ssc-367 - Ship Structure Committee

member’s nominal diameter and thickness. The member mass per unit
length m is taken to include the mass of the member steel including
sacrificial corrosion allowance, anodes, and contained fluid. For
the submerged portion of the member, the added mass of the
surrounding water is also included. This added mass is the mass of
water that would be displaced by a closed cylinder with a diameter
equal to the nominal member outside diameter plus two times the
appropriatemarine growth thickness.
Because of insufficient knowledge of the effect of marine growth on
vortex shedding, the member diameter “d” in vortex-shedding
parameters Vr, Re, KS, and the member effective mass = in parameter
Ks do not incluc(e any allowance for the presence of marine growth.
D.3.
SLISCEPTIBILITYTOVORTEX SHEDDING
,/—.
The vortex shedding phenomena may occur either in water or in air.
The susceptibility discussed and the design guidelines presented are
applicable for steady current and wind. Wave induced vortex
shedding has not been investigated in depth. Since the water
particle velocities in waves continually change both in magnitude and
direction (i.e. restricting resonant oscillation build-up), it may be
reasonable to investigate current-induced vortex shedding and
overlook wave actions.
To determine susceptibility of a member to wind- or current-induced
vortex shedding vibrations, the reduced velocity (Vr) is computed
first. For submerged members, the stability parameter (Ks) is also
calculated. Vortex shedding susceptibility defined here is based
upon the method given in Reference D.8, with a modified lower bound
for current-induced shedding to reflect present thinking on this
subject (ReferenceD.9).
D-7