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The nature and dynamics of time-dependent deformation along major seismic zones including the influence of irregularities in fault geometry on the earthquake cycle, and the processes contributing to the state of stress and rates of strain in plate interior regions were studied. The principle findings of the research are discussed.
Results are presented for an extensive study of the influence of damped flexible supports on the stability-threshold speed of a symmetric rotor mounted in nonlinear fluid-film bearings. A stability analysis is conducted by applying the Routh criteria and calculating the damped eigenvalues of the system. Stability maps are given in dimensionless form for a range of support stiffness, damping, and mass ratios. The effect of rotor imbalance on the stability of rotor systems is examined, and it is shown that time transient orbits of shaft and support motions clearly indicate their dynamic behavior for both stable and unstable operating speeds. Simple design criteria are proposed for choosing the support stiffness and damping on the basis of rotor weight and journal clearance to promote optimum stability. It is concluded that the use of a flexible damped support system may increase the stability threshold of a plain journal bearing and that damper supports should promote smoother and quieter machine operation by suppressing oil whirl and attenuating unbalanced rotational forces.
A simple approach for computing acceleration and velocity of a structure from the strain is proposed in this study. First, deflection and slope of the structure are computed from the strain using a two-step theory. Frequencies of the structure are computed from the time histories of strain using a parameter estimation technique together with an autoregressive moving average model. From deflection, slope, and frequencies of the structure, acceleration and velocity of the structure can be obtained using the proposed approach. Simple harmonic motion is assumed for the acceleration computations, and the central difference equation with a linear autoregressive model is used for the computations of velocity. A cantilevered rectangular wing model is used to validate the simple approach. Quality of the computed deflection, acceleration, and velocity values are independent of the number of fibers. The central difference equation with a linear autoregressive model proposed in this study follows the target response with reasonable accuracy. Therefore, the handicap of the backward difference equation, phase shift, is successfully overcome.
Optimizing the trajectory of a low thrust space vehicle usually means solving a nonlinear two point boundary value problem. In general, accuracy requirements necessitate extensive computation times. In celestial mechanics, regularizing transformations of the equations of motion are used to eliminate computational and analytical problems that occur during close approaches to gravitational force centers. It was shown in previous investigations that regularization in the formulation of the trajectory optimization problem may reduce the computation time. In this study, a set of regularized equations describing the optimal trajectory of a continuously thrusting space vehicle is derived. The computational characteristics of the set are investigated and compared to the classical Newtonian unregularized set of equations. The comparison is made for low thrust, minimum time, escape trajectories and numerical calculations of Keplerian orbits. The comparison indicates that in the cases investigated for bad initial guesses of the known boundary values a remarkable reduction in the computation time was achieved. Furthermore, the investigated set of regularized equations shows high numerical stability even for long duration flights and is less sensitive to errors in the guesses of the unknown boundary values.
The motion of high energy charged particles in ideal oblique MHD shocks has been studied extensively. The orbits of charged particles can be solved exactly from Lorentz force equation. It is found that a charged particle may cross the shock front many times before it leaves the shock and it is energized during crossings. The most energetic particles are those with initial pitch and phase near the boundary between crossing and reflected particles. The reflected particles cross the shock about twice as many times as the passing particles do. The energy gain increases for larger values of shock strength and speed. If reflection occurs, the energy gain is larger for smaller angles between the field and shock surface. The introduction of scattering results in a few more higher energy particles.
Infrared geosynchronous satellite data with an interval of 5 min between images are used to estimate thunderstorm top ascent rates on two case study days. A mean vertical velocity of 3.4 m/sec for 23 clouds is calculated at a height of 8.7 km. This upward motion is representative of an area of approximately 10 km on a side. Thunderstorm mass flux of approximately 2 times 10 to the 8th power kg/sec is calculated, which compares favorably with previous estimates. There is a significant difference in the mean calculated vertical velocity between elements associated with severe weather reports (omega = 4.9 m/sec) and those with no such reports (2.4 m/sec). Calculations were made using a velocity profile for an axially symmetric jet to estimate the peak updraft velocity. For the largest observed omega value of 7.8 m/sec the calculation indicates a peak updraft of approximately 50 m/sec.
The optimal control model (OCM) of the human operator is used to predict the effect of simulator characteristics on pilot performance and workload. The piloting task studied is helicopter hover. Among the simulator characteristics considered were (computer generated) visual display resolution, field of view and time delay.
