Chen, William M.

Pandya, Shishir A.

NASA Technical Reports Server

Writing Grid Scripts in 
CGT
Shishir Pandya, William Chan
https://ntrs.nasa.gov/search.jsp?R=20190027558 2019-09-26T20:04:39+00:00Z
Geometry Preparation
STEP 1: Obtain surface representation
CGT Tool: cad2srf (CAPRI Library required)
Input: CAD, Output: Surface Triangulation
STEP 2: Obtain seam curves
• Aircraft
• Leading and trailing edges
• wing/body junction
• tail/body junction
• Rocket
• Axisymmetric body definition
• protuberance junctions
• Sharp features
CGT Tool: cad2srf
Input: CAD; Output: Curves
CGT Tool: seamcr, lsect
Input: Structured patches; Output: Curves
CGT Tool: seamcrt
Input: Surface Triangulation; Output: Curves
CGT Scriptlib Tools: CreateSeamCur
Input: Structured patches, Triangulation; Output: Curves
Option 2: DIY
CGT Scriptlib Tools: 
CreateLine, CreateCurve, 
CreateAirfoilComponent, 
CreateParsecFoil, 
CreateCylGrids, 
CreateFrustumGrids
Option 3: Commercial Tools
Ansa, PointWise, Star-CCM+, 
etc…
Option 4: Open Software
Ogen
Configuration or 
Component?
Configuration:
• Grid-centric
• Written for static geometries
• Rules must be followed
• Set root names
• Define input variables, defaults
• Surface files: *.srf
• Volume files: *.vol
• Each file contains 1 grid
• Framework provided
• Short main script
• BuildSurf
• BuildVol
• BuildPeg5i
• Peg5, X-rays supported
Component:
• Component-centric
• Written for repeated components and 
moving-body cases
• Rules must be developed by each user
• Best practice: 
• Define input variables
• Flexible filenames: *.sur, *.vol, 
*.cut, *.xry
• Each file contains multiple grids for 
a component
• Framework contained in a main script
• Longer main script
• Contains all calls for surface, volume, 
and connectivity according to user’s 
choice.
• Supports X-rays (Overflow)
• Basic support for Peg5, and c3p.
Surface Mesh Generation
• Curve Manipulation
• TFI grids
• Hyperbolically marched grids
• Collar grids
• Assure proper surface coverage
Curve Manipulation
STEP 1: Identify curves that can be 
concatenated
CGT Tool: grided
Input: Curves, Grids; Output: Curves, Grids
CGT Scriptlib Tools: ConcatGrids, 
ConcatGrids2, ConcatGridsn, 
AutoConcateGrids
Input: Curves, Grids; Output: Curves, Grids
STEP 2: Identify curves that need to be split
CGT Tool: grided
Input: Curves, Grids; Output: Curves, Grids
CGT Scriptlib Tools: ExtractSubs, 
ExtractGrids, GedSplitJkl, GedSplitXyz
Input: Curves, Grids; Output: Curves, Grids
Curve Manipulation (cont.)
STEP 3: Redistribute
CGT Tool: srap
Input: Curves, Grids; Output: Curves, Grids
CGT Scriptlib Tools: SrapRedist
Input: Curves, Grids; Output: Curves, Grids
TFI Patches
STEP 1: Identify TFI patch curves
• Aircraft
• LE, TE, Root, Tip
• Rocket
• Portions of protuberances
CGT Tool: OVERGRID
Input: Ref. Surface, Curves; Output: Grid
CGT ScriptLib Tool: CombineGrids
Input: Curves, Grids in multiple files; Output: 
Curves,Grids in one file
STEP 2: Create TFI patches
• Aircraft
• Top of wing, Bottom of wing
• Portions of other parts
• Rocket
• Portions of protuberances
CGT Tool: surgrd
Input: Ref. Surface, Curves; Output: Grid
CGT ScriptLib Tool: GenTFI
Input: Ref. Surface, Curves; Output: Grid
TFI
Collar Grids
STEP 2: Create collar grids
• Identify Starting curves
• Aircraft
• Wing/Body junction
• Tail/Body junction
• Rocket
• Protuberances/Stack junction
CGT Tool: surgrd
Input: Ref. Surface, Curves; Output: Grid
CGT ScriptLib Tool: GenHypSurGrids
Input: Ref. Surface, Curves; Output: Grid
STEP 1: Identify Starting curves
• Aircraft
