karamba - parametric structural analysis

Comment

Comment by karamba on May 2, 2011 at 12:15pm

In Karamba all calculations are 3D. If you want to calculate a 2D truss you have to support all nodes at least against out of plane movements. The eigenmodes must exist: calculate the first ten or so and make sure that you set the displacement scale in the model view to a sufficiently high value.

There will be the possibility of prestressing the elements in future releases of Karamba. In the meantime try to apply pairs of axially directed forces at the endpoints of elements you want to lengthen or shorten.

If you want to simulate the effects of large displacements with Karamba you have to apply the external forces in steps: load the initial geometry with a small fraction of the eventual forces, take the thus deformed structure as the basis for another step etc.

 

Comment by Carlo Rousseeuw on May 2, 2011 at 10:27am

 

Thanks for the reply and information, however it is a 2D truss with the loads in the 2D plane, so normally it should be able to be analyzed as a truss ? When I calculate the eigenmodes they don't show up or don't exist, so i quess it is stable. Should I draw a 3D stable structure ?

 

Another question: Is there a possibility to add an initial strain on a member to simulate a pneumatic cilinder as a truss member ?

Comment by karamba on May 2, 2011 at 2:42am

Hi Carlo,

Your structure is probably kinematic. A truss element has only axial stiffness. A node in a truss structure therefore needs to be connected to at least three truss elements that do not lie in a common plane in order to be stable. See also section 4.8.1 "Bending stiffness" in the Karamba manual. You can check your structure for moveable parts by calculating its eigenforms: the first few eigenforms will be the kinematic modes.

Currently there is no direct way for obtaining stress or strain values - you can however compare the length of your truss members before and after deflection and calculate axial strains from that. Beware of the fact that Karamba is based on the assumption of small deflections: rotations entail length-changes which might spoil your calculations.

Comment by Carlo Rousseeuw on May 1, 2011 at 4:45pm

Wonderfull tool !

I'm trying to analyse a truss though:

If I adjust the boolean to False for "Beam Bending". The model doesn't analyze anymore. What am I doing wrong here ?

And is there a way to get the stresses or strains (values) in the beams or truss members ?

Thanks in advance !

 

Comment by Alessandro Liuti on April 11, 2011 at 2:41am

Hi, I need as soon as possible to use a simple finite elements solver, so I found an "escape plan" to make karamba work with Rhino sr 9 and Windows 7 64 bit. The solution is temporary and pretty drastic, but however works: I downgraded Grasshopper from 0.8.0007 to 0.8.0003, installed karamba 0.9.0., and turned 'memory load *.GHA on. I hope this is only a momentary solution, and I hope I've been useful to find a solution to the original problem, somehow.

Comment by David Shook on April 10, 2011 at 8:59pm

I have Windows 7 (64-bit), Rhino 4 SR9, GH 0.8.0007, Karamba 0.9.04 and have the same problem stated below by Alessandro.  It appears that the latest version of Karamba does not work with the current service pack of Rhino.  Grasshopper screen turns red as it did before.

 

This is a great plug-in and I hope Karamba can make a new version for this problem.

Comment by Robert Vier on April 8, 2011 at 11:46am

 

On Windows 7 64, Rhino4 SR8 it all works perfectly fine for me. Might be caused by the new Service release, think I'll try to reproduce this.

Maybe try installing different versions of .NET Framework (new version of GH uses 3.5 I think, but there also are 2.0, 4.0 ..)

 

Good Luck

Comment by Alessandro Liuti on April 8, 2011 at 11:15am

Hi, I have the same problem of many other users with karamba 0.9.04: GH 0.8.0007 + Rhino4 sr9 + Windows 7 64 bit -> error "fem.karambaPINVOKE".

I tried to fix it also by running "memory load *.GHA", but the error still persists.

 

waiting for a kind reply, thanks for the plugin.

Comment by Manuel on April 5, 2011 at 10:47am

Hi, i tried the new version 0.9.04 with grasshopper 0.8.0007, rhino4 sr8 and win7 x64, but im getting the 'rem.karambaPINVOKE' error in the analize component. I turn on the memory load in grasshopperdevelopersettings but doesnt work either.

please help, tomorrrow i want to show this to my students.

 

Thanks for your plugin.

Comment by David Shook on March 18, 2011 at 10:13am

FYI.  I tried Rhino SR9 with Grasshopper 0.8.0007 and Karamba 0.9.01 and received numerous error (screen eventually turned red).  I tired changing the 'memory load' options mentioned below, but no effect.  For now I have gone back to Grasshopper 0.8.0003.

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