Scientific and Technical Aerospace Reports Volume 38 July 28, 2000

ias flow can increase insertion loss by as much as 10 dB at frequencies in the range of 500 - 1400 Hz compared to no grazing
flow. The effectiveness of the negative bias flow is diminished as the grazing flow velocity is increased.
Derived from text
Degrees of Freedom; Linings; Sound Transmission; Response Bias; Flow Characteristics
20000066584 Institute TNO of Applied Physics, Delft, Netherlands
Acoustic Radiation from Beam-Plate Systems
Petersson, B. A. T., Institute TNO of Applied Physics, Netherlands; Oct. 07, 1999; 27p; In English
Contract(s)/Grant(s): A97/KM/131; TNO Proj. 008.00653/01.01
Report No.(s): TD-99-0056; TPD-HAG-RPT-990159; Copyright; Avail: Issuing Activity
Based on a recently developed theoretical description for combinations of arbitrary deep beams and thin plates, numerical
results for the acoustic radiation are presented. Fluid loading of the radiating beam-plate configuration is rigorously taken into
account. For most configurations studied, the radiation principally follows that of a point excited plate. With respect to thin plates,
fluid loading is confirmed to be influential for the radiation characteristics whereas the actual configuration of the structural system
enables the radiation for Helmholtz numbers at and above the dilatational resonance of the beam to exceed that of the directly
excited plate. It is thus demonstrated that owing to the waveguide behaviour of the beam, enhanced radiation results from the
dilatational resonance and above in comparison with what would have been predicted based on Euler-Bernoulli theory. In the
range below the dilatational resonance, the analysis further indicates that marked structural alterations do not affect the radiation
correspondingly.
Author
Sound Waves; Waveguides; Numerical Analysis; Thin Plates
20000066603 Physics and Electronics Lab. TNO, The Hague, Netherlands
Environmentally Adaptive Sonar Techniques: A Literature Survey and Recommendations for Further Research Final
Report
Eecen, P. J., Physics and Electronics Lab. TNO, Netherlands; Lam, F.-P. A., Physics and Electronics Lab. TNO, Netherlands;
Simons, D. G., Physics and Electronics Lab. TNO, Netherlands; September 1999; 33p; In English
Contract(s)/Grant(s): A99/KM/651; TNO Proj. 28804
Report No.(s): TD-99-0246; FEL-99-A207; Copyright; Avail: Issuing Activity
This report describes a literature survey on environmentally adaptive sonar technology. Many papers are summarized and
reported in a literature list. The international projects on environmentally adaptive sonar technology are described. Many techniques
are summarized and the report concludes with a list of recommendations for a succeeding project on environmentally adaptive
sonar technology. Also, a comprehensive list of methods and equipment concerning environmental parameter estimation is
included.
Author
Sonar; Underwater Acoustics; Real Time Operation; Frequencies; Marine Technology; Tracking (Position)
20000066615 Southampton Univ., Signal Processing and Control Group, UK
Model for the Control of the Sound Radiated by an Aircraft Panel Excited by a Turbulent Boundary Layer
Maury, C., Southampton Univ., UK; Gardonio, P., Southampton Univ., UK; Elliott, S. J., Southampton Univ., UK; June 2000; 90p;
In English
Report No.(s): ISVR-TR-287; Copyright; Avail: Issuing Activity
This aim of this report is to present a simplified but relevant model for predicting the vibro-acoustic response of an aircraft
panel excited by a turbulent boundary layer. This analytical model provides an insight into tile physical properties of the TBLexcited
panel and enables the performance limitations to be derived for various idealized active control systems. This report is
divided into three main parts. The first part justifies the simplifying assumptions of the flat plate model for an aircraft panel. Furthermore,
it describes how the spectral densities of the panel response can be obtained from an analysis of the system response
to a harmonic deterministic excitation and a statistical model for the turbulent boundary layer. The second part focuses on the
modal formulation used to solve the flow-structure interaction problem in the frequency domain; criteria are discussed under
which the cross-modal coupling of the structural modes call be neglected when excited by a turbulent boundary layer. The modelling
of the pressure field induced by the turbulent boundary layer which acts as a distributed random excitation field on the structure
is described. The third part presents simulation results in which the verification of the approximations and the influence of
the main physical parameters art discussed, together with a comparison between experimental and predicted results. The way in
which the structural modes and the radiation modes of the plate contribute to the vibro-acoustic response are also examined. One
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