PAT312, Section 11, December 2006 S11-1 Copyright 2007 MSC.Software Corporation SECTION 11 FINITE ELEMENT MESHING

PAT312, Section 11, December 2006 S11-2 Copyright 2007 MSC.Software Corporation

PAT312, Section 11, December 2006 S11-3 Copyright 2007 MSC.Software Corporation FINITE ELEMENTS l A finite element model is a hypothetical discretization of a component or a system into small regularly shaped regions where the analysis is actually performed

PAT312, Section 11, December 2006 S11-4 Copyright 2007 MSC.Software Corporation FINITE ELEMENTS l Finite elements come in different shapes and forms BarTri TetHexWedge Quad l Linear and parabolic elements

PAT312, Section 11, December 2006 S11-5 Copyright 2007 MSC.Software Corporation INTRODUCTION TO FINITE ELEMENT MESHING l Meshing a model consists of several tasks: l Create appropriate geometry l Parametric or non-parametric l Remove unneeded features, e.g. small corners l Specify the element topology (e.g. parabolic) and size l Specify a mesher, e.g. Paver l Identify the mesher for each region, and how the meshers will be controlled l MSC.Patran has several meshing algorithms: l IsoMesh (mapped mesher) l Paver (free mesher) l TetMesh l Sweep mesh

PAT312, Section 11, December 2006 S11-6 Copyright 2007 MSC.Software Corporation FINITE ELEMENTS Topology and Physical Properties l The MSC.Patran Finite Element application handles issues related to mesh topology, e.g. which nodes are connected together l The physical properties associated with these elements will be handled in the MSC.Patran Properties application, e.g. 2D bending shell element or 2D solid plane stress element

PAT312, Section 11, December 2006 S11-7 Copyright 2007 MSC.Software Corporation BASICS & DEFINITIONS

PAT312, Section 11, December 2006 S11-8 Copyright 2007 MSC.Software Corporation

PAT312, Section 11, December 2006 S11-9 Copyright 2007 MSC.Software Corporation MSC.PATRAN MESHING ALGORITHMS

PAT312, Section 11, December 2006 S11-10 Copyright 2007 MSC.Software Corporation In the example above Surface 1:2 are congruent, Surface 2:3 are congruent, and Surface 4:5 are congruent. However, Surface 3:4 are not congruent. Two of the individual mesh paths are labeled a and b. There are five other mesh paths. l All IsoMesh mesh paths are identified by the IsoMesher l An IsoMesh mesh path is a set of topologically parallel geometric edges (e.g. non-intersecting edges) ISO (MAPPED) MESHER (Cont.) STEPS IN ISOMESH CREATION Gap is larger than Global Model Tolerance a a a a b b b

PAT312, Section 11, December 2006 S11-11 Copyright 2007 MSC.Software Corporation l The IsoMesher determines the number of elements across the width (edges) of each mesh path, based on the following priority: 1. Adjoining meshed regions that are topologically congruent 2. Mesh Seeds on an edge (controls creation of nodes on curve or edge) 3. Global Edge Length (GEL) l Note: Number of elements is independent between mesh paths l The IsoMesher determines the physical location of each node to be created from the vector function defining the shape of the geometry, e.g. l The IsoMesher creates the nodes and element connectivity l Note: The IsoMesher can be used only with geometry that is defined parametrically ISO (MAPPED) MESHER (Cont.) (X,Y,Z) = function ( 1, 2 )

PAT312, Section 11, December 2006 S11-12 Copyright 2007 MSC.Software Corporation ISO (MAPPED) MESHER (Cont.) l When no mesh seeds or adjoining mesh occur in a mesh path, the Global Edge Length and the longest edge in the mesh path determine the number of elements per edge as follows: Global Edge Length Longest Geometric Edge Length Number of Elements =

PAT312, Section 11, December 2006 S11-13 Copyright 2007 MSC.Software Corporation PAVER (FREE) MESHER FOR SURFACES l Used with all surface types l The Paver meshes at the surface boundary (perimeter) first, then, moves spiraling into the interior; the Paver does not follow parametric directions, e.g. x1,x2 l Only the Paver recognizes associated (hard) points and curves inside surfaces X Y Z X Y Z X Y Z

PAT312, Section 11, December 2006 S11-14 Copyright 2007 MSC.Software Corporation PAVER MESHER FOR SURFACES (Cont.) l The number of elements per edge are based on the following priority: l Adjoining meshed regions that are topologically congruent l Mesh Seeds l Global edge length

PAT312, Section 11, December 2006 S11-15 Copyright 2007 MSC.Software Corporation ISO (MAPPED) MESH VS PAVER (FREE) MESH MESH SURFACES ISOMESH l Surface must be parametric – 3 or 4 sided l Parameterization followed l Interior elements are controlled by edge constraints (e.g. mesh seed) l Interior associated geometry not recognized l User control l Different smoothing algorithms l Can select different element patterns, e.g. triangular elements on surface PAVER l Any surface including N-sided l Parameterization not used l Interior elements are not controlled by edge constraints l Interior associated geometry is recognized l User control l Curvature check for curved surfaces l Min./Max. element edge lengths

