Lalith Wijerathne

Application of High Performance Computing to Earthquake Hazard and Disaster Estimation in Urban Area

Integrated earthquake simulation (IES) is a seamless simulation of analyzing all processes of earthquake hazard and disaster. There are two difficulties in carrying out IES, namely, the requirement of large scale computation and the requirement of numerous analysis models for structures in an urban area, and they are solved by taking advantage of High Performance Computing (HPC) and by developing a system of automated model construction. HPC is a key element in developing IES, as it needs to analyze wave propagation and amplification processes in an underground structure; a model of high fidelity for the underground structure exceeds a degree-of-freedom larger than 100 billion. Examples of IES for Tokyo Metropolis are presented; the numerical computation is made by using K computer, the supercomputer of Japan. The estimation of earthquake hazard and disaster for a given earthquake scenario is made by the ground motion simulation and the urban area seismic response simulation, respectively, for the target area of 10,000

Fast Finite Element Analysis Method Using Multiple GPUs for Crustal Deformation and its Application to Stochastic Inversion Analysis with Geometry Uncertainty

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Viscoelastic Crustal Deformation Computation Method with Reduced Random Memory Accesses for GPU-Based Computers.

10,000 m.

Development of Scalable Three-Dimensional Elasto-Plastic Nonlinear Wave Propagation Analysis Method for Earthquake Damage Estimation of Soft Grounds.

Abstract Crustal deformation computation using 3-D high-fidelity models has been in heavy demand due to accumulation of observational data. This approach is computationally expensive and more than 10 5 repetitive computations are required for various application including Monte Carlo simulation, stochastic inverse analysis, and optimization. To handle the massive computation cost, we develop a fast Finite Element (FE) analysis method using multi-GPUs for crustal deformation. We use algorithms appropriate for GPUs and accelerate calculations such as sparse matrix-vector product. By reducing the computation time, we are able to conduct multiple crustal deformation computations in a feasible timeframe. As an application example, we conduct stochastic inverse analysis considering uncertainties in geometry and estimate coseismic slip distribution in the 2011 Tohoku Earthquake, by performing 360,000 crustal deformation computations for different 8 × 10 7 DOF FE models using the proposed method.

Effects of Local Spin on Overall Properties of Granule Materials

The computation of crustal deformation following a given fault slip is important for understanding earthquake generation processes and reduction of damage. In crustal deformation analysis, reflecting the complex geometry and material heterogeneity of the crust is important, and use of large-scale unstructured finite-element method is suitable. However, since the computation area is large, its computation cost has been a bottleneck. In this study, we develop a fast unstructured finite-element solver for GPU-based large-scale computers. By computing several times steps together, we reduce random access, together with the use of predictors suitable for viscoelastic analysis to reduce the total computational cost. The developed solver enabled 2.79 times speedup from the conventional solver. We show an application example of the developed method through a viscoelastic deformation analysis of the Eastern Mediterranean crust and mantle following a hypothetical M 9 earthquake in Greece by using a 2,403,562,056 degree-of-freedom finite-element model.

Practical Method for Damage Evaluation Based on Point Estimate Considering Uncertainty of Structural Properties

In soft complex grounds, earthquakes cause damages with large deformation such as landslides and subsidence. Use of elasto-plastic models as the constitutive equation of soils is suitable for evaluation of nonlinear wave propagation with large ground deformation. However, there is no example of elasto-plastic nonlinear wave propagation analysis method capable of simulating a large-scale soil deformation problem. In this study, we developed a scalable elasto-plastic nonlinear wave propagation analysis program based on three-dimensional nonlinear finite-element method. The program attains 86.2% strong scaling efficiency from 240 CPU cores to 3840 CPU cores of PRIMEHPC FX10 based Oakleaf-FX [1], with 8.85 TFLOPS (15.6% of peak) performance on 3840 CPU cores. We verified the elasto-plastic nonlinear wave propagation program through convergence analysis, and conducted an analysis with large deformation for an actual soft ground modeled using 47,813,250 degrees-of-freedom.

On some recent achievements of earthquake simulation

This paper proposes continuumnization of a set of rigid body spherical particles which are regularly arranged and connected by springs. Continuumnization converts translation and spin of all particles to spatially varying functions, together with derivation of material properties from spring constants. It is shown that a function of particles’ spin tends to vanish in the limit as the radius of the particles goes to zero. The governing equations of the functions of translation and spin are studied for a symmetric assembly of rigid body particles. The characteristic equation of the governing equations shows the presence of high-frequency modes of spin, as well as waves which correspond to P- and S-waves of ordinary continuum.

META-MODELING FOR CONSTRUCTING MODEL CONSISTENT WITH CONTINUUM MECHANICS

This study introduces a practical method for evaluating structural damage based on a large-scale simulation targeting expansive areas, like whole cities. In such a seismic simulation that deals with numerous building structures, it is desirable to estimate the damage based on a stochastic evaluation considering the uncertainty of structural properties. This is because an accurate modeling of numerous building structures, according to each designed value, would require a great deal of time. However, a damage evaluation considering the model uncertainty generally involves numerous calculations and is inadequate for such a large-scale simulation. Therefore, we propose a method using the point estimate technique which can estimate the probability of damage under model uncertainty from a small number of calculations. The applicability and usefulness of the proposed method is evaluated by comparing it to the method based on a Monte Carlo simulation.

AUTOMATED CONSTRUCTION OF CONSISTENT LUMPED MASS MODEL FOR ROAD NETWORK

Abstract This paper presents some recent achievements of earthquake simulation, which is divided into the seismic wave propagation simulation and the seismic structure response simulation. These achievements are based on rigorous mathematical treatment of continuum mechanics problems, and numerical algorithms of solving the problems are developed. A multi-scale analysis method is developed for the seismic wave propagation simulation; numerical dispersion is reduced by introducing a new discretization scheme. A smart treatment of crack initiation and propagation is developed for the seismic structure response simulation, so that a numerical experiment is made for failure processes by using numerous samples of one structure.