Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “gravity”

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.

At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Long-Term Global Morphology of Gravity Wave Activity Using UARS Data

Progress in research into the global morphology of gravity wave activity using UARS data is described for the period March-June, 1998. Highlights this quarter include further progress in the analysis and interpretation of CRISTA temperature variances; model-generated climatologies of mesospheric gravity wave activity using the HWM-93 wind and temperature model; and modeling of gravity wave detection from space-based platforms. Preliminary interpretations and recommended avenues for further analysis are also described.

Eckermann, Stephen D.↗
NASA NTRS1997

Laser-Induced Incandescence Measurements in Low Gravity

A low-gravity environment offers advantages to investigations concerned with soot growth or flame radiation by eliminating of buoyancy-induced convection. Basic to each type of study is knowledge of spatially resolved soot volume fraction, (f(sub v). Laser-induced incandescence (LII) has emerged as a diagnostic for soot volume fraction determination because it possesses high temporal and spatial resolution, geometric versatility and high sensitivity. Implementation and system characterization of LII in a drop tower that provides 2.2 sec of low-gravity (micro)g) at the NASA Lewis Research Center are described here. Validation of LII for soot volume fraction determination in (micro)g is performed by comparison between soot volume fraction measurements obtained by light extinction [20] and LII in low-gravity for a 50/50 mixture (by volume) of 0 acetylene/nitrogen issuing into quiescent air. Quantitative soot volume fraction measurements within other laminar flames of ethane and propane and a turbulent diffusion flame in (micro)g via LII are also demonstrated. An analysis of LII images of a turbulent acetylene diffusion flame in 1-g and (micro)g is presented.

VanderWal, R. L.↗
NASA NTRS1998

The Mars Gravity Simulation Project

Human beings who make abrupt transitions between one gravitational environment and another undergo severe disruptions of their visual perception and visual- motor coordination, frequently accompanied by "space sickness." Clearly, such immediate effects of exposure to a novel gravitational condition have significant implications for human performance. For example, when astronauts first arrive in Earth orbit their attempts to move about in the spacecraft and to perform their duties are uncoordinated, inaccurate, and inefficient. Other inter-gravitational transitions for which these difficulties can be expected include going from the 0 g of the spacecraft to the. 16 g of the Moon, from 0 g to the .38 g of Mars, and from 0 g back to the 1.0 g of Earth. However, after astronauts have actively interacted with their new gravitational environment for several days, these problems tend to disappear, evidence that some sort of adaptive process has taken place. It would be advantageous, therefore, if there were some way to minimize or perhaps even to eliminate this potentially hazardous adaptive transition period by allowing astronauts to adapt to the altered gravitational conditions before actually entering them. Simultaneous adaptations to both the altered and the normal gravitational environment as a result of repeatedly adapting to one and readapting to the other, a phenomenon known as dual adaptation. The objective of the Mars Gravity Simulator (MGS) Project is to construct a simulation of the visual and bodily effects of altered gravity. This perceptual-motor simulation is created through the use of: 1) differential body pressure to produce simulated hypo-gravity and 2) treadmill-controlled virtual reality to create a corresponding visual effect. It is expected that this combination will produce sensory motor perturbations in the subjects. Both the immediate and adaptive behavioral (postural and ambulatory) responses to these sensory perturbations will be assessed.

Korienek, Gene↗
NASA NTRS1999

Granular Superconductors and Gravity

As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (approx. 10(exp -6) g cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with a relatively high percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 104 was reported above a stationary (non-rotating) superconductor. In experiments using a sensitive gravimeter, bulk YBCO superconductors were stably levitated in a DC magnetic field and exposed without levitation to low-field strength AC magnetic fields. Changes in observed gravity signals were measured to be less than 2 parts in 108 of the normal gravitational acceleration. Given the high sensitivity of the test, future work will examine variants on the basic magnetic behavior of granular superconductors, with particular focus on quantifying their proposed importance to gravity.

Noever, David↗
NASA NTRS1999

Mars Gravity and Topography Interpretations

New models of the topography of Mars and its gravity field from the Mars Global Surveyor mission are shedding new light on the structure of the planet and the state of isostatic compensation. Gravity field observations over the flat northern hemisphere plains show a number of anomalies at the 100 to 200 mGal level that have no apparent manifestation in the surface topography. We believe that these anomalies are probably the result of ancient impacts and represent regions of denser material buried beneath the outer depositional crust. Similar anomalies are also found in the region of the north polar ice cap even though a gravity anomaly resulting from the 3 km high icecap has not been uniquely identified. This leads us to speculate that the ice cap is largely compensated and is older than the timescale of isostatic compensation, about 10(exp 15) years.

