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1 © 2013 ANSYS, Inc. February 7, 2014 ANSYS Confidential
15.0 Release
Lecture 6A:
Geometry Modeling For CFD
Introduction to ANSYS DesignModeler
2 © 2013 ANSYS, Inc. February 7, 2014 ANSYS Confidential
In this lecture we will learn about: • Fluid Body Extraction
– Internal
– External
• Symmetry Modeling
• Watertight Body Preparation & Conformal Meshing
– Surface Extensions
– Connect
• Use of Lines and Sketches for CFD Modeling
• Zero Thickness Surface Modeling
Geometry Modeling for CFD
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Preprocessing Workflow
Sketches and Planes
Geometry Import Options
3D Operations
Bi-Directional
CAD/ Neutral
Geometry Cleanup and Repair
Automatic
Cleanup
Simplification,
Mid-surface,
Fluid Extraction
Extrude, Revolve,
Sweep, etc
3D Operations
Booleans,
Decompose, etc.
Import/ Geometry Creation
Geometry Modifications
Meshing Solver
Meshing Methods
Hybrid Mesh: Tet,
Prisms, Pyramids
Hexa Dominant,
Sweep meshing
Global Mesh Settings
Local Mesh Settings
Sizing, Controls,
etc.
Assembly
Meshing
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• Creates internal fluid volume
• Two options
– By Cavity : user must select all wetted surfaces
– By Caps : user must create closing surfaces at inlets and outlets, and select bodies
Fill
Details View of Fill
Internal fluid volume extracted using Fill
Cap surface bodies must be selected
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Enclosure
• Creates enclosure around the bodies
– Useful for external aerodynamic analysis
– Can be used for extracting internal flow domain
• Input
– All or selected bodies
– Shape of enclosure
– Extent of enclosure
• Output
– A frozen body around the selected parts with specified extents
– Internal flow volume as a result of automatic Boolean subtract
• Supports symmetry models
• Full or partial models can be included in enclosure
Enclosure created for an airplane
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Enclosure: External Flow Example
Model
Using Symmetry
User Defined Shape Enclosure
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Symmetry
• Defines symmetry for the model
• Input
– All or selected bodies
– Up to three symmetry planes
• Operation
– Symmetry planes slice the model
• Output
– Sliced model (part lying on the positive side of the axis is retained)
Details View of Symmetry
Note : Faces that are coincident with the symmetry plane are tagged with a “Symmetry” named selection under AMP
Using Symmetry
Tip: The symmetry tool can be used as visualization tool when discovering the model (then the operation is deleted)
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Symmetry: Example
Full Model
Symmetry using XY plane
Symmetry using XY & ZX plane
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Surface Extension
• Allows extension of surface bodies to the desired extent
• Extension type
– Natural: Based on gradients of selected edges
– User Defined: User specifies the direction
Model with gap Model with gap closed
Details View of Surface Extension
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Connect
• Aligns and possibly joins a set of vertices, edges or faces
• Properties
– Location property
– T-junction property
Details View of Connect
Vertex Connect
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Connect: Example (1)
Edge Connect
Model with a gap
Location: Interpolated
Location: Preserve First
Both edges moved to interpolated location
Second edge moved to first edge location
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Connect: Example (2)
Edge Connect
Model with a gap Using
T-Junction
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Face Connect
• Additional options as per edge connect
Connect: Example (3)
Model with a gap
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Connect After Shared Topology
• Connect feature can be used after the Share Topology feature to selectively share faces between two bodies of a multibody part
– This can be used to:
• Fix face sharing failures after Shared Toplogy
• Can be used for Selective sharing of faces in conjunction with Selective Shared Topology
• The advantage of Connect feature is that
– It takes user defined tolerance to Connect faces which failed due to smaller Shared Topology tolerance
• This ensures conformal meshing
• Please be careful in choosing tolerance value, as high values may result in deformation of model at some places
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Why is Concept Modeling(Lines and Faces) relevant for CFD users?
