RSPLINE

Bulk Data Entry

RSPLINE – Interpolation Constraint Element

Description

Defines multi-point constraints for the interpolation of displacements at grid points.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
RSPLINE	EID	D/L	G1	G2	C2	G3	C3	G4
	C4	G5	C5	G6	…	…
	…	…

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
RSPLINE	73	0.05	27	28	123456	29		30
	123	75	123	71

Field	Contents
EID	Unique element identification number. No default (Integer > 0)
D/L	Ratio of the diameter of the elastic tube to the sum of the lengths of all segments. Default = 0.1 (Real > 0.0)
G#	Grid point identification number. No default (Integer > 0)
C#	Components to be constrained. See comment 2. Default = blank (blank or any combination of the Integers 1 through 6)

Comments

1.	Displacements are interpolated from the equations of an elastic beam passing through the grid points. This is a linear method only element.

A blank field for C# indicates that all six degrees-of-freedom at G# 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 G#, not a C#. 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.	Dependent (that is constrained) degrees-of-freedom assigned by one rigid element may not also be assigned dependent by another rigid element or by a multi-point constraint.

4.	Degrees-of-freedom declared to be independent by one rigid body element can be made dependent by another rigid body element or by a multi-point constraint.

5.	Rigid elements (including RSPLINE), unlike MPCs, form part of the model and do not need to be selected from within a subcase definition.

6.	Rigid elements are ignored in heat transfer problems.

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.

8.	The independent degrees-of-freedom that are the rotation components most nearly parallel to the line joining the regions should not normally be constrained.

9.	The default RSPLINE implementation has larger-than-expected in-plane rotation at the two RSPLINE end nodes and where RSPLINE have sharp angles. Applying PARAM,RSPLICOR reduces such rotation and yields better results.