Force normal to surface during bending

Rahul_P1

Hi,

i´am dealing with a OptiStruct model performing a topology optimisation. The model can be considered as a cantilever beam with a force on one side and fixed displacements on the other side.

The following question came up to me: I want the force to be normal to the surface throughout the whole calculation/deformation.
How should i define my model to get this result? For know I used a PLOAD4, but i don´t know what happens to this vector throughout the calcuation!?

thanks for your help!
Thomas

Rahul_P1

Hi Thomas,

This kind of a follower force is generally done in a nonlinear analysis, You may have to set up the model for a non linear geometric analysis NLGEOM and then proceed with setting up the optimization entities.

First you need to create a follower coordinate system on a node at the end of the model, i.e. near to where the loads are applied. create from analysis>systems> create using node reference subpanel , (it has to be specifically from this panel to create the required cord3r system)
This creates a CORD3R system which whose orientation is determined by the position or displacement of the nodes which are used to form its axes.

To assign the loads on the end of the beam to follow the coordinate system, use the assign
subpanel. Change the drop-down selector to loads, select the loads With the system selector enabled, select the system created in the last step, and click set reference to associate the loads to the system. Click return to exit the panel.

On the Analysis page, use the loadsteps panel to create a loadstep of Type geometric nonlinear (impl static) with SPC set to the constraints load collector, LOAD set to the load collector with the force, and NLPARM set to the NLPARM load collector (created to control the non linear analysis) see help about the parameters to be entered in nlparm and how to do a nlgeom analysis.

See Training Altair University > STRUCTURAL > ANALYSIS > NONLINEAR STATIC > Beam comparison NLGEOM / NLSTAT where a nlgeom analysis is performed with a follower force.

http://training.altairuniversity.com/structural/analysis/nonlinear/beam-comparison-to-nlstat/

see also Training Altair University > STRUCTURAL > ANALYSIS > NONLINEAR STATIC > Compression of a Rubber Spring (NLGEOM)

and Altair OptiStruct > OptiStruct Tutorials and Examples > Tutorials > Large Displacement Finite Element Analysis:
OS-1500: Nonlinear Implicit Analysis of Bending of a Plate