ssc-367 - Ship Structure Committee

8.4 METHODS OF MINIMIZING VORTEX SHEDDING OSCILLATIONS
Because the environmental factors that cause vortex-induced
oscillations (wave, current and wind) cannot be controlled,
minimizing the oscillations depends primarily on the physical
characteristicsof the structure.
There are several ways to solve the problem of vortex-induced
oscillations:
●
Controlof structuraldesign (length,diameter, end fixity)to
obtainmember naturalperiodsto avoid the critical velocity.
●
Control of structuraldesign to have sufficiently high values
of effective mass and inherent damping to avoid the critical
velocity.
●
Altering the pattern of the approachingflowto modify vortex
shedding frequency.
Further discussion on this subject is presented in Section D.8 of
Appendix D.
8.5
RECOMMENDATIONS
Fatigue damage due to vortex shedding is best prevented during the
design of the structure by sizing the members (length-to-length
ratio, rigidity, damping, etc.) to ensure that critical velocity
values are avoided. If geometric, design schedule or-economic
constraints preclude resizing of members susceptible to VIV, the
total fatigue damage due to local (VIV) and global response should
be computed and the integrity of those members verified. If a
limited number of members are found to be susceptible to fatigue
failure, the flow around such members may be modified through the
use of devices and spoilers.
8-6