ANSYS-Explicit Dynamics Meshing Part A

What is required of Meshes for Explicit Applications?

Uniform element size (in finest zoned regions)

– Smallest element size controls the time step used to advance the solution in time

– Explicit analyses compute dynamic stress waves that propagate throughout the entire mesh

Element size controlled by the user throughout the mesh

– Not automatically dependent on geometry

Implicit analyses usually have static region of stress concentration where mesh is refined (strongly dependent on geometry)

In explicit analyses, the location of regions of high stress constantly change as stress waves propagate through the mesh

– Mesh refinement is usually used to improve efficiency

Mesh transitions should be smooth for maximum accuracy

Hex-dominant meshing preferred

– More efficient

– Sometimes more accurate for slower transients

Mesh

Right-click Mesh in the Outline Tree to:

– Insert

Method

Sizing

-Important for Explicit

Contact Sizing

Refinement

Mapped Face Meshing

Match Control

Pinch

Inflation

– Update

– Generate Mesh

– Preview Surface Mesh

– Show Sweepable Bodies

– Preview Inflation

– Clean

– Rename

Meshing Methods

Solid Bodies

-Automatic

-Tetrahedron

-Hex Dominant

-Sweep

-Multizone

-CFX-Mesh

Surface Bodies (Shells)

-Quadrilateral Dominant

-Triangles

-Uniform Quad / Tri

-Uniform Quad

Line Bodies (Beams)

-Automatic

Meshing Methods – Solid Bodies

Tetrahedrons

– Advantages

An arbitrary volume can always be filled with tetrahedra

Can be generated quickly, automatically, and for complicated geometry

– Disadvantages

Element and node counts are higher than for a hex mesh with a similar mesh density

Generally not possible to align the cells with a flow direction

Not well suited for thin solids or annuli due to non-isotropy of geometry and nature of

Element

Tetrahedrons - Patch Conforming

-Default Tetrahedron Mesher

-All Faces, Edges, Vertices of the geometry are respected during mesh generation

-Delaunay Method

-Not good for Explicit Dynamics

Tetrahedrons - Patch Independent

-Recommended Tet mesher for Explicit

-Faces, Edges, Vertices not always respected

-Octree Method

-Element size Defined By

-Maximum Element Size

-Approx. number of Elements

Hex Dominant

– Useful for meshing bodies that cannot be swept

– Recommended for meshing bodies with large interior volumes

– The hex-dominant meshing algorithm creates a quad-dominant surface mesh first, then pyramid and tetrahedral elements are filled in as needed

Always check interior of mesh for good element structure

“Control Messages” will appear to warn you if volume may not be suitable for hex-dominant meshing

Hex Dominant

Sometimes produces a better (more uniform) mesh if a size control is placed on one or more edges / surfaces of a body

Mesh Methods – Sweeping

– Sweep

Sweeping from a single source face to a single target face

– Thin Sweep

Good at handling multiple sources and targets for thin parts

– Multizone

Uses a free decomposition approach

– Attempts to automatically slice geometry into sweepable regions

Supports multi-source and multi-target

Sweep methods for generating pure hex meshes

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ANSYS-Explicit Dynamics Meshing Part B

http://www.cadfamily.com/HTML/Article/ANSYS-Explicit%20Dynamics%20Meshing%20Part%20B_813.htm