Interconnection between non-linear analyses - Ansys APDL script

[RMANERA]

Hello, I need help with my script on Ansys APDL, if possible.

I'm working with two different loads applied to a tube and because of that I need to perform two non-linear analyzes (Geometrically and Materially non-linear Analysis with Imperfections - GMNIA) in sequence.
Basically I would like to simulate a bar of an offshore jacket type truss (annex), the structural elements are under lateral external pressure and soon after the equipment will be installed, introducing the effect of axial compression.

(i) First external lateral pressure
(ii) Second Axial Compression

In the case of simulation:

The first analysis will be the lateral external pressure, coming from the form obtained from the 1st buckling mode and the geometric and material nonlinearity will be added. My intention at this stage is just to obtain the deformation and stress arising from any pressure. The maximum value already determined in another analysis.
The second analysis will be in the sequence of the first analysis, however, the tube will be under the effect of axial compression and the procedure will continue until obtaining the last load.

I am not able to make this interconnection between the analyses. Any tips?

I have already try many ways, but didn´t worked.

 

[PedroCarneiro22]

Hello,

Did you try to use different load step in your analysis?

 

[RMANERA]

By Basic Analysis Guide:
Multiframe restart does not support the arc-length method (ARCLEN), reading and solving multiple load steps (LSSOLVE), or nested *DO loops.

That´s my problem, the arc-length method have no support to restart the analysis.

Thanks for your attention,

 

[RMANERA]

I didn´t understand what´s happen when I change the lateral external pressure (LEP) to axial compression (COMP).

The value of both SEQV are so different. As you can see, the value of "COMP" are downer than the LEP.

I think that this should to be the opposit.

What do you think about it?

 

[PedroCarneiro22]

It is difficult to have an opinion wihout have more information.
What are the element type you are using?
What are the loads and the boundary conditions?

 

[RMANERA]

Hi

Attached follows my script.

1) My last comment:
I didn´t understand what´s happen when I change the lateral external pressure (LEP) to axial compression (COMP).
The value of both SEQV are so different. As you can see, the value of "COMP" are downer than the LEP.

2)
I always got errors messages about some elements with excessive distortion.


Thank you for your atention

 

[PedroCarneiro22]

please try to rectify the annex i am not able to open it.

 

[RMANERA]

Done

 

[PedroCarneiro22]

If i understand correctly first you do a buckling analysis and after you use de deformed shape of the buckling analysis to start the other two simulations.
After you apply an eternal pressure in the elements of the tube and after a load in the Z axis in top and bottom nodes of the tube keeping the same boundary conditions through all the analysis and introducing the uncertainties in the material.
Is my interpretation correct?
What do you want to simulate with the load in the z direction keeping the same constraints of the other simulations?

 

[RMANERA]

I want to get the maximum value axial compression.


Attached is a figure on the general scheme

 

[PedroCarneiro22]

Sorry, i am not able to give you a definitive answer. Maybe try to change the way you impose the second load, try for example apply a distributed load in the line instead of load the nodes.

 

[RMANERA]

anyway thank you PedroCarneiro22

 

[PedroCarneiro22]

Do you achieved some progress meanwhile?

 

[RMANERA]

yes, two things were wrong

1) The arc-length method cannot be used in a multiframe restart. So, I stopped to use this method

2) After completing step 1 of the analysis, I was deleting the loads before starting step 2. I stopped deleting, and the results got better.


I call this script by STEPS



Attached follows my script.

 

[RMANERA]

Right now, I am performing a nonlinear geometric and material analysis on a tube with the application of two loads simultaneously.

I want to understand what the program does when I apply two loads simultaneously, and what are the differences between the method I called STEPS, as mentioned in my previous post.

For exemple, with the respective values:

PC = 150 kN (Axial Compression)
PP = 0,26 kN/cm² (external lateral pressure)

Below are the settings for the analysis in Ansys:

TIME,150
NSUBST,50,1000,10
ARCLEN,ON,25,0.001
ARCTRM,U,25,0,UX
AUTOTS,OFF

The relationship between the two loads are quite different.

What precautions do I have to take when working with more than one load?

When I applied TIME,150 what is the program procedure with PP loading?

Attached follows my script.

 

[PedroCarneiro22]

In principle, as referred in the other post you should not have significant differences if you run a static analysis with material properties that are not changing with time.