Once the data is in the wavevector-frequency domain, the propagation wavenumber of each specific wave type can be estimated by fitting a circle to each collection of spectral peaks. The temporal domain measurements are transformed into the frequency domain using a Fourier transform, then, the spatial domain measurements are transformed into the kx,ky wavevector domain using two Fourier transforms. The submerged plate is mechanically shaken and a scanning laser vibrometer is used to measure normal velocity on one surface. This paper develops an inverse method to estimate, in water, the shear wave speed in an isotropic, thick, elastomeric plate. This model assumes single-layered panels. The sound speed is typically determined to an accuracy of +/- 30 m/s, as judged from a propagation-of-error calculation. Four (or fewer) adjusted parameters accommodate the measurements over the stated frequency decade, even for samples that exhibit significant dispersion. The sound speed and attenuation determination technique employs least-squares fitting of a causal model to the measurements. After the stated 20 min settling time, however, the phases return to the values obtained prior to rotation, or after temperature stabilization, to within +/- 1/2 deg. Temperature stabilization within the medium as well as the material is also required before measurements can take place. These differences are distributed randomly across frequency. For example, rotating the panel 10 degrees, then immediately returning to the original position, causes the observed phases to differ by up to 10 deg from those obtained prior to the disturbance. It was observed that a "settling time" of approximately 20 min is required to obtain reproducible phase measurements if the experiment is disturbed even slightly. Although the methods were developed over the frequency decade 10-100 kHz, they are not limited to that band. Presented also is a procedure for determining the phase speed and attenuation of the panel material. He retired and lived in Garland Texas later in life.A technique for measuring the change in phase produced by the insertion of a panel between a projector and receiver is described. This award allowed him to continue his research at the Underwater Sound Reference Detachment of the Naval Research Lab at Orlando.ĭubbelday’s achievements include designing and constructing an acoustic tank facility, developing an aluminum-based material transparent to sound with a density equivalent to water, holding a patent for a ferrofluid transducer, authoring 45 publications, and still being greatly cited in research these days.Īside from his professional career, Dubbelday and his wife married in the Netherlands and raised two daughters in Florida. Furthermore, he received the “Science Faculty Professional Development Award” from the National Science Foundation (NSF). Dubbelday was an outstanding physics and oceanography professor at Florida Tech for twenty years (1961-1981) and was known for his intellect, integrity, and dedication to students, making him the Florida Tech Teacher of the Year in 1980 at the annual award ceremony organized by the Student Government Association (SGA).ĭuring his years at Florida Tech, he did not only serve as a professor, but he was also engaged in hydroacoustic research. Dubbelday earned his doctorate in nuclear physics from the Vrije Universitet, a university in Amsterdam, The Netherlands. Dubbelday establish an endowed scholarship fund in honor of the eminent Florida Tech faculty member.ĭr.
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