Simcenter Madymo Simcenter Madymo - Info on SUPPORT_RESTRAINT usage
2024-08-06T06:52:42.000-0400
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Summary
Using support restraints enables an easy way to attach facet and/or FE nodes to a body in Madymo.
Details
General:
A SUPPORT_RESTRAINT is an option/way that enables to attach bodies to FE or facet nodes e.g. if a support is not possible to be used as of other kinematic constraints, e.g. as of prescribed structural motion. MB springs are created in 3 orthogonal directions for each node specified in the support restraint. The support restraint coordinate system is co-linear to the corresponding body local coordinate system. The same characteristic is used for the 3 axes. Using the CHAR to define the spring stiffness (N vs m) and DAMP_COEF (Ns/m) is optional but it is recommended to define the spring properties via a CHAR. Using DEFINEs for the spring characteristic may be convenient too from modelling perspective, to enable updating these at a centralized location, either within system level (local scope) or on Madymo level (global scope).
Note: a support restraint stiffness of 1E6 N/m is often from stability perspective sufficient. It’s for robustness/stability generally better to provide a linear loading (user-defined) CHAR only, although non-linearity properties within a support restraint CHAR can be defined,
Remarks:
- Automatic creation of a stiffness and damping value will be done (based on time step) if no CHAR is defined within the support restraint. Note: If e.g. the initial integration time step is modified, this will automatically change the support restraint values and may, as of that, impact the results.
- Unless intended, it is recommended to use at least 3 nodes, not in line, per support restraint to have all 6 DOF constrained to avoid rotation
- If no BODY is defined within a support restraint, the reference space is used
- More nodes in the NODE_LIST may be needed if the applied forces are large (due to lever-arm e.g.) to better fixate the support restraint
- For a facet mesh DENSITY_NULL is optional and by default the density value is zero. If a support restraint is attached to nodes of a facet mesh without DENSITY_NULL, the nodal masses are zero. As of that, a body will not be ‘attached’ to the facet surfaces. Defining DENSITY_NULL, with a small non-zero value is sufficient e.g. to enable the attachment.
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The reprint file will list support restraint info based on the used definition of the characteristic, As examples:
- SUPPORT_RESTRAINTs are not affected by damaged shell and solid elements during the simulation. This may result in inaccurate/unpredictable model responses in case (nodes of) failed elements are involved in such constraint definitions.
- To tie two surfaces, TIED_SURFACE is an option (instead of using two support restraints with a common body e.g.)
- Support restrains can be of use in coupling to connect FE nodes of the coupling partner to a body on the Madymo side (e.g. to attach a Madymo belt system to the vehicle)
The KBA Simcenter Madymo - How to insert entities selected from the graphical interface in XMADgic shows how to select nodes graphically in XMADgic for the NODE_LIST.
Please contact your local Simcenter Madymo support organization for further questions/details on this topic.