VOFTools 5: An extension to non-convex geometries of calculation tools for volume of fluid methods

The VOFTools library includes useful tools for performing the geometrical operations that typically arise in volume of fluid (VOF) methods. We present a major improvement of VOFTools to extend its use to non-convex geometries without the need for costly convex-decomposition techniques. A thorough adaptation of the different routines has been carried out to meet the challenges of the new geometries and to maintain, and even improve, the efficiency and robustness of the previous tools. Specifically, we upgraded the routines for (1) truncating a polyhedron with a half space, (2) computing the interface position to cut off a certain volume fraction from a cell in PLIC (piecewise linear interface calculation) reconstruction and (3) computing the volume of a material body, defined by an implicit function, that is contained inside a mesh cell. To assess the performance of the supplied routines, different tests, which are provided in FORTRAN and C, were implemented for several 2D and 3D non-convex geometries. New version program summary Program Title: VOFTools Program Files doi: http://dx.doi.org/10.17632/brrgt645bh.3 Licensing provisions: GPLv3 Programming language: FORTRAN and C, with C interfaces Journal reference of previous version: J. Lopez, J. Hernandez, P. Gomez, C. Zanzi, R. Zamora, VOFTools 3.2: Added VOF functionality to initialize the liquid volume fraction in general convex cells, Comput. Phys. Comm. 245 (2019) 106859. Does the new version supersede the previous version?: Yes Reasons for the new version: Extension to non-convex geometries without the need for costly convex-decomposition techniques. Summary of revisions: The main features added with respect to the previous VOFTools version are the following: The inte3d, enforv3d (originally presented in [1]) and initf3d [2] routines for volume truncation, conservation enforcement and initialization operations in VOF methods, respectively, have been extended to non-convex geometries following the methodology presented in [3], without the need for costly convex-decomposition techniques. Among other aspects, the main change in implementation affects the arrangement of the vertices of the regions resulting from any of the above operations. To this end, the newpol3d subroutine has been updated by replacing Algorithm 3 in [1] by the new Algorithm 1, which is briefly presented below. Let us consider a generic polyhedron, either convex or non-convex, of J face boundaries, with NIPVO(j) vertices sequentially connected and forming a closed loop on each face boundary j. Vertex number i(p), assigned to vertex with index i of face boundary j, is stored using the two dimensional array IPVO(j, i) = i(p) (the highest value of the vertex number is denoted as NTP). The NIPV1 and IPV1 arrays are used to define the new region resulting from the geometric operation under consideration. For every vertex i p located inside the half-space used in a truncation operation or the material body used in a volume fraction initialization operation, the array element IA(i(p)) is set to 1, and 0 otherwise. According to [3], a key vertex of a new face boundary j is a new vertex IPV1(j, i) whose next vertex IPV1(j, i + 1) has an IA value equal to 1.