azimuthal variations are not two rapid. The effects of the radial velocity profile in corotating streams on the magnetic fields were examined using kinematic approximation and a variety of field configurations on the inner boundary. Kinematic and dynamic effects are discussed.

Burlaga, L. F.↗
NASA NTRS1988

Geodesy by radio interferometry - Determination of vector motions for sites in the western United States

The use of VBLI to study plate tectonic motion, plate boundary deformation, earth dynamics, and the crustal motions in the western U.S. is discussed. Results from dual frequency (S and X band) mobile VLBI experiments between October 1982 and February 1987 are presented. It is suggested that significant northwest motion is occurring well east of the San Andreas fault.

Gordon, David↗
NASA NTRS1989

Load-shortening behavior of an initially curved eccentrically loaded column

To explore the feasibility of using buckled columns to provide a soft support system for simulating a free-free boundary condition in dynamic testing, the nonlinear load-shortening behavior of initially imperfect, eccentrically loaded slender columns is analyzed. Load-shortening curves are obtained for various combinations of load eccentricity and uniform initial curvature and are compared, for reference purposes, with the limiting case of the classical elastica. Results for numerous combinations of initial curvature and load eccentricity show that, over a wide range of shortening, an axially loaded slender column exhibits load-deflection compliance which is of the same order as that of a straight but otherwise identical cantilever beam under lateral tip loading.

Fichter, W. B.↗
NASA NTRS1990

A comparison of time-optimal interception trajectories for the F-8 and F-15

The simulation results of a real time control algorithm for onboard computation of time-optimal intercept trajectories for the F-8 and F-15 aircraft are given. Due to the inherent aerodynamic and propulsion differences in the aircraft, there are major differences in their optimal trajectories. The significant difference in the two aircrafts are their flight envelopes. The F-8's optimal cruise velocity is thrust limited, while the F-15's optimal cruise velocity is at the intersection of the Mach and dynamic pressure constraint boundaries. This inherent difference necessitated the development of a proportional thrust controller for use as the F-15 approaches it's optimal cruise energy. Documented here is the application of singular perturbation theory to the trajectory optimization problem, along with a summary of the control algorithms. Numerical results for the two aircraft are compared to illustrate the performance of the minimum time algorithm, and to compute the resulting flight paths.

Calise, Anthony J.↗
NASA NTRS1993

An experimental and analytical study of a lifting-body wind-tunnel model exhibiting body-freedom flutter

Flutter analysis of the proposed National Aerospace Plane indicates that in the subsonic to transonic flight regime, the vehicle may be susceptible to an instability known as body-freedom flutter. Body-freedom flutter is a dynamic instability involving a vehicle rigid-body mode coupling with one or more of the vehicle's elastic modes. In the case of the NASP, the body-freedom flutter predicted by analysis involves the short-period mode of the vehicle coupling with the pivot mode of the all-movable wings. A wind-tunnel test was designed to investigate this phenomenon. Parameter studies included variations in wing-actuator stiffness, wing-pivot shaft location along the root chord, and thickness of the fuselage. The wind-tunnel test was conducted in the NASA Langley Transonic Dynamics Tunnel. Flutter boundaries were measured in the wind tunnel for three configurations and a model divergence point was measured on a fourth configuration. At the last flutter point obtained during the test, body-freedom flutter proved to be rather violent. The analysis used in this study incorporated thin-wing theory aerodynamics and did a fairly good job of predicting the flutter boundaries.

Soistmann, David L.↗
NASA NTRS1994

Application of neural networks to unsteady aerodynamic control

The problem under consideration in this viewgraph presentation is to understand, predict, and control the fluid mechanics of dynamic maneuvers, unsteady boundary layers, and vortex dominated flows. One solution is the application of neural networks demonstrating closed-loop control. Neural networks offer unique opportunities: simplify modeling of three dimensional, vortex dominated, unsteady separated flow fields; are effective means for controlling unsteady aerodynamics; and address integration of sensors, controllers, and time lags into adaptive control systems.

