Learning Forum

[kmh7]

I was trying to simulate the expansion of a heart valve using LS-PrePost. The first step was to model the balloon inflation (no stent), and I used a linear_fluid keyword. The simuation runs until approximately 52% complete, after which the job terminates. No reason could be found for the termination within the message and .out files. A visualization of the job shows that the balloon appears to inflate to approximately half of its designated inflation volume. I used the same material properties for the rubber (though in ABAQUS I created a rubber with Density, Damping, and Elasticity, and the damping for an elastic material in LS-Dyna mentions only beam elements) that I did in ABAQUS. I modeled this using a fluid exchange property in ABAQUS, and had no issues. Any input would be greatly appreciated.

lsrun.stdout.txt

[Aniket Chavan]

Hello,nAnsys staff can not download images and attachments on the student portal, so if you want to reach a larger audience to get answers from, please insert higher resolution images inline.n-AniketnHow to access Ansys help linksnGuidelines for Posting on Ansys Learning Forumn

[Jim Day]

I can see there's a rapidly degrading (reducing) time step, which is often evidence of a growing instability.  The first things to try are:n - Use version R11.1.0 double precision rather than R11.0.0 single precision.n - Reduce the time step scale factor. If the default value of 0.9 is used, try 0.8 or 0.7.n - Since the analyst is using SMP, be sure they set ncpu to a negative value.n - Set ISNAN=1 in *CONTROL_SOLUTION to check for NaNs and write additional output when an NaN is sensed.nn Additional tips for approaching solution instability are provided in this text file ... nArrayIf you're using *MAT_ELASTIC for the rubber part, I would suggest you switch to *MAT_OGDEN_RUBBER.Jim Dayn

[kmh7]

nThank you. I am actually using fabric for that part. How does one change the analysis to double precision?.Also, I fixed that error and added the stent, and it now runs to 56% but terminates with an error of out-of-range velocities on the solid stent part. I modeled the stent with type 10 and added hourglass control type 4 (0.03), and have a negative minimum time step and added mass scaling. Any suggestions on how to fix that? n

[Jim Day]

To run a double precision analysis, you select an executable that has _d in the filename rather than _s. To confirm, the banner in your d3hsp output file will say if the analysis was single precision or double precision.nAn out-of-range velocity is just another symptom of an unstable analysis. Please refer back to the instability.tips mentioned in my last post.