RBE3 Elements

In ANSYS, the purpose of an RBE3 card is to distribute the force/moment applied at the master node to a set of slave nodes, taking into account the geometry of the slave nodes as well as weighting factors.

In HyperMesh, RBE3 is created using the RBE3 panel (1D page). It is a HyperMesh element that includes multiple 1-D elements, which are defined between a single dependent (master) node and one or more independent (slave) nodes.

ANSYS RBE3 elements are different from Nastran RBE3 elements. In ANSYS, the RBE3 card is used to distribute the force/moments from the master node to a set of slave nodes. Whereas in Nastran, these elements define the rigid body motion. In HyperMesh, the ANSYS RBE3 card is mapped as an RBE3 element. Therefore, when creating the RBE3 elements in HyperMesh for the ANSYS template, the following points should be noted.

1.	When an RBE3 element is created in HyperMesh, the DOFs are defined for the master as well as for the slave nodes. However, since the slave node DOFs are not applicable in ANSYS, they are not exported.

By default, when an RBE3 element is created in HyperMesh, the same weight factor that is applied at the master node is also applied on all the slave nodes. The update subpanel on the RBE3 panel allows you to modify the weight factors for the individual slave nodes. Since the master node weight factor is not applicable in ANSYS, it is not exported.

3.	The RBE3 elements created in HyperMesh using other solver templates, such as Nastran, are exported according to ANSYS template terminology.

Exporting HyperMesh RBE3 Elements

Two parameter arrays are exported for each RBE3 element. The first array contains slave node IDs and the second array contains slave node weights. These arrays appear in the beginning of the exported file.

Exportation of the SLAVE# array:

*DIM,SLAVE#,ARRAY, NS, 1, 1

*SET,SLAVE#( 1, 1, 1), ID_1

*SET,SLAVE#( 2, 1, 1), ID_2

*SET,SLAVE#( 3, 1, 1), ID_3

*SET,SLAVE#( NS, 1, 1), ID_NS

Where:

# is the HyperMesh element ID of the RBE3.
NS is the number of slave nodes within the RBE3.
ID_1, ID_2, ID_3,…,ID_NS are the IDs of the slave nodes.

Exportation of the WEIGHT# array:

*DIM,WEIGHT#,ARRAY, NS, 1, 1

*SET,WEIGHT#( 1, 1, 1), WF_1

*SET,WEIGHT#( 2, 1, 1), WF_2

*SET,WEIGHT#( 3, 1, 1), WF_3

*SET,WEIGHT#( NS, 1, 1), WF_NS

Where:

# is the HyperMesh element ID of the RBE3.
NS is the number of slave nodes within the RBE3.
WF_1, WF_2, WF_3,…,WF_NS are the weighting factors corresponding to each slave node.

Each RBE3 element is written using an RBE3 card with the following format:

RBE3, Master_ID, DOF, SLAVE#, WEIGHT#

Where:

Master_ID is the ID of the master node.

DOF	is the degrees of freedom checked in the RBE3 panel for RBE3 element with ID #. The DOF is exported as follows:

U if ux is checked

UY if uy is checked

UZ if uz is checked

ROTX if rotx is checked

ROTY if roty is checked

ROTZ if rotz is checked

UXYZ if ux, uy, and uz are checked

RXYZ if rotx, roty, and rotz are checked

ALL if all are checked

If a combination of DOFs not listed above is checked, several RBE3 cards will be exported for the same element. For example, if ux, uy, and roty are checked, three RBE3 cards will be exported as follows:

RBE3, Master_ID, UX, SLAVE#, WEIGHT#

RBE3, Master_ID, UY, SLAVE#, WEIGHT#

RBE3, Master_ID, ROTY, SLAVE#, WEIGHT#

SLAVE# is the name of the slave node ID array as described in step 1.

WEIGHT# is the name of the weighting factor array as described in step 1.

Where # is the RBE3 element ID.

The exportation location is the CP or CERIG elements.

ANSYS FE Input Translator Support for RBE3

Importing the ANSYS exported files

In ANSYS, RBE3 is not an element; it is created by a command called RBE3. ANSYS does not export these RBE3s as an RBE3 card, but rather as a set of constraint equations (CE). The HyperMesh-ANSYS FE input translator imports CE equations as CE equations only, and not as RBE3 elements.

Importing the HyperMesh exported files

Since HyperMesh writes out RBE3 elements using RBE3 cards, the H_ANSYS FE input translator imports the HyperMesh exported RBE3 cards as RBE3 elements.