The eccentric face seal with a tangentially varying film thickness
Eccentric face seal with tangentially varying film thickness, analyzing leakage flow proportional to eccentricity and surface waviness
Sneck, H. J.↗
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Ephemeris of a highly eccentric orbit - Explorer 28.
An ephemeris has been obtained for Explorer 28 (IMP 3) which agrees well with 2 years of radio observations and with SAO observations a year later. This ephemeris is generated over the 3 year lifetime by a numerical integration method utilizing a set of initial conditions at launch and without requiring further differential correction. Because highly eccentric orbits are difficult to compute with acceptable accuracy and because a long continuous arc has been obtained which compares with actual data to a known precision, this ephemeris may be used as a standard for computing highly eccentric orbits in the earth-moon system. Orbit improvement was used to obtain the initial conditions which generated the ephemeris. This improvement was based on correcting the energy by adjusting the semimajor axis to match computed times of perigee passage with the observed. This procedure may generate errors in semimajor axis to compensate for model errors in the energy; however, this compensation error is also implicit in orbit determination itself.
Lowrey, B. E.↗
Solutions of the motion of synchronous satellites with arbitrary eccentricity and inclination
A first order, semianalytical theory for the long term motion of resonant satellites is presented. The theory is valid for all eccentricities and inclinations and for all commensurability ratios. The method allows the inclusion of all the zonal and tesseral harmonics as well as luni solar perturbations and radiation pressure. The method is applied to a synchronous satellite including only the J sub 2 and J sub 22 harmonics. Global, long term solutions for this problem, eccentricity, argument of perigee, and inclination are obtained.
Nacozy, P. E.↗
Buckling of eccentrically stringer-stiffened cylindrical panels under axial compression
The paper presents numerical results, based on Donnell shell theory, for the axial compressive buckling loads for eccentrically stringer-stiffened circular cylindrical panels, in a study of the effect of boundary conditions and panel width on the buckling load. The two cases of inside and outside stiffeners were considered. The complete cylinder buckling load was reached only for panels under classical simply supported boundary conditions. The prevention of circumferential displacement is found to be the most important in-plane boundary condition from the point of view of increasing the buckling load. Clamping is found more effective in increasing the buckling loads of panels with free circumferential edge displacement than of panels with zero edge displacement. When panel width is equal to or greater than 180 deg, the panel buckling loads are within 10% of the complete cylinder load for all cases except one simply supported panel with outside stringers. Buckling loads were higher for outside stringers, except for very narrow panels that are restrained against circumferential edge displacement. Eccentricity effects are generally similar for clamped and simply supported panels with the same in-plane boundary conditions.
Sobel, L. H.↗
Gravitational spectra from the tracking of planetary spacecraft in eccentric orbits
Two dimensional gravitational spectra are derived from simple harmonic analysis of range rate tracking data on planetary orbiters. The eccentricity of the orbit is arbitrary and results are shown to vary substantially with the aspect angle of the tracking line of sight with the orbit plane. The development for arbitrary start with stop times (with respect to periapsis) uses modified eccentricity functions evaluated by quadrature. Simulations with a point-masses model of Venus using tracking data on the Pioneer Venus Orbiter show excellent predictions of the average orbiter spectrum over one Venus day. The Venus gravitational signal should be above the tracking noise level for arc lengths longer than 40 deg (in true anomaly) about periapsis and for terms as high as 55th degree. analysis has been made of tracking residuals from a short arc fit to Mariner Mars 9 data over the Hellas Basin (using a complete 6th degree field). Results are most consistent with higher residual gravitational power than predicted from Kaula's rule for Mars.
Wagner, C. A.↗
Dynamics of short eccentric plain seals with high axial Reynolds number
Plain seals with high axial flow rates produce large stiffness and damping coefficients that can help stabilize high-speed rotating machinery. When the shaft is eccentric in the seal, a Bernoulli effect low-pressure region occurs on the large-clearance side of the shaft. A fluid-restoring force tends to center the shaft and reduce vibrations. This work extends the previous theory for short plain centered seals to large eccentricities using a perturbation analysis. Surface roughness effects are also included. An analysis of seals used in the Space Shuttle main engine hydrogen fuel turbopump indicates the desirability of plain seals over the labyrinth type. Experimental results confirm this.
