M. L. L. Wijerathne

HPC Enhanced Large Urban Area Evacuation Simulations with Vision based Autonomously Navigating Multi Agents.

Abstract An evacuation simulation code based on Multi Agent Systems (MAS), with moderately complex agents in 2D grid envi- ronments, is developed. The main objective of this code is to estimate the effectiveness of the measures taken to smoothen and speedup the evacuation process of a large urban area, in time critical events like tsunami. A vision based autonomous navigation algorithm, which enables the agents to move through an urban environment and reach a far visible destination, is implemented. This simple algorithm enables a visitor agent to navigate through urban area and reach a destination which is several kilometers away. The navigation algorithm is verified comparing the simulated evacuation time and the paths taken by individual agents with those of theoretical. Further, a parallel computing extension is developed for studying mass evacuation of large areas; vision based autonomous navigation is computationally intensive. Several strategies like communication hiding, dynamic load balancing, etc. are implemented to attain high parallel scalability. Preliminary tests on the K-computer attained strong scalability above 94% at least up to 2048 CPU cores, with 2 million agents.

Tensor field tomography based on 3D photoelasticity

A new method for non-destructive measurement of arbitrary 3D stress state using photoelasticity has been developed. The new approach, namely, load incremental approach, is an attempt to solve the non-linear inverse problem of 3D photoelasticity by considering change in stress state for a load increment and linearizing the non-linear governing equation. As long as the applied load increment is small and photoelastic images are taken with high resolution in load increment, this method works and can reconstruct arbitrary 3D stress state. Numerical simulations clarify the effect of (i) the material sensitivity, (ii) the number of the observations and (iii) the constraint on the observation directions on the performance of the proposed method. These results provide the fundamental data for designing the experimental setup for 3D photoelasticity.

Strengthening of Parallel Computation Performance of Integrated Earthquake Simulation

AbstractThe parallel scalability of the seismic response analysis (SRA) module of the Integrated Earthquake Simulator (IES) is enhanced to achieve near-ideal scalability. In previous studies, the SRA module was enhanced with standard distributed memory parallel computing techniques. However, some bottlenecks seriously hinder its scalability. Parallel computing performance is significantly improved by eradicating all the bottlenecks; input/output modules are enhanced with advanced MPI functions, a static load balancer is introduced, and the link to seismic structure analysis programs is strengthened. Details of the bottlenecks, remedies implemented, and other performance enhancements are presented. With a moderate size problem, it is demonstrated that the modified SRA module has near-ideal scalability. Further, it is shown that this near-ideal scalability is sustained even in the simulation of a large urban area.

3D dynamic simulation of crack propagation in extracorporeal shock wave lithotripsy

Some experimental observations of Shock Wave Lithotripsy(SWL), which include 3D dynamic crack propagation, are simulated with the aim of reproducing fragmentation of kidney stones with SWL. Extracorporeal shock wave lithotripsy (ESWL) is the fragmentation of kidney stones by focusing an ultrasonic pressure pulse onto the stones. 3D models with fine discretization are used to accurately capture the high amplitude shear shock waves. For solving the resulting large scale dynamic crack propagation problem, PDS-FEM is used; it provides numerically efficient failure treatments. With a distributed memory parallel code of PDS-FEM, experimentally observed 3D photoelastic images of transient stress waves and crack patterns in cylindrical samples are successfully reproduced. The numerical crack patterns are in good agreement with the experimental ones, quantitatively. The results shows that the high amplitude shear waves induced in solid, by the lithotriptor generated shock wave, play a dominant role in stone fragmentation.

A quick earthquake disaster estimation system with fast urban earthquake simulation and interactive visualization

Abstract In the immediate aftermath of an earthquake, quick estimation of damage to city structures can facilitate prompt, effective post disaster measures. Physics based urban earthquake simulations, using measured ground motions as input, are a possible means of obtaining reasonable estimates. The difficulty of such estimation lies in carrying out the simulation and arriving at a thorough understanding of large scale time series results in a limited amount of time. We developed an estimation system based on fast urban earthquake disaster simulation, together with an interactive visualization method suitable for GPU workstations. Using this system, an urban area with more than 100,000 structures can be analyzed within an hour and visualized interactively.

