Multiphysics Coupling Using SPH for Coastal Structures Subject to Tsunami-Driven Hydrodynamic and Debris Impact Loads

This paper investigates the behavior of a tsunami-like bore carrying debris impacting a structure, examining the variability of the debris impact forces simulated using smoothed particle hydrodynamics (SPH) and assessing different contact formulations and their significance for design codes. One of the key aspects in current tsunami-resistant design codes in Japan and the US is the lack of consensus on the role and significance of floating debris and its interaction with structures. The meshless SPH method is ideal to simulate this complex interaction but has not been comprehensively validated or investigated in this application. The present work quantifies the variability inherent in the random nature of tsunami-induced debris behavior, which is crucial to realize reasonably conservative tsunami-resilient design. The open-source SPH code, DualSPHysics, is first rigorously validated against existing laboratory experiments of debris dam-break flows impacting a square prism, capturing the oblique collision of debris with the structure. A reduced version of the full experimental domain reproduces the same hydrodynamics at 26%–57% of the computational time. Then, coupled with a multiphysics engine, Project Chrono, to solve collision of solid objects accurately, it is shown that using the nonsmooth contact formulation in the SPH predictions for debris impact force is essential to obtain close agreement with the laboratory measurements and avoid noise-like high-frequency oscillation of a numerical origin not identified by previous studies. Sensitivity analysis examining variation in the initial debris position also confirms that an SPH solver with a multiphysics library enables us to explain the experimental variability and quote the stochastic uncertainty far quicker than other approaches. Finally, a number of underlying issues in well-known design equations of debris impact force are clarified and analyzed in a quantitative manner, relating to the added mass of water surrounding debris, the one-degree-of-freedom model, and the superposition on hydrodynamic loads.