Zuber, Maria T.↗
NASA NTRS1999

Viscosity Measurement of Highly Viscous Liquids Using Drop Coalescence in Low Gravity

The method of drop coalescence is being investigated for use as a method for determining the viscosity of highly viscous undercooled liquids. Low gravity environment is necessary in this case to minimize the undesirable effects of body forces and liquid motion in levitated drops. Also, the low gravity environment will allow for investigating large liquid volumes which can lead to much higher accuracy for the viscosity calculations than possible under 1 - g conditions. The drop coalescence method is preferred over the drop oscillation technique since the latter method can only be applied for liquids with vanishingly small viscosities. The technique developed relies on both the highly accurate solution of the Navier-Stokes equations as well as on data from experiments conducted in near zero gravity environment. In the analytical aspect of the method two liquid volumes are brought into contact which will coalesce under the action of surface tension alone. The free surface geometry development as well as its velocity during coalescence which are obtained from numerical computations are compared with an analogous experimental model. The viscosity in the numerical computations is then adjusted to bring into agreement of the experimental results with the calculations. The true liquid viscosity is the one which brings the experiment closest to the calculations. Results are presented for method validation experiments performed recently on board the NASA/KC-135 aircraft. The numerical solution for this validation case was produced using the Boundary Element Method. In these tests the viscosity of a highly viscous liquid, in this case glycerine at room temperature, was determined to high degree of accuracy using the liquid coalescence method. These experiments gave very encouraging results which will be discussed together with plans for implementing the method in a shuttle flight experiment.

Antar, Basil N.↗
NASA NTRS1998

Gravity Field Mapping of Mars with MGS

Tracking of the MGS spacecraft in orbit at Mars by the Deep Space Network since last September has provided doppler and range measurements that are being used to improve the model of the Mars gravity field. During most of October 1997, April 1998, and June thru August 1998 high quality tracking data were obtained while the periapse was in the northern hemisphere at altitudes in the 170 to 190 km range. The eccentric orbit had a period of about 11.5 hrs and an inclination of about 96.2 degrees so that low altitude tracking was obtained over most of the northern hemisphere, including the north polar icecap. Data from the earlier Mariner 9 and Viking missions have been added to the MGS data and a series of experimental gravity models developed from the combined datasets. These models have generally been of degree and order 70 and are a significant improvement over earlier models that did not include the MGS data. Gravity anomalies over the north polar cap region of Mars are generally less than 50 to 100 mgals and show no obvious correlation with the topography. Successive MGS orbits derived using these new models are showing agreement at the 100 meter level, and this has been confirmed with the laser altimeter (MOLA) on MGS These comparisons are expected to improve significantly as more tracking data get included in the solution and the MGS orbit becomes more circular giving a more balanced geographical distribution of data at low altitude. This will happen early in 1999 as the orbit approaches the mapping configuration of a circular orbit at about 400 Km.

Smith, David E.↗
NASA NTRS1998

Inferences About the Early Moon from Gravity and Topography

Recent spacecraft missions to the Moon have significantly improved our knowledge of the lunar gravity and topography fields and have raised some new and old questions about the early lunar history. It has frequently been assumed that the shape of the Moon today reflects an earlier equilibrium state and that the Moon has retained some internal strength. Recent analysis indicating a superisostatic state of some lunar basins lends support to this hypothesis. On its simplest level the present shape of the Moon is slightly flattened by 2.2 +/- 0.2 km while its gravity field, represented by an equipotential surface, is flattened only about 0.5 km. The hydrostatic component to the flattening arising from the Moon's present-day rotation contributes only 7 m. This difference between the topographic shape of the Moon and the shape of its gravitational equipotential has frequently been explained as the "memory" of an earlier Moon that was rotating faster and had a correspondingly larger hydrostatic flattening. To obtain this amount of hydrostatic flattening from rotation alone, and accounting for the contribution of the present-day gravity field, the Moon's rotation rate would need to be about 15 times greater than at present leading to a period of under 2 days. Maintaining its synchronous rotation with Earth would require a radius for the Moon's orbit of order 9 earth radii. Unfortunately, our confidence in the observed lunar flattening is not as great as we would like.

