18.

2 Release

Module 3: Importing CAD with CFD Surface Mesh

Introduction to ANSYS Fluent Meshing

1 © 2017 ANSYS, Inc. 1/23/21

 Working with Closed Regions

• What you will learn from this presentation

− Introduction to workflows, Cad import and Cad preparation
− Reading in and working with a Surface from another package
− Basic Cad import options
− Size Field creation, terminology and usage
− Size Fields during import

2 © 2017 ANSYS, Inc. 1/23/21

 Preprocessing Workflow
Geometry
Geometry Import
Import Geometry
Geometry
Mesh
Mesh Import
Import Meshing
Meshing Solver
Solver
Operations
Operations
Geometry
Geometry Creation
Creation

Surface
Geometry Import Geometry Cleanup Remeshing
and Repair
Options
Meshing
Boundary Modify
Methods
Import CAD/STL
Hybrid Mesh:
Diagnostics Tet,Hexcore,
Prisms, Pyramids

Hole Filling
Read Mesh Thin Sweep

Gap Closing
Cutcell

Faceted
Geometry
Geometry Global Mesh
Preparation
Operations Sizing
Operations
Plane Surface,
Faceted Booleans Local Mesh
Revolve Edges,
Sweep Edges, etc
with Build Sizing
Topology
Create Box, Proximity,
Frustrum, Cylinder, Curvature, Body of
Fluid Extraction
etc Influence, Soft,
with Wrapper
Hard, etc.

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 Workflow for Working with Clean CAD
Create surface mesh upstream or
import with CFD Surface Mesh

Improve Surface mesh if needed

Set Volume Mesh controls

Prism/Tet/Hexcore options

Create Volume Mesh

44 © 2017 ANSYS, Inc. 1/23/21

 Reading Files

• Fluent Meshing can Read:

− Mesh files (.msh) (will retain volume elements)
− Boundary Mesh files (.msh) (will remove volume elements)
− Fluent Case files (.cas) (solver information retained on switching to solver mode)
• Fluent Meshing can Import:
− Mesh formats such as CGNS, PATRAN, NASTRAN, Fluent 2D, etc.
− STL files via Import  CAD
− Neutral CAD formats: STEP, IGES, ACIS, Parasolid
− CAD using Workbench CAD readers

5 © 2017 ANSYS, Inc. 1/23/21

 Preparing the Geometry in CAD (I)

• There are several benefits to using geometry tools to carry out some preparatory steps in
a CAD tool (e.g. Design Modeler (DM) or SpaceClaim Direct modeler (SCDM)) prior to
import into Fluent Meshing
− Extract Fluid
− Delete unwanted parts
− Defeature
− Close holes/gaps
− Fix faulty surfaces (faceting can fail)
− Set up boundary names (Named Selections)
with user-friendly tools such as extend to
limits (DM) or the Power Selection tool (SCDM)

Note that Naming from CAD tools will also be passed across
Note
e.g.that Naming from
Publications CADor
in CATIA tools
Facewill
NamealsoAttributes
be passedfrom
across
NX.
e.g. Publications in CATIA or Face Name Attributes from NX.
6 © 2017 ANSYS, Inc. 1/23/21
 Preparing the Geometry in CAD (II)

• Share topology can be invoked in both SCDM and DM to ensure a single

connected surface exists between bodies in a “Multi-Body Part” as with
Ansys Meshing
Design Modeler – Share Topo SpaceClaim– Share Topo

R18.1 and up, use Share tool in

the Workbench tab

R18.0 and earlier, set Share

Toplogy property for assembly to
Share

• Import Multi-body-part CAD models

with the option “One Object per Part”

7 © 2017 ANSYS, Inc. 1/23/21

 Surface Mesh Export From Ansys Meshing

• Surface Mesh only (no volume) applying size

functions etc. in ANSYS Meshing
− Choose a tetrahedral volume option to get all
triangular surface mesh
− Use Preview  Surface Mesh to get the surface mesh
“shell”
− File Export in format “Fluent Input Files (*.msh)”

• Optionally hex mesh some volumes

− Fluent Meshing allows pyramid or non-conformal
transition from pre-hexed volumes

8 © 2017 ANSYS, Inc. 1/23/21

 External Surface Mesh Import - Workflow

• CFD Surface Mesh CAD import automatically

produces Mesh Objects of adequate RMB
connectivity and quality
− The user should always verify by using Diagnostics
that connectivity and quality are good enough
before proceeding to volume meshing

