Chen, William M.

Pandya, Shishir A.

NASA Technical Reports Server

1!
 A CHIMERA GRID TOOLS TUTORIAL !
William M. Chan and Shishir A. Pandya!
 NASA Ames Research Center!
12th Symposium on Overset Composite Grids and Solution Technology, 
Atlanta, Georgia, October 6 - 9, 2014!
2!
OVERVIEW!
- Chimera Grid Tools (CGT)!
   - Introduction!
   - Pre-processing!
   - Post-processing!
!
- Demos!
   - OVERGRID (brief overview, grid generation utilities,!
                           grid connectivity diagnostics, solution viewer)!
   - Pre-processing script creation (rocket example)   !
   - TRILOAD line loads integration tool!
A more detailed OVERGRID demo is available at:!
The OVERGRID Graphical User Interface in Chimera Grid Tools (Parts 1, 2, 3)!
http://www.nas.nasa.gov/publications/ams/2014/05-13-14.html!
http://www.nas.nasa.gov/publications/ams/2014/05-20-14.html!
http://www.nas.nasa.gov/publications/ams/2014/05-29-14.html!
!
3!
TYPICAL MODELING AND SIMULATION PROCESS USING 
OVERSET GRIDS!
CAD model of 
geometry!
Overset volume 
grids!
Overset surface 
grids!
Results (aerodynamic loads, flow features, 
6-dof motion, etc.)!
Flow solution!
Grid connectivity information 
(iblanks, interpolation stencils)!
CGT, Overture, 
Gridgen, etc.!
PEGASUS5, 
OVERFLOW/DCF, 
Suggar++, !
Pundit,!
Overture!
Overflow, 
Overture,!
INS3D, etc.!
CGT, Overture, Fieldview, 
Tecplot, Ensight!
CGT, Overture, 
Gridgen, etc.!
4!
CHIMERA GRID TOOLS (CGT) Version 2.1!
What is CGT!
- A collection of software tools!
  for pre- and post-processing!
  of overset grid CFD!
  computations!
Authors!
- William Chan, Stuart Rogers, Shishir Pandya, David Kao,!
  Pieter Buning, Robert Meakin, David Boger, Steve Nash!
!
Availability!
- U.S. citizens/permanent residents working under U.S.!
   organization in the U.S.!
- Fill out and return Software Usage Agreement form!
- Source (Linux, Unix, Mac OS-X)!
- Executables (Mac 10.5, Windows-XP)!
- Version 2.1+ available for use by authors’ associated projects!
https://ntrs.nasa.gov/search.jsp?R=20190027557 2019-09-26T20:04:42+00:00Z
5!
INSTALLATION, DOCUMENTATION, TUTORIALS!
Installation software requirements!
- Fortran 90 compiler (ifort, pgf90, gfortran 4.4+)!
- C compiler (gcc, icc, pgcc)!
- OpenGL, X11, Tcl/Tk libraries (OVERGRID)!
                           Tcl/Tk 8.5.8 or earlier for CGT 2.1!
                           Tcl/Tk 8.6.2 or earlier for CGT 2.1+!
- Python, swig, matplotlib package or gnuplot (OVERSMART)!
- Tcl wish, xmgrace or gnuplot (OVERPLOT)!
!
Installation instructions!
- chimera2.1/doc/{INSTALLATION.html, overgrid.html}!
!
Documentation!
- chimera2.1/doc/man.html!
Recommended tutorials!
- chimera2.1/gui/tutorial/*                 (OVERGRID)!
- chimera2.1/examples/scriptlib/*    (CGT script library)!
6!
EXECUTABLES!
Run configure script to generate Makefiles!
!
configure -- help     (get list of options)!
!
Executables!
 - single precision!
 - double precision!
 - og (overgrid executable)!
 - smart.so (oversmart shared library)!
!
Big/little Endian!
 - controlled by compiler flag (pgf90)!
 - controlled by environment variable (ifort, gfortran)!
 - conversion using p3dConvert or overConvert!
!
OVERGRID can auto-detect single/double precision, big/little endian!
7!
PRE-PROCESSING STEPS AND BEST PRACTICE!
Task: Given complex geometry definition, create input files needed!
          for overset grid CFD analysis!
          - Grid file containing overset volume grids and iblanks!
          - Connectivity file containing fringe points, donor stencils,!
            interpolation coefficients!
          - Flow solver input file with boundary conditions for each grid!
          - Input file for performing forces and moments integration on!
            components of interest!
          - Input files for coupled physics!
             - Prescribed/6-DOF input files for relative motion problems!
             - Species convection!
             - Structural deformation!
!
Best practice: !
 - Develop pre-processing script to create all input files needed above!
 - Use CGT’s OVERGRID to check and visualize individual steps!
 - Use CGT’s Script Library to record steps into script!