It is anticipated that terrestrial reference systems for geodynamics studies which include adopted plate motion models will be introduced for the analysis of both LAGEOS satellite and very long baseline interferometry ranging data. One of the possible approaches involves adjustment of ground station coordinates in conjunction with solutions for Universal Time 1 (UT1) and polar motions as functions of time. Another method uses principal value decomposition to reduce the number of degrees of freedom being solved for by three. In a third alternative, the values of UT1 and polar motion derived from the available data by means of the initial set of coordinates are kept fixed, and an appropriate block of data is reanalyzed using the previously determined values of UT1 and polar motion so that a new set of station coordinates can be derived.
Results obtained by Forbes et al. (1981) on the basis of time delay measurements between ISEE 1 and ISEE 2 imply that the plasma flow and the boundary contracting velocity were nearly the same, whereas the expanding boundary velocity was not accompanied by any significant plasma sheet plasma motion. In the present study, this observation is discussed in conjunction with electric field data. The study is based on electric field data from the spherical double probe experiment on ISEE 1. Electric field data from GEOS 2 are used to some extent to monitor the electric fields near the geostationary orbit during the considered eve nts. Electric field data during CDAW 6 events are discussed, taking into account positions of ISEE 1/ISEE 2 and GEOS 2; March 22, 0600-1300 UT; and March 22, UT; and March 31, 1400-2400 UT.
The structure of homogeneous turbulence in the presence of a high shear rate is studied using results obtained from three-dimensional time-dependent numerical simulations of the Navier-Stokes equations on a grid of 512 x 128 x 128 node points. It is shown that high shear rate enhances the streamwise fluctuating motion to such an extent that a highly anisotropic turbulence state with a one-dimensional velocity field and two-dimensional small-scale turbulence develops asymptotically as total shear increases. Instantaneous velocity fields show that high shear rate in homogeneous turbulent shear flow produces structures which are similar to the streaks present in the viscous sublayer of turbulent boundary layers.
The simultaneous measurements of VHF radar and HF Doppler array systems are used to observe three-dimensional wind speeds and gravity waves with the purpose of determining the density perturbations at different heights of mesosphere and thermosphere induced by the convective motions associated with subtropical heavy rainfall during the time period of the raining season. Frequency, horizontal wavelength, vertical wavelength, and phase velocity of the gravity waves are determined from the Fourier power spectral analysis of horizontal and vertical wind velocities. The results are compared with those of density perturbations caused by typhoons, tropical storms, and winter-time drizzles associated with convective motions. It is shown that the maximum amplitude of the density perturbations caused by the gravity waves is +/- 10 pct which is greater than that of density perturbations caused by gravity waves associated with weak convective motions in winter time and is smaller than that caused by the gravity waves associated with tropical storms.
The development of an analysis to predict the unsteady compressible flows in blade boundary layers and wakes is presented. The equations that govern the flows in these regions are transformed using an unsteady turbulent generalization of the Levy-Lees transformation. The transformed equations are solved using a finite difference technique in which the solution proceeds by marching in time and in the streamwise direction. Both laminar and turbulent flows are studied, the latter using algebraic turbulence and transition models. Laminar solutions for a flat plate are shown to approach classical asymptotic results for both high and low frequency unsteady motions. Turbulent flat-plate results are in qualitative agreement with previous predictions and measurements. Finally, the numerical technique is also applied to the stator and rotor of a low-speed turbine stage to determine unsteady effects on surface heating. The results compare reasonably well with measured heat transfer data and indicate that nonlinear effects have minimal impact on the mean and unsteady components of the flow.
The present study investigates the evolution of streamwise vortices in a plane mixing layer and their role in the generation of small-scale 3D motion in a closed-return water facility. Spanwise-periodic streamwise vortices are excited by a time-harmonic wavetrain with spanwise-periodic amplitude variations synthesized by a mosaic of 32 surface film heaters flush-mounted on the low partition. The onset of streamwise vortices is accompanied by significant distortion in the transverse distribution of the streamwise velocity component. The presence of inflexion points, absent in corresponding velocity distributions of the unforced flow, suggests the formation of locally unstable regions of large shear in which broadband perturbations already present in the base flow undergo rapid amplification, followed by breakdown to small-scale motion. The cores of the primary vortices are significantly altered as a result of spanwise nonuniform excitation. The 3D features of the streamwise vortices and their interaction with the base flow are inferred from surfaces or rms velocity fluctuations and an approximation to cross-stream vorticity using 3D single component velocity data.
