Journal of the Korean Society of Tribologists and Lubrication Engineers, 2014
A more accurate expression for effective viscosity is obtained using a linear regression of the d... more A more accurate expression for effective viscosity is obtained using a linear regression of the data from Fukui-Kaneko's model, which are obtained through numerical calculations based on the linearized Boltzmann equation. Veijola and Turowski's expression is adopted as a base function for effective viscosity. The four coefficients in that equation are optimized, and sensitivity analysis is conducted for these coefficients. The results show that the coefficient for the first-order Knudsen number is the most accurate, whereas the coefficient in the exponential of the Knudsen number is the least accurate compared with Fukui-Kaneko's results. The expression for effective viscosity is accurate within 0.02% rms of Fukui-Kaneko's results for the inverse Knudsen numbers from 0.01 to 100 and surface accommodation coefficients ranging from 0.7 to 1.
Transactions of the Society of Information Storage Systems, 2015
An archive system is designed to store data for a long time without loss. However, many important... more An archive system is designed to store data for a long time without loss. However, many important factors such as temperature, dust, vibration, and humidity must be considered to design a successful archive system. Read/write devices, for example optical disk drives(ODDs), in an archive system generate heat while they are in operation. Fans are usually used to remove heat but the air flow accompanies dust into the system result in system failure. In this study, an archive system with six ODDs is chosen as an analysis model and flow together with temperature distributions are computed using a CFD simulation package. Flow analysis is focused on four cooling fans at the rear panel and temperature distribution is studied for various cases of fan operation. From the temperature point of view, fans give significant effects on 4 th to 6 th ODDs compared to the 1 st to 3 rd ODDs. Also, it is noticed which fan is the most important as far as cooling is concerned.
APMRC 2004 Asia-Pacific Magnetic Recording Conference, 2004.
ABSTRACT In this paper, the aerodynamically dissipated power loss in hard disk drives is studied.... more ABSTRACT In this paper, the aerodynamically dissipated power loss in hard disk drives is studied. The effects of rotational speed and form factor on the dissipation power loss are analyzed and compared to experimental results using 3.5", 2.5" and 1" disks. The torque coefficients for laminar and turbulent models are derived for various enclosure conditions. We implement experiments using a vacuum chamber and calculate frictional power loss by disk rotation. For a 1-inch disk, the power dissipation agrees well with the laminar model, which is inversely proportional to the half power of Reynolds number. The frictional power consumption by 3.5-inch disk is similar to the air turbulent model. Finally, we propose the drive enclosure geometry to minimize the aerodynamic power loss based on the experimental results
The idea of a curved stabilizer with damping orifices is applied to the high speed rotating flexi... more The idea of a curved stabilizer with damping orifices is applied to the high speed rotating flexible optical disk system in order to reduce the disk deflection and the axial run-out of the disk. A track of orifices is drilled along the edge of a curved annular stabilizer. The effects of the diameter and length of each orifice, number of orifices, and radial position of the orifices on the reduction of axial runout of the disk are investigated experimentally together with the effects of the inner radius for the air flow, initial gap height, and rotational speed. The experimental results showed that the curved stabilizer with orifices can reduce the axial run-out of the disk at 10,000 rpm within 0.010 mm over the entire span of the disk.
This is a welcome study, and a difficult one, as it bridges two disciplines and attempts to build... more This is a welcome study, and a difficult one, as it bridges two disciplines and attempts to build an intellectual framework for the understanding of a potential new class of lubricants. The authors deserve our congratulations and our gratitude. From Figs. 2(c) and 3(c), one sees, as the authors also point out, that the load-bearing pressure of a liquid crystal is higher than that of a Newtonian liquid, and that this difference is quite large. Is it possible to estimate whether this increase in load capacity can extend the hydrodynamic regime to significantly lower velocities as we had speculated in the referred paper? I would be grateful if the authors helped us relate the calculations to observable reality. In particular, how realistic do the authors consider the number of layers they calculated, or rather, what fluid film thickness do they represent? What conclusions can one draw on the friction coefficient? Finally, would the authors specify what further experiments would be useful to guide further theoretical progress or, in other words, what information is required?
