The rotary subwoofer is a novel acoustic transducer capable of projecting infrasonic signals at high sound pressure levels. The projector produces higher acoustic particle velocities than conventional transducers which translate into higher radiated sound pressure levels. This paper characterizes measured performance of a rotary subwoofer and presents a model to predict sound pressure levels.

As many nuclear plants approach the end of their initial 40 year license period, inspection or replacement of their reactor internals bolts must be considered. This is consistent with the Materials Reliability Program (MRP 227/228) guideline for plant life extension [1,2]. Assurance of the internals structural integrity is essential for continued safe operation of these plants. If there is no suspicion or indication of bolt failure, simple inspection is normally more cost-effective than replacement. Inspection vendors have inspected thousands of internals bolts with conventional and Phased Array UT but different head configurations and bolt capture mechanisms mandate specific qualifications for each bolt type. In some cases, complex bolt and head geometries coupled with counter-bore and locking bar interferences render classical UT inspections difficult or impossible. A range of solutions to inspect reactor internals including these difficult-to-inspect-by-conventional-UT baffle bolts has been developed by several vendors [3]. This presentation references developments to make bolt inspection a relatively quick and easy task through adaptations to the SUSI submarine inspection platform, the extensive UT qualification work suitable for conventional UT plus more recent advanced nonlinear resonant techniques to distinguish between flawed or loose, vs. acceptable bolts where conventional UT cannot be applied. Initial evaluations show that these advanced techniques may have the ability to reliably detect smaller flaws than previously possible with conventional techniques as well as provide information on bolt tightness.

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A multi-disciplinary group of researchers at the University of Minnesota Center for Applied and Translational Sensory Science (catss.umn.edu) are designing and pilot testing the perceptual effects of infrasound, in collaboration with Eminent Technologies (rotarywoofer.com). An infrasound generator simulates the acoustic signature of audible sound and infrasound generated by wind turbines in the field. With the support of Xcel Energy, the team of engineers, otologists, hearing scientists, and balance experts are evaluating the effects of infrasound only, acoustic turbine sound, and combined infrasound and acoustic sound. We are testing listeners’ quiet detection, masked detection, discrimination, and rating of signals. Pilot results will be described. Together we hope to test the range of perceptual responses to turbine-generated infrasound and audible sound. [Work supported by Xcel Energy RD4-12 to Jeffrey Marr, St. Anthony Falls Laboratory.]