You can use the Underconstrained
Bodies utility to detect any rigid (or free) body modes of bodies that are
not adequately supported by fixtures, connectors, or bonded interaction
conditions.
Available in SOLIDWORKS Simulation Standard and SOLIDWORKS Premium.
To open the Underconstrained
Bodies PropertyManager do one of the following:
- From a static study tree, right-click Connections
and click Underconstrained Bodies
.
- From the CommandManager, select Diagnostic Tools, and
click Underconstrained Bodies
.
As a best practice, before you run the Underconstrained
Bodies utility, define realistic materials, loads, and boundary
conditions for your model. The study properties should reflect, as accurate as
possible, the operating loads and boundary conditions of the model you are trying to
analyze.
The
Underconstrained Bodies algorithm can detect local
singularities (elements with zero or almost zero stiffness) in the decomposed global
stiffness matrix that could be indicative of a rigid body motion. The algorithm is
able to detect cases where the contrast between neighboring stiffness terms in the
global stiffness matrix is legitimately very large and does not necessarily lead to
singularities. Such models can include:
- Parts with tapered geometry where the stiffness changes
significantly across the part’s profile.
- Assemblies with parts that have large discrepancies in
their material stiffness properties.
- Parts with localized extreme rigidities at locations where
you apply connectors or remote loads.
- Thin parts modeled as shells that have inherently very
small rotational stiffness.
The
Underconstrained Bodies algorithm does not detect
local singularities for the global stiffness matrix for such models, if the parts
are sufficiently constrained.
For each part of an assembly, the algorithm checks for free translations and
rotations in the global X, Y, and Z direction. It is also able to detect instability
issues in assemblies with chain (or hinge) mechanisms between parts. In cases where
free body modes are detected, the Underconstrained Bodies
utility animates them accordingly by adjusting the corresponding stiffness and force
to produce a bounded response that reflects a rigid (or free body) motion in a given
direction.
Stabilize any rigid body modes with the appropriate translational or
rotational restraints, before you proceed with the analysis. See also SOLIDWORKS Simulation Help: Use Soft Spring to Stabilize Model and Preventing Rigid Body Motion.