14,259 research outputs found
A laboratory study of the subjective response to helicopter blade-slap noise
The test stimuli recorded during a recent field study consisted of 16 sounds, each presented at 4 peak noise levels. Two helicopters and a fixed-wing aircraft were used. The impulsive characteristics of one helicopter were varied by operating at different rotor speeds, whereas the other helicopter, the noise of which was dominated by the tail rotor, displayed little variation in blade-slap noise. Thirty-two subjects made noisiness judgments on a continuous, 11 point, numerical scale. Preliminary results indicate that proposed impulsiveness corrections provide no significant improvement in the noisiness predictive ability of Effective Perceived Noise Levels (EPNL). For equal EPNL, the two categories of helicopter stimuli, one of which was far more impulsive than the other, showed no difference in judged noisiness. Examination of the physical characteristics of the sounds presented in the laboratory highlighted the difficulty of reproducing acoustical signals with high-crest factors
A study of the usefulness of Skylab EREP data for earth resources studies in Australia
There are no author-identified significant results in this report
Sound measurements and observations of the MOD-OA wind turbine generator
Sound measurements are reported for a wind velocity of about 5 m/s and a power output of about 70 kW. Both broadband and narrowband data were obtained for a range of distances and azimuth angles from the machine. Both discrete frequency and broadband components were identified. Loading harmonics at multiples of the blade passage frequency and electrical generator harmonics at multiples of the shaft speed dominated the spectrum below 100 Hz. The 10,000 Hz peak is believed to be of mechanical origin in the nacelle and the other arises from blade aerodynamic sources. Aural detection distances of about 525 m upwind and 850 downwind were observed
Status and capabilities of sonic boom simulators
The current status and capabilities of sonic boom simulators which might be used in future studies of the effects of sonic boom on people, animals, or structures is summarized. The list of candidate simulators is based on a literature search which was confined to the United States and Canada. Some of the simulators are fully operational, others could be made operational with a modest investment, and still others would require a major investment. For the sake of the completeness, some simulators which were the subject of a previous review, but which no longer exist, are also included herein
Wind turbine acoustic standards
A program is being conducted to develop noise standards for wind turbines which minimize annoyance and which can be used to design specifications. The approach consists of presenting wind turbine noise stimuli to test subjects in a laboratory listening chamber. The responses of the subjects are recorded for a range of stimuli which encompass the designs, operating conditions, and ambient noise levels of current and future installations. Results to date have established the threshold of detectability for a range of impulsive stimuli of the type associated with blade/tower wake interactions. The status of the ongoing psychoacoustic tests, the subjective data, and the approach to the development of acoustic criteria/standards are described
Water utilization, evapotranspiration and soil moisture monitoring in the south east region of south Australia
There are no author-identified significant results in this report
Shock Theory of a Bubbly Liquid in a Deformable Tube
Shock propagation through a bubbly liquid filled in a deformable cylindrical tube is considered. Quasi-one-dimensional
bubbly flow equations that include fluid-structure interaction are formulated, and the steady shock
relations are derived. Experiments are conducted in which a free-falling steel projectile impacts the top of an air/water
mixture in a polycarbonate tube, and stress waves in the tube material are measured. The experimental data indicate
that the linear theory cannot properly predict the propagation speeds of shock waves in mixture-filled tubes; the shock
theory is found to more accurately estimate the measured wave speeds
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