For the Smart Geometry 2012 Workshop in February, David Shook prepared a brief introduction into Karamba and finite element analysis (FEA).
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Karamba is a finite element analysis (FEA) program like many others, but has novel application in the parametric environment for real-time structural analysis. The analysis automatically updates with any change to the grasshopper (GH) environment. Participants should review all noted resources. In addition to these a listing of key modeling points is provided below:
- Karamba only works in meters. If you use Karamba convert your Rhino units to meters.
- Karamba generates a structural analysis model based on the generated GH geometry. It only analyzes 2D lines.
- Curves and polylines should be exploded/converted into individual lines. Be sure all lines connect at points as intended. Often times this can be a difficult task as designers all too often are imprecise in the generation of geometry in the Rhino environment. We will be providing tools to assist in this.
- Surfaces cannot be analyzed by Karamba. It is possible to generally understand global surface behavior with a thoughtfully generated mesh, but this should be done with caution. A recent plug in called Lunchbox is helpful with this.
- Supports are critical for the understanding of structural performance. Be very careful in assigning what points will be supports and what motions they resist. Generally it is difficult to fully “fix” a support (i.e. Tx, Ty, Tz, Rx, Ry, Rz), it is generally best to only “pin” the support (i.e. Tx, Ty, Tz).
- Eigen mode analysis is a great way to understand your model without even knowing what the loads will be on it. Eigen mode analysis computes what are generally called ‘mode shapes’. A mode shape is a type of deformation that the model could experience. For applications we typically encounter the “first mode” is the most important as it describes the weakest ‘mode’ of deformation. The first mode is thus the weak deformation the global system can experience. It should be note that they are generally computationally expensive to computer so users shouldn’t leave the analysis block in the ‘Enabled’ state during routine GH work. Mode shapes are also a great way to ‘debug’ your geometry issues noted above in item No.1. If some lines are not connecting to points as you expect them to the line will typically ‘fly off into space’ in the first model and make is very clear what the connectivity issues are for your model. Once your connectivity issues are solved you should see generally global deformations as your first mode.
- The “LineToBeam” block is generally the first Karamba block as it converts a set of lines into points and ‘beams’. From this point on in Karamba it is not a line, but a ‘beam’. It is generally best to use the Pt outputted by the “LineToBeam” block from this point on as well as the “LineToBeam” block does merge notes within a prescribed tolerance.