Transcript Document

Mesh Morph 2.0 Tutorial
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Mesh Morph has 3 main tools (Methods); 2.5D Hex Mesh, Copy Pave Mesh,
and Loft Hex Mesh. The main purpose of the tool is hex meshing and the
2.5D Method is the primary tool for that.
•2.5D Hex Mesh: Extrudes hex elements from a
starting shell mesh along a path bounded by shell
elements.
•Copy Pave Mesh: Copies a Paved mesh from one
surface/face to a topologically identical one.
• Loft Hex Mesh: Lofts a Hex mesh between a paved
trimmed surface and a topologically identical unmeshed
trimmed surface.
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Definition of a 2.5 D solid or Mesh region.
A 2.5D solid has an obvious extrusion path through the solid/region. Through
this extrusion path, the cross section can change shape, but the topology must
remain constant. That means that the number of holes and edges must remain
the same. As a result of this limitation, all side faces or surfaces will be 4 sided.
Blind Hole
Fillet Area of a larger part
Tapered Press fit shaft with shear pin
Not a 2.5D solid/region, but is
made up of 4 simple 2.5D regions.
Not a 2.5D solid/region, but can
be modified to be one.
Shape changes from square to round. Hole
Changes from round to square.
Section of a turbine blade with cooling channels
Not a 2.5D solid/region
Modified solid from above is now
a 2.5D solid
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This metal fitting is NOT a 2.5D region, but can be
divided into 7 different 2.5D meshing regions.
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2.5D Hex Mesh
This feature is the main purpose of the tool and the main focus of this document.
You start with just shell elements, typically on faces of a solid, but no solid is required. All faces will be
meshed accept the end face (End Surface).
Smoothing parameters that control the smoothing
of each layer. Normally the defaults should be
used.
Smoothing strategies if either starting mesh
(Bottom Elements) or ending face (End Surface) is
significantly convex or concave.
Starting mesh, typically a trimmed surface or
complex face of a solid. Input is Either elements or
meshed face(s)/surface(s).
Sides of the 2.5D meshing region. The mesh must
be a structured iso-mesh type mesh. Input Can be
geometry (meshed) or elements.
OPTIONAL. The “End Surface” is the surface or
face at the opposite end of the “Bottom Elements”
in the solid. It must have the same topology as the
surface in the “Bottom Elements” databox. This is
only required if it is NOT flat. This is used to
project the final layer of elements on to.
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2.5D Hex Mesh - Example
1)
This part is actually a fillet area of a more
complicated part. Original faces and created
surfaces are combined to create this geometry.
2)
The surfaces are meshed and equivalenced.
4)
3)
Resulting Hex Mesh
The red elements (surface selected) are selected at
the “Bottom Elements” and the green elements (by
selecting the surfaces) are selected in the “Side
Elements” data box.
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2.5D Hex Mesh – Use of Other Features
Inner hex layers not effected by convex top and bottom faces.
Inner mesh layers will tend to be flat.
End mesh does not match face contour.
Mesh Direction
Selecting optional “End Surface” fixed the problem.
Inter-Layer Smoothing fixes the problem. This smoothing is
done after the first phase of the meshing is complete. If the
starting or ending face is so concaved that a layer of hexes end
up outside the solid, this option may not work. This option is
usually used in addition to the optional “End Surface”.
Mesh Direction
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2.5D Hex Mesh – Common User Error
You will get this error if:
• You forget to equivalence.
• The side does not match the starting mesh (cracks in mesh)
• The side mesh does not have a consistent number of rows of elements. Often this happens if
you forget to mesh the inside of holes or when the side mesh inside a hole does not have the
same number of rows as the outer face mesh.
Check for free edges and inspect side mesh to make sure all sides are meshed and there are a consistent
number of mesh rows.
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2.5D Hex Mesh – Limitations and Work-Around
There is a limit to how much distortion and the kind of distortion the region can be subject to. Some kinds of distortion is
more sensitive than others. Simple edits to the solid can fix many of the problems if it is not too extreme.
1.10
(Top)
Large relative hole position change
End Mesh (Bottom), Very bad smoothing
problems the farther down the solid you get.
(Top)
(bottom)
(bottom)
1.5
Adding vertices opposite
the hole on the top and
bottom helps the edge
mesh track the hole.
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Significant improvement
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2.5D Hex Mesh – Limitations and Work-Around – Other examples
Cut view of distorted mesh
Too much distortion to fix. Solution: ask
designer to not make diagonal holes this steep.
Twisting Hole – This is a 30 deg. twist.
Solution: edit the geometry and remove the twist.
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2.5D Hex Mesh – Limitations and Work-Around – Other examples
Large Distortions….No Problems here, almost. This part twists, changes shape from square to round and round to square. It
also scales .5x and than back to normal scale again.
Bottom
Top
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Middle
This distortion is
unavoidable
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2.5D Hex Mesh – Known Bugs
•The wrong element normals for the starting mesh (Bottom
Elements) can cause inside out elements. Patran can fix them
under normal element verify if there are problems.
•Higher order elements are not supported. Modify the
elements after hex meshing in Elements form and convert them
to the higher order elements.
•If there are no nodes in the center of the mesh (only boundary
nodes) it will fail with a trace back.
•If you are running on a PC, to avoid screen flashing, minimize
all other windows and applications behind Patran.
•It is slow, so don’t test with 50,000 shell elements unless you
like watching grass grow.
•The other main options, which were not covered here can
have trouble with Parasolids because you can not control
where vertices are placed.
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