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Sound measurements on operating machinery in reverberant environments are difficult to analyze. Adaptive noise algorithms [C. C. Tan, IECON, 703–708 (1985)] are available to reduce the amount of background noise in the measured data. Due to the reverberation of the environment, proper placement of the microphones is important to achieve the greatest noise cancellation from the algorithm. Measurements were taken on bearings with known flaws under different loads and speeds. Results of these measurements will show the effectiveness of sound pressure measurements, and sound intensity measurements, to detect bearing flaws with the help of the adaptive noise cancellation algorithm when the microphones are properly placed.

The influence of welded joints on the accuracy of analytical structural acoustic models is investigated. A beam with a T-shaped rib attached to it is studied. Welding a t-joint causes geometry variation, static stress, and material variations that are not currently included in computational models of the structural acoustics of a t-joint. Two techniques of processing the experimental data are used to show that the geometry and the static stresses caused by welding can have a significant impact on waves propagating past the joint and the resulting radiated sound power. Likewise experimental results show that the material variation caused by the welding of the joint has minimal impact on the wave propagation and sound radiation from the beam. The processing techniques are a phase-speed tracking filter and wave-number filtering. The phase-speed tracking filter shows an increase in the phase speed of propagating waves near the joint. There is also a reduction in the group delay of wave packets propagating past the joint and a change in the reflection coefficient of structural waves incident on the joint. The wave-number filtering is used to quantify the amount of far-field sound radiation from the area of the t-joint on the beam. Finally an analytic model that describes a rib as imparting a force and moment on a beam in reaction to the incident structural waves is modified to include the influence of the weld fillet geometry and static stress induced by welding. [Work supported by ONR, Dr P.B. Abraham Scientific Officer.]

Experiments will show how rib and weld discontinuities on a beam effect wave propagation and far-field sound radiation. Numerous aluminum and steel beams were constructed using a different rib and weld configuration. The beam dimensions were 5 cm × 0.635 cm × 2.44 m and the ribs had T-shaped cross sections of slightly varying dimensions. The beams were then suspended and sound pressure 2.5 cm from the beam surface was measured with a microphone. By changing the physical construction of the attachment area of the ribs it was possible to isolate and analyze the effects of the different construction parameters. Also, the existence and effect of residual stresses in the beams due to the construction process was investigated. Analysis of the data showed that both the ribs and the welds produced changes in the far-field sound radiation and the phase speed of the propagating waves. Also, the geometry and the means of attachment of the rib affected the sound field. Transmission and reflection coefficients were calculated, along with travel times of the waves, to verify the changes in phase speeds that were found. [Work supported by ONR, Contract No. N00014-93-1-0493.]