VOFTools 3.2: Added VOF functionality to initialize the liquid volume fraction in general convex cells

An updated version of the VOFTools library for convex geometries is presented to add a functionality for volume fraction initialization, which is important for any VOF (volume of fluid) method. The earlier version of the library includes efficient analytical and geometrical routines for area and volume computation, truncation operations that typically arise in VOF methods, area and volume conservation enforcement in PLIC (piecewise linear interface calculation) reconstruction and computation of the distance from a given point to the reconstructed interface. The updated version incorporates an accurate initialization procedure, based on local grid refinement, to determine the liquid region bounded by a convex polygonal or polyhedral cell and a given implicitly-defined liquid interface. Also, two bugs have been fixed. 2D and 3D tests are provided in the software package to assess the accuracy of the implemented initialization procedure.本文提出了面向凸几何的VOFTools库更新版本，新增了体积分数初始化功能，该功能对任意VOF (Volume of Fluid, 流体体积) 方法均具有重要意义。该库的早期版本已包含高效的解析与几何计算程序，可实现面积与体积计算、VOF方法中常见的截断操作、PLIC (Piecewise Linear Interface Calculation, 分段线性界面重构) 重构过程中的面积与体积守恒保障，以及给定点到重构界面的距离计算。本次更新版本新增了基于局部网格加密的精准初始化流程，用于确定由凸多边形或凸多面体网格单元与给定隐式定义的流体界面所围限的流体区域。此外，该版本还修复了两处程序漏洞。软件包中附带了二维与三维测试用例，用于评估所实现的初始化流程的准确性。