Particle tracking has several important applications for solute transport studies in aquifer systems. Travel time distribution at observation points, particle coordinates in time and streamlines are some practical results providing information of expected transport patterns and interaction with boundary conditions. However, flow model complexity and simultaneous displacement of multiple particle groups leads to rapid increase of computational requirements. MODPATH is a particle tracking engine for MODFLOW models and source code displays potential for parallel processing of particles. This article addresses the implementation of this feature with the OpenMP library. Two synthetic aquifer applications are employed for performance tests on a desktop computer with increasing number of particles. Speed up analysis shows that dynamic thread scheduling is preferable for highly heterogeneous flows, providing processing adaptivity to the presence of slow particles. In simulations writing particles position in time, thread exclusive output files lead to higher speed up factors. Results show that above a threshold number of particles, simulation runtimes become independent of flow model grid complexity and are controlled by the large number of particles, then parallel processing reduces simulation runtimes for the particle tracking model MODPATH.

翻译：粒子追踪在含水层系统中溶质运移研究具有重要应用价值。观测点处的运移时间分布、粒子时空坐标及流线等成果可为预期运移模式与边界条件相互作用提供信息支撑。然而，随着渗流模型复杂度的提升及多粒子群同步位移的开展，计算需求呈指数级增长。MODPATH作为MODFLOW模型的粒子追踪引擎，其源代码具备粒子并行处理的潜力。本文基于OpenMP库实现该并行功能，通过在台式计算机上逐步增加粒子数量，采用两个合成含水层案例进行性能测试。加速比分析表明：动态线程调度机制更适用于强非均质渗流环境，可自适应处理慢速粒子群；在记录粒子时序位置的模拟中，线程独占输出文件能获得更高加速比。研究结果显示，当粒子数量超过临界阈值后，模拟运行时间不再受渗流模型网格复杂度影响，而是由大规模粒子群主导控制。此时，并行处理可显著降低MODPATH粒子追踪模型的模拟运行时间。