Page 154 - Pipelines and Risers

Vortex-induced Vibrations (VIV) and Fatigue 127

Response
The characteristic maximum response amplitude is shown graphically in Figure 9.3 below
@NV, 1998).

Maximum Vibration Amplitudes - IN-LINE VORTEX SHEDDING

Note: K=K s,d

Figure 9.3 Amplitude response model for in-line VIV.

Stress Range
The in-line response of a pipeline span in current dominated conditions is associated with
either alternating or symmetric vortex shedding. Contribution from the both first in-line
instability region (1.0+<2.5) and the second instability region (2.5<V~<4.5) are included in
this section. The stress range, S, may be approximately calculated by the in-line VIV
Response Model:
S=2.SA=,, .(A,lD).D (9.8)
where:

S~=l,,,is the unit stress amplitude (stress due to one meter in-line mode shape deflection)
which is to be estimated by a dedicated FE analysis package.

(A@) is non-dimensional in-line VIV response amplitude.