Smith, David E.↗
NASA NTRS1999

The Effects of Gravity on ZBLAN Glass

Heavy metal fluoride glass fibers show promise in applications such as surgical lasers, spectroscopy and imaging fiber bundles. ZBLAN, which is within this class has been studied for a number of years. ZBLAN's theoretical attenuation coefficient is approximately 0.002 dB/km which is much better than that of fused silica at 0.2 dB/km. However, due to impurities and crystallites the attenuation coefficients achieved to date are considerably larger than those of fused silica. Impurities can be controlled with better processing techniques. Crystallization has been found to be a function of gravity. It is found that heating to the crystallization temperature in unit gravity results in crystallization while heating in reduced gravity does not. The exact mechanism for this phenomenon is not known but is speculated to be related to stress.

Tucker, Dennis S.↗
NASA NTRS1998

Inferences About the Early Moon From Gravity and Topography

Recent spacecraft missions to the Moon have significantly improved our knowledge of the lunar gravity and topography fields, and have raised some new and old questions about the early lunar history. It has frequently been assumed that the shape of the Moon today reflects an earlier equilibrium state and that the Moon has retained some internal strength. Recent analysis indicating a superisostatic state of some lunar basins lends support to this hypothesis. On its simplest level, the present shape of the Moon is slightly flattened by 2.2 +/- 0.2 km while its gravity field, represented by an equipotential surface, is flattened only about 0.5 km. The hydrostatic component to the flattening arising from the Moon's present day rotation contributes only 7 m. This difference between the topographic shape of the MOon and the shape of its gravitational equipotential has frequently been explained as the "memory" of an earlier moon that was rotating faster and had a correspondingly larger hydrostatic flattening. To obtain this amount of hydrostatic flattening from rotation alone, and accounting for the contribution of the present-day gravity field, the Moon's rotation rate would need to be about 15x greater than at present, leading ot a period of < 2 days. Maintaining its synchronous rotation with Earth would require a radius for the Moon's orbit of approximately 9 Earth Radii. Unfortunately, our confidence in the observed lunar flattening is not as great as we would like. The uncertainty of .02 km may not properly reflect the limitations of the Clementine dataset, which did not sample poleward of latitudes 81 N and 79 S. Also, the large variation of topography +/- 8 km seen on the MOon dwarfs our estimate fo the flattening. Further the lunar south pole is on the edge of, or possibly inside the massive deep, South Pole-Aitken Basin. Thus, polar radii could be underestimated. This would yield a smaller flattening, which would imply a greater lunar rotation period and orbital radius. However, Basin compensation states and analyses of support and relaxation of topography at long wavelengths point to a lunar shape that has retained a flattening from an earlier faster rotation period.

Smith, D. E.↗
NASA NTRS1989

The Origins of Air Parcels Uplifted in a Two Dimensional Gravity Wave in the Tropical Upper Troposphere During the NASA Stratosphere Troposphere Exchange Project (STEP)

During January and February 1987, as part of the Stratosphere-Troposphere Exchange Project, the NASA ER-2 made 11 flights from Darwin, Australia to investigate dehydration mechanisms in the vicinity of the tropical tropopause. After the monsoon onset in the second week of January, steady easterly flow of 15-25 ms (exp -1) was established in the upper troposphere and lower stratosphere over northern Australia and adjacent seas. Penetrating into this regime were elements of the monsoon convection such as overshooting convective turrets and extensive anvils including cyclone cloud shields. In cases of the latter, the resulting flow obstructions tended to produce mesoscale gravity waves. In several instances the ER- 2 meteorological and trace constituent measurements provide a detailed description of the structure of these gravity waves. Among these was STEP Flight 6, 22-23 January. It is of particular interest to STEP because of the close proximity of ice-laden and dehydrated air on the same isentropic surfaces. Convective events inject large amounts of ice into the upper troposphere and lower stratosphere which may not be completely removed by local precipitation processes. In the present instance, a gravity wave for removed from the source region appears to induce relativity rapid upward motion in the ice-laden air and subsequent dessication. Potential mechanisms for such a localized removal process are under investigation.

