LaGriTLos Alamos Grid Toolbox

Carl Gable

meshing.lanl.gov lagrit.lanl.gov

LaGriT

• Mesh Generation

• Mesh Optimization

• Geometric Computing

• Element and Node Set Manipulation

• IO, Boundary Conditions, Initial Conditions

LaGriT: Mesh Generation

Delaunay point connection– 2D triangulation– 3D tetrahedralization

LaGriT: Mesh Generation

• 2D arbitrary (concave) polygon triangulation

LaGriT: Mesh Generation

• Block structured i,j,k connectivity

• 2.5D Stacking of z(x,y) surfaces

2x5

3x2

LaGriT Mesh Optimization• Refine

– edge, face, element

– Rivara

• Refine– field value, field gradient, aspect ratio,

volume, arbitrary point

LaGriT Mesh Optimization

• Derefine–edge length, volume, aspect

Original Elements Filter: Remove small area and high aspect ratio elements while maintaining geometry.

LaGriT Mesh Optimization• Smooth

– elliptic, laplace, random

• Massage - refine-derefine-smooth

LaGriT Geometry

• Constructive Solid Geometry

surface/s_a/intrface/cylinder/x1,y1,z1/x2,y2,z2/radius surface/s_b/intrface/cylinder/x1,y1,z1/x2,y2,z2/radius surface/s_c/intrface/box/xmin,ymin,zmin/xmax,ymax,zmax/ region/r_ring/gt s_c and gt s_b and le s_a

Element Element Intersection• Mesh-Mesh Element Intersection

– Determine elements of mesh_a that are intersected by mesh_b

mesh_a

mesh_b

LaGriT Geometric Computing

point line tri quad tet pyr hexpoint X X X X X X Xline X X X X X Xtri X X X X X X

quad X X X X X Xtet X X X X X Xpyr Xhex X X X X X X

• Mesh-Mesh Element Intersection– Compute intersection of mesh_a with mesh_b

• Mesh-Mesh Intersection– Compute the line of intersection between two

triangulated surfaces in 3D space

Example: Mesh-2-Mesh Intersect

Intersect fault surfaces with mesh to select elements to be refined with quadtree type refine.

LaGriT Element and Node Set Manipulation

• Point and Element Sets: PSET, ELTSET– Attribute: le,lt,ge,gt,eq,ne

• e.g. nodes/elements with saturation > 0.5

– Geometry: xyz, rtz, rtp• e.g. nodes/elements inside a box, cylinder, sphere

– Region• e.g. identify all nodes/elements inside a region

– Logical: union, intersect, not• e.g. nodes/elements inside a sphere and saturation > 0.5

• e.g. nodes/elements inside a sphere or saturation > 0.5

LaGriT Element and Node Manipulation Commands

• Translate

• Scale

• Rotate: rotatept, rotateln

• Filter

• Perturb

• Remove

• Multi-Key Sort

• Reorder

• KDTree Search

LaGriT Grid Attributes• Real and integer node and element attributes

• Element area, element volume

• aspect ratio, dihedral angle, solid angle, min/max edge length ratio

• Identify Sliver, Wedge, Needle, Cap

• Unit normal, area normal vector

• Synthetic normal to surface nodes

• Volume/Area integration of floating point node or cell attributes

• Dual mesh connectivity

• Voronoi and median volume and face area

LaGriT Output Options

• PyLith

• GeoFEST

• FEHM

• AVS, GMV, Tecplot

• STL, FLAG, X3D

Mesh Manipulation

• Extract Lower D - 3D – 2D – 1D– Volume, Face, Line

• Extract 2D Surface (plane, isosurface, arbitrary triangulation) from 3D mesh

• Extract Line (well bore) from 3D mesh

Mesh Manipulation• Extract 2D Surface (plane) from 3D mesh.

Example: Mesh-2-Mesh Interpolate

Source mesh with attribute defined on nodes.

Sink mesh with attributes interpolated from source mesh. Nodes in sink mesh outside source mesh are identified.

0,0 0,0

Example Mesh-2-Mesh Interpolation

Voronoi – NearestPoint Integer Interpolation

Colors of fine quad mesh indicate nearest node of low resolution points.

Same Geometry, Different Mesh Method

METIS Interface• Supports METIS mesh partition algorithm calls

Partition:metis /partition/ metis_partmeshnodal / node / 32 metis /partition/ metis_partmeshdual / dual / 32

Reorder: metis / reorder / metis_edgend / dual metis / reorder / metis_nodend / node

What is the LaGriT Interface?

• Command Line Driven• Control File Driven• Call from Fortran, C, C++• Data structures can be accessed and

manipulated by user• Developer interface for extension and

user modules• Platforms: Linux, Mac, Sun, SGI

What LaGriT Is Not

• No GUI interface• No advancing front algorithm• No interface for ACIS, Autocad, … CAD • Not unstructured hex mesh (see Cubit)

Southern California Earthquake Center (SCEC) Community Fault Model (CFM)

Landers

Hector Mine

~54km EW~60km NS~17km Z

Finite Element Mesh With CFM Landers & Hector Mine Faults

Tet

Asp

ect R

atio

• Tetrahedral Finite Element MeshTetrahedral Finite Element Mesh

• 340km EW, 360km NS, 124km Z340km EW, 360km NS, 124km Z

• Element size ~50km far fieldElement size ~50km far field

• Element size ~500m near faultsElement size ~500m near faults

Mojave Block Model

Original Block Triangles

Filtered Block Triangles: Remove small area and high aspect ratio elements while maintaining geometry.

LaGriT

meshing.lanl.gov lagrit.lanl.gov