ABSTRACT The present study is a numerical simulation about the dynamics of a flexible disk couple... more ABSTRACT The present study is a numerical simulation about the dynamics of a flexible disk coupled to thin air film and rotating close to a rigid rotating wall. The idea of a flexible disk rotating in a close proximity of a rigid rotating wall is introduced and studied with two new types of flat stabilizers, co-rotating and counter-rotating flat stabilizers, besides the well-known fixed-stabilizer type which has been studied extensively in earlier works. In the present study, the flexible 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 cell centered finite volume method (FVM) and solved numerically with the 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 effect of inertia and coriollis forces on the disk displacement and air-film pressure is studied, also the dependence of these forces on the rotation speed, initial gap size and inlet-hole radius is investigated. A transient numerical code is developed to compare the stability boundaries for 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.
ABSTRACT In the present work, the behavior of a flexible disk rotating close to a fixed, a co-rot... more ABSTRACT 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. (C) 2009 The Japan Society of Applied Physics
In this paper, we present a numerical study about the dynamics of a flexible disk rotating close ... more 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.
ABSTRACT The air flow field around a conical type solid immersion lens (SIL) system is simulated ... more ABSTRACT The air flow field around a conical type solid immersion lens (SIL) system is simulated numerically and confirmed with experiment using a micro-particle image velocimetry (PIV) system. It is found that the back-flow from the downstream of the SIL is a major candidate for the contamination of the SIL. Five modifications are proposed to suppress the particle conveying mechanism, the back-flow. Among these modifications a method using two flow-bypasses reduces the back-flow most effectively, which connects the top surface of the SIL system and two side-holes of the lens holder where the static pressure is the minimum.
Transactions of the Society of Information Storage Systems, 2011
In the last couple of years, the flexible optical disk(FOD) system that consists of a thin polyca... more In the last couple of years, the flexible optical disk(FOD) system that consists of a thin polycarbonate(PC) film of 95 µm thick, a rigid stabilizer, and a high speed spindle motor has been spotlighted as the next-generation optical system for archival use of digital data. The air film between the rotating disk and stabilizer provides a means for damping out the lateral disk vibrations. However, its damping-capability drops significantly as the rotational speed of the disk exceeds a specific limit and, eventually, the disk vibration propagates inward causing the whole span of the disk exhibits large vibration amplitudes. Based on the numerical simulations as well as the experimental results, the present work aims to evaluate the damping coefficient of the air-film near the outer region of the disk where the capillary type orifices are applied to the edge of the curved stabilizer.
Journal of the Korean Society of Tribologists and Lubrication Engineers, 2014
A more accurate expression for effective viscosity is obtained using a linear regression of the d... more A more accurate expression for effective viscosity is obtained using a linear regression of the data from Fukui-Kaneko's model, which are obtained through numerical calculations based on the linearized Boltzmann equation. Veijola and Turowski's expression is adopted as a base function for effective viscosity. The four coefficients in that equation are optimized, and sensitivity analysis is conducted for these coefficients. The results show that the coefficient for the first-order Knudsen number is the most accurate, whereas the coefficient in the exponential of the Knudsen number is the least accurate compared with Fukui-Kaneko's results. The expression for effective viscosity is accurate within 0.02% rms of Fukui-Kaneko's results for the inverse Knudsen numbers from 0.01 to 100 and surface accommodation coefficients ranging from 0.7 to 1.
Transactions of the Society of Information Storage Systems, 2015
An archive system is designed to store data for a long time without loss. However, many important... more An archive system is designed to store data for a long time without loss. However, many important factors such as temperature, dust, vibration, and humidity must be considered to design a successful archive system. Read/write devices, for example optical disk drives(ODDs), in an archive system generate heat while they are in operation. Fans are usually used to remove heat but the air flow accompanies dust into the system result in system failure. In this study, an archive system with six ODDs is chosen as an analysis model and flow together with temperature distributions are computed using a CFD simulation package. Flow analysis is focused on four cooling fans at the rear panel and temperature distribution is studied for various cases of fan operation. From the temperature point of view, fans give significant effects on 4 th to 6 th ODDs compared to the 1 st to 3 rd ODDs. Also, it is noticed which fan is the most important as far as cooling is concerned.
APMRC 2004 Asia-Pacific Magnetic Recording Conference, 2004.
