1 / 33

CHAPTER 7 - ELEMENT LIBRARY

CHAPTER 7 - ELEMENT LIBRARY. CONTENTS. APPLICABILITY AND ELEMENTS ELEMENT DEFINITIONS COORDINATE SYSTEMS SOLID ELEMENTS SHELL ELEMENTS BEAM/ROD ELEMENTS SPRINGS AND DAMPERS DAMPERS LUMPED MASSES.

dai
Télécharger la présentation

CHAPTER 7 - ELEMENT LIBRARY

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CHAPTER 7 - ELEMENT LIBRARY

  2. CONTENTS • APPLICABILITY AND ELEMENTS • ELEMENT DEFINITIONS • COORDINATE SYSTEMS • SOLID ELEMENTS • SHELL ELEMENTS • BEAM/ROD ELEMENTS • SPRINGS AND DAMPERS • DAMPERS • LUMPED MASSES

  3. Used to model structuresElements available: SolidsQuadrilateral ShellsTriangular ShellsTriangular MembranesBeamsRodsSprings and DampersLumped MassesRigids APPLICABILITY AND ELEMENTS

  4. ELEMENT DEFINITIONS • Entities defining an element are: • Grid point locationsThe coordinates of a grid point are defined using a GRID card • ConnectivityThe shape of an element is described by a Cxx card • PropertyA Pxx card specifies the mathematical element formulation • MaterialA DMATxx, DYMATxx or a MATxx card specifies the material type and parameters • Identification Numbers (IDs): • Each card is referred to by its ID, which must be unique in the corresponding entity.The cards can be referred to as often as you like.

  5. Hierarchy of References by IDsRelating cards by referring to their IDs can be visualized by a tree: ELEMENT DEFINITIONS (continued) Connectivity Property Grids Material Yield Model Failure Model Shear Model ... Example: Triangular Shell Element Definition DMATEP, 15, 7850., 210E9, .3 PSHELL, 5, 15, .1 CTRIA3, 55, 5, 1, 2, 10 GRID, 1, , 0., 1., 0. GRID, 2, , 0., 2., 0. GRID, 10, , 1., 1.,` 1.

  6. Basic coordinate systemThis is the default reference, rectangular coordinate system (coordinate system 0). All other coordinate systems and geometry must ultimately be defined relative to this system. Element geometry definition in basic coordinate systemCalculations performed in (local) element system Output by default in basic coordinate systemLocal coordinate systemGrid points can be defined in a user defined local coordinate systemSome constraints and loading can be defined in a user defined local coordinate systemTypes of coordinate systemRectangular (x, y, z) Cylindrical (R, , Z) Spherical (R, , ) COORDINATE SYSTEMS

  7. Used to model volumetric parts of structuresConsist of 8 grid points (hexagonal element)PENTA and TETRA hexagonal elements are degenerated forms of the 8 node HEXA elementGrid points have only 3 DOFsStandard solids use global coordinate system for numerical calculationsThe Lagrangian solids with orthotropic material use a local element coordinate system SOLID ELEMENTS

  8. SOLID ELEMENTS PSOLID - Single point quadrature The element uses one point Gauss integration to determine the stresses and is very cheap to use. PSOLID, 10, 20 Avoid PENTA and TETRA The PENTA and TETRA elements are degenerate forms of the HEXA element and give very poor performance. TETRA is particularly bad.

  9. Use the entities GRID CHEXA PSOLIDExample of the definition of the Lagrangian solid 71 with property id 100 and material 200 GRID, 1, 0., 0., 0. GRID, 2, 1., 0., 0. GRID 3 to 8 CHEXA, 71, 100, 1, 2, 3, 4, 5, 6, + +, 7, 8 PSOLID, 100, 200 SOLID GEOMETRY DEFINITION

  10. Used to model thin structures, where the thickness is small compared to the lengthShell grid points have 6 DOFsQuadrilateral shell element coordinate system SHELL ELEMENTS Zelem G4 Yelem G3 Xelem G1 G2 Belytschko-Tsay and Hughes-Liu Zelem G4 Yelem G3 Xelem G1 G2 Key-Hoff

  11. SHELL ELEMENTS (continued) • CQUAD4 • Belytschko-Tsay • Constant strain element based on the C0-Mindlinshell formulation with one point Gauss quadrature. • Very efficient element which gives good results at large strains in bending. • Element geometry is assumed to be flat and the results in warping can become inaccurate. • Thickness is constant over the element. • PSHELL1, 10, 20, BLT, , , , , , + • +, 0.8

