ICEM Mesh for CFD Analysis

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ICEM Mesh for CFD Analysis | Manualzz

ICEM Mesh for CFD Analysis

2

Index

1.

Introduction to ICEM

2. Geometry Handling

3. Shell Meshing

4. Volume Meshing

5. Prism Meshing

6. Mesh Preparation Before Output to Solver

7. Output to Solver

8.

ICEM CFD Hexa

3

1. Introduction to ICEM

What is a Mesh?

4

• Mesh

– Volume comprised of elements used to d iscretize a domain for numerical solutio n

• Structural

• Fluid dynamics

• Electromagnetics

• Other

– Elements

• 0D – Node element

– Point mass

– Constraint, load location

• 1D – Lines

– Bars, beams, rods, springs

– 2D mesh boundary

• 2D – Surface/Shell

– Quads

– Tris

– Thin sheet modeling

– 2D volume

– 3D mesh boundary

• 3D - Volume

– Tetra

– Pyramid

– Penta (prism)

– Hexa

– Solid modeling

– 3D fluid modeling

• Formats

– Unstructured

– Block Structured

– Nodes

• Point locations of element corners

5

Ansys ICEM CFD Features

Geometry Creation/Repair/Simplification

– Including Mid-Plane Extractions/Extensions

– Most geometry intended to be imported

Powerful Meshing tools

– Tetra/Prism from CAD and/or existing surface mesh

– Shell meshing: structured, unstructured

– Hex-dominant, swept, Structured hexa, Extruded quads, Body-fitted and stair-step Cartesian

– Hybrid meshing (merging, multi-zone)

Advanced mesh editing

Solver Setup

Output to 100+ Solvers

Scripting … and much more…

6

Utility

Icons

GUI and Layout

Utility Menu

Selection Toolbar

Model

Tree

Data Entry

Panel

Function Tabs

Message

Window

Histogram

Window

Display Triad

7

File and Directory Structure

• Use of many files

– Not one large common database

– For faster input/output

• All files can optionally be associated within a Project

– Establishes working directory

– Settings (*.prj) file contains associated file names

• Primary file types:

– Tetin (.tin): Geometry

• Geometry entities and material points

• Part associations

• Global and entity mesh sizes

• Created in Ansys ICEM CFD or CAD Interface

– Domain file (.uns)

• Unstructured mesh

– Blocking file (.blk)

• Blocking topology

– Attribute file (.fbc, .atr)

• Boundary conditions, local parameters & element types

– Parameter file (.par)

• solver parameters & element types

– Journal and replay file (.jrf, .rpl)

• Record of performed operations (echo file)

.fbc

.tin

.par

.uns

.rpl

.prj

.blk

.jrf

8

Mouse Usage

• ‘Dynamic’ viewing mode (click and drag)

– left:

– middle:

– right: rotate (about a point) translate

– Wheel

• Selection mode (click) zoom (up-down) screen Z-axis rotation (sideways) zoom

– left:

– middle:

– right: select (click and drag for box select) apply operation unselect last selection

F9

toggles the mouse control to Dynamic mode while in Select mode

Toggle Dynamics

button also

– does this

• Spaceball allows for dynamic motion even while in select mode

9

Utility Menus

File Menu

(file i/o)

Edit Menu

View Menu

Info Menu

Settings

Menu

(preferences)

Help Menu

10

File menu

• To open/save/close

– Projects

• Will open/save/close all as sociated files including

• Geometry (*.tin)

• Mesh (*.uns)

• Attributes… (*.fbc, *.atr)

– All file types can be opened/sa ved/closed independently

• Also to

– Import/Export Geometry/Mesh

– Invoke scripting

• Exit

Save frequently!

Several common functions are duplicated as utility icons:

Open Project Save Project

Open/Save/Close

Geometry

Open/Save/Close

Mesh

Open/Save/Close

Blocking

11

Other Commonly Used Utilities

• Edit > Undo/Redo

Also here

• View

– Fit

Fit visible entities into screen

– Box Zoom

– Standard views

Top, Bottom, Left, etc.

Can also select X, Y, Z axis of display triad in lo wer right hand corner of main view screen to ori ent to standard views, e.g. selecting “X” will orie nt “right”

Isometric – select blue dot within triad

• Measure

– Distance

– Angle

– Location

– Local Coordinate System

• Used by:

• Select location

• Measuring

• Node/point movement/creation

• Alignment

• Loads

• Transformation

– Surface display

• Wireframe

• Solid

• Transparent

Help

• Menu Driven

– Searchable

– Includes tutorials

– Programmers guide (for ICEM

CFD/Tcl scripting procedures)

• Hyper-link to specific topic

12

Bubble explanation with cursor positioning

Common Function Tabs

Geometry

Mesh

Blocking

Create/Modify geometry

Set mesh sizes, types and methods

Set global mesh options

Auto create Shell, Volume, Prism meshes

Initialize blocking

Split/modify blocks

Generate structured hexa mesh

Edit Mesh

Check errors/problems, Smooth, Refine/Coarsen,

Merge, repair mesh, Transform, etc.

Set Boundary Conditions and Parameters

Write mesh for 100+ solvers.

13

Output

14

Structural Function Tabs

• Only available when solver is set to Abaqus, Ansys, Autodyn, LS

-Dyna, or Nastran

Settings->Product

must also be set to an FEA version

Properties

Create, read, write out material properties

Apply to geometry/elements

Constraints

Set constraints, displacements, define contacts, initial velocity, rigid walls

Set force, pressure and temperature loads

Loads

Solve options

Set parameters, attributes, create subcases, write out input file, run solver

15

Selection Toolbar

During select mode, popup selection toolbar appears

– Some tools are common to all, others are contextual

– Linked to select mode hotkeys

– Filtering of entities and mass-selection methods

Geometry

Polygon

Select By Part

Select all

Cancel

Only visible

Flood fill to Curve

Flood fill to Angle

Entity Filter

Mesh attached to Geometry

Mesh

Blocks

Toggle Dynamic

Mode (F9)

Circle

By Subset

Entire/Partial toggle

Faceted

Geometry

Segments

Set Flood Fill angle

All Shells

Toggle between mesh and geometry

From

Corners

In between segments

16

Model Tree

• To toggle on/off various sections of the model

• Main Categories are:

– Geometry, Mesh, Blocking, Parts

– Local Coord Systems, Element Properties,

Connectors, Displacements, Loads and Ma terial Properties

• Toggle check boxes to blank/unblank

– Blanked/inactive

– Visible/active

– Partially visible/active: some sub members turned on, some turned off

• Click on plus sign to expand tree

– Expose sub members

• Right mouse click for display options

17

Model Tree: Parts

Parts

– Grouping of mesh, geometry, and blocking entities

• Based on boundary condition/property

• Based on mesh size (can set mesh size by part)

• Based on material property

• Just to partition large model

– Select to blank/unblank all entities within part

– Color coded: Part name matches entity screen display

Right Mouse Button

on

Parts

to access:

Create Part

Create Assembly

Delete Empty Parts

Etc.

RMB

on specific part names allows options to modify or delete th e parts

Properties

are shown as a sub branch of the part

– Double Left Click or RMB > Modify to modify element pro perties

Workflow

Typical ICEM CFD Workflow:

Create/open new project

Import/Create geometry

Build topology/Clean geometry/Create geometry

Mesh model (Possibly Hex Blocking)

Check/edit mesh

Output to Solver

18

General Order of Workflow

Accessing from Workbench

• Ansys ICEM CFD 14.0 is not fully linked inside Workbench

– Export files from Mechanical Model (Simulation) or Meshing Application to open in ICEM CFD

19

• Some ICEM CFD capabilities have been integrated into the Meshing

Application

– Tetra octree (patch independent)

– 3D blocking fill (Multizone)

– Autoblock (2D, uniform quad)

– Body fitted cartesian

20

Workbench Interactive Link

• Ansys ICEM CFD can be accessed from Workbench from certain mesh methods

Insert a meshing method

– MultiZone

– Patch Independent tetrahedrons

• Set

Write ICEM CFD Files

to

Interactive

Generate mesh

Edit or remesh within ICEM CFD,

save project, then exit ICEM CFD

– Don’t edit geometry in ICEM CFD

21

2.

Geometry Handling

Geometry handling

ANSYS ICEM CFD was designed to mainly import geometry, not create complicated geometries, although many geometry tools are provided

22

An accurate solution reflects the underlying geometry. To get such, ICEM CFD provides:

 Geometry import

– From CAD package

– 3 rd party formats (step, acis, etc…)

– Via Workbench/ Design Modeler

 Surface geometry kernel

– Imported solids are converted to surfaces

 Many internal CAD tools

– Geometry creation

– Geometry modification

– Geometry fixing

This Jet engine model was built solely with

ICEM CFD geometry tools

23

Geometry Import

CAD from just about any source

• Workbench Readers – for most CAD imports

– Anything that Workbench can import can also be imported into I

CEM CFD using Workbench readers

– Requires a Workbench installation!

• 3 rd

-party import

– ACIS (.sat)

– DWG/DXF

Parasolid

STEP/IGES

GEMS

• Direct CAD Interfaces

– Legacy interfaces which are not updated. Use

Workbench Reader s

instead for current CAD versions

– Set up ICEMCFD/AI*E meshing requirements within CAD envir onment

• Saved within CAD part for parametric geometry changes

– Directly write out ICEM formatted geometry (tetin file)

• No 3 rd party exchange (clean!)

– ProE, Unigraphics, Solidworks, Catia V4, IDEAS (IDI)

– ProE, UG, and Solidworks imports require CAD libraries; CAD s oftware and licensing must be available

24

Geometry Import - other so urces

When CAD is not available, an old legacy model or x-ray scan of the part can be imported as geometry. This input is a coll ection of facets (triangulated surfaces).

• Faceted Data

– Nastran

– Patran

– STL (most common)

– VRML

– Other solver formats (indirectly from mesh conversion)

• Formatted Point Data

– Auto curve/surface creation from regular table of points

Open Geometry

• Geometry saved as “tetin” (*.tin file)

– Legacy name as an abbreviation of “tetra input.”

– Surface geometry kernel

• Any imported solid models are represented as a series of watertight surfaces

– Surfaces are internally represented as triangulated data

• Resolution or approximation of true bspline surface data set by

Triangulation Tolerance

in

settings>model

• Smaller value = better resolution

• 0.001 works best for most models

• Use a high tri tolerance to work with a large model, but lower the tolerance when it comes time to compute the mesh

• Not used if surfaces are already facetized (e.g.

