wrapping, fixing and sewing objects -...

© 2011 ANSYS, Inc. December 21, 2012

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14.5 Release

Lecture 8: Wrapping, Fixing and Sewing

Introduction to ANSYS Fluent Meshing


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Agenda

• Assembly Meshing Workflow

• Pre-Wrap Settings

– Real Creations

– Virtual Creations

• Wrapping Methods

• Gap Removal

• Thickness Removal

• Surface Mesh Creation

• Tips and Tricks

– Feature Suppression with shrink-wrap

– Special TUI commands


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Agenda



– Real Creations



• Gap Removal



• Tips and Tricks




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Wrap Flow Volume

Assembly meshing Workflow Schematic

Gap closing

Auto Mesh

-Prism Setup

-Tet or HexCore

Individual “Wrap” or Change to “Wrap”

Extract Flow-volume (only)

Multiple Fluids/Solids Extract Fluid + Solid

Gap closing

Make “Mesh”+Improve Improve

Sew

Create Size Function/ Material points

Cap Inlet/Outlets, Create Domains/BOI

Tessellated or Conformal CAD import Import

Real Creations

Wrapping Operations

Surface mesh

Volume mesh

Virtual Creations


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• We will refer to the new area of the GUI as the Task Page and use this to carry out “Object-Based” meshing which is a new concept at R14.5 compared to earlier “Domain-Based” meshing as outlined on Training DAY1

Assembly Meshing Workflow GUI

“Real Creation” for Geometry/Refinement Zones

“Virtual Creation” for Meshing/Management

Object Manipulation/Modification

Surface Mesh Operations

Volume Mesh Operations


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Agenda



– Real Creations



• Gap Removal



• Tips and Tricks




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• Before proceeding to the wrapping of objects, the user must first ensure the geometry is in the correct state to extract flow/solid volumes

• This could mean creating the external bounding box or cylinder or it could mean capping inlets/outlets/interiors

• There are a number of tools in the new workflow to enable the user to do that easily

Pre-Wrap Geometry Creation


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• Using Absolute user can select zones and hit Compute to auto-populate bounding box coordinates

• Switch to Relative and supply a Delta in each direction to give space around the objects you draw the bounding box around

• Supply an Edge Length to specify constant facet size on box

• If creating a piece of geometry e.g. the outer domain the user should select Create Object

• If creating box for refinement region only the user should deselect Create Object

Create Box


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• In some cases, you may want to create a cylinder

within the existing geometry (e.g., creating an

MRF zone for problems involving moving parts

such as rotating blades or impellers).

• By Locations allows you to specify the locations ( X Pos, Y

Pos, Z Pos) of the points P1 and P2, defining the cylinder

axis or using Select Points to pick them graphically

• By Nodes allows you to specify the nodes corresponding to

the points defining the cylinder axis or arc points at the

centre of the cylinder.

• Radius specifies the radius of the cylinder to be created

– Specify different R1 and R2 to create frustrum

• Edge Length specifies the size of the cells to be created for

the cylindrical surface mesh.

• Preview allows you to preview the cylinder to be created

• Create Object should be selected if user is creating

geometry, e.g. flow domain. For refinement regions an

object is not required.

Create Cylinder (Caps)

P1 P2

r1 r2


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• The Cylinder tool can also be very useful for patching gaps/holes for cylindrical geometry. Method:

– Select 3 Arc, 1 Height Node

– Select Nodes… Choose nodes 3 on one edge and 4th on opposite edge

– Deselect Caps and Create Object

– Give Edge Length, Preview and Create

Create Cylinder (No Caps)

N1 N2

N3 HN4

N3 N2

N1

HN4

Example – annular patch Example – Frustrum “side” patch

CREATE CREATE


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Agenda



– Real Creations



• Gap Removal



• Tips and Tricks




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Size Functions

Size Function Types • Curvature: Specify Min, Max size, Max Angle

between normals and Growth Rate. (Can be applied to edge or face zones.)

