Hi to everyone!

I'm modeling some lines which are in a LNG plant on a ship. I've to consider structure displacements in vertical and in both lateral directions.
I've noted results aren't entirely right:
- considering only lateral displacements, in the proximity of each rigid restraints, Caesar calculates vertical forces due to pipe weight and also lateral forces due to friction (value=0.3).
-considering both lateral displacements and vertical displacement, Caesar doesn't consider forces due to friction and all values are null.

Why? I hope somebody can help me.

Regards

Italtecnica,

Your presentation of the problem is very weak and it does not properly explain the problem that you are facing. I guess you need to check your input and load combinations first or at least provide your input file to discuss on the forum.

Are the structural displacements sourced by the pitch and roll action on the ship?
So, I would consider those displacement on the occasional load cases. The Coade CAESAR II Technical Referance Manual Page 6-20 indicates that "If nonlinear effects are modelled in the system these combinations are not straight forward. ...... With nonlinear effects modelled in the system, the occasional deflections (and stresses) are influenced by the operating position of the piping."

I would say if the input is correct the results will be as you expect.
If you do not want everything public, provide all the information you have to Coade to discuss further.

Hope it helps.

Ibrahim Demir

I 'll try to explain in a better way.

I've to consider two primary things:
-inertial accelerations due to pitch and roll action on the ship, but I haven't to consider them separately. I have only one acceleration value.
-structural displacements, which are considered on operating load case, because the ship is constantly subjected to pitch and roll actions.

I've to consider also ship deflections due to hogging and sagging.

To model a rigid restraint,for lateral guide + vertical restraint, I am behaved in this way:
-lateral guide in Y direction with gap and with connecting node to input structural displacements
-vertical restraint in Z direction with friction (0.3) and connecting node to input displacements due to ship deflection
(ship deflection as an angle of 0.3 degrees)

Below is shown one of the operating case:
W+D1+T1+P1+U1+WIN1

where:
D1-structural displacements
U1-inertial acceleration
W-weight
T1-operating temperature
P1-pressure
WIN1-wind

Considering this, I expect to find in the report vertical forces,lateral and axial forces due to friction, but I see forces in Z directions due to weight, lateral forces in Y direction due to guide and axial forces which are null and it'is wrong for me.

I hope the explanation is completly now

Regards

For a restraint to "pick up" friction in CAESAR II:

a) the pipe must be in contact with the restraint - so a restraint with a gap that isn't closed won't see friciton

b) the friction multiplier (on the "Load Case Options" tab of the Static Load Case Editor) must not be zero.

The pipe is in contact with the restraint because I used restraint in Z direction (vertical) without gap, considering friction=0.3
In "Load case Options", the friction multiplier is 1.

So,what could be the problem? The description is correct; maybe Caesar isn't able to calculate vectors of forces due to friction out of horizontal plain

Regards

No that isn't the case. In CAESAR II, friction acts in a plane normal to the support direction.

Italtecnica,

Send your Caesar II file with an e-mail to techsupport@coade.com and I will take a look at it. I am confident I can review your file and describe the behavior you are seeing.

This may be worth posting here as someone else may have this question someday and can find it in a search.

The problem here was that vertical restraints with Cnodes had vertical displacements defined on the Cnodes, but no horizontal displacements (they were blank). Blanks in the displacement vectors indicate that the node is free, not fixed. Leaving the Cnode horizontal displacements blank will result in a frictionless support since the Cnode is free horizontally. Adding zeroes for the horizontal displacements fixes the Cnode horizontally, but does not fix the pipe node since there were no lateral restraints. This means that the pipe is able to slide against the Cnode with resistance due to friction.