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Node values vs element values

Question asked by Stefano Tiburzi on Sep 6, 2015
Latest reply on Jan 29, 2016 by Steven Soeder

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Hello everyone. A brief premise: as far as I know, both node values and element values are obtained averaging the Gaussian point of each tetraedrical element of the mesh model. Refining the mesh should result in converging of the maximum stress and displacemente for both visualization AND the reduction between the nodal maximum stress and elemental one.

The element values has the advantage of level the singularities due to a bad model while refinig is the leading process for the same goal in node values plot. There shouldn't be a "true" o "better" plot if I choose to use one or the other.

Now, this is my problem. After many attempt to have a converging analyis (h-adapative method went always in faling the mesh), I finally found a satisfying meshing for the plot but here is the downsize: maximum stress in element values is below tha yield stress (170 Mpa) and only in one ( ! ) element (circa 166 MPa), the maximum stress in nodal values is above the yield stress (226 MPa) in a small area, very negligible compared to the model.

What should I do or what would you do? Try to find an answer or a similar case to mine but I'm stuck in a crossroad no more knowing if what I'm doing is right or wrong. I'dd appreciate your help, please.

Thanks in advance.

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Stefano Tiburzi Sep 6, 2015 6:30 AM

A little update. With the same mesh size, I run a new analisys increasing the Jacobian nodes to 16. Here the results:

Element values plot

Element values section near the maximun stress:

Node values plot:

Node valus Iso clipping (170 MPa limit):

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Steven Soeder @ Stefano Tiburzi on Jan 29, 2016 9:20 AM

Disclaimer: I'm extremely green (read: n00b) when it comes to simulation, however I am working on a fairly complex analysis myself right now which has me studying a lot on adaptive meshing to better understand my own problems. My thoughts offered are simply my interpretation of what I've read on the subject and are not based on much experience.

One thing I'm a little confused on in your original statement was that you said that solving with H-Adaptive ON always failed.

You then said you finally found a solution that solved.

So, was this solution finally found with H-Adaptive meshing turned ON, or did you play with mesh controls manually until you got something that worked?

I'm just wondering, if you found it by manually playing with mesh controls - have you tried running another study with adaptive meshing since you got this solution?

Couple of questions on your adaptive mesh settings:

Have you tried bumping up the maximum loops for H-Adaptive?

What about decreasing the accuracy tolerance (e.g. to 90-95%)?

Have you played with the bias setting at all? Looking at the stress distribution in your screenshots, my first thought is that a fairly heavy bias toward localized accuracy would probably be acceptable.

Lastly, if your concern is specifically with the nodal vs elemental discrepancies, have you tried solving with the P-Adaptive meshing option?
I would think p-adaptive might help with this particular concern, as you may need better optimization of element shapes to get the nodal-elemental convergence desired.

Best of luck!!

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Stefano Tiburzi Sep 6, 2015 6:30 AM
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A little update. With the same mesh size, I run a new analisys increasing the Jacobian nodes to 16. Here the results:
Element values plot
Element values section near the maximun stress:
Node values plot:
Node valus Iso clipping (170 MPa limit):
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- Steven Soeder @ Stefano Tiburzi on Jan 29, 2016 9:20 AM
  Mark Correct
  Correct Answer
  Disclaimer: I'm extremely green (read: n00b) when it comes to simulation, however I am working on a fairly complex analysis myself right now which has me studying a lot on adaptive meshing to better understand my own problems. My thoughts offered are simply my interpretation of what I've read on the subject and are not based on much experience.
  
  One thing I'm a little confused on in your original statement was that you said that solving with H-Adaptive ON always failed.
  You then said you finally found a solution that solved.
  So, was this solution finally found with H-Adaptive meshing turned ON, or did you play with mesh controls manually until you got something that worked?
  I'm just wondering, if you found it by manually playing with mesh controls - have you tried running another study with adaptive meshing since you got this solution?
  
  Couple of questions on your adaptive mesh settings:
  Have you tried bumping up the maximum loops for H-Adaptive?
  What about decreasing the accuracy tolerance (e.g. to 90-95%)?
  Have you played with the bias setting at all? Looking at the stress distribution in your screenshots, my first thought is that a fairly heavy bias toward localized accuracy would probably be acceptable.
  
  Lastly, if your concern is specifically with the nodal vs elemental discrepancies, have you tried solving with the P-Adaptive meshing option?
  I would think p-adaptive might help with this particular concern, as you may need better optimization of element shapes to get the nodal-elemental convergence desired.
  
  Best of luck!!
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Node values vs element values

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