• Sometimes the imported files contain issues like:
— Missing Faces
— Corrupt Faces
— Details which require cleanup by selective geometry recreation
— For cleaning, patching, recreating surfaces & stitching a water tight body, several line and surface creation options of concept modeling are used
• CFD models also require some solids/thin bodies to be modeled as zero thickness surfaces
— Examples are baffles, fins, zero thickness pipe walls, fan shrouds, etc.
— For above mentioned cases, mid-surfacing tools need to be used
• Sometimes 2D modeling operations also require use of concept modeling tools
Concept Modeling Tools
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Lines from Points
[Main Menu] Concept Lines From Points
– Points can be any 2D sketch points, 3D model vertices or Point Feature (PF) points.
– A point segment is a straight line connecting two selected points.
– The feature can produce multiple Line Bodies, depending on the connectivity of the chosen point segments.
Point 1
Point 2
Line Body
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Lines from Edges
[Main Menu] Concept Lines From Edges
– Creates line bodies based on existing 2D and 3D model edges
– Can produce multiple line bodies depending on the connectivity of the selected edges and faces
– Can select edges and/or faces through two fields in the detail window then “Apply”
Line Bodies
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Selected line Fraction = 0.5 Fraction = 0.25
Split Edges
[Main Menu] Concept Split Edges – Splits line body edges into two pieces
– Split location is controlled by the Fraction property (e.g. 0.5 = split in half).
– Other Options:
• Split by Delta: Distance between each split is given by Delta along the edge
• Split by N: Number of Divisions of the Edge
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Surfaces From Edges (1)
[Main Menu] Concept Surfaces from Edges
– Creates surface body using line body edges as the boundary
– Line body edges must form non-intersecting closed loops
– Each closed loop creates a frozen Surface Body
– The loops should form a shape such that a simple surface can be inserted into the model:
• Planes, cylinders, tori, cones, spheres and simple twisted surfaces
Planar surface Non-planar surface
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Surfaces From Edges (2)
• Creates surfaces from existing body edges
• Can be solid or line body edges
• Edges must produce non-intersecting closed loops
Existing solid body edges are selected for new surface boundary.
New, frozen, surface body generated (note, solid body is hidden).
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Surfaces From Sketches
[Main Menu] Concept Surfaces from Sketches – Creates surface bodies using sketches as boundaries (single or multiple sketches are OK) – Base sketches must be closed profiles which are not self intersecting – May choose to “Add” or “Add Frozen” operations – Can reverse normal direction “No” in Orient With Plane Normal field – Can enter thickness which will be used in creating the FE model
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Mid-Surface
• Extracts surface body that is midway between existing solid body faces
• Two Options:
– Manual: Operates only on user specified face pairs
– Automatic: Provides option to search for other matching face pairs
Details View of Mid-Surface
Mid-Surface created for a pipe geometry
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Mid-Surface: Manual
Manual Method • Set the Selection Method to “Manual”
• Select pair of faces, one pair at a time, in Face Pairs input
• The order of selection determines the surface normal direction
• Notice the first surface picked is displayed in purple, the second is shown in pink
• When the selection is finalized the selected pairs are displayed in dark and light blue colors
Details View of Mid-Surface
2nd Pick
1st Pick
Normal Direction
Solid Model Color of faces during selection Color of faces after selection
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Mid-Surface: Automatic
Automatic Method • Switching the Selection Method from “Manual” to “Automatic” exposes several additional
options
– Bodies to search: Limits search to visible bodies, selected bodies or all bodies
– Minimum and maximum threshold sets search range (thickness) for face pairs
• Options like Extra Trimming are very useful with “Automatic” method
– Provides options for situations where trimming problems with surface bodies occur
• Preserve Bodies? allows you to save the solid bodies from which surfaces are created (default is No)
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Summary
What have we learnt in this session?
• Fluid Body Extraction
• Symmetry Modeling
• Watertight Body Preparation & Duplicate Face Removal
• Modeling of Lines and Surfaces for Simplification/Repair
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Workshop 6.1A – Geometry Cleanup & Fluid Extraction