Dytran官方经典培训讲义_chapter10_BC(共17张)(PPT 17页)

1、SECTION 10LAGRANGIAN BOUNDARY CONDITIONS第1页，共17页。SINGLE POINT CONSTRAINT - SPCPrevents a point moving in a particular direction. Must be initialized in the Case Control section:SPC = SIDAny SPCn entries not selected in case control are ignored.The displacement coordinate system of the constrained gr

2、idpoint 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

3、.SPC=100 BEGIN BULK. . .SPC, 100, 27, 123SPC1, 100, 156, 19, THRU, 28第2页，共17页。ROTATIONAL BOUNDARY CONDTION SPC2Used to model rotational boundary conditions on gridpoints.Must be selected in Case ControlSPC = SID 第3页，共17页。SINGLE POINT CONSTRAINT IN LOCAL COORDINATES SPC3Used to define a single point

4、constraint in a local coordinate system or a cascade of two local coordinate systems.Must be selected in Case Control.SPC = SID 第4页，共17页。ENFORCED MOTIONPrescribes the motion of grid points. Force of pressure loading - TYPE = 2 in TLOAD1 definition.Must be selected in Case Control.Any loading (TLOADn

5、 entry) not selected in Case Control is ignored. Enforced motion can be prescribed in a local coordinate system.第5页，共17页。ENFORCED GRID POINT MOTIONSpecified points can have their velocity set. Velocity - TYPE = 2 in TLOAD1 definitionTLOAD1, 100, 110, , 2, 120DAREA defines magnitude of translational

6、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, 1

7、20, +, 0.0, 0.0, 1.0, 1.0, ENDTFORCE, 110, 27, , -6.0, , 1.0第6页，共17页。ENFORCED MOTIONFORCE in CORDXXXIf 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 第7页，共17页。RIGID WALLS - WALLModels a rigid plane which specified ”

8、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 MethodNodes

9、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,0.2SET1, 102, 1, THRU, 1999第8页，共17页。TIED CONNECTIONSTwo meshes with different coarseness are permanently tied together during the analysis.Allows beam, shell and solid

10、 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 togetherGrid points tied to a surfaceSh

11、ell edge tied to a shell surface第9页，共17页。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.Fo

12、rces: slave points master pointsVelocities:master points slave pointsExample: Two solids are tied together along their common surface 7 and 8.RCONN, 1, SURF, SURF, 7, 8第10页，共17页。GRID POINTS TIED TO A SURFACE (RCONN)Individual grid points are tied to a surface.Slave surface type is GRID and OPTION mu

13、st 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, NORMALSET1, 3, 1, THRU, 10第11页，共17页。SHELL EDGE TIED TO A SHELL SURFACEConnec

14、ts 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

15、 7.RCONN, 1, GRID, SURF, 3, 7, SHELLSET1, 3, 1, THRU, 10第12页，共17页。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 spotweld

16、s, but elements can not fail.Example: Nodes 1 to 28 will have the same displacement in x and z-direction as node 55.RBE2,12,55,13,1,THRU,28Instead 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.

17、The name of the RBE2 will become FR.Example: Nodes 1 to 28 and 55 will behave like a rigid body. The name will be FR12.RBE2,12,55,FULLRIG,1,THRU,28第13页，共17页。KINEMATIC JOIN (KJOIN)Shell to solid grid point connection.Joins shell to solid elements by applying kinematic conditions to the shell grid poi

18、nts.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 52. All nodes within a tolerance of 1e-5 are connected.KJOIN, 2, 333,1e-5, 0.5SET1, 333, 30, 32, 40, 42, 50, 52Ro