Towards exascale simulations of granular fluidization in offshore wind turbine foundations

Fully-resolved micromechanical simulations coupling the Lattice Boltzmann Method (LBM) with the Discrete Element Method (DEM) provide high-fidelity insights into granular fluidization. However, the substantial computational demands of such simulations require efficient implementations on supercomputing architectures. This work presents a comprehensive performance analysis of a fully-resolved LBM-DEM model to study granular fluidization, i.e., piping erosion, during the installation of an offshore caisson foundation. The performance evaluation focuses on real-world workloads rather than simplified benchmark problems to obtain realistic performance insights. The study considers a diverse range of state-of-the-art HPC hardware architectures, namely the LUMI and MareNostrum 5 EuroHPC supercomputers, both CPU and GPU partitions. The results demonstrate that GPU-based systems generally outperform the CPU-based systems. Strong and weak scaling analyses were conducted with up to 512 nodes, and parallel efficiencies reached up to 92%. Nonetheless, the results also indicate that atomic add operations on GPUs can become a bottleneck for the parallel efficiency at large scales. Moreover, the study reveals a close link between physical variations of the setup and significant scaling implications, underscoring the need to consider physical model characteristics in scaling assessments.