Oscillations, Waves, and Interactions - GWDG

Applied physics at the “Dritte” 7
was the improvement of adaptive filter algorithms with fast convergence, yet low
numerical complexity [37,38].
These activities ended with the retirement of Dieter Guicking (1998); some more
projects on active flow control and related problems were performed in the working
group of Dirk Ronneberger, see Section 5 and his contribution to this book [39]. For
more details on the historical development, fundamentals, and the state of the art of
active sound and vibration control see the article by D. Guicking [40] in this book.
5 Flow acoustics and flow control
Sound propagation through ducts is influenced by superimposed fluid flow. These
interactions have been studied at the institute theoretically and experimentally in
research groups headed by Fridolin Mechel (1960–1966) and thereafter by Dirk Ronneberger
until to his retirement 2006. Experimental facilities comprised wind tunnels
and ducts with recirculating water or oil flow, the latter because of the thicker boundary
layer. In the wind tunnels, the interaction of sound propagation and mean flow
was studied under various aspects: in ducts with absorbing lining without and with
absorber cassetting [41], in rigid-walled ducts with turbulent air flow [42], also under
the influence of wall roughness [43]. Much work was devoted to the investigation of
cross-sectional discontinuities [44], acoustical [45] and vibrational [46] control of the
boundary layer, the acoustic impedance of an orifice in the flow duct [47] or at the side
wall [48], the directivity of sound radiation from the duct end [49], and the influence
of nonlinear interaction of instability waves in a turbulent jet [50].
In the 1980s, intensive experiments were performed on the noise radiation of rolling
automobile tyres and have contributed to a better understanding of the noise generation
mechanisms [51].
Since the late 1990s, the focus was shifted to active control of flow parameters,
both in air and water [52–56]. Some recent research results are presented at another
place in this book [39].
6 Underwater sound
Erwin Meyer and his team had done intensive research work on water-borne sound
until 1945 at the Heinrich-Hertz-Institut in Berlin. They studied the mechanisms
of sound absorption in sea water, and they developed new absorbers of underwater
sound: rib-type absorbers for the lining of anechoic water basins, and thin-layer
two-circuit resonance absorbers as reflection reducing coatings for underwater objects.
The research results, which could not be published during war time, have been
collected in a US Navy Report [57] which today is still recognised as a treasure of
information for researchers in this field all over the world.
Meyer and his team continued the hydroacoustic research at Göttingen with financial
support by the British “Department of Scientific and Industrial Research”
(DSIR), later by the “Department of Naval Physical Research” (DNPR). The research
contract started in 1948 and was continued year after year for a record breaking period
of time until 1978, long after Erwin Meyer’s death.