STL, VRML)

Tri tolerance =

0.1

25

Tri tolerance = 0.001

Geometry Creation Tools

First 3 icons to create geometry

Screen Select

Explicit Coordinates

Base Point and Delta

Center of 3 Points/Arc

Based on 2 Locations

Curve Ends

Curve-Curve Intersect ion

Parameter along a Cu rve

Project Point to Curve

Project Point to Surfa ce

From Points

Arc Through 3 Points

Arc from Center Point/2 Points on Plane

From Curves

Surface Parameter

Curve Driven

Surface-Surface Intersection

Sweep Surface

Project Curve on Surface

Surface of Revolution

Segment Curve

Concatenate Curves

Loft Surface Over

Several Curves

Surface Boundary Extraction

Offset Surface

Modify Curves

Midsurface

Create Midline

Segment/Trim Surface

Create Section Curves

Merge/Reapproximate

Surface

26

Untrim Surface

Curtain Surface

Extend Surface

Geometry

Simplification

Convex Hull

Cartesian

Shrinkwr ap

Create Std

Geometry

Sphere

Box

Cylinder

Plane

Disc

Trim normal to curve

27

Create Body

• Material point and body

– Material point used by tetra octree to instruct which volume regions to keep

• Volume elements will be in the same part as the material point

– Used in hexa blocking as a part for placing blocks

– Material point method is most robust

By Topology

method automatically creates a material point in every closed volume

• Requires

build diagnostic topology

first to determine connectivity

• Can save you the work of creating a lot of material points for each region

• Any regions not completely closed (yellow curves indicating gaps/holes) will not get a material point so this is less robust

Faceted Geometry Handling

Create/Modify Faceted

28

Convert from Bspline

Create Curve

Move nodes

Merge nodes

Create segment

Delete segment

Split segment

Restrict segments

Move to new curve

Move to existing curve

Convert from B-spline

Create Triangles

Coarsen Surface

Delete Triangles

Create new Surface

Split Triangles

Merge Edges

Split Edges

Restrict Triangles

Delete Triangles

Swap Edges

Move Nodes

Move to new Surface

Merge Nodes

Move to new Surface

Merge Surfaces

Align Edge to Curve

Close Faceted Holes

Trim by Screen Loop

Trim by Surface Loop

Repair Surface

Create Curve

Facetted (triangulated) surfaces

Geometry Handling

Repair Geometry

Transformation Tools

29

Build Diagnostic

Topology

Check Geometry

Close Holes

Remove Holes

Stitch/Match Edges

Split Folded Surfaces

Adjust varying Thickness

Modify surface normals

Bolt hole detection

Button detection

Fillet detection

Translate

Rotate

Mirror

Scale

Translate & Rotate

Three Points

Curve to Curve

Restore Dormant

Entity

Curves/points originally made inactive - ignored by meshing tools

Restore to activate again -seen as constraints by meshing tools

Delete

Points

Curves

Surfaces

Bodies

Any Entity

Build topology with filtering

30

Building Topology – Determine Connectivity

Geometry -> Repair Geometry -> Build Diagnostic Topology

• To diagnose potential geometry problems

– Shows potential leakage (tetra octree) before meshing

– Shows where surface mesh may not be connected

– Patch dependent surface mesher requires build topology

Tolerance

• Specifies allowable gap between surfaces

• Size should be set reasonably to ignore small gaps, but not ignore le akage (tetra octree) or remove important features

• Default is 1/2500 th of the diagonal of the bounding box

• Connectivity is set up between surface edges that meet within the to lerance

• Filtering should be off when using to determine connectivity

Edge 1

Edge 2

Tolerance

31

Building Topology – Color Coding

Color coding

• Topology curves are color coded to indicate their surface connection status

– green = unconnected, yellow = single, red = double, blue = multiple, Grey = dormant (filtered out)

– Turn color coding off/on in Model tree > Geometry > Curves > Color by count

– Red curves indicate two surfaces meet within the tolerance, This is what you want for a solid model.

– Yellow curves will usually indicate some repair is required

Can you spot the hole in the solid?

Now you can find the hole

Yellow curves indicate that the surface is probably missing or the gap is greater than the tolerance

Red curves indicate that surfaces meet within the tolerance setting

Build Topology

Build Topology – Extract Curves and Points

Automatically extracts curves and points from the surfaces

Filter by angle

(default 30 degrees)

Filter Points:

Points between two curves whose tangency is belo w the feature angle will be “filtered out” (made dormant)

Filter Curves:

Curves between two surfaces whose tangency is bel ow the feature angle will be “filtered out” (made dormant)

No filtering

Tetra octree and patch dependent surface mesher enforce nodes on the curves

32

Filtering

Needs smaller mesh size at fillets

Build Topology – Segment Surfaces

Automatically segments all surfaces where curves either make a complete loop on the surface or span across the surface

Turn

Split surface at T-connections

off to turn off segmenting

You can then delete any surfaces you don’t want

Build topology

33

Check off to disable segmenting

34

Tolerance setting

• Set adequate tolerance!

– Example: some multiple (blue) edges. This indicates tha t more then two surfaces meet within the tolerance setti ng

– Turning on the surfaces reveals one surface is now missi ng.

– In this case, the tolerance (0.2) was set to greater than th e thickness (0.1). One of the surfaces was seen as a “dup licate” within the tolerance and removed. UNDO

You will need to exercise care not to damage your model with buil d topology

Too small is safer but indicates more gaps

Too big can alter the model in bad ways

– Rule of thumb: tolerance should be about 1/10 th smalle st foreseen mesh size or smallest feature that you wish t o capture

Build topology will delete duplicate geometry because its tolerance is zero

0.1

35

Building Topology – Other Options

New Part Name

Inherit Part:

Default: new curves and points will i nherit the part names from surfaces they are ext racted from

– Check off

Inherit Part

to type a new name o r choose from the list

Single curve cleanup

• Merges single edge curves with a second toleran ce while resolving sliver surfaces (normally large r than base tolerance)

Split Surface at T-connections

• Resulting mesh will conform to common edge e ven though the surface is not split into two sepa rate surfaces

• Will also split a surface into separate surfaces if the curves form a closed loop or span across th e surface

Split Surface at Interior Curves

• Surfaces trimmed along curves that don’t span s urface or form a closed loop

• Resulting mesh will conform to curve

36

Building Topology – Other Options

– Method

All parts

, default method

Only visible parts

– Build topology is only run on active

Parts

in the model tree

– Inactive Parts are not affected

Selection

– Build topology on one or more surface entities

– Part by part

• Build topology is run on one part at a time

• Use with assemblies to keep parts separate

• Otherwise build topology may fix gaps, create T-connections or rem ove duplicates across Parts

– Delete unattached curves and points

• Removes unattached curves (green) and points after running build t opology

• Easy clean-up of unwanted curves/points

• Users may, however, wish to keep these curves/points for constructi on purposes (turn option off)

37

3. Shell Meshing

38

Introduction to Shell Meshing

• Usages of shell meshing:

– Thin sheet solid modeling (FEA) – stamped parts

– 2D cross sectional analysis (CFD)

– Input for volume meshing (FEA/CFD) – Delaunay, Advancing Front, T-grid

Filling a surface mesh is faster than tetra octree but requires well-connected geometry

• Procedure

– First need to decide mesh setup parameters

Mesh method

– Algorithm used to create mesh

Mesh type

– quad/tri/mix

Mesh sizes

Small enough to capture physics, important features

Large enough to reduce grid size (number of elements)

»

Memory limitations

»

Faster mesh/solver run

Set mesh sizes on parts, surfaces, and/or curves

Based on edge length

– Can have different types/methods set on different surfaces

39

Global Mesh Setup

Mesh Setup Icons

Global Mesh Setup

– To change defaults globally for size, method and type

– For entire model

– For Shells

– For Volume

– For Prism

– To set periodicity

• Parameters relative to scale factor

– Max size

– Min size limit

– Max deviation

Mesh

tab

Global Mesh Size

For entire model

Scale factor

• Global setting by which many local settings are multiplied

• Good for scaling overall mesh

Global Element Seed Size

• Maximum possible element size in model

• Default size if don’t wish to set local sizes

Curvature/Proximity Based Refinement

• Automatically creates smaller element size to better capture geometry

• Only for Patch Independent method and tetra octree

40

Global Shell Meshing Parameters

Shell Mesh Setup

– From

Global Mesh Setup

tab

– Set surface mesh parameters globally

• Defaults for the selected mesh method

Methods

Autoblock

Patch dependent

Patch independent

Shrinkwrap

Delaunay

Type

• All Tri, Quad w/one tri, Quad dominant, All quad

– Options for different methods

– Global types and methods can be overridden by

Surface Mesh Setup

– Local settings

Compute Mesh

Part Mesh Setup

Part Mesh Setup

(pop up spread sheet)

– Set mesh parameters on all entities within part

Max. size

• Multiplied by global

Scale Factor

= actual size

• Quad layers grown from curves (e.g. rings around holes), use these 3 parameters:

Height:

First layer quad height on curves

Height ratio:

growth ratio which determines the heights of each subsequent layer

Num layers:

Number of rings/inflation layers

• For quad layers, the minimum required to be set is

height

(for 1 layer) or

numlayers

(height = max. size)

• If done in the

Part Mesh Setup

spreadsheet you must toggle on

Apply inflation parameters to curves

Or set on individual curves

41

42

Local Surface Mesh Setup

• Surface Mesh Setup

– Same parameters as part mesh setup but also includes:

Mesh type

Mesh method

– Select surfaces first from screen, set sizes/parameters and

Apply

– Mesh method/type will override global shell mesh settings for selected surface(s)

– Will override

Part Mesh Setup

settings if set afterward

– Display

• Right mouse, select in Model tree on

Surfaces > Tetra/Hexa Sizes

– 1 Icon appears for each surface

– Gives you a visual estimate of prescribed max. size

43

Local Curve Mesh Setup – General

Curve Mesh Setup

General

• Same as

Surface Mesh Setup

• But also can prescribe

Number of nodes

– Instead of element size

• Also includes node biasing along curves

Side 2

Arrow shows side

1 and side

2

Side 1

– Initial spacing from either curve end

– Bunching laws

– Expansion ratios from either curve end

– Matching of node spacing to adjacent curves

– For a better description, refer to the

Hexa chapter –

Edge Parameters

• Select curves first, middle mouse to accept selection, then type in parameters/ sizes -

Apply

Display

• Right mouse select in Model Tree,

Curves -> Curve

Tetra/Hexa Sizes

or

Curve Node

Spacing

Tetra sizes

Node spacing

Local Curve Mesh Setup – Dynamic and Copy

Curve Mesh Setup

Dynamic

• Adjust mesh parameters on screen

• Interactively toggle displayed values near curve with left (to increase)/right mouse (to decrease) keys

Copy Parameters

• Copy parameters set on one curve to others

• e.g. parallel curves downstream

Curve Mesh Setup

will override

Part Mesh Setup

parameters if set afterward

Left mouse to increase

Right mouse to decrease

44

45

Mesh Methods

Algorithm used to create mesh

• Patch Dependent

– Based on loops of curves surrounding patches

– Best for capturing surface details and creating quad dominant mesh with good quality

• Patch Independent

– Robust octree algorithm

– Good for dirty geometry, ignoring small features, gaps, holes

• Autoblock

– Based on 2D orthogonal blocks

– Best for mapped meshing, mesh follows contours of geometry

• Shrinkwrap

– Automatic defeaturing

– Quick Cartesian algorithm

– Allows ignoring of larger features, gaps and holes

• Delauney (beta options)

– Allows for transition in mesh size

• Coarser towards surface interior

– Tri only

• Set in

Global

Mesh Setup

or locally using

Surface

Mesh Setup

46

Patch Dependent Method

• Patch defined by a closed loop of curves

– Typically each surface defines a patch

• Loop defined by boundary curves

• Curves automatically created by

Build

Diagnostic Topology

- a must!

