The Lumped Mechanical System (lms) interface (), found under the Structural Mechanics branch () when adding a physics interface, is intended to model displacements and forces in a mechanical system using a circuit representation with lumped components such as masses, springs, and dampers. In addition to the displacement and force sources in the system, terminal nodes are used to define forces, displacements, velocities, accelerations, or impedances as boundary conditions. The physics interface supports stationary, frequency-domain, eigenfrequency, and time- domain analysis. The models created with the Lumped Mechanical System interface can also include connections to distributed finite element models.

When the Lumped Mechanical System interface is added, one default node is also added to the Model Builder — Fixed Node (a boundary condition which acts as “ground”). Then, from the Physics toolbar, add more features in the model builder. You can also right-click Lumped Mechanical System to select physics features from the context menu.

The Label is the default physics interface name.

The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.

The default Name (for the first physics interface in the model) is lms.

When Create unique nodes for new components is selected, newly added components will be assigned unused node names. The components will be disconnected from the rest of the system and the nodes should be updated to reflect the actual system connections. When this setting is deselected, new components will be connected to the lowest-numbered nodes, starting from 0.

When Check for hanging nodes before solving is selected, a check for hanging (not connected) nodes is performed before solving the equations. An error message is displayed if one or more hanging nodes are present in the system.

Select Include gravity and specify Acceleration due to gravity (g) in order to add gravity force on all the mass components. It is possible to exclude the gravity force contribution from a selected mass component at the physics feature level.