Dr. Victor W. Sparrow, associate professor of acoustics, and Judy Rochat, a doctoral candidate in the Graduate Program in Acoustics, developed the technique and described improvements to it today (Dec. 4) at the annual meeting of the Acoustical Society of America in San Diego, Calif., in the session on Noise and Engineering Acoustics: Noise Modeling and Outdoor Sound Propagation.
Sparrow and Rochat's new simulation technique, called a finite difference method, can compute the penetrating sonic boom noise for both simple and complex ocean surfaces, corresponding to calm and rough seas. Using the new technique, the Penn State researchers found that a somewhat complex wavy ocean surface only slightly augments the underwater noise from a sonic boom.
Recently, through a stroke of luck, Sparrow was able to confirm that simulations developed through the new computational technique closely match actual ocean observations. In a case of discovery favoring the prepared mind, Sparrow heard a report, in summer 1997, from a Canadian research team that was measuring ambient ocean noise as part of a project unrelated to his. A supersonic aircraft just happened to pass overhead as they were taking underwater measurements. The booms produced by the aircraft were an annoyance to the Canadians but a gift to Sparrow since the observations confirmed the reliability of the Sparrow/Rochat approach.
Sparrow says, "One would have had to spend millions of research dollars to arrange an expedition to make the underwater sonic boom recordings that the Canadians researchers got by chance."
Rochat adds that it is currently illegal to fly supersonically over land. So, supersonic planes use sea routes. She says that we can expect a new breed of supersonic passenger aircraft to be operating early in the next century, making the need for ways to gauge the possible underwater disturbances newly imperative.
Sparrow notes that all whales are mammals and some species hear over much of the same range of frequencies that humans do. However, he is quick to point out that he and his research group will not be looking into the effects of the sound levels the new fleet of supersonic planes will have on marine life. They are leaving that to the biologists. Sparrow says that by using the new simulation method and other techniques, engineers will be able to tell aircraft designers what the whales and fish will hear before the new planes are built. As a result, the aircraft designers and manufacturers should be able to minimize effects in the range that the biologists indicate may be problematic for marine life.
At the meeting Sparrow also presented a paper in the session on Noise, Musical Acoustics and Underwater Acoustics: Session in Honor of Robert W. Young. That paper described the application of another complementary tool, the boundary element method (BEM), to simulate the sonic boom noise reaching the whales.
The Sparrow and Rochat research was supported, in part, by grants from the National Aeronautics and Space Administration.
EDITORS: To contact Sparrow or Rochat during the meeting, call the Acoustical Society of America meeting message board at (619) 291-7131. After the meeting, Sparrow is at (814) 865-3162 or at sparrow@helmholtz.acs.psu.edu by e-mail. To contact Judith Rochat, call (814) 867-7834 or rochat@sabine.acs.psu.edu by e-mail.