8!
PRE-PROCESSING USING CGT!
Geometry Creation and Manipulation!
!
Surface Grid Generation!
   - on triangulation or CAD!
   - algebraic, hyperbolic!
!
Volume Grid Generation!
   - near-body curvilinear (hyperbolic)!
   - off-body Cartesian!
!
Domain Connectivity Inputs!
   - Xray map creation and hole-cut instructions!
   - PEGASUS5!
!
Flow Solver Inputs (OVERFLOW)!
   - boundary conditions!
   - component hierarchy and prescribed/6-DOF dynamics!
   - prescribed dynamics animation (overgrid) !
9!
GEOMETRY CREATION!
Script Library has macros to create!
!
-  Points!
-  Straight lines!
-  Analytic curves!
-  Cylinders!
-  Frustums!
-  Cartesian boxes!
-  Airfoil shapes!
-     >  NACA 4 and 5 digit series!
-     >  PARSEC (CGT 2.1+) !
Combine with basic macros to 
generate more complex shapes!
!
-  Translate!
-  Scale!
-  Rotate!
-  Mirror!
-  Extract!
-  Concatenate!
-  Revolve!
-  Duplicate!
Native CAD (Pro-E, Catia V5, Parasolid, OpenCASCADE, !
                      SolidWorks, UniGraphics, FELISA, STEP)!
   - Use CAPRI library (CADNexus) as interface to convert native CAD!
     parts into surface triangulations!
   - Need CAD license and CAPRI users license!
   - CGT surface grid generator has option to project back to original!
     CAD but usually a fine surface triangulation is sufficient!
!
STEP, IGES!
   - Solids can be converted to BRep, then use CAPRI as interface to!
     convert to surface triangulations!
!
Surface Triangulation!
   - CART3D (.tri, .triq) (.trix in CGT 2.1+)!
   - UCD (.ucd)!
   - FAST (.fst)!
   - STL (.stl), FRO (.fro) (CGT 2.1+)!
!
Structured Surface Grids (PLOT3D format)!
10!
GEOMETRY INPUT!
11!
OVERGRID!
- CAD interface via CAPRI!
- Geometry/grid processing!
   (structured quads,!
    triangulations)!
- Grid processing,!
  redistribution, projection!
- Surface and volume!
  grid generation (TFI,!
  hyperbolic, Cartesian)!
- Hole cutter generation!
- Grid diagnostics!
- Flow solver inputs!
  and b.c. preparation!
- Multi-component!
  dynamics input/animation!
- Standard atmosphere,!
  mass properties, 6-dof!
  input calculators!
- Simple solution viewer!
- Debris trajectory inputs!
- Strand/AMR Cartesian!
  grid viewer!
Supported platforms – Linux, Mac OS-X,Windows-XP!
12!
CGT SCRIPT LIBRARY!
Tcl macros -10x more compact scripts, > 3x faster development time!!
Low – Mid Level!
- File manipulation (e.g., combine files, format conversion,…)!
- Geometry creation (e.g., points, lines, analytic curves, cylinders,...)!
- Grid information (e.g., interrogate grid dimensions, coordinates,!
   arc lengths, formats,…)!
- Grid editing (e.g., extract, concatenate, split, duplicate, swap/!
   reverse indices, scale, translate, rotate, mirror, revolve, …)!
- Grid redistribution!
- Surface grid generation (TFI and hyperbolic)!
- Volume grid generation (hyperbolic and Cartesian)!
- X-ray hole cutter generation and hole cut instructions creation!
- Pegasus5 input preparation!
- Force/moments computation inputs!
- OVERFLOW boundary conditions inputs and namelist i/o    !
Top Level!
   - Grid-based approach (Configuration Management Scripts, peg5)!
   - Component-based approach (duplicated/moving comp., X-rays)!
13!
PRE-PROCESSING STRATEGY USING SCRIPTS!
Scripting approach!
   - rapid replay of all steps!
   - easy to parameterize inputs (e.g., grid stretching, spacings, etc.)!
   - easy to make small changes!
   - recommended even for one-of-a-kind cases!
   - modification needed if surface topology changes!
!
Surface Grid Generation!
   - generate grids from !
        - surface triangulation (from CAD, or supplied)!
        - surface feature curves (from CAD, supplied, or manually created)!
!
Volume Grid Generation!
   - near-body hyperbolic grids, off-body Cartesian grids!
!
Domain Connectivity, Force/Moments Computation, Flow Solver Inputs!
   - construct and store common database in script !
     (boundary conditions, component definitions, etc.)!
14!
DISTRIBUTED TEAM-BASED SCRIPT DEVELOPMENT!
- Identify components of a complex configuration!
- A component is a geometric part and may be modeled by one or more grids!
!
- Create stand-alone script for each component!
