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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Present-day kinematics of the Rivera plate and implications for tectonics in southwestern Mexico

A model for the present-day motion of the Rivera plate relative to the North America, Cocos, and Pacific plates is derived using new data from the Pacific-Rivera rise and Rivera transform fault, together with new estimates of Pacific-Rivera motions. The results are combined with the closure-consistent NUVEL-1 global plate motion model of DeMets et al. (1990) to examine present-day deformation in southwestern Mexico. The analysis addresses several questions raised in previous studies of the Rivera plate. Namely, do plate motion data from the northern East Pacific rise require a distinct Rivera plate? Do plate kinematic data require the subduction of the Rivera plate along the seismically quiescent Acapulco trench? If so, what does the predicted subduction rate imply about the earthquake recurrence interval in the Jalisco region of southwestern Mexico?

Demets, Charles↗
NASA NTRS1995

Surface Deformation Caused by Pressure Changes in the Fluid Core

Pressure load Love numbers are presented for the mantle deformation induced by the variation of the pressure field at the core mantle boundary (CNB). We find that the CMB geostrophic pressure fields, derived from 'frozen-flux' core surface flow estimates at epochs 1965 and 1975, produce a relative radial velocity (RRV) field in the range of 3mm/decade with uplift near the equator and subsidence near the poles. The contribution of this mechanism to the change in the length of day (l.o.d) is small --- about 2.3 x 10(exp -2) ms/decade. The contribution to the time variation of the ellipticity coefficient is more important --- -1.3 x 10(exp -11)/yr.

Fang, Ming↗
NASA NTRS1999

Glacial Isostatic Adjustment Observed with VLBI and SLR

In global geodetic solutions vertical rates of site motion are usually estimated relative to the geocenter (center of figure) of the solid earth. The velocity of the geocenter is estimated assuming that the plates are rigid, that the velocities of the plates equal those in NUVEL-1A (DeMets et al. 1990, 1994) and that the uplift, subsidence, and intraplate deformation due to glacial isostatic adjustment is negligible.

postglacial rebould mantel viscosity crustal movem↗
NASA NTRS1984

Geophysical interpretation of satellite laser ranging measurements of crustal movement in California

As determined by satellite laser ranging the rate of contraction of a 900 kilometer baseline between sites located near Quincy in northern California and San Diego in southern California is about 61 to 65 mm/yr with a formal uncertainty of about 10 mm/yr. The measured changes in baseline length are a manifestation of the relative motion between the North America and Pacific tectonic plates. This long baseline result is compared to measurements made by more conventional means on shorter baselines. Additional information based on seismicity, geology, and theoretical modelling is also analyzed. Deformation lying within a few tens of kilometers about the major faults in southern California accounts for most, but not all of the observed motion. Further motion is attributable to a broader scale deformation in southern California. Data suggesting crustal movements north of the Garlock fault, in and near the southern Sierra Nevada and local motion at an observatory are also critically reviewed. The best estimates of overall motion indicated by ground observations lie between 40 and 60 mm/yr. This lies within one or two standard deviations of that deduced by satellite ranging but the possibility of some unresolved deficit cannot be dismissed. The long time scale RM2 plate tectonic model of Minster and Jordan predicts a contraction between 47 and 53 mm/yr depending on the extension rate of the Basin and Range. Thus the ground based observations, satellite laser ranging (SLR) results, and RM2 rates differ at about the 10 mm/yr level and are consistent with one another within the data and model uncertainties.

Cohen, S. C.↗
NASA NTRS1998

Summary of Research Report

Ten papers, published in various publications, on buckling, and the effects of imperfections on various structures are presented. These papers are: (1) Buckling mode localization in elastic plates due to misplacement in the stiffner location; (2) On vibrational imperfection sensitivity on Augusti's model structure in the vicinity of a non-linear static state; (3) Imperfection sensitivity due to elastic moduli in the Roorda Koiter frame; (4) Buckling mode localization in a multi-span periodic structure with a disorder in a single span; (5) Prediction of natural frequency and buckling load variability due to uncertainty in material properties by convex modeling; (6) Derivation of multi-dimensional ellipsoidal convex model for experimental data; (7) Passive control of buckling deformation via Anderson localization phenomenon; (8)Effect of the thickness and initial im perfection on buckling on composite cylindrical shells: asymptotic analysis and numerical results by BOSOR4 and PANDA2; (9) Worst case estimation of homology design by convex analysis; (10) Buckling of structures with uncertain imperfections - Personal perspective.

