Flexible strips in Simscape Multibody

As part of a school project, we want to model a flexible solar sail. The sail contains 4 flexible strips that allow it to fold in on itself and unfold at will, like window shutters. The strips must be perfectly solid when the sail is unfolded or completely folded to do this. For the modeling, we wanted to use Simscape Multibody, using flexible solids, and we wondering if it was possible to represent this folding and unfolding mechanism.

Thanks for your help and/or advices for our project!

Answer 1

[Sanchari]

Hello Raïna,

I understand that you want to model a flexible solar sail using Simscape Multibody and want to know whether it is possible to represent the folding and unfolding mechanism there.

Modelling a flexible solar sail with folding and unfolding capabilities in Simscape Multibody can be challenging, as Simscape Multibody is primarily designed to simulate rigid body dynamics. However, you can approximate the behaviour of flexible structures by using a combination of rigid bodies and joints that allow for the necessary motion.

Here's a conceptual approach to model the folding and unfolding mechanism using Simscape Multibody:

1. Rigid Body Approximation for Folding Mechanism: Approximate each flexible strip with a series of rigid segments connected by revolute joints. This will allow the strips to fold and unfold like a linked chain. The number of segments will determine the smoothness of the folding motion.
2. Revolute Joints: Use revolute joints to connect the segments. For each joint, you can specify the range of motion to ensure that the segments can fold onto each other and extend to a flat, solid configuration.
3. Actuation: To simulate the sail's ability to fold and unfold at will, you would need to include actuators in your model that apply the necessary forces or moments to the joints to drive the motion. You can use motion drivers or apply torques to mimic the actuation mechanism.
4. Locking Mechanism: To represent the strips being "perfectly solid" when fully unfolded or folded, you can implement a locking mechanism in the simulation. This can be done by using conditional statements in the Simscape language to lock the revolute joints when they reach the fully folded or unfolded positions.
5. Sensors and Controllers: Incorporate sensors to measure the angles of the joints and use a controller to drive the folding and unfolding motion based on the desired trajectory.
6. Switching Between States: Simulating a material that can switch between a completely solid state and a flexible state is not directly supported, as the properties of the flexible bodies are typically linear and defined prior to simulation. To represent this behaviour, you may need to simulate the two states separately or use a custom solution that alters the stiffness of the joints or bodies dynamically during the simulation, which can be quite complex and may require s-functions or custom MATLAB functions.
7. Contact Forces: If the strips interact with each other or with other parts of the structure during folding and unfolding, you may need to model contact forces. This can be done using the contact force elements available in Simscape Multibody.

Keep in mind that while Simscape Multibody can simulate the kinematic behaviour of the folding mechanism, it does not inherently simulate the deformation of flexible materials. For more accurate modelling of flexible materials, you would need to use specialized software or tools that can handle flexible body dynamics, such as ANSYS or Abaqus, and potentially couple them with Simscape Multibody for a co-simulation.

You can refer the following links to know further about how to model flexible bodies using Simscape Multibody:

1. Flexible body models in Simscape: https://www.mathworks.com/matlabcentral/fileexchange/47051-flexible-body-models-in-simscape-multibody?s_tid=srchtitle_support_results_1_flexible%20model%20simscape%20multibody
2. Multibody dynamics: https://www.mathworks.com/help/sm/multibody-dynamics.html?searchHighlight=flexible%20model%20simscape%20multibody&s_tid=srchtitle_support_results_8_flexible%20model%20simscape%20multibody
3. Technical Paper on Modeling Flexible Bodies with Simscape Multibody Software: https://www.mathworks.com/content/dam/mathworks/tag-team/Objects/s/Modeling-Flexible-Bodies-Simscape-Multibody-171122.pdf
4. Flexible body modelling in SimMechanics: https://www.mathworks.com/matlabcentral/fileexchange/11027-modeling-flexible-bodies-in-simmechanics?s_tid=srchtitle_support_results_4_flexible%20model%20simscape%20multibody

Hope this information is helpful to you!