How does the General Flexible Beam block work in Simulink

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Avi Rudich
Avi Rudich on 3 Dec 2020
Edited: Pratheek Punchathody on 15 Feb 2021
I've been using the General Flexible Beam block in simulink to try to figure to model a flexible robot, but it's been a nightmare trying to validate it. It is basically a black box with no available information. The documentation for the block is here: https://www.mathworks.com/help/physmod/sm/ref/generalflexiblebeam.html It doesn't specify what beam bending model they are using or how the motions are calculated.
The flexible beams in my model are solid rectangular prisms. When I double the width of the beam, it seems to bend exactly the same amount. The only parameter that seems to really affect my result is the Young's Modulus. There is a value for discretization, which defaults to 1. In most beam bending models, discretization is the number of rigid components that form the beam, but in this case discretization = 1 is still a beam made of many components. The visualization for the beam doesn't change when I raise the discretization (I don't see smaller rigid components).
I also have a problem with excessively slow simulation (only sometimes). It gets really slow when the beam doesn't bend very much during the motion of the robot. My theory is that the solver uses smaller timesteps because the main motions are small harmonic oscilation of the beam (or something like that).
Is there an article somewhere that explains how this block works in detail? Is there any good alternative flexible beam model to use?
I tried the lumped parameter model I found here: https://www.mathworks.com/matlabcentral/fileexchange/47051-flexible-body-models-in-simscape-multibody, which is easier to understand, but I gave up on this model because my simulink model failed to assemble for high levels of discretization, but was able to assemble for low levels of discretization. Raising discretization should only increase the accuracy of a model.

Answers (1)

Pratheek Punchathody
Pratheek Punchathody on 15 Feb 2021
Edited: Pratheek Punchathody on 15 Feb 2021
The General Flexible Beam block models a slender beam of constant, general cross-section that can have small and linear deformations. These deformations include extension, bending, and torsion. The block calculates the beam cross-sectional properties, such as the axial, flexural, and torsional rigidities, based on the geometry and material properties that you specify.
Refer to the documentation on General Flexible Beam which explains about Slender extrusion with elastic properties for deformation.

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