   - generation of surface and volume grids!
   - domain connectivity inputs (X-ray maps)!
   - solver boundary conditions!
   - forces and moments integration inputs!
!
- Each component script can be created by different developers!
- Use file repository system to update script so that each team member can get!
  most up-to-date version of each script!
!
- Share global parameters file (e.g., wall spacing, global spacing, str. ratio, etc.)!
!
- Each developer is responsible for grid connectivity of individual component!
!
- Create master script to call component scripts, assemble final grid system,!
  generate input files for domain connectivity, force/ moment integration, flow!
  solver!
15!
POST-PROCESSING USING CGT!
Forces and Moments Computation (mixsur/overint, usurp)!
!
Solution Convergence Analysis!
   - solution/turb. model residuals, forces/moments!
   - one page overview (oversmart)!
   - individual plots (overplot)!
!
Flow Visualization (overgrid)!
   - scalar and vector functions!
   - turb. model dependent variables, species partial densities!
   - unsteady 2-D movies!
!
Component Line Loads (triload)!
   - cumulative line loads!
   - sectional Cp!
!
Dynamics Animation (overgrid)!
   - 6-DOF dynamics output from flow solver!
16!FORCES/MOMENTS INTEGRATION APPROACH 1 – !
INTEGRATE ON HYBRID SURFACE MESH!
CGT Modules: MIXSUR, OVERINT!
Hybrid mesh generator (MIXSUR)!
- Automatically blank overlapping quads!
- Automatically fill narrow gap with triangles!
- Very fast but may sometimes contain a few bad triangles!
  (200 surface grids, 2 million+ surface pts, 22 sec., 1 proc.) !
Integration tool (OVERINT)!
- Integrates on non-overlapping quads and triangles!
- Integrates linear function exactly!
Chan, W. M., Enhancements to the Hybrid Mesh Approach to Surface 
Loads Integration On Overset Structured Grids, AIAA Paper 2009-3990!
17!
OVERINT OUTPUT FILES (RECENT DEVELOPMENTS)!
- Surface distributions of local forces and moments!
- Four unstructured surface triangulation files, each with!
  cell-centered scalar variables (extended CART3D .i.tri format)!
!
     (1) Cell ΔF !
     (2) Cell ΔF / Cell area!
     (3) Cell ΔM!
     (4) Cell ΔM / Cell area!
 !
-  Scalars: X, Y, Z components of forces/moments!
                 total magnitude, pressure, viscous, momentum contributions!
                 local cell area !
18!FORCES/MOMENTS INTEGRATION APPROACH 2 – !
INTEGRATE ON WEIGHTED QUADS!
CGT Module: USURP!
Quad panel weights calculator and integrator (USURP)!
- Automatically computes panel weight for each quad!
- Always returns a result by integrating over all quads!
- No hybrid mesh => no visual checks !
- Does not integrate linear function exactly!
- Also has standalone and OVERFLOW modes !
W1 = 1!
W2 = (AQ-AOV)/AQ!
!
AQ = Area of quadrilateral!
AOV = Area of overlap!
!
Boger, D. and Dreyer, J., Prediction of Hydrodynamic Forces and Moments for 
Underwater Vehicles Using Overset Grids, AIAA Paper 2006-1148!
Polygon 
subtraction 
in 3-D!
19!
SOLUTION CONVERGENCE ANALYSIS: OVERPLOT!
Forces/Moments Panel (.fomoco)!
 - Single coef. plot with!
   option to add more coefs.!
!
 - Six coef. matrix plot!
   (Fx, Fy, Fz, Mx, My, Mz)!
20!
SOLUTION CONVERGENCE ANALYSIS: OVERSMART SUMMARY PAGE!
Space Shuttle Launch Vehicle!
10,000 Time Steps, 636 Grids, 3-Sub-iterations (resid file: 19 million lines)!
21!
SOLUTION VISUALIZATION!
- 6-DOF component trajectories!
- Flow variables!
    - Surface triangulations!
       - vertex and cell-centered scalars!
!
    - Overset structured surface and volume grids!
       - steady (scalars and vectors)!
       - unsteady (scalars)!
       - 2-D moving body with adaptive grids (scalars) !
22!
COMPONENT TRAJECTORIES VISUALIZATION FROM SIX-DOF 
COMPUTATIONS!
(OVERGRID module)!
23!
VISUALIZATION OF VERTEX-CENTERED DATA ON SURFACE 
TRIANGULATIONS!
Surface Cp!
Standard CART3D triq file!
24!
VISUALIZATION OF CELL-CENTERED DATA ON SURFACE 
TRIANGULATIONS!
Local Pitching 
Moment Magnitude!
Recent addition: Extended CART3D tri file with cell-centered scalars!
                             Local forces/moments tri file output from OVERINT!


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