Zur Identifikation selbsterregter aeroelastischer Kräfte im Zeitbereich
Neuhaus
Christian
Neuhaus, Christian
aut
2010-07-01
2014-08-12
de
<p>The flow around a section of a line like slender structure, e.g. a mast or a wide spanned
bridge, interacts with the section’s motion. Forces as a reaction of the flow induce deformations
to the elastic structure. These deformations change the flow conditions
around the section and therewith the resulting forces. The forces on the section due to
the motion of the section itself are called aeroelastic or self excited forces. The interaction
leads to a coupled aeroelastic system including the mechanical properties of the
structure and the flow around it. Several phenomena may occur, related to the instability
of the coupled system. Aeroelastic phenomena, depending on the respective
mechanism, are called flutter, galloping and divergence. They play an important role
in aeronautics from the beginning of the 20th century. The relevance of these phenomena
for structures of civil engineering was disclosed by the disaster of the TACOMA
NARROWS Bridge 1940. Henceforward a great amount of scientific work in civil engineering
has been done and the aeroelastic stability is nowadays established for all vulnerable
structures.
The aeroelastic forces on an oscillating section can be described in the frequency and
in the time domain. This is often realised using linearization around a mean angle of
attack of the oncoming flow. The most common linear mathematical model is a time
domain model using frequency dependent parameters, called Scanlan derivatives. The
first part of this work presents the basic analytical models for the description of the
self excited forces and a comparison of experimental methods for their determination.
The consequences of the linearization on the applicability of the mathematical models
approximating the aeroelastic forces are educed.
In the second part a new experimental rig for the determination of SCANLAN derivatives
using the forced vibration method is presented and analysed. It has been mounted
in the boundary layer wind tunnel at Ruhr-Universität Bochum. This rig allows experiments
in a wide frequency range and in three degrees of freedom. Sets of 18
SCANLAN derivatives for three section models are shown and analysed regarding the
adaptability of instationary and quasi-steady theory. The interaction of self excited
forces and forces as a result of vortex shedding is observed analogous to former studies.
An identification of aeroelastic forces in the time domain, defined as indicial or step
response functions, is presented in the third part of this work. Two main strategies are
implemented and compared. An approximation of the frequency response functions,
given by the measured SCANLAN derivatives, by rational functions using terminology
of system theory and an identification in the time domain based on nonstationary motions
of the section are presented. Difficulties and constraints due to the determination
of time domain functions are worked out. The existence of indicial functions, derived
in the frequency domain using rational function approximation, for a two degree of
freedom model is verified in the time domain.</p>
urn:nbn:de:hbz:468-20100820-102122-7
2014-08-12T08:32:14.905Z
2014-08-12T09:03:34.426Z
published
Diss
fbd/bauingenieurwesen/diss2010/neuhaus