Scientific and Technical Aerospace Reports Volume 38 July 28, 2000

important conclusion is that for subsonic turbulent flows, each structural mode radiates sound independently. A suitable strategy
for the active structural acoustic control of the sound power transmitted through the panel would thus be independent feedback
control of each structural mode in the low-frequency domain. It is also shown, however, that independent control of the panel’s
radiation modes is also possible, and that this could provide a more efficient control strategy, since a smaller number of radiation
modes than structural modes needs to be controlled for a given level of performance.
Author
Active Control; Mathematical Models; Panels; Turbulent Boundary Layer; Aircraft Noise; Harmonic Excitation; Harmonic
Radiation
20000066625 Department of the Navy, Washington, DC USA
Phase Fluctuation Enhanced Adaptive Processor
Wagstaff, Ronald A., Inventor; Mobbs, Jackson A., Inventor; Feb. 04, 2000; 31p; In English
Patent Info.: Filed 4 Feb. 2000; US-Patent-Appl-SN-09,498,348
Report No.(s): AD-D019714; No Copyright; Avail: Issuing Activity (Defense Technical Information Center (DTIC)), Microfiche
The invention uses phase fluctuations in each frequency bin to modify the exponents of pressure amplitudes (or power magnitudes)
for each successive realization of a signal. As the magnitudes of the phase fluctuations decrease (i.e., signal has small magnitudes
and the noise has large ones), the exponents increase. The modified pressures are summed and averaged. The resulting
average is then raised to an exponent that is the average of the exponents of the individual pressures (or power magnitudes). All
individual exponents and the averaged exponent in each bin are preferably bounded between optimal values of 2 and -4. The exponents
will be negative for noise (attenuation), and in between for clutter signals.
DTIC
Signal Processing; Sonar; Noise Reduction; Underwater Acoustics; Random Noise
20000067667 Georgia Inst. of Tech., Acoustics and Aerospace Technologies Branch, Atlanta, GA USA
Active Control of Liner Impedance by Varying Perforate Orifice Geometry
Ahuji, K. K., Georgia Inst. of Tech., USA; Gaeta, R. J., Jr., Georgia Inst. of Tech., USA; Mar. 31, 2000; 206p; In English
Contract(s)/Grant(s): NAG1-1734
Report No.(s): GTRI-A5004/2000-1; No Copyright; Avail: CASI; A10, Hardcopy; A03, Microfiche
The present work explored the feasibility of controlling the acoustic impedance of a resonant type acoustic liner. This was
accomplished by translating one perforate over another of the same porosity creating a totally new perforate that had an intermediate
porosity. This type of adjustable perforate created a variable orifice perforate whose orifices were non-circular. The key objective
of the present study was to quantify, the degree of attenuation control that can be achieved by applying such a concept to the
buried septum in a two-degree-of-freedom (2DOF) acoustic liner. An additional objective was to examine the adequacy of the
existing impedance models to explain the behavior of the unique orifice shapes that result from the proposed silding perforate
concept. Different orifice shapes with equivalent area were also examined to determine if highly non-circular orifices had a significant
impact on the impedance.
Derived from text
Active Control; Orifices; Geometry; Acoustic Impedance; Linings; Resonance
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ATOMIC AND MOLECULAR PHYSICS
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20000062712 Gesellschaft fuer Schwerionenforschung m.b.H., Darmstadt, Germany
Examination of the e(sup +) and e(sup +)e(sup -) pair emission from heavy ion collisions at the EPoS II spectrometer
Baumann, J.; Dec. 31, 1996; 150p; In German; In English
Report No.(s): DE99-715815; GSI-96-05; No Copyright; Avail: Department of Energy Information Bridge
In the course of examination of the positron and positron-electron pair emission from heavy ion collisions at the Coulomb
barrier, the research groups EPOS I and ORANGE have found a number of line structures in the measured positron energy and
cumulative pair energy spectra which up to present could not be fully explained, as theoretical interpretations so far remain incon-
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