Extrusions

Extrusions
In This Section:
•
Normal
•
Rotate
•
Translate
•
Path
•
Face assembly
•
Combo
•
Hybrid grids
•
Create a 3D extruded
axisymmetric grid
•
Aft continuation for
sting or rocket type
geometries.
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Extrusion Overview
•
Normal extrusion includes both
Algebraic and Hyperbolic
methods.
•
Selection required: a connector or
connectors to extrude domains, a
domain or domains to extrude
blocks.
•
If both connectors and domains are
selected, the connectors will be
ignored.
134
Normal Extrusion
•
Normal extrusion is available
for extruding connectors and
domains.
•
Setup: set Attributes,
Boundary Conditions and Run
parameters.
135
Normal Extrusion
Normal – Hyperbolic Attributes
•
Enforce minimum and maximum
marching step sizes.
•
For connectors a marching plane
and direction can be specified . For
domains you can reverse the
marching direction using Flip.
•
Connector extrusion can be
constrained to database surfaces.
•
Standard hyperbolic smoothing
parameters. Use a Kinsey Barth
value of 3.0 when extruding from
significantly concave regions.
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Normal Extrusion
Normal – Algebraic Attributes
•
Enforce minimum and
maximum marching step
sizes.
•
Connector extrusion can be
constrained to database
surface.
•
Laplacian style smoothing is
used locally on both extrusion
directions for each point and
extrusion step size. You can
adjust the number of
iterations each type of
smoothing is run.
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Normal Extrusion
Normal – Boundary Conditions
•
Select Type.
•
Adjust any type related settings.
•
Use Set Boundary Condition to
save the new BC to the
boundary.
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Normal Extrusion
Normal – Boundary Conditions
•
Adjacent Grid forces selected domain boundaries to lie on
an adjacent, connected structured domain.
•
Arbitrary Plane automatically determines a plane in
which each boundary connector of an unstructured domain
lies and forces that boundary to remain in plane during
prism extrusion.
•
Database Constrained forces selected domain
boundaries to lie on an adjacent database surface.
•
Constant X, Y, Z holds the corresponding coordinate
direction constant for all points on the selected boundary.
•
Splay causes the selected boundaries to move outward as
extrusion proceeds. Not available for unstructured
domains.
•
Symmetry X, Y, Z keeps the grid symmetric in the
corresponding coordinate direction on the selected
boundary.
139
Normal Extrusion
2nd
•
For our example case we will import the
“cone-db.pw” database and turn off all
layers but the “Construction” layer.
•
Set a default Dimension of 31, a
Begin Δs of 0.1 and an End. Δs of 5.0.
•
Now create a 2 Point Curve connector
on the cone profile curve by first picking
the nose point and then the aft most
point. Note that the 2 Point Curve
command will give you a Line on
Database segment type when both
points lie on the same database entity.
•
Finally, select the connector and
perform a hyperbolic Normal extrusion
in the XY plane using an initial spacing
of 0.01, a growth rate of 1.2, X and Y
Symmetry BCs, and for 39 steps.
1st
140
Rotate Extrusion
•
Simple setup: specify
number of steps , angle of
rotation, and specify the
rotation axis.
•
Attributes tab provides
control for the Step Size
Method: Equal or
Subconnector, as will as
Orientation and Stop
Conditions.
141
Rotate Extrusion
•
For our example, rotate the
symmetry domain 180
degrees with 20 steps.
•
The original cone database
axis can serve as rotational
extrusion axis here as well.
142
Translate Extrusion
•
Simple setup: specify number
of steps , direction, and
distance.
•
Attributes tab provides
control for the Step Size
Method: Equal or
Subconnector, as will as
Stop Conditions.
143
Translate Extrusion
Now for our case extrude the
aft exit domain 16 steps
through a distance of 100
units along the X axis
direction.
