Different result with linear and quadratic mesh
- Marcelo
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15 years 4 months ago #2705
by Marcelo
Different result with linear and quadratic mesh was created by Marcelo
Hello
I´m analyzing a structure with Salome version 3.2.9 and I got a huge difference on the results depending of the mesh used. The meshes were tetrahedron linear and tetrahedron quadratic, but all the others hypotheses are the same. The structure is a conical inverted pyramid, the internal faces are loaded with pressure of 0.15 MPa and the top face is fixed. The max stress found in quadratic mesh was 1.07e+03 MPa and in linear mesh was 65 MPa. I´m quite new in FEM and I don’t know what is the correct one.
1) What should I believe (linear or quadratic)?
2) Why are the results so different?
Thanks in advance.
I´m analyzing a structure with Salome version 3.2.9 and I got a huge difference on the results depending of the mesh used. The meshes were tetrahedron linear and tetrahedron quadratic, but all the others hypotheses are the same. The structure is a conical inverted pyramid, the internal faces are loaded with pressure of 0.15 MPa and the top face is fixed. The max stress found in quadratic mesh was 1.07e+03 MPa and in linear mesh was 65 MPa. I´m quite new in FEM and I don’t know what is the correct one.
1) What should I believe (linear or quadratic)?
2) Why are the results so different?
Thanks in advance.
- kwou
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15 years 4 months ago #2706
by kwou
Interest: structural mechanics, solar energy (picture at 'my location' shows too little pv panels)
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kind regards - kees
Replied by kwou on topic Re:Different result with linear and quadratic mesh
Hello Marcelo,
hard too say what to believe. Can you attach you comm and med file so we can have a look?
kind regards - kees<br /><br />Post edited by: Kees Wouters, at: 2009/03/19 20:18
hard too say what to believe. Can you attach you comm and med file so we can have a look?
kind regards - kees<br /><br />Post edited by: Kees Wouters, at: 2009/03/19 20:18
Interest: structural mechanics, solar energy (picture at 'my location' shows too little pv panels)
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kind regards - kees
- Boloni
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15 years 4 months ago #2707
by Boloni
Replied by Boloni on topic Re:Different result with linear and quadratic mesh
What's the fineness of your linear mesh ? Try to diminish the mesh size and run a simulation again. I had the same problem and the answers I got were: use hexa or quadratic elements
- Marcelo
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15 years 4 months ago #2708
by Marcelo
Replied by Marcelo on topic Re:Different result with linear and quadratic mesh
Here are the files
- drawing: moega.stp
- tetrahedron linear: linear.med and linear.comm
- tetrahedron quadratic: quad.med and quad.comm
if I have to post others files tell me
the pyramid has square of 10650 mm on top and ~550 mm on button with 5075 mm of height. Unit of force is N and pressure is MPa
the material is steel (E = 210e3 MPa and Nu = 0.3)
for both meshes use the hypotheses of average length = 800 mm
I have problem to use a smaller mesh size, because of "lack of memory"
I wrote wrong the max stress, in fact it is 69.2 MPa in linear and in quadratic is 493 MPa
Thanks for the answers
- drawing: moega.stp
- tetrahedron linear: linear.med and linear.comm
- tetrahedron quadratic: quad.med and quad.comm
if I have to post others files tell me
the pyramid has square of 10650 mm on top and ~550 mm on button with 5075 mm of height. Unit of force is N and pressure is MPa
the material is steel (E = 210e3 MPa and Nu = 0.3)
for both meshes use the hypotheses of average length = 800 mm
I have problem to use a smaller mesh size, because of "lack of memory"
I wrote wrong the max stress, in fact it is 69.2 MPa in linear and in quadratic is 493 MPa
Thanks for the answers
Attachment moega.gz not found
- Alessandro
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15 years 4 months ago #2709
by Alessandro
Replied by Alessandro on topic Re:Different result with linear and quadratic mesh
Look at this discussion:
caelinux.com/CMS/index.php?option=com_jo...;id=2529&catid=4
I found the same difference and Joel Cugnoni answered to me to forget to use linear meshes for structural problems.
caelinux.com/CMS/index.php?option=com_jo...;id=2529&catid=4
I found the same difference and Joel Cugnoni answered to me to forget to use linear meshes for structural problems.
- Marcelo
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15 years 4 months ago #2710
by Marcelo
Replied by Marcelo on topic Re:Different result with linear and quadratic mesh
Hi Alessandro
Thanks for the attencion. I´ve already seen your topic, but in your case the error is 12% and I foud more than 7x in the results of stress.
Anyway should I use only quadratic on structural problems?
If i could get a smaller mesh the results would be more similar?
Thanks for the attencion. I´ve already seen your topic, but in your case the error is 12% and I foud more than 7x in the results of stress.
Anyway should I use only quadratic on structural problems?
If i could get a smaller mesh the results would be more similar?
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