Allaire, P. E.↗
Choice reaction time to movement of eccentric visual targets during concurrent rotary acceleration
This study investigates the influence of concurrent rotary acceleration on choice reaction time (RT) to a small, accelerating visual cursor on a cathode-ray tube. Subjects sat in an enclosed rotating device at the center of rotation and observed a 3-mm dot accelerating at different rates across a cathode-ray tube. The dot was viewed at various eccentricities under conditions of visual stimulation alone and with concurrent rotary acceleration. Subjects responded to both vertical and horizontal dot movements. There was a significant inverse relationship between choice RT and level of dot acceleration (p less than .001), and a significant direct relationship between choice RT and eccentricity (p less than .001). There was no significant difference between choice RT to vertical or horizontal dot motion (p greater than .25), and choice RT was not significantly affected by concurrent rotary acceleration (p greater than .10). The results are discussed in terms of the effects of vestibular stimulation on choice RT to visual motion.
Hamerman, J. A.↗
Binary model of Circinus X-1. I - Eccentricity from combined X-ray and radio observations
A binary star model is used to account for the 16.59-d flaring behavior of the X-ray emission from Circinus X-1. The orbital eccentricity of 0.8 + or - 0.1 is derived from the X-ray light curve by assuming that the sharp X-ray cut-off every 16.59-d is a result of bound-free absorption in the primary star's stellar wind. The shape of the light curve has changed over the last eight years, and this is interpreted as due to orbital precession of the binary system. Simultaneous radio and X-ray observations of the flare from Circinus X-1 on February 1-5, 1978 are reported. These are accounted for within the framework of the model. The radio observations at 5 GHz are used independently to derive a high value of the orbital eccentricity (e = 0.7).
Murdin, P.↗
Effect of load eccentricity and substructure deformation on ultimate strength of shuttle orbiter thermal protection system
The effect of load eccentricity and substructure deformation on the ultimate strength and stress displacement properties of the shuttle orbiter thermal protection system (TPS) was determined. The LI-900 Reusable Surface Insulation (RSI) tiles mounted on the .41 cm thick Strain Isolator Pad (SIP) were investigated. Substructure deformations reduce the ultimate strength of the SIP/tile TPS and increase the scatter in the ultimate strength data. Substructure deformations that occur unsymmetric to the tile can cause the tile to rotate when subjected to a uniform applied load. Load eccentricity reduces SIP/tile TPS ultimate strength and causes tile rotation.
Sawyer, J. W.↗
Long-term motion of resonant satellites with arbitrary eccentricity and inclination
A first-order, semi-analytical method for the long-term motion of resonant satellites is introduced. The method provides long-term solutions, valid for nearly all eccentricities and inclinations, and for all commensurability ratios. The method allows the inclusion of all zonal and tesseral harmonics of a nonspherical planet. We present here an application of the method to a synchronous satellite including J2 and J22 harmonics. Global, long-term solutions for this problem are given for arbitrary values of eccentricity, argument of perigee and inclination.
Nacozy, P. E.↗
Theory for Eccentric and Misalined Annular Seals
Theory describes behavior of eccentric and angularly-misalined incompressible-fluid shaft seals. Direct and cross-coupled stiffness and damping coefficients expressed in terms of degree of eccentricity and coefficients of concentric system.
Jackson, E.↗
The variations in eccentricity and apse precession rate of a narrow ring perturbed by a close satellite
The first-order perturbations of orbital eccentricity and apse precession rate for the case of a narrow ring, due to a close satellite whose orbit is also eccentric, are described by means of a Hamiltonian. The present treatment covers cases in which the satellite crosses the ring, and the level curves of the Hamiltonian are displayed for several parameter values. The results obtained are applied to the interaction of Saturn's F ring with its inner shepherd satellite.
Borderies, N.↗
The eccentric Saturnian ringlets at 1.29 R(s) and 1.45 R(s)
The shapes and kinematics of the Titan and Maxwell ringlets of Saturn's C ring are studied. The ringlets are narrow and eccentric, with mean widths of about 25 km for Titan and abut 64 km for Maxwell, and with eccentricities of order 10 to the -4th. They have sharp edges on a scale of about 1 km, normal optical depths of roughly 0.5-2.0, normal optical depth of the surrounding region, and positive linear width-radius relations. The Titan ringlet is the only feature whose dynamics appears to be completely determined by an external satellite; the kinematics of the Maxwell ringlet are determined solely by Saturn's nonspherical gravity field. The comparatively large measured optical depths and large inferred mass extinction coefficients for the ringlets suggest an environment and particle size distribution different from the remainder of the C ring and presumably caused by the mechanism responsible for ring confinement.
