Author(s): Jun Mitsui; Corrado Altomare; Alejandro J. C. Crespo; Jose M. Dominguez; Shin-Ichi Kubota; Tomohiro Suzuki; Moncho Gomez-Gesteira

Linked Author(s): Corrado Altomare

Keywords: Numerical modelling; Tetrapods; Breakwater; Tsunami

Abstract: In 2011, the tsunami in Japan caused big damages in the coastal protection structures where a large number of armour units installed at the breakwaters were scattered. This work presents a numerical tool to simulate the behaviour of concrete armour units under wave action, which will help to design breakwater that will be long-lasting and effective in protecting the coast. The Smoothed Particle Hydrodynamics (SPH) methodology is a meshless approach suitable for simulating multi-body and body-fluid interactions. SPH is based on a Lagrangian description of fluid motion in which continuum properties are reformulated in terms of smoothed quantities at discrete locations named “particles”. SPH can be conveniently adopted to simulate free-surface flows and for capturing highly nonlinear behaviour of wave-structure interactions or fluid-driven objects. The DualSPHysics code (Domínguez et al., 2021) is an open source code developed to use SPH for real engineering problems. Recently, DualSPHysics has been coupled with Project Chrono library (Canelas et al., 2018), a general-purpose simulation package for multi-body problems with support for large systems. Project Chrono solves the solid-solid interaction in terms of surface contacts. In this work, we will reproduce the hydrodynamic behaviour of the tetrapods against a solitary wave, which constitutes a novel application of DualSPHysics to a real problem. The use of a meshless Lagrangian model like this one is possibly the only reasonable way to face this kind of problem. Tetrapods that can eventually experience any kind of movement, even colliding each other, will be almost impossible for conventional mesh-based models. The movement of the units during the simulation are compared with physical model experiments. The experimental campaign includes: i) two initial arrangement of the tetrapods (1-row and 2-layers), ii) several wave heights of the solitary wave (scaled values of 2.6, 4.5, 6.4 cm), iii) different material of the impermeable mound (smooth surface with polyvinyl chloride panel and rough surface with sandpaper). The exact geometry of the tetrapods, mass and material is defined in the simulations. For the block-block and block-mound interactions, the actual friction coefficient is used by Project Chrono and these values were also obtained experimentally. During the experiments it was observed that PVC cases are the most likely to move, and all movements were caused by sliding while movements of tetrapods were smaller in the cases with sandpaper (sliding or overturning). The damage simulated in the numerical model, defined here as the percentage of tetrapods that were moved and the mean and maximum displacements of the units, will be compared with the experimental data for validation. Canelas et al., 2018. Extending DualSPHysics with a Differential Variational Inequality: modeling fluid-mechanism interaction. APOR, 76:88-97. Domínguez et al., 2021. DualSPHysics: from fluid dynamics to multiphysics problems. Computational Particle Mechanics. doi:10.1007/s40571-021-00404-2.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221181

Year: 2022