Friday, March 26, 1993 4:00 p.m. Professor Vladislav G. Mikhalevich General Physics Institute Russian Academy of Sciences, Moscow This seminar reviews research activity in laser photoacoustics at the General Physics Institute in Moscow. Laser light can be used to excite strong acoustic fields in which nonlinear phenomena become significant. An advantage of this method is…
Friday, March 12, 1993 4:00 p.m. Professor Mukul M. Sharma Department of Petroleum Engineering A comparison of Young’s moduli and Poisson’s ratios obtained from ultrasonic laboratory measurements with static moduli obtained under identical stress conditions shows that the Young’s moduli are 1 to 6 times higher under ultrasonic loading conditions. A comparison of these two…
Friday, March 5, 1993 4:00 p.m. Frank A. Boyle Applied Research Laboratories Recent experimental backscatter data suggests a volume scattering mechanism involving trapped gas bubbles. A model for shallow grazing angle high frequency acoustic backscatter from sediment is developed. The model begins with a pore distribution function, obtained from measurements of the grain size distribution…
Tuesday, February 23, 1993 3:30 p.m. Deborah A. Summa Applied Research Laboratories The discovery of strong piezoelectric activity in macromolecules such as poly(vinylidene fluoride) (PVDF) and its copolymers has made possible a class of flexible, lightweight, inherently broadband transducers which exhibit virtually no lateral coupling. Recent technological advances have made possible the mass production of…
Friday, February 19, 1993 4:00 p.m. Youseph Yazdi Department of Electrical and Computer Engineering The University of Texas at Austin Intravascular ultrasonic imaging permits physicians to view real time cross sectional images of blood vessels in the body. This permits the direct measurement of vessel stenosis (narrowing) due to plaque formation and other structural anomalies…
Friday, February 5, 1993 4:00 p.m. Professor David T. Blackstock Applied Research Laboratories and Mechanical Engineering Department The University of Texas at Austin Nonlinear acoustics (also called finite-amplitude acoustics) is about very loud sound, that is, waves of very high intensity. The main difference between ordinary (small-signal) acoustics and nonlinear acoustics is in propagation speed.…
Friday, January 29, 1993 4:00 p.m. G. Douglas Meegan Earth and Environmental Sciences Division Los Alamos National Laboratory Rocks are typically highly disordered solids which consist of complicated networks of microfractures and pore spaces. Consequently, rocks exhibit a strong acoustic nonlinearity when compared to intact materials. The results of wave propagation, resonance, and quasi-static measurements…
Friday, December 4, 1992 2:00 p.m. Turker Kuyel Department of Music The University of Texas at Austin Real time computer simulation of room acoustics has important applications in music production, recording and also in multimedia. Computer generated acoustic environments also have important applications in making architectural decisions on the construction of concert halls, etc. Real…
Friday, November 20, 1992 4:00 p.m. John T. Post Electrical and Computer Engineering Department The University of Texas at Austin Modern day acoustic horns have an extensive and colorful past. The understanding and use of the acoustic horn is traced from its origins as a device for ‘summoning,’ to its use as an impedance matching…
Monday, November 9, 1992 4:00 p.m. Al. A. Kolomenskii General Physics Institute Moscow, Russia Theoretical and experimental results are presented on the laser generation of surface acoustic waves in isotropic solids and in single-crystals. Two main mechanisms are considered: a thermo-optical one and a mechanism connected with the ablation of a substance. In anisotropic crystals…
Friday, November 6, 1992 4:00 p.m. David Nelson Acoustic Systems Austin, Texas The impulse response of a space may be obtained by cross-correlation of a “white noise” signal broadcast into the space and that arriving at a given point. An especially favorable choice for the stimulus is a Maximum Length Sequence because of its low…
Wednesday, October 28, 1992 4:00 p.m. Professor Oleg V. Rudenko Department of Physics Moscow University, Russia A theoretical model for nonlinear geometrical acoustics is developed by simplifying the general and parabolic nonlinear wave equations on the basis of high frequency approximations. Physical phenomena associated with high acoustic intensities, such as nonlinear refraction and self-defocusing, and…
Monday October 26, 1992 3:00 p.m. Leick Robinson “A ray theory model of sonic boom propagation through a turbulent ground layer” Bart Lipkens “Further reports on the propagation of spark produced N waves through turbulence” Robin O. Cleveland “Waveform freezing of sonic booms in the atmosphere” Michael R. Bailey “Isolation of a negative pressure pulse…
Friday, October 23, 1992 4:00 p.m. Michalakis A. Averkiou Mechanical Engineering Department The University of Texas at Austin Measurements of intense pulses generated by directive sources in liquids with strong absorption are compared with theoretical predictions based on a time domain numerical solution of the KZK nonlinear parabolic wave equation. The classic phenomenon referred to…
Friday, October 9, 1992 3:30 p.m. Stirling Scott Dodd Applied Research Laboratories A dip at two kilohertz in the ambient sea noise sound level spectrum, taken with the Captor Improvement Project Vertical Line Array, is described. Limitations of existing ambient sea noise models are discussed. An approach is detailed for the creation of a model…
Friday, September 25, 1992 3:30 p.m. Elizabeth Langworthy Miller Applied Research Laboratories The possibility of using a geophone to detect ocean acoustic waves beneath a layer of ice is investigated. A very brief review of continuum mechanics is given, along with the velocity potentials of the waves in the ice, air, and water. Absorption is…
Friday, September 18, 1992 4:00 p.m. E. A. Zabolotskaya Department of Mechanical Engineering and The General Physics Institute Russian Academy of Sciences Nonlinear Rayleigh wave propagation is investigated theoretically. The analysis is based on the Hamiltonian formalism. Nonlinear propagation and distortion of plane waves is considered with this method (technique). Coupled equations for the harmonic…
Friday, September 11, 1992 4:00 p.m. Tom Van Doren Department of Mechanical Engineering The University of Texas at Austin This wildly exciting seminar will describe a theoretical and experimental investigation of the propagation of finite-amplitude sound in multiple waveguide modes of a rectangular duct with rigid walls. Two quasilinear analytical solutions for second harmonic generation…
Friday, May 1, 1992 3:00 p.m. Michalakis A. Averkiou “Propagation of pulsed finite amplitude sound beams in a liquid with strong absorption” Michalakis A. Averkiou “Reflection of focused sound beams from curved surfaces” Bart Lipkens “The propagation of plane N waves through a statistically isotropic turbulent field as a singular perturbation problem” Douglas E. Reckamp…
Friday, April 24, 1992 3:00 p.m. James A. Hawkins, Jr. Mechanical Engineering The University of Texas at Austin We have developed, using Hamilton’s variational principle, a model which describes the propagation of acoustical disturbances (sound) in bubbly sediments. The sediment is taken to be a solid frame saturated by a fluid (in the sense of…