Friday, September 14, 1990 4:00 p.m. L. A. Ostrovsky Institute of Applied Physics of the USSR Academy of Sciences 603600 Gorky, USSR The concept of negative energy waves in hydrodynamics and acoustics is discussed. Being excited, such waves decrease the total energy of a system which is possible only in nonequilibrium, potentially unstable systems, e.g.,…
Friday, June 8, 1990 4:00 p.m. T.S. Margulies Johns Hopkins University Theories for infinitesimal, planar sound wave propagation in a dilute suspension of rigid particles has been investigated by generally three approaches: (1) wave scattering, (2) hydrodynamic, and (3) ad hoc approaches specific to particular systems. Here, a hydrodynamic development that uses spatially averaged continuum…
Friday, May 5, 1990 4:00 p.m. Eugene E. Kim Mechanical Engineering The University of Texas at Austin A two-dimensional KZK (Khokhlov-Zabolotskaya-Kuznetsov) equation is used to model the nonlinear effects in a sound field that is excited by nonaxisymmetric source conditions. An algorithm developed in Norway, which numerically solves the KZK equation in the frequency domain,…
Friday, April 27, 1990 4:00 p.m. Professor Dennis Wilson Mechanical Engineering The University of Texas at Austin Several idealized linear models will be used to illustrate the fundamental difference in a sound pressure field produced by subsonic vs. supersonic body motion. This linear theory will then be modified to account for attenuation due to dispersion…
Friday, April 20, 1990 4:00 p.m. Tom Van Doren Mechanical Engineering The University of Texas at Austin I. Scattering of sound by sound: The interaction of two finite amplitude tones in a rectangular duct generates sound at the sum and difference frequencies of the two tones. This generation can be described using a quasilinear theory…
Friday, April 13, 1990 4:00 p.m. Kenneth A. Cunefare Department of Mechanical Engineering Pennsylvania State University The numerical treatment of a discrete quadratic expression for the total acoustic power radiated by a three-dimensional extended structure, derived from a boundary element formulation of the Helmholtz Integral Equation, leads to an improved understanding of the sensitivity and…
Friday, April 6, 1990 4:00 p.m. Professor David T. Blackstock Department of Mechanical Engineering and Applied Research Laboratories The University of Texas at Austin Evanescent waves, which are disturbances that are not true waves at all, turn up in many fields of science and engineering. Examples to be discussed in this seminar are primarily from…
Friday, March 23, 1990 4:00 p.m. Chuck Bradley Department of Mechanical Engineering The University of Texas at Austin A theoretical and experimental investigation of the propagation of linear and nonlinear acoustic waves in a waveguide loaded with a periodic array of scatterers is presented. It is first shown that the waves which occur in a…
Friday, March 9, 1990 4:00 p.m. Dr. Kenneth H. Stokoe, II Brunswick-Abernathy Regents Professor Department of Civil Engineering The University of Texas at Austin The use of stress waves in nondestructive testing and evaluation of geotechnical materials has increased significantly over the past two decades. Shear and Rayleigh waves are the two types of seismic…
Friday, March 2, 1990 4:00 p.m. Dr. Craig Champlin Speech Communication The University of Texas at Austin Otoacoustic emissions (OAEs) are low-level sounds that originate in the inner ear, but can be recorded in the human ear canal. These sounds come in two general classes sounds that occur during or following acoustic stimulation are called…
Wednesday, February 7, 1990 2:00 p.m. A videotape of the PBS program NOVA dealing with the acoustics of music will be shown. The program covers a variety of topics including construction of musical instruments, synthesizer development, and psychological phenomena associated with music. Both historical and modern developments of the selected topics are covered.
Friday, December 8, 1989 4:00 p.m. Dr. Edward J. Powers Department of Electrical and Computer Engineering The University of Texas at Austin In this presentation, the key ideas underlying the use of digital higher-order spectral analysis to identify nonlinear systems are described. Of particular importance is the fact that the approach to be described is…
Monday, December 4, 1989 3:00 p.m. Dr. F.W. de Wette Department of Physics The University of Texas at Austin Lattice dynamics describes the vibrational motions in solids on the atomic scale; acoustics is the long-wave-length or acoustic limit of this description. After a short introduction of the formalism of lattice dynamics and of the notion…
Friday, November 17, 1989 4:00 p.m. “A High-frequency Omnidirectional Source for a Robot End Effector” by Jack Leifer and Ilene J. Busch-Vishniac “Effects of Boundary Conditions on the Propagation and Interaction” by Jacqueline Naze Tjotta, James A. TenCate, and Sigve Tjotta “The Application of Hamilton’s Principle to a Bubbly Liquid of Finite Amplitude Sound Beams”…
Friday, October 27, 1989 4:00 p.m. David T. Blackstock Department of Mechanical Engineering and Applied Research Laboratories The University of Texas at Austin The amount of heating of a material through which sound passes depends on the acoustic absorption of the sound wave. Absorption of small-signal sound is well understood, but in many applications, particularly…
Friday, October 20, 1989 4:00 p.m. Professor Russell F. Pinkston Department of Music The University of Texas at Austin An inexpensive real time computer music system has been developed at the Electronic Music Studios of The University of Texas at Austin. The system was designed to facilitate both teaching and composition; it can be implemented…
Monday, October 9, 1989 3:00 p.m. Jeff Harrell Department of Electrical Engineering The University of Texas at Austin For acoustic arrays (microphones or loudspeakers), the main beamwidth of the radiation pattern is determined by the spacing between the elements in terms of λ. Thus area coverage depends upon frequency. We have demonstrated that by controlling…
Monday, October 2, 1989 3:00 p.m. Jan Garmany Institute for Geophysics The University of Texas at Austin Of all elastic wave propagation problems, none eludes our intuition more than anisotropy. Even the formidable problem of propagation in a 3D heterogeneous medium seems less intimidating because we have an intuitive sense (and some computational tools) for…
Wednesday, June 28, 1989 3:00 p.m. Y. G. Shchemelev Department of Radiophysics Gorky State University, USSR It has become clear that Burgers’ equation is a standard equation for a wide class of waves in nonlinear, nondispersive media, worthy of accepting a place alongside the classical linear hyperbolic equation. It is possible to derive an asymptotic…
Wednesday, May 17 4:00 p.m. “Reflection of Focused Sound From Curved, Rigid Surfaces” by Michalakis A. Averkiou and Mark F. Hamilton “Effects of Absorption on the Scattering of Sound by Sound” by Corinne M.Darvennes, Mark F. Hamilton, Jacqueline Naze Tjotta, and Sigve Tjotta “Finite Amplitude Acoustic Propagation In a Periodic Structure” by Charles E. Bradley…