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Help needed with boundary loads in a valve

Posted 1 mar 2011, 19:43 GMT-5 Version 4.1 3 Replies

Dan Student
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Hello,

I am trying to evaluate the stresses present on the walls of a valve system. I have attached the model I am working on. It seems that no convergence can be reached. I was doing similar things in COMSOL 3.5a. Can someone assist me in how I can get this model to work.

I am just applying a force equivalent to a pressure of 190 psi to the walls, this can be seen in the attached file. This should not take long or be difficult, I just cant get it to work in the new version and my school deleted the old COMSOL.

Thank you for your time,
Daniel

Attachments:

3 Replies Last Post 2 mar 2011, 16:00 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 2 mar 2011, 02:21 GMT-5
Hi

first of all you should normally work in the first and 4th quadrant in 2D-axi = all to the right of the vertical axis, as "r" horizontal variable is normally always greater than "0" (r>=0)

Flip your geometry with a mirror transformation

Then apply your pressure as a "surface normal" pressure, change the "load type", you need only 1 "boundary load" independently in which direction the surface points out

Finally you might have a surprise in the dimension, you are in meters, is it really 3 meters high ? (Might be right ;)

--
Good luck
Ivar
Hi first of all you should normally work in the first and 4th quadrant in 2D-axi = all to the right of the vertical axis, as "r" horizontal variable is normally always greater than "0" (r>=0) Flip your geometry with a mirror transformation Then apply your pressure as a "surface normal" pressure, change the "load type", you need only 1 "boundary load" independently in which direction the surface points out Finally you might have a surprise in the dimension, you are in meters, is it really 3 meters high ? (Might be right ;) -- Good luck Ivar
Dan Student
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Posted: 1 decade ago 2 mar 2011, 14:21 GMT-5
Thank you Ivar,

I followed your suggestions...and changed the units... I still however am not able to reach a valid solution. I tried to add contact pairs, but when I went to put the contact boundary load I was getting errors that wouldn't allow me to place the pressure value. Again, I have attached the model. If there is anything else that you could tell me, I would greatly appreciate it. This is just so weird to me, as I could do this sort of simulation in 3.5 with ease.

Thank you for your help and time,
Daniel
Thank you Ivar, I followed your suggestions...and changed the units... I still however am not able to reach a valid solution. I tried to add contact pairs, but when I went to put the contact boundary load I was getting errors that wouldn't allow me to place the pressure value. Again, I have attached the model. If there is anything else that you could tell me, I would greatly appreciate it. This is just so weird to me, as I could do this sort of simulation in 3.5 with ease. Thank you for your help and time, Daniel
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 2 mar 2011, 16:00 GMT-5
Hi

well I have some problems too, to really understand your model. First of all you should not apply the pressure to internal boundaries where you have already applied continuity conditions, then I suppose you have some O-ring groves or something like that, so nornally your parts are not "welded" as they are now with the continuity condition.

If you remove the hollow regions and leave just the main cylinder boundary with a pressure it will start to solve, but it converges slowly, mainly because your fillets and sides link in with singularities where you have very high stress concentration values and these disturb the solver stability. You need to set at least 100 iteration on your solver (Fully Coupled 1 node) then you start to see some small "red" regions with high stress.

One difficulty is that if you apply an "assembly condition", it is not obvious (for the solver) how these parts would separate. You might need to consider several models with only a few parts starting with the "outer" shell, then adding other parts with the intermediate "chambers", Ibelieve you have some piston system in there so you might need to simulate the fluid withan ALE mesh and have the parts moving too

--
Good luck
Ivar
Hi well I have some problems too, to really understand your model. First of all you should not apply the pressure to internal boundaries where you have already applied continuity conditions, then I suppose you have some O-ring groves or something like that, so nornally your parts are not "welded" as they are now with the continuity condition. If you remove the hollow regions and leave just the main cylinder boundary with a pressure it will start to solve, but it converges slowly, mainly because your fillets and sides link in with singularities where you have very high stress concentration values and these disturb the solver stability. You need to set at least 100 iteration on your solver (Fully Coupled 1 node) then you start to see some small "red" regions with high stress. One difficulty is that if you apply an "assembly condition", it is not obvious (for the solver) how these parts would separate. You might need to consider several models with only a few parts starting with the "outer" shell, then adding other parts with the intermediate "chambers", Ibelieve you have some piston system in there so you might need to simulate the fluid withan ALE mesh and have the parts moving too -- Good luck Ivar

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