• If a surface mesh has been imported from

another package, start by creating new
Objects by accessing the appropriate panel
from Unreferenced in the tree
− Select Face and optionally Edge Zones
− Choose Object Name, Type and Cell Zone type

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 CAD Import – Typical Options

• Optional single file or multi-file import

• Standard Options
− Import Curvature Data from CAD to base curvature
calculations on CAD surfaces and not on faceted
geometry
− Append will add any CAD files to the currently
loaded geometry rather than overwrite
• Edge Zones are added based on face-face
(Feature) angle and are added to edges
already existing in the CAD
• Length Unit is set here and used thereafter

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 CAD Import – Importing Options

• Basic CAD Options include:

– Capability to read any CAD files within lower subdirectories if multi-file import is chosen
– Save PMDB allows saving of a database file which is quicker to re-read
– Import Named Selections brings names through from geometry tools
– Choose granularity of boundary zones and Objects and how they are separated

11 © 2017 ANSYS, Inc. 1/23/21

 Import with CAD Faceting

• A light representation of faceted geometry is

generated
– Inputs are based upon length unit chosen
(m, mm, etc.)
– Tolerance specifies a minimum facet size. It is
recommended to use a value that is roughly 10
times smaller than the CFD surface mesh min size
– Max size sets the limits for maximum facet size
– Merge Nodes within machine tolerance (optional)

• Import with CAD Faceting option will result

in Geometry Objects

CAD Faceting is recommended for very large models and for models
where wrapper based workflows are planned to be used

12 © 2017 ANSYS, Inc. 1/23/21

 Import with CFD Surface Mesh

• High Quality, CFD surface meshes are generated

– Inputs are based upon Length Unit chosen
(m, mm, etc.)
– Use Size Field File (option will be described later)
– Min Size specifies the min mesh size which will be
reached in areas of high curvature/proximity
– Max Size specifies a maximum mesh size
– Growth Rate controls the max size change away from
areas of curvature or proximity
– Curvature and/or Proximity can be invoked to controls
the mesh density around curves or between gaps

CFD Surface Mesh takes more time but is recommended for

• simple to medium geometry or
• where conjugate heat transfer is planned to be used

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 Import with CFD Surface Mesh
– Curvature Normal Angle controls the mesh density
around curves.
• An angle of 18, should produce 20 cells around a circle
– Proximity enables the use of the edge and/or face
proximity size function for creating the CFD Surface Mesh
• based on the number of cells per gap specified
– Cells Per Gap specifies the number of elements to be
generated in the gap for the proximity size function
– Auto-Create Scoped Sizing will automatically create the
corresponding Curvature and/or proximity size controls
– Save Size Field (option will be described later)
• Import with CFD Surface Mesh option will result
in Mesh Objects

NOTE: For “clean” CAD It is strongly recommended to always import using the option: One Object per part
• This will ensure that Share topology is maintained

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 CAD import/management
• Import using CAD Assemblies
– Activate in the CAD import – Options … panel

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 CAD import/management

• Using the Cad Assemblies mode for CAD import in Fluent meshing has several
advantages
− It essentially represents the CAD tree in the same way it is presented in the CAD package it
was created, maintaining all sub-assembly levels
− It allows the user to re-import (update), very quickly, selective parts or bodies of the model
using different faceting qualities, and topology representations from a neutral database file
− Geometry and mesh objects can easily be created using only the assemblies/parts/bodies
that are needed for the analysis
− A link is maintained between the Geometry/Mesh objects and corresponding CAD objects
(locked ) for easy updates and design changes
− Face-zone labels can be assigned to entities and these are preserved throughout the Fluent
Meshing workflow
− Faster visualisation

• Overall time saving in part management of huge models

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 CAD Assemblies

• CAD Assemblies workflow example

1. Select external bodies to update

– Graphically select outside bodies
• Using box/polygon or manual selection

2. Update (from Graphics or tree)

– Opens the Update panel
– Change to CFD surface mesh
– Set relevant parameters
– Update and Close

17 © 2017 ANSYS, Inc. 1/23/21

 CAD import/management

• CAD Assemblies workflow example

3. Create Mesh Object

• Turn on the Face Edges
– A CFD Surface mesh has been created
• Object -> Create (from tree)
– Opens the create Object panel
– Select a suitable name
– Select mesh type
– Create

18
Check out “CAD-to-mesh using Fluent Meshing” Youtube video
© 2017 ANSYS, Inc. 1/23/21
 CAD import/management mode

• Characteristics
– Cad Assemblies are using different Color-palette, Context menus and
Short-cuts compared to Object based mode
– Icons exists for a majority of Short-cuts
• Use Ctrl-h to see all Short-cuts
– Selection filter; Cad Object and CAD Zones
• CAD Zones are highlighted in yellow
• CAD Objects are highlighted in orange
– Various Context menus
• Draw Options

