A simple library for parsing and handling Fluent "case" files intended for computational fluid dynamics (CFD) simulations written in C. Copyright 2011-2018 Ioannis Nompelis
This is a very simple library that can be used to parse "case" files prepared for use by the Fluent software package. It is meant to be used for loading an unstructured grid that has been assigned boundary conditions in the form of face groups. The existing minimal structures can be used to build additional data structures (as needed) in order to perform simulations directly. Parsing provides verbose output, including line-numbers of key points in the file, and echos comments.
The library can be compiled against the HDF5 libraries whereby acting as a converter from a typical ASCII file to a cross-platform binary with the same structure. Using this functionality, the converter can be used to build binary files, which in turn can be used for parallel reading of very large grids. The memory foot-print of the library when it acts as a converter is extremely small.
An example Makefile has been included, as well as a Makefile.comm which provides a template for compile-time options for different compilers. A driver (test.c) has also been included in this distribution. The driver demonstrates how to initialize, read (parse) into memory, handle and clean the case-file object; both grid loading and converting to HDF5 examples are found in the driver. A routine is also included to plot the different face groups with AMTEC's TecPlot. This routine collects the vertices associated with each 2D (face) element in the same way that they were going to be visualized with plain OpenGL calls or creating OpenGL display lists, or creating vertex arrays. This acts as an example for visualizing the grid with organic software as needed.
IN 2016/09/22
A Fortran interface to the library and a driver code to illustrate how to use this library API from a Fortran code have been added. Doing 'make lib' will build the library. Doing 'make test' will build a C driver code to read a file named "grid.cas" and make TecPlot style files of all face-groups in the case file. Doing 'make' will build the library and compile the Fortran driver called "test.f" to an executable. The executable opens a file called "grid.cas" and makes a TecPlot-style file of all cells (volume elements). This demo uses an excerpt of a separate library that constructs volume elements; this code is included in this bundle.
The Fortran demonstration driver along with the element library code can be used to directly build a serial or shared-memory parallel (OpenMP/POSIX threaded) numerical solver. To do this, one needs to be build on top of the "make_cells()" subroutine and by forming additional arrays as needed.
IN 2017/10/24
A second and more useful example of a Fortran demonstration has been added in which derived structures from a loaded mesh are built, such as the element/cell and face centroids.
IN 2017/11/06
A third useful example of a Fortran demonstration has been added in which the spatial gradient of an imposed field-variable is computed using a Weighted Least-Squares method. This demonstration is built on top of the previous (demo2) code as it uses the element centroid structures.
This demonstration is useful for evaluating the accuracy of the weighted least squares approach when different weights are used. In the present demonstration, the common form of inverse-distance is used as the weight for each of the cells that contribute to a given cell's gradient estimation. The Fortran routine "test_gradient()" can be modified to alter the trial-field, compute the field's analytical spatial derivatives, change the form of the weights used, and be modified to compute a normed error. The linear system formed by the WLS method is assembled in this routine without regard for arithmetic efficiency as it is only for instruction purposes.
(NOTE FOR PERSONS WHO ARE INTERESTED IN BUILDING A SOLVER ON TOP OF THIS CODE: This gradient estimation can be used for evaluating any term in a PDE involving first derivatives, and they are expected to be second order accurate. In CFD performed using the finite volume method, this form is used to compute viscous fluxes at faces and in some cases higher-order inviscid fluxes. Also, when threading, the gradient calculation should be completely parallelizable.)
IN 2017/11/08
Separated methods for testing gradient reconstructions. The following methods are presently implemented:
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My Weighted Least-Squares (WLS) method based on a hyper-plane regression
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The WLSQ(N) as described in:
Eiji Shima, Keiichi Kitamura, and Takamori Haga, ``Green-Gauss/Weighted-Leas Squares hybrid Gradient Reconstruction for Arbitrary Polyhedra Unstructured Grids,'' Technical Notes, AIAA Journal, Vol. 51, No. 11, November 2013.
The code can very easily be modified to test additional methods.
IN 2017/11/10
Added functionality to allow for plot3d exporting of multi-block structured grids. This works for case-files that have been built by such grids.
IN 2018/01/29