CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   Main CFD Forum (http://www.cfd-online.com/Forums/main/)
-   -   Simple 1D Stress FE Model (http://www.cfd-online.com/Forums/main/74062-simple-1d-stress-fe-model.html)

Jonny6001 March 23, 2010 17:15

Simple 1D Stress FE Model
 
Hello, I am reading a book about finite elements with regards to stress analysis. I'm pretty sure the book is full of mistakes, which makes following and doing the examples fairly difficult.
I have posted a 1D analysis from the book, I'm not even sure how he comes up with some of the numbers in the calculations.

I do understand the method but what hasn't exactly "clicked" is the sign convention or the displacement of each node equating to the change in element length. The author has (u1-u2), then on the last element he switches to (u4-u3), is there a reason for this or is it because u4 is the last node?

Would someone mind having a really quick look at the images I posted to give their oppinion. But definetely his answers do not satisfy the simulataneous equations.

Thanks a lot for your time.

http://img2.imageshack.us/img2/3816/scan0001xo.jpg
http://img203.imageshack.us/img203/8407/scan0002r.jpg
http://img242.imageshack.us/img242/3311/scan0003e.jpg
http://img43.imageshack.us/img43/5510/scan0004al.jpg

meb March 25, 2010 06:22

FEM beams
 
Hi Jonny,
just a quick glance to the rod in compression (I'm sorry but I haven't time to go in the details of formulas, especially for debug an error!).
If you are interested in beams I have developed a solver. First for FSI of cantilever beams in 2D and then a general one valid for 3d space frame.
You can take a look to this paper (in Italian) http://www.pcm.unifi.it/Aias/XXXI_CO...TI/PDF/149.pdf.
I have also a MathCAD worksheet implementation for 3d space frame (but I still haven't published a pdf version on the web); the version valid for plane stress is here: http://www.uniroma2.it/didattica/TCM..._piano_TCM.pdf.
We have also used 3d beam in FSI in the past: in this case you have to create an interface between the FEM nodes at the centre of the cross section and the CFD nodes on the actual skin.

MEB


All times are GMT -4. The time now is 21:40.