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#75012 - 09/14/20 05:49 PM Looking for FPSO/ship piping CAESAR II model with displacem
Mandeep Singh Offline
Member

Registered: 12/15/99
Posts: 597
Loc: Houston, Tx, USA
Hello all,

I am looking for an FPSO or offshore CAESAR II model, with a lot of displacements.

Do you use excel or something similar to compute restraint displacement from FPSO or ship movement?

If you have the above, can you share a sample?

thanks in advance.

Regards,
Mandeep
_________________________
Best Regards,
Mandeep Singh
CADWorx & Analysis Solutions
Hexagon PPM

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#75015 - 09/15/20 09:23 AM Re: Looking for FPSO/ship piping CAESAR II model with displacem [Re: Mandeep Singh]
Michael_Fletcher Offline
Member

Registered: 01/29/10
Posts: 884
Loc: Louisiana, US
Mandeep,

Unfortunately, I do not have any files to share. I wasn't an FPSO guy, but I did do offshore platforms.

Also, please take below information to be *my* understanding of how things have to be done, and not as instruction to you on how to operate your own software. smile

It's generally out of the realm of the stress analyst to calculate hogging and sagging, and left to the civil / structural group to provide the displacements. Also, these points need to be conveyed or plotted on beam drawings in some way.

The displacements are provided (or should be provided) as xyz coordinates as xyz displacements. Hard anchors should be avoided anywhere except dead center of the hull, because this would extend the challenge of having to consider applying rotation to the pipe.

Generally, you would be provided two or three data sets: Standard, Hurricane, and Transport.

Where needed, I could interpolate across points along common beams. Horizontal displacements are assumed negligible* (more below). The CSA group assumes to include pipe loads for a static case.

They are then input into CAESAR as U-bolted supports, cnoded to unused nodes*(see below), and displacements applied to those nodes. For each data set, you input it twice - positive and negative for sagging/hogging.

* from above.
This method has significant implications.
1. You can't directly input a stiffness for a support unless you're specifying a restraint.
2. Likewise, you can't directly input a displacement for said support unless you're specifying a restraint.

If you absolutely need these horizontal loads incorporated, you have to start modeling fake beams of some type and CNODE those into your model. In which case, you take a rigid element from CL of pipe to bottom of pipe, put in the appropriate restraint type, CNODE that to another rigid element, and on that element, place an anchor with another CNODE with the CNODE possessing the XYZ displacements. The nature of the second set of rigid elements is up to the analyst, but generally make it super stiff.

There's no great way, I don't think, to ease the transition of inputting all this data into CAESAR - just that the best way to currently check it (I think) would be to copy and paste it from CAESAR back to Excel, and use whatever Excel Power Query magic is needed to have Excel point out the differences between original data and CAESAR data to help make sure they both align.

I hope this helps.

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#75016 - 09/15/20 09:44 AM Re: Looking for FPSO/ship piping CAESAR II model with displacem [Re: Mandeep Singh]
Mandeep Singh Offline
Member

Registered: 12/15/99
Posts: 597
Loc: Houston, Tx, USA
thanks Michael, Yes I am looking for industry experience.

So, you apply displacements only to restraints, right. The piping is connected to structure/ship using restraints, so displacements are only transfered through restraints.

You are using rigid elements to go to pipe OD, is that for large diameter pipes only or all pipes?
_________________________
Best Regards,
Mandeep Singh
CADWorx & Analysis Solutions
Hexagon PPM

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#75018 - 09/15/20 02:20 PM Re: Looking for FPSO/ship piping CAESAR II model with displacem [Re: Mandeep Singh]
Michael_Fletcher Offline
Member

Registered: 01/29/10
Posts: 884
Loc: Louisiana, US
Sagging/hogging is movement of the support due to deflection of the hull, and thus the displacement is applied only to the otherwise unused CNODE of the restraint.

As far as rigid elements to OD, it's admittedly typically computationally unnecessary in most cases, where radial thermal growth can be neglected.

I guess I take the effort to do it this way because it makes it easier to visually identify something fishy is going on with the modeling technique, and to pay close attention if you have to modify it.


Edited by Michael_Fletcher (09/15/20 02:33 PM)

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#75019 - 09/15/20 08:05 PM Re: Looking for FPSO/ship piping CAESAR II model with displacem [Re: Mandeep Singh]
Mandeep Singh Offline
Member

Registered: 12/15/99
Posts: 597
Loc: Houston, Tx, USA
Thanks Michael.

I welcome if others have some samples to share.
_________________________
Best Regards,
Mandeep Singh
CADWorx & Analysis Solutions
Hexagon PPM

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