Experimental Study on Flow-Induced Disk Flutter Dynamics by Measuring the Pressure Between Disks

2006 ◽  
Vol 129 (3) ◽  
pp. 368-375 ◽  
Author(s):  
Shigenori Takada ◽  
Norio Tagawa ◽  
Atsunobu Mori ◽  
Yoshiaki Mizoh ◽  
Masaru Nakakita
Keyword(s):  
Pressure Fluctuation ◽  
High Speed ◽  
Static Pressure ◽  
Dynamic Pressure ◽  
Hard Disk Drives ◽  
Laser Doppler Vibrometer ◽  
Disk Drives ◽  
Flow Induced Vibrations ◽  
The Mean ◽  
Disk Flutter

It is important to clarify the characteristics of flow-induced vibrations in hard disk drives in order to achieve an ultrahigh magnetic recording density. In particular, it is necessary to reduce the flow-induced disk vibrations referred to as disk flutter. This paper describes the correlation between the disk vibration amplitude and the pressure fluctuation between a pair of high-speed corotating disks. It also reveals the effects of the arm thickness and arm shape on the disk vibrations and the static pressure between the disks. The disk vibrations were measured using a laser Doppler vibrometer (LDV). The static pressure downstream of the arm between a pair of narrow disks was measured by a method in which a side-hole needle was used as a measurement probe. In addition, the direction of air flow along the trailing edge of the arm was measured using a hot-wire anemometer. The experimental results revealed that the arm inserted between the disks suppresses the disk vibrations. However, the shape and thickness of the arm did not quantitatively affect the disk vibrations. The root-mean-square (RMS) static pressure fluctuation downstream of the arm decreased remarkably, whereas the mean static pressure increased when the arm was inserted between the disks. Furthermore, the circumferential variations in both the RMS and mean static pressures reduced when the arm was inserted. Therefore, it is suggested that the disk vibrations are excited by an increase in the static pressure fluctuation, mean dynamic pressure, and circumferential variation in the static pressure between the disks. Consequently, the disk vibrations can be suppressed by inserting the arm or a spoiler.

Narrowband Performance of Active Control on Flow-Induced Vibrations Inside Hard Disk Drives

2013 ◽  
Author(s):  
Hequn Min ◽  
Xiaoyang Huang ◽  
Qide Zhang ◽  
Xin Xia
Keyword(s):  
Active Control ◽  
Hard Disk Drives ◽  
Laser Doppler Vibrometer ◽  
Hard Disk ◽  
Disk Drive ◽  
Modal Testing ◽  
Disk Drives ◽  
Feedback Error ◽  
Flow Induced Vibrations ◽  
Narrow Bands

This paper presents an experimental study of digital narrowband active control on the flow-induced vibrations (FIV) on the head gimbals assembly (HGA) in a working hard disk drive (HDD). Firstly, the modal testing on the HDD was carried out, in which the disk modes were analyzed with a 1-D laser Doppler vibrometer (LDV) and the HGA vibration modes with a 3-D LDV. Secondly, a digital feedback control close-loop was implemented in experiments to suppress the FIV spectrum peaks on the HGA. In this close-loop, the HGA vibrations detected by the LDV were used as feedback error signals, then the signals was passed through a digital controller to generate feedback signals to drive a piezoelectric disk to actuate feedback acoustic pressure around the HGA. Active control experiments were conducted in narrow bands on five principal peaks in the HGA off-plate vibration spectrum, around 1256Hz, 1428Hz, 2141Hz, 2519Hz and 3469Hz, respectively. It is shown that distinct suppression of at least 10 dB can be achieved on all these HGA vibration peaks.

Pressure Fluctuations and Flow-Induced Vibration Measurements in a Hard Disk Drive under Different Rotation Speeds

2012 ◽  
Vol 197 ◽  
pp. 292-296 ◽  
Author(s):  
He Qun Min ◽  
Xiao Yang Huang ◽  
Qi De Zhang
Keyword(s):  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
Hard Disk Drives ◽  
Experimental Studies ◽  
Laser Doppler Vibrometer ◽  
Hard Disk ◽  
Disk Drive ◽  
Disk Drives ◽  
Flow Induced Vibration ◽  
Causal Nexus