– Can remove or filter out curves to define multisurface patches

• Delete curves

• Turn on filter points/curves when building topology

• Only uses curve sizes (curve nodes seed loop perimeter)

• Paving algorithm used to fill interior of loop

– Interior nodes typically projected to surface

– Adjacent loops share nodes at common edge making mesh conformal throughout

• Default method, fastest method

Filtered or deleted curves

(dormant) loop 1 loop 2 loop 3

Build topology MUST be done first to build surface connectivity and curves

47

Patch Dependent – Common Options

• All method options set from

Global

Mesh Setup -> Shell Meshing P arameters

section

General

Ignore Size

• Small features, such as sliver surfaces smaller than defined value are ignored. Merges loops behind the scenes

• Will override max. size setting if smaller

Surrounding mesh done afterwards is conformal to existing mesh

Respect line elements

• Line elements (bars) on existing mesh are respected

• Maintains conformal mesh between newly created mes h and existing mesh on adja cent surfaces

Sliver Surface,

0.6 mm wide

Ignore size =1,

Sliver surface is ignored

48

Patch Dependent Mesher - Boundary option

Boundary

Protect given line elements

• Keeps existing line elements which are small er than the Ignore size

• Grayed out unless

Respect line elements

is on

Smooth boundaries

• Smoothes the mesh boundaries after mesh ge neration. May not respect the initial node spa cing set on curves

Offset type

Interior

Force mapping

• Forces mapped mesh on regular (4 sided) sur faces to desired degree (0-1)

• Adjusts the number of nodes on opposite side s (0.2 = change number nodes by 20%)

Project to surfaces

• Interior nodes project to surface rather than i nterpolate position

Adapt mesh interior

• Allows transition to larger element size in the interior of the surface (uses surface max size

)

Standard

Simple

Would require too many nodes increased from original setting based on force mapping setting

49

Patch Dependent Mesher - Repair option

Repair

Try harder

• For loops that fail with requested paving algorithm

• Levels (0-3) to make further attempts to create grid

0

- No further attempts, failed surface(s) marked and put into a subset

1

- Simple triangulation of surface, converted to requested type

2

- Same as 1, but dormant curves activated

3

- Run octree, same as patch independent

Improvement Level

• Levels (0-3) to improve mesh quality

0

- Laplace smoothing only

1

- STL tri mode, with conversion to quads (if requested)

2

– tri to quad conversion, splitting of bad quads

3

- allow nodes to move along boundary

Other options and fuller descriptions may be found in the

H elp

menu.

Patch Independent

• Uses robust Octree method

– Volumetric tetra elements created around geometry

– Faces mapped to surfaces

– Only surface mesh is retained

– Discussed in more detail in

Volume Mesh

lecture

• Mesh sizes defined on surfaces and curves

• Can walk over details, thin gaps, small holes

– Relative to mesh size

• Nodes and edges don’t have to be lined up with surface edges

– Only lined up where curves exist

50

Matches up with previously meshed surfaces

Volume around is first meshed

Nearest nodes projected to surface and only surface mesh is left

51

Autoblock

• Surface (2D) blocks are created automatically from each surface

– Internal, blocks aren’t recognized or visible

– For further description of blocking, refer to Hexa chapter

• Blocks structurally connected

– Conformal mesh between blocks and surfaces

• Structured blocks result from 4-sided surfaces

– For regular or four-sided blocks, structured

(mapped) mesh follows contours of geometry

• Best for recognizing rounds or fillets

• Irregular (non-4 sided) or trimmed surface patches may be unstructured

Mesh sizes set on surfaces or curves

• Options

Ignore size

Mapped

or

free

(unstructured as in patch dependent)

Build Topology

MUST be run beforehand

52

Shrinkwrap

• Cartesian (rectilinear) method

– Can ignore larger features, gaps, holes

• Cube faces partially projected to geometry

• Quickest method for creating surface mesh

• Can’t recognize sharp features

– Currently in development phase

• Best for “wrapping” geometry

– Quick and dirty surface meshing of complex geo metries

• For “solid” models

– Not recommended for thin sheet solids

• Options

No. of smooth iterations

• To improve grid quality

Surface projection factor

• To fully project to original geometry (1.0), t o not project at all (0.0), or partially (0.0 < f actor < 1.0)

53

Mesh Types

• Mesh Types

– Set in

Global Mesh Setup > Shell Mesh Parameters

or

Surface Mesh Setup

(local upon selected surface entities

• Global defaults overridden by local settings or

Compute Mesh

options

Global settings

All Tri

Quad w/one Tri

• Almost all quad except with one tri per surface

• Single tri allows transition between uneven mesh distribution on loop edges

• Where pure quad will fail

Quad Dominant

• Allows for several transition triangles

Local

• Very useful in surface meshing complicated surfaces where a pure quad mesh may have poor quality surface settings

All Quad

• These mesh types will look different with the different mesh methods

All quad, autoblock

Examples done with patch dependent mesher

54

Compute Mesh

• Once sizes, methods and types are set – ready to compute!

• Select

Mesh > Compute Mesh > Surface Mesh Only

– Most of the time can just select

Compute

at bottom of panel which will create shell mesh for entire model

(In put = All)

– Other options

Overwrite Surface Preset/Default Mesh Type/Method

• To quickly override global and local settings

• Avoid going back to other Mesh Setup menus to change parameters

– Input

• Can mesh

All

(default – entire model)

Visible

– only visibly displayed surfaces/geometry

Part by Part

– Parts meshed separately

– Mesh will be non-conformal between parts

From Screen

– Select entities to mesh from screen

55

4.

Volume Meshing

Introduction to Volume Meshing

56

• To automatically create 3D elements to fill volumetric domain

– Generally termed “unstructured”

• Mainly tetra

– Full 3D analysis

• Where 2D approximations don’t tell the full story

– Internal/External flow simulation

– Structural solid modeling

– Thermal stress

– Many more!

• Standard procedures

– Start from just geometry

• Octree tetra

– Start from existing shell mesh

– Robust

– Walk over features

• Cartesian

– Fastest

• Have to set sizes

– Both geometry and shell mesh

• Delauney/T-grid

• Octree tetra

– Quick

• Advancing Front

– Portions of model already meshed

– Smoother gradients, size transition

• Hex Core

– Prism layers

• Hex Dominant

– Set sizes on rest

• “Prism”

57

General Procedure

• First decide volume mesh parameters

Global Mesh Setup >

Volume Meshing

Parameters

– Select

Mesh Type

– Select

Mesh Method

for selected

Type

– Set options for specific

Methods

• Set mesh sizes

– Globally

• As in

Shell Meshing

– Locally

Part/Surface/Curve Mesh

Setup

• As in

Shell Meshing

• For

From geometry

:

– Octree

– Cartesian

• Define volumetric region

– Typically for octree on complex models

– Multiple volumes possible

• Load/create surface mesh

– As in

Shell Meshing chapter

– For

Delauney, Advancing Front,

ANSYS TGrid, Hex-Dominant

• Either of these types run from geometry will automatically create surface mesh using global and local Shell Mesh settings without any user input/editing

• If in doubt, run Shell Mesh first, then from existing mesh

• Compute Mesh

– Mesh > Compute

Mesh > Volume Mesh

• Define density regions

(optional)

• Applying mesh size within volume where geometry doesn’t exist

• Compute Prism (optional)

– As separate process

– Also option to run automatically following tetra creation

58

Body/Material Point

• Define Volumetric Domain

– Optional

• Recommended for complex geometries

• Or multiple volumes

Geometry -> Create Body

Material Point

• Centroid of 2 points

– Select any two locations whose mid-point is within volume

– Preferred, because more robust than

By Topology method

• At specified point

– Define volume region at a “point” within volume

By Topology

• Defines volume region by set of closed surfaces

• Must first

Build Diagnostic Topology

to determine connectivity

– Will fail if gaps/holes in body

Entire model

– Automatically define all volumes

Selected surfaces

– User selects surfaces that form a closed volume

Mesh Types

59

Tetra/mixed

– Most used type

– Pure tetra

– With prism layers

• Prisms from tri surface mesh

• Hexas from quad surface mesh

• Tetra and/or hex core filling interior

• Pyramids to cap off any quad faces from prism sides, hex core, or hex prism layers

– With hex core

• Available in Cartesian type too

• Hexa filling majority volume

• Tetra (from Delauney algorithm) used to fill between surface or top of prism layers and hex core

• Pyramids to make conformal between tetra and hex quad faces

– Hybrid mesh can be created by merging with a structured hex mesh

Tetra/Prism

Pure tetra

Tetra/Prism/Hexcore

Mesh Types - Continued

• Hexa-Dominant

– Uses existing quad mesh

– Good quality hex near surface

– Somewhat poor in interior

– Typically good enough for static structural analysis but not CFD

– Not covered in detail here

60

• Cartesian

– Methods available in Cartesian

Staircase

Body fitted

Hexa-Core

– Automatic pure Hexa

– Rectilinear mesh

– Fastest method for creating volume mesh

– Not covered in detail here

61

Mesh Methods - Octree

• Type -

Tetra/Mixed

– Method -

Robust (Octree)

• Same as Shell Meshing > Patch Independent

– Retains volumetric tetras

• Good choice for complex and/or dirty geometry

• Good if you don’t want to spend too much time with geometry cleanup

• Good if you don’t want to spend too much time with detailed shell meshing

• Good if you don’t want to spend time defeaturing geometry

• Just set appropriate mesh sizes on geometry

– Global sizes (max size, curvature/proximity based)

– By parts (

part mesh setup

spreadsheet)

– Surfaces

– Curves

– Review

Shell Meshing

chapter

Part/Surface/Curve Mesh Setup

62

Octree Method Characteristics

• Octree process

– Volume first generated independent of surface model

– Tetras divided near regions where sizes are set smaller

– Nodes are projected to model surfaces, curves and points

– Surface mesh is created when outside tetras are cut away

Mesh detail

• Resulting mesh is independent of the underlying arrangement of surfaces

– Not all surface edges need to be captured!