• Proximity: As above except you specify the number of cells per gap instead of the max angle between normals. (Can be applied to edge or face zones.)

• Meshed: The size is determined from the mesh size on the geometry (not suitable for CAD STL). (Can be applied to edge or face zones.)

• Soft: Specify the Max size and the growth rate. The local size is allowed get smaller based on other size functions (e.g. curvature and proximity). (Can be applied to edge or face zones.)

• Hard: Specify a fixed min size for the zone. The local size fixed and is not allowed to get smaller or larger. (Can be applied to edge or face zones.)

• BOI (Body of Influence): Select a zone from the list of zones to serve as a body of influence. Defines the max size of cells within that volumetric region and acts as an arbitrarily shaped refinement region for capture of flow features such as turbulent wakes.

If the BOI is only used for refinement purposes users should ensure not to include these bodies in cutcell creation


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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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Size Functions – Create Defaults • Create Defaults 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 best sizings for a problem. Often, proximity on all zones can be overkill and increase mesh size considerably and either small hard sizes on specific boundaries or proximity SF between only a few Face/Edge zones will give

the best result. Note also that 18 degrees angle is a coarse, conservative default setting and could be decreased by the user for better curvature capture.


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Material Point for Internal Flow

• “Compute” gets centroid coordinates of any current selection. Here we use ctrl-z to select the zone “solid-2” and compute gives it’s centre point for the inner-fluid material point creation.


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Material Point for External Flow

• We can change the numbers in the form directly and press ENTER to update the material point display. E.g. Here we move until well outside geometry and create “outer-fluid”


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• Group creation is a useful tool for meshes with large numbers of boundaries so we can select/deselect them quickly

• Select Face Zones for the group from the list and hit Create

• The name given will appear as a filter under “Face Zone Groups” in forms throughout Fluent Meshing

• Choose to Activate a group to show only the Face Zones belonging to that group in other lists in Fluent Meshing

– Very useful for manual fix/clean-up when using Boundary Modify on Mesh type objects

Create Groups


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Agenda



– Real Creations



• Gap Removal



• Tips and Tricks




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• Goals of Wrapping: – Create conformal faceting (low-quality, closed surface mesh) on

selective bodies

• Can optionally be done during import

• Needed for Gap closing

– Extracting the wetted or “flow surface” from capped solids

• Surface mesh of wetted region based on material point

– Wrap to connect together multiple solids

• Wrapping does not take care of face quality – this is done in the Surface Mesh Improve step later in the workflow

Wrapping

Material points can be used to extract wetted region from solid geometry


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• There are two different wrapping methods for tessellated, un-connected faceted CAD

• Shrink-Wrap : Easy-to-use, integrated, classic TGrid wrapper technology

• Defeaturing, walk over details

• Handles dirtier geometries better

• The smaller size the better capture

Shrink-Wrap


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• Cut-Wrap : Wrapping based on Cutcell technology

– Generally higher fidelity feature capture

– Needs better quality cad to work (connected)

Cut-Wrap


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Shrink-Wrap Vs Cut-Wrap

Pros Cons

Generally faster than cut-wrap Lower quality feature capture

Ability to walk over small gaps/holes Cannot capture zero thickness baffles – will inflate to a thickness

Good connectivity of input mesh not required Poor feature capture in sharp corners can produce “webbing”

Beta hole closing feature can be used to find holes

Shrink-Wrap

Pros Cons

Better feature capture Slower than shrink-wrap

Captures zero thickness baffles well Cannot walkover gaps

Captures sharp angles better due to cell cutting techniques

Requires better connected mesh than shrink-wrap

Less prone to “webbing” across thin gaps than shrink-wrap

Beta hole closing will help but may not find all holes

Cut-Wrap


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• Clearly, both shrink-wrap and cut-wrap have their advantages/disadvantages

