FEA verification with hand calculations 3

[Student BE]

Hi,

many people advise to do hand calculations in order to verify FEA results at least approximately. Some even say that they always do these hand calculations. However, I Wonder how it is possible to do such calculations. I know that in static solid mechanics constructions can be simplified to basic elements: beams, bars, frames, trusses, plates, curved beams etc. But it's only possible in case of fairly simple shapes.

Also in other fields (for example buckling, modal analysis) there are some equations that allow hand calculations for specific problems.

But how to do these calculations for example in fluid dynamics ? Even square channel flow would be hard to evaluate. I doubt anyone uses Navier-Stokes equations in such cases.

And as an example of something hard to verify with hand calculations (going back to static stress analysis) can you say how to calculate this (obly the way to do it, without any numbers of course):

https://4437c3e4-a-62cb3a1a-s-sites...mJtPhZ_gBcgTs8ojBJ4-U3xwI3M15F&attredirects=0

or this:

https://keislerautomation.com/products/nanb-miata-front-lower-control-arms

and this:

http://pelecollins.com/f3-drag-racer/f3-fea/

P.S. From what I know it's not possible to use FEM in hand calculations of anything more complicated than simple bar or couple of beams so I guess it's not the way people do it.

 

[rb1957]

"how to simplify real structures to these basic cases" ... years, and years, of experience with successes and failures.

another day in paradise, or is paradise one day closer ?

 

[mats_lindqvist]

I usually check reaction forces, and that displacements are in the correct order of magnitude. This can be verified with hand calc's; free body diagram, displacement of a similar size but "simple" part. Also compare with handbook data for fillet stresses and measurements, if you have such data. If your part is constrained in a statically indeterminate manner, i.e. over constrained, you need to consider to include more of the structure in the analysis, include contacts etc. Sometimes the load history is not known, is such cases, strain gauge measurements are valuable.

Hand calc's is a basic check you don't have any unit errors, wrong constraints etc.