Civil Engineering Reference
In-Depth Information
Fig. 6.3
Typical response variation with mean wind velocity
Finally, a comment regarding the use of aerodynamic derivatives is appropriate. As
discussed in chapter 5.2, motion induced forces may change the combined flow and
structural stiffness (as well as damping), and thus, the current resonance frequencies are
functions of the mean wind velocity. In the dynamic response calculations below this
effect is fully included in the relevant frequency-response-functions. However, in the
quantification of aerodynamic derivatives and their contribution to total stiffness and
damping it is assumed that the effect of changing resonance frequencies may be ignored.
For the response calculations in this chapter motion induced load effects may then be
taken at a reduced velocity
VB
/(
)
where
is the predetermined resonance frequency
ω
ω
based on structural properties alone and at
V
=
. Otherwise, iterations are required.
Thus, it is assumed that the response calculations are not taken in close vicinity to a
motion induced instability limit. However, in the determination of an instability limit as
shown in chapter 8, this effect can not be ignored, and
0
ω
will be taken at the relevant
i
critical wind velocity,
. Thus, the determination of
in chapter 8 will demand
V
V
cr
cr
iterations.