• CAD assemblies
– Tree
– Selection Helper

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 CAD import/management

• CAD Management functionalities

– Many of the CAD management operations are available from both the tree and
through Graphics Short-cuts/Icons
– Update
• Reimport using new faceting parameters
– Object
• Creating and managing Geom/Mesh
objects from CAD Assembly
– State,…
- Cad objects are locked when
corresponding Geom/Mesh
objects are created
- Suppress instead of delete
– Modify,…
- Edge zones, Naming

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 CAD import naming conventions
• Import of CAD with Share Topology invoked in DM/SpaceClaim
– By default, the import by part (or file) does NOT use the part-name as prefix
R17.0 R18.0

• Option to Import CAD with or without features

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 CAD import - Object Type Recap

Geometry Objects:
Disconnected, poor
quality e.g. STL or CAD
Faceting

Mesh Objects:
Connected, high
quality triangle
mesh

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 CFD Surface Mesh - Curvature Normal Angle

• Curvature Normal angle refines the mesh size to capture changes in

curvature on the geometry. Lower curvature angles will give more
refinement as shown here.

23 © 2017 ANSYS, Inc. 1/23/21

 CFD Surface Mesh - Edge Proximity

Edge Proximity OFF Edge Proximity ON

Edge Proximity during CFD Surface Mesh import is relevant if the user wishes to try
to create the volume mesh from the original imported geometric faceting.
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 Sizing Definitions

• The CFD Surface Mesh controls are only a sub-

set of the Size Definition capabilities in Fluent
Meshing
• The Scoped Sizing Controls in Fluent Meshing are
very flexible and allow users to both
− Define Global sizing functions to quickly get a mesh or
Curvature
− Add Local sizing controls to e.g.
• Ensure a specific size is used in a specific area of the
geometry or
• Apply curvature/proximity to a finer level only in
i ty
certain areas x im
Pro
• Add refinement regions using “Body of influence”

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 Creating Size Fields using Scoped Sizing

• Access Scoped Sizing controls from the Model option in the Tree

− There are 6 different types of Scoped size controls

− These can be scoped to
• Objects or Zones
• Mesh or Geometry object types &
Unreferenced
• Wildcard strings or selections
− Option to create, modify, delete,
draw, list, write or read Scoped
Sizing
− Compute or Delete size fields
− Invoke size field Filters
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 Size Field Filters

• Using the Scale Factor in the Size Field Filter,

faces, solids or the full CFD model can quickly
be re-meshed with different mesh densities
Scale = 1.5

Scale = 0.7

Original mesh density

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 Scoped Sizing - Proximity

• Scoped Sizing gives access to face proximity

• Proximity size functions examine
− The proximity between selected edges or faces
− Refines sizes down to the limit of the user-specified minimum to resolve gaps properly.
− User specifies number of cells
Required across the gap in this case.

surface to be
remeshed

cells per gap = 2 cells per gap = 4

28 © 2017 ANSYS, Inc. 1/23/21

 Scoped Sizing - Proximity

• In this example normals are pointing inwards

• With Ignore orientation OFF

the surface mesh is not refined
along the groove length

• With Ignore orientation ON

the surface mesh is refined
along the groove length

Ignore Orientation disabled Ignore Orientation enabled

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 Scoped Sizing - Soft and Hard

• Hard size function sets fixed size

• Soft size function sets a maximum size
• Both can be applied to edge zones or face zones

soft size
function defined

hard size
function
defined

soft size
influenced by
hard size
hard size on function on
remeshed adjacent
surfaces
surface

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 Scoped Sizing - Meshed

• Meshed size function allows us to take the sizes based on sizes given on
zones already present
• In the below example a meshed SF is applied to the grey zone
− The adjacent green zone is remeshed to grow smoothly from that sizing

zone to be zone remeshed using

remeshed meshed size function

premeshed premeshed
face zone face zone

31 © 2017 ANSYS, Inc. 1/23/21

 BOI: Body of Influence

• BOI can be used to limit the boundary mesh size within a volumetric region
• In the example below the surface mesh is remeshed with a BOI restricting
the growth at the rear of the car on the symmetry plane
• BOI is in essence a soft size control

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 BOI: Arbitrary Shaped Bodies of Influence

