CFX-4
Introductory Training (Dec 1999)
5 -1
CFX-4.3 V4.3.1H
Lecture 5
Constraints,Patches,Mesh and
Analysis
CFX-Build
CFX-4
Introductory Training (Dec 1999)
5 -2
CFX-4.3 V4.3.1H
Steps in Model Creation
- build wireframe using points,curves,surfaces
and solids.
- define constraints for solids with area mismatch.
- define boundary conditions (inlet,outlet,walls).
- mesh all surfaces.
-generate internal volume mesh and geo file.
Geometry
Constraints
Patches
Mesh
Analysis
CFX-4
Introductory Training (Dec 1999)
5 -3
CFX-4.3 V4.3.1H
Constraints
? used to specify an
interface connection
between adjacent block
faces with unequal
areas.
? consistent mesh
between two solids
which do not meet at a
whole face.
Parent Face
Child Face
CFX-4
Introductory Training (Dec 1999)
5 -4
CFX-4.3 V4.3.1H
Constraints
There are 2 types of constraints in CFX Build.
1,Simple
2,Advanced
? Simple constraints- A single child face constrains the
parent face,The child face must lie completely within
the parent face.
? Advanced constraints- One or more child faces
constrain the parent face,Edges on a child face may
coincide with edges on the parent face.
CFX-4
Introductory Training (Dec 1999)
5 -5
CFX-4.3 V4.3.1H
Creating Constraints
? ensure existence of
aligned points.
? specify corresponding
parent/child origins.
? define direction
points.
? define direction ratios.
? determine if parent-
shape toggle is
necessary.
CFX-4
Introductory Training (Dec 1999)
5 -6
CFX-4.3 V4.3.1H
Parent/Child Points
? parent points:
any of four
points
surrounding the
parent face.
? child points
any of four
points
surrounding the
child face.
12
3 4
56
7 8
CFX-4
Introductory Training (Dec 1999)
5 -7
CFX-4.3 V4.3.1H
Alignment of Points
? Ensure surface paths are aligned,
? May need to rotate child surface.
Wrong Right
CFX-4
Introductory Training (Dec 1999)
5 -8
CFX-4.3 V4.3.1H
Alignment of Directions
? occurs by specifying the points which
represent the parent and child first direction.
? parent and child directions must be similar.
S1
C1
E1
S2 C2 E2
First
Direction
Second Direction
CFX-4
Introductory Training (Dec 1999)
5 -9
CFX-4.3 V4.3.1H
Direction Ratios
? specify the ratios of the number of cells on
either side of the child face
S1 # of cells upstream of child face in 1st direction
E1 # of cells downstream of child face in 1st
direction
S2 # of cells upstream of child face in 2nd direction
E2 # of cells downstream of child face in 2nd
direction.
? 1st direction ratio = R1 = S1/(S1 + E1).
? 2nd direction ratio = R2 = S2/(S2+E2).
CFX-4
Introductory Training (Dec 1999)
5 -10
CFX-4.3 V4.3.1H
Examples of Direction Ratios
R1 = 2/(2+2) = 0.5
R2 = 2/(2+2) = 0.5
R1 = 2/(2+2) = 0.5
R2 = 3/(3+1) = 0.75
2
1
2
1
CFX-4
Introductory Training (Dec 1999)
5 -11
CFX-4.3 V4.3.1H
Parent Shape
? Need to have the toggle ‘Use Parent Shape’ on
if you wish to manifold the elements
surrounding the child face to the parent face,
? For example:
Parent Shape OFF Parent Shape ON
CFX-4
Introductory Training (Dec 1999)
5 -12
CFX-4.3 V4.3.1H
Advanced Constraints
? Create subordinate surfaces which cover the
parent face,
? One or more of these surfaces may be a patch.
? These surfaces should be created explicitly
with the CREATE Action on the Geometry
Form.
CFX-4
Introductory Training (Dec 1999)
5 -13
CFX-4.3 V4.3.1H
Example of Advanced Constraint
? Three patches created initially.
? Another 12 surfaces created for the Advanced
Constraint.
Patch 1
Patch 2
Patch 3
CFX-4
Introductory Training (Dec 1999)
5 -14
CFX-4.3 V4.3.1H
Advanced Constraint Creation
? Need to create hard curves on the edges of the parent face.
? On the geometry form,set the Action/Object/Method to
Associate/Curve/Curve to create a hard curve at the
intersection of the edge of each subordinate surface and parent
edge,Mesh nodes will occur on the endpoints of this hard
curve.
? When you mesh advanced constraints,first mesh all
subordinate and child surfaces,Second mesh parent and all
other surfaces in the model,It may be necessary to use mesh
seeds to ensure a consistent,structured mesh.
