Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows not re

About the development of the FEM module/workbench.

Moderator: bernd

Posts: 1768
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Hi josheeg,
I did a "quick and dirty" cfd-run, to get a feeling what forces are
put on the tubes
profile: span=2500 mm, length 1100 mm, thickness 140 mm
windspeed: 10 m/s = 36 km/h
drag-x=2,15 N (which gives cd=0,1)
total lift 145 N (both wings produce 29 kg lifting force)
For each wing-tube you should use a load of 145/2 /2,5=29 N/m
perpendicular to the wind direction.
wing_cfd.JPG (72.43 KiB) Viewed 614 times
velocity.JPG (23.7 KiB) Viewed 614 times
Posts: 1768
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

When looking at the pressure-distribution, there should be an additional
Moment. The left tube gets more load then the right one.
But how to get the momentum in paraview?
momentum_tubes.JPG (28.33 KiB) Viewed 611 times
josheeg
Posts: 82
Joined: Tue Nov 12, 2013 3:10 pm

Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Wow impressive analysis.
I got the 98 in tube with carbon fiber material under 100 newtons abs deflection. Does when it turns red show it will break?
Or when will it show signs and wear?
98flexunder100N.png (190.8 KiB) Viewed 591 times
If red means it will break the next shorter tube may need to be used because when a kite is setup in crosswind and tethered it gets more forces on it I don't think the wikipedia equation is right but here is my one page.
one page CWKP.png (76.76 KiB) Viewed 591 times
70-90km/h at 7m/s wind.
schupin
Posts: 400
Joined: Sun Jan 21, 2018 1:43 pm

Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Freecad won't show you if it break.
From a material point of view, you're modeling a very simple material behaviour : linear elasticity.

It means that the stress rises lineary when the strain increases. The slope of this beahoviour law is the Young modulus you entered.
In your FEM calculation, you never gave a "max strain" or "max stress" value. So FC won't know it for you.

In your case, you have to know when the linear behaviour ends.
If you look this picture :

(taken from here : https://en.wikipedia.org/wiki/Stress%E2 ... rain_curve)

Your model is valid if you stay in the first linear part of the curve (in blue). If you excess (for your material) this area, you're simulation will be meaningless.
So, in your documentation, perhaps you have a linear elasticity limit ?
If you find a stress or strain limit, you'll have to look on your results to see if you've passed this limit or not.
josheeg
Posts: 82
Joined: Tue Nov 12, 2013 3:10 pm

Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

600 ksi is that a unit it is in tensle strength. They have data sheets at dragon plate.
Will it compare with my analysis?
Screenshot_2018-08-23-02-22-54.png (345.75 KiB) Viewed 561 times
bernd
Posts: 10527
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

@schupin
very well explained
josheeg
Posts: 82
Joined: Tue Nov 12, 2013 3:10 pm

Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

I see in the wikipedia article

"This stress is called the tensile stress because every part of the object is subjected to tension. The SI unit of stress is the newton per square meter, which is called the pascal.
1 pascal = 1 Pa = 1 N/m2"

So I should be looking for pascal or N/m^2?
josheeg
Posts: 82
Joined: Tue Nov 12, 2013 3:10 pm

Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

600 ksi to ~4k Mpa
shown in this online calculator.
Then I looked at some of the different analysis results mesh radio button options for stress and the max seems well below 4k Mpa so it should not break under loading?
600ksitompadragonplatecf.png (778.84 KiB) Viewed 519 times
vonmasstressmpa.png (191.22 KiB) Viewed 519 times
maxprincipalstress.png (190.57 KiB) Viewed 519 times
maxsheer67mpa.png (227.49 KiB) Viewed 519 times
schupin
Posts: 400
Joined: Sun Jan 21, 2018 1:43 pm

Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Yes, it seems to be right.

As a first approach, you can look a the von mises stress and put the max value to 4GPa (or 4 000MPa).
If you see anything red, it means the the stress exceed your max value and it might break.

You might have to think about a "safety factor". Just for an idea, you can say that your limit is 0.8*4100MPa = 3250 MPa.
I started to read some interesting thing here that explains quite clearly these notions : http://feaforall.com/calculate-safety-factor/
bernd
Posts: 10527
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

- create a Vtk pipeline
- create a scalar filter
- set scalar clip options to van Mises stress
- set in result clip option to Surface with edges and van Mises stress
- set to your maximaum allowabalse stress

in the screen you see all nodes above 350 N/mm2 from the FEM 3D example and transparent all stresses.

Screenshot_20180823_231946.png (493.46 KiB) Viewed 495 times