144
Path Extrusion
Simple setup: select path
connector(s), whether to
maintain orientation with
respect to the path and set
number of steps.
145
Path Extrusion
•
As an alternative to the previous
translational extruded aft block, now
create a path connector with
distribution to use instead with the
Path type. This approach allows you
to stretch the grid going aft as part
of the extrusion.
•
First, Undo the previous block, or
use Edit, Delete Special (Ctrl
+Delete) to delete the block with its
domains and connectors.
•
Create a new two point connector
with Dimension of 11, a Begin. Δs
of 6.0 and End. Δs of 20. Start it at
any of the aft plane nodes and end it
100 units in the +X direction.
•
Finally, select the aft exit domain
again and perform a Path extrusion
using this new path connector.
146
Extrude Edge/Face Assembly
•
Interactive tool for
controlling how multiple
connectors will be
combined into edges and
domains into faces.
•
Assemble tab appears
immediately upon entry
with multiple entities. Run
tab replaces Assemble on
Done.
•
Edge/Face assemblies
cannot be modified after
moving on to the Run tab.
You must exit Extrude and
return to change assembly
layout.
147
Combo Extrusion
It is also possible to combine the
extrusion of structured and
unstructured domains into a
hybrid grid. Here is an example of
a translational combo extrusion of
the airfoil geometry.
148
Creating Hybrid Grids
Pointwise supports construction
and export of hybrid grids –
grids which contain a mixture of
cell types.
Cell types currently supported
by Pointwise include
quadrilaterals, triangles,
hexahedra, tetrahedra, prisms,
and pyramids.
With the exception of pyramids,
grid construction with all of
these cell types has already
been discussed. A simple 2D
example is shown here.
149
Creating Hybrid Grids
An example of a simply 3D hybrid grid is
shown here. The unstructured block
contains two types of cells, tetrahedra
and pyramids.
The pyramids were created automatically
by the unstructured solver along the
upper surface of the unstructured block to
interface the tets below with the
structured domains bounding that
surface.
The inset shows the pyramids in the first
layer of cells in the unstructured block in
a view looking up from below – the wing
leading edge is on the right.
150
Pyramids and the Unstructured Solver
The characteristics of the pyramids
generated by the unstructured solver can
be controlled just like those of tetrahedra.
The controls are located on the attributes
tab of the Solve command:
Min. Height setting the minimum
allowable pyramid height.
Max. Height setting the maximum
allowable height.
Aspect Ratio specifying the aspect ratio
used to scale nominal pyramid height to
give the true pyramid height.
151
Structured Viscous Layers
Most hybrid grids are
constructed for viscous
analyses. Generally they are
created with either a prism
(left) or hex (right) viscous
layer, both of which provide
proper grid structure and
growth through the
thickness of the layer. The
remainder of the volume is
usually filled with tets.
152
Hybrid Example Setup
For our example case we will import
the “class-3dunstr.pw” project and
delete the three connectors
extending from the cone to the
farfield. This leaves the database,
the domain on the cone, and the
farfield domain.
153
Hybrid Prism Extrusion
•
Now extrude the prism layer using the
domain on the cone and Normal
extrusion type.
•
Set the initial spacing to 0.01, growth
rate to 1.2, and Constant X and Z BCs.
•
March for 25 steps.
154
3D Hybrid
•
Create the three
connectors from the prism
layer final front to the
farfield. Use a default
Dimension of 15, Begin.
Ds of 0.7 and an End. Ds
of 10.0. This beginning
constraint value should be
close to the spacings found
in the final prism layer in
the marching direction.
•
Close the symmetry
domains and exit domain
by selecting only the
perimeter connectors for
each and using Assemble
Domains on the toolbar
one at a time.
155
3D Hybrid
•
Select these three new domains, the
farfield domain, and the prism
extrusion final domain.
•
Click Assemble Blocks.
•
Note message window update: “Info: 1
blocks created, 0 domains unused.”
Syllabus
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