Faller, William E.↗
NASA NTRS1998

Composition Measurements at the Magnetopause and in the Plasma Mantle

This final report describes activities under NASA grant NAGW-4049 to Lockheed Missiles and Space Company. The report covers the entire period of the grant from 15 August 1994 to 31 January 1998. The original grant was for 3 years ending in August 1997; however the grant was extended 6 months to accomodate additional data analysis that added significantly to the scientific results. This is a grant under the NASA Supporting Research and Technology Program for the analysis and interpretation of the combined scientific data from the ISEE-1 Plasma Composition Experiment and the AMPTE/CCE Hot Plasma Composition Experiment. These combined data sets were used in a study of the Earth's magnetopause to develop a fundamental understanding of plasma entry and dynamics at the boundary and formation and maintenance of the low latitude boundary layer under a variety of solar wind and magnetospheric conditions and at a wide range of local times.

Gary, S. P.↗
NASA NTRS2008

MESSENGER Observation of Mercury's Magnetopause: Structure and Dynamics

MESSENGER'S 14 January 2008 encounter with Mercury has provided new observations of the magnetopause of this small magnetosphere, particularly concerning the effect of the direction of the interplanetary magnetic field (IMF) on the structure and dynamics of this boundary. The IMF was northward immediately prior to and following the passage of the MESSENGER spacecraft through Mercury's magnetosphere. However, several-minute episodes of southward IMF were observed in the magnetosheath during the inbound portion of the encounter. Evidence for reconnection at the dayside magnetopause in the form of well-developed flux transfer events (FTEs) was observed in the magnetosheath following some of these southward-B, intervals. The inbound magnetopause crossing seen in the magnetic field measurements is consistent with a transition from the magnetosheath into the plasma sheet. Immediately following MESSENGER'S entry into the magnetosphere, rotational perturbations in the magnetic field similar to those seen at the Earth in association with large-scale plasma sheet vortices driven by Kelvin-Helmholtz waves along the magnetotail boundary at the Earth were observed. The outbound magnetopause occurred during northward IMF B(sub z) and had the characteristics of a tangential discontinuity. These new observations by MESSENGER may be combined and compared with the magnetopause measurements collected by Mariner 10 to derive new understanding of the response of Mercury's magnetopause to IMF direction and its effect on the rate of solar wind energy and mass input to this small magnetosphere.

Slavin, J. A.↗
NASA NTRS2021

Effects of Spin-Orbit Resonances and Tidal Heating on the Inner Edge of the Habitable Zone

Much attention has been given to the climate dynamics and habitable boundaries of synchronously rotating planets around low mass stars. However, other rotational states are possible, including spin–orbit resonant configurations, particularly when higher eccentricity orbits can be maintained in a system. Additionally, the oscillating strain as a planet moves from periastron to apoastron results in friction and tidal heating, which can be an important energy source. Here, we simulate the climate of ocean-covered planets near the inner edge of the habitable zone around M to solar stars with the NASA GISS ROCKE-3D general circulation model, and leverage the planetary evolution software package, VPLanet, to calculate tidal heating rates for Earth-sized planets orbiting 2600 and 3000 K stars. This study is the first to use a 3D general circulation model that implements tidal heating to investigate habitability for multiple resonant states. We find that for reference experiments without tidal heating, the resonant state has little impact on the radial position of the inner edge because for a given stellar flux, higher-order states tend to be warmer than synchronous rotators, but for a given temperature, have drier upper atmospheres. However, when strong tidal heating is present, the rotational component implies a strong dependence of habitable conditions on the system evolution and rotational state. Since tidal and stellar heating both decrease rapidly with orbital distance, this results in a compact orbital width separating temperate and uninhabitable climates. We summarize these results and also compare ROCKE-3D to previously published simulations of the inner edge.

Spin-Orbit Resonances↗
NASA NTRSDate not supplied

Fluid-Structure Interaction Simulations of the ASPIRE SR03 Supersonic Parachute Flight Test

Research into parachute performance continues to be a source of significant investment from the National Aeronautics and Space Administration to mitigate risks and to enable a variety of exploration missions, including landing on Mars as well as returning to Earth. The cost of flight tests to certify any changes to the current state-of-the-art parachute designs limits the development of next generation parachute systems. Fluid-structure interaction simulations could help accelerate this process once validated. The Launch, Ascent, and Vehicle Aerodynamics team is developing the capability to perform such fluid-structure interaction simulations by coupling a higher-order Cartesian immersed boundary computational fluid dynamics solver with adaptive mesh refinement to a finite element structural dynamics solver in space and time. We continue the effort to validate this tool with the Advanced Supersonic Parachute Inflation Research Experiments SR03 flight test featuring a strengthened parachute akin to the Mars 2020 mission that landed the Perseverance rover on Mars, and a higher freestream dynamic pressure prior to inflation. The effect of the flow conditions’ angle of attack and of the initial parachute shape are quantified. The impact of relaxing modeling assumptions with regards to radial stiffeners on the parachute canopy is also investigated. Results demonstrate improvements in agreement with the pull force recorded during the SR03 flight test as the initial conditions of the flow and parachute are brought closer to those experienced in flight, and further improved when the radial stiffener modeling assumptions are relaxed.

