Tendon failure in FAST modeling

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Abhinay.Goga
Posts: 21
Joined: Tue Oct 25, 2016 8:12 am
Organization: Hochschule Flensburg
Location: Germany

Re: Tendon failure in FAST modeling

Postby Abhinay.Goga » Fri Jun 26, 2020 5:10 am

Dear Jason and Matt,

Thanks. The floater is OlavOlsen Semi-submersible star floater. My aim is to validate fiber ropes instead of conventional catenary chains. My connections of lines look like the following:

"Line LineType UnstrLen NumSegs NodeAnch NodeFair Flags/Outputs
(-) (-) (m) (-) (-) (-) (-)
1 chain 60 6 4 1 -
2 chain 60 6 5 2 -
3 chain 60 6 6 3 -
4 fiber 80 8 7 4 "ptsd"
5 fiber 80 8 8 5 "ptsd"
6 fiber 80 8 9 6 "ptsd"
7 chain 60 6 10 7 -
8 chain 60 6 11 8 -
9 chain 60 6 12 9 -"

Based on your suggestion, I ran complete static situation without any initial offsets. The performance of the floater seems reasonable with increase in surge and heave. However, the anchor tensions seems not in order. Can anyone please clarify, why there is such behavior on anchors?

Thanks and regards
Abhinay Goga
Attachments
Anchor tensions.jpg
Anchor tensions.jpg (60.02 KiB) Viewed 151 times
Line loss Surge.jpg
Line loss Surge.jpg (64.61 KiB) Viewed 151 times

Matt.Hall
Posts: 26
Joined: Tue Apr 05, 2011 2:41 pm
Organization: NREL
Location: Boulder, CO

Re: Tendon failure in FAST modeling

Postby Matt.Hall » Fri Jun 26, 2020 9:30 am

Dear Abnhinay,

The results you're seeing are as I'd expect. My understanding was you were only concerned with simulating the results of a line failure on the floater itself. You'll see the code I helped you with simply zeroes the forces of the failed line on the platform; it does not do anything to physically free the line from the floater. So the line still acts attached to the platform and has the corresponding tensions. Only the floater does not feel the line anymore.

Hopefully this approach meets your needs. If you actually wanted to model the effect of the simulated failure within the mooring system as well, it would be considerably more complicated. You would need to add additional states to the system for the freed line end, which would convert from "vessel" to "connect" type. These capabilities will be developed eventually, but they aren't quick to do.

Best,
Matt

Abhinay.Goga
Posts: 21
Joined: Tue Oct 25, 2016 8:12 am
Organization: Hochschule Flensburg
Location: Germany

Re: Tendon failure in FAST modeling

Postby Abhinay.Goga » Sat Jun 27, 2020 1:56 am

Dear Matt,

Understood that the source code you helped with creates a Pseudo event of transient line loss. Thanks for all the guidance and support. For my thesis, the implemented model is suffice. Looking forward to future improvements on the glue codes.

Kind regards
Abhinay Goga


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