• They can also be used together to achieve best-of-both by applying one and then another to the resulting object

• E.g. user may apply shrink-wrap to defeature a certain area of an object then apply cut-wrap to the resulting defeatured object to achieve better feature capture in other areas

– Example later in lecture

Combinations


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• The Goal is to, for each object, create a conformal tessellation suitable for repair operations or as the final mesh

– Size Function must be defined

– Select one or several objects to be wrapped sequentially

– A wrapped object will result for each chosen

– Use Cut-wrap or Shrink-wrap

– Click Wrap

• New Wrap Object and corresponding zones are created

• Note: Internal surfaces are removed

Wrap Individual Object Surfaces

Wrap


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• The Goal is to simplify the problem by unifying multiple solids into one and at the same time ignore any interior voids and faces

– Size Function must be defined

– Select several objects to be wrapped together

– A single wrap object will result

– Add New Object name

– Optionally set priority

– Select Shrink or Cut - Wrap

– Click Wrap

• New Wrap Object and corresponding zones are created

• Note: Internal surfaces are removed

Wrap Unified Solid Surface

Wrap


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• Shrink-Wrap has additional options

• Extra refinement level reduces the size function min and max values by half for each increment, to produce a very fine capturing of details

• Two imprint iterations are normally sufficient but this number can be increased if needed

• Aggressive imprint can also further improve the feature capturing

• Defaults generally work well

• Coarsening can be done in the Surface Mesh Improve panel later if mesh is over-refined for feature capture at this stage

Shink-Wrap Options


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• Goal: To extract the surface mesh of the fluid volume from a set of solid objects and caps

• Fluid Surface setup

– Size function must be defined

– Select all Objects to be wrapped

– Add a Name and Priority for the wrapped surface

– Material Point defined and selected

– Select Shrink or Cut-Wrap

– Click Wrap

• Fluid Surface Results

– New Wrap boundary zone(s) created

– New Wrap Object created

Wrap Fluid Surface

Wrap


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Internal Wrap and External Wrap

Internal Material Point Wrap External Material Point Wrap

Material Point Material Point

Internal fluid surfaces External fluid surfaces


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Agenda



– Real Creations



• Gap Removal



• Tips and Tricks




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• “Gap” closing is actually two different operations

– Closing gaps between parts

– Remove thickness (by projection) of a part

• Both operations assume that the Objects are of type “wrap” i.e. that the facets are suitably refined and are fully conformal

Remove Gaps


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• Remove Gaps Between Objects

– Only relatively simple, close to planar, gaps can be closed in R14.5

– Parameters

• Gap Distance

– Use average

• Percent margin

– Allow for gap distance variations

– Options

• Gap Type

– Face – Face

– Face - Edge

• Order

– Which boundary should move ?

– List will show priority of object

• It is Strongly recommended to Mark (and Unmark) faces to verify that only triangles in the gap are used

– Remove

• The resulting model is still of type “wrap”

• Triangles in the gap are projected, so overlapping faces will remain after gap removal

Remove Gaps Between Objects


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Agenda



– Real Creations



• Gap Removal



• Tips and Tricks




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• Closing gaps

– Remove Thickness in Objects (Mid-surfacing)

• Only relatively simple mid-surfacing is possible at 14.5

– Parameters

• Gap Distance

– Average Thickness of section

• Percent margin

• Critical angle

– Allowed variation from parallel faces

• Optionally create new Features

– Recommended

• It is Highly recommended to save the files before any Gap operations

– Remove

• If multiple gaps/thin sections exists within an object

– Separate out “gap” faces

– Create new objects from these

Remove Gaps Thickness Between Objects


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Agenda



– Real Creations



• Gap Removal



• Tips and Tricks




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• The Sew operation produces CFD-Ready surface meshes

– “Sew” together disconnected assemblies (Equivalent to “Share Topology” in DM ) to a conformal mesh , and automatically improves the quality.