Flow-induced vibration (FIV) of a head gimbals assembly (HGA) in hard disk drives (HDDs) limits the positioning accuracy of magnetic head in the HGA for higher HDD magnetic recording density. The pressure fluctuations characterize turbulent fluctuations exciting the HGA off-track vibration (HGA-OTV). In this paper, experimental studies have been carried out to investigate the spectrum characteristics correspondence between pressure fluctuations around an HGA and the simultaneous HGA-OTV under different HDD rotation speeds. A practical and effective experimental setup has been implemented to enable the simultaneous measurements on both the pressure fluctuation and HGA-OTV signals, where pressure fluctuations are measured with a pressure transducer through a small hole on the HDD top cover and the direct HGA-OTV signals are detected through a laser Doppler vibrometer. Results under conditions of three different HDD rotation speeds of 7200, 9000, 10800 rpm have been investigated and compared. It is shown that the HGA off-track vibration spectra are highly associated with those of the pressure fluctuations in terms of principal peaks in four frequency bands around 1.8 kHz, 2.5-3.5 kHz, 7-7.5 kHz and 11.5-12.5 kHz. With increasing HDD rotation speed, it is shown that the spectrum magnitudes of both the pressure fluctuation and the HGA off-track vibration increase correspondingly, while the principal peak positions in spectra of either pressure fluctuation or the HGA off-track vibration always hold the line. This study demonstrates a causal nexus from the pressure fluctuation to the HGA off-track vibration and suggests the feasibility of controlling the HGA-OTV through suppression of pressure fluctuations around the HGA.

Stress and Vibration Analysis of Motor Back Plate in HDD

2011 ◽  
Vol 275 ◽  
pp. 97-100 ◽  
Author(s):  
Geun Sub Heo ◽  
Oh Hyun Kang ◽  
Cheol Woo Park ◽  
Sang Ryong Lee ◽  
Choon Young Lee
Keyword(s):  
Resonant Frequency ◽  
High Speed ◽  
Vibration Mode ◽  
Hard Disk Drives ◽  
Mode Analysis ◽  
Design Parameters ◽  
Disk Drives ◽  
Ansys Software ◽  
Back Plate ◽  
Plate Shape

In the present study, we have simulated stress characteristics and vibration modes in the back plate of head-stack driving motor of 2.5 inch small sized hard disk drives (HDDs). The magnets in head-stack driving motor have large magnetic fields, and therefore, the resulting large force may induce fracture and deformation in the back plate of the motor. Since the high-speed motion of head-stack motor generates high frequency vibration, we analyzed the vibration mode to avoid resonant frequency. ANSYS software was used in this study to check the deformation of back plate with the following design parameters: thickness of plate, the number of support beams, and the width of support beams. From the vibration mode analysis, we obtained a stable plate shape whose operating frequency is off the resonant frequency.

Characterization of Dynamics of Unstable Fuel-Rich Flame

2021 ◽  
Author(s):  
M. Weber ◽  
J. Song ◽  
J. G. Lee
Keyword(s):  
Heat Release ◽  
Pressure Fluctuation ◽  
Emission Intensity ◽  
Velocity Fluctuation ◽  
Dynamic Pressure ◽  
Phase Delay ◽  
Thermoacoustic Instability ◽  
Band Emission ◽  
Unstable Combustion ◽  
The Mean

Abstract The flame dynamics during unstable combustion occurring in a model gas turbine combustor under fuel-rich conditions analogous to idle and sub-idle conditions in an aero-engine is characterized by simultaneous measurement of flame emissions and dynamic pressure fluctuation as well as high-speed imaging. Pressure fluctuation during unstable combustion causes linearly increasing velocity fluctuation at the combustor inlet. The fluctuation level of CH*-band emission which is mainly from soot linearly increases with respect to the combustor inlet velocity fluctuation up to ∼40% of mean velocity while that of OH*-band emission which is from OH* is non-linear. Highspeed imaging shows that the OH*-band emission fluctuation occurs mainly near the dump plane but the CH*-band emission fluctuation occurs downstream of it. When the pressure fluctuation is more than 1% of mean pressure, there exists an almost constant phase delay between emissions from OH*- and CH*-band and dynamic pressure fluctuations and the phase delay satisfies the Rayleigh criterion. In addition, the Rayleigh integral made over the whole flame and one period of oscillation of thermoacoustic instability becomes positive. These may suggest either OH*- or CH*-band emission can be used as a representation of heat release. However, the observations that the mean OH*-band emission intensity increases but the mean CH*-band emission intensity does not as the mean equivalence ratio increases and the fluctuation level of emission in OH*-band increases but that in CH*-band emission does not as the pressure fluctuation level increases strongly suggest that the emission from OH*-band should be considered as a representation of heat release for sooty flames under the employed operating condition in this study.