Selkirk, Henry B.↗
NASA NTRS1999

Context-Specific Adaptation of Gravity-Dependent Vestibular Reflex Responses (NSBRI Neurovestibular Project 1)

Impairment of gaze and head stabilization reflexes can lead to disorientation and reduced performance in sensorimotor tasks such as piloting of spacecraft. Transitions between different gravitoinertial force (gif) environments - as during different phases of space flight - provide an extreme test of the adaptive capabilities of these mechanisms. We wish to determine to what extent the sensorimotor skills acquired in one gravity environment will transfer to others, and to what extent gravity serves as a context cue for inhibiting such transfer. We use the general approach of adapting a response (saccades, vestibuloocular reflex: VOR, or vestibulocollic reflex: VCR) to a particular change in gain or phase in one gif condition, adapting to a different gain or phase in a second gif condition, and then seeing if gif itself - the context cue - can recall the previously-learned adapted responses. Previous evidence indicates that unless there is specific training to induce context-specificity, reflex adaptation is sequential rather than simultaneous. Various experiments in this project investigate the behavioral properties, neurophysiological basis, and anatomical substrate of context-specific learning, using otolith (gravity) signals as a context cue. In the following, we outline the methods for all experiments in this project, and provide details and results on selected experiments.

Shelhamer, Mark↗
NASA NTRS1996

Effects of Gravity and Shear on the Dynamics and Stability of Particulate and Multiphase Flows

The main objectives of this project are to understand the differing particulate and multiphase flow behaviors that will occur in space and in Earth's gravity. More specifically, the project is concerned with understanding the effect of shear and gravity on two relatively ideal suspensions with significant inertial effects. The first is a gas-solid suspension at small Reynolds numbers and finite Stokes numbers. In this type of suspensions the inertia of the particle phase is significant while the hydrodynamic interactions are dominated by viscous forces in the suspending fluid. The other is a bubble suspension at small Weber and large Reynolds numbers. The hydrodynamic interactions in such suspensions are dominated by the inertial effects in the suspending fluid, but these inertial interactions can be described using potential flow theory. Our main objective is to examine the effects of shear and gravity on the average properties and stability of these two suspensions.

Sangani, Ashor S.↗
NASA NTRS1999

Mars Gravity Field Model Development from Mars Global Surveyor Tracking Data

Since Feb. 99 the MGS spacecraft has been in a near circular orbit at about 400 km altitude. The MGS has been regularly tracked by the Deep Space Network (DSN) at X-band and for a 3 week period in February was tracked almost continuously for an intensive gravity modeling activity that would form the basis of the orbital computations for the rest of the mission. The data collected during this calibration period and the earlier SPO and Hiatus periods have now been used to develop a new gravity field model for Mars that is showing considerable new detail in both the northern and southern hemispheres. Until February no data at 400 km altitude or lower had been acquired on any previous mission south of about 35S and all the previous data were of significantly lower quality. Low altitude data (-170 km) were obtained over the higher latitudes of the northern hemisphere during the SPO periods but because of the high eccentricity of the orbit nothing of similar quality was obtainable for the southern hemisphere. The new models are of spherical harmonic degree and order 70 or higher and are suggesting large anomalies are often associated with the large impact features. Gravity data have also been obtained over both the northern and southern polar ice caps. The MGS orbit quality resulting from the use of these newer models is better than any previous Mars missions and is approaching the ten's of meter level that had been hoped would be eventually realizable.

Lemoine, F. G.↗
NASA NTRS1997

A Biomechanical Comparison of 1-G and Fully-Loaded Simulated Zero-Gravity Locomotion

Exercise will almost certainly play an integral part in minimizing the bone mineral loss and muscular atrophy that occur during spaceflight. It has been hypothesized that an effective exercise regimen can be developed to elicit loads on the lower extremities and require muscle actions which resemble those encountered on Earth. The Penn State Zero-Gravity Simulator (PSZS) is a device which suspends subjects horizontally from multiple latex cords, with each cord negating the weight of a limb segment. A treadmill mounted on the wall under the PSZS enables subjects to run in simulated 0G. Subjects wear a harness to which a number of springs, which provide a gravity replacement load, are connected. The opposite end of each spring is connected to the side of the treadmill. During exercise, astronauts currently wear a similar harness in which the spring tethering load pulls at both the waist and shoulders. Ground reaction forces, muscular activations, and joint angles of the left leg during overground, treadmill, and fully-loaded zero-gravity simulated (ZLS) locomotion were assessed in order to gain insight into the effectiveness of the exercise regimen used by NASA to prevent the muscular atrophy and bone demineralization which occur in weightlessness. There were three hypotheses to this research. It was hypothesized that there will be no differences in peak ground reaction forces and peak loading rates between overground gait and gait in the full body weight loaded conditions in the ZLS. A second hypothesis was that that there will be no differences in hip, knee, and ankle joint positions between walking or running overground, on a standard treadmill, and in full bodyweight loaded conditions in the ZLS. The third hypothesis was that the muscular activations, as a percentage of maximal voluntary contraction, will be similar between walking or running overground, on a standard treadmill, and in full body-weight loaded conditions in the ZLS.