Porco, C.↗
A new constraint on Saturn's zonal gravity harmonics from Voyager observations of an eccentric ringlet
The results obtained by Porco et al. (1984) from an analysis of the kinematics of an eccentric ringlet in Saturn's inner ring are used to add an additional constraint to the gravity solution of Null et al. (1981) and thus to derive the first experimental estimate of the Saturn's J6 gravitational field. On the assumption that the eccentricity of this ringlet is forced by the satellite Titan, the location of the Titan apsidal resonance is determined to an accuracy of + or - 13 km, which in turn provides a strong constraint on Saturn's zonal gravity harmonics. Combining this constraint with the results of Null et all. and adopting a priori values for J8, J10, and J12 based on interior models, new estimates are obtained for the first three zonal gravity coefficients J2, J4, and J6.
Nicholson, Philip D.↗
Nonlinear static and dynamic finite element analysis of an eccentrically loaded graphite-epoxy beam
The Dynamic Crash Analysis of Structures (DYCAT) and NIKE3D nonlinear finite element codes were used to model the static and implulsive response of an eccentrically loaded graphite-epoxy beam. A 48-ply unidirectional composite beam was tested under an eccentric axial compressive load until failure. This loading configuration was chosen to highlight the capabilities of two finite element codes for modeling a highly nonlinear, large deflection structural problem which has an exact solution. These codes are currently used to perform dynamic analyses of aircraft structures under impact loads to study crashworthiness and energy absorbing capabilities. Both beam and plate element models were developed to compare with the experimental data using the DYCAST and NIKE3D codes.
Fasanella, Edwin L.↗
Effect of Eccentricity on the Static and Dynamic Performance of a Turbulent Hybrid Bearing
The effect of journal eccentricity on the static and dynamic performance of a water lubricated, 5-recess hybrid bearing is presented in detail. The hydrostatic bearing has been designed to operate at a high speed and with a large level of external pressurization. The operating conditions determine the flow in the bearing to be highly turbulent and strongly dominated by fluid inertia effects. The analysis covers the spectrum of journal center displacements directed towards the middle of a recess and towards the mid-land portion between two consecutive recesses. Predicted dynamic force coefficients are uniform for small to moderate eccentricities. For large journal center displacements, fluid cavitation and recess position determine large changes in the bearing dynamic performance. The effect of fluid inertia force coefficients on the threshold speed of instability and whirl ratio of a single mass flexible rotor is discussed.
Sanandres, Luis A.↗
Muscle preservation in long duration space missions: The eccentric factor
In our quest to understand, and eventually prevent, the loss of muscle strength and mass that occurs during prolonged periods in microgravity, we have organized our research approach by systems and useful terrestrial analogs. Our hypothesis was that: The eccentric movement, or lengthening component, of dynamic, resistive exercise, is required for the production of the greatest gains in strength and muscle hypertrophy in the most metabolically efficient, and time effective manner. The exercises selected were leg presses, leg (knee) extensions, and hamstring curls. In this 30 week study, 38 male subjects, between the ages of 25 and 50, were divided into four groups. One group performed 5 sets of 8-12 repetitions per set of conventional concentric/eccentric (CON/ECC) exercises. Another group performed only the concentric (CON) movement on the same schedule. The third group performed twice the number of sets in the concentric only mode (CON/CON), and the last group served as controls. We interpret these data as convincing evidence that the eccentric component of heavy resistance training is required along with the concentric for the most effective increase in strength and muscle fiber size in the least time. We also conclude that such heavy exercise of any such muscle group need not consume inordinately long periods of time, and is quite satisfactorily effective when performed on 72 hour centers.
Buchanan, Paul↗
The Use of Eccentric and Circular Orbits in the Design of a Mars Network Constellation
This study examined different constellation configurations to determine their suitability for the Mars Network. Some variations on the baseline case of four circular orbits were initially studied. Eccentric orbits were then used to determine their effects on several figures of merit that were selected as representative of the design goals. It was eventually found that the use of eccentric orbits in combination with circular orbits can improve aspects of some navigation and communication figures of merit. The ability to use orbits at different inclinations helps smooth coverage over the middle and upper latitudes for these figures of merit. This configuration has more variability than one consisting of circular orbits, so the occurrence of unfavorable arrangements also results in degradation of some figures of merit. Some cases were used which improved different figures of merit, so a solution could be chosen depending on specified requirements.
Anderson, Rodney↗