ABAQUS 6.12 Fluid exchange with environment interaction requires two nodes? 2

[crustaccione]

I have a cylinder set up, and I want to model the leakage of the air inside the cylinder into the environment and monitor the pressure on the walls. Problem is, when I set up the interaction, I have an error of

TWO REFERENCE NODES MUST BE SPECIFIED ON THE DATA LINE OF THE *FLUID EXCHANGE KEYWORD

I have two interaction properties specified, namely the cavity in the cylinder with one reference point inside, as well as defined the internal surface of the cylinder. The other interaction property is the fluid exchange with the bulk modulus specified.

Problem is when I set up the fluid exchange interaction to 'with environment', there is no other place to specify a second reference node. I don't know how to get around this because I can't put two ref. nodes, and I get the error message if I don't.

Attached is the image of the interaction 'with environment'.

 

[crustaccione]

I've tried reading through the online manual but it says NOTHING about having two reference nodes. I really hope someone can help me out here.

http://127.0.0.1:2080/v6.13/books/usi/default.htm?startat=pt03ch15s13hlb10.html

 

[akabarten]

Hi,

For sure if you want to define fluid exchange between your fluid cavity and environment
you need to use only one reference node in *FLUID EXCHANGE keyword.

Check Abaqus documentation:
Abaqus Analysis User's Manual, 11.5.3 Fluid exchange definition, Flow between a single cavity and its environment.

User interface for fluid cavity in Abaqus/CAE is new. As I know 6.12 is first version with this feature.
Perhaps it is a bug in Abaqus/CAE. Try update your inputdeck manually with any text editor.

Regards,
Bartosz

 

[crustaccione]

Hi akabarten, thanks for your response.

I followed the user manual at every step, but it just doesn't mention anything about having two reference nodes. I'm thinking of just making a huge tank to act as the "environment" for now just so I can get the project moving along.

It doesn't help that the new interface for posting questions to Dassault is extremely un-user-friendly.

 

[IceBreakerSours]

As akabarten has mentioned, two reference nodes are not required in the fluid exchange keyword. Are there are two fluid cavities in your model?

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http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[crustaccione]

No, I know there's no two reference nodes required for environment interaction but somehow ABAQUS (I'm using 6.13) wants it. I uploaded a screenshot to show what's happening.

I have a fluid cavity inside a cylinder (Interaction Property cavity, Interaction first cavity), the fluid exchange with environment (Interaction Property exchange, Interaction Int-2). I don't have a second cavity (funnel cavity is suppressed).

In Interaction first cavity it only allows me to pick one Reference node, which is subsequently used in Int-2. I tried doing a fluid exchange interaction between two cavities (each with a reference Cavity point) and it worked, it just doesn't work for 'To environment' because I can't select two nodes.

I even tried creating a set with two reference nodes, but it doesn't show up in the list of eligible sets when I try to select a fluid cavity point in first cavity.

 

[IceBreakerSours]

Open the INP that you are running and check inside the INP how many *FLUID CAVITY, NAME=s you have.

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http://www.eng-tips.com/faqs.cfm?fid=376

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[crustaccione]

Here's from my input file:

** INTERACTIONS
**
** Interaction: Int-2
*Fluid Exchange, name=Int-2, property=exchange
_PickedSet42
** Interaction: first cavity
*Fluid Cavity, name="first cavity", behavior=cavity, refnode=_PickedSet42, surface=Part-1-1."cup inner surface",
ambient pressure=2e+07​

the refnode specified in *Fluid Cavity has only one node inside, as I explained before I can't make it show up when I pick a cavity point.

 

[akabarten]

Hi,

I was surprise a little bit your problem since I am using *FLUID EXCHANGE with one ref. node a lot at it always works.
I took a look for Simulia Knowledge Base and found bug report BR10000128140:

The documentation omits to state that the possibility to not specify the second reference point in the keyword *Fluid Exchange in order to simulate the fluid exchange between a cavity and its environment is not available in Abaqus/Standard.
The analysis generates the following warning message and produces incorrect results as if the keyword has been ignored:
***WARNING: TWO REFERENCE NODES MUST BE SPECIFIED ON THE DATA LINE OF THE
*FLUID EXCHANGE KEYWORD
The workaround is to explicitly define the second point.

THIS PROBLEM WILL BE FIXED ON SIMULIA Abaqus Unified FEA VERSION V6R2013x GA level.
THIS PROBLEM WILL BE FIXED ON SIMULIA Abaqus Unified FEA VERSION 6.13 GA level.
Additional Closure Information:
The warning message is changed in to an error in 6.13-1

So I am guessing you are using Abaqus/Standard where I am using Abaqus/Explicit.

Regards,
Bartosz

 

[crustaccione]

THANK YOU SO MUCH. I've been trying to search the knowledge base for a fix but I can't. I might have a copy of Explicit in my school's computer, I might try that later.

Otherwise, based on whatever I've done so far, should it theoretically work in Explicit?

 

[IceBreakerSours]

I do not see anything particularly odd in what you've done so far. Bugs are rare, but you certainly encounter them from time to time. Ask the Simulia guys if there is a bug fix available for download.

Are you new to this forum? If so, please read these FAQ:

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083