Elishakoff, Isaac↗
NASA NTRS1998

Leg intramuscular pressures during locomotion in humans

To assess the usefulness of intramuscular pressure (IMP) measurement for studying muscle function during gait, IMP was recorded in the soleus and tibialis anterior muscles of 10 volunteers during treadmill walking and running by using transducer-tipped catheters. Soleus IMP exhibited single peaks during late-stance phase of walking [181 +/- 69 (SE) mmHg] and running (269 +/- 95 mmHg). Tibialis anterior IMP showed a biphasic response, with the largest peak (90 +/- 15 mmHg during walking and 151 +/- 25 mmHg during running) occurring shortly after heel strike. IMP magnitude increased with gait speed in both muscles. Linear regression of soleus IMP against ankle joint torque obtained by a dynamometer produced linear relationships (n = 2, r = 0.97 for both). Application of these relationships to IMP data yielded estimated peak soleus moment contributions of 0.95-1.65 N . m/kg during walking, and 1.43-2.70 N . m/kg during running. Phasic elevations of IMP during exercise are probably generated by local muscle tissue deformations due to muscle force development. Thus profiles of IMP provide a direct, reproducible index of muscle function during locomotion in humans.

Clinical Trial↗
NASA NTRS2005

Preliminary investigation of Zagros thrust-fold-belt deformation using SAR interferometry

Most of the Zagros deformation resulting from the convergence of Arabia and Eurasia takes place in the Southeast Zagros. To apply the SAR interferometry geodetic technique, a few ERS 1 & 2 satellite images were used to map this continuing deformation proven by GPS. Interferograms over 7 years show surprisingly high coherence. The unwrapped phases display a high correlation with topography reflecting atmospheric noise in addition to the desired tectonic signal. We estimate two simple linear trends and remove them from interferograms. The preliminary results show local uplift rates with a likely minimum of 1-2 mm/yr. These early crude results will be tested by more data in project No. 3174.

tectonics↗
NASA NTRS2013

Conceptual Design and Structural Analysis of an Open Rotor Hybrid Wing Body Aircraft

Through a recent NASA contract, Boeing Research and Technology in Huntington Beach, CA developed and optimized a conceptual design of an open rotor hybrid wing body aircraft (HWB). Open rotor engines offer a significant potential for fuel burn savings over turbofan engines, while the HWB configuration potentially allows to offset noise penalties through possible engine shielding. Researchers at NASA Langley converted the Boeing design to a FLOPS model which will be used to develop take-off and landing trajectories for community noise analyses. The FLOPS model was calibrated using Boeing data and shows good agreement with the original Boeing design. To complement Boeing s detailed aerodynamics and propulsion airframe integration work, a newly developed and validated conceptual structural analysis and optimization tool was used for a conceptual loads analysis and structural weights estimate. Structural optimization and weight calculation are based on a Nastran finite element model of the primary HWB structure, featuring centerbody, mid section, outboard wing, and aft body. Results for flight loads, deformations, wing weight, and centerbody weight are presented and compared to Boeing and FLOPS analyses.

Gern, Frank H.↗
NASA NTRS2019

Forecasting the Structure and Orientation of Earthbound Coronal Mass Ejections

Coronal Mass Ejections (CMEs) are the key drivers of strong to extreme space weather storms at the Earth that can have drastic consequences for technological systems in space and on ground.The ability of a CME to drive geomagnetic disturbances depends crucially on the magnetic structure of the embedded flux rope, which is thus essential to predict. The current capabilities in forecasting in advance(at least half a day before) the geo effectiveness of a given CME is however severely hampered by the lack of remote-sensing measurements of the magnetic field in the corona and adequate tools to predict how CMEs deform, rotate, and deflect during their travel through the coronal and interplanetary space as they interact with the ambient solar wind and other CMEs. These problems can lead not only to over estimation or underestimation of the severity of a storm, but also to forecasting "misses" and "false alarms" that are particularly difficult for the end-users. In this paper, we discuss the current status and future challenges and prospects related to forecasting of the magnetic structure and orientation of CMEs. We focus both on observational- and modeling-based (first principle and semiempirical) approaches and discuss the space- and ground-based observations that would be the most optimal for making accurate space weather predictions. We also cover the gaps in our current understanding related to the formation and eruption of the CME flux rope and physical processes that govern its evolution in the variable ambient solar windbackground that complicate the forecasting.

