Before delving into the exact MATLAB syntax for running a simulation, it's good to consider the concept of a flexible multibody model and how SPACAR Light ties into that.

In general, a multibody model is a collection of bodies that are interconnected. Such a model typically represents a mechanism, a linkage or a structure. The bodies could be fully rigid, or have some flexibility. The points of interconnection typically represent the joints (revolute joint, spherical joint, etc.) or contact points of the system.

[examples]

With a description of the geometry of the bodies, the material properties, and some kind of input to the model, the behavior of the entire multibody model can be simulated. This way, the actual system that the multibody model represents can be analyzed in terms of e.g.

• kinematics (position, velocity and acceleration),
• statics (deflection and stress due to applied forces),
• natural frequencies and buckling loads, and
• fully time-dependent dynamic behavior.

In SPACAR (as in most other finite element and multibody software), the bodies are usually referred to as elements, and the points of interconnection as nodes. The full version of SPACAR features a range of different elements for modeling a variety of systems. While powerful, this does increase the complexity of creating a model.

In SPACAR Light, we're only considering one type of element: the 3-D flexible beam element. Also, the type of analysis is only going to be static (including natural frequencies and buckling loads). Both choices are well suited to the analysis of flexure mechanisms and reduce complexity for the user.

[example of flexure mechanism turned multibody model]

When SPACAR Light in installed correctly, it is typically invoked using the MATLAB command

out = spacarlight(nodes,elements,nprops,eprops,rls)

With the basic concept of a multibody model outlined above, this command is already very revealing; it shows that the user has to provide five inputs:

1. Coordinates of the nodes in nodes
2. Elements that connect the nodes in elements
3. Node properties (such as boundary conditions, applied loads and inertia) in nprops
4. Sets of element properties (such as dimensions, material constants and flexibility) in eprops
5. 'Releases' to deal with overconstrained (statically indeterminate) systems in rls

The first four inputs are typically fairly self-evident. It is only the fifth rls input that can be confusing for beginning users (because the solution to overconstraints is not obvious). There is a separate page on dealing with the rls input.

On the following pages, each input will be detailed. There is a walkthrough example in which all steps towards a simulation are explained. For complete reference, the full syntax list provides details of each command. Additional examples of models are also available.