– Typically used for conjugate heat transfer or multi-fluid problems

– Operation

• Pick all objects taking part in the Sew operation

• Add a New Object Name

• Sew

– This will produce an Object of type “mesh” and prepare it for Volume meshing

Sew

Single face Overlapping faces

Multi-connected Edges

Sew


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• The purpose of Improve is to Improve the surface mesh quality

• Objects taking part in Improve must be of type “Mesh”

– The Create Mesh Object option can be used to convert a model of type “Wrap” to type “Mesh” and improve the mesh at the same time

– Option to apply coarsening if additional refinement was used during wrap

• There are four drivers for Quality improvements

– Skewness

• Default and recommended

– Size Change

• Important to keep under 5 for good convergence

– Aspect Ratio

– Area

• Aggressive method to remove very small and bad triangles

Improve


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• A flow volume has been extracted in the Flow Surface operation

• It is converted from Wrap to Mesh Object without coarsening

Improve - Example

Create Mesh Object


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Agenda



– Real Creations



• Gap Removal



• Tips and Tricks




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• Very small detailed areas can be meshed but will

– Push cell count up massively

– Increase cell count in areas which are not interesting from the problem perspective

• Users need methods to remove such features and shrink-wrap can be used for this purpose to “walk over” features.

• General Method:

– Show feature edges for object you wish to defeature

– Graphically select edges to remove

– Delete selected edges from the Edge Zone

– Apply size function to the object surfaces – suggest curvature only with min size large enough to “walk over” small features. No proximity refinement for Edges!

– Shrink wrap object to walk over features

– Cut wrap the resulting shrink-wrapped object to improve feature capture

– Directly improve if only one object or subsequently use sew to connect this object to others

– Example in next slide

Feature Suppression


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Feature Suppression with Shrink-Wrap

Object with unwanted screw thread

Object features (from CAD import)

Ctrl-e and F4 to box select with RMB

Edges Selected

Edges Deleted Shrink Wrapped Shrink Wrapped object cut-wrapped

Improved


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Agenda



– Real Creations



• Gap Removal



• Tips and Tricks




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• There are several commands only available in the Text Interface which can be very useful

– Under /objects/

• delete-unreferenced-faces-and-edges will delete these entities which don’t belong to any object

• improve-feature-capture improves feature capture on a given object by projecting onto underlying Edge Zones

• create-and-activate-domain creates a domain from a given object to enable user to go to domain type mesh creation

• update will update out-of-date objects (modified outside workflow)

– Under /objects/wrap/set/ or /objects/sew/set

• include-thin-cut-edges-and-faces allows user to specify edges and faces near sharp angles for better feature capture there

– Under /material-point/

• delete-all-material-points

• list-material-points

– Faces may remain marked after gap closing and to unmark issue the command:

• /Boundary/unmark-selected-faces

TUI Commands


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• How do we know if all holes have been patched? – Size function should be defined

– Material points could be defined

– Issue (gui-find-holes) on the command line

• The Find Holes GUI will appear

• Select all Objects and draw

• Use material point, or create new point on-the-fly

• External is usually the End point

• Issue; Init, Re-region, Trace

– If there is a leak, it would be indicated on the screen. May need to use slider bars to look inside.

• After the leak is patched, find new holes using

– Re-region + Trace

– Note this tool uses Shrink-Wrap functionality so may not pick up all leaks Cut-Wrap will encounter

Hole finder – Hidden Beta feature


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14.5 Release

Appendix Typical User Workflows


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• Some Useful Text User interface commands – Delete Material point(s)

• /material-point/delete-material-point or delete-all-material-point

– Sometimes Objects needs to be updated, particularly if you use Boundary – Manage Face Zone to modify the Zones in an Object

• /objects/update

– Faces maintains marked after gap closing

• /Boundary/unmark-selected-faces

•

Fluent Meshing 14.5 Useful TUI commands


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• Using Free for trouble shooting – Free faces show up blue in the graphics window

– After Conformal CAD import, Wrap or Sew operation, only 0-thickness baffles should have free nodes

• Display Free only and Do not Draw Edge Zones

• Ctrl A – zoom in to Free faces.

