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SECTION 10
LAGRANGIAN BOUNDARY CONDITIONS
PDAYT312081, Section 31,0M, Saercphte2m0b0e1r 2002
S10-1
SINGLE POINT CONSTRAINT - SPC
Prevents a point moving in a particular direction. Must be initialized in the Case Control section:
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.
Used to model rotational boundary conditions on gridpoints.
Must be selected in Case Control
SPC = SID
PDAYT312081, Section 31,0M, Saercphte2m0b0e1r 2002
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.
Must be selected in Case Control.
SPC = SID
PDAYT312081, Section 31,0M, Saercphte2m0b0e1r 2002
S10-4
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
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.
PDAYT312081, Section 31,0M, Saercphte2m0b0e1r 2002
S10-10
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
ignored. Enforced motion can be prescribed in a local coordinate system.
PDAYT312081, Section 31,0M, Saercphte2m0b0e1r 2002
S10-5
ENFORCED GRID POINT MOTION
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
PDAYT312081, Section 31,0M, Saercphte2m0b0e1r 2002
S10-9
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:
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
S10-3
SINGLE POINT CONSTRAINT IN LOCAL COORDINATES – SPC3
Used to define a single point constraint in a local coordinate system or a cascade of two local coordinate systems.
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
PDAYT312081, Section 31,0M, Saercphte2m0b0e1r 2002
PDAYT312081, Section 31,0M, Saercphte2m0b0e1r 2002
S10-8
TIED CONNECTIONS
Two meshes with different coarseness are permanently tied together during the analysis.
RCONN, 1, GRID, SURF, 3, 7, NORMAL SET1, 3, 1, THRU, 10
PDAYT312081, Section 31,0M, Saercphte2m0b0e1r 2002
S10-11
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:
KINEMATIC Method Nodes are put back on the Surface. Impulse 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
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 = 100 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
PDAYT312081, Section 31,0M, Saercphte2m0b0e1r 2002
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.
