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Hydrostatic pressure doesn't adapt the the rubber displacements

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Message 1 of 7
xavier.montalegre
536 Views, 6 Replies

Hydrostatic pressure doesn't adapt the the rubber displacements

Hi,

 

In my non linear analysis, I use hydrostatic pressures on a rubber element. During the simulation, the rubber moves, and the hydrostatic pressure doesn't change with the nodes new positions. Its value stays the same at each timestep, keeping the value of the rubber's initial position (even if follow displacement is ticked).

 

Could you help me with that please?

 

Xavier

6 REPLIES 6
Message 2 of 7

Hello Xavier,

 

You mention two things here.  Value of pressure and the pressure moving as part displaces.

 

The value of the pressure is controlled by the load curve.  If the value is not doing what you expect please check and verify the load curve.

 

If the direction of the pressure remains at the initial direction and does not adapt to the displacement of the rubber go to the definition dialog of the pressure and check the "Follows Displacement" checkbox.

Message 3 of 7

Hi Marwan,

The value of the hydrostatic pressure is like before (when you saw the
model yourself the other day), value from 0 to 1: 1 being the maximal value
defined on the hydrostatic pressure box. Follow displacement is also
checked.

A problem we haven't seen is due to the hydrostatic pressure in itself:

The hydrostatic pressure is applied on an initial element position. Then,
the nodes move, so do their altitudes. But if we inquire the loads at any
time, the hydrostatic pressure at a same node doesn't change, and keeps the
timestep 0's value.

As if the hydrostatic pressure doesn't consider nodes altitude changes. The
Follow displacement seems not to work.
Message 4 of 7

The load curve gives to the hydrostatic pressure the initial value.

 

Afterward, the fluid surface point doesn't gives to the hydrostatic pressure the new value at each timestep.

 

If I am not clear enough, i can send you picture of my problem.

Message 5 of 7

Hi Xavier,

 

I just did a test, and it appears that the pressure is updating as my body moves. See the attached animation. The length of the pressure arrows change as my part moves, and it comes to an equilibrium at a position that I would expect.

 

Is your analysis setup for "large displacement" or "small displacement"? This is a setting under the Element Definition for each part.

 

I do see one problem in the Results environment. You can select a load and inquire on its value, but the window is showing the magnitude as "nan" (meaning that it does not know what the value is). Otherwise, it looks okay to me.



John Holtz, P.E.

Global Product Support
Autodesk, Inc.


If not provided already, be sure to indicate the version of Inventor Nastran you are using!

"The knowledge you seek is at knowledge.autodesk.com" - Confucius 😉
Message 6 of 7

Hi John,

I defined my element as a hyperelastic-Moonley Rivlin material, and I have
no choice to use Large Displacement analysis (I can't change this option).

So if you are telling me that the "inquire loads" show the wrong value, how
can I check the "updated" value?
Message 7 of 7

Hi Xaivier,

 

I should have mentioned that I am using Sim Mech 2017. What version are you using?

 

In one of your posts, you mentioned that the pressure was not updating. How do you know the pressure value is not changing?

 

Can you attach an archive of your model? Or at least some images to show what is happening with your model.

 

 



John Holtz, P.E.

Global Product Support
Autodesk, Inc.


If not provided already, be sure to indicate the version of Inventor Nastran you are using!

"The knowledge you seek is at knowledge.autodesk.com" - Confucius 😉

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