– Surfaces edges only captured if curve exists there

• Delete curves to ignore hard edges

• Or filter points/curves under

Build Diagnostic Topology

Sliver ignored

Geometry

Mesh

Octree Tetra Process

Initial conditions

– Geometry including surfaces, curves and points (from

Build Topology

)

– Mesh size set globally and/or on surfaces/curves/densities

– Optional material point could also be created

– All saved in the tetin file

63

The Octree process creates an initial mesh of “Maximum

size” elements which fills a region around and through a bounding region completely encapsulating the geometry.

64

Tetra Process, Cont’d

– Mesh then subdivided to meet the entity size parameters

– Factor of 2 in 3-dimensions, hence the name Octree

– Nodes are adjusted (projected) and edges are split/swapped to conform to the geometry

– Automatic “flood fill” process finds volume boundaries

– Initial element assigned to part name of material point

– Adjacent layers added to same part until boundary surfaces are reached

– Multiple volumes are supported for multi-region or multi-material problems

– Elements outside the domain are marked into a reserve part name called

ORFN

, then deleted

Flood fill

•User defined volumes kept

ORFN

region is discarded

Material point

65

Tetra Process, Cont’d

• Smooth

– Octree mesh is initially composed of regular right angle tetras

– Smoother can be set to run to improve quality

– Or run afterwards:

Edit Mesh -> Smooth Mesh Globally

66

Geometry Requirements for Octree Tetra

• Tetra requires a reasonably enclosed surface model

– Run

Build Diagnostic Topology

to find gaps/holes

– Octree can tolerate gaps smaller then the local element size (1/10 th the element size or less)

• Keep points and curves at key features and hard edges

Filter curves and points

by angle with

Build Diagnostic Topology

• Create Material points to define volumes

– Will create a material point if none exists

(named

CREATED_MATERIAL#

)

• Set Global, Part, Surface, Curve Size Parameters

– Similar to

Shell Meshing

section

Geometry Repair tools quickly locate and fix these problems.

Missing inlet surface

Hole highlighted by yellow single edge curve

Using Points and Curves with Tetra Octree

• Curves and points included

• Mesh size specified on curves and surfaces

Mesh captures detail

67

• Curves and points not included

• Mesh size specified only on surfaces

Coarse mesh ‘walks over’ detail in surface model

• Curves and points affect which features are captured by the mesh!

• Build Topology easily creates the necessary points and curves easily with filter by angle

68

Tetra Octree - Options

• Setup options:

Global Mesh Setup > Volume Meshing parameters

Run as batch process

• Runs as a separate process. GUI will stay interactive.

Fast Transition

• Allows for a faster transition in element size from finer to coarser

• Reduced element count

Edge Criterion

• Split elements at a factor greater than set value to better capture geometry

Define Thin cuts

• Tool for resolving thin gaps, sharp angles

• User selects pairs of opposing parts

• Resolves elements jumping from one side to another

Smooth

• Automatically smoothes after grid generation process

Coarsen

Fix Non-manifold

• Automatically tries to fix elements that jump from surface to another surface

– For a more detailed description go to

Help > Help Topics > Help

Manual > Mesh > Global Mesh Setup > Volume Meshing

Parameters > Tetra/Mixed > Robust (Octree)

69

Compute Mesh – Tetra Octree

• Run options:

Compute Mesh > Volume Meshing Parameters

Create Prism Layers

• Will create prisms marked under

Part Mesh Setup

• Immediately after tetra calculation

• Prism layers grown into existing tetra mesh

Create Hexa-Core

• Will retain tri surface mesh (or tri and prisms), throw away tetra mesh and regenerate volume

• Fill volume interior with Cartesian hexas

• Cap off hexas with pyramids

• Map tetra to tri or top prism face with Delaunay filling algorithm

Input

• Select Geometry

All, Visible

Part by Part

• Meshes each part separately

• Mesh not conformal between parts

From file

• Select tetin file (save memory by not have it loaded)

Use Existing Mesh Parts

• Select

Parts

that are already surface meshed

• Merges nodes to preexisting surface mesh

• Uses

Make Consistent

to match octree volume mesh to existing surface mesh

70

Curvature/Proximity Based Refinement

Curvature/Proximity Based Refinement

Octree

only

– Automatically subdivides to create elements that are smaller than the prescribed entity size in order to capture finer features

Min size limit value

entered is multiplied by the global

Scale Factor

and is the minimum size allowed for the automatic subdivision

– Used primarily to avoid setting up meshing parameters specifically for individual entities thus allowing the geometry to determine the mesh size

– Convenient for geometry with many fillets of varying curvature

Min Size Limit: multiplied by Scale

Factor = global minimum

Prescribed element size: Surface/Curve Max. Element Size times Scale Factor

Prescribed size is adequate here

Auto subdivision at tighter radius of curvature

71

Curvature Based Refinement

Refinement

– Approximate number of elements along curvature if extrapolated to 360 o

– To avoid subdivision always to global minimum which would otherwise result in too many elements

– Subdivision will stop once number of elements along curvature is reached

– Won’t exceed global minimum set by

min size limit

value

• Example

– Specified refinement achieved with larger elements

– Global minimum (

min size limit

) not realized, not necessary to capture curvature

Prescribed size

Refinement = 12

Min size limit

72

Proximity Refinement, Elements in Gap

Elements in Gap

– Number of cells desired in narrow gaps

– To avoid subdivision always to global minimum which would otherwise result in too many elements

• Subdivision will stop once number of cells in gap is reached

– Will not override global minimum (

Min size limit

)

• Example

– Only one element in gap

– Can’t go smaller than Min size limit

– Have to set smaller Min size limit

Prescribed size

Cells in Gap = 5

Prescribed size

Min size limit

Min size limit (1/5 th smaller)

Cells in Gap = 5

73

Thin Cuts

•Define thin Cuts

– Only works with Tetra Octree

– To avoid ‘holes’ in thin solids/narrow gaps when mesh size is much larger than gap

– Define thin cuts by selecting two parts and then Add them to the list of defined Thin cuts

• The two sides of the thin cut must be in different parts

If the face of a tetra element has a surface/line node on part

A

” then it may not have a surface/line node on part “

B

B

A c

Note; If the surfaces of the two parts,

A

and

B

, meet, then the contact curve must be in a third part,

c

, or the thin cut will fail.

74

Edge Criterion

Edge criterion

– For

tetra octree

only

– A number 0 – 1

– 0.2 (the default) means if more than 20% of an edge crosses a surface or curve, then split the edge

– Has an effect similar to globally applying a

thin cut

– Smaller numbers will cause more splitting. The closeest node will be projected to the surface

– Use prudently. Too small a number results in strange globs of refined mesh

>

0.2

Split edge

75

Mesh Methods - Delaunay

Type -

Tetra/Mixed

– Method -

Quick (Delauney)

Start from a good quality, closed surface mesh

– Can be quad and tri elements

– From Shell Mesh

– From Octree

– From imported surface mesh

Initially distributes nodes so as the centroid of any tetra is outside the circumsphere of any neighboring tetra

• Setup Options:

– Delaunay Scheme

Standard

: Delaunay scheme with a skewness-based refinement

TGlib

: TGrid Delaunay volume grid generation algorithm that utilizes a more gradual transition rate near the surface and faster towards the interior

– Use AF : TGrid Advancing Front Delaunay algorithm which has smoother transitions than the pure Delaunay algorithm.

– Memory Scaling Factor: To allocate more memory than originally

– Spacing Scaling Factor: Growth ratio from surface (1 – 1.5 typically)

– Fill holes in volume mesh: Use to fill holes/voids in existing volume mesh . E.g. if bad quality region is deleted

– Mesh internal domains : For multiple sets of closed volumes in one model

– Flood fill after completion: For multiple volumes – Will assign tetras within closed volume to Part designated by Body or Material Point

– Verbose output: For troubleshooting

Mesh Methods – Advancing Front

76

• Type -

Tetra/Mixed

– Method -

Smooth (Advancing Front)

• Same as

Quick (Delauney)

but

• Uses advancing front method that marches tetras from surface into interior

• Algorithm from GE/CFX

• Results in more gradual change in element size

– “Better” but finer mesh, more elements than Delaunay

– Elements grow slowly for first few layers from surface, then growth rate increases into volume more

– Input surface mesh has to be of fairly high quality

• Setup Options:

Do Proximity Checking

– Check to properly fill small gaps

– Longer run time

• Can create pyramids from quads

– Quads need to be a 10 aspect ratio or less

– Delaunay can handle much higher quad aspect ratios

• Respects densities

Mesh Methods – ANSYS TGrid

77

Tetra/Mixed

ANSYS TGrid

• Runs Tgrid through an extension module

• Good mesh quality

• Fast mesh generation

• Setup Options:

Flood fill after completion

: Same as octree Flood fill

Verbose output

: This option writes more messages to help in debugging any potential problem

• Will not respect densities

• Will not mesh to quads. It converts them to triangles

• Similar to Advancing Front, but does not group elements as close near surface

78

Compute Mesh – Delaunay, Adv. Front, TGrid

• Run Options:

– Similar options as octree except cannot mesh to part geometry and part mesh (option:

Use existing mesh parts

)

Create Prism Layers

available for both

Hexa-Core not available for

Advancing Front, ANSYS TGrid

Volume Part Name

• For newly created tetras

• Can choose

Inherited

to use material

Input

All Geometry

– Will run shell mesh first with no user input/editing

– Using parameters from

Model/Part/Surface/Curve Mesh Setup

– Review

Shell Meshing

chapter

– If doubtful as to shell mesh quality, run

Shell Mesh

first, then use

Existing Mesh

Existing Mesh

– Most common method. Surfaces already meshed

Part by Part

– Meshes each part separately. Nodes are not connected

From File

– Saves memory. Surface mesh does not need to be loaded

79

Comparison

80

Density Region

Create Mesh Density

–Define volumetric region with smaller mesh size where no geometry exists, e.g. wake region behind a wing

–Not actual geometry!

• Mesh nodes not constrained to density object

• Can intersect geometry

–Can create densities within densities

• Always subdivides to smallest set size

–Set

Size

• Max size within – multiplied by global

Scale Factor

Ratio

expansion ratio away from density object

Width

Number of layers from object before mesh size is allowed to growth

Type

Points

– Select any number of points

Size

and

Width

(number of layers) will determine

“thickness” of volume if number of points selected is 1-3

–4-8 creates polyhedral volume

Entity bounds

– define region by bounding box of selected entities

Density from 2 points makes a line.

