A method for calculating fluid motion around an object placed in a fluid containing a gas-liquid interface using the Immersed Boundary Method is introduced. Instead of cumbersome algorithms such as the existing the Volume Of Fluid method, the level set method and so on, a simplified algorithm is proposed by directly solving a variable in terms of pressure divided by the fluid density. Some calculated results of the application of the method with k-ω turbulence model are shown.

Breaking waves entrains huge amounts of air bubbles into bulk seawater, which is involved in turbulence produced in splash-up breaking processes. Buoyant bubbles arriving wave surfaces aggregate to form clusters behind the wave front (so-called whitecap). While a series of the bubble dynamics are believed to be relevant to air-sea momentum transfers and gas exchanges, microscopic bubble behaviors on whitecap water surface in wave breaking turbulence have not been understood. This article introduces previous research progress on mechanical interactions between bubble and turbulence in bulk water under breaking waves, interactions of rising bubble with water surface in addition to interactions among bubbles floating on surface resulting in formation of whitecap water.

Smoothed Particle Hydrodynamics (SPH), which is a Lagrangian meshless method, is known as very useful method for large deformation problems, such as movement of wave absorbing blocks and sliding of a caisson breakwater. This study aims to simulate the movement of tsunami boulders and storm boulders, comparing with the hydraulic experiment, and evaluating the transport characteristics. The study also aims to clarify the scattering process of armour blocks on the additional rubble mound behind breakwaters against tsunami overflows. The series of simulation show the difference of movement characteristics between tsunami and storm boulders are caused by the difference of acting direction of tsunami and random waves on boulders, and hydrodynamic forces acting on the block differed depending on the block shape and initial water level conditions.

Characteristics of tsunami flow in cities are three-dimensional, highly non-linear and non-hydrostatic. A fully three-dimensional free-surface fluid model is required to simulate such a flow field. Fluid simulations in the field of coastal engineering are often large-scale since large areas are the subject of the simulations. The numerical model must be not only accurate but also efficient. In recent years, the lattice Boltzmann method (LBM) has attracted much attention as a novel simulation method and has been successfully applied to various engineering fields. Moreover, the cumulant LBM has attracted attention because it has excellent numerical stability even for high Reynolds number flows. The single-phase free-surface flow model using the cumulant LBM is a suitable approach for simulating violent flow fields in coastal engineering. In this study, we propose a single-phase free-surface flow model based on the cumulant LBM using the volume-of-fluid (VOF) model. We demonstrate that the cumulant LBM is stable under violent flows and reproduces the pressure field well compared with the traditional single relaxation time model. We find that a larger bulk viscosity can reduce the numerical oscillation of the impact pressure acting on a structure, although a bulk viscosity that is too large reduces the accuracy and stability. The results of the proposed model are in good agreement with previous experimental results.