RBE3

Bulk Data Entry

RBE3 – Interpolation Constraint Element

Description

Defines the motion at a "reference" grid point as the weighted average of the motions at a set of other grid points.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
RBE3	EID	blank	REFGRID	REFC	WT1	C1	G1,1	G1,2
	G1,3	WT2	C2	G2,1	G2,2	etc.	WT3	C3
	G3,1	G3,2	etc.	WT4	C4	G4,1	G4,2	etc.
	"UM"	GM1	CM1	GM2	CM2	GM3	CM3	blank
	blank	GM4	CM4	GM5	CM5	etc.		blank
	"ALPHA"	ALPHA

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
RBE3	14		100	1234	1.0	123	1	3
	5	4.7	1	2	4	6	5.2	2
	7	8	9	5.1	1	15	16
	UM	15	123	5	13	7	3
	ALPHA	1.45e-5

Field	Contents
EID	Unique element identification number.
REFGRID	Reference grid point. This is the dependent GRID. Some, or all, of the dependent degrees-of-freedom of this grid can be made independent by redefining all of the dependent degrees-of-freedom following the UM flag. (Integer > 0 or <PartName.number>) See comment 9.
REFC	Global components of motion whose values will be computed at the reference grid point. Any of the digits 1, 2, ..., 6 with no embedded blanks. (Integer > 0)
WTi	Weighting factor for components of motion on the following entry at grid points Gi,j. (Real)
Ci	Global components of motion that have weighting factor WTi, at grid points Gi,j. Any of the digits 1, 2, ..., 6, with no embedded blanks. (Integer > 0)
Gi,j	Grid point whose components Ci have weighting factor WTi in the averaging equations. (Integer > 0 or <PartName.number>) See comment 9.
UM	Optional flag indicating that a data set redefining the entire dependent degree-of-freedom set is to follow. The default is that all of the components in REFC at the reference grid point form the dependent degree-of-freedom set. See comments 4, 5 and 6.
GMi	Grid points with components in the redefined dependent degree-of-freedom set. (Integer > 0 or <PartName.number>) See comment 9.
CMi	Components of motion at GMi in the redefined dependent degree-of-freedom set. Any of the digits 1 through 6, with no embedded blanks. (Integer > 0)
"ALPHA"	Optional flag indicating that a thermal expansion coefficient (ALPHA) is to follow.
ALPHA	Thermal expansion coefficient (see comment 10). (Real > 0.0 or blank)

Comments

1.	It is recommended that for most applications only the translation components 123 be used for Ci. An exception is the case where the Gij are collinear. A rotation component may then be added to one grid point, to stabilize its associated rigid body mode for the element.

2.	Blank spaces may be left at the end of a Gij sequence.

3.	The default for the dependent degree-of-freedom set should be used except in cases where you want to redefine some or all REFC components as the dependent degree-of-freedom set. If the default is not used for the dependent degree-of-freedom set:

•	The total number of components therein (that is, the total number of dependent degrees-of-freedom defined by the element) must be equal to the number of components in REFC (four components in the example).

•	The components therein must be a subset of the components mentioned in REFC and Gij_Ci.

•	The coefficient matrix [Rm] in the constraints equation [RM] {um} + [Rn] {un} = 0 must be nonsingular, where um denotes the dependent degree-of-freedom set and un denotes the independent degree-of-freedom set.

When the AMSES or AMLS eigenvalue solver is used, the UM data should be used when loaded RBE3 have more than 500 DOF. Large loaded RBE3 will dramatically increase the run times for AMSES or AMLS because the residual vectors will contain many DOF, unless the UM data is used to make the loaded center GRID independent. When UM data is used, the stiffness matrix becomes full for all the independent DOF of the RBE3, which can increase the run time for very large RBE3. The number of grids can be reduced using a HyperMesh macro. The macro is listed as Script 1068 in the Altair HyperWorks Script Exchange:

www.altairhyperworks.com

5.	UM data should not be used on large unloaded RBE3, as this will lead to an increase in the run time. The UM field is not supported in Large Displacement Nonlinear Analysis.

6.	Dependent degrees-of-freedom assigned by one rigid element may not also be assigned dependent by another rigid element or by a multi-point constraint, and may not be specified on SPC data. For Large Displacement Nonlinear Analysis, SPC can be applied to the Dependent Grid (REFGRID).

In version 5.0, the RBE3 element calculation was modified in order to make the results independent of the units used in the model. For this purpose, the weights of the rotational degrees-of-freedom have been scaled by the square of the average distance between the independent grid points and the reference point. This change will only affect the results if independent grid points with rotational degrees-of-freedom exist in the RBE3 element. The previous RBE3 formulation can be enforced with the debug statement debug, OLDRBE3,1.0.

8.	Rigid elements are ignored in heat transfer analysis.

Supported local entries in specific parts can be referenced by the use of “fully qualified references” on RBE3 entries in the model. A fully qualified reference (“PartName.number”) is similar to the format of a numeric reference. “PartName” is the name of the part that contains the referenced local entry (part names are defined on the BEGIN Bulk Data Entry in the model). “number” is the identification number of a referenced local entry in the part “PartName”. See Parts and Instances in the User’s Guide for detailed information on the use of fully qualified references.

10.

The thermal expansion effect will be computed, if you supply the thermal expansion coefficient ALPHA, and the thermal load is requested by the TEMPERATURE(INITIAL) and TEMPERATURE(LOAD) subcase information entries. The temperature of the element is taken to be the average of the temperatures at all the nodes of the element.

11.	This card is represented as an rbe3 element in HyperMesh.