Benchmark data for validating coupled fluid-solid models was obtained through underwater drop experiments involving circular, rectangular, and L-shaped objects. Image processing was used to analyze the motion of these objects, and each experiment was repeated 10–15 times to ensure reproducibility. Four types of coupled methods (SPH-DEM, LBM-DEM, FDM-DEM and FVM-DEM) were used to simulate the experiments and evaluate the dynamics of the underwater drops as a validation approach. To facilitate validation and improve the accuracy of coupled fluid-solid models for other researchers, the resulting benchmark data will be published as an appendix to this paper.

This paper proposes a method for transforming damage behavior into discontinuous deformation by utilizing the duality between Voronoi diagrams and Delaunay triangulation (Voronoi-Delaunay duality). Continuum damage models, which replace fracture by the degradation of material stiffness, are well-suited for unstructured meshes composed of triangular or tetrahedral finite elements. Based on this compatibility, the proposed approach converts an unstructured Delaunay mesh into a Voronoi diagram, enabling the representation of damage behavior as discontinuous deformation. This transformation allows continuum-based numerical analyses to capture fracture phenomena in a discontinuous manner. After demonstrating the effectiveness of the proposed method through several numerical examples, the approach is applied to a mesoscale fracture simulation of reinforced concrete. The results show that the proposed method can successfully reproduce (visualize) complex three-dimensional fracture behavior at the mesoscale.

In disaster-affected areas, the impact of land use changes from the past to the present on disaster risk is often discussed, but most of these observations are qualitative. However, quantitative analysis could provide valuable information for disaster prevention and mitigation. This study aims to analyze the impact of land use changes through a series of heavy rainfall disaster simulations. Past and present models of a real region that experienced an extreme rainfall disaster were prepared, with flooding and landslides represented in the simulations. The results quantitatively demonstrated that, to reduce flood damage effectively, it is essential not only to implement basin maintenance, but also to prioritize safety in residential area selection and to proceed with land development in a careful manner. Finally, the potential advantages and limitations of the proposed approach are discussed.