PAT312, Section 11, December 2006 S11-16 Copyright 2007 MSC.Software Corporation ISO (MAPPED) MESH VS PAVER (FREE) MESH (Cont.) Simple Surfaces Iso Mesh Surface 36 Paver Mesh

PAT312, Section 11, December 2006 S11-17 Copyright 2007 MSC.Software Corporation MESH PRIORITY IsoMesh and Paver Meshes 1. First, this surface was meshed using the Paver 2. Second, this surface was meshed using IsoMesh (note the seeds are identical, but the meshes are different) GEL = 1/4GEL = 1/2GEL = 1/3 3. Last, this surface was meshed using the Paver (matched existing meshes) All surfaces are 1 x 1

PAT312, Section 11, December 2006 S11-18 Copyright 2007 MSC.Software Corporation ISOMESH PARAMETERS l IsoMesh parameters l Mesh smoothing parameters l Mesh Patterns

PAT312, Section 11, December 2006 S11-19 Copyright 2007 MSC.Software Corporation PAVER PARAMETERS l Paver Parameters l Allow triangular elements l Odd element count on boundary l Curvature check l mesh refinement on curved boundaries l Internal element size control l Default range is smallest to largest elements on boundary

PAT312, Section 11, December 2006 S11-20 Copyright 2007 MSC.Software Corporation MESH CONTROL USING MESH SEEDS Mesh seeds are used to guide the mesher by specifying the number of elements to be created Mesh seeds are useful in mesh transition Note: (1) seeded for 2 elements (2) seeded for 6 elements (3) seeded for 4 elements

PAT312, Section 11, December 2006 S11-21 Copyright 2007 MSC.Software Corporation MESH TRANSITION l Mesh seeds can be used to cause the mesh to transition between two different mesh densities l Mesh transitions must occur across a single face when meshing solids (IsoMesh) No (ambiguous)

PAT312, Section 11, December 2006 S11-22 Copyright 2007 MSC.Software Corporation TETRAHEDRAL MESHER TET MESH l Solid mesher that generates tetrahedral elements for solids defined with an arbitrary number of faces (B-Rep solids) l Uses Delauney algorithm l Uses tria mesh on faces to generate tetrahedral elements in the interior of the solid. MSC.Patran performs the following: l Mesh Vertices l Mesh Edges l Mesh Faces l Mesh Solids

PAT312, Section 11, December 2006 S11-23 Copyright 2007 MSC.Software Corporation TETRAHEDRAL MESHER TETMESH (Cont.) l Robust and fast l Meshes B-Rep solids with silver faces l Global parameters for meshing l Global edge length l Create P-element mesh (allows elements with greater distortion) l Curvature check – more elements at curved geometry, e.g. more elements on fillets l Allows excellent mesh control: l Creates meshes congruent to adjoining meshed regions (2D or 3D) that are topologically congruent l Creates meshes that follow mesh seeds and hard points on solid edges

PAT312, Section 11, December 2006 S11-24 Copyright 2007 MSC.Software Corporation SWEEP MESHER l Sweep a lower order element (or node) through space to create higher order element, i.e. a quad is swept into a hex l Several sweeping techniques are available (Extrude, Glide, etc.) to handle complex configurations l Mesh from a sweeping has no association with geometric entities, hence, properties and LBCs must be applied directly on the finite elements 1D bar elements Glide 1D to 2D Glide curve

PAT312, Section 11, December 2006 S11-25 Copyright 2007 MSC.Software Corporation ASSOCIATED POINTS/CURVES l Associated points/curves are used for controlling meshing of regions (including interior) of the model l Associated points/curves are regular geometric entities that have been associated with parent geometry l Associated Geometry is also referred to as Hard Geometry Surface quad meshed Face quad meshed Hex mesh created by sweeping quad elements down Curve is associated to face of solid 1 Mesh seeds applied on edge Surface created by extruding Curve 1 up l What meshers could be used?

PAT312, Section 11, December 2006 S11-26 Copyright 2007 MSC.Software Corporation ASSOCIATION OF FINITE ELEMENTS TO GEOMETRY l When geometry (i.e. curve, surface, solid) is meshed (i.e. Isomesh, Paver) the mesh (finite elements) is associated automatically to the geometry l If a mesh is imported onto geometry (i.e. File/Import, Finite Elements/Transform) it is not automatically associated to the geometry; it must be associated manually, e.g. Finite Elements/Associate l Why is it important to have a mesh associated to geometry? Application region in Loads/BCs and/or Properties

PAT312, Section 11, December 2006 S11-27 Copyright 2007 MSC.Software Corporation

PAT312, Section 11, December 2006 S11-28 Copyright 2007 MSC.Software Corporation MSC.PATRAN FINITE ELEMENT APPLICATION

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PAT312, Section 11, December 2006 S11-30 Copyright 2007 MSC.Software Corporation FINITE ELEMENT FORM l Set an objective, such as creating a mesh l Provide the details to complete the task, i.e. element type Action Object Type

PAT312, Section 11, December 2006 S11-31 Copyright 2007 MSC.Software Corporation

PAT312, Section 11, December 2006 S11-32 Copyright 2007 MSC.Software Corporation