10,605 research outputs found
Improved method for aerodynamic analysis of wing-body-tail configurations in subsonic and supersonic flow
Method permits analysis of noncircular bodies and calculation of wing-body interference effects in presence of body closure, two features not previously available. In addition, use of vortex distribution, having linear variation in streamwise direction, results in improved chordwise pressure distributions on wing and tail surfaces
Forward acoustic performance of a model turbofan designed for a high specific flow (QF-14)
Forward noise and overall aerodynamic performance are presented for a high-tip-speed fan having an exceptionally high average axial Mach number at the rotor inlet. This high Mach number is intended to attenuate forward noise at both the design-speed takeoff point, and at the unconventional low-pressure-ratio, design-speed approach point. As speed was increased near design, all forward noise components were reduced, and rear noise in the discharge duct was increased, indicating that the high Mach number flow at the rotor face is attenuating forward noise at takeoff. The fan at takeoff is some 5.5 to 11 dB quieter than several reference fans. Data at the point closest to approach indicated tentatively that the design-speed approach mode was 3 dB quieter than the conventional mode
Direct calculation of interfacial tensions from computer simulation: Results for freely jointed tangent hard sphere chains
We develop a methodology for the calculation of surface free energies based
on the probability distribution of a wandering interface. Using a simple
extension of the NpT sampling, we allow the interface area to randomly probe
the available space and evaluate the surface free energy from histogram
analysis and the corresponding average. The method is suitable for studying
systems with either continuous or discontinuous potentials, as it does not
require explicit evaluation of the virial. The proposed algorithm is compared
with known results for the surface tension of Lennard--Jones and Square Well
fluid, as well as for the interface tension of a bead--spring polymer model and
good agreement is found. We also calculate interfacial tensions of freely
jointed tangent hard sphere chains on athermal walls for a wide range of chain
lengths and densities. The results are compared with three different
theoretical approaches, Scaled Particle Theory, the Yu and Wu density
functional theory and an analytical approximation based on the latter approach.
Whereas SPT only yields qualitative results, the last two approaches are found
to yield very good agreement with simulations.Comment: 20 pages, 6 figures, Phys. Rev. E in press
A Partial Taxonomy of Substitutability and Interchangeability
Substitutability, interchangeability and related concepts in Constraint
Programming were introduced approximately twenty years ago and have given rise
to considerable subsequent research. We survey this work, classify, and relate
the different concepts, and indicate directions for future work, in particular
with respect to making connections with research into symmetry breaking. This
paper is a condensed version of a larger work in progress.Comment: 18 pages, The 10th International Workshop on Symmetry in Constraint
Satisfaction Problems (SymCon'10
Laser-like X-ray Sources Based on Optical Reflection from Relativistic Electron Mirror
A novel scheme is proposed to generate uniform relativistic electron layers
for coherent Thomson backscattering. A few-cycle laser pulse is used to produce
the electron layer from an ultra-thin solid foil. The key element of the new
scheme is an additional foil that reflects the drive laser pulse, but lets the
electrons pass almost unperturbed. It is shown by analytic theory and by 2D-PIC
simulation that the electrons, after interacting with both drive and reflected
laser pulse, form a very uniform flyer freely cruising with high relativistic
gamma-factor exactly in drive laser direction (no transverse momentum). It
backscatters probe light with a full Doppler shift factor of 4*gamma^2. The
reflectivity and its decay due to layer expansion is discussed.Comment: 5 pages, 3 figures, submitted, invited talk on the workshop of
Frontiers in Intense Laser-Matter Interaction Theory, MPQ, March 1-3, 2010
- …