Kilpua, E. K. J.↗
NASA NTRSDate not supplied

Impact of DORISx Post Seismic Deformation and Seasonal Corrections on the DPOD2020 Solution

As one of the tracking systems used for the altimeter missions (such as TOPEX/Poseidon, Envisat, Jason-1/-2/-3, CryoSat-2, Saral/AltiKa, Sentinel-3A/-3B, HY-2A/C/D, Jason-CS/Sentinel-6A, SWOT), the position of the DORIS tracking stations provides a fundamental reference for the estimation of the precise orbits and so, by extension is fundamental for the quality of the altimeter data analysis and derived products. Due to the time evolution of the DORIS ground network, stations included in ITRF2020 may have been decommissioned and stations that were added to the tracking network after 2021.0 are, by definition, not part of ITRF2020. Therefore, to satisfy operational requirements for precise orbit determination and routine delivery of geodetic products, the International DORIS Service maintains the DORIS terrestrial reference frame for Precise Orbit Determination (DPOD) solutions. Since 2016, the DPOD products are computed by the IDS Combination Center (CC) as a DORIS cumulative position and linear velocity solution aligned to the latest available ITRF and using the latest IDS weekly combined series. Mid-2023, the IDS CC started the computation of the second version of the DPOD2020 based on the IDS 20 weekly solutions from 1993.0 to 2023.0. With that new solution, the IDS CC will include Post Seismic Deformation (PSD) corrections for some DORIS sites such as Socorro Island. These DPOD PSD corrections are determined from the analysis of DORIS coordinate time series only. The second version will also include optional annual and semi-annual station corrections. The presentation will describe the analysis used for extracting the PSD and seasonal DORIS station corrections, compare such corrections to those derived for ITRF2020, and evaluate the impact these new corrections have on station positioning and satellite POD.

Guilhem Moreaux↗
NASA NTRS1988

Geodetic Measurement of Deformation East of the San Andreas Fault in Central California

Triangulation and trilateration data from two geodetic networks located between the western edge of the Great Valley and the San Andreas fault have been used to calculate shear strain rates in the Diablo Range and to estimate the slip rate along the Calaveras and Paicines faults in Central California. Within the Diablo Range the average shear strain rate was determined for the time period between 1962 and 1982 to be 0.15 + or - 0.08 microrad/yr, with the orientation of the most compressive strain at N 16 deg E + or - 14 deg. The orientation of the principal compressive strain predicted from the azimuth of the major structures in the region is N 25 deg E. It is inferred that the measured strain is due to compression across the folds of this area: the average shear straining corresponds to a relative shortening rate of 4.5 + or - 2.4 mm/yr. From an examination of wellbore breakout orientations and the azimuths of P-axes from earthquake focal mechanisms the inferred orientation of maximum compressive stress was found to be similar to the direction of maximum compressive strain implied by the trend of local fold structures. Results do not support the hypothesis of uniform fault-normal compression within the Coast Ranges. From trilateration measurements made between 1972 and 1987 on lines that are within 10 km of the San Andreas fault, a slip rate of 10 to 12 mm/yr was calculated for the Calaveras-Paicines fault south of Hollister. The slip rate of the Paicines fault decreases to 4 mm/yr near Bitter.

Sauber, Jeanne M.↗
NASA NTRS1987

Block rotations, fault domains and crustal deformation

Much of the earth's crust is broken by sets of parallel strike-slip faults which are organized in domains. A simple kinematic model suggests that when subject to tectonic strain, the faults, and the blocks bound by them, rotate. The rotation can be estimated from the structurally-determined fault slip and fault spacing, and independently from local deviations of paleomagnetic declinations from global values. A rigorous test of this model was carried out in northern Israel, where good agreement was found between the two rotations.

