Automatic Meshing in Fluids - Ansys · 2012-08-21 · Automatic & Robust Meshing –...

Automatic & Robust Meshing in Fluidsg

2011 ANSYS Regional Conferences

© 2011 ANSYS, Inc. August 25, 20111

Automatic & Robust Meshing – Assembly Meshing

Assembly Meshing enables dramatically reduced time to mesh for typical CAD models by eliminating the tedious

Assembly Meshing

geometry clean‐up

Top‐down approach to mesh all parts atTop down approach to mesh all parts at once• Uses Virtual Bodies (material points) to automatically extract internal regions from assembliesfrom assemblies

• Supports:– Meshing solids from sheet bodies– Conformal mesh between parts pwithout requiring multibody parts

– Overlapping bodies– Tet (linear) and CutCell (hex‐dominant) mesh types


mesh types– Inflation

Agenda

1 The Customer Problem1. The Customer Problem

2. Assembly meshing overview

3 New Features3. New Features1. Flow Volume Extraction

2. Sharp Angle, Thin Sections

3. Contacts and Leak closing

4. Demo: Mixing Tank

f5. Miscellaneous features

6. Summary


Automatic & Robust Meshing in Fluidsg

The Customer Problem


Assembly Meshing Motivation

CFD users need a quick way to generate the fluid volume mesh from complex assemblies of geometric solid parts.

G l f i l i f d ( dGeometry tolerances often require more accurate resolution of data (and more work to achieve it) that the mesh later ignores as the mesh size is relatively much larger.

• Th t t b i t t ith h th d th t i h• The parts may not be in contact with each other, and they may contain sharp angles, thin sections and gaps.

• Poor CAD models that don’t form watertight solid geometry.

By combining the flow volume extraction and meshing operations, the overall meshing time and efficiency of the meshing workflow can be improved.

Solution:So ut o :

• Assembly meshing


Assembly Meshing in Fluids: P C iProcess Compression

Mesh GenerationMesh SetupGeometry Prep

The overall meshing process can often get elongated if the geometry is complex:

lexity

Mesh Generation

Mesh Setup

Geometry Prep

High Complexity

odel Com

pl

Mesh Generation

Mesh Setup

Geometry Prep

Med Complexity

Mo

Mesh Generation

Mesh Setup

Geometry Prep

Low Complexity


Time to Mesh

Assembly Meshing: P C iProcess Compression

Assembly meshing reduces the overall meshing time, byAssembly meshing reduces the overall meshing time, by combining the flow volume extraction and meshing operations.

lexity

Part Meshing:

Mesh Generation

Mesh Setup

Geometry Prep

odel Com

pl

MeshMesh

Assembly Meshing:

Geometry Note: Mesh Generation time

Mo Mesh

GenerationMesh Setup

Geometry Prep

Note: Mesh Generation time is slightly longer, but overall time is significantly reduced.


Time to Mesh

A tomatic & Rob stAutomatic & Robust Meshing in Fluids

Assembly meshing:

Flow Volume, Inflation, Sharp Angle, Thin Sections


R14 Assembly Meshing: Characteristics

• Maintains characteristics from CutCell at R13– High fraction of hex and prismatic cells

– Supports global size functions feature capture tessellation etc controls– Supports global size functions, feature capture, tessellation, etc. controls

– Operates on parts, multi‐body parts, etc. with new option to define virtual bodies

– Patch independent: • Eliminates the need for pinch control and VT operations

• Creates conformal meshes across parts in contact– Eliminates the need for multi‐body part generation in CAD

• Ability to create flow volumes from a “closed” set of bodies (sheet or solid)– Eliminates the need for Boolean/Fill operations in CAD

• Supports both CutCell and Tetrahedral meshes– Tetrahedral meshes supported by CFX and Mechanical

solvers


R14 Assembly Meshing: Fl V l E i

Flow volume extraction: Three simple steps

Flow Volume Extraction

Flow volume extraction: Three simple steps1. Define Coordinate system inside the Fluid Void

2. Insert a Virtual body

33. Assign the proper CoordinateSystem to the Material Point

4. Done

#2

#3

© 2011 ANSYS, Inc. August 25, 201110

#1

R14 Assembly Meshing:K S lid M hKeep Solid Mesh

In the Assembly Meshing panel, you can choose to keep or discard the mesh in all solidskeep or discard the mesh in all solids

Parts can be marked

© 2011 ANSYS, Inc. August 25, 201111

Parts can be marked as Fluids/Solids

R14 Inflation Improvements

Industrial Example:• 68 Million cells, 5 inflation layers

Speed and Flexibility of inflation:• Several improvements to both • Total Mesh Time:

•R13: 6 hrs 39 mins•R14: 3 hrs 38 mins

Several improvements to both assembly and part meshing

– Better quality during stair stepping

– Better handling of high aspect ratio inflation

– Improved Speed of inflation creation ~30‐100%

• Assembly Meshing Flexibility– Cutcell: Full support of 2‐stage inflation– Cutcell: Full support of 2‐stage inflation

