Narrow Results

In 2011, the tsunami generated by the Great East Japan Earthquake devastated infrastructure along the Pacific coast of northeastern Japan. In particular, the collapse of bridges resulted in much disruption to traffic, which led to delays in recovery after the disaster. We are developing a multi-scale and multi-physics tsunami disaster simulation tool to evaluate the safety and damage of infrastructure from huge tsunami. Multistage zooming tsunami analysis is one of the possible methods for implementing a high-resolution three-dimensional (3D) tsunami inundation simulation for a city. In this research, a virtual wave source that includes transition layers is proposed for a coupled simulation based on 3D particle simulation. The zooming analysis has been undertaken using the same particle method and a two-dimensional (2D) finite difference simulation. The 3D particle coupled simulation has been examined and validated.

Tuned Sloshing Dampers (TSD) are passive devices, working based on shallow liquid sloshing in a rigid tank to suppress the horizontal structural vibrations induced by wind loading or earthquake excitations. The key parameters in design of a TSD could be referred to the natural frequency of the liquid sloshing motion and the inherent damping of the TSD during the excitation. Due to the highly nonlinear behavior of the liquid free-surface occurring in TSDs, accurate prediction of the TSD-structure’s behavior during strong excitations is highly desirable. In the current paper, Weakly Compressible form of Smoothed Particle Hydrodynamic (SPH) method is used to simulate the flow within rectangular TSDs during large movements. Characteristics of the flow such as wave height and sloshing forces acting on the container’s walls are calculated and compared with the existing experimental and numerical data. A hybrid SPH-Finite Element Method (FEM) was developed to investigate the seismic response of MDOF structures equipped with multiple TSDs. The proposed model was employed to evaluate the dynamic response of MDOF structures under severe seismic excitations with different frequency contents. The results showed that depending on the frequency content of the ground motion, having the TSDs tuned to a frequency close to the natural frequency of the structure could significantly alter the seismic response of the structures. The effectiveness of TSD is also related to the higher modes effect for MDOF structures and location of TSDs placed on the structural floors.

The standard weakly compressible Smoothed Particle Hydrodynamics (WCSPH) is successfully applied to multi-phase problems involving fluids with similar densities, but when density ratio increases at some order of magnitude, serious instability phenomena occur at the interface. Several remedies have been proposed based on numerical correctives that deviate from standard formulation, increasing the algorithm complexity and, sometimes, the computational cost. In this study, the standard SPH has been adapted to treat free-surface multi-phase flows with a large density ratio through a modified form of the governing equations which is based on the specific volume (i.e. the inverse of particle volume) instead of density: the former is continuous across the fluid interface while the latter is not and generates numerical instability. Interface sharpness is assured without cohesion forces; kernel truncation at the interface is avoided. The model, relatively simple to implement, is tested by simulating two-phase dam breaking for two configurations: kinematic and dynamic features are compared with reference data showing good agreement despite the reduced computational effort.

The smoothed particle hydrodynamics (SPH) method has been proved as a powerful algorithm for fluid mechanics, especially in the simulation of free surface flows with high speeds or drastic impacts. The solid boundary treatment method is important for the accuracy and stability of the numerical results, as the support domain of fluid particles is truncated near the vicinity of the boundary. This paper presents two commonly used methods for simulating a solid boundary in SPH simulations. Emphasis is placed on the description of the methods, definition of the boundary particles’ parameters, and discussion of their advantages and shortcomings. The classical dam break simulation is conducted using self-developed code and open source models such as DualSPHysics and PySPH in order to investigate the effects of the boundary methods. The results show that methods based on dynamic boundary particles can simulate the free water surface well with a good agreement with experimental results. The conclusions can also be used in research for boundary implementation methods for practical ocean and coastal engineering problems with free surface flows.

Wave breaking over a submerged step with a steep front slope and a wide horizontal platform is studied by smoothed particle hydrodynamic (SPH) method. By adding a momentum source term and a velocity attenuation term into the governing equation, a nonreflective wave maker system is introduced in the numerical model. A suitable circuit channel is specifically designed for the present SPH model to avoid the nonphysical rise of the mean water level on the horizontal platform of the submerged step. The predicted free surface elevations and the spatial distributions of wave height and wave setup over the submerged step are validated using the corresponding experimental data. In addition, the vertical distributions of wave-induced current over the submerged step are also investigated at both low and high tides.

The wave impact on marine structures is concerning in ocean and coastal engineering. Cylinders are important components of various marine structures such as piers of sea-crossing bridge, columns of oil and gas platforms and subsea pipelines. In this study, the interaction of solitary wave with a submerged horizontal cylinder and a surface-piercing vertical cylinder are numerically studied by the Smoothed Particle Hydrodynamics (SPH) code SPHinXsys. SPHinXsys is an open-source multi-physics library based on the weakly compressible SPH and invokes the low-dissipation Riemann solver for alleviating numerical noises in the simulation of fluid dynamics. The capability of SPHinXsys in reproducing the fluid fields of solitary wave propagating through cylinders is demonstrated by comparing with the experimental data. With the validation in hand, the features of the wave–structure process are examined.

Waves play a very important role in the mixing process of oil slick, and greatly affect the distribution of oil pollutants in the water column near sea surface. In this study, the mixing process of spilled oil under breaking waves is simulated by using a multiphase SPH-based model. The model is an extension of our previous model. Modifications for two-phase flow are introduced to solve the instability problems caused by the high density ratio at interfaces. The surface tension between two fluids is also included in the multiphase model. The model is tested by simulating the deformation of an initially square droplet in another fluid due to surface tension, which is a classic problem usually used to test the two-phase flow model. The density ratio between the two fluids has been set to be 1/1000. The results show that the new set of SPH formulations can well deal with the large density difference at the interface of two fluids. And then it is applied to simulate wave breaking where the water surface is covered by a layer of oil. The mixing process of surface oil slick in water column is demonstrated.

The paper presents a weakly compressible Smoothed Particle Hydrodynamics (SPH) model to investigate the wave breaking of coastal slope. The SPH method is a mesh-free Lagrangian approach which is capable of tracking the large deformations of the free surface with good accuracy. To verify this numerical simulation, three different types of wave breaking, namely, spilling, plunging and surging breaking are successfully simulated. The computations are validated against the experimental data and a good agreement is observed. The velocity and pressure distributions are analyzed and visualized. The turbulent transport mechanism including vorticity and turbulent kinetic energy on the simulation results are also investigated in further detail. The SPH modeling is shown to provide a promising tool to predict the breaking characteristics of different waves.