Zero fluid exchange when rMassRate is negative in the subroutine vufluidexch
 

I want to calculate an airbag (fluid cavity) inflating and deflating repeatedly. ABAQUS CAE can only finish a single state by setting mass flow rate or volumetric flow rate, inflation (negative value), or deflation (positive value). So I want to use the subroutine "vufluidexch" to realize it by setting the mass flow rate varying over time.

When verifying the subroutine, the rMassRate of the subroutine is set to a single positive value, and the result is consistent with the same positive value calculation in CAE.

But, the result shows that there is always no flow rate in the job of the subroutine with a negative value, which is the same as the job of zero flow rate. However, the CAE jobs of the same positive, negative, and 0 can give correct results and normal operations.

I want to ask how to solve the problem about this subroutine. No problem is found by checking the manual. The manual says, "rMassRate: mass flow rate. The mass flow rate is negative if the flow is into the primary cavity." in "Abaqus User Subroutines Reference Guide 1.2.17". So it seems like that we can realize it theoretically.

How can I manage to inflate and deflate one period in a job or a step?
Is there something I ignored in the manual? Or is it a version problem?

And please let me know if I missed something crucial or what I did wrong.
A particularly simple subroutine I used is attached.

Thank you!

hello, I come back to reply to this question by myself, there is a sentence in the manual:

"A positive mass/heat energy flow rate indicates flow from the primary fluid cavity to the secondary fluid cavity. A negative value for mass flow rate will be ignored if the fluid exchange is between a cavity and its environment." from Conventions for defining mass flow/heat energy flow rate in" Abaqus User Subroutines Reference Guide" 1.2.17.

absolutely I missed this important point. I will find another way to figure out my project.

thanks.