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Introduction to Lagrange

Chapter 10 - Lagrangian Boundary Conditions MSC.Dytran Seminar Notes

CHAPTER 10 - LAGRANGIAN BOUNDARY CONDITIONSCHAPTER 10 - LAGRANGIAN BOUNDARY CONDITIONS

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Introduction to Lagrange

Chapter 10 - Lagrangian Boundary Conditions MSC.Dytran Seminar Notes

CONTENTS

• Single Point Constraints - SPCn

• Enforced Velocities - FORCE/MOMENT

• Rigid Walls - WALL

• Tied Connections - RCONN

• Rigid Body Elements

RBE2

KJOIN

BJOIN

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Introduction to Lagrange

Chapter 10 - Lagrangian Boundary Conditions MSC.Dytran Seminar Notes

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=100 BEGIN BULK

. . .

SPC, 100, 27, 123SPC1, 100, 156, 19, THRU, 28

Single Point Constraint - SPC

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Introduction to Lagrange

Chapter 10 - Lagrangian Boundary Conditions MSC.Dytran Seminar Notes

Rotational Boundary Condition - SPC2

Used to model rotational boundary conditions on gridpoints

Must be selected in Case Control

SPC = SID

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Introduction to Lagrange

Chapter 10 - Lagrangian Boundary Conditions MSC.Dytran Seminar Notes

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

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Introduction to Lagrange

Chapter 10 - Lagrangian Boundary Conditions MSC.Dytran Seminar Notes

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.

ENFORCED MOTION

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Introduction to Lagrange

Chapter 10 - Lagrangian Boundary Conditions MSC.Dytran Seminar Notes

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 = 100 BEGIN BULK ...TLOAD1, 100, 110, , 2, 120TABLED1, 120,,,,,,,, ++, 0.0, 0.0, 1.0, 1.0, ENDTFORCE, 110, 27, , -6.0, , 1.0

ENFORCED GRID POINT MOTION

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Introduction to Lagrange

Chapter 10 - Lagrangian Boundary Conditions MSC.Dytran Seminar Notes

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

ENFORCED MOTION

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Introduction to Lagrange

Chapter 10 - Lagrangian Boundary Conditions MSC.Dytran Seminar Notes

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 deeperCan have friction

• KINEMATIC MethodNodes are put back on the SurfaceImpuls is applied to NodesCan not have friction

WALL, 101, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0, 102,++,PENALTY,0.2SET1, 102, 1, THRU, 1999

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Introduction to Lagrange

Chapter 10 - Lagrangian Boundary Conditions MSC.Dytran Seminar Notes

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

TIED CONNECTIONS

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Introduction to Lagrange

Chapter 10 - Lagrangian Boundary Conditions MSC.Dytran Seminar Notes

TWO SURFACE TIED TOGETHER (RCONN)

Two surfaces are permanently tied together during the analysis

Master surface : always attached to the coarse meshSlave surface : always attached to the finer mesh

Lumping forces and velocities according to shape functions

Forces : slave points master pointsVelocities : master points slave points

Example: Two solids are tied together along their common surface 7 and 8

RCONN, 1, SURF, SURF, 7, 8

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Introduction to Lagrange

Chapter 10 - Lagrangian Boundary Conditions MSC.Dytran Seminar Notes

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 NORMALMaster 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

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Introduction to Lagrange

Chapter 10 - Lagrangian Boundary Conditions MSC.Dytran Seminar Notes

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 SHELLMaster 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

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Introduction to Lagrange

Chapter 10 - Lagrangian Boundary Conditions MSC.Dytran Seminar Notes

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 andz-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

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Introduction to Lagrange

Chapter 10 - Lagrangian Boundary Conditions MSC.Dytran Seminar Notes

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 andshell nodes32, 42 and 52 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

R1R2

R3 C

SOLIDS

SHELLS

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Introduction to Lagrange

Chapter 10 - Lagrangian Boundary Conditions MSC.Dytran Seminar Notes

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 reachedAll nodes within a tolerance of 1e-4 are

connected

BJOIN, 1, 333, 1.E-4, FOMO, 1.E6SET1, 333, 31, THRU, 2000