Hi to all,

I have to model an anchor point (nozzle) and pipeline connecting to it. But I don't want to model the whole tank and the nozzle. Does it have a way to model an anchor point with initial displacements acting on it? Because when i do it at the conventional way CAESAR II don't get it and say that there is problem because that it is not OK to have at same point anchor and displacements.

Thanks in advance!

Crowley,

If you want to use Anchor with displacements (floating anchor) then you may provide a cnode at anchor (it should be such a node which doesn't exist in your model) & now define displacements at this cnode.

The other way round is to directly define displacements at the node you intend to rather than using Anchor restraint.

Both will serve the same purpose.


I guess this helps you!!!

Thank you very much for the immediate and accurate answer!

I have another doubt.

When I directly model the displacements in the node that should be anchor, the software understands it as a free end with displacements. But when i put in action and wind load and that became problem, because there is no restrictions in nodes. But in reality it is not like that, because that nodes are nozzles of the equipment. So I will have to put some restrictions, but how to model them accurately?

I did that:

At the node which is end of flange and beginning of the nozzle i put anchor at the last node. Than i create new node which is 1mm away from the last (in reality it should be 1 mm inside the nozzle) and put on it the displacements. Than i go back to previous and connect the node with anchor to the node with displacements.Is that correct, or i miss something?

Crowley,

Seems like there is something amiss!!

When you model displacements , it is nothing but thermal growth of the equipment at the concerned temp.Mind you, but this is not a free end but has imposed displacements. I hope when you gave displacements, you didn't left rotations as blank (or else it will be considered free in calc). Ideally , you should put rotations also. If unavailable, put zero for a conservative approach ( though not always conservative in few cases).

What I understand from your quote is you want to perform wind analysis without modelling equipment.

Now the displacements you imposed are thermal & the equipment (say,tower or column)will have some deflection during wind i.e wind sway.

Calculate the displacements for this wind sway for the concerned nozzle or get in touch with equipment/Mechanical discipline or vendor.

Your load cases should look like

LC1- W+T1+P1 (Sus)
LC2- W+T1+P1+D1(Ope)
LC3- W+T+P+D1+D2+Win (Ope)

where D1-Thermal disp at temp
D2- Deflectiion of nozzle during Wind
Win- Wind vector in concerned direction

& other cases you may build accordinngly.

N.B: D2- is for wind effect on equipment &
Win- is for wind effect on pipe.

I hope this helps.

On a simpler note, this is something that I learned when playing around with floating anchors myself a while back.

If you define an anchor and then use a C-NODE to impart a displacement, it is important that you zero any of the displacement segments that you are not using. For instance, if you wanted to go 1.25" in the X and a rotation of 0.25" around the X, you would enter those in the X and Rx spots. But the rest of that column remains empty. If you leave it empty, Caesar will not treat it as a restriction! You have to specify zero displacement in every dimension you are not displacing.

Yes, that was the problem! When i fill the other cells with zeros - it is OK. Thanks you SJ and Clayton! Very clear answers

When you specify pre-defined displacements you need to evaluate what the displaced point really represents. If you're displacing a nozzle connection, then it is really a compeltely fixed point (all 6 DOFs are restrained in some manner). Without the displacements you would model this as an anchor - since this is a simpler form of input.

In general, to displace a boundary condition you only need to specify displacements, you don't have to specify a restraint, associate that with a CNODE, then displace the CNODE. Simply specify the appropriate displacements at the node and you're finished.

In the displacement fields, "blank means that DOF is free, zero means that DOF is fixed".

Examples:

1) A "Y" support with 0.5" of settlement: Model this as a displaced node (boundary condition): DX = blank - it's free, DY = -0.5, DZ = blank - it's free, RX = blank - it's free, RY = blank - it's free, RZ = blank - it's free.

2) A nozzle on a vertical vessle with 1/4" upward growth: Model this as a displaced node (boundary condition): DX = 0.0 - it's fixed, DY = 0.25, DZ = 0.0 - it's fixed, RX = 0.0 - it's fixed, RY = 0.0 - it's fixed, RZ = 0.0 - it's fixed.

Hi to all.

I would like to say hello to all here and to ask something regarding this subject.

When I have supports, and their anchors to the ground are a job for civil engineer in my company. Then I use CAESAR II to determine all the forces in that support which is start data for them. However, sometimes if the forces are big in ANC and the pipeline is at height of 2m (for example), then they have to have quite big foundations for those support.

Several times they asked me if it is possible to determine how much can I allow my anc to move because it would decrease their forces and moments to the foundations. And now, here I am.

I read this thread and that is what I need. However, I think I am missing something.

I modeled an simple pipe in caesar with points 10-20 & 20-30. I gave ANC at point 10 and ANC at point 30. Then I replaced ANC at point 30 with all displacements 0. I got the same results (as said in your posts above). However, when I tried to give an axial movement at point 30 (DX = 20mm) I got the same results (all the forces, stresses and displacements remained the same). Is this ok?

Because I expected some changes in stresses and forces. In practice it would mean that pipe and anc are moving together.

At least, I expected to see that DX of 20mm at point 30

Thank you in advance for your help,

Kind Regards

Check your load case definition, did you include "D1"?

Stupid. Yea... that was it.

Thanks a lot.

Kind Regards

No, not stupid - this is an easy mistake to make.