turn on suggestions

Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.

Showing results for

- Navigation
- Simcenter
- Forums
- Blogs
- Knowledge Bases

- Siemens PLM Community
- Simcenter
- CAE Simulation - Femap Forum
- Liner Static vs NL Static analysis thin plate

Options

- Subscribe to RSS Feed
- Mark Topic as New
- Mark Topic as Read
- Float this Topic for Current User
- Bookmark
- Subscribe
- Printer Friendly Page

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

09-10-2017 06:24 AM

Hello!

I am confused by the results of the analysis of a thin plate under its own weight.

E=21000 kN/cm

u=0.33

Plate 300х29cm with thickness 0.1cm

In liner static i have inadequate resalts, total translation 464.5 cm

In nonliner static its ok, total translation 1.118 cm

I understand that non-linear analysis typically reduces displacements, but not as much)

Please explain why I can not consider this task in a linear formulation and why this happens?

Solved! Go to Solution.

10 REPLIES

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

09-10-2017 07:27 AM

Hello!,

You are suffering stiffening effect, in linear static is totally ignored, but in nonlinear analysis this is detected as a geometric nonlinearity, please post your model and we will take a look to it, OK?.

Best regards,

Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

09-10-2017 07:54 AM

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

09-10-2017 12:31 PM

Post the model again, not available!.

Best regards,

Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

09-10-2017 01:40 PM

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

09-10-2017 02:32 PM

Not success, I don't see the file, make sure to ZIP the FEMAP file, also check that is set public, not private, for any reason your file do not appear visible to me ready to download.

Best regards,

Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

09-10-2017 03:57 PM

I have a bad day realy)

https://drive.google.com/open?id=0B4DAnh4O_N-zZUFKZi1lclJuOEE

Thank you for your patience!

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

09-10-2017 05:51 PM

Dear Kolotilov,

You are considering an extreme case, then the big differences found:

- The plate thickness t=0.1 is very low, compared with element size = 5.0, the ratio is 5/0.1=50, then the behaviour is extremely nonlinear by geometry, what you get here with a linear static analysis is useless. Please note you get a maximum resultant displacement of 465, when the thickness is 0.1 units, then NX NASTRAN is telling you that the problem is nonlinear, forgot linear static results, OK?.
- Also the plate is pinned at both ends, not fully constrained. If you run a linear static analysis and plot reactions forces using a FREEBODY diagram you will see only vertical reactions. Not lateral forces exist, than the assumption is reasonable, from the point of view of simplistic linear static analysis.

- But if you run a nonlinear analysis activating the geometric nonlinearities (large displacements effect + stress stiffening effects) and plot reactions forces you will be surprised to see the same vertical reactions forces of the linear static analysis, plus also HORIZONTAL reactions forces. But please note, the value of horizontal reaction forces is 2.2473/0.03294 = 68.2 times bigger than the vertical ones, how could it be if I only have a vertical load of gravity AZ=-1g??.

This nonlinear analysis consider the membrane forces of the shell elements, when the linear static analysis simply ignore at all. The plate is under dead gravity load, then is working in tension, so here we are the **stress stiffening effect**.

The term "**stress stiffening effect**" refers to a coupling between membrane stress and lateral displacements associated with bending. The bending stiffness of a beam, arc, plate or shell is increased by tensile membrane stress, and decreased by compressive membrane stress, ie, stress softening effect, ie, buckling.

**Stress stiffening effect is negligible for massive bodies**, but the example here is a extremely **thin-walled plate**, then the problem is extremely non-linear by geometry, understood?.

In summary, double-check your results always running both linear & nonlinear analysis, OK?.

Best regards,

Blas.

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

09-12-2017 01:38 PM

Thak you very match, Blas!

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

10-04-2017 04:55 PM

Follow Siemens PLM Software

© 2018 Siemens Product Lifecycle Management Software Inc