Akemi Nishida

Development of APIs for Desktop Supercomputing

We developed the Script Generator API to support Grid users to develop their own Grid-enabled client application. The Script Generator API automatically generates a Grid-enabled workflow script needed to execute jobs on a Grid system. The Script Generator API enables users to develop their application with the complex job flow which cannot be generated using existing workflow tools. We implemented the Script Generator API in our Grid infrastructure and utilized it to the three-dimensional virtual plant vibration simulator. By developing Grid-enabled client application for the three-dimensional virtual plant vibration simulator, we confirmed the usability of the Script Generator API.

Development of Three-Dimensional Virtual Plant Vibration Simulator on Grid Computing Environment ITBL-IS/AEGIS

Center for computational science and e-systems of Japan Atomic Energy Agency is carrying out R&D in the area of extra large-scale simulation technologies for solving nuclear plant structures in its entirety. Specifically, we focus on establishing a virtual plant vibration simulator on interconnected supercomputers intended for seismic response analysis of a whole nuclear plant. The simulation of the whole plant is a very difficult task because an extremely large dataset must be processed. To overcome this difficulty, we have proposed and implemented a necessary simulation framework and computing platform. The simulation framework based on the computing platform has been applied to a linear elastic analysis of the reactor pressure vessel and cooling systems of a nuclear research facility, the HTTR. The simulation framework opens a possibility of new simulation technologies for building a whole virtual nuclear plant in computers for virtual experiments.Copyright

Load combination of aftershocks and tsunami for tsunami-resistant design

Occurrence of huge tsunami and numerous aftershocks are expected after a gigantic subduction earthquake occurs. Therefore, the important coastal structures (tsunami refuge buildings, seawalls and nuclear power plants etc.) must be designed against tsunami as well as ground shaking. In tsunami-resistant design, it is needed to consider that tsunami may arrive at the structure in a short time after the mainshock from the experience of 2011 Tohoku earthquake. When the action effects both from aftershocks and tsunami to the structure occur simultaneously, practically reasonable assessment of load combination from aftershocks and tsunami is needed. In order to treat the load combination problem reasonably, stochastic load combination technique can be used, which requires stochastic modeling of action effects from aftershocks and tsunami. Once the combined action effect is estimated reasonably, the reliability analysis follows, where load and resistance factors can be obtained under the condition that the conditional target reliability for a limit state function is given. Load combination method of aftershocks and tsunami on the tsunami-resistant design is demonstrated at some sites in Japan. Finally, load and resistance factor design format for the tsunami-resistant design is proposed.

Component-Wise Meshing Approach and Evaluation of Bonding Strategy on the Interface of Components for Assembled Finite Element Analysis of Structures

The finite elements are extensively utilized to solve various problems in engineering fields with the growth of computing technologies. However, there is a lack of methodology for analyses of huge assembled structures. The mechanics on the interface of each components, for instance, contact, bolt joint and welding in assembly is a key issue for important huge structure such as nuclear power plants. On the other hand, it is well known that as finite element models become large and complex, construction of detailed mesh becomes a bottleneck in the CAE procedures. To solve these problems, the authors would like to introduce component-wise meshing approach and bonding strategy on the interface of components. In order to assemble component-wise meshes, the penalty method is introduced not only to constrain the displacements, but also to introduce classical spring connection on the joint interface, although penalty method is claimed that it is not suitable for iterative solver. In this paper, the convergence performance of an iterative solver with penalty method is investigated and the detailed component-wise distributed computation scheme is described with numerical examples.

