Pre- and Post-Processing

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  What external tools are available for pre-processing Cart3D triangulations?
  Post processing Options?
  Force and Moment Extraction using CLiC
  On-the-fly component-based force and moment extraction
  Point and line "sensors" for data collection
  What about CGNS?

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File Import Tools:
Cart3D comes with several tools for for importing data. Most of these are documented on the Surface Modeling pages. These tools allow you to import geometry from STL, DXF, OFF, FNF triangulations, or from structured surface meshes in LaWGS or Plot3D format. Using these tools you can easily convert your input geometry into Cart3D as a single component, configuration, or a final wetted surface. In addition to those distributed with the package, other geometry import tools are available through the discussion group.
 
Native Triangulations:
A number of packages can write Cart3D triangulations natively, these include (among others) Pointwise, OpenVSP, ESP/OpenCSM, Tecplot. We also have plugins for the popular Blender animation and modeling package, Contact us if you're interested in this. In addition to the plugins and native support in existing packages, an open source software library is available through the NASA software catalog for natively reading and writing Cart3D triangulations which you can link to from any source code package.

Overgrid:
But what about actually viewing and manipulating these components? Fortunately, several users and collaborators have developed tools to allow you to do this. Of those that have found their way back to us, William Chan's Overgrid package is one of the best and the most accessible. Overgrid is actually part of NASA's Chimera Grid Tools CGT) package, but thanks to a happy collaboration with the CGT team, the software can read, manipulate and write Cart3D single component, configuration, or  wetted surface triangulations. For viewing triangulations, and moving components, its extremely useful. CGT's "triged" command line tool is also very powerful. Here are a couple of screen shots showing overgrid's triangulation editor:  

click to enlarge either image

One final note. Although within Cart3D, we don't enforce file naming conventions, Overgrid does expect triangulations to conform to the naming conventions listed here. Overgrid is available through the NASA Software Catalog

autoInputs
   Once you have an surface triangulation, autoInputs is a new utility that automatically generates the input.c3d and preSpec files that the mesher (cubes) needs to get going. This utility befitted greatly from beta-testing and we strongly recommend its use by both novice and experienced users alike. Read all about autoInputs on the mesh generation page.

trix
    The aptly-named trix utility performs format convertion, component/config translations, rotations, and more. The default action is to convert the input files to the Cart3D extended triangulation (VTK) format. Shape sensitivties (if present) are automatically adjusted to reflect any geometry manipulations. trix can also be used to move/rotate selected disconnected components with respect to others in the configuration.

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Volume/Surface Visualization:
Cart3D solutions are plottable using a variety of commercially available (and free) scientific visualization packages. The most popular are Tecplot Inc.'s Tecplot 360 and Fieldview products along with Kitware's Paraview package (see Note 2). Here is a table summarizing the postprocessing options supported by cubes, flowCart and some of the auxiliary programs:
 

program	dataset type	commercial post-processor supported
intersect	surface triangulation	Tecplot, Fieldview, Paraview
cubes	cutting planes	Tecplot, Fieldview, Paraview
mgPrep	cutting planes	Tecplot, Paraview
c3dvis	3D volume mesh + flow variables	Tecplot, Fieldview, Ensight, Paraview
flowCart, adjointCart	surface triangulations + cutting Planes + flow variables	Tecplot, Fieldview, Paraview

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  CLiC: Force and Moment Extraction using CLiC (Post-Process)

CLiC is a Component based force and moment module developed as a post-processor and data-extractor for Cart3D. Its an extremely flexible and powerful package. Using clic, you can extract Cp cuts on any component or group of components in your configuration, you can compute LDM (lift, drag, moment) for components, component groups or configurations. You can also use it to extract the usual bevy of point-moments, line-moments ("hinge moments") etc.. If you want to see some of what it was designed to do, take a look at the original ISO software project plan (here, 64kb acrobat format). Clic can be run as a postprocessor, or called directly through an API. The clic home page will get you started with the package. 
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Starting with version Cart3D v1.4, you can now extract force and moment histories of any component or component group while the simulation is in progress. flowCart's "-his" flag has always given "forces.dat" and "moments.dat" with load evolutions on the entire geometry in the simulation. However, using the new "$__Force_Moment_Pro..." section in input.cntl permits much more flexibility. This section relies upon a GMP-style component hierarchy and automatically outputs a clic-like loads summary table in "loadsTri.dat" at the end of the run.

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Also starting with v1.4, you can extract data along any number of discrete points or lines within the computational domain. Need to do a wake survey? Want to compare with off-body data or irregularly placed pressure taps? This is by far the most accurate way of instrumenting specific locations in the flow field. You specify point or line sensors using 1-line additions to the "$__Post_Processing:" section in input.cntl and at the end of your run you'll see data files ID'd using the sensor names "lineSensor<Name>.dat". Data from an arbitrary list of point-sensors gets collected in "pointSensors.dat". 
Point sensors can also be used in the the "$__Convergence His...:" section in input.cntl. In this case, they work like "strip-chart" recorders of data at a particular point in the flow. This allows you to monitor convergence at discrete off-body locations to help understand what's going on in your simulation. When used as convergence monitors, each point sensor produces a "pointSensor_<Name>.dat" file with the state vector and Cp's as a function of iteration count.

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Good question. There is currently no CGNS standard for Cartesian grids, but it is something that we'd very much like to support and we're working with the CGNS team to develop this standard. When this is done, we'll add CGNS support into Cart3D. Of course The CGNS system already does support unstructured surface triangulations and we do have translators for Cart3D surface triangulations (all types) and CGNS. These were written by the CGNS team and you should drop a note to CGNS-Support@CGNS.org to get a copy of these translators. 

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last update December, 2024.