McCrory, Jean L.↗
NASA NTRS2000

Generation of Bubbly Suspensions in Low Gravity

Generation of a uniform monodisperse bubbly suspension in low gravity is a rather difficult task because bubbles do not detach as easily as on Earth. Under microgravity, the buoyancy force is not present to detach the bubbles as they are formed from the nozzles. One way to detach the bubbles is to establish a detaching force that helps their detachment from the orifice. The drag force, established by flowing a liquid in a cross or co-flow configuration with respect to the nozzle direction, provides this additional force and helps detach the bubbles as they are being formed. This paper is concerned with studying the generation of a bubbly suspension in low gravity in support of a flight definition experiment titled "Behavior of Rapidly Sheared Bubbly Suspension." Generation of a bubbly suspension, composed of 2 and 3 mm diameter bubbles with a standard deviation <10% of the bubble diameter, was identified as one of the most important engineering/science issues associated with the flight definition experiment. This paper summarizes the low gravity experiments that were conducted to explore various ways of making the suspension. Two approaches were investigated. The first was to generate the suspension via a chemical reaction between the continuous and dispersed phases using effervescent material, whereas the second considered the direct injection of air into the continuous phase. The results showed that the reaction method did not produce the desired bubble size distribution compared to the direct injection of bubbles. However, direct injection of air into the continuous phase (aqueous salt solution) resulted in uniform bubble-diameter distribution with acceptable bubble-diameter standard deviation.

Nahra, Henry K.↗
NASA NTRS2000

Effect of Melt Convection at Various Gravity Levels and Orientations on the Forces Acting on a Large Spherical Particle in the Vicinity of a Solidification Interface

Numerical modeling was Undertaken to analyze the influence of both radial and axial thermal gradients on convection patterns and velocities claiming solidification of pure Al and an Al-4 wt% Cu alloy. The objective of the numerical task was to predict the influence of convective velocity on an insoluble particle near a solid/liquid (s/l) interface. These predictions were then be used to define the minimum gravity level (q) required to investigate the fundamental physics of interactions between a particle and a s/l interface. This is an ongoing NASA founded flight experiment entitled "particle engulfment and pushing by solidifying interfaces (PEP)". Steady-state calculations were performed for different gravity levels and orientations with respect to the gravity vector The furnace configuration used in this analysis is the quench module insert (QMI-1) proposed for the Material Science Research Facility (MSRF) on board the International Space Station (ISS). The general model of binary alloy solidification was based on the finite element code FIDAP. At a low g level of 10(exp -4) g(sub o) (g(sub o) = 9.8 m/square s) maximum melt convection was obtained for an orientation of 90 deg. Calculations showed that even for this worst case orientation the dominant forces acting on the particle are the fundamental drag and interfacial forces.

Bune, Andris V.↗
NASA NTRS1999

Inversion of Gravity Fields From the Spacecraft Orbital Data Using an Adjoint Operator Approach

In perturbation approximation, the forward problem of orbital dynamics (equations with initial conditions) is linear with respect to variations of coordinates and/or velocities of the spacecraft and to corresponding variations of the gravity field in the models used. The linear operator adjoint to the linear operator of such forward problem turns out to be instrumental in inversion of differences between observed and predicted coordinates/velocities in terms of the updates of harmonics in the initial gravity field model. Based on this approach, the solution of resulting adjoint problem of orbital dynamics can be used to directly evaluate the matrix of partial derivatives of observable differences with respect to the gravity field harmonics. General discussion of the adjoint problem of orbital dynamics is given and an example of a mathematical formalism for the practical retrieval algorithm is presented.

Ustinov, E. A.↗