Karamba3D

Comment

Comment by madmax on October 16, 2011 at 8:58am

hey guys!

i want to try karamba example out of the manual, but analyze component turns red...

do you have any ideas where the problem is?

it would be nice if you could help me!

Comment by Karamba3D on October 13, 2011 at 12:58pm

Beams with bending switched off transmit normal force only. A node that connects to such elements has three degrees of freedom. In case of a planar truss add out of plane supports at all nodes (see also subsection 'Bending stiffness' of section 'How to change beam properties' in the karamba manual).

Comment by Joshua Seskis on October 12, 2011 at 8:43pm

Having some trouble getting a pinned truss to perform. It works if I allow the beams to bend but when its pin jointed it doesn't like it. Any ideas?

 

Arch%20Truss%20Karamba.gh

 

Is it because its trying to be pin jointed at the roller and pin supports? If so how do I remove that?

Comment by Joshua Seskis on September 29, 2011 at 10:33am

Here is some WIP to share:

 

Portal Frame Model

Portal Frame Model w/ Galapgos

CSV File for Sections

 

Deflections are not right at the moment but will sort them out tomorrow. Pretty happy with the models behaviour.

 

Comment by Joshua Seskis on September 29, 2011 at 8:31am

Any update on when the learning examples will be available? I feel like I just cant set up my modules right.

 

What type of accuracy or units do people work in for their Rhino file when they work with karamba?

Comment by Joshua Seskis on September 28, 2011 at 9:30pm

Ok here are the modules I have used to verify.

Karamba Cantilever

Egret Cantilever

 

I just built the same model in SG:

30m Cantilever

Incaste

2kN point Load at end

And drew the section in the section creator based on the Chinese steel manuals (S235).

 

Comment by Jon Mirtschin on September 28, 2011 at 1:44pm

Hi Josh,

 

Thanks for the confidence, but I would certainly double check anything computed by Egret (I haven't had the time or opportunity I'd like to progress and validate it).  I did quickly set up your verification model, the file can be downloaded here:

http://www.grasshopper3d.com/group/geometrygym/forum/attachment/dow...

I would suggest updating Egret from http://www.geometrygym.com/downloads , if you do, you should also see a deformation of 74.844504 (my gh definition assumes mm rhino document units).  If you want to send me the spacegass model, I'll take a look at it for you.

 

Comment by Karamba3D on September 28, 2011 at 9:34am

Here the definition:

Comment by Karamba3D on September 28, 2011 at 9:30am

Karamba uses a Young's Modulus of 21000[kN/cm2] and by default the thickness is 1/30 of the diameter of the tube. For D=100mm this results in t=3.33333 (etc.).

If you set both values according to the hand-calculation below you get the exact result of 74.844504m.

Comment by Joshua Seskis on September 28, 2011 at 7:13am

Haha good timing Luke!

 

I am writing a paper on Parametric structural analysis and just ran through all my analysers to see where I went wrong. I have it pretty much the same.

 

Example - CHS 100mm x 4mm

Deflection Calcs:

Manual - 64.6m

SG - 60.6m

Karamba - 61.5

Egret - 74.3

 

Now I am CERTAIN Egret is a result of a bug (I sincerely doubt Jon has made an error and it has been playing up on my computer probably because its full of shit).

 

I ran another model at 50mm depth of CHS to see if they maintain similar ratios. They do. I wanted to check that I could use Karamba and Egret for Galapagos modelling, so they are both pretty good.

 

Thank you for the check, its good to have a second set of eyes on problems like this.

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