? Warning,CFX-Build does not perform any checks to ensure
that subordinate faces cover the parent face or that hard points
are correctly placed,Take care when using advanced
constraints.
CFX-4
Introductory Training (Dec 1999)
5 -15
CFX-4.3 V4.3.1H
Constraints - General
? Constraints are applied during the analysis
stage of CFX-Build.
? Recommend using multi-block rather than
constraints.
CFX-4
Introductory Training (Dec 1999)
5 -16
CFX-4.3 V4.3.1H
Examples of Constraints
child
faces
parent
face
Advanced Constraint
child
face
parent
face
Simple Constraint
child
face
parent
face
CFX-4
Introductory Training (Dec 1999)
5 -17
CFX-4.3 V4.3.1H
Example of Constraints
? Simple constraints may not be used for
adjacent surfaces on which advanced
constraints are defined,Rather both must be
advanced constraints.
Advanced
Constraint
Advanced
Constraint
CFX-4
Introductory Training (Dec 1999)
5 -18
CFX-4.3 V4.3.1H
Steps in Model Creation
- build wireframe using points,curves surfaces
and solids.
- define constraints for solids with area mismatch.
- define boundary conditions (inlet,outlet,walls,etc.).
- mesh all surfaces.
-generate internal volume mesh and geo file.
Geometry
Constraints
Patches
Mesh
Analysis
CFX-4
Introductory Training (Dec 1999)
5 -19
CFX-4.3 V4.3.1H
Patches
? specify boundary regions and types.
? name of the patch defines the patch type.
? 2-D
inlet,press,outlet,wall,symmet,cndbdy,blkbdy,
user2d.
? 3-D
solid,solcon,porous,user3d.
? valid inlet patch names:
inlet_1,inlet1,inlet,etc.
CFX-4
Introductory Training (Dec 1999)
5 -21
CFX-4.3 V4.3.1H
Steps in Model Creation
- build wireframe using points,curves surfaces
and solids.
- define constraints for solids with area mismatch.
- define boundary conditions (inlet,outlet,walls).
- mesh all surfaces.
-generate internal volume mesh and geo file.
Geometry
Constraints
Patches
Mesh
Analysis
CFX-4
Introductory Training (Dec 1999)
5 -22
CFX-4.3 V4.3.1H
Meshing
? The IsoMesher is mainly used to create
a structured grid for CFX-4.
? Paver has VERY limited usage,
because it creates unstructured surface
mesh.
CFX-4
Introductory Training (Dec 1999)
5 -23
CFX-4.3 V4.3.1H
Meshing
? number of elements per edge is based on the
following priority:
mesh seeds
adjoining mesh regions which are topologically
congruent
global edge length.
CFX-4
Introductory Training (Dec 1999)
5 -24
CFX-4.3 V4.3.1H
Mesh Seeds
? Explicitly specify the number of elements for an
edge,
? Inconsistent mesh seeding may cause errors.
? Use Ensure Consistent Seeding toggle when
specifying mesh seeds.
CFX-4
Introductory Training (Dec 1999)
5 -25
CFX-4.3 V4.3.1H
Global Edge Length
? When no mesh seeds or adjoining mesh
occurs in a path,the Global Edge Length and
the longest edge in the mesh path determines
the number of elements per edge.
length of longest geometrical edge in path
Global Edge Length# of elements =
CFX-4
Introductory Training (Dec 1999)
5 -26
CFX-4.3 V4.3.1H
Meshing Surfaces
? Mesh must be 4 sided (displayed with green
lines).
? If there are any magenta colored surfaces,
decomposition of the surface is necessary.
CFX-4
Introductory Training (Dec 1999)
5 -27
CFX-4.3 V4.3.1H
Steps in Model Creation
- build wireframe using points,curves surfaces
and solids.
- define constraints for solids with area mismatch.
- define boundary conditions (inlet,outlet,walls).
- mesh all surfaces.
-generate internal volume mesh and geo file.
Geometry
Constraints
Patches
Mesh
Analysis
CFX-4
Introductory Training (Dec 1999)
5 -28
CFX-4.3 V4.3.1H
Analysis
? Last stage of the mesh generation process.
? Several options
equivalencing
reblocking
2d axisymmetric problem set up
calculate mesh quality.
? Specify solids for internal volume meshing
? VOLMSH starts batch creation of the geo file.
CFX-4
Introductory Training (Dec 1999)
5 -29
CFX-4.3 V4.3.1H
Analysis Options
? application of constraints and equivalencing
scaling of geometry
coordinate system
volume mesh generator and parameters
mesh quality checking
orthogonality,grid expansion,cell volume,skew ratio,...