  12. SHELL ELEMENTS (continued) • CQUAD4 • Hughes-Liu • Constant strain element based on the C0 Mindlin shell formulation with one point Gauss quadrature. • More complex and more expensive to use than the Belytschko-Tsay element. • Element geometry is assumed to be curved, but can become inaccurate in warping mode. • Thickness may vary over the element • Especially used for large bending when the material used is elastic plastic (with failure)PSHELL1, 10, 20, HUGHES, , , , , , + +, 0.8

  13. SHELL ELEMENTS (continued) • CQUAD4 • Key-Hoff • Same element definition as Belytschko-Tsay with improvements. • Warped element geometry • ”Transverse shear” option provides physical stiffness in warping mode • Accurate results at very large strains in bending as well as warping mode. • No hourglass control needed for the warping mode. • About twice as expensive as the Belytschko-Tsay element. • PSHELL1, 10, 20, KEYHOFF, , , , , , + • +, 0.8 • The PSHELL entry, when used with CQUAD4 elements • assumes Key-Hoff formulation. • PSHELL, 10, 20, 0.1

  14. CTRIA3C0-triangleEfficient, accurate triangular element giving good results in bending. It is stiffer than a quad formulation and so should only be used for transition regions, or in problems dominated by bending.PSHELL1, 10, 20, C0-TRIA, , , , , , + +, 0.8The PSHELL entry, when used with CTRIA3 elements assumes C0-triangle formulation.PSHELL, 10, 20, 0.8MembraneFormulation specifically for membrane action only (the element can not carry bending).PSHELL1, 10, 20, MEMB, , , , , , + +, 0.8 SHELL ELEMENTS (continued)

  15. Use the entities -GRID -CQUAD/CTRIA -PSHELL/PSHELL1/PCOMPExample of the definition of the Belytschko-Tsay shell element 71 with PID = 100, material 200 and thickness .1Grid 1, 1, 0., 0., 0. Grid 2, 2, 1., 0., 0. Grid 3, 2, 0., 1., 0. Grid 4, 4, 1., 1., 0. CQUAD, 71, 100, 1, 2, 3, 4 PSHELL1, 100, 200, BLT, , , , , , + +, .1 SHELL GEOMETRY DEFINITION

  16. Used to model very slender structural componentsBeam consist of 2 grid points (1D element)Beam grid points have 6 DOFsBeam element coordinate system BEAM ELEMENTS Zelem Yelem G3 G1 G2 Xelem -X-axis through grid G1 and G2 -XY-plane defined by external point G3 with y-axis normal to x-axis. -Z-axis normal to x-axis and y-axis.

  17. BEAM ELEMENTS (continued) • CBAR, CBEAMBelytschko-Schwer (default)Resultant Plasticity • This is a very efficient bar element, using resultant plasticity. This means that the whole section yields at once and the element goes from elastic to the full plastic moment. It is not suitable if the partially yielded behavior is important. • Linear Moment • A linear variation of bending moment is modeled. The element can yield at either end. • There is no difference in element formulation in MSC.Dytran between using CBAR and CBEAM unlike in MSC.Nastran.

  18. Definition of beam propertiesThe following data must be defined Area: A Inertias: Iyy, Izz Torsion constant: J Plastic moduli: Zy, Zz (only if plastic)Example:PBAR, 10, 20, 49.3, 10054.0, 333.0, 5193.0 PBEAM1, 10, 20, BELY,,,,, + +, 49.3, 10054.0, 333.0, 5193.0, 651.8, 85.07For PBAR is used, the plastic moduli for a rectangular section are used. BEAM ELEMENTS (continued)

  19. BEAM ELEMENTS (continued) • CBAR, CBEAMHughes-Liu • General Sections, Partial Yielding • The Hughes-Liu element is much more expensive to use, but can model partial yielding. It also allows general cross-sections to be defined and can model more complex material models. Only use it if you need one of its features. • Constant Moment • Only a constant variation of bending moment is represented. • Define Shape and Size of Section • The shape can be rectangular, circular, Z, T, hat, C or U shaped. • Example of a rectangular beam 200mm x 100mm PBEAM1, 10, 20, HUGHES, , , , RECT,,+ +, 200.0, 200.0, 100.0, 100.0

  20. BEAM ELEMENTS (continued) • CBAR, CBEAMComposite Beam • Shape and materials used can be arbitrary. • Based upon Hughes-Liu element formulation. • Example of a rectangular beam 200mm x 100mm PBCOMP, 10, 20, …

  21. Integration of Beam ElementsTwo types of integration:Gauss (default) PBEAM1, 10, 20, , GAUSS, , , , , + +, 200.0, 200.0, 100.0, 100.0Lobatto PBEAM1, 10, 20, , LOBATTO, , , , , + +, 200.0, 200.0, 100.0, 100.0 BEAM ELEMENTS (continued)