• Wing/Body junction
• Tail/Body junction
• Rocket
• Protuberances/Stack junction
CGT Tool: OVERGRID
Concatenate, Break-up Grids
STEP 1: Identify grids that can be 
concatenated, or need to be split
CGT Tool: OVERGRID
STEP 2: Concatenate grids
CGT Tool: grided
Input: Ref. Surface, Curves; Output: Grid
CGT ScriptLib Tool: ConcatGrids, 
ConcatGrids2, ConcatGridsn, 
AutoConcateGrids
Input: Ref. Surface, Curves; Output: Grid
STEP 3: Split grids
CGT Tool: grided
Input: Ref. Surface, Curves; Output: Grid
CGT ScriptLib Tool:
ExtractGrids,GedSplitJkl, GedSplitXyz, 
ExtractSubs, SplitToNGrids
Input: Ref. Surface, Curves; Output: Grid
Assure Complete 
Surface Coverage
STEP 1: Identify gaps, improper overlaps
CGT Tool: OVERGRID
STEP 3: Fill gaps
• TFI
• Hperbolic surface marching
CGT Tool: surgrd
Input: Ref. Surface, Curves; Output: Grid
CGT ScriptLib Tool: GenTFI, GenHypSurGrids
Input: Ref. Surface, Curves; Output: Grid
STEP 2: Identify/Create Curves
CGT Tool: seamcr, seamcrt
Input: Ref. Surface; Output: Curves
CGT ScriptLib Tool: CreateSeamCurs
Input: Ref. Surface, Curves; Output: Grid
Volume Mesh Generation
Option 2: Configuration scripts
CGT Scriptbin Tool: BuildVols
Input: Surface grid; Output: Volume grid
Option 1: Interactively
CGT Tool: hypgen
Input: Surface grid; Output: Volume grid
Option 3: Component scripts
CGT Scriptlib Tool: GenHypVolGrids, 
GenUniformBox, GenStretchedBox, 
CreateCore, BuildGeneralPlumeGrids, …
Input: Surface grid; Output: Volume grid
Option 4: Higher-level component scripts
CGT Scriptlib Tool: BuildAxisymGrids
Input: Axisym. curve or Surface grid; Output: 
Volume grid with caps
Connectivity
Option 2: Configuration scripts
CGT Scriptbin Tool: BuildPeg5i
Input: Volume grid; Output: Grid Connectivity
Option 1: Manual
Option 3: Component scripts
CGT Scriptlib Tool: AddCutterID, 
SetCutterCutee, WriteOvr2InpFile
Output: OVERFLOW input
Step 4: Remove orphans
CGT Tool: OVERGRID
Diagnose Module
Step 1: Write connectivity inputs to 
file
Step 3: Run connectivity code
Option 1: Manual
Tools: DCF/OVERFLOW, Pegasus5, etc.
Input: Volume grid; Output: Connectivity
Option 2: Component scripts
CGT Scriptlib Tool: RunConnectivityCode
Input: Volume grid; Output: Connectivity
Step 2: Create x-rays
DCF/OVERFLOW only
CGT Scriptlib Tool: CreateXrayMap
Input: Cutter, Output: X-ray
Boundary Conditions
Option 2: Configuration scripts
CGT Scriptbin Tool: WriteOvfi
Output: Grid BC file
Option 1: Manual
Option 3: Component scripts
CGT Scriptlib Tool: AddGridNames, 
AddBCInfo, WriteBCInfo
Output: Component BC file
Step 1: Setup BCs
Option 2: Configuration scripts
CGT Scriptbin Tool: BuildOveri
Input: Grid BC files; Output: Overflow inputs
Option 1: Manual
Option 3: Component scripts
CGT Scriptlib Tool: ProcessBCInfo, 
WriteOvr2InpFile
Input: Component BC files; Output: 
OVERFLOW input
Step 2: Process and write Overflow 
input file
FOMOCO Inputs
Option 2: Configuration scripts
CGT Scriptbin Tool: WriteOvfi
Output: Grid BC file
Option 1: Manual
Option 3: Component scripts
CGT Scriptlib Tool: 
AddFomocoSubset, 
AddFomocoMegaComp, 
WriteFomoInfo
Output: Component Fomo file
Step 1: Setup integration surfaces
Option 2: Configuration scripts
CGT Scriptbin Tool: BuildOveri
Input: Grid BC files; Output: Overflow inputs
Option 1: Manual
Option 3: Component scripts
CGT Scriptlib Tool:
ProcessFomoInfo, WriteOvr2InpFile
Input: Component Fomo files; Output: 
OVERFLOW input
Step 2: Process and write FOMOCO 
input file


Writing Grid Scripts in CGT

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