The

width

defines the radius of the cylinder

81

Periodicity

Define Periodicity

• Forces mesh alignment across periodic sides

• For meshing and solving only one section of symmetrically repeatable geometry

Rotational Periodic

• Enter

Base

,

Axis

, and

Angle

Translational Periodic

• Enter dX, dY, dZ offset

Tip: Placing material point close to midplane makes tetra octree obey periodictiy easier

82

5.

Prism Meshing

83

Prism Meshing

Inflation layers

To better simulate boundary layer effects

Mesh orthogonal to surface with faces perpendicular to bou ndary layer flow direction

Procedure

Set

Global Prism Parameters

Select

Parts

to grow layers from

Typically wall boundaries and holes

Set Local Parameters for each part

Local overrides global

Zero or blank entries will defer to global settings

Run mesher

From existing mesh

Extrude into tetra/hexa mesh

Extrude from surface tri mesh, then fill volumes

Run automatically during

Volume Mesh

creation

84

Prism - Global Parameters

Global Prism Parameters

Growth law

exponential

: height = h(r)

(n-1)

[n is layer #]

linear

: height = h(1+(n-1)(r-1))

wb-exponential

: height = h*exp((r-1)(n-1))

Initial height

of first layer – h in formulae above

• Auto calculated if not specified

– Based on factor of edge length of base triangle/quad

– Height determined so that top layer volume is slightly less t han that of tetra/hex just above it

Number of layers

n

Height ratio

r

Total height

- of all layers

– Usually specify 3 of the above 4 parameters

Compute params

will calculate the remaining parameter (

total height

usua lly left blank)

– Or specify only

Height ratio

and

Number of layers

for auto calculation of init ial height

– Individual surface/curve height/ratio/layers will override these global de faults if set

Other global parameters

Total height explained later

Height ratio

(r)

Initial height

(h)

Growth Law Comparison

The growth rate of

Wb-exponential

is greater than

exponential

The growth rate of

exponential

is greater than

linear

85

Linear

Exponential

Wb-Exponential

86

Smooth Tetra/Prism Transition

• Leave initial height as “0”

– This causes the initial height to float in order to reduce the volume change between the last prism and adjacent tetra.

Initial height specified

Initial height = 0

87

Setting Prism Parameters on Parts

Prism extrusion areas defined by the parts

Mesh > Part Mesh Setup

Toggle on

Prism

for parts where inflation layers are desired

Surface mesh (tri/quad) gets extruded into prisms

Set

Height, Height Ratio, Num Layers

Will use global defaults if not set or zero

Applying these settings causes these parameters to be applied to each individual surface within each part

If

Apply inflation parameters to curves

is toggled on, they will also be set on each curve within each part

88

Setting Prism Parameters on Volume Parts

Normally toggle prism on only for parts that contain surfaces (becomes surface mesh)

Can also toggle on prism for parts that contain material points (becomes volume mesh)

For interior surface mesh, this defines the allowable volumes for extrusion

Selecting no volume parts has the same result as selecting all volume parts

Only one volume part selected

Edge of Interior surface

Both or no volume parts selected

Setting Prism Parameters on Surfaces

Mesh > Surface Mesh Setup

• You can specify different local

height

and

ratio

on any selected surface without moving the surface to a new part

• Usually set

height

and/or

ratio

smaller on specific surfaces to avoid collision

Height on part = 0.4

Height = 0.2

89

Collisions occurred when the height was

0.4 on all surfaces

No collisions after

90

s

Setting Prism Parameters on Curve

Mesh > Curve Mesh Setup

• You can get Prism to transition linearly across a surface by not setting a height (height = 0) on the surface, but instead set a different height on each curve on the opposite sides of the prism surface

Height ratio

and

Num. of layers

have no affect on prism for curve settings

Height =

0.01

Height = 0 on surface

Height = 0.003

91

Run Prism

Can run separately

Mesh > Compute Mesh > Prism Mesh

The

Select Parts for Prism Layer

button pops up the same menu as the

Part Mesh Setup

, except non-prism related col umns aren’t displayed

Input

Existing Mesh

From File (saves memory by not not loading mesh)

Or run automatically linked into volume mesh

Toggle on Create Prism Layers when tetra meshing

Not advisable if this is the first mesh for a particular geome try

Must be confident about setup parameters and sizing

Running prism separately allows you to smooth and error-c heck the tri or tetra mesh first.

92

Input as Surface or Volume Mesh

Input can be a surface mesh or volume mesh

– Surface mesh

– Must be a closed boundary mesh

– Must specify a volume part

– Use tetra fill methods after:

Delaunay

Advancing Front

Ansys TGrid

– Volume mesh

– Moves and reconnects tetras

Delaunay fill

Prism extrudes into existing tetras

93

Prism – Quality Control Options

Fix marching direction

– Maintains normal from surface

– Can cause intersections with other mesh

Min prism quality

– Either re-smooth directionally or cap/replace with pyramids if quality not met (minimum allowed = 1x10-6)

Ortho weight

– Weighting factor for node movement from 0 - improving triangle quality, to 1 - improving prism orthogonality

Fillet ratio

Max prism angle

Max height over base

See next slides

Prism height limit factor

Ratio multiplier (m)

– For varying exponential growth: height = h(r)

(n-1)

(m)

(n-1)

94

Prism Options – Fillet Ratio

– Blends prism grid lines around sharp corners

• 0 = no fillet

• 1 = fillet ratio equals last prism height

– Improves angles further away from the corner

– Orients prisms more in direction of flow

– If meshing tight spaces with tight curves (less than 60 o

), may not have space for a fillet ratio

Fillet Ratio = r/h r h

Fillet Ratio = 1.0

Fillet Ratio = 0.0

Fillet Ratio = 0.5

Prism options – Max Prism Angle

– Controls prism layer growth around bends or adhering to adjacent surfaces

– If the

Max

(internal)

Prism Angle

is not met, the prism layers will end and be capped off with pyramids in those locations

– Usually set in the 120 o to 179 o range

– Experience pays off here. If extruding from one part and not its neighbor, and the angle between the two surfaces is greater than the

Max Prism Angle

, the prisms will detach and be capped off with pyramids. This prevents bending the prisms that might create lowerquality internal angles. However, the pyramids are usually of lower quality, too.

– It’s usually better to run prism along adjacent surfaces until it can meet at a smaller angle, leaving quad faces. Pyramids will be avoided.

95

160 o

Original mesh

Max prism angle = 180 o

Pyramids

Max prism angle = 140 o

.

96

Prism Options – Max Prism Angle - Continued

• A high (up to 180 o

)

Max Prism Angle

keeps the prism layers connected around tight bends.

– Set this at 180 to prevent pyramids where possible

Max Prism Angle = 140

Max Prism Angle = 180

97

Prism Options – Max Height Over Base

– Restricts prism aspect ratio

– Prism layers stop growing in regions where prism aspect ratio would exc eed specified value

• Number of prism layers would not be preserved locally

Base (b)

– Mesh is made conformal with pyramids at prism boundaries

– Acceptable values vary widely (typically 0.5 – 8)

Height

(h)

h/b

Largest height over smallest base length

Pyramids

Max Height Over Base not set

Max Height Over Base = 1.0

Prism Options – Prism Height Limit Factor

– Restricts prism aspect ratio

• Prism height will not expand once this factor is met

– Uses the same height over base factor as the previous metric except prism layers are not capped off with pyramids

Base (b)

– Preserves the specified number of prism layers

– Will fail if sizes of adjacent elements differ by more than a factor of 2

– Acceptable values vary widely (typically 0.5 – 8)

Height

(h)

h/b

Largest height over smallest base length

98

Limit factor not set

Limit factor = 0.5

99

Prism Options-Part Control

New volume part

– Can specify new Part for prism elements

• Must specify if extruding from surface-only mesh

• If extruding into volume mesh, prism will inherit tetra volume Part if not specified

Side part

– For quad faces on side boundary

Top part

– For tri faces capping off top of last prism layer

Extrude into orphan region

– Extrude prisms away from existing volume, not into it

– Must specify

new volume, side and top

part, or the y’ll be in ORFN

Leaving these parts blank will inherit the names from the current mesh

100

Prism Options - Smoothing

Prepares tri/tetra for best prism quality

– Set surface/volume steps to 0 if only extruding one layer or if tri/tetra mesh is already smoothed

Otherwise defaults adequate

Value depends on model/user experience

– Set surface smoothing steps to zero for a tri/tetra mesh that is already smoothed

– Triangle quality type

Laplace typically best for eventual prism quality

Other types may be better when marching directions condense at inside corners

– Max directional smoothing steps

Redefines extrusion direction based on initial prism quality

• internally calculated for each layer

Other Advanced Prism Meshing Parameters

– Detailed in Help menu (usually left default)

101

Prism Parameters File

Read a Prism Parameters File

– To set all prism values from a prism settings file (*.prism_params)

– Written to the working directory every time prism is run

102

Smoothing a Tetra/Prism Mesh

After generating prisms:

Edit Mesh > Smooth Mesh Globally

– Prisms are smoothed during prism generation

– If input mesh was a tetra mesh, the tetras adjacent to the last prism layer will be messed up

– First smooth only the tetras and tris

• Set

PENTA_6

to

Freeze

• Don’t want to modify the prism layers at this point

– Once tetra and tri elements are as smooth as possible, smooth all elemen ts

1 st step

– Set

PENTA_6

to

Smooth

– Decrease the

Up to quality

value so as not to distort prism elements t oo much

2 nd step

The prisms get compromised a bit when everything is on smooth

103

Splitting Prism Layers

– If many prism layers are desired, it is faster, but less ro bust – to create “fat” layers and then split them with mesh editing

Edit Mesh > Split Mesh > Split Prisms

Fix ratio: The layer is split such that its resulting layers e mploy the given growth ratio (height is free variable)

Fix initial height:

The layer is split such that its first sub-la yer is of the given height (ratio is free variable)

– Specify the number of layers to result from each existi ng layer

– Can split specified or all existing layers

104

Redistributing Prism Layers

Redistribute prism layers after splitting

Edit Mesh > Move Nodes > Redistribute Prism Edge

Fix ratio:

The initial height and subsequent layer heights will be adjusted to achieve this growth ratio

Fix initial height:

The growth ratio is the variable that will be a djusted to achieve this initial height

– The total prism thickness remains fixed and layers are adjust ed within this thickness

105

6.