Parallel Scalability Enhancements of Seismic Response and Evacuation Simulations of Integrated Earthquake Simulator

We developed scalable parallel computing extensions for Seismic Response Analysis (SRA) and evacuation simulation modules of an Integrated Earthquake Simulator (IES), with the aim of simulating earthquake disaster in large urban areas. For the SRA module, near ideal scalability is attained by introducing a static load balancer which is based on the previous run time data. The use of SystemV IPC as a means of reusing legacy seismic response analysis codes and its impacts on the parallel scalability are investigated. For parallelizing the multi agent based evacuation module, a number of strategies like communication hiding, minimizing the amount of data exchanged, virtual CPU topologies, repartitioning, etc. are used. Priliminary tests on the K computer produced above 94% strong scalability, with several million agents and several thousand CPU cores. Details of the parallel computing strategies used in these two modules and their effectiveness are presented.

Inverse Analysis Method for Photoelastic Measurement of 3D Stress State

A new nondestructive method for identifying boundary conditions applied on a 3D linear elastic body is developed based on the load incremental approach, which linearizes the nonlinear governing equation of photoelasticity by considering small increments in applied load. Direct stress identification based on load incremental approach is highly sensitive to measurement errors and involves considerable amount of computations. On the other hand, identification of boundary conditions based on load incremental approach and thereby the state of stress is not only less sensitive to measurement errors but also involves less computation. This boundary conditions identification can be considered as an introduction of equilibrium condition and the property of linear elasticity to overcome the shortcomings of direct stress identification.

Application of HPC to Earthquake Hazard and Disaster Estimation

This paper presents the application of high performance computing to the earthquake disaster and hazard estimation, which is the first step taken to mitigate or reduce earthquake disasters. Capability computing is used in the seismic response analysis of important structures. A non-linear dynamic finite element method is developed to solve a high fidelity model of such structures. Explained are two examples of such capability computing. Capacity computing is used as new method of earthquake hazard and disaster evaluation for a densely populated urban area. Integrated earthquake simulation, which seamless analyzes the wave propagation pro- cess, the structure seismic response process, and the reaction process for earthquake disaster. Two examples of such integrated simulations are presented.

3D stress field tomography based on photoelasticity

Publisher Summary A new method for nondestructive measurement of arbitrary 3D stress state, using photoelasticity, has been developed. The new approach, load incremental approach, is an attempt to solve the nonlinear inverse problem of 3D photoelasticity by considering change in stress state for a load increment and linearizing the nonlinear governing equation. As long as the applied load increment is small and photoelastic images are taken with high resolution in load increment, this method works and can reconstruct arbitrary 3D stress state. A new approach for nondestructive measurement system for arbitrary 3D stress state, using photoelasticity, is studied. As a next step, a new experiment should be developed for the measurement of 3D stress state based on the proposed load incremental approach. The conclusions from the simulations are used as basic data for designing this measurement system.

Conversion between solid and beam element solutions of finite element method based on meta-modeling theory: development and application to a ramp tunnel structure

In this study, a new method for conversion of solid finite element solution to beam finite element solution is developed based on the meta-modeling theory which constructs a model consistent with continuum mechanics. The proposed method is rigorous and efficient compared to a typical conversion method which merely computes surface integration of solid element nodal stresses to obtain cross-sectional forces. The meta-modeling theory ensures the rigorousness of proposed method by defining a proper distance between beam element and solid element solutions in a function space of continuum mechanics. Results of numerical verification test that is conducted with a simple cantilever beam are used to find the proper distance function for this conversion. Time history analysis of the main tunnel structure of a real ramp tunnel is considered as a numerical example for the proposed conversion method. It is shown that cross-sectional forces are readily computed for solid element solution of the main tunnel structure when it is converted to a beam element solution using the proposed method. Further, envelopes of resultant forces which are of primary importance for the purpose of design, are developed for a given ground motion at the end.