29,175 research outputs found
Recent developments in Vorton Theory
This article provides a concise overview of recent theoretical results
concerning the theory of vortons, which are defined to be (centrifugally
supported) equilibrium configurations of (current carrying) cosmic string
loops. Following a presentation of the results of work on the dynamical
evolution of small circular string loops, whose minimum energy states are the
simplest examples of vortons, recent order of magnitude estimates of the
cosmological density of vortons produced in various kinds of theoretical
scenario are briefly summarised.Comment: 6 pages Latex. Contribution to 1996 Cosmology Meeting, Peyresq,
Franc
Heat-transfer tests on the Rockwell International space shuttle orbiter with and without simulated protuberances
Aerothermodynamic tests on the forward half of the Rockwell International Space Shuttle Orbiter Configuration 140C were conducted at Mach number 8. The phase-change paint and thin-skin thermocouple techniques were used to determine the aerodynamic heating rates on the Orbiter models during simulated atmospheric reentry. Smooth 0.04-scale models and models with scaled protuberances and indentations which simulated the windshields, cargo bay door hinges, vents, and thruster nozzles were tested over an angle-of-attack range from 20 to 45 deg at yaw angles from -5 to 5 deg and at Reynolds numbers, based on the total Orbiter scaled length, from 2.15 to 15.9 million. Comparisons of the model heat-transfer rates obtained with a smooth surface and with scaled protuberances are presented
Analysis of airfoil transitional separation bubbles
A previously developed local inviscid-viscous interaction technique for the analysis of airfoil transitional separation bubbles, ALESEP (Airfoil Leading Edge Separation) has been modified to utilize a more accurate windward finite difference procedure in the reversed flow region, and a natural transition/turbulence model has been incorporated for the prediction of transition within the separation bubble. Numerous calculations and experimental comparisons are presented to demonstrate the effects of the windward differencing scheme and the natural transition/turbulence model. Grid sensitivity and convergence capabilities of this inviscid-viscous interaction technique are briefly addressed. A major contribution of this report is that with the use of windward differencing, a second, counter-rotating eddy has been found to exist in the wall layer of the primary separation bubble
Analysis of transitional separation bubbles on infinite swept wings
A previously developed two-dimensional local inviscid-viscous interaction technique for the analysis of airfoil transitional separation bubbles, ALESEP (Airfoil Leading Edge Separation), has been extended for the calculation of transitional separation bubbles over infinite swept wings. As part of this effort, Roberts' empirical correlation, which is interpreted as a separated flow empirical extension of Mack's stability theory for attached flows, has been incorporated into the ALESEP procedure for the prediction of the transition location within the separation bubble. In addition, the viscous procedure used in the ALESEP techniques has been modified to allow for wall suction. A series of two-dimensional calculations is presented as a verification of the prediction capability of the interaction techniques with the Roberts' transition model. Numerical tests have shown that this two-dimensional natural transition correlation may also be applied to transitional separation bubbles over infinite swept wings. Results of the interaction procedure are compared with Horton's detailed experimental data for separated flow over a swept plate which demonstrates the accuracy of the present technique. Wall suction has been applied to a similar interaction calculation to demonstrate its effect on the separation bubble. The principal conclusion of this paper is that the prediction of transitional separation bubbles over two-dimensional or infinite swept geometries is now possible using the present interacting boundary layer approach
Renormalisation of gravitational self interaction for wiggly strings
It is shown that for any elastic string model with energy density and
tension , the divergent contribution from gravitational self interaction can
be allowed for by an action renormalisation proportional to . This
formula is applied to the important special case of a bare model of the
transonic type (characterised by a constant value of the product ) that
represents the macroscopically averaged effect of shortwavelength wiggles on an
underlying microscopic model of the Nambu-Goto type (characterised by ).Comment: 11 pages, Latex; original 8 page version extended to include
estimates of relevant orders of magnitude. To be published in Physical
Review,
Fabrication and evaluation of advanced titanium and composite structural panels
Advanced manufacturing methods for titanium and composite material structures are being developed and evaluated. The focus for the manufacturing effort is the fabrication of full-scale structural panels which replace an existing shear panel on the upper wing surface of the NASA YF-12 aircraft. The program involves design, fabrication, ground testing, and Mach 3 flight service of full-scale structural panels and laboratory testing of representative structural element specimens
The use of a simplified structural model as an aid in the strain gage calibration of a complex wing
The use of a relatively simple structural model to characterize the load responses of strain gages located on various spars of a delta wing is examined. Strains measured during a laboratory load calibration of a wing structure are compared with calculations obtained from a simplified structural analysis model. Calculated and measured influence coefficient plots that show the shear, bending, and torsion characteristics of typical strain gage bridges are presented. Typical influence coefficient plots are shown for several load equations to illustrate the derivation of the equations from the component strain gage bridges. A relatively simple structural model was found to be effective in predicting the general nature of strain distributions and influence coefficient plots. The analytical processes are shown to be an aid in obtaining a good load calibration. The analytical processes cannot, however, be used in lieu of an actual load calibration of an aircraft wing
Dynamical Stability of Witten Rings
The dynamical stability of cosmic rings, or vortons, is investigated for the
particular equation of state given by the Witten bosonic model. It is found
that there exists a finite range of the state parameter for which the vorton
states are actually stable against dynamical perturbations. Inclusion of the
electromagnetic self action into the equation of state slightly shrinks the
stability region but otherwise yields no qualitative difference. If the Witten
bosonic model represents a good approximation for more realistic string models,
then the cosmological vorton excess problem can only be solved by assuming
either that strings are formed at low energy scales or that some quantum
instability may develop at a sufficient rate.Comment: 11 pages, LaTeX-ReVTeX (v.3), 2 figures available upon request, DAMTP
R-94/1
ALESEP: A computer program for the analysis of airfoil leading edge separation bubbles
The ALESEP program for the analysis of the inviscid/viscous interaction which occurs due to the presence of a closed laminar transitional separation bubble on an airflow is presented. The ALESEP code provides a iterative solution of the boundary layer equations expressed in an inverse formulation coupled to a Cauchy integral representation of the inviscid flow. This interaction analysis is treated as a local perturbation to a known solution obtained from a global airfoil analysis. Part of the required input to the ALESEP code are the reference displacement thickness and tangential velocity distributions. Special windward differencing may be used in the reversed flow regions of the separation bubble to accurately account for the flow direction in the discretization of the streamwise convection of momentum. The ALESEP code contains a forced transition model based on a streamwise intermittency function and a natural transition model based on a solution of the integral form of the turbulent kinetic energy equation. Instructions for the input/output, and program usage are presented
Solar radiation observation stations with complete listing of data archived by the National Climatic Center, Asheville, North Carolina and initial listing of data not currently archived
A listing is provided of organizations taking solar radiation data, the 166 stations where observations are made, the type of equipment used, the form of the recorded data, and the period of operation of each station. Included is a listing of the data from 150 solar radiation stations collected over the past 25 years and stored by the National Climatic Center
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