GranumFL: an agentic, GPU-accelerated coupled DEM–SPH program for debris flows on real terrain
Year: 2026
Type: article
Abstract: Debris flows on real hillsides involve grains, water and terrain together, yet the programsthat couple discrete elements with smoothed particle hydrodynamics on a GPU are eithercommercial and resolved at the grain scale or research codes that an engineer cannot setup without programming. This paper presents GranumFL, which couples a weakly com-pressible SPH water phase with a DEM grain phase through the unresolved formulation ofRobinson, Ramaioli and Luding (2014), runs both phases on one CUDA GPU, lays out acase on a digital elevation model, and exposes every step to a large-language-model agentthrough 20 Model Context Protocol tools. Each phase was calibrated against publishedbenchmark results. The DEM phase reproduces the Chung and Ooi impact benchmarkswithin 0.09 % of Hertz’s solutions and 0.19◦ of Kratos, and the DEM8 penetration testwithin the spread of eight open-source codes, in 1.1 min on an RTX 5090, as fast as thededicated GPU codes. For a sedimenting porous block, the coupled phase is closer totheory than the reference implementation of Robinson et al. at every resolution compared(−2.7, +9.3 and +14.4 % against +5, +15 and +22 % at h/d = 2, 5 and 6), whereas for asingle grain it is accurate only for 2.5 ≤ h/d ≤ 4, because of the grain’s own volume in theporosity at small h/d and a truncated buoyancy at large h/d, in a dense fixed bed it gives1.5 to 3.3 times Ergun’s pressure drop, and a loose submerged column collapses too farwith a base pore pressure of the wrong sign, so dense granular assemblies with their porepressure remain the open problem. The SPH phase follows the Martin and Moyce dambreak within 3.0–3.1 % RMS and hydrostatics within 0.68 %, and in SPHERIC Test 2 itfollows the water heights within about 8 % and times the impact on the box within 3 msbut over-predicts the peak pressure near the floor, at about the speed of DualSPHysicson a V100 at the coarser spacing. The CPU and GPU agree to three digits, and the waterphase sustains 1.6–1.9×108 particle updates per second up to 12 million particles, 55 to 66times a 30-thread CPU. In four independent trials an LLM agent, driving only the MCPtools, set up and edited the 2026 Patong (Phuket) debris-flow site from plain-languagerequests and passed all 33 objective checks, and two trials found on their own that thesteepest-descent path on the Copernicus surface model does not follow the reported route.
Author: Youwai, Sompote
Language: English
Subfield: Management, Monitoring, Policy and Law
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7225061164