{"id":3668,"date":"2014-05-22T09:27:27","date_gmt":"2014-05-22T14:27:27","guid":{"rendered":"https:\/\/blogs.mathworks.com\/seth\/?p=3668"},"modified":"2014-05-22T09:27:27","modified_gmt":"2014-05-22T14:27:27","slug":"flexible-bodies-in-simmechanics","status":"publish","type":"post","link":"https:\/\/blogs.mathworks.com\/simulink\/2014\/05\/22\/flexible-bodies-in-simmechanics\/","title":{"rendered":"Flexible Bodies in SimMechanics"},"content":{"rendered":"\r\n

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

\"Flexible<\/p>\r\n\r\n

The Lumped Parameter Approach<\/strong><\/p>\r\n\r\n

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.\r\n\r\n

\"Lumped<\/p>\r\n\r\n

The Fundamental Element<\/strong><\/p>\r\n\r\n

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:<\/p>\r\n\r\n

\"One<\/p>\r\n\r\n

Assembling the Beam<\/strong><\/p>\r\n\r\n

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:<\/p>\r\n\r\n

\"Self-Modifying<\/p>\r\n\r\n\r\nTo implement this block, we follow the self-modifying subsystem<\/a> workflow suggested by Seth in a previous post<\/a>. In the Mask Initialization tab of the subsystem, we define a function that deletes the content of the subsystem and redraws it when needed.<\/p>\r\n\r\n

\"Mask<\/p>\r\n\r\n

To delete the content, we use delete_line<\/tt><\/a> and delete_block<\/tt><\/a>.<\/p>\r\n\r\n

\"Deleting<\/p>\r\n\r\n

To redraw the subsystem, we use add_block<\/tt><\/a> and add_line<\/tt><\/a>.<\/p>\r\n\r\n

\"Drawing<\/p>\r\n\r\n\r\n\r\n

The Result<\/strong><\/p>\r\n\r\n

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

First mode
\r\n\"Mode<\/p>\r\n

Second Mode
\r\n\"Mode<\/p>\r\n

Third mode
\r\n\"Mode<\/p>\r\n\r\n

Now it's your turn<\/strong><\/p>\r\n\r\n

Here are a few tips if you want to dig deeper in this area:<\/p>\r\n\r\n