Nur, A.↗
NASA NTRS1987

Displacements of the earth's surface due to atmospheric loading - Effects of gravity and baseline measurements

Atmospheric mass loads and deforms the earth's crust. By performing a convolution sum between daily, global barometric pressure data and mass loading Green's functions, the time dependent effects of atmospheric loading, including those associated with short-term synoptic storms, on surface point positioning measurements and surface gravity observations are estimated. The response for both an oceanless earth and an earth with an inverted barometer ocean is calculated. Load responses for near-coastal stations are significantly affected by the inclusion of an inverted barometer ocean. Peak-to-peak vertical displacements are frequently 15-20 mm with accompanying gravity perturbations of 3-6 micro Gal. Baseline changes can be as large as 20 mm or more. The perturbations are largest at higher latitudes and during winter months. These amplitudes are consistent with the results of Rabbel and Zschau (1985), who modeled synoptic pressure disturbances as Gaussian functions of radius around a central point. Deformation can be adequately computed using real pressure data from points within about 1000 km of the station. Knowledge of local pressure, alone, is not sufficient. Rabbel and Zschau's hypothesized corrections for these displacements, which use local pressure and the regionally averaged pressure, prove accurate at points well inland but are, in general, inadequate within a few hundred kilometers of the coast.

Van Dam, T. M.↗
NASA NTRS1966

X-ray analysis of fatigue damage in copper

A Warren-Averbach x-ray line profile analysis was applied to, broadened x-ray diffraction peaks from copper deformed in fatigue. The copper specimens were fatigued by four point bending at various strain amplitudes, and measurements were made at various fractions of the total fatigue life. The analysis results in an estimation of 1) an average coherently diffracting domain size in a direction normal to the diffracting planes; and 2) a strain distribution function. The strain distribution function is in terms of the root mean square strain, <ϵ^(2)> where ϵ is averaged over a given distance at all points in the diffracting crystals. This rms strain is expressed as a function of averaging distance for a direction normal to the diffracting planes. The rms strains were found to be a function of the fatigue strain amplitude level, increasing with amplitude and reaching a maximum limiting value during the first 2% of the fatigue life. The strains were normally larger in the 4lO0 direction compared to the <111> direction and the absolute values were quite small. These results may be explained by assuming the dislocations are present in the form of dipoles because the lattice strain around a dipole is much less than around single dislocations. Conclusions arrived at in this analysis are in agreement with current theories of fatigue damage in metals. The result that maximum hardening is achieved during the initial few percent of the fatigue life is confirmed by many other investigators using entirely different analytical techniques. It is felt that the structure of the material is changing during this initial hardening stage to an eventual steady state characteristic of the testing conditions. A unique substructure is developed which thereafter persists, and the remainder of the fatigue test is taken up by crack propagation through this substructure until ultimate failure occurs by fracture. The formation of this steady state structure is dependent on the maximum fatigue strain amplitude and on the frequency and temperature of cycling for a particular material.

COPPER↗
NASA NTRSDate not supplied

Coastal Land Change Due to Tectonic Processes and Implications for Relative Sea-Level Rise in the Samoan Islands

Of the major coastal land change mechanisms responsible for relative sea-level change, tectonic subsidence is generally quoted as ranging from < mm/yr to 1 cm/yr. However, we documented coseismic and ongoing post-earthquake surface displacements from continuous GPS and tide gauge/altimetry data that indicated rapid subsidence on two of the major Samoan Islands of 12 - 20 cm during and following the 8.1 2009 Tonga-Samoa earthquake. Earlier results and our modeling of GRACE-derived gravimetric data provided a preliminary forecast of future relative sea-level rise through rapid land subsidence [Han et al., 2019]. Of course these numerical forecasts of time-dependent deformation are only as good as our input observations and our assumed rheological models. As part of our current NASA Earth Surface and Interior study, we are obtaining a wider range of data to constrain and test alternate models of ongoing postseismic deformation across American Samoa and Upolu, Samoa: (1) times series of altimetry plus tide gauge data processed to complement the cGPS data available to provide high-temporal resolution, point measurements of uplift/subsidence, (2) InSAR derived observations of surface deformation across the highly vegetated Samoan Islands, (3) evaluating and using NASA satellite lidar data (ICESat-I & ICESat-II, GEDI) for fusion with multi-source topographic data sets and for estimating topographic change on the decadal time scale. We are evaluating and using these new observations to better understand and separate out local, island-wide, and multi-island subsidence patterns and to evaluate the high impact of rising sea-level in a tectonically active region.

