Masaaki Hayashi

Read and write characteristics of Co-Ni-Zr-M/Cr thin films for longitudinal recording

The magnetic and crystallographic properties and read and write characteristics of sputtered C/Co-Ni-Zr/Cr and C/Co-Ni-Zr-M/Cr (M=V, Nb, Ta, Cr, Mo, W, Cu, Si, Al, Ru and Pt) thin films are investigated. The saturation magnetic flux density B/sub s/ of all C/Co-Ni-Zr-M/Cr films decreases as the amount of additive element increases. The coercivity of C/Co-Ni-Zr-Cr/Cr and C/Co-Ni-Zr-Pt/Cr is higher than that of C/Co-Ni-Zr/Cr films with comparable B/sub s/. The larger the perpendicular anisotropy K/sub p/ and the smaller the anisotropy constant K/sub n/, the lower the media noise N and the higher the S/N ratio. The reduction of K/sub n/ and N are strongly connected to grain separation and grain size reduction. The larger the B/sub s/.tmag, the higher E/sub II/ and N and the lower D/sub 50/ and the S/N ratio. All films except those with Si, Ru, and Pt additives have large K/sub p/, a small K/sub n/, and a high S/N ratio. In particular, C/Co-Ni-Zr-M/Cr (M=Cr, Mo, W, and Al) disks have a better S/N ratio and D/sub 50/ than C/Co-Ni-Zr/Cr disks. >

Magnetic and crystallographic properties of sputtered Co-Ni-Zr films on Cr, Mo and W underlayer

Read and write characteristics and magnetic and crystallographic properties of sputtered Co-Ni-Zr on Cr, Mo, and W underlayers are investigated. The crystal grains of the underlayer and the magnetic layer are rice-like and consist of 2 to 10 columnar subgrains. The coercivity of composite films depends on the size of subgrains, reaching a maximum when the magnetic crystal size is about 40 nm. Media noise is proportional to the square root of the length of the rice-like grains; this can be explained by particle-noise theory. >

Synchronized Vibrations of a Circular Cylinder in Cross Flow at Supercritical Reynolds Numbers

Synchronized vibrations of a circular cylinder in a water cross flow at supercritical Reynolds numbers were measured. Turbulence intensities were varied to investigate the effect of the Strouhal number on the synchronization range. Self-excited vibration in the drag direction due to symmetrical vortex shedding began only when the Strouhal number was about 0.29, at a reduced velocity of 1.1. The reduced velocities at the beginning of lock-in vibrations caused by Karman vortex shedding decreased from 1.5 to 1.1 in the drag direction and from 2.7 to 2.2 in the lift direction, as the Strouhal number increased from 0.29 to 0.48.

Elaboration of the System Based Code Concept — Activities in JSME and ASME: (1) Overview

This paper is the first one of the series of four papers that describe ongoing activities in the Japan Society of Mechanical Engineers (JSME) and the American Society of Mechanical Engineers (ASME) on the elaboration of the System Based Code (SBC) concept aiming at its application to nuclear structural codes and standards. This paper includes a brief introduction to the SBC concept and the technical features of structural evaluation methodologies that are being developed for use in the SBC concept; Load and Resistance Factor Design based reliability assessment methods and the JSME guidelines for reliability evaluation of static components of sodium-cooled fast reactors. Also described is the ongoing collaboration of JSME and ASME at the Joint Task Group for System Based Code established in the ASME Boiler and Pressure Vessel Code Committee which is developing alternative rules for ASME B&PV Code Section XI Division 3, inservice inspection requirements for liquid metal reactor components.Copyright

Elaboration of the System Based Code Concept — Activities in JSME and ASME: (2) Development of Evaluation Tools Based on LRFD

In the System Based Code (SBC), a reliability target is defined according to the importance of components (risk and/or failure probability), and the grade of material, design, manufacture and maintenance are chosen to satisfy the reliability target. Therefore, a reliability assessment of the components plays an important role in the concept of SBC. In the reliability assessment guidelines of SBC under development in JSME, the Load and Resistance Factor Design (LRFD) method and the Monte Carlo method will be applied to reliability assessment. Along with a development plan of the SBC, examination of the target reliability according to the importance of components and preparation of the LRFD methods and assessment of partial safety factor for some failure modes are underway. Until now, the LRFD methods have been developed for burst due to internal pressure, plastic collapse due to membrane and bending stress, fatigue, plastic collapse of a pipe having a circumferential crack, and buckling of a thin wall cylinder. This paper describes the action plans for the development of the reliability assessment methods and examination results till date.Copyright

Analytical Evaluation of Unsteady Thermal Hydraulic Characteristics in Shell and Tube Heat Exchangers

Many shell & tube heat exchangers are used in nuclear power plants. Unsteady thermal hydraulic phenomena have been studied in shell & tube heat exchangers to improve their safety and reliability and to extend their lifetime based on experience obtained from long periods of plant operation. We investigated unsteady flow in shell & tube heat exchangers by using computational fluid dynamics (CFD) analyses. The inlet flow on the shell side was separated and flow in several directions. A large part of the flow crossed over the tube bundle, and some parts of the flow took two circuitous roots (up and down) along the inner surface of the shell. Separated circuitous flows collided again where a baffle plate had been cut off. A pair of symmetric vortexes could be seen in that location. Some parts of the circuitous flow moved backwards into the tube bundle due to vortexes. These vortexes were unstable and changed their size and location. A pair of vortexes changed from symmetric to asymmetric. As a result, the direction of flow in the tube bundle near the vortexes changed continuously. Variations in vortexes simulated through CFD analyses could also be seen in tests on the actual size. Fluid temperature fluctuations around tubes were also evaluated through CFD analyses. Unsteady phenomena with changes from symmetric to asymmetric vortexes could be observed in the shell & tube heat exchanger and were simulated through CFD analyses with a detached eddy simulation (DES) turbulence model.© 2006 ASME