Mesh Preparation Before Output to

Solver

106

Mesh Preparation Before Output to Solver

What will you learn from this presentation:

 Checking and Improving the quality of the mesh

 Manipulating the elements

 Subsets

Usage of Edit Mesh tools

• To diagnose and fix any problems and improve mesh quality

• To convert element types

• Refine and/or coarsen mesh

• Manual and automatic tools

• For imported as well as internally created mesh

107

Mesh Checks

To diagnose mesh connectivity problems

Errors

– most likely to cause problems in:

Solver translation

Solver input

Solution convergence/run

Possible Problems

– “Unclean surface mesh”

Unwanted elements

Unwanted holes/gaps

May result in incorrect solution

Can check any combination of errors/possible problems at any one time

Individually select

Clicking on

Error

or

Possible Problems

headings will select all options in column – selecting again will de-select all

Set Defaults

will select the most common checks for the current mesh type (2D or 3D)

Check Mode

Create Subsets

– creates a subset of elements for each problem found (will run through all selected checks)

Check/Fix Each

– offers automatic fixing of indicated problem (needs user decision after each problem found)

108

Mesh Checks - Mesh Errors

Duplicate Elements

Elements that share all nodes with other elements of the same type

Uncovered Faces

Volumetric element faces that are neither attached to the face of another volumetric element nor to a surface element (boundary face)

Missing Internal Faces

Volumetric elements that are adjacent to another of a different part with no surface element between them

Periodic Problems

Inconsistency in the pattern of nodes/faces between periodic sides

Special check for rotating (sector) or translational periodic grids

Select pairs of parts to check

Volume Orientation

Left handed elements due to incorrect connectivity (node numbering of cell)

Surface Orientations

Surface

elements whose attached volume elements share part of the same space

Hanging Elements

Line (bar) elements with a free node

(node not shared by any other element)

Penetrating Elements

Surface element(s) that intersect or penetrate through other surface elements

Disconnected Bar Elements

Bar elements where both nodes are unattached to any other elements

109

Mesh Checks - Possible Problems

Multiple Edges

Surface elements with an edge that shares three or more elements

Can include legitimate T-junctions

Triangle Boxes

Groups of 4 triangles that form a tetrahedron with no actual volume element inside

2 -Single Edges

Surface element with 2 free edges (not shared by another surface element)

Single-Multiple Edges

Surface element with both free and multiple edges

Stand-Alone Surface Mesh

Surface elements that don't share a face with a volumetric element

Single Edges

Surface elements with a free edge

Can include legitimate hanging baffles

2D-only mesh boundaries are single

Delaunay Violation

Tri elements with nodes that are within the circumsphere of adjacent tri elements

– legacy quality criteria

Overlapping Elements

Continuous set of surface elements that occupy the same surface area (surface mesh that folds on to itself within a small angle)

Non-manifold vertices

Vertices whose adjacent surafce elements’ outer edges don't form a closed loop

Typically found in tent-like structures where surface elements jump from one surface to another across a narrow gap or sharp angle

Unconnected Vertices

Vertices that are not connected to any elements

Can always be deleted

110

Mesh Checks – Check Mode

If

Create Subsets

was selected

Will go through all checked criteria without interruption

Elements that have a particular error/problem are put into a subset with the same diagnostic type name

Subsets activated in Model Tree

Turn off all parts or shells to view subsets

If

Check/Fix Each

was selected

Will be prompted with options one criteria at a time

Fix:

Automatically fix the error/problem

Recommended only for

Duplicate Elements,

Uncovered Faces, Missing Internal Faces,

Volume Orientations, Unconnected Vertices

Create Subset

Ignore

For example, multiple edges may be legitimate t-junctions; single edges may be legitimate free edges

Valid multiple edges usually form closed loops

111

Mesh Quality Display

A diagnostic check of individual element quality

Mesh types to check

– Allows you to select the mesh types to check

1D (Line elements)

2D (Tri and/or Quad)

3D (Tetra, Penta, Hexa and/or Pyramid)

Elements to check

– By part and subset

All

Active parts

Visible subsets

Visible subsets and active parts

Refresh Histogram

– Refreshes the histogram displayed

Quality type

– Specifies the Quality criterion for display

48 quality criteria available

Some checks don’t apply to all element types

Selecting a histogram bar will display the elements in that range

112

Mesh Smoothing

Automatically improve element quality

All element types

Necessary to have geometry loaded

Nodes are moved to improve the element quality

Automatic node movement constrained by node projection type to geometry type – e.g. curve nodes will be constrained to move only on curves

Histogram is automatically displayed/updated after smoothing

User chooses:

Criterion

Up to value

Smooth Mesh Type

Smooth

: Element types actively smoothed; quality of type appears as part of histogram.

Freeze

: Nodes are held in place during the smoothing process.

These elements not shown in histogram

Float

: Nodes can be moved along with adjacent smoothed elements, but quality ignored; not shown in histogram

Example: Freeze Prisms and Pyramids while smoothing Tetra.

Float surface elements

113

Mesh Smoothing

Advanced Options

Smooth Parts/Subsets

Smooth all parts, visible parts (activated in model tree), or visible subsets

Quick, local smoothing

Laplace smoothing

Gives more uniform mesh size relative to neighboring elements and equal angles

Recommended for TRI only – smooth Tetra after with

Laplace turned off and tri’s froze

Recommended prior to prism generation

Not just worst 1%

Factors in all elements instead of only the worst 1% of those beneath quality value and their neighbors

Can improve quality but takes much longer

Violate geometry

Unconstrain nodes slightly from geometry within user defined tolerance – absolute or relative to minimum edge length of mesh elements

114

7.

Output to Solver

Output to Solver - Selecting Solver

Selecting solver

Use the red toolbox in the

Output

tab to select the solver format

This same menu is accessed with

Settings > Solver

123 solver formats available

All output formats can be set with the

Output Solver

pulldown

Help on each solver format can be found on the Ansys website: http://www.ansys.com/Products/Other+Products/ANSYS+ICEM+CFD/Outp ut+Interfaces/Output+Interfaces+TOC

Also found in

Help >

Output Interfaces

ABAQUS

ADINA

AUTOCFD

CFD++

ACE-U AcFlux ACRi

AIRFLO3D ALPHA-FLOW ANSYS

BAGGER CEDRE

CFL3D CFX-4

CGNS CHAD

CONCERT3D CRSOL

DSMC-SANDIA DTF

C-MOLD

CRUNCH

EM

CFD-ACE

CFX-5

COBALT

CSP

EXODUS

ACUSOLVE

ATTILA

COMCO

DATEX

FANSC

FASTEST-3D FASTU

FLEX

FENFLOSS

FLOTRAN FLOWCART

FIDAP FIRE

FLOW-LOGIC FLUENT V4

FLUENT V6 GASP GLS3D(ADH) GMTEC GSMAC-DF

VULCAN

WIND

CFDesign WINDMASTER

CFX-TASCflow ZEN

SCRYU

STARCD

TDF

SC/Tetra

STARS USM3D

USMKV3V

VECTIS

TGRID

SpecElem

VRML STL

VSAERO/USAERO TLNS3Dmb

Trio_U SPECTRUM-CENTRIC

GUST

ICU

KIVA-3

MACS

HAWK

IDEAS

KIVA-4

MAGREC

HDF

IMPNS

LAURA

MAZe

N3SNATUR NASTRAN NEKTON

NSU3D

PATRAN

NS3D NUMECA

PHOENICS PLOT3D

IBM-BEM

INCA

ICAT iPLES

TSAR

UGRID

LL-DYNA3D LS-DYNA3D

MOUSE MULTIBLOCK

UH3D

USA

NOPO NPARC SAUNA

PAB3D

PMARC

PARC

POLYFLOW

SPLITFLOW

TNO

TEAM

TRANAIR

POLY3D

POPINDA

PRECISE

RADIOSS

RTT

115

116

Mesh Formats

i j k

There are 2 types of mesh formats that solvers read

Unstructured

Most solvers use unstructured formats

Some examples are

Fluent, Ansys CFX, CFD++, Abaqus, Ansys

Nodes have an ID and location

The ICEM CFD unstructured mesh has a

*.uns

extension and can be made from any mesher in ICEM CFD

Multiblock structured

Some older CFD solvers require this format

Examples are

Plot3D, CFX-TASCFLOW, KIVA-3V

CGNS

supports both unstructured and multiblock structured

Nodes have IJK index designation and location

The ICEM CFD structured mesh has many files:

Project.1

,

project.2

,

project.3

, etc… for each mesh domain

A topology file,

topo_mulcad_out.top

, that describes how each domain is connected to the other domain.

A dummy file,

Project.multiblock

, that enables selection of all the multiblock mesh files of that project name by selecting this one file

Only an ICEM CFD hexa blocking is capable of being written out in multiblock structured format

117

Boundary Conditions

P

art highlights white when selected

BC’s shown for solver Fluent_V6

Both CFD and FEA solvers allow boundary conditions to be set

Output > Boundary Conditions

BC’s are set on mesh elements grouped by part names

Tree structure organizes part names by dimension

(2D, 3D, etc) of geometry and mesh in the part

Any part containing mixed dimensions (ex. curves and tri’s) will be grouped into

mixed/unknown

Use

File> Attributes > Save Attributes As…

to save the BC file (*

.fbc

and *

.atr

extensions)

118

Parameters

Some structural solvers have global parameters

Output > Edit Parameters

If the solver type requires global parameters, you must bring up this menu before writing out and press

Accept

, even if not changing any parameters

Then use

File > Parameters > Save Parameters As…

to save the file (*

.par

extension)

Example parameters shown for ANSYS solver

119

Write Input

Output > Write Input

to write the solver file

It will ask you to save a boundary condition file

(*

.fbc

) and the project

It’s always safe to save these when asked, but not necessary if you know you saved them and didn’t make any changes since then

It will then ask for the ICEM CFD mesh file to translate

*

.uns

file if the solver requires an unstructured mesh

*

.multiblock

file if the solver requires a structured mesh

A final menu will pop up that has specific options for the solver translation being used

The example on the left is for

Fluent_V6

All translators will require a boundary condition file even if no BC’s are set

A empty BC file will contain just the part names

There will always be a name for the output file

120

Special Structural Solvers

5 Special structural solvers

There are 5 structural solvers that have extended boundary condition setup – called loads and constraints – which are set using the

Common

Structural Solver

dropdown

These are

Nastran

,

Ansys

,

LS-Dyna

,

Abaqus

, and

Autodyn

These are set using the 4 extra tabs;

Properties

,

Contraints

,

Loads

, and

Solve Options

Nastran

Ansys and Abaqus

LS-Dyna and Autodyn

Constraints tab

All functions are only available for

LS-Dyna

and

Autodyn

Define contact

” is allowable with

Ansys

and

Abaqus

Nastran

only allows the first two functions

121

Special Structural Solvers - Procedure

Define which elements to write out

First define a

material

in the

Properties

tab

Then define an element property on the element types and parts you want to write out

3D property for volume elements

2D property on shells

1D property on line elements

0D property on node elements

Define any

Loads

and

Constraints

in the other tabs (optional)

Use the

Solve Options

tab to write the mesh to the solver

Solve Options > Write/View Input File

Can submit solver run if the corresponding environment variable is set to find the solver executable

For Ansys, it is ANSYS_EXEC_PATH

122

Special Structural Solvers – Write Input

If using the

Properties

,

Loads

, and

Constraints

tabs for one of the 5 special structural solvers, then use the

Solve Options

tab to write the file, not the

Output

tab

The

attribute

file (*

.atr

) is the BC file used with these special structural solvers

The

attribute

file is replaced with the boundary condition file (*

.fbc

) when using the

Output

tab

Any elements set to

All

or

None

will override any properties set in the

Properties

tab if not set to

Defined

To communicate with the

Output

tab, click on

Advanced

, and then click

Create Attribute

& Parameter Files

You can then

Edit Parameters

and

Edit

Attributes

here or in the Output tab

The attributes will then be the same as the boundary conditons

View input file here or in your own text editor

123

8.