ESM↗
NASA NTRSDate not supplied

Fluid-Structure Interaction Simulations of the ASPIRE SR03 Supersonic Parachute Flight Test

Research into parachute performance continues to be a source of significant investment from the National Aeronautics and Space Administration to mitigate risks and to enable a variety of exploration missions, including landing on Mars as well as returning to Earth. The cost of flight tests to certify any changes to the current state-of-the-art parachute designs limits the development of next generation parachute systems. Fluid-structure interaction simulations could help accelerate this process once validated. The Launch, Ascent, and Vehicle Aerodynamics team is developing the capability to perform such fluid-structure interaction simulations by coupling a higher-order Cartesian immersed boundary computational fluid dynamics solver with adaptive mesh refinement to a finite element structural dynamics solver in space and time. We continue the effort to validate this tool with the Advanced Supersonic Parachute Inflation Research Experiments SR03 flight test featuring a strengthened parachute akin to the Mars 2020 mission that landed the Perseverance rover on Mars, and a higher freestream dynamic pressure prior to inflation. The effect of the flow conditions’ angle of attack and of the initial parachute shape are quantified. The impact of relaxing modeling assumptions with regards to radial stiffeners on the parachute canopy is also investigated. Results demonstrate improvements in agreement with the pull force recorded during the SR03 flight test as the initial conditions of the flow and parachute are brought closer to those experienced in flight, and further improved when the radial stiffener modeling assumptions are relaxed.

ESM↗
NASA NTRSDate not supplied

Fracture of Charring Avcoat With Meshfree Material Response-Coupled Fracture Approach

Fracture of thermal protection systems (TPS) is typically unfavorable, but often unavoidable. TPS can fracture during entry, manufacturing or from impact. Many NASA missions use ablative materials for TPS, including the fore-body for Dragonfly (PICA) and Orion for Artemis-I (Avcoat). The material response to thermal and mechanical loads during entry is integral to TPS sizing, design and analysis. The fracture of TPS also depends, and can be caused by, the change of material properties during entry. Simulations that resolve fracture of TPS due to thermo-mechanical forces can identify TPS failure mechanisms and be applied to conditions inaccessible to ground testing. We present simulation work using a mesh-free/Lagrangian approach to solving continuum mechanics, coupled to material response. Two different materials are simulated under different model entry-like boundary conditions. The dynamic crack structure is analyzed and compared across simulations. Crack analyses inform the role of design features, such as entry trajectories and manufacturing-influenced material properties, play in TPS fracture.

Andrew P Santos↗
NASA NTRSDate not supplied

Changes in the Ozone Chemical Regime Over the Contiguous United States Inferred By the Inversion of NOx and VOC Emissions Using Satellite Observation

To investigate changes in the ozone (O3) chemical production regime over the contiguous United States (CONUS) with accurate knowledge of concentrations of its precursors, we applied an inverse modeling technique with Ozone Monitoring Instrument (OMI) tropospheric nitrogen dioxide (NO2) and total formaldehyde (HCHO) retrieval products in the summers of 2011, 2014, and 2017, years in which United States National Emission Inventory were based. The inclusion of dynamic chemical lateral boundary conditions and lightning-induced nitric oxide emissions significantly account for the contribution of background sources in the free troposphere. Satellite-constrained nitrogen oxide (NOx) and non-methane volatile organic compounds (NMVOCs) emissions mitigate the discrepancy between satellite and modeled columns: the inversion suggested 2.33-2.84 (1.07-1.34) times higher NOx over the CONUS (over urban regions) and 0.28-0.81 times fewer NMVOCs emissions over the southeastern United States. The model-derived HCHO/NO2 column ratio shows gradual spatial changes in the O3 production regime near urban cores relative to previously defined threshold values representing NOx and VOC sensitive conditions. We also found apparent shifts from the NOx-saturated regime to the transition regime (or the transition regime to the NOx-limited regime) over the major cities in the western United States. In contrast, rural areas, especially in the east-southeastern United States, exhibit a decreased HCHO/NO2 column ratio by -1.30 ± 1.71 with a reduction in HCHO column primarily driven by meteorology, becoming sensitive to VOC emissions. Results show that incorporating satellite observations into numerical modeling could help policymakers implement appropriate emission control policies for O3 pollution.

