Free Span Full Fatigue
Free Span Full Fatigue
(OP)
Hi guys,
Regarding free span analysis according DNV RP F105 I've the following question:
Is there a minimum gap ratio (free span clearance/External Pipeline Diameter) that lead to VIV onset (i.e. below that limit no VIV occurs)?
I found in a document that with gaps ratio below 0.3 no VIV occurs, but I don't have a clear reference on that.
Thank you for your help.
Regarding free span analysis according DNV RP F105 I've the following question:
Is there a minimum gap ratio (free span clearance/External Pipeline Diameter) that lead to VIV onset (i.e. below that limit no VIV occurs)?
I found in a document that with gaps ratio below 0.3 no VIV occurs, but I don't have a clear reference on that.
Thank you for your help.





RE: Free Span Full Fatigue
Everything can vibrate, what you want to avoid is vibration at or near resonant, or "natural" frequency, so stay out of the range.
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: Free Span Full Fatigue
maybe there is a misunderstanding because with free span clearance/External Pipeline Diameter I meant a different thing (see attached).
Anyway I agree with you that a very important thing is the other ratio (free span length/external diameter).
Thank you
RE: Free Span Full Fatigue
Then again, the current as you get closer to the bottom could tend to decrease too, due to roughness and boundary layer effects. There must be practical limits there, as soon you would start getting a higher velocity over the top of the pipe than under it and the votex shedding frequency would start breaking up. I would guess something like that when you get closer than 2 x the pipe diameter to the bottom, bottom effects would start to become more significant. You could try to do some "hand work" based on simple streamline analysis for a cylinder near a wall, or if you're versed in CFD .. even better.
From "BigInch's Extremely simple theory of everything."
RE: Free Span Full Fatigue
But in DNV RP F105 there is no mention of this general statement
I would use that reference for my scope.
RE: Free Span Full Fatigue
From "BigInch's Extremely simple theory of everything."
RE: Free Span Full Fatigue
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