Hiroshi Akiba

Large scale drop impact analysis of mobile phone using ADVC on Blue Gene/L

Existing commercial finite element analysis (FEA) codes do not exhibit the performance necessary for large scale analysis on parallel computer systems. In this paper, we demonstrate the performance characteristics of a commercial parallel structural analysis code, ADVC, on Blue Gene/L (BG/L). The numerical algorithm of ADVC is described, tuned, and optimized on BG/L, and then a large scale drop impact analysis of a mobile phone is performed. The model of the mobile phone is a nearly-full assembly that includes inner structures. The size of the model we have analyzed has 47 million nodal points and 142 million DOFs. This does not seem exceptionally large, but the dynamic impact analysis of a product model, with the contact condition on the entire surface of the outer case under this size, cannot be handled by other CAE systems. Our analysis is an unprecedented attempt in the electronics industry. It took only half a day, 12.1 hours, for the analysis of about 2.4 milliseconds. The floating point operation performance obtained has been 538 GFLOPS on 4096 node of BG/L.

Direct analysis method for probabilistic fracture mechanics

A new method for solving problems of probabilistic fracture mechanics (PFM) is proposed. A process of crack growth is reduced into an iterative integration equation with respect to the probabilistic distribution functions of crack geometry using approximate independence, which we have introduced. The integration equation which has a form of Stieltjes integral is solved by a numerical method. Some PFM problems are solved using the present method, and the results are compared with those by the MC method. Failure probabilities obtained from both calculations agree well. Execution time of the present method is shown to be remarkably short.

Seismic response analysis of full-scale boiling water reactor using three-dimensional finite element method

This paper presents the three-dimensional finite element seismic response analysis of full-scale boiling water reactor BWR5 at Kashiwazaki-Kariwa Nuclear Power Station subjected to the Niigata-ken Chuetsu-Oki earthquake that occurred on 16 July 2007. During the earthquake, the automatic shutdown system of the reactors was activated successfully. Although the monitored seismic acceleration significantly exceeded the design level, it was found that there were no significant damages of the reactor cores or other important systems, structures and components through in-depth investigation. In the seismic design commonly used in Japan, a lumped mass model is employed to evaluate the seismic response of structures and components. Although the lumped mass model has worked well so far for a seismic proof design, it is still needed to develop more precise methods for the visual understanding of response behaviors. In the present study, we propose the three-dimensional finite element seismic response analysis of the full-scale and precise BWR model in order to directly visualize its dynamic behaviors. Through the comparison between both analysis results, we discuss the characteristics of both models. The stress values were also found to be generally under the design value.

Recursive Distribution Method for Probabilistic Fracture Mechanics

This paper proposes a new method for Probabilistic Fracture Mechanics (PFM). The present method gives a recursive formula for a joint probability distribution function of crack geometry, which is obtained from random variables of the initial crack geometry and a deterministic time-evolution law of the variables. A numerical example of Light Water Reactor (LWR)s piping is solved by the present method, and the results are compared with those of the Monte Carlo (MC) method. It is clearly shown that both results agree sufficiently well, while CPU time of the present method is remarkably short.

Recursive distribution method for probabilistic structural integrity analysis

The Recursive Distribution (RD) method represents a time-evolution law of a joint distribution function of a random vector which follows a deterministic time-evolution law under the prescription of an initial random vector. The recursive formula for the distribution function can be decomposed into the absolutely continuous part and the singular part, which is the Lebesgue decomposition of the distribution function. In this paper, a theory of the Lebesgue decomposition of the recursive formula is discussed, and a numerical algorithm of the RD method is given. The present method is applied to a probabilistic fracture mechanics analysis for piping integrity problem. In order to calculate the probability of the unstable fracture of the pipe, it is needed to evaluate the singular part of the Lebesgue decomposition. A numerical example and its comparison with the MC method are presented.