• CutCell and inflation in two separate steps

– Tetrahedron: Uses pre‐inflation• Faster more layers and better quality

© 2011 ANSYS, Inc. August 25, 201112

• Faster, more layers, and better quality

R14 Assembly Meshing: A i I fl i

Also supported for Flow volume extraction

Automatic Inflation

Also supported for Flow volume extraction

• Program controlled inflation acts only on Fluid Bodies

CutCell + Inflation Tetrahedron + Inflation

© 2011 ANSYS, Inc. August 25, 201113

R14 Assembly Meshing:Sharp angle handling• A special cell cutting algorithm has been d l d t l t h 3D ldeveloped to properly capture sharp 3D angles

• Insert a “Sharp Angle” and pick adjacent faces

• Example:Example:

Sharp angles in the Flow volume of drill bit

Mesh without Sharp Angle

Mesh with Sharp AngleMesh with Sharp Angle

© 2011 ANSYS, Inc. August 25, 201114

R14 Assembly Meshing Leak Handling

CFD users often need to extract the flow volume from CAD using Fill, Stitch or Boolean operationsStitch or Boolean operations.

Because of missing rubber seals, bad CAD, imposed tolerances, etc., gaps appear in the model and creation of the flow volume might fail.

Finding and closing these gaps in CAD can be tedious.

Solution:

Assembly meshing solves this problem in several ways:y g p y1. Tolerances only need to be resolved to level of discretization of mesh

2. Gaps that are still too large can be visualized through leakage identification

© 2011 ANSYS, Inc. August 25, 201115

3. Tools to guide mesher in resolving gaps

Image Courtesy of Delphi Harrison Thermal Systems

R14 Assembly Meshing Leak Handling:L k P h

Find leaks using material points:( )

Leakage Path

• Any time you are using material points (for internal flow), and it is leaking to the outside, you can automatically see the leak‐path together with the surface mesh

There is a small gap between the valve plug and the valve seat

© 2011 ANSYS, Inc. August 25, 201116

R14 Assembly Meshing Leak Handling:C (I f ) R i

Using Contacts for Assembly meshing:

Contact (Interface) Regions

Using Contacts for Assembly meshing:• Workbench has extensive capabilities to detect contact (interfaces) between parts.

• Until now that contact information has been of little use to• Until now, that contact information has been of little use to FLUENT users, but that is changing at R14.

• Contacts have several purposes for Assembly Meshing:Assembly Meshing:– Closing of small gaps using contact sizing

– Find thin sections

Find Contacts– Find Contacts

• Features at contact pairs are preserved

• Contacts are also used in Fluid Surface picker helper

For example, in this image the circled edges would be removed without contact defined since the feature angle is below the default

© 2011 ANSYS, Inc. August 25, 201117

picker helper angle is below the default (40 degrees)

R14 Assembly Meshing Leak Handling:Cl i L k

Closing a leak: Three simple steps

Closing LeaksPick the face of the valve plug (blue)and the edge of the valve seat (red)

Closing a leak: Three simple steps1. Define a Contact between

the entities that are leakingEdge/face or Face/Face– Edge/face or Face/Face

2. Drag and drop the contacton top of the Mesh Icon

Creates a Contact sizing

#1

– Creates a Contact sizing

3. Adjust Contact sizing– Use roughly 1/5 of min‐size

4 bl hi4. Assembly Meshing

#2

© 2011 ANSYS, Inc. August 25, 201118

#3

R14 Assembly Meshing:Fi di Thi S i

Why locate thin sections (3D bodies)?

Finding Thin Sections

Why locate thin sections (3D bodies)?• The assembly meshing method produces better quality meshes if thin baffles and fins are well resolved

• By using the Find Thin Sections tool, these can be found in advance and appropriate sizing can be applied

© 2011 ANSYS, Inc. August 25, 201119

A t ti & R b tAutomatic & Robust Meshing in Fluids

Assembly meshing: Mixing Tank Demo

© 2011 ANSYS, Inc. August 25, 201120

R14 Assembly Meshing

Miscellaneous features:• Size Function improvementsSize Function improvements

– Separate Min size for Curvature and Proximity

– Less mesh clustering

– Support for Body of Influence

• Add the Fluid Surfaces to the Virtual Body– Uses Connections and Extend to Connection picker helper to pick all the boundaries of the of the fluid body

– Allow for adding property to fluid body (curvature angle)

– Needed when creating fluid regions from surface bodies only

– More memory/speed efficient when Keep Solid Mesh is off

© 2011 ANSYS, Inc. August 25, 201122

• “Mesh Unite” Fluid or Solid bodies using Mesh Groups– To simplify setup and improve quality of the mesh

SUMMARY

A bl M hi Ad t

Automatic & Robust Meshing in Fluids

Assembly Meshing Advantages:• Improved turnaround time

– Fewer manual steps

– Fewer geometry cleanup operations

– Avoids fluid extraction and other Boolean operationsp

• Cell count reduction of 50%

– CutCell vs. Patch Conforming tet

• High fraction of Hex cells• High fraction of Hex cells

• Can find and close gaps in the model

• Supports 2‐stage inflation

© 2011 ANSYS, Inc. August 25, 201123

A t ti & R b tAutomatic & Robust Meshing in Fluids

THANK YOU 2011 ANSYS Regional Conferences

© 2011 ANSYS, Inc. August 25, 201124

Automatic Meshing in Fluids - Ansys · 2012-08-21 · Automatic & Robust Meshing –...

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