Wave Propagation Analysis of Piping Structures

It is becoming important to carry out detailed modeling procedures and analyses to better understand the actual phenomena. Because some accidents caused by high-frequency vibrations of piping have been recently reported, the clarification of the dynamic behavior of the piping structure during operation is imperative in order to avoid such accidents. The aim of our research is to develop detailed analysis tools and to determine the dynamic behavior of piping systems in nuclear power plants, which are complicated assemblages of different parts. In this study, a three-dimensional dynamic frame analysis tool for wave propagation analysis is developed by using the spectral element method (SEM) based on the Timoshenko beam theory. Further, a multi-connected structure is analyzed and compared with the experimental results. Consequently, the applicability of the SEM is shown.Copyright

A Parametric Study for the Seismic Response Analysis of a Nuclear Reactor Building by Using a Three-Dimensional Finite Element Model

Research and development of three-dimensional vibration simulation technologies for nuclear facilities is one mission of the Center for Computational Science and e-Systems of the Japan Atomic Energy Agency (JAEA). A seismic intensity of upper 5 was observed in the area of High-Temperature Engineering Test Reactor (HTTR) at the Oarai Research and Development Center of JAEA during the 2011 Tohoku earthquake. In this paper, we report a seismic response analysis of this earthquake using three-dimensional models of the HTTR building. We performed a parametric study by using uncertainty parameters. Furthermore, we examined the variation in the response result for the uncertainty parameters to create a valid 3D finite element model.Copyright

Development of a New Mathematical Framework for Seismic Probabilistic Risk Assessment for Nuclear Power Plants – Plan and Current Status –

After the severe accident in Fukushima Daiichi Nuclear Power Station, safety improvement and enhancement have been installed. In midterm and long term, continuous efforts to improve and enhance safety are required, and technical basis and fundamentals are needed to achieve them.

Influence of Differences Between Seismic Safety Evaluation Methods for Equipment and Piping of a Nuclear Facility

The objective of this research was to investigate the influence of differences between methods for evaluating the seismic safety of the equipment and piping of a nuclear facility. For the input ground motion, one wave was chosen from among 200 waves of input ground motions of maximum acceleration of 700–1100 cm/s2 created for the Oarai District of the Ibaraki Prefecture. Seismic safety evaluations were performed using the conventional method, which relies on floor response spectrum data, and using the multi-input method. The differences between the two methods were summarized. The target equipment and piping system were cooling systems in a model plant. It was found that the response predicted by the multi-input method was approximately half of the response predicted by the conventional method. The third trial evaluation method using the floor response of a three-dimensional building model as input was also reported.Copyright

Structural Analysis for Assembly by Integrating Parts

Almost all industrial products are assembled from multiple parts, and this is true for all sizes of products. As an example, a nuclear facility is a large structure consisting of more than 10 million components. This paper discusses a method to analyze an assembly by gathering data on its component parts. Gathered data on component may identify ill conditioned meshes for connecting surfaces between components. These ill meshes are typified by nodal point disagreement in finite element discretization. A technique to resolve inconsistencies in data among the components is developed. By using this technique, structural analysis for an assembly can be carried out, and results can be obtained by the use of supercomputers, such as the K computer. Numerical results are discussed for components of the High Temperature Engineering Test Reactor of the Japan Atomic Energy Agency.© 2014 ASME

Current Status and Future Direction of Full-Scale Vibration Simulator for Entire Nuclear Power Plants

CCSE/JAEA promotes the research and development of the three- dimensional vibration simulator for seismic evaluation of a nuclear power plant (NPP) to further improve reliability of seismic safety of NPPs. We have applied this simulator to elastic analysis of the reactor pressure vessel and cooling systems of a nuclear research facility called the High Temperature engineering Test Reactor (HTTR). We have also developed the capability to analyze seismic fluid phenomena in the virtual vibration simulator by implementing OpenFOAM on a supercomputer at JAEA in order to analyze the operating conditions and transitional phenomena of an NPP. We have implemented a function to simulate two-phase turbulence. As a first step investigated the effect of turbulence on the dynamics of three-dimensional dam break flow on the basis of the incompressible Reynolds-averaged Navier-Stokes (RANS) equations with the volume of fluid (VOF) function. We have found that when the Launder-Gibson (LG) model is used, the tip velocity over the ground and impact pressure on the vertical wall are in good agreement with experimental results.