A numerical study of the oil-lubricated herringbone-grooved journal bearing is presented for the case of eight circular-profile grooves on the sleeve surface. The governing differential equation derived from the mass balance is solved by using the finite difference method. Some of the groove geometries are constrained because of the groove forming processes. Optimal values for various bearing parameters are obtained to maximize the radial force and to improve the stability characteristics. Results are compared with the plain and rectangular-profile grooved journal bearings. Radial force, attitude angle, stiffness and damping coefficients, and stability map are given for optimal configurations.
In this paper, we present a numerical study about the dynamics of a flexible disk rotating close to a rigid rotating wall. Two new types of flat stabilizers, co-rotating and counter-rotating flat stabilizers, are introduced besides the well-known fixedstabilizer type which has been studied extensively. The disk is modeled using linear plate theory and the air flow between the flexible disk and the rigid wall is modeled using Navier-Stokes and continuity equations. The flow equations are discretized using finite volume method (FVM) and solved numerically with semi-implicit method for pressure-linked equations (SIMPLE) algorithm, while the spatial terms in the disk model are discretized using finite difference method (FDM) and time integration is performed using fourth-order Runge-Kutta method. The transient numerical simulation is performed to compare the stability boundaries of the different types of flat-stabilizer at a wide range of circumferential mode numbers. The numerical results showed an improved stability of the flexible disk when rotating close to a counter-rotating flat-stabilizer compared with co-rotating and fixed flat-stabilizers.
Higher data storage capacities and higher data transfer rates will be required in next-generation information storage devices. However, there is a limit to the rotational speeds of conventional disk structures. Hence, conventional disks will not be able to achieve high data transfer rates of over 250 Mbps that is required for next-generation storage devices. To increase the data transfer rate of a disk, flexible optical disks have been studied with the goal of stable rotation at a high speed, using a stabilizer to reduce disk oscillations. If a flexible optical disk is implemented in a near-field recording (NFR) system, simultaneous high data transfer rates and high-density recording should be possible. In an NFR system, it is very important to maintain the gap between the solid immersion lens (SIL) and the disk at distances below tens of nanometers. In this study, to simultaneously achieve high data storage capacity and high data transfer rate, we propose an improved gap servo control system for an SIL-based NFR system with a flexible optical disk. To enable robust control at a high rotational speed, a repetitive controller was designed and applied to the NFR servo algorithm. In both simulation and experiment, the newly designed gap servo controller stably maintained the gap distance in the SIL-based NFR system using a flexible optical disk.
In the present work, the behavior of a flexible disk rotating close to a fixed, a co-rotating, and a counter rotating flat-stabilizers in open air is investigated both experimentally and numerically. The Navier-Stokes equations along with the continuity equation representing the flow in the air-film are discretized using the finite volume method and solved numerically with the SIMPLE algorithm. An experimental test-rig is designed to investigate the effects of the rotation speed, the initial gap height and the inlet-hole size on the flexible disk displacement and its vibration amplitude. Finally, a comparison between the experimental and the numerical results is made.
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