HCHO/NO2 factorInverse modelingOzone chemical regi↗
NASA NTRS1982

Space platforms and meteorological applications

The use of Shuttle launched and tended space platforms (SP) for research and earth observations in LEO are examined. SPs will accommodate instruments for extended time periods, requiring a Shuttle visit for maintenance and package exchange once every six months. Designs have included off-the-shelf hardware to reduce cost, and comprise instruments for studies of cosmic rays, solar physics, materials processing, space plasma physics, and environmental observations. Solar cell power arrays are detailed, along with thermal control, data management, and attitude control subsystems. Meteorological applications are discussed in terms of the Lower Atmospheric Research Satellite (LARS), for research into coupling of radiative, chemical, and dynamical processes, interactions between the earth's surface, boundary layer, and troposphere, and dynamic and energetic relationships between lower atmospheric processes. Flight configurations and add-on concepts for the SP to lead to a manned space station are indicated.

Mitchell, K. L.↗
NASA NTRS1992

Effects of g-jitter and cross-diffusion on the onset of convection in doubly diffusive systems

The effects of a modulated gravity field in doubly diffusive layers with and without cross-diffusion are studied. Attention is focused on the determination of linear stability criteria for such systems. Floquet theory is used to establish the stability criteria by a systematic analysis of the topology of the neutral curves from which stability boundaries can be constructed. Convective stability boundaries for gravity-modulated doubly cross-diffusive systems are presented for the cases of dynamically free and rigid boundaries. Two physically different forms of layer stratification are considered: (1) imposed independent gradients of two components and (2) a solute gradient induced by a fixed temperature gradient.

Terrones, Guillermo↗
NASA NTRS1993

Flowfield dynamics in blunt fin-induced shock wave/turbulent boundary layer interactions

Fluctuating wall pressure measurements were made on centerline upstream of a blunt fin in a Much 5 turbulent boundary layer. By examining the ensemble average wall pressure distributions for different fixed shock foot positions, it was shown that local fluctuating wall pressure measurements are due to a distinct pressure distribution, P(i), which undergoes a stretching and flattening effect as its upstream boundary translates aperiodically between the upstream influence and separation lines. The locations of the maxima and minima in the centerline wall standard deviation distribution can be accurately predicted using this distribution, providing quantitative confirmation of the model. This model also explains the observed cross-correlations and ensemble average measurements within the interaction. Using the P(i) model, wall pressure signals from under the separated flow region were able to reproduce the position-time history of the separation shock foot. The negative time delay peak in the cross-correlation between the predicted and actual shock foot histories shows that the separated region fluctuations precede shock foot motion.

Brusniak, L.↗
NASA NTRS1994

Flowfield dynamics in blunt fin-induced shock wave/turbulent boundary layer interactions

Fluctuating wall pressure measurements have been made on centerline upstream of a blunt fin in a Mach 5 turbulent boundary layer. By examining the ensemble averaged wall pressure distributions for different separation shock foot positions, it has been shown that local fluctuating wall pressure measurements are due to a distinct pressure distribution, Rho(sub i), which undergoes a stretching and flattening effect as its upstream boundary translates aperiodically between the upstream influence and separation lines. The locations of the maxima and minima in the wall pressure standard deviation can be accurately predicted using this distribution, providing quantitative confirmation of the model. This model also explains the observed cross-correlations and ensemble average measurements within the interaction. Using the Rho(sub i) model, wall pressure signals from under the separated flow region were used to reproduce the position-time history of the separation shock foot. Further, the negative time delay peak in the cross-correlation between the predicted and actual shock foot histories suggests that the separated region fluctuations precede shock foot motion. The unsteady behavior of the primary horseshoe vortex and its relation to the unsteady separation shock are described.

Dolling, David S.↗