Disasters, such as sediment disaster caused by heavy rain and Tsunami disaster caused by an earthquake, are multiphase flow phenomena of fluid (water) and solid (soil). For damage prediction and countermeasure, fluid-solid analysis method is necessary since there is a scale limitation for an experiment. In this study, we develop multiphase simulator utilizing the Incompressible Smoothed Particle Hydrodynamics method (ISPH method) for fluid and Discrete Element Method (DEM) for solid. The interaction between ISPH method and DEM is implemented by considering an interaction force between fluid and solid. Free surface judgement is an important factor to obtain a good fluid analysis result. We utilize a method proposed by Marrone et al. to improve the free surface detection in a solid domain. In a simple validation test, dam break flow of water and glass beads, we validate and verify our method. At last, the method is applied to scouring analysis with a coarse graining particle model.

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In Fukushima decommissioning, to predict the distribution of boron species in the fuel debris is important because it affects the risk of re-criticality. Thus, the eutectic melting and relocation behavior of boron carbide (B₄C) control rod materials receive remarkable attention. Our recent experiment dynamically visualized the behavior of the eutectic melt, but it stayed in the original location even after the melting. However, mechanism for the no relocation was not clarified. In the current study, the behavior of the eutectic melt was analyzed by the simple eutectic model based on the moving particle semi-implicit (MPS) method. The obtained results indicated that the no relocation in the experiment may be explained by the isothermal solidification of the eutectic melt due to the diffusion of the boron.

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Free surface flow problems occur in disaster simulations such as tsunami flow in urban area. In this situation, a non-hydrostatic free surface model is required to perform a tsunami inundation simulation. It is, however, difficult to carry out three-dimensional large-scale tsunami simulations because of the computing of the pressure Poisson equation in the incompressible flows.
In current study, we have developed a fully explicit three-dimensional free surface model by the lattice Boltzmann method with the Piecewise Linear Interface Reconstruction approach. In addition, we have used pseudo Level Set function generated by the interface fraction to determine the interface normal vector accurately based on the Simple - Coupled Level Set and Volume of Fluid method. Through the classical dam-breaking problem, we demonstrated that our model has a convergence of model accuracy according to the spacing grid sizes. Besides, our model can calculate the interface shapes seamlessly and settle the artificial oscillations.

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This paper presents a coupling method of FEM for free surface flow and structure. This method is required for development of numerical analysis system in evaluating structural damage caused by debris collision. Debris is assumed to be a simple-shaped rigid body, and the calculation process of interaction between fluid FEM and rigid body is described in this paper. Furthermore, the numerical results are validated by comparing with an experimental result.

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In big earthquakes, tumbled furniture such as bookshelves and desks in rooms may become fatal obstacles that obstruct people from evacuating. Recently, quake-proof furniture are getting popular to prevent accidents in earthquakes. It is important to understand the overturning behaviors of furniture with and without quake-proof countermeasures under seismic excitations, as well as the behaviors and damages of the building itself. In this paper, the motion behaviors of furniture were analyzed using the Adaptively Shifted Integration (ASI) -Gauss code utilizing frictional contact algorithm based on the sophisticated penalty method. The numerical results were validated by comparing with the experimental results. The numerical code was also applied to a motion analysis of a furniture placed at each floor of an RC building.

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This paper proposes a method for simulating 3D fracture behavior of reinforced concrete using finite-strain material models and demonstrates the validity of the method. The finite-strain formulation is applied so that the geometrical nonlinearity can be considered in the fracture simulation. The fracture behavior of concrete is modeled by a finite-strain damage model which is based on the modified von-Mises criterion and fracture mechanics for concrete. The finite-strain von-Mises plasticity is applied to the plastic behavior of reinforcing bars. We first show the formulation of finite-strain damage model for concrete and finite-strain plasticity model for steel. A numerical example of RC beam with different shear reinforcements is presented to demonstrate the validity of the proposed method. The comparison between the numerical and experimental results offer valuable insight into the applicability of the proposed method to 3D fracture simulation of reinforced concrete in consideration of geometrical nonlinearity.

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A fundamental study is made on a method of numerical measurement of the effective viscosity of Solid-Liquid mixture, in which gravimetric type capillary viscometer is employed for the measurement procedure. The Hagen-Poiseuille equation is applied to evaluate the effective viscosity with the data obtained from a series of numerical test in a control volume and the Space-Time averaging procedure. The behaviour of sediments in the control volume is represented as spherical rigid bodies and is analysed with the Distinct Element Method (DEM), the interaction between liquid and sediments is considered with the help of the Finite Cover Method (FCM). Several numerical examples are presented to examine the viscosity dependence on the volume fraction and particle motions.

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This paper presents a finite element analysis method for damage estimation of Tsunami evacuation building. To estimate the wave force applied to the building in wave propagation problems, we have developed a three-dimensional free surface flow analysis code based on the volume of fluid (VOF) method. A numerical code based on the ASI-Gauss technique is applied to evaluate the behavior of framed structures. As numerical examples, estimation of Tsunami wave force on the evacuation buildings are presented to show the validity of the method. The applied wave force and damages of the structure obtained by the present method are compared between several inflow conditions and building shapes.

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We have aimed to develop a method to prevent destruction of the earth structures by reverse fault. In this study, we carried out the development of the centrifugal experimental apparatus and a reverse fault simulator by using Granular Element Method to investigate the fundamental knowledge about the deformation behavior of granular media upon the reverse fault. The centrifugal model test and granular element simulations were performed. By the centrifugal model test, we showed some important information, such that the progressive direction of the shear band depends on the confining pressure. Moreover, we showed that the developed reverse fault simulator can reproduce the results of the centrifugal model test. And we showed that it will be able to control artificially the progressive direction of the shear band and the surface displacement by the reverse fault simulation from GEM.

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In fluid-rigid body interaction simulation based on the particle method, incompressible Smoothed Particle Hydrodynamic (ISPH) method is used to resolve the problem of fluid particles’ motion and impact load on the structure in the meanwhile DEM based on the penalty method is commonly applied to deal with the contact problem of rigid bodies. However, the accuracy of penalty method relies on a relatively small time increment. In this paper, the impulse-based rigid body dynamics is applied to deal with the collision contact problem instead of the conventional penalty method for robust and faster computation.

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