RSPLINE

Interpolation Constraint Element

Description: Defines multipoint constraints for the interpolation of displacements at grid points.

Format:

Example:

Field	Definition	Type	Default
EID	Element identification number.	Integer > 0	Required
D/L	Ratio of the diameter of the elastic tube to the sum of the lengths of all segments.	Real > 0.0	0.1
Gi	Grid point identification number.	Integer > 0	Required
Ci	Components to be constrained. See Remark 2.	1 ≤ Integers ≤ 6	Required

Remarks:

1. Displacements are interpolated from the equations of an elastic beam passing through the grid points.
2. A blank field for Ci indicates that all six degrees of freedom at Gi are independent. Since G1 must be independent, no field is provided for C1. Since the last grid point must also be independent, the last field must be a Gi, not a Ci. For the example shown G1, G3 and G6 are independent. G2 has six constrained degrees of freedom while G4 and G5 each have three.
3. The constraint coefficient matrix is affected by the order of the Gi Ci pairs on the RSPLINE entry. The order of the pairs should be specified in the same order that they appear along the line that joins the two regions. If this order is not followed, then the RSPLINE will have folds in it that may yield some unexpected interpolation results.
4. The independent degrees of freedom that are the rotation components most nearly parallel to the line joining the regions should not normally be constrained.
5. A dependent degree of freedom assigned by one element cannot be assigned dependent by another rigid element or MPC entry and cannot be additionally constrained (e.g., single-point constraint).
6. Degrees of freedom declared to be independent by one rigid body element can be made dependent by another rigid body element or by a multipoint constraint.
7. Rigid elements, unlike MPCs, are not selected through the Case Control Section.
8. Forces of multipoint constraint may be recovered with the MPCFORCES Case Control command.