• BOI can be used to refine the mesh

− On surfaces
− On volumes
• Boundary Zones and Edge Zones which are “Unreferenced” by any Objects
can be used as entities for size functions as well

We can create an
“unreferenced” surface
here to apply a more
refined mesh sizing using
a hard/soft sizing to help
capture the shear layer

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 Size Field Handling

• When a Size field has been Computed (or read)

− Scoped Sizing operations become greyed out
− To change the Scoped Sizing definitions, the available Size
Field must first be deleted

• It is possible to Write and Read Size Fields

− File  Write  Size Field
− File  Read  Size Field
• The common extension for Size fields are “name.sf”

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 Import CAD with Size Field

• An existing Size Field file (*.sf) can be utilized during CAD

import for CFD Surface Mesh CAD Import
− It gives the user the ability to obtain a high-quality surface
mesh with extended, local control of the sizing at CAD
import
− Possible to have full control over sizing at import by
1. Using CAD Faceting (STL like) to quickly obtain a CAD import
which will allow the definition of the sizing function and apply
– e.g. needed face-face proximity, hard/soft sizing to specific surfaces,
etc
2. Save the sizing function and use it again when reading the same
CAD file with CFD Surface Mesh.

35 © 2017 ANSYS, Inc. 1/23/21

 Save Size Field on Import

• The user also has the ability to save the size

field generated during standard CFD Surface
Mesh Import

• Allows user to import this Size Field later and

use for remeshing /wrapping/cutcell/tetra etc.

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 Size Field Visualization

• After computing the Size Field we can verify the

local size distribution

• Size probes
− Click on or use (Ctrl-Y)
− Use RMB on the model

• Size Contours
− Use Short-cuts (Ctrl-t) then (Ctrl-c)

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 Typical Workflow for Sizing

1. Assign Scoped Sizes to face/edge zones

− globally and locally

2. Compute the Size Field

3. Visualise the Size Field after computation
4. Check whether the Size Field is fit for purpose
− e.g. is it resolving the small gaps needed?
Size Probe
5. Optionally delete Size Field, modify the size controls
and re-compute
6. Use Size Field to: Re-import with CFD surface mesh,
wrap, remesh, create tet mesh, create Cutcell mesh

Here, additional size functions would be needed

to resolve trailing edge (e.g. hard or proximity)
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 Workshop WS03 – CAD Import and Meshing from
CFD Surface Mesh Import

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 Appendix

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 CAD import/management

• CAD Assemblies workflow example

1. Let’s prepare the brake assembly for meshing

– Select the Assembly from the tree and draw

2. Assign a Face Zone Label

– Change to Zone selection
• Pick the “brake cover “
– Select the “Label” icon
• This will open the
Manage Labels Panel
– Assign Label names
- Use default Create/Add
label option
- The label name will remain
throughout the meshing
process
41 © 2017 ANSYS, Inc. 1/23/21
 CAD import/management

• CAD Assemblies workflow example

3. Select external bodies to update

– Deselect the brake assembly from
the tree (Ctrl-LMB) and graphically
select outside bodies
• Using box/polygon or manual selection

4. Update (from Graphics or tree)

– Opens the Update panel
– Change to CFD surface mesh
– Set relevant parameters
– Update and Close

42 © 2017 ANSYS, Inc. 1/23/21

 CAD import/management

• CAD Assemblies workflow example

5. Create Mesh Object

• Turn on the Face Edges
– A CFD Surface mesh has been created
• Object -> Create (from tree)
– Opens the create Object panel
– Select a suitable name
– Select mesh type
– Create
• Object -> Update from CAD (from tree)
– Advanced options

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 CAD import/management
Select visible
• CAD Assemblies workflow example

6. Suppress remaining bodies in object

• Change in display and tree
– CAD Objects that has been transferred
to Mesh Objects are locked
• Pick the remaining 670 objects !
– Use select Visible
• Suppress
- Using graphics Icon
- Tree- Icon changed to indicate suppressed

Using this workflow, only necessary parts are

transferred into objects for CFD meshing

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 CAD import/management

• CAD Assemblies Replacement example

1. Prepare for replacement
– From CAD Assemblies I have created a Geometry object (displayed)
– A new Cad Assembly has been appended to the existing assembly, including
a new design

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 CAD import/management

• CAD Assemblies Replacement example

2. Replace
– Take the new assembly, use RMB -> object Replace
• Pick up the old object from the pop-up panel and Replace

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 CAD import/management

• CAD Assemblies Replacement example

3. Final state
– Link broken between old CAD and new object and new link established

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 Periodic Matching of Sizes

• Periodicity is used to enforce conformally matched periodic meshes after

meshing
• Set-up of periodicity is accessible from Model tree, Scoped sizing and Size
Function panels
• By defining Periodicity, periodic Size function and re-projection of periodic
zones during surface wrapping are also invoked
− Use Define and then choose 6 points + Angle to define the periodicity
1 2 3