Detailed characterization of neotectonics evolution of the Valle de San Felipe and Arroyo Grande regions in northern Baja California. Reoccupied GEOMEX GPS sites, and occupied a regional GPS (Global Positioning System) network. The Baja California peninsula in Mexico offers a unique setting for studying the kinematic evolution of a complex, active strike-slip/rift plate boundary. We are currently conducting remote sensing, geologic, and geodetic studies of this boundary. The combined data sets will yield instantaneous and time integrated views of its evolution. This proposal solicits renewed funding from NASA to support remote sensing and geologic studies. During the late Cenozoic, Baja California has been the locus of changing fault geometry that has accommodated components of the relative motion between the North America and Pacific plates. Contemporary slip between the two plates occurs in a broad zone that encompasses much of southern California and the Baja California Peninsula. The transfer of slip across this zone in southern California is relatively well understood. South of the border, the geometry and role of specific faults and structural provinces in transferring plate margin deformation across the peninsula is enigmatic. Results We use Landsat Thematic Mapper imagery of the Baja California Peninsula to identify recent and active faults, and then conduct field studies that characterize the temporal and spatial structural evolution of the plate margin. These data address questions concerning the neotectonic development of the Gulf of California, the Baja California Peninsula, and their role in evolution of the post-Miocene Pacific - North American plate boundary. Moreover, these studies provide constraints on the geometry of active faults, allowing more exact understanding of the results of ongoing NASA-supported geodetic experiments. In addition, anticipated publication of the TM scenes will provide a widely available geological data base for relatively little-known peninsula California. Achievements include development of an ArcInfo data base of Landsat and SPOT imagery, detailed field studies of Neogene structures in northeastern Baja California, and new constraint on Pacific - North America plate motion at Baja California latitudes. These results are reported in maps, manuscripts and data products which are published or near completion.
Valve systems in rocket propulsion systems and testing facilities are constantly subject to dynamic events resulting from the timing of valve motion leading to unsteady fluctuations in pressure and mass flow. Such events can also be accompanied by cavitation, resonance, system vibration leading to catastrophic failure. High-fidelity dynamic computational simulations of valve operation can yield important information of valve response to varying flow conditions. Prediction of transient behavior related to valve motion can serve as guidelines for valve scheduling, which is of crucial importance in engine operation and testing. In this paper, we present simulations of the diverse unsteady phenomena related to valve and feed systems that include valve stall, valve timing studies as well as cavitation instabilities in components utilized in the test loop.
A pool boiling apparatus was mounted on a counterweighted platform which could be dropped a distance of nine feet. By varying the size of the counterweight, the effective gravity field on the equipment was adjusted between zero and unity. A study of boiling burnout in water indicated that a variation in the critical heat flux according to the one quarter power of gravity was reasonable. A consideration of the transient burnout process was necessary in order to properly interpret the data. A photographic study of nucleate boiling showed how the velocity of freely rising vapor bubbles decreased as gravity was reduced. The bubble diameters at the time of breakoff from the heated surface were found to vary inversely as gravity to the 1/3.5 power. Motion pictures were taken to illustrate both nucleate and film boiling in the low gravity range.
We perform an expansion study of the Balmer dominated outer shock of the SNR0519−69.0 in the LMC by using a combination of newHSTWFC3 imagery obtained in 2020 and archival ACS images from 2010 and 2011. Thanks to the very long time baseline, our proper motion measurements are of unprecedented accuracy. We find a wide range of shock velocities, with the fastest shocks averaging 5280 km s−1and the slowest grouping of shocks averaging just 1670 km s−1. We compare the Hα images from HST with X-ray images from Chandra and mid-IR images from Spitzer, finding a clear anti-correlation between the brightness of the remnant in a particular location and the velocity of the blast wave at that location, supporting the idea that the bright knots of X-ray and IR emission result from an interaction with a dense inhomogeneous circumstellar medium. We find no evidence for X-ray emission, thermal or nonthermal, associated with the fastest shocks, as expected if the fastest velocities are the result of the blast wave encountering the lower density ambient medium of the LMC. We derive an age of the remnant of≤670±70 yr, consistent with results derived from previous investigations.
In late 2022, the Human Autonomy Teaming Lab (NASA Ames Research Center) conducted a manned, human-in-the-loop (HITL) simulation. This HITL was the lab’s second Hazard Perception and Avoidance (HPA) technical work under NASA’s Advanced Air Mobility (AAM), Automated Flight and Contingency Management (AFCM) Sub-Project. The goals were to assess detect and avoid technology for manned, electric vertical takeoff and landing (eVTOL) aircraft. This simulation tested Resolution Advisory (RA) responses and return-to-course (RTC) maneuvers for the second version of the Airborne Collision Avoidance System’s (ACAS) rotary-wing (Xr) variant. This was conducted at the center's Vertical Motion Simulator (VMS), on a motion-based platform, and was configured to fly eVTOL aircraft while maneuvering for intruding traffic. Variables for this study included ACAS Xr modes (i.e., TA/RA and DAA) and phases of flight (i.e., Cruise, Hover, and Approach). The data collected included response times, losses of well clear, and pilots' noncompliances to alerts and guidance as well as subjective ratings like acceptability and perceived workload. Additional details and future anticipations are also discussed.