  22. CRODTension/Compression only This is a simple tension/compression element.Efficient The rod element is very efficient. Only the area is defined.Example: CROD, 1, 10, 2, 3 PROD, 10, 20, 10.73 ROD ELEMENTS

  23. Use the entities: -GRID -CBAR/CBEAM/CROD -PBAR/PBEAM/PBEAM1/PRODExample of the definition of beam element 71 with PID = 100 and material 200. Grid, 1, 0., 0., 0. Grid 2, 1., 0., 0. Grid 3, 0., 0., 1. CBEAM, 71, 100, 1, 2, 3. PBEAM, 100, 200, 100., 25., 25.,, 30. BEAM/ROD GEOMETRY DEFINITION

  24. Used to model structural behavior that can be described by a spring or damper behaviorSprings and dampers consist of two grid pointsGrid points can have 3-6 DOFsAvailable are the following elements with linear as well as non-linear behavior - Springs with orientation - CSPR - Scalar springs - CELAS - Dampers with orientation - CVISC - Scalar dampers - CDAMP SPRINGS AND DAMPERS

  25. SPRING ELEMENTS • CSPR - Springs with Orientation • CSPR springs connect two grid points. The force in the element always acts in the direction of the two grid points. If the element undergoes large rotations, the direction of the force will change during the analysis. • CELASn - Scalar springs • CELAS1 and CELAS2 springs can connect one or two grid points. The force in the element always acts in the specified direction regardless of the relative positions of the grid points.CELAS1 elements reference PELASn property entries and can be linear or nonlinear. The property data forCELAS2 elements is included on the element definition. These elements can only be linear.

  26. Three Types of springs selected by the PSPRn/PELASn entry SPRING DEFINITION Force 1 - Linear Elastic (PSPR, PELAS) The force is linearly proportional to the displacement. Failure on tension/compression You must give the stiffness PSPR, 30, 2.7E6 2 - Nonlinear Elastic (PSPR, PELAS1) The force is not proportional to the displacement, but there is no permanent deformation. You must give the force displacement characteristic on a TABLED1 entry. It can be of any shape. PELAS1, 30,32 TABLED1,32,,,,,,,,+ +,-1.,-1.E6,0.,0.,1.,1.E9,ENDT K = 2.7E6 Displacement Force Displacement

  27. SPRING DEFINITION (continued) • 3 - User Defined Springs (PSPREX, PELASEX) • Spring characteristics defined with user subroutines.

  28. APPLICATION OF NONLINEAR SPRINGS Gaps PSPR1, 100, 110 TABLED1,110,,,,,,,,+ +,-1,-1.0E6,0.,0.,1.,0.,ENDT Cables PSPR1, 30,32 TABLED1,32,,,,,,,,+ +,-1.,0.,0.,0.,1.,1.E6,ENDT Component Failure PSPR1, 30,32 TABLED1,32,,,,,,,,+ +,-1.,-1.E6,1.,1.E6,1.,0.,2.0,0.,+ +,ENDT Force Displacement Force Displacement Force Displacement

  29. DAMPER ELEMENTS • CVISC - Dampers with Orientation • CVISC dampers connect two grid points. The force in the element always acts in the direction of the two grid points. If the element undergoes large rotations, the direction of the force will change during the analysis. • CDAMPn - Scalar dampers • CDAMP1 and CDAMP2 dampers can connect one or two grid points. The force in the element always acts in the specified direction regardless of the relative positions of the grid points.CDAMP1 elements reference PDAMPn property entries and can be linear or nonlinear. The property data for CDAMP2 elements is included on the element definition. These elements can only be linear.

  30. Three types of dampers selected by the PVISCn/PDAMPn entry DAMPER DEFINITION Force 1 - Linear (PVISC, PDAMP) The force is linearly proportional to the relative velocity of the end points in the direction of the damper. Failure on tension/compression You must give the damping constant, C. PDAMP, 30, 2.7E6 2 - Nonlinear (PVISC1, PDAMP1) The force is not proportional to the velocity. You must give the force-velocity characteristic on a TABLED1 entry. It can be of any shape. PVISC1, 30,32 TABLED1,32,,,,,,,,+ +,-1.,-1.E6,0.,0.,1.,1.E9,ENDT C = 0.3 Velocity Force Velocity

  31. 3 - User Defined (PVISCEX)Damper characteristics defined with user subroutines. DAMPERS

  32. CONM2Used to add mass and/or inertia to a Lagrangian grid point All grid points must have mass, either by virtue of the properties of the structural elements attached to the gridpoints, or by using a CONM2.Example of the definition of a CONM2 id 7 adding mass of .1 to grid point 9:CONM2,7, 9,, .1REMINDER - ALWAYS USE MASS UNITS IN DYTRAN !!!! LUMPED MASSES

  33. Using TAB characters in the input deck COMMON PROBLEMS

More Related