Learning Forum

[Diane]

Hello,

I am running a static structural simulation of an animal's upper airway. I am applying a pressure on the airway walls and I am checking at which pressure the walls come into contact using the Contact Tool (Gap) in the solution. For more details about the model please refer to the discussion below.

Hello,

My model is a 2D cross section of the upper airway as shown in the image below (constrictors to the left and hard/soft palate to the right).

I am applying a negative pressure normal to the inner walls of the airway, pushing the walls to move towards each other and the airway area to decrease gradually (the model is static). An example of total deformation is shown in the image below.

The objective is to determine the pressure at which the airway collapses which means that I would want to determine the pressure at which the opposite airway walls touch or are very near (distance between walls is smaller than a specified threshold). The contact between the opposite airway walls is frictional, the pressure is ramped and the analysis is split into 15 initial substeps.

I am currently using the contact tool (status) to approximate the time at which the walls touch and then checking to which pressure this time corresponds but it is very rough and doesn't seem correct. Is there a way I can get the exact value of pressure at which the airway walls come into contact for the first time?

Best regards,

Diane

[Diane]

Hello again, nI thought it would be helpful to add some screenshots of the Newton Raphson Residual Force. nn nBest regards, nDiane n

[Gary_S]

In the solve.out, it tells why the solution has stopped. n ************************************************************************n The number of ERROR and WARNING messages exceeds 10000. n Use the /NERR command to increase the number of messages. n The ANSYS run is terminated by this error. n ******************************************************************nnIf you look further up in the solve.out, I see this same warning repeating over and over...n *** WARNING *** CP = 18.453 TIME= 13:03:08n SURF153 element 14344 has more than one solid element underneath it. n Since KEYOPT(3) = 10, this element will be dropped. nnWhen you increase the number of substeps, this error is then issued many more times (per substep), and the solve is stopped.nnAdjusting the number of errors/warnings with /neer is not a good idea at all.nWe need to find out why the warning is being issued, and resolve it. nIt seems like you may have multiple boundary conditions applied to the same feature.

[Diane]

Hello Gary, nThank you for your response. nIs there a way I can get more details on this warning that keeps repeating? Can I know which is SURF153 for example? nBest regards, nDiane n

[Gary_S]

I cant be 100% sure, but here are some clues:nThe warning SURF153 element XXX has more than one solid element underneath it. .  seems to indicate that you have applied a load at nan intermediate surface between bodies. Imagine a simple 2 cube model with contact between the cubes, then also applying a force on the mating contact face. nWe need to find the element numbers that are affected. nProcess of elimination would be my first suggestion. Try the run with minimum boundary conditions. (Like a fixed support and a pressure). Add/suppress conditions/contacts/parts back in until the warning recurs.nAnother method:The warnings give an element number. You can use the Named Selection worksheet the select an element by number or range of numbers.

[Diane]

Hello Gary, nSorry for the delayed reply. Thank you very much, your comments were really helpful. nFor now, I got rid of the issue by just increasing the number of warnings or errors with the /NERR command but I will look into getting rid of the warning later when I optimize the model. nThanks again! nBest regards, nDiane n