Cable simulation, Boundary conditions

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Permalink Reply by Panagiotis Michalatos on July 19, 2012 at 9:28am

In general you cannot do cable simulations in millipede. Millipede is based on Static analysis [small displacements, rigid assemblies of beams, columns truss like structures and shell elements ]. Any non linear effects that involve large deformations require dynamic simulations. For example as long as a cable is under tension you can treat it as a truss element however when one cable collapses all simulation results are unreliable. Even commercial engineering software makes it difficult to analyze tensegrity structures for example. You can "fake" the analysis of some tensegrity structures in static analysis software [IF you are sure they are correctly designed [not about to collapse on themselves] and are in equilibrium they are in the small displacement regime and don't require dynamic analysis] but these types of analyses do require rather specialized knowledge. 

In addition millipede assumes that all connections between frame elements are moment joints [a cantilevering beam connected to a column won't just drop but will bend and transfer some bending action to the column too]. Cables and trusses assume pin joint conditions between elements [free rotation around all axes] but these systems too require dynamic analysis when they are under-constrained, as is the case if there are non rigid assemblies [not thoroughly triangulated]. That's why the ability to release the end nodes of beam elements was not added to the millipede interface.

Permalink Reply by Vangel Kukov on July 19, 2012 at 10:35am

Thank you for your reply.
I read that prestressed cable structures can be simulated as linear elements in static analysis and I though that I can set the degrees of freedom of a Frame element with the Support type component but it's obviously not that simple.
Thank you again for your instant reply.