Guy on Simulink

Simulink & Model-Based Design

Flexible Bodies in SimMechanics

This week we see how to create flexible bodies in SimMechanics. For that, we will use techniques seen in previous posts like Building Models with MATLAB Code and Self-Modifying Subsystems.

Flexible Beam

The Lumped Parameter Approach

Using a lumped parameter approach, we can approximate a flexible body using a series of rigid bodies connected by springs and dampers. The material properties and the cross section of the flexible body determines the spring stiffness and damping coefficients.

Lumped Flexible Beam

The Fundamental Element

To begin, in SimMechanics, we create one element to be duplicated as many times as needed and store it in a library. For a beam bending about one axis, our fundamental element looks like:

One Element

Assembling the Beam

Now that we have one element, we can create a subsystem that will assemble as many elements as desired. Here is what the final result looks like:

Self-Modifying Flexible Beam

To implement this block, we follow the self-modifying subsystem workflow suggested by Seth in a previous post. In the Mask Initialization tab of the subsystem, we define a function that deletes the content of the subsystem and redraws it when needed.

Mask Initialization

To delete the content, we use delete_line and delete_block.

Deleting the beam

To redraw the subsystem, we use add_block and add_line.

Drawing the beam

The Result

Flexible bodies open a lot of possibilities. One of them is vibration analysis. With a beam composed of 25 elements, I have been able to observe the first three normal modes of the beam:

First mode
Mode 1

Second Mode
Mode 2

Third mode
Mode 3

Now it's your turn

Here are a few tips if you want to dig deeper in this area:

Try modeling flexible bodies in SimMechanics and let us know what you think by leaving a comment here.

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