ABSTRACT In this paper, the aerodynamically dissipated power loss in hard disk drives is studied.... more ABSTRACT In this paper, the aerodynamically dissipated power loss in hard disk drives is studied. The effects of rotational speed and form factor on the dissipation power loss are analyzed and compared to experimental results using 3.5", 2.5" and 1" disks. The torque coefficients for laminar and turbulent models are derived for various enclosure conditions. We implement experiments using a vacuum chamber and calculate frictional power loss by disk rotation. For a 1-inch disk, the power dissipation agrees well with the laminar model, which is inversely proportional to the half power of Reynolds number. The frictional power consumption by 3.5-inch disk is similar to the air turbulent model. Finally, we propose the drive enclosure geometry to minimize the aerodynamic power loss based on the experimental results
The idea of a curved stabilizer with damping orifices is applied to the high speed rotating flexi... more The idea of a curved stabilizer with damping orifices is applied to the high speed rotating flexible optical disk system in order to reduce the disk deflection and the axial run-out of the disk. A track of orifices is drilled along the edge of a curved annular stabilizer. The effects of the diameter and length of each orifice, number of orifices, and radial position of the orifices on the reduction of axial runout of the disk are investigated experimentally together with the effects of the inner radius for the air flow, initial gap height, and rotational speed. The experimental results showed that the curved stabilizer with orifices can reduce the axial run-out of the disk at 10,000 rpm within 0.010 mm over the entire span of the disk.
This is a welcome study, and a difficult one, as it bridges two disciplines and attempts to build... more This is a welcome study, and a difficult one, as it bridges two disciplines and attempts to build an intellectual framework for the understanding of a potential new class of lubricants. The authors deserve our congratulations and our gratitude. From Figs. 2(c) and 3(c), one sees, as the authors also point out, that the load-bearing pressure of a liquid crystal is higher than that of a Newtonian liquid, and that this difference is quite large. Is it possible to estimate whether this increase in load capacity can extend the hydrodynamic regime to significantly lower velocities as we had speculated in the referred paper? I would be grateful if the authors helped us relate the calculations to observable reality. In particular, how realistic do the authors consider the number of layers they calculated, or rather, what fluid film thickness do they represent? What conclusions can one draw on the friction coefficient? Finally, would the authors specify what further experiments would be useful to guide further theoretical progress or, in other words, what information is required?
ABSTRACT The present study is a numerical simulation about the dynamics of a flexible disk couple... more ABSTRACT The present study is a numerical simulation about the dynamics of a flexible disk coupled to thin air film and rotating close to a rigid rotating wall. The idea of a flexible disk rotating in a close proximity of a rigid rotating wall is introduced and studied with two new types of flat stabilizers, co-rotating and counter-rotating flat stabilizers, besides the well-known fixed-stabilizer type which has been studied extensively in earlier works. In the present study, the flexible 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 cell centered finite volume method (FVM) and solved numerically with the 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 effect of inertia and coriollis forces on the disk displacement and air-film pressure is studied, also the dependence of these forces on the rotation speed, initial gap size and inlet-hole radius is investigated. A transient numerical code is developed to compare the stability boundaries for 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.
ABSTRACT In the present work, the behavior of a flexible disk rotating close to a fixed, a co-rot... more ABSTRACT 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. (C) 2009 The Japan Society of Applied Physics
In this paper, we present a numerical study about the dynamics of a flexible disk rotating close ... more 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.
ABSTRACT The air flow field around a conical type solid immersion lens (SIL) system is simulated ... more ABSTRACT The air flow field around a conical type solid immersion lens (SIL) system is simulated numerically and confirmed with experiment using a micro-particle image velocimetry (PIV) system. It is found that the back-flow from the downstream of the SIL is a major candidate for the contamination of the SIL. Five modifications are proposed to suppress the particle conveying mechanism, the back-flow. Among these modifications a method using two flow-bypasses reduces the back-flow most effectively, which connects the top surface of the SIL system and two side-holes of the lens holder where the static pressure is the minimum.
Transactions of the Society of Information Storage Systems, 2011
In the last couple of years, the flexible optical disk(FOD) system that consists of a thin polyca... more In the last couple of years, the flexible optical disk(FOD) system that consists of a thin polycarbonate(PC) film of 95 µm thick, a rigid stabilizer, and a high speed spindle motor has been spotlighted as the next-generation optical system for archival use of digital data. The air film between the rotating disk and stabilizer provides a means for damping out the lateral disk vibrations. However, its damping-capability drops significantly as the rotational speed of the disk exceeds a specific limit and, eventually, the disk vibration propagates inward causing the whole span of the disk exhibits large vibration amplitudes. Based on the numerical simulations as well as the experimental results, the present work aims to evaluate the damping coefficient of the air-film near the outer region of the disk where the capillary type orifices are applied to the edge of the curved stabilizer.
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