44,980 research outputs found
Prediction of blade-vortex interaction noise from measured blade pressure
The impulsive nature of noise due to the interaction of a rotor blade with a tip vortex is studied. The time signature of this noise is calculated theoretically based on the measured blade surface pressure fluctuation of an operational load survey rotor in slow descending flight and is compared with the simultaneous microphone measurement. Particularly, the physical understanding of the characteristic features of a waveform is extensively studied in order to understand the generating mechanism and to identify the important parameters. The interaction trajectory of a tip vortex on an acoustic planform is shown to be a very important parameter for the impulsive shape of the noise. The unsteady nature of the pressure distribution at the very leading edge is also important to the pulse shape. The theoretical model using noncompact liner acoustics predicts the general shape of interaction impulse pretty well except for peak amplitude which requires more continuous information along the span at the leading edge
Effect of Thermal Fluctuation on Spectral Function for the Tomonaga-Luttinger Model
We examine the spectral function of the single electron Green function at
finite temperatures for the Tomonaga-Luttinger model which consists of the
mutual interaction with only the forward scattering. The spectral weight, which
is calculated as a function of the frequency with the fixed wave number, shows
that several peaks originating in the excitation spectra of charge and spin
fluctuations vary into a single peak by the increase of temperature.Comment: 10 pages, 6 eps figure
The QCD axion beyond the classical level: A lattice study
The axion is a hypothetical elementary particle postulated by the
Peccei-Quinn theory to resolve the strong CP problem in QCD. If axions exist
and have low mass, they are a candidate for dark matter as well. So far our
knowledge of the properties of the QCD axion rests on semi-classical arguments
and effective theory. In this work we perform, for the first time, a fully
dynamical investigation of the Peccei-Quinn theory, focussing on the axion
mass, by simulating the theory on the lattice. The results of the simulation
are found to be in conflict with present axion phenomenology.Comment: 16 pages, 9 figures; theoretical considerations refined, numerical
results on larger lattices added, text corrected and improve
Improved methods for calculating the thickness noise
Advanced methods to compute the rotor thickness noise which is predominant in the case of high speed rotor were developed. These methods were deduced from a previous method by transforming the integral coordinate, commuting the order of integration and differential, and/or performing chordwise integration analytically with some adequate assumption. The necessary computational times and waveforms obtained by the previous and three advanced methods were compared. It was then concluded that the advanced methods could save the computational time compared with the previous method with the same accuracy
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