Rob McDonald – Cal Poly

VSP Workshop August 21 & 22, 2014

VSP File Types & VSP Meshing

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VSP v2 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) –  Design file (des, XDDM)

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

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VSP v3 Input Representations •  Input

–  Parametric geometry (vsp) (vsp3) Incompatible change –  Background image (jpg) –  Surface textures (tga, jpg) –  Automation script (txt) (as) Incompatible change –  Airfoil definition (af) (dat) VSP, Selig, Lednicer formats –  Fuselage section definition (fxs) –  Cabin definition (cab) Removed –  Wireframe as mesh (hrm) –  Wireframe as surfaces (hrm) Removed –  Triangulated mesh (stl, NASCART) (tri) Added Cart3D –  Vorlax case file (cas) Removed –  Design file (des, XDDM)

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

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VSP v2 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) –  Design file (des, 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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VSP v3 Output Representations •  Output

–  Parametric geometry (vsp) (vsp3) Incompatible change –  Screen capture (jpg) –  Automation script (txt) Removed –  Wetted area/volume report (txt, csv) –  Drag buildup report (tsv) –  Area ruling report (txt) (txt) Added planar slice –  Mass properties report (txt) –  Wireframe (hrm) –  X3D 3D Web model (x3d) –  Felisa (fel) Removed –  Untrimmed surfaces (3dm) (stp) Replaced with STEP –  Design file (des, 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 Removed

(stl, NASTRAN, Calculix) –  Vorlax case file (cas) Removed –  Vorlax geometry & input (inp) (csv, m) Added Degen Geom

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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

Smooth Bezier

Surface

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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

Smooth Bezier

Surface

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Quadrilateral Wireframe

Unintersected Triangle

Wireframe

Triangle Mesh

Intersected Triangle

Wireframe

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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

5

4

3

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Export Unintersected (after)

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Execute CompGeom (before) 1

2

3

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Execute CompGeom (after)

1

14

Export CompGeom 1

2

5

4

3

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Practice Session •  Unintersected

•  CompGeom –  Save for Cart3D tutorial

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

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CFD Mesh Generator

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CFD Mesh •  Surface mesh generator

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

•  Preferred for most CFD tools –  CBAero –  Pointwise –  AFLR3 –  Fun3D –  FlightStream –  TetGen

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Local Radius of Curvature

Greatest Principal Normal Curvature r = 1k

r

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Curvature Meshing Criteria

l =N > 2; r ⋅2 ⋅sin π

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.

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Rigorous 3D Growth Limiting

Off (faster)

On (slower)

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Source Types Point Line Box

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Sourcing

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

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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

File on the wiki.

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

Intersect Subsurfaces

Choose Set

Mesh Output

‘Go’ Button

Rigorous Limiting Switch

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Display

Display Switches

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

Select Surface

Source Type Chooser

Add/Delete Buttons

Mesh Output

‘Go’ Button

Component Source List

Individual Source Editor

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Domain Half Mesh Switch

Far Field Switch

Far Field Mesh Size

Far Field Comp/Box Switch

Mesh Output

‘Go’ Button

Far Field Component List

Far Field Box Controls

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Domain Modeling

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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

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

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Command Line / API Coming Soon!