Monday, 6 June 2011

Grasshopper GSA Form Finding Examples

I sat in on the recent Oasys GSA webinar on form finding conducted by Pete Debney, for those that missed it, don't despair.  A recording of it, as well as the presentation and example models can be found here:

I think it's a great resource and introduction/explanation of some of the form finding options provided by the Oasys GSRelax solver.

I also think each of the 3 example models are well suited to a parametric exploration using Grasshopper (using the Geoemetry Gym plugin to exchange the model data with GSA), and I'm posting these definitions here so you can try for yourself.

The gsa relax solver is not included in the standard evaluation license, but you can email them and ask for access to it.  I'm still enhancing the plugin in a few areas, you might see toolbars wander if you run GSA as a background service (ie if you don't have GSA running when you open the grasshopper definition, the plugin will start it in the background for you).  If you do have GSA open and Grasshopper appears to "freeze", activate GSA and close any confirmation dialogs that might appear.

Generating the model with geometric shapes using  BullAnt will be enhanced shortly, as well as any user requests so send them through.  Make sure you have latest GSA and BullAnt plugins from here: and the definitions are derived on the basis of a rhino document being open with metre units.

Force Density form finding of a cablenet bridge.  Grasshopper Definition

Compression Shell form finding using Analysis properties.  Grasshopper Definition

Soap Film form finding of tensile membrane with back stay  Grasshopper Definition


  1. Hi,

    Have downloaded the three Grasshopper Definitions as well ass the required ssiGSA and StructDrawRhino and has got a license.

    But when I run the file I get errors like 'The archive contains an unrecognized object: sdrConnectCurves'.

    Any suggestions of what to do?


  2. Hi Alex,

    That message suggests the version of StructDrawRhino installed is earlier than the version when I implemented that function.

    Please note when updating you need to ensure a compatible version of Grasshopper is installed (typically 0.8.009 or newer, although a "breaking" version will be uploaded shortly), and that you update all installed Geometry Gym plugins (otherwise if versions are incompatible it can crash Rhino when starting). If you have problems, please email me and I will help.



  3. Dear Jon,

    I'm really new with StructDrawRhino and Grasshopper (using it for two weeks). I am trying to build a sort of template for a simple hypar membrane structure using the form finding options in StructDrawRhino.

    I downloaded the soap film form finding example to see how your program is working exactly with force density options. When I opened the file, I found out the half is missing (maybe because it is made in an older grasshopper version?). Is it possible to load up this file again? I really like to see an example of using StructDrawRhino for form finding.

    Thanks in advance,

  4. Hi Wouter,

    I only have some basic solver options in StructDrawRhino (force density relaxation and mesh inflation). I started developing a plugin Egret, but a lack of time is preventing it advancing. There reason most of the definition is missing is because you don't have the GSA plugin installed (

    These examples call on the Solver engine of Structural Analysis software GSA from Oasys. It used to be free for students, but there is a 30 day evaluation version. These particular examples use the GSRelax solver and you will have to email Oasys to request this. Hope this helps, Jon

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