Subsea Pipeline Free Span VIV & Fatigue Calculator
Screen subsea pipeline seabed spans for cross-flow and in-line vortex-induced vibrations (VIV), calculate natural frequencies, and evaluate DNV-RP-F105 fatigue risk.
Span Geometry & Structural Stiffness
Boundary Conditions & Flow Velocity
VIV Screening & Frequency Response
| Span Fundamental Natural Frequency (f0): | -- Hz |
| Steel Pipe Bending Rigidity (EI): | -- MN·m² |
| Vortex Shedding Strouhal Freq (fs): | -- Hz |
| In-Line VIV Onset Threshold: | VR ≥ 1.0 |
| Cross-Flow VIV Lock-in Threshold: | VR ≥ 2.2 |
| Max Allowable Span Length (Screening): | -- m |
Recommended Tools & Equipment
Tested hardware and components for high reliability
Frequently Asked Questions
What causes subsea pipeline free spans on the ocean floor?
Subsea pipeline free spans occur when seabed bathymetry features uneven depressions, mega-ripples, sandwaves, boulder fields, or marine trenches, leaving a segment of the pipe completely suspended above the seabed without continuous soil support. Progressive seabed scouring caused by bottom currents also washes away sand from beneath laid pipelines.
What is the physical difference between in-line and cross-flow VIV?
In-line VIV occurs at lower current velocities (reduced velocity VR between 1.0 and 2.2), causing oscillations parallel to the flow direction with relatively small vibration amplitudes (approx 0.10 to 0.15 pipe diameters). Cross-flow VIV triggers when VR exceeds 2.2, causing violent transverse oscillations perpendicular to flow with large amplitudes reaching 1.0 to 1.3 diameters, accelerating fatigue damage by orders of magnitude.
How are hazardous free spans remediated offshore?
Offshore intervention techniques include: (1) Pre-installed or post-lay rock dumping from specialized fall-pipe rock placement vessels to fill depressions; (2) ROV-deployed engineered grout bags pumped with micro-cement beneath the pipe; and (3) Helical VIV suppression strakes fitted to the outer jacket to disrupt vortex shedding coherence.