1. CHAPTER 10 - LAGRANGIAN BOUNDARY CONDITIONS

2. CONTENTS Single Point Constraints - SPCn
Enforced Velocities - FORCE/MOMENT
Rigid Walls - WALL
Tied Connections - RCONN
Rigid Body Elements
RBE2
KJOIN
BJOIN

3. Single Point Constraint - SPC
Prevents a point moving in a particular direction
Must be initialized in the Case Control section:
SPC = SID
Any SPCn entries not selected in case control are ignored
The displacement coordinate system of the constrained gridpoint determines the direction that the constraint is applied in
Can be used to model boundary conditions and planes of symmetry Any component in grid coordinate system can be constrained
Components in a grid coordinate system are referred by digits 1 to 6. Any combination is possible, e.g. 23,156
SPC= BEGIN BULK
. . .
SPC, 100, 27, 123 SPC1, 100, 156, 19, THRU, 28

4. Rotational Boundary Condition - SPC2
Used to model rotational boundary conditions on gridpoints
Must be selected in Case Control
SPC = SID

5. SINGLE POINT CONSTRAINT IN LOCAL COODINATES - SPC3
Used to define a single point constraint in a local coordinate system or a cascade of two local coordinate systems
Must be selected in Case Control
SPC = SID

6. ENFORCED MOTION
Prescribes the motion of grid points Force of pressure loading - TYPE = 2 in TLOAD1 definition Must be selected in Case Control Any loading (TLOADn entry) not selected in Case Control is ignored Enforced motion can be prescribed in a local coordinate system.

7. ENFORCED GRID POINT MOTION
Specified points can have their velocity set Velocity - TYPE = 2 in TLOAD1 definition TLOAD1, 100, 110, , 2, 120 DAREA defines magnitude of translational or angular velocity per DOF FORCE defines magnitude and direction of translational velocity MOMENT defines magnitude and direction of angular velocity Velocity can vary arbitrarily with time The TABLED1 entry gives the variation of velocity TLOAD = BEGIN BULK TLOAD1, 100, 110, , 2, 120 TABLED1, 120,,,,,,,, + +, 0.0, 0.0, 1.0, 1.0, ENDT FORCE, 110, 27, , -6.0, , 1.0

8. ENFORCED MOTION
FORCE in CORDXXX If on a FORCE entry a CID is referenced, the enforced motion is processed in a local coordinate system FORCE, 110, 27, 2 , -6.0, , 1.0

9. RIGID WALLS - WALL
Models a rigid plane which specified ”slave” points can not penetrate
Used to model hard, undeformable target
Define a point on the wall and a vector perpendicular to it, pointing towards the model
Two kinds of contact:
PENALTY Method: Allowed penetration Force increases as nodes penetrate deeper Can have friction
KINEMATIC Method Nodes are put back on the Surface Impuls is applied to Nodes Can not have friction
WALL, 101, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0, 102,+
+,PENALTY,0.2
SET1, 102, 1, THRU, 1999

10. TIED CONNECTIONS
Two meshes with different coarseness are permanently tied together during the analysis
Allows beam, shell and solid meshes to be tied together without the need for coinciding grid point locations
Possible gaps between the meshes can be requested to be closed
Not recommended in areas where stress peaks or failure is expected
Three types of tied connections:
• Two surfaces tied together
• Grid points tied to a surface
• Shell edge tied to a shell surface

11. TWO SURFACE TIED TOGETHER (RCONN)
Two surfaces are permanently tied together during the analysis
Master surface : always attached to the coarse mesh
Slave surface : always attached to the finer mesh
Lumping forces and velocities according to shape functions
Forces : slave points master points
Velocities : master points slave points
Example: Two solids are tied together along their common surface 7 and 8
RCONN, 1, SURF, SURF, 7, 8

12. GRID POINTS TIED TO A SURFACE (RCONN)
Individual grid points are tied to a surface
Slave surface type is GRID and OPTION must be set to NORMAL Master surface must be defined as a set of segments
Only the translational degrees of freedom are tied
Example: The node 1 to 10 of a beam mesh are tied to the shell surface 7
RCONN, 1, GRID, SURF, 3, 7, NORMAL
SET1, 3, 1, THRU, 10

13. SHELL EDGE TIED TO A SHELL SURFACE
Connects beams or shell-edges to shell elements
Slave surface type is GRID and OPTION must be set to SHELL Master surface must be defined as a set of segments
Translational and rotational degrees of freedom are tied.
Example: The edge grid points 1 to 10 of a shell mesh are tied to the shell surface number 7
RCONN, 1, GRID, SURF, 3, 7, SHELL
SET1, 3, 1, THRU, 10

14. RIGID BODY ELEMENTS (RBE2)
Defines a set of grid points that form a rigid body
This entry allows particular degrees of freedom of a set of grid points to be tied together so that they always move the same amount
Used to model spotwelds, but elements can not fail
Example: Nodes 1 to 28 will have the same displacement in x and z-direction as node 55
RBE,12,55,13,1,THRU,28
Instead of defining tied components, it is also possible to use the FULLRIG option This causes the set of grid points to behave like a single rigid body element The name of the RBE2 will become FR<number>
Example: Nodes 1 to 28 and 55 will behave like a rigid body The name will be FR12
RBE,12,55,FULLRIG,1,THRU,28

15. KINEMATIC JOIN (KJOIN)
Shell to solid grid point connection
Joins shell to solid elements by applying kinematic conditions to the shell grid points
A normal JOIN would result in a hinge connection in which only the translational DOFs are coupled
Solves the closure problem for the different DOF of shell and solid elements
Constitutes stiff connection between shells and solids Stiffness of join is user defined
Example: Kjoin between solid nodes 30, 40 and 50 and shell nodes 32, 42 and All nodes within a tolerance of 1e-5 are connected
KJOIN, 2, 333,1e-5,, 0.5
SET1, 333, 30, 32, 40, 42, 50, 52
Rotation at C follows from
the motion of the system Ri R1 R2 R3 C
SOLIDS
SHELLS

16. BREAKABLE JOIN (BJOIN)
Defines a breakable join between shell or beam grid points
Joins shell or beam grid points and allows for the break of the join when a failure criterion is satisfied
Failure models :
Constant Force or Moment
Components Failure
Spotweld like behavior
User defined
Breakable join can have offset (spotweld modeling)
Example: Breakable join that fails after 1.e6 is reached All nodes within a tolerance of 1e-4 are connected
BJOIN, 1, 333, 1.E-4, FOMO, 1.E6
SET1, 333, 31, THRU, 2000