基于GPU集群异构并行计算的大规模多场耦合相场模型模拟研究

Based on multicomponent alloy single-phase system multi-grain growth model and the lattice Boltzmann method to calculate momentum, mass and energy transfer, a multi-phase system multicomponent alloy three-dimensional phase-field model coupling flow field, temperature field and solute field is established. Combing MPI message passing model and shared memory model CUDA, a high performance computing method based on MPI+CUDA is proposed. Taking Al-4wt.%Cu for example, through the concurrent execution of multi-process and multi-thread to solve phase-field model in large-scale three-dimensional domain, improve computational efficiency and accuracy, solving the problems of large calculation amount, low efficiency and limited to qualitative research exist when solve phase-field model using traditional method. The interactions between natural convection and solid-liquid interface, and the effects of natural flow on the stability of accelerating growth flat interface and solid-liquid interface morphology transformation are studied, further in-depth understanding of structure formation mechanism during solidification process is also did to reappear evolution trend of the interface morphology and growth kinetics. To verify the reliability of the simulation results, the comparison with classical theory of crystal growth as well as the experimental results under the same condition are did to refine and improve the calculation model, achieve a deep understanding to structure formation mechanism during olidification process and the influence characteristics of the flow on solidification structure.

本项申请基于多元合金单相系统多晶粒生长模型及计算动量、质量和能量传输的格子Boltzmann方法，建立一个耦合流场、温度场和溶质场等外场的多元合金三维相场模型。将MPI消息传递模型和共享内存模型CUDA结合，提出一种基于MPI+CUDA混合编程模型的高性能计算方法，以Al-4wt.%Cu合金为例，通过多进程和多线程的并发执行实现大规模三维区域内相场模型的求解，提高计算效率及求解精度，解决传统求解相场模型存在的计算量大、效率低、限于定性研究等问题。研究自然对流与固-液界面的相互作用，自然流动对加速生长的平界面稳定性和固-液界面形貌转变的影响，进一步深入了解凝固过程组织形成机制，再现界面形貌和生长动力学的演化趋势。为验证模拟结果的可靠性，将其与晶体生长经典理论进行比较，同时将模拟结果与同条件下的实验结果对比分析，以完善和改进计算模型，达到深入理解凝固过程组织形成机制及流动对凝固组织的影响特点。

将多元合金单相系统多晶粒纯扩散相场模型与计算动量、质量及能量传输的LBM相耦合，建立了模拟强迫流动、自然对流作用下合金枝晶生长、共晶组织生长等的多尺度、多场耦合相场模型；考虑晶界缺陷与溶质在晶界处富集对区域自由能的影响，建立了多次相变中固－固相变的形核模型；建立了多相场连续相变模型；耦合液-固相变和固-固相变模型建立了新的液-固-固多次相变多相场模型；分别基于水平集和相场法，与不可压缩流体的连续性方程、N-S方程、电场方程、磁场方程等控制方程耦合，建立了气液两相流中多气泡融合和运动的三维多场耦合模型。. 以Al-Cu合金、Fe-C合金、高纯丁二腈(SCN)等为例，开展多物理场耦合条件下的数值模拟，研究了强迫流动、自然对流与固-液界面的相互作用，流动对平界面稳定性和固-液界面形貌转变的影响，包晶相变过程中奥氏体演化过程，横向约束条件下枝晶与共析组织演化过程，初始共析层片间距、界面能、扩散系数及过冷度对层片状珠光体组织的影响，多次相变中固-固相变形核过程，等轴晶与枝晶状的δ晶粒表面包晶相变演化过程，多次相变过程中微观组织的连续演化过程，定向凝固柱状晶结构中非择优枝晶晶粒取向角与方位角对择优枝晶上二次枝晶的影响，气液两相流多场耦合模型中气泡的运动、融合等现象。. 针对多场耦合相场模型大规模数值模拟中存在的多尺度、多模型的非线性耦合及计算效率低、计算空间有限等关键问题，基于CPU/GPU异构模式，研究了MPI+CUDA混合粒度异构并行、多节点CPU+GPU异构集群Multi-GPU并行、基于OpenCL+GPU高性能并行、MPI+OpenMP混合编程对h型自适应有限元法并行等高性能并行计算方法及其优化方案，实现大规模三维多场耦合相场模型的求解，提高计算效率及其求解精度；将各计算方法对比，评价模型和算法的有效性并不断完善和改进。. 为验证模拟结果的可靠性，将其与晶体生长经典理论及实验结果比较;将同条件下采用不同计算方法与传统求解方法的模拟结果对比分析，验证并行算法的可靠性及加速性能，不断优化算法使其达到最佳性能。