Pulsatile and Steady Pressure-Flow Relations in the Vascular Bed of the Hind Leg of the Dog

1956 ◽  
Vol 185 (2) ◽  
pp. 351-354 ◽  
Author(s):  
James E. Randall ◽  
Ralph W. Stacy
Keyword(s):  
Measurement Accuracy ◽  
Static Pressure ◽  
Dynamic Pressure ◽  
Flow Diagram ◽  
Pressure Flow ◽  
Pulsatile Pressure ◽  
Instantaneous Pressure ◽  
Flow Diagrams ◽  
The Mean ◽  
The One

Instantaneous pressure and flow in the femoral artery of the dog were recorded under steady and pulsatile pressure conditions. Static pressure-flow diagrams and dynamic pressure-flow diagrams over the pulse pressure range at different points in the cardiac cycle were constructed. A comparison was made of the flow corresponding to a) normal pulsatile conditions, and b) static pressures equal to the mean of the pulsatile pressures. The static pressure-flow diagrams were consistent with those described by other workers, and were essentially linear in the ranges studied. Changing from steady to pulsating pressures altered the flow from 40.4 ml/min. to 40.9 ml/min. This difference was less than the measurement accuracy of the flow, although statistical analysis indicated significance to 1%. The dynamic pressure-flow diagram appeared as a ‘loop,’ the shape of which indicated that in 12 of 13 animals, the system was mass controlled and the heart rate was higher than the resonant frequency. In the one exception, the phase angle was negligible and the system was apparently in resonance.

Focusing Actuator for Magneto-optical Disk Drives

1993 ◽  
Vol 5 (4) ◽  
pp. 326-331
Author(s):  
Junichi Ichihara ◽  
◽  
Koichi Tezuka ◽  
Akihiko Makita
Keyword(s):  
High Speed ◽  
Hard Disk Drives ◽  
Higher Order ◽  
Optical Disk ◽  
Leaf Spring ◽  
Disk Drives ◽  
Mechanical Resonance ◽  
High Speed Rotation ◽  
Speed Rotation ◽  
And Performance

Magneto-optical disk drives have some disadvantages compared with hard disk drives such as low access speed and low data rate. A small-light optical head and high speed rotation of the drive would improve the performance , as well as achieving over write. This paper details the development of a small-light focusing actuator, which can be used in high speed rotation of disks and make optical heads small and thin. It discusses the actuator suspension which raises the frequencies of higher order mechanical resonance. It also includes a parallel leaf spring suspension with the visco-elastic damping layer. It experimentally evaluates the vibration characteristics. Results show that the frequencies of higher order mechanical resonance are above 50kHz. The actuator is driven by a novel moving coil motor which makes the moving part thin and stiff. This paper describes the design and performance of the motor.

scholarly journals In Situ Measurement of Seeking Speed and Seeking Induced Head-Disk Interface Instability in Hard Disk Drives

2015 ◽  
Vol 2015 ◽  
pp. 1-7
Author(s):  
Yu Wang ◽  
Xiongfei Wei ◽  
Yanyang Zi ◽  
Kwok-Leung Tsui
Keyword(s):  
High Speed ◽  
Hard Disk Drives ◽  
Laser Doppler Vibrometer ◽  
Voice Coil Motor ◽  
In Situ Measurement ◽  
Head Disk Interface ◽  
Magnetic Head ◽  
Interface Instability ◽  
Disk Interface

This paper investigated the instability of head-disk interface caused by the voice coil motor (VCM) end crashing the crash stop during the seeking of magnetic head. To make the whole process of that clear, an in situ measurement method based on maximum likelihood estimation and extended Kalman filter for seeking speed at component level was developed first and was then calibrated by a high speed camera. Given a crash between VCM end and crash stop that may be a consequence of the continuous increasing seeking speed, the seeking speed was carefully controlled by using our developed method to find a critical value that may induce vigorous head-disk interface instability. Acoustic emission sensor and laser Doppler vibrometer were used to capture the transient dynamic behaviors of magnetic head when the crash is happening. Damage analysis and mode identification were carried out to reveal the relationship between the damage patterns on disk surface and head dynamics. The results of this study are helpful to optimize the track seeking profile during the HDD operation, as well as the design of components such as head and head arm.

Sign in / Sign up

Export Citation Format

Share Document