15,494 research outputs found
Numerical methods and a computer program for subsonic and supersonic aerodynamic design and analysis of wings with attainable thrust considerations
This paper describes methodology and an associated computer program for the design of wing lifting surfaces with attainable thrust taken into consideration. The approach is based on the determination of an optimum combination of a series of candidate surfaces rather than the more commonly used candidate loadings. Special leading-edge surfaces are selected to provide distributed leading-edge thrust forces which compensate for any failure to achieve the full theoretical leading-edge thrust, and a second series of general candidate surfaces is selected to minimize drag subject to constraints on the lift coefficient and, if desired, on the pitching moment coefficient. A primary purpose of the design approach is the introduction of attainable leading-edge thrust considerations so that relatively mild camber surfaces may be employed in the achievement of aerodynamic efficiencies comparable to those attainable if full theoretical leading-edge thrust could be achieved. The program provides an analysis as well as a design capability and is applicable to both subsonic and supersonic flow
A computer program for wing subsonic aerodynamic performance estimates including attainable thrust and vortex lift effects
Numerical methods incorporated into a computer program to provide estimates of the subsonic aerodynamic performance of twisted and cambered wings of arbitrary planform with attainable thrust and vortex lift considerations are described. The computational system is based on a linearized theory lifting surface solution which provides a spanwise distribution of theoretical leading edge thrust in addition to the surface distribution of perturbation velocities. The approach used relies on a solution by iteration. The method also features a superposition of independent solutions for a cambered and twisted wing and a flat wing of the same planform to provide, at little additional expense, results for a large number of angles of attack or lift coefficients. A previously developed method is employed to assess the portion of the theoretical thrust actually attainable and the portion that is felt as a vortex normal force
An aerodynamic analysis computer program and design notes for low speed wing flap systems
The expanded capabilities for analysis and design of low speed flap systems afforded by recent modifications of an existing computer program is described. The program provides for the simultaneous analysis of up to 25 pairs of leading-edge and trailing-edge flap deflection schedules. Among other new features of the program are a revised attainable thrust estimation method to provide more accurate predictions for low Mach numbers, and a choice of three options for estimation of leading-edge separation vortex flow effects. Comparison of program results with low speed experimental data for an arrow wing supersonic cruise configuration with leading-edge and trailing-edge flaps showed good agreement over most of the range of flap deflections. Other force data comparisons and an independent study of airfoil and wing pressure distributions indicated that wind-tunnel measurements of the aerodynamic performance of twisted and cambered wings and wings with leading-edge flaps can be very sensitive to Reynolds number effects
Statistical features of the thermal neutron capture cross sections
We discuss the existence of huge thermal neutron capture cross sections in
several nuclei. The values of the cross sections are several orders of
magnitude bigger than expected at these very low energies. We lend support to
the idea that this phenomenon is random in nature and is similar to what we
have learned from the study of parity violation in the actinide region. The
idea of statistical doorways is advanced as a unified concept in the
delineation of large numbers in the nuclear world. The average number of maxima
per unit mass, in the capture cross section is calculated and related
to the underlying cross section correlation function and found to be , where is a characteristic mass
correlation width which designates the degree of remnant coherence in the
system. We trace this coherence to nucleosynthesis which produced the nuclei
whose neutron capture cross sections are considered here.Comment: 7 pages, 6 figures. To appear in Acta Physica Polonica B as a
Contribution to the proceedings of:Jagiellonian Symposium of Fundamental and
Applied Subatomic Physics, June 7- 12, 2015 Krakow, Polan
Stick-slip statistics for two fractal surfaces: A model for earthquakes
Following the observations of the self-similarity in various length scales in
the roughness of the fractured solid surfaces, we propose here a new model for
the earthquake. We demonstrate rigorously that the contact area distribution
between two fractal surfaces follows an unique power law. This is then utilised
to show that the elastic energy releases for slips between two rough fractal
surfaces indeed follow a Guttenberg-Richter like power law.Comment: 9 pages (Latex), 4 figures (postscript
Predictability of Self-Organizing Systems
We study the predictability of large events in self-organizing systems. We
focus on a set of models which have been studied as analogs of earthquake
faults and fault systems, and apply methods based on techniques which are of
current interest in seismology. In all cases we find detectable correlations
between precursory smaller events and the large events we aim to forecast. We
compare predictions based on different patterns of precursory events and find
that for all of the models a new precursor based on the spatial distribution of
activity outperforms more traditional measures based on temporal variations in
the local activity.Comment: 15 pages, plain.tex with special macros included, 4 figure
The Coulomb Sum and Proton-Proton Correlations in Few-Body Nuclei
In simple models of the nuclear charge operator, measurements of the Coulomb
sum and the charge form factor of a nucleus directly determine the
proton-proton correlations. We examine experimental results obtained for
few-body nuclei at Bates and Saclay using models of the charge operator that
include both one- and two-body terms. Previous analyses using one-body terms
only have failed to reproduce experimental results. However, we find that the
same operators which have been used to successfully describe the charge form
factors also produce substantial agreement with measurements of the Coulomb
sum.Comment: 11 pages, Revtex version 3.0 with 3 Postscript figures appended, ANL
preprint PHY-7473-TH-9
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