Rob McDonald – Cal Poly

VSP Workshop August 23, 2012

VSP File Types & VSP Meshing

2

VSP Input Representations •  Input

–  Parametric geometry (vsp) –  Background image (jpg) –  Surface textures (tga, jpg) –  Automation script (txt) –  Airfoil definition (af) –  Fuselage section definition (fxs) –  Cabin definition (cab) –  Wireframe as mesh (hrm) –  Wireframe as surfaces (hrm) –  Triangulated mesh (stl, NASCART) –  Vorlax case file (cas)

•  Coming soon –  Design file (des, xdes, XDDM)

http://www.openvsp.org/wiki/doku.php?id=representations

3

VSP Output Representations •  Output

–  Parametric geometry (vsp) –  Screen capture (jpg) –  Automation script (txt) –  Wetted area/volume report (txt, csv) –  Drag buildup report (tsv) –  Area ruling report (txt) –  Mass properties report (txt) –  Wireframe (hrm) –  X3D 3D Web model (x3d) –  Felisa (fel) –  Untrimmed surfaces (3dm)

•  Coming soon –  Design file (des, xdes, XDDM)

–  Trimmed surfaces (srf) –  Unintersected triangulated components

(tri, possibly others) –  Intersected triangulated components

(stl, NASCART, tri, msh, pov) –  Isotropic triangulated surface mesh

(stl, poly, tri, obj, msh, NASCART) –  Structural mesh

(stl, NASTRAN, Calculix) –  Vorlax case file (cas) –  Vorlax geometry & input (inp)

http://www.openvsp.org/wiki/doku.php?id=representations

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Paths to Cart3D Quadrilateral

Wireframe

Cart3D intersect

CompGeom

Export… CART3d File (.tri)

Export… CART3d File (.tri)

Unintersected Triangle

Wireframe

Triangle Mesh

Intersected Triangle

Wireframe

CFD Mesh Output .tri

Bicubic Bezier

Surface

5

Paths to Cart3D Quadrilateral

Wireframe

Cart3D intersect

CompGeom

Export… CART3d File (.tri)

Export… CART3d File (.tri)

Unintersected Triangle

Wireframe

Triangle Mesh

Intersected Triangle

Wireframe

CFD Mesh Output .tri

Bicubic Bezier

Surface

6

Quadrilateral Wireframe

Unintersected Triangle

Wireframe

Triangle Mesh

Intersected Triangle

Wireframe

7

Recommended for Today

Pros / Cons of Paths

•  Pros –  Speed –  Robustness –  Derivatives with

design framework

•  Cons –  Robustness

•  Coincident faces •  Nacelles

–  Extra step

Unintersected

•  Pros –  Speed –  Robustness –  Special cases

•  Cons –  Robustness

•  Pros –  Triangle Quality –  Special cases

•  Cons –  Robustness

CompGeom CFD Mesh

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Export Unintersected (before) 1

2

3

4 5

9

Export Unintersected (after)

10

Execute CompGeom (before) 1

2

3

11

Execute CompGeom (after)

1

12

Export CompGeom 1

2

3

4 5

13

Practice Session •  Unintersected

•  CompGeom –  Save for Cart3D tutorial

•  Resolution Effects (quads to triangles directly) –  Num Pts –  Num XSecs

14

CFD Mesh Generator

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CFD Mesh •  Surface mesh generator

–  Isotropic triangles (no stretching) –  Bicubic Bezier surfaces –  Bezier intersection curves –  Sourcing control –  Curvature control –  Optional wakes –  Optional half-models

•  Preferred for most CFD tools –  CBAero –  TetGen –  AFLR3 –  VLE

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Local Radius of Curvature

Greatest Principal Normal Curvature r = 1k

r

17

Curvature Meshing Criteria

l =N > 2; r !2 !sin !

N( )N " 2; r ! 4 N

#

$%

&%

l = r > g; 2 2 ! r ! g" g2

r # g; 2 ! g

$%&

'&

g

l

l

Num CircleSegments = 8

Max Gap Num Circle Segments

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Growth Ratio Limiter

0 2 4 6 8 10

1

1.2

1.4

1.6

1.8

2

X

Gro

wth

Rat

io

Limits length of next edge to ratio of current edge.

19

Source Types Point Line Box

20

Sourcing

Attached to components (u, w) Size in model units (length) Sphere of influence (radius)

21

Mesh Criteria Precedence

Max Gap Num Circle Segments

Min Edge Len

Max Edge Len

Sources

Growth Ratio

Smallest Edge Across Criteria

Subject to Constraints

Above & Below

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Turning Mesh Criteria ‘OFF’

Criteria Direction Value Scaled? Max Edge Len large 100.0 (scaled) Growth Ratio large 10.0 Sources none Max Gap large 10.0 (scaled) Num Circle Segments small 0.00001 Min Edge Len small 0.000001 (scaled)

Sometimes it is useful to turn a mesh criteria ‘OFF’.

Max = Min will turn ‘OFF’ Max Gap &

Num Circle Segments Max Gap Num Circle

Segments

Min Edge Len

Max Edge Len

Sources

Growth Ratio

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Meshing Strategy

1. Set Max based on model dimensions •  Set Min = Max (turning off MG and NCS) •  No Sources •  Adjust Max & Min until satisfied (uniform coarsest)

2. Set Min to smaller value •  Say Min = Max/20

3. Choose MG or NCS as preferred curvature parameter (CP) •  Set other curvature parameter (OCP) ‘OFF’ •  Adjust CP until satisfied •  Adjust Min as required (are smallest edges small enough?)

4. Adjust OCP (optional) 5. Add mesh sources as required

•  Resolve flow features

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‘Top’ Model

http://hangar.openvsp.org/vspfiles/106

Constant curvature (constant radius)

Increasing curvature (decreasing radius)

Extreme curvature (vanishing radius)

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CFD Mesh GUI

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Global Global Source Adjustment

Global & Curvature Meshing Criteria

Half Mesh Switch

TetGen Far Field

Mesh Output

‘Go’ Button

27

Display Source Display Switch

Mesh Display Switch

Mesh Output

‘Go’ Button

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Output File Output Switches

Mesh Output

‘Go’ Button

File Paths

File Browser Button

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Sources Component Chooser

Add Default Button

Source Type Chooser

Add/Delete Buttons

Mesh Output

‘Go’ Button

Component Source List

Individual Source Editor

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Wakes Wake Length

Wake Angle

Component Chooser

Wake Switch

Mesh Output

‘Go’ Button

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Practice Session •  CFD Mesh

–  ‘Top’ model –  Experiment with meshing parameters –  Turn all criteria off – ‘play’ with one at a time –  Follow meshing strategy

•  Resolution Effects (quads to bicubic Bezier patches) –  Num Pts –  Num XSecs –  Computational cost (Build Target Map)

•  CFD Mesh –  ‘Your’ model –  Follow meshing strategy

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Command Line Unintersected:

vsp –batch airplane.vsp –tri CompGeom:

vsp –batch airplane.vsp –compgeom –tri CFD Mesh:

vsp –batch airplane.vsp –cfdmesh 1.0 (1.0 is refinement factor)

Each command will output corresponding ‘airplane.tri’.