ANSYS Explicit Dynamics - TUTORIALS...Explicit Dynamics: Meshing ANSYS Explicit Dynamics Explicit...

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Transcript of ANSYS Explicit Dynamics - TUTORIALS...Explicit Dynamics: Meshing ANSYS Explicit Dynamics Explicit...

  • 1-1 ANSYS, Inc. Proprietary

    2009 ANSYS, Inc. All rights reserved. February 27, 2009

    Inventory #002665

    Chapter 5 Explicit Dynamics: Meshing

    ANSYS Explicit Dynamics

  • Explicit Dynamics: Meshing

    1-2 ANSYS, Inc. Proprietary

    2009 ANSYS, Inc. All rights reserved. February 27, 2009

    Inventory #002665

    Training Manual 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

  • Explicit Dynamics: Meshing

    1-3 ANSYS, Inc. Proprietary

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    Training Manual Mesh

    Right-click Mesh in the Outline Tree to:

    Insert

    Method

    Sizing

    Contact Sizing

    Refinement

    Mapped Face Meshing

    Match Control

    Pinch

    Inflation

    Update

    Generate Mesh

    Preview Surface Mesh

    Show Sweepable Bodies

    Preview Inflation

    Clean

    Rename

    Important for Explicit

  • Explicit Dynamics: Meshing

    1-4 ANSYS, Inc. Proprietary

    2009 ANSYS, Inc. All rights reserved. February 27, 2009

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    Training Manual 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

  • Explicit Dynamics: Meshing

    1-5 ANSYS, Inc. Proprietary

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    Training Manual

    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

    Meshing Methods Solid Bodies

  • Explicit Dynamics: Meshing

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    Training Manual Meshing Methods Solid Bodies

    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

    Curves in Geometry are Reflected in the Mesh

  • Explicit Dynamics: Meshing

    1-7 ANSYS, Inc. Proprietary

    2009 ANSYS, Inc. All rights reserved. February 27, 2009

    Inventory #002665

    Training Manual Meshing Methods Solid Bodies

    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

    Curves in Geometry NOT reflected in the Mesh

    Max. Element Size = 2.5 mm Max. Element Size = 1.0 mm

  • Explicit Dynamics: Meshing

    1-8 ANSYS, Inc. Proprietary

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    Training Manual

    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

    Solid Model with Hex dominant mesh :

    Tetrahedrons 443 (9%)

    Hexahedron 2801(62%)

    Wedge 124 (2%)

    Pyramid 1107 (24%)

    Meshing Solid Bodies

  • Explicit Dynamics: Meshing

    1-9 ANSYS, Inc. Proprietary

    2009 ANSYS, Inc. All rights reserved. February 27, 2009

    Inventory #002665

    Training Manual Meshing Methods Solid Bodies

    Hex Dominant Sometimes produces a better (more uniform) mesh if a size control is

    placed on one or more edges / surfaces of a body

  • Explicit Dynamics: Meshing

    1-10 ANSYS, Inc. Proprietary

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    Training Manual 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

  • Explicit Dynamics: Meshing

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    Training Manual Meshing Methods Sweeping

    Multizone

    Direct decomposition of complex geometries at the time of meshing to create a hex mesh

    Select source and target surfaces for the Multizone sweep mesher

  • Explicit Dynamics: Meshing

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    Training Manual Sweep vs. Thin Sweep

    Use Sweep When:

    The side faces are not thin

    You only have 1 source and 1 target

    The sweep direction changes along the path

    Use Thin Sweep When:

    The side faces are thin

    In general, thin means that the side faces are small in relation to the source faces (aspect ratio of sides/sources is ~ 1/5th)

    You only have multiple sources and targets

    Path is linear

    Sweep

    Thin Sweep

  • Explicit Dynamics: Meshing

    1-13 ANSYS, Inc. Proprietary

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    Training Manual Sweep vs. MultiZone

    Use Sweep when you have a multibody part where some bodies should be meshed with Sweep, and some with Patch Conforming Tet

    Preview Sweepable Bodies shows all bodies that are sweepable

    Use MultiZone when

    you are meshing single body parts that are too complicated for Sweep

    you have multiple sources and targets you need to respect

    Example:

    Using Sweep, the single body part (left) must be manually sliced into a Multibody part containing five bodies (center) to obtain a pure hex mesh (right)

    With Multizone, it is meshed automatically!

  • Explicit Dynamics: Meshing

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    Training Manual Thin Sweep vs. MultiZone

    Use Thin Sweep when you have a thin solid part where the source and target faces

    dont exactly match, and you dont care about the features on the target side

    Multiple source Multiple target

    Multiple sources captured Multiple targets ignored

  • Explicit Dynamics: Meshing

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    Training Manual Thin Sweep vs. MultiZone

    Use MultiZone when you have a thin solid part where the source and target faces dont exactly match, and you care about the features on both sides

    Multiple source Multiple target

    Multiple sources captured Multiple targets captured

  • Explicit Dynamics: Meshing

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    Training Manual Meshing Methods - Solid Bodies

    This is the default Method for Explicit

    Ensures that preferred Hex meshes are generated whenever bodies can be

    swept

    If any bodies are not swept, the tetrahedron meshes generated for these bodies

    should be remeshed by inserting a method that generates a Patch Independent

    Tet. mesh for those bodies

    Automatic (Patch Conforming/Sweeping)

    Sweepable bodies are automatically swept

    If a solid body cannot be swept it will be meshed using the Patch

    Conforming Tetrahedron mesher

  • Explicit Dynamics: Meshing

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