ICEM CFD Hexa

124

What is Blocking?

• A hexa mesh is created by first making a “blocking”

– A blocking breaks down a geometry into large brick-shapes and structures the directio n of grid lines by the arrangement of the blocks

– Each “block” is easily meshed with a pure Cartesian mesh

• Some blocks can be defined as “swept” and be unstructured along one face

– Block entities (faces, edges, and vertices) are projected onto the geometry

– The blocking is saved to an independent file, and can be loaded onto a different geom etry

Mesh with projection

Blocking

Mesh without projection

Geometry

Approach – Top Down and/or Bottom Up

Block structure is created independent of geometry

– “Top down” topology creation

• The user as sculptor instead of brick layer

• One-step creation of advanced topologies (O-grid)

O-grid

– “Bottom up” topology creation

• Blocking is built up like “laying bricks”

– Create blocks

– Extrude face

– Copy topologies

125

– Combinations of top-down and bottom-up methods can be used

Geometry Requirements for Hexa

Use same geometry (tetin) as used with Tetra

– Does not necessarily need to be a completely enclosed volume

Associating

Face to Surface

to a dummy point family or

Interpolation

can effectively mesh where geometry doesn’t exist

Blocking

126

Geometry

– Points and curves are not required but are very useful

• Use

Build Diagnostic Topology

to quickly build all curves and points

– Block structure is projected to geometry

• Surfaces – automatically with manual override

• Curves and points – manually projected

Geometry/Blocking Nomenclature

• Geometry

– Point

– Curve

– Surface

– Volume

• Blocking

– Vertex

– Edge

– Face

– Block

Vertex

Edge

Curve

Point

Face

Surfaces

Note: “curve” refers to lines, arcs, and splines (1D geometry)

127

Block

Blocking process

• Structure blocking to capture the shape of the geometry

– Top down

• split and discard unused blocks

– Bottom up

• create block by extrusion, creating, copying

• Associate blocking to geometry

– Usually just edges to curves

• Move vertices onto geometry

– Manual and automatic methods

• Assign mesh sizes

– Quickly by setting sizes on surfaces and/or curves

– Fine tune by setting edge distributions

• View mesh and check/improve quality

• Write out mesh

128

129

Initialize Blocking-3D or 2D

• New Blocking

3D Bounding Box

• One 3D volume block encompassing selected entities

2D Planar

• One 2D block on XY plane around entire 2D geometry

• First rotate geometry to XY plane

• No surfaces required

2D Surface Blocking

• Discussed next slide

130

Initialize Blocking-2D Surface

2D Surface Blocking

– Each surface becomes one 2D block

– Free blocks – fully unstructured

• Most robust

Mapped

– structured

• Aligned mesh along 4 block boundary edges

Geometry

2D blocking

Unstructured

– Must

Build Diagnostic Topology

first

• It needs the connectivity information

– Can always convert blocks between free and mapped afterward:

Edit Block > Convert Block Type

131

Structuring Blocking to Fit Geometry

Top down approach

Split the block to capture the underlying shape

Start with one block which encloses the entire geometry

Delete unused blocks

Note: Deleted blocks are put into the part

VORFN by default, so they can be re-used later if wanted

132

Associate Blocking to Geometry

• Associate blocking to geometry

– Usually just Edges to Curves

– In the final mesh, edges will take the shape

(be projected to) these curves

– Right click on

Edges > Show Association

in the model tree to display the association arrows

133

Move Vertices onto geometry

• Move vertices to better represent the shape

– All visible or selected vertices can be projected to the geometry at once

– Can be moved individually along the geometry

– Single or multiple at a time

– Along fixed plane or line/vector

Moving Vertices of Different Association

134

• Color indicates type of association and how a vertex will move

(edges also follow these colors, except red)

– Red

• Constrained to a point

• Can’t be moved unless association is changed

– Green

• Constrained to a curve

• Vertex slides along that particular curve

– White (black on light background)

• Constrained to surfaces

• Vertex will slide along any ACTIVE surface (surface parts which are turned on in the model tree)

• If not on a surface, it will jump to the NEAREST ACTIVE surface when moved

– Blue

• Free (usually internal) vertex

• Select NEAR

(

not on) the vertex on the edge to move along edge direction

135

Assign Mesh Size

• Assign mesh sizes

– Hexa sizes can be assigned on surfaces and curves for a quick mesh

– Need to

Update sizes

to apply to surface/curve sizes to edges

– Or set edge-by-edge for fine tuning

• Automatic

Copy to parallel edges

136

Edge Parameters

Spacing 2 = 1.0

Side 2

Ratio 2 = 1.5

17 meshing laws

Side 1 (base of arrow) params

Ratio 1 = 1.5

Spacing 1 = 1.0

Requested

Side 2 (head of arrow) params

Side 1

Actual

Arrow indicates side 1 and side 2

Spacing can be linked to another edge

Spacing 1

– distance between first two nodes on side 1

Ratio 1

– growth ratio from side 1 toward center

Spacing 2

– distance between first two nodes on side 2

Ratio 2

– growth ratio from side 2 toward center

Max Space

– Maximum element length along edge

137

View Pre-Mesh

• Pre-Mesh

– Create mesh at any stage of the process

– Mesh with different projection methods

– Use

Project faces

(default) to fully represent the geometry

– View only certain surface mesh by turning on only that

Part

in the model tree

– Use

Scan planes

to view internal mesh (covered later)

No projection

Face projectio n

Checking Quality

• Using the Quality Histogram

– Determinant

• Measurement of element deformation (squareness)

• Most solvers accept > 0.1

• Shoot for > 0.2

– Angle

• Element minimum internal angles

• Shoot for >18 degrees

– Aspect ratio

– Volume

– Warpage

• Shoot for < 45 degrees

– Many more metrics

You can display elements in a given range by selecting the histogram bar

138

139

Write Mesh

• Convert pre-mesh to a permanent mesh

– Two formats depending on what your solver takes

• Unstructured: Cells defined by node numbers (connectivity)

• Structured: Multiblock – cells defined by i, j, k index

– Blocking changes will no longer affect this mesh

Using the

File>Blocking>Save

… menu only writes the mesh to disk

Pre-Mesh>Convert to

…” a mesh from the model tree saves and immediately loads the mesh

Ogrid Definition

• An O-grid is a series of blocks created in one step which arranges grid lines into an

“O” shape or a wrapping nature

• 3 basic types created through the same operation all referred to as “O-grids”

• O-grid

• C-grid (half O-grid)

O-grid C-grid

• L-grid (quarter O-grid)

• Reduce skew where a block corner must lie on a continuous curve/surface

L-grid

• Cylinders

• Complex geometries

• Improves efficiency of node clustering near walls for CFD applications

O-grid

140

No O-grid

Creating Ogrid

• Select blocks for O-grid

– Can select by visible, all, part, around face, around edge, around vertex, 2 corner method, or individual selection

5 blocks in 2D

7 blocks in 3D

141

Select specific blocks or around face, edge, or vertex

Note: Internal block has all internal (blue) edges and vertices

Ogrid – Adding Edges/Faces

• Adding faces during O-grid creation

– O-grid “passes through” the selected block faces

– In general, add faces on the “flat parts”

– Adding a face actually adds blocks on both sides of the face

O-grid passes through this face

Half O-grid

(C-grid)

• Examples of uses

– Pipe ends

– Symmetry planes

– Complex geometries

142

O-grid passes through this face

143

Ogrid – Adding Multiple Edges/Faces

• Any number of faces can be added around a selected block

– If all the faces are added around a block, the result is no change since the

O-grid passes through all the faces

Quarter O-grid

(L-grid)

Quarter O-grids can be used to block triangular shapes

Seen as a C-grid in one direction and an L-grid in another direction

144

Ogrid – Around Blocks

• Select

Around block(s)

to create the O-grid around the selected blocks

– Useful for creating wrap-around grid around a solid object

– Examples

• Flow over a cylinder

• Boundary layer resolution around an airplane or car body

145

Scaling Ogrid

• O-grids can be re-sized after or during creation

– By default the O-grid size is set to minimize block distortion

– You are actually scaling all parallel O-grid (radial) edges to the selected edge

– The selected edge is given a factor of 1

– Numbers < 1 will shrink the edge and thus create a larger inner block

Factor = 0.3

Selected edge factor = 1

146

Why Create an Ogrid?

Before O-grid

This mesh can be improved by using an O-grid

– An example of bad mesh in the block corners

Right mouse click on the histogram to access options like

show

,

replot

, or

done

147

Index Scheme

• All blocks and vertices are defined with a global index scheme

– Initial block has i,j,k indices aligned with Cartesian x,y,z, global coordinates

– Subsequent blocks created by the split operation will maintain that orientation

– O-grids will not conform to this orientation, so each O-grid creates a new index direction (O3,

O4, etc…) (i,j,k correspond to dimension 0,1,2)

– Vertex Indices can be displayed by right clicking on

Vertices > Indices

in the model tree i=1 j=2 k=4 O-grid3=1

1 2 4 3:1

148

Using Index Control

Select corners

is often faster than toggling the index arrows

• Blocks can be turned off and on based on indices

– Use the index control to turn blocks off and on

– Many operations can be applied to only the visible blocks

• Split blocks

• Rescale O-grid

Resets everything to fully visible

149

VORFN Part

• A region of blocks called VORFN surrounds the blocking

– The reserved part name

VORFN

is created in the model tree when blocking is initialized

– It is used to maintain the global index scheme

– Indices begin at 0 (in

VORFN

region)

– Deleting blocks normally (non-permanently) just changes the part to

VORFN

• Blocks can be moved back out of

VORFN

to another part

– Deleting blocks

permanently

gets rid of the block and rebuilds

VORFN

as an O-grid

Original

VORFN

Selected blocks are actually removed and

VORFN

is rebuilt

(as an Ogrid)

Turn on to see

VORFN

VORFN becomes an O-grid after deleting blocks permanently

Removing Splits and Ogrids

• Splits and O-grids can be deleted by using

Merge vertices > propagate

– Select two vertices at the ends of an edge running in the direction you want to delete

