Abaqus and surface based cavities

[UMEngineer]

I've been tasked with creating a 3D model of a demo inflatable structure here in our lab. The goal is to inflate it in ABAQUS, and I have been making some progress in using the *FLUID CAVITY keyword. However I'm noticing odd things in my results. I have the pressure of the gas increase to 4psi in a tabular form, however as I watch the frame by frame, the stress concentrations on the structure vary oddly, and the model deforms oddly. Almost as if it was a ball being pressed back and forth against the floor, expand contract, that kind of deal. I'm not really sure what is causing it.

Another problem I seem to have, is a few jobs I run, the input file gets submitted and cleared, but ABAQUS never attempts to start ABAQUS/Explicit, it just sits there int he running state. When I monitor it, no signs of incrementation is occuring, however the process is running in the background, it happens on any new jobs I run since yesterday. Older saved .cae files work fine.

Last problem I'm having at the moment, is more of a how-to question. We want this model to inflate from 0psi to operating pressure, but I can't seem to figure it out in ABAQUS. I've read over the example file on the side impact airbag, but I can't seem to figure out how to get a reference mesh, and then the mesh of the folded structure.


If anyone can help, I greatly appreciate. I hate asking for help, but I've been stuck on this for a few long days. I can submit my input files if anyone thinks th at may help.

[Jorgen]

I have used *FLUID CAVITY a number of times without any problems. Have you tried to use Standard instead of Explicit? The problem that you described might be due to your explicit setup.

-Jorgen

[UMEngineer]

*FLUID CAVITY can only be used in Abaqus/Explicit, at least in 6.8.1. It is solving now, I believe due to improper defining of terms. The issue I've now come to is defining a reference mesh. A method to do that escapes me.

[geraldanyasodor]

Hi UMEngineer,

please I need help for the *Fluid Cavity Modell definition. Am trying to form a tube applying fluid cavity method (Abaqus v6.8.1).
Attached is my Input file, maybe one can figure out why it is not working or guide lines to modell fluid cavity.


Thanks all
gerald anyasodor

[UMEngineer]

What exactly isn't working, are there any errors associated with it? If I were to guess, I think it may have to do with your FLUID CAVITY definition, you have a lot of options in there, so it's very easy to write in a syntax error. When I get to a computer with abaqus, Ill see if I can try out your input file.

[geraldanyasodor]

Hi UMEngineer,

thanks for your reply,

I created the model in ABAQUS CAE; Part>Mesh>create Mesh>Orphan mesh>Edit mesh>offset surface....,then
instanced the orphan mesh in assembly, create sets, surfaces, step, boundary conditions and write the input file.

I now edit input file to define Fluid cavity,
*FLUID CAVITY, Name=Pneumatic_test, Ambient pressure=1.013250e05,
Ref node=Set-Ref_nodepkt, Ambient temperature=2.950000e+02,
Surface=Surf-cavity_Surf-cavity_SPOS, Minimum volume=INITIAL VOLUME,
BEHAVIOR=AIR, Adiabatic
**
*FLUID BEHAVIOR, Name=AIR
*MOLECULAR WEIGHT
0.0289
*CAPACITY, TYPE=POLYNOMIAL
28.110, 1.967E-3, -1.966E-9, 0.0

when the input file is imported back to ABAQUS;
1. if the fluid cavity definition is in the History Data region, the modell does not appear
2.if the fluid cavity definition is in the Model Data region, the modell does shows and with warning message:

Keywords/parameters *Fluid Behavior and *Fluid cavity in the input
file not supported by the input file reader when imported into Abaqus v6.8. This holds also for all Keywords;*Capacity,
*molecular Weight..etc. in the definition.

I cannot at the moment figure out if it is a case of faulty modelling or input file edition or both, hence would request
both consideration and help.

regards
gerald anyasodor

[Mr. Inventor]

I have also the need to modell a fluid cavity in Abaqus/Standard.

I need a way to create axisymmetric Fluid Elements in Abaqus/CAE.

[geraldanyasodor]

Hi Mr. Inventor,

Abaqus/CAE v6.8-1: you can modell fluid cavity only in 3D modeling space
and Abaqus/Explicit.
regards
geraldanyasodor

[geraldanyasodor]

Hi All,

would appreciate solution to the fluid cavity definition
error message by data check: NO DATA CARDS PROVIDED FOR * FLUID CAVITY

regards
geraldanyasodor