4 5 6
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 Size Function Panel

• Size Function Setup 1

1. Set Global Controls – decide absolute min,
max and growth rate for your mesh
4
2. Select Face Zones of interest OR
3. Select Edge Zones of interest 2 3

4. Apply size function type and inputs for 5

those Zones (e.g. soft, hard, curvature,
proximity). Can have multiple sets here e.g.
proximity or hard only on a few specified
Zones
5. Compute Size Field
6. Use computed Size Field for operations such
as remeshing, cutcell or wrapping
50 © 2017 ANSYS, Inc. 1/23/21
 “Quick” Size Function Defaults

• The “Create Defaults” button will use Global

min, max and growth rate inputs to create
1. Curvature size function on all Edge Zones
(default 18 degrees angle)
2. Curvature size function on all Face Zones
(default 18 degrees angle)
3. Proximity size function on all Edge Zones
(default 3 cells across gap)
4. Proximity size function on all Face Zones
(default 3 cells across gap)

“Create Defaults” should be used with caution and best results will occur when user
takes some time to consider the best sizings for a problem. For simple geometries it
can be a useful tool for a quick “look-see” test.

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 Size Function – Draw Sizes

• Draw Sizes will overlay boxes onto the display showing specified
− Min size
− Max size

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 STL Geometry from Spaceclaim 1

• Exporting from SpaceClaim to Fluent Meshing

− Checklist for STL export
• Save As STL
• Export options
• File
– For multi-assembly – “Per component”
– For single assembly – “Per body”
• Resolution; Custom
– Deviation : use 1/10 of min-size
– Angle : ~ ½ of expected curvature angle
– Facet Maximum edge length : ~Max size
• This will create one STL per body/part

• Fluent Meshing stl import

• File > Import > CAD…
– Multiple file read option
– Pattern: *stl
– One Object per file

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 STL Geometry from Spaceclaim 2

• STL import from SpaceClaim

− Good quality conformal faceting
− Often results in zero free faces – conformal remeshing possible

SpaceClaim Fluent Meshing

54 © 2017 ANSYS, Inc. 1/23/21
 One Object Per File

• One Zone Per File is useful when each

object or set of surfaces is contained in a
file with a meaningful name
− E.g. STL files named by part/body
− Import all *.stl files within folder
− One zone per file will name objects and face
zones after the file name

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 CAD Import Text User Interface (I)

56
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 CAD Import Text User Interface (II)

57
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 CAD Import Text User Interface (III)

58
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 CAD Importer Executable

• To kill the CAD import

− go to the process list and look for python.exe.
− If you kill this the CAD import is terminated but the Fluent interface remains live

59 © 2017 ANSYS, Inc. 1/23/21

 Simple Example – Using Size Functions

BOI Shape

*Top face hidden here

• The simple example shows a problem of flow past two extruded ellipses
• Named Selections are shown at the side as created in DM
• A BOI shape can be arbitrary and here the purple shape is used to refine
the mesh
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 Step 1 – Set Global Controls and Draw Sizes

• Add inputs for Min, Max and Growth

Rate then apply and Draw Sizes to
check the validity of inputs

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 Step 2 – +1 Curvature Size Function
Curvature SF on walls

• Curvature SF ensures Wrapped Result with Above SF

refinement on the walls
of the extruded ellipses
• However, the gap is not
refined and a wrap will
give the result shown
with un-resolved gap Resolved

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 Step 3 – +1 Proximity Size Function
Proximity SF on walls

• Proximity SF adds Wrapped Result with Above SF

refinement in the gap
• We now have at least
3 cells in the gap

Resolved

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 Step 4 – +1 BOI Size Function

• BOI SF adds refinement on the Wrapped Result with Above SF

boundaries to limit the mesh

size to the value specified
(1mm here)

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 Step 5 – +1 Proximity Size Function

• Finally, a second Wrapped Result with Above SF

proximity SF is added
to the top and bottom
surfaces to ensure at
least 3 cells between
them as well.

Resolved
65
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 Step 6 – Use Size Function for Tet

Resolved Wake

• When we come to Auto Mesh,

in the Tet mesh panel we
choose Cell Sizing based on Size
Function as well to ensure the
BOI refinement region is
captured.

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