Jeanne Sauber-Rosenberg↗
NASA NTRS2017

Mechanism of Supercooled Water Droplet Breakup near the Leading Edge of an Airfoil

This work presents the results of an experimental study on supercooled droplet deformation and breakup near the leading edge of an airfoil. The results are compared to prior room temperature droplet deformation results to explore the effects of droplet supercooling. The experiments were conducted in the Adverse Environment Rotor Test Stand (AERTS) at The Pennsylvania State University. An airfoil model placed at the end of the rotor blades mounted onto the hub in the AERTS chamber was moved at speeds ranging between 50 and 80 m/sec. The temperature of the chamber was set at -20˚C. A monotonic droplet generator was used to produce droplets that fell from above, perpendicular to the path of the airfoil. The supercooled state of the droplets was determined by measurement of the temperature of the drops at various locations below the droplet generator exit. A temperature prediction code was also used to estimate the temperature of the droplets based on vertical velocity and the distance traveled by droplets from the droplet generator to the airfoil stagnation line. High speed imaging was employed to observe the interaction between the droplets and the airfoil. The high speed imaging provided droplet deformation information as the droplet approached the airfoil near the stagnation line. A tracking software program was used to measure the horizontal and vertical displacement of the droplet against time. It was demonstrated that to compare the effects of water supercooling on droplet deformation, the ratio of the slip velocity and the initial droplet velocity must be equal. A case with equal slip velocity to initial velocity ratios was selected for room temperature and supercooled droplet conditions. The airfoil velocity was 60 m/s and the slip velocity for both sets of data was 40 m/s. In these cases, the deformation of the weakly supercooled and warm droplets did not present different trends. The similar behavior for both environmental conditions indicates that water supercooling has no effect on particle deformation for the limited range of the weak supercooling of the droplets tested and the selected impact velocity. The assumption of a constant surface tension value was further supported by the equal trend of the Bond number obtained for supercooled and room temperature droplets.

in-flight icing↗
NASA NTRS2017

Atmospheric Form Drag Coefficients Over Arctic Sea Ice Using Remotely Sensed Ice Topography Data, Spring 2009-2015

Sea ice topography significantly impacts turbulent energy/momentum exchange, e.g., atmospheric (wind) drag, over Arctic sea ice. Unfortunately, observational estimates of this contribution to atmospheric drag variability are spatially and temporally limited. Here we present new estimates of the neutral atmospheric form drag coefficient over Arctic sea ice in early spring, using high-resolution Airborne Topographic Mapper elevation data from NASA's Operation IceBridge mission. We utilize a new three-dimensional ice topography data set and combine this with an existing parameterization scheme linking surface feature height and spacing to form drag. To be consistent with previous studies investigating form drag, we compare these results with those produced using a new linear profiling topography data set. The form drag coefficient from surface feature variability shows lower values [less than 0.5-1 × 10(exp. −3)] in the Beaufort/Chukchi Seas, compared with higher values [greater than 0.5-1 ×10(exp. −3)] in the more deformed ice regimes of the Central Arctic (north of Greenland and the Canadian Archipelago), which increase with coastline proximity. The results show moderate interannual variability, including a strong increase in the form drag coefficient from 2013 to 2014/2015 north of the Canadian Archipelago. The form drag coefficient estimates are extrapolated across the Arctic with Advanced Scatterometer satellite radar backscatter data, further highlighting the regional/interannual drag coefficient variability. Finally, we combine the results with existing parameterizations of form drag from floe edges (a function of ice concentration) and skin drag to produce, to our knowledge, the first pan-Arctic estimates of the total neutral atmospheric drag coefficient (in early spring) from 2009 to 2015.

sea ice↗