tension simulation for networks

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microelly2
Posts: 4690
Joined: Tue Nov 12, 2013 4:06 pm
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tension simulation for networks

I'm looking for a ready to run method to simulate the tension forces in a rubber band network
the force is proportional to the lenght of a segment (hooke)

I pin some points (in the vide I use arcs to mark them)
the network is a sketch object with coincidence constraints only and the fixed positions of the pinned points.

phpBB [video]

is there a fem module and a tutorial how to get this running?
thanks for a tipp.
Posts: 1906
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: tension simulation for networks

Hi microelly2,
what you wanna do is a shape optimization of a tensile structure.
For engineers this is one of the toughest stuff you can do!
Good luck and some hints...
https://www.b-tu.de/great-engineers-lex ... rfindungen
Posts: 1906
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: tension simulation for networks

Hi microelly,
can you give some more explanation on the video?
If I understand the process correct, you use a starting grid and then
"relax" the grid. What is the criterion? To get the global minimum of the strain energy?
There is a state at 0:06 where two grid members in my opinion are under "pressure",
not tension. Otherwise there would be no static equilibrium possible. Is it a planar grid
or 3D? regards thomas
phase1.JPG (27.66 KiB) Viewed 1370 times
DeepSOIC
Posts: 7829
Joined: Fri Aug 29, 2014 12:45 am
Location: Saint-Petersburg, Russia

Re: tension simulation for networks

Sat Nov 11, 2017 5:28 pm
If I understand the process correct, you use a starting grid and then
"relax" the grid. What is the criterion? To get the global minimum of the strain energy?
To me it looks like an iterative process with fixed number of iterations, where on each iteration each point is moved along the net force vector.
microelly2
Posts: 4690
Joined: Tue Nov 12, 2013 4:06 pm
Contact:

Re: tension simulation for networks

DeepSOIC wrote:
Sat Nov 11, 2017 9:35 pm
Sat Nov 11, 2017 5:28 pm
If I understand the process correct, you use a starting grid and then
"relax" the grid. What is the criterion? To get the global minimum of the strain energy?
To me it looks like an iterative process with fixed number of iterations, where on each iteration each point is moved along the net force vector.
yes that's it at the moment. i calculate for each vertex the sum of all its edge vectors as force.
it is a 2D sketcher simulation because I want the easy way to add more constraints to the model.
bernd
Posts: 10973
Joined: Sun Sep 08, 2013 8:07 pm
Location: Zürich, Switzerland

Re: tension simulation for networks

Still I do not really understand what data do you input, and what you would like to analyse. Since it is sketch based I assume all members are in a plane. Furthermore rubber usually behaves highly nonlinear when leaving linear stress, strain range. In which range are you? Your edges are staight, but rubber usually has no bending stiffness. What do you assume?

Bernd
microelly2
Posts: 4690
Joined: Tue Nov 12, 2013 4:06 pm
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Re: tension simulation for networks

bernd wrote:
Sun Nov 12, 2017 12:42 pm
Still I do not really understand what data do you input, and what you would like to analyse. Since it is sketch based I assume all members are in a plane. Furthermore rubber usually behaves highly nonlinear when leaving linear stress, strain range. In which range are you? Your edges are staight, but rubber usually has no bending stiffness. What do you assume?

Bernd
in the simplest case the force is the hooke force if a line is longer than mk = 2,
its a simple linear model and can be changed later. if the length is less than 2 then there is no force.

Code: Select all

``````	f=0.01

for n in g2.nodes():

nbs=g2.neighbors(n)
v0=g2.node[n]['vector']

for nb in nbs:

mk=2
tf=g2.node[nb]['vector'] -v0
if tf.Length > mk:
fac= 1.0*(tf.Length-mk)/mk
tf=tf * fac
else:
r += tf

(a,b)=list(conix[n])[0]

rc=sk.movePoint(a,b,v0+ r*f,0)
g2.node[n]['vector2']=v0+ r*f
rc=sk.solve()
``````
regis
Posts: 721
Joined: Sun Jul 12, 2015 8:17 am
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Re: tension simulation for networks

microelly2 wrote:
Sat Nov 11, 2017 1:32 pm
I'm looking for a ready to run method to simulate the tension forces in a rubber band network
the force is proportional to the lenght of a segment (hooke)

I pin some points (in the vide I use arcs to mark them)
the network is a sketch object with coincidence constraints only and the fixed positions of the pinned points.

phpBB [video]

is there a fem module and a tutorial how to get this running?
thanks for a tipp.
cool stuff,
this reminds me of this

phpBB [video]

phpBB [video]
microelly2
Posts: 4690
Joined: Tue Nov 12, 2013 4:06 pm
Contact:

Re: tension simulation for networks

regis wrote:
Sun Nov 12, 2017 5:49 pm

cool stuff,
this reminds me of this
having some of the grasshopper features would be a nice thing.
I still look for a fast open source solution,
otherwise I will work on my slower version.
microelly2
Posts: 4690
Joined: Tue Nov 12, 2013 4:06 pm
Contact:

Re: tension simulation for networks

I used the idea of abdullah to describe a next dimension by a circle
to get an easy to run sketch configuration.

phpBB [video]