– Middle click, then

Confirm

– The second vertex merges to the first vertex when

Merge to average

is off, and the merge will be propagated

– If deleting an O-grid, only select the vertices of one radial edge

Deleting a split

Deleting an O-grid

2

1

150

2

1

151

Extrude Face

• Select block face (select face or use two corner method)

– Interactive

• Drag with the pointer

– Extrude a Fixed distance

• Enter distance

2 corner method

– Extrude along curve

• Select curve

Extrude along curve

Select face

Set Location

Set X, Y, and/or Z of selected vertices

– Select

Ref. Vertex

, then select vertices to move or use the index control and select all visible vertices (“v”)

– Select directions to move (Modify X, Y, Z)

• Can use a local coordinate system (cylindrical, Cartesian)

• If cylindrical coor. System, (x, y, z) becomes (r,

θ, z)

– Enter values or use the values from the

Ref. vertex

or screen location

– Method can be

Set Position

or

Increment

Apply

152

Select these vertices

Z-dir z

Set z coordinate of vertices

Align Vertices

Align multiple vertices in one plane with vertices in another plane (or split dimension)

– Select

Along edge direction

, then select the edge that connects the two planes, or runs approximately normal to the split plane that you want to move inside

– Select

Reference vertex

, then select any vertex in the plane you want to align to. These vertices will remain fixed

– Select the plane to allow vertex movement within (XY, YZ, XZ, or User Defined). The

User Defined

plane must be specified with a normal vector, such as (1 1 0)

Apply

Select any of these vertices as reference

153

All visible vertices not sharing the reference index will be moved

Move vertices in this plane

Select this edge

154

Create Blocks – 2D to 3D

A 2D blocking can be extruded into a 3D blocking by three different methods

Multizone Fill

• Auto creation of 3D blocking from enclosed 2D surface blocks

Translate

Rotate

Rotate

Number of nodes in circumferential direction

Extrudes points into curves and curves into surfaces where

3D geometry doesn’t exist

Surface mesh and scan planes

155

Create Block – Wedge

Degenerate

– Select 6 vertices or locations

– Order is important (see picture)

– Grid lines converge at vertices 1 and 4

– Results in penta6 (prism) elements along one edge

Quarter-O-Grid

– Results in all Hexa “wedge” (Y configuration)

4

1

6

5

3

2

Quarter-O-Grid

Degenerate

156

Create Block – Swept Block

Swept

(Unstructured)

– Select 6 vertices or locat ions

– Different order than deg enerate, quarter o-grid

– Results in unstructured mesh

– Some tris/prisms

• Can also

Convert Block Type

– To

Structured

– To

Unstructured

(2D)

– To

Swept

(3D)

– Hex blocks as well as de generate wedges

2

1

6

5

4

3

Collapse Blocks

Collapsing blocks

– Select edge to define collapse direction

– Select blocks to collapse

– Results in a degenerate block (converges to penta6

(prism) elements)

– Degenerate block is often deleted

Select edge

157

Example: meshing around knife-edge wings

158

Select these two vertices

Split Vertex

Separates or undoes merged vertices, including vertices merged due to a collapsed block

– Select any numbers of vertices and middle click

Apply

– If you have deleted any blocks permanently after vertices were merged, this operation may not work to undo the merge. This is because a new index scheme is configured when blocks are permanently deleted

159

Periodicity in Geometry

First must be specified in tetin file

Global Mesh Size -> Set up Periodicity

Translational

• Enter vector which specifies magnitude and direction

Rotational

• Enter

Axis

vector – only specifies direction

• Enter

Base

point that axis goes through

• Enter

Angle

in degrees

21.1765

o

(360/17)

Base (0 0 0)

Axis (0 0 1)

Periodicity in Blocking

Vertices then made periodic in blocking

– Select

Edit Block -> Periodic Vertices -> Create

– Select pairs of vertices at a time

– The second vertex of each pair will move to the periodic position of the first vertex

– When you move one vertex, its pair will move with it

– Subsequent splits will also be periodic

– Visually verify with

RMB

on

Vertices -> Periodic

, and

Faces -> Periodic Faces

in model tree

– A face becomes periodic only if its 4 corner vertices are periodic

160

Subsequent splits are also periodic

161

2 Ways of Blocking the Same Geometry

• Creating a fork by Merge vertices

Delete block

Merge 2 vertex pairs

Merge 2 more vertex pairs

2 Ways of Blocking the Same Geometry

• Creating a fork by Extrude faces

162

Extrude 1

Extrude 2

Associate

163

Multiple Ways of Blocking the Same Geometry

• Creating a fork with Top-down methods

split

Two quarter

O-grids

Delete blocks

Move vertices

One quarter

O-grid

One quarter

O-grid

164

Topology

What is common in these?

Their block topology

Topology

All these parts have the same basic topology

Blocking strategy for all pipes are similar.

Single block with O-grid

The only difference is the number of splits

added to help control the blocking

Create the one block, then split, and add O

-grid last

This helical blocking is quickly created with extrude along curve

165

Single block with o-grid splits

Single block with 5 splits and o-grid

Single block with multiple splits and ogrid

Extend Split

Think of a split as a plane (even though it does not have to be planar)

Select an edge at the outside of this “plane” and it will extend in all directions

Split only goes through the displayed blocks

Use the index control to limit the displayed blocks

Select edge

Select edge

166

Select

Project vertices

to have it automatically project new visible vertices to the nearest place on their associated geometric entities

Shaping Edges – Split Edge

Edges are by default linear before projection

Edges can be shaped using split edge

Spline

Linear

Control point

Use

Move vertex

to move splits after splitting

Spline

Multiple splits

167

Linear

Original edge

Control point

Split edge will also override the automatic interpolation of edges during mesh computation

168

Shaping Edges – Split Edge Example

Using split edge to shape block faces to make a hole where it doesn’t exist in the geometry

Geometry

(gear)

169

Shaping Edges – Link Edge

Use one edge to control the shape of another

Select source edge then target edge(s)

Enter factor (higher number = greater curvature)

Source edge

Target edge

Factor = 0.9

Factor = 1.3

Factor = 0.5

170

Bottom-Up Meshing Methods

Top-down is, generally, more

robust

Bottom-up methods improve

flexibility

Transform Blocks

Translate

Rotate

Mirror

Scale

2D to 3D

extrusion

Translate

Rotate

– Block independently and merge

Extrude face

Create block

171

Transforming Blocks

Simply transform selected blocks or make a copy and merge the transformed copy with the previous blocking

Select blocks to transform

Select

Method

Translate

Rotate

Mirror

Scale

Enter parameters necessary for method

Mirror example

172

Create Block – Hexa (Vertex Locations)

Select 8 vertices

Create block types

Hexa

8 vertices or locations (selection order is important)

(Choose a vector direction and do the same order on opposite faces)

2 faces

Quarter O-grid

(Y-grid)

Degenerate

5

1

2

6

3 7

4

8

Select 2 faces

173

Create Block – Hexa (Geometry Locations)

What if I don’t have 8 vertices to select?

Select the vertices that you do have

Press middle mouse button

Select the rest of the locations on the screen

The same order must be maintained as before

1

3

4

2

7

5

6

8

Press middle button

174

Merge Vertices

One by one

Multiple within tolerance

When merging individually, select two vertices at a time

With

Merge to average

off, the second vertex will merge to the first

With

Merge to average

on, both vertices merge to the middle of the two

Use to join separate topologies together

Use to make degenerate blocks

1

2

2

1

Delete Blocks – Permanently

Delete blocks will, by default, move blocks to the part

VORFN, which is more stable than permanently deleting blocks (doesn’t recompute indices)

However, there are some situations where deleting permanently is useful

Deleting all of VORFN can serve as a repair tool in complex topologies (indices get reconfigured)

Deleting individual blocks will free up node connectivity across VORFN blocks

175

Equal number of nodes across hole

Delete block permanently

Number of nodes can be unequal

176

Three Basic uses of O-Grids

Three basic uses of O-grids

Capture the shape of the geometry

Usually done early in the blocking process

Improve element quality in block corners where surfaces do not make a corner

(smooth transition at block corner)

Improve efficiency of node clustering near walls

Boundary layer resolution

These last two are usually accomplished with the same O-grid, and done late in the blocking process

Quarter O-grid

Example of using an O-grid to capture the basic shape as the first step in the process

177

Refinement

Defines integer multipliers of elements across block interfaces

Can only be used with certain solvers

Refine: Factor > 1 (enter integer)

Coarsen: Factor < 1 (enter fraction – 1/2, 1/3, etc.)

Select refinement edge direction or select “All”

Select block(s) to refine within

Factor

= 1/3

Resolve Refinements

Creates 1-to-1 node connections for refinements done on the blocking

Only works on refinement ratio multiples of 3

Operates on the unstructured mesh only

Multiple steps of refinement and resolving refinements can be done (3, 9, 27,

1/3, 1/9, 1/27, etc…)

178

179

Edge Parameters – Linked Bunching

Link node counts and distribution law to another edge

Can link to one master edge or a series of edges with the same end-bounds

Select the large edge first

Select the small edge on side 1 when selecting the

Link

Edge

Side 2

Side 1

The long edge gets linked to all these shorter edges

Match Edges

Matches the end spacing to another edge

Reference edge and target edge must meet at the same vertex

Does not link spacing

The effect is usually only noticed when the target edge has an end spacing larger than the reference edge.

Target edge

180

In this example, the side 1 node spacing of the target edge is set to the same node spacing as side 2 of the reference edge

Reference edge

Split Face

Split Face

is actually a split block operation

Split Face

splits the adjacent blocks in a non-active part

(usually VORFN), and what is left visible is the end of the split on the visible faces

Select Face to split

Left click on edge and drag split

Split will be normal to the selected edge

181

Select face

Select edge

Face split is normal to selected edge

VORFN blocks are what gets split

182

Merge Blocks

Merge blocks

Select blocks to merge, then middle click

Apply

You cannot merge blocks of different parts unless you first change them to the same part

Select these blocks

183

Merge Faces

Merge Faces

Select 2 corners diagonally across faces to merge

Apply

You cannot select across O-grids because this is a different index direction

This actually merges blocks on both sides of the selected faces

Selected faces

Select diagonally across vertices

Merge Face

actually merges blocks on both sides of the faces

184

Output Blocks

Reduces number of blocks in a multiblock mesh, which reduces solver time

Three steps (in order)

1.

Initialize

output bocks

2.

Turn on

Output blocks

3.

Merge blocks (automatic or manual)

Before

29 blocks

After

8 blocks

Initializing output blocks to the full blocking

BEFORE merging blocks will prevent the mesh from being altered when merging blocks

Output blocks

can be toggled on and off between the merged blocking and the full blocking

185

감사합니다

.

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