Noise radiation from drill steels : and other experimental investigations in acoustics and fluid mechanics

Abstract: Drill rod noise has become a major noise source in percussive drilling. Generation of flexural waves, which seem to be responsible for most of the noise, is studied in a model with dynamic photoelasticity and in the real drill rod with strain gauge technique. The effect of the holder of the drill rod is investigated, and it is found, that the amplitudes of the flexural waves can be decreased by introducing visco-elastic damping material in the holder. It is also shown, that this will decrease the emitted noise. Generation and propagation of turbulent spots on a water table are studied. A new photographic technique is developed to register structures within the spot. Streaks elongated in the streamwise direction are found to penetrate the spot, and it is observed that undulations on the streaks lead to chaotic motion. Comparisons with theory show that the theory accounts fairly well for the spreading angle, whereas the propagation speeds are larger than the observed values. Tape-recordings of test subjects before and after a 5-day voice training program are analysed to find objective measures of changes in the voice. Frequency analysis shows, that the fundamental frequency and the variation are increased. It is also shown that the amplitude of the formants above 1000 Hz are increased compared to those below 1000 Hz.