Grasshopper

algorithmic modeling for Rhino

Attached below is the example file shown in this image I posted a while back:

http://www.grasshopper3d.com/photo/soap-film-elements-and-geodesic-...

The soap-film 2d triangular element properly discretizes the area continuum forces, so they are independent of meshing density, unlike simply using a network of 1d springs.

The warp and weft stresses can also be set separately allowing greater control of the shape (making them equal will give minimal surfaces).

Because the soap film elements alone do not have any in-plane stiffness, it can often be useful to have some spacer elements to keep the nodes well distributed.

Also, if mesh edges follow geodesics on the surface, it helps keep the strips straight when unrolled, allowing more efficient use of material.

The G-string component can be used for both - keeping the nodes well spaced, and aligning edges with geodesics. It pulls each node toward a combination of its neighbours, but taking only the part of the force tangential to the surface, so it does not interfere with the shape of the surface, only affecting how the nodes are distributed on it.

The "GeoIndex" input lets you choose which neighbours will be used here. In this example, a quad mesh is used, and index 0 and 2 give the neighbours in the warp direction, while 1 and 3 are in the weft direction. Note that it is the triangulation of this quad mesh that is used for the actual soap-film elements.

There is also a "spacing" option. If this is true, the nodes will try and space out evenly along the geodesic, while if it is false, only the direction is affected. In this example it is set to false for the warp and true for the weft.

The example also includes use of the stripper and unroller components to get the flat strips. I have shown the result of splitting in either direction, and as you can see, only one of these is straight.

Finally, if all of this sounds overly complex, don't worry - for quick studies you can still use the simpler approach of just turning all edges of a mesh into springs, and provided you have a decent starting mesh, the result will be very similar to using the 2d element method given here. This is just provided for those that want to take things to greater degree of accuracy and further towards fabrication.

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Thank you very much for this explanation Daniel, I'm going to try your amazing components again:) The axample put a big smile on my face, look   --->   :)

Thanks Daniel for this example, this is really great work you've done.

The G-string component works well - but I've noticed only with soap film elements.

Any suggestions if I have a pattern of geodesic curves on a surface and want to relax them a bit?  I want to find a happy medium between pure geodesics and equally spaced curves lying on a surface.  The geodesics help minimise major axis bending in straight cladding elements, while the equal spacing is more aesthetically pleasing.  The cladding elements I'm dealing with can handle some major axis bending - hence wanting to find a happy balance.

The g-strings are only needed when you are relaxing the form while simultaneously relaxing the node distribution on that surface.

If you have already fixed the shape it is actually simpler -you can use PullToMesh to keep nodes on the surface, and either bending or zero rest length springs to straighten them out and make them geodesic.

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