GuiCommand:Container| {{GuiCommand Name: FEM ConstraintRigidBody MenuLocation: Model , Mechanical boundary conditions and loads , Rigid body constraint Workbenches: FEM_Workbench Version: 1.0 SeeAlso: FEM_ConstraintDisplacement }} {{GuiCommandFemInfo Solvers: CalculiX }}
FEM ConstraintRigidBody
Description
Defines the CalculiX\'s rigid body constraint that constrains the motion of the nodes of a selected geometrical entity to the motion of a reference node whose location is defined by the user. In practice, this can be used to apply a boundary condition or load that will be propagated to the selected object. Since the reference node has rotational degrees of freedom, it\'s possible to apply a moment load or a rotational boundary condition to any face this way. The location of the reference node can be selected, if it\'s offset from a geometrical entity, a remote load (a force acting on a lever) can be applied.
Usage
- There are several ways to invoke the command:
- Press the
Rigid body constraint button. - Select the Model → Mechanical boundary conditions and loads → Rigid body constraint option from the menu.
- Press the
- Press the Add button.
- In the 3D view select the geometrical element(s) (vertices, edges or faces but not a mix of them) to which the constraint should be applied. To remove objects from the selection, press the Remove button and click on them.
- Specify the coordinates of the reference node. After closing the task panel, a spherical symbol will show this location.
- Choose modes for the 3 translational and 3 rotational degrees of freedom (DOFs):
- Free - default, no boundary condition or load on that DOF
- Constraint - displacement/rotation boundary condition with a specified value (default: 0 = fixed) on that DOF - for rotation, one needs to set an axis (X, Y or Z) and specify the Angle
- Load - force/moment load with a specified value on that DOF
Limitations
- Currently, the moment units can be somewhat confusing. To apply 1 N*m, one needs to set 1 J in the input field (those units are equivalent).
- The feature can be applied only to vertices, edges and faces for now, support for solids (to make whole volumes/parts rigid) should follow in the future.
- The selected object is made rigid. To apply loads in a more flexible way, one would need to use CalculiX\'s distributing coupling constraints which are currently unsupported.
Notes
- This constraint is the standard way of applying torque to arbitrary parts. The other options are the Local coordinate system (only for cylindrical faces) or a pair of forces but the rigid body constraint should be sufficient in pretty much all the cases.
- No other constraints/boundary conditions should be applied to the nodes involved in a rigid body constraint.
- When applying this constraint to a vertex or an edge, one should set a proper rotational DOF (in the case of an edge, the one that will prevent the rotation about it) to zero.
- This feature uses the *RIGID BODY card in CalculiX.
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