• If nothing appears (assuming no baffles), the wrap/sew operation was successful

• If not, fix using – Merge Nodes

– Boundary Modify

Fluent Meshing 14.5 Trouble shooting


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• The use of Groups in Assembly meshing – Using Boundary Modify to improve a surface mesh

• When an Object of type Mesh is created, a mesh group is also formed

• Boundary Modify is the most advanced tool for Surface mesh quality improvements and repair

– In Groups, pick the newly created mesh Group and Activate it

– Now Boundary Modify can be used (F11)

– Assign Local Size Function

– Displaying selective faces of final mesh

– Removing unwanted objects in large assemblies

•

Fluent Meshing 14.5 Using Groups


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Fluent Meshing 14.5 Volume Mesh improve

• Using Auto node move

– Auto Node move is the most advanced Volume mesh quality improvement tool

• Auto Node Move allows user to

1. Select max quality target

2. Select Cell zones for improve

3. Select boundaries where nodes can move

4. Allow or disallow movement from the boundary

5. Set angle at which nodes are allowed to move (to allow/disallow movement on feature edges)

6. Set # of iterations of improve

7. Apply improvement


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Requirements:

• Mesh Flow Volume from CAD Assembly

• Good quality CAD (well connected objects)

• CAD contains sharp angles and/or zero thickness baffles user wishes to resolve accurately

User Workflow 1 Conformal Tess.

CAD Import

Create geometry

and/or caps

Improve

Auto Mesh

Fluid surface

Cut-Wrap

Set Size

Functions

Set Material Point

Switch Object(s)

to Wrap type

Remove Gaps

Check/Fix

Connectivity/Quality


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Requirements:

• Mesh Flow Volume from CAD Assembly

• CAD is “sloppy” with lots of disconnected surfaces

• CAD contains small features to ignore

• No gaps to close between objects


CAD Import

Create geometry

and/or caps

Improve/Coarsen

Auto Mesh

Fluid surface

Shrink-Wrap

Set Size

Functions

Set Material Point

Delete unwanted

feature edges


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Requirements:

• Mesh Flow Volume and solids from CAD Assembly

• Good quality CAD (well connected objects)

• All solids can be “lumped” into one zone


CAD Import

Create geometry

and/or caps

Improve

Auto Mesh with

“Keep Solids”

Unified Solid

Surface Cut-Wrap

Set Size

Functions

Set Material Point

Switch Object(s)

to Wrap type

Remove Gaps

Cap Inlets/Outlets


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Requirements:




• All solids can be “lumped” into one zone


CAD Import

Create geometry

and/or caps

Auto Mesh with

“Keep Solids”

Unified Solid

Surface Shrink-

Wrap

Set Size

Functions

Set Material Point

Remove Gaps

Delete unwanted

feature edges

Check/Fix


Cap Inlets/Outlets


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Requirements:


• CAD is clean

• CAD contains baffles/sharp features to capture

• Solids meshed separately – different materials

User Workflow 5 Conformal CAD

Import

Create geometry

and/or caps

Check/Fix


Auto Mesh with

“Keep Solids”

Set Size

Functions

Remove Gaps

Sew all Objects

Set Material Point


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Requirements:




• Solids meshed separately – different materials

User Workflow 6 CAD Import

Create geometry

and/or caps

Check/Fix


Auto Mesh with

“Keep Solids”

Individual Object

Surfaces Shrink-

Wrap for solids

Set Size

Functions

Remove Gaps

Delete unwanted

feature edges

Sew all Objects

Set Material Point

wrapping, fixing and sewing objects -...

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