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

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

Postby josheeg » Wed Aug 08, 2018 2:59 am

Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows not responding. ??? :?: :geek: :ugeek:
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bernd
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Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Postby bernd » Wed Aug 08, 2018 7:03 am

Without any example file and with no FreeCAD version it is difficault to help you. Furthermore it would be interessting which FEM mesh obj did you use, Netgen or Gmsh.

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

Postby josheeg » Wed Aug 08, 2018 1:28 pm

Ok Freecad 0.17 stable release
windows 10
This is the assembly
frame_VTOL_Plane_union_analysis.FCStd
(227.32 KiB) Downloaded 16 times
I only seen tutorials in gmesh.
Attachments
cube_v_threaded_1_in.FCStd
(38.3 KiB) Downloaded 12 times
pcft__5_4_24_in.FCStd
(10.83 KiB) Downloaded 13 times
pcft_5_4_98_in.FCStd
(10.82 KiB) Downloaded 13 times
threaded_tube_connector.FCStd
(14.78 KiB) Downloaded 13 times
thschrader
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Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Postby thschrader » Wed Aug 08, 2018 5:01 pm

Hi josheeg,
loaded your vtol-model. The length is 5200 mm. Is that right?
You have only one FemConstraintForce-card. The total loading
is 1 N (=100 grams). That cant be true. As Harry said,
it is easier to use the old fashioned way. Calculate the tubes
by hand, calculate the cube-connectors with FEM. For the tubes,
you have only 2 different subsystems. FC_FEM is a very useful tool,
but I think in your case it makes no sense to waste hours of time, when you can
have a "paper-solution" within minutes.
regards Thomas
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josheeg
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Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Postby josheeg » Wed Aug 08, 2018 5:30 pm

The force on other systems is 3100 newtons.

1/16 of that 194 newtons

and 620 newtons would be tests I would wonder how the tubes would be effected.

the material properties would be
density
460 kg/mm^3
youngs model 34000000 psi
poisson ratio 0.20

How would I do the hand calculations?
mat.png
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thschrader
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Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Postby thschrader » Wed Aug 08, 2018 5:55 pm

josheeg wrote:
Wed Aug 08, 2018 5:30 pm
How would I do the hand calculations?
By using elementary statics. Please dont read that as an insult.
How should your end-model look like? What is your wish?
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HarryvL
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Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Postby HarryvL » Wed Aug 08, 2018 7:21 pm

@josheeg, it is actually quite difficult for us to see what you are trying to model. Would you have a picture (photograph) or sketch of what the physical reality looks like? What is this assembly representing in real life and what real- life forces are working on it? Weight or wind loading or what?? Where do the distributed loads originate from? It is only then that we can advise how to model physical reality and what approximations would be introduced by the model.
josheeg
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Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Postby josheeg » Thu Aug 09, 2018 4:57 am

:D :lol: I have been reading the papers on cross wind kite power systems. I found my 3d robotics drone kit was fun.
The pixhawk mini px4 has a VTOL plane configuration so I wanted to mount 4 motors on the 24" .5" tubes the carbon fiber props for drones I seen the largest were 30". Dragon plate carbon fiber tubes come in .5 inch with the connector system.
Flying foam had standard foam wing cores with two holes for tubes. They seam to be down so wecutfoam may be my go.

Cross wind kite power systems seem to have to be efficent, light strong, modular and large wings that can hold force.

So I wanted to model it so I felt comfortable putting that much electronics and things up in the air to try to make a windturbine.

VESC are regenerative speed controllers so when the drone is flying in its crosswind flight path the throttle command should go down and it should charge its batteries when tethered. 98x24" per wing
quadplanevtol.png
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HarryvL
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Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Postby HarryvL » Thu Aug 09, 2018 11:15 am

Oh it's an airplane frame :shock:

Just a few questions and observations then:

Where do you plan to attach your 4 engines?

How do you attach the wings and what is their composition?

In a conventional design the plane derives strength and stiffness from ribs, stringers and skin (like a thin-wall composite beam) or an monocoque stress-skin. Is it your intent that in your design the stiffness comes from a bending frame of 0.5" tubes?

Anyway, pending a better understanding of how your design works, I would in the first instance model your frame as simple beam elements (available in FreeCAD)

Where to apply static loads and supports depends on where your engines sit and the flight mode (lift off and landing vs horizontal flight). Also in a very skinny design (which you are aiming for (?) dynamic loads need to be considered.

Finally, you may well find that appurtenances (like the wings) provide much greater strength and stiffness than the skinny tubular structure itself.

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

Postby HarryvL » Thu Aug 09, 2018 8:32 pm

I had another look at your model and have the following observations:

Under the support and loading conditions you impose there are really only 2 types of behaviour possible:

1) No or very little deformation at all:
pcft_5_4_24_in_03 (fully fixed)
pcft_5_4_24_in_06 (fully fixed)
pcft_5_4_24_in_04 (in between fully fixed elements and not loaded)
pcft_5_4_98_in_03 (in between fully fixed elements and not loaded)
pcft_5_4_24_in_09 (only loaded in tension, no bending)
pcft_5_4_24_in_13 (not loaded)

2) Loaded as a simple cantilever in the x-z plane
all remaining elements.

The tip displacement of a cantilever under uniformly distributed load is u=q*L^4 /(8EI), where q=load per unit of length, L=length and EI=bending rigidity (see textbooks). You can verify that by modelling your system with simple 1-dimensional elements of equivalent EI to your tubes.

Modelling this with 3D elements is really not the thing to do.