E. H. Ong

Flow-Induced Slider Vibration in a Functional Hard Disk Drive: Influence of Air Shroud

An air shroud is designed and placed within a commercially available hard disk drive operating at 15 000 rpm. Large eddy simulations of the turbulent airflow characteristics resulting from both the models, with and without air shroud, are carried out by assuming the read/write head is at the disk middle diameter. The numerical model consists of about nine million tetrahedral cells with the largest and smallest sizes of the cell volumes being 2.5 mm3 and 0.35 mm3 , respectively. The dynamic Smagorinsky-Lily model is employed to mimic the effect of small-scale eddies in the turbulent airflow. Numerically predicted airflow characteristics are compared against the LDA measurements and found to be in good agreement. The wind blowing on the surfaces of the head gimbals assembly is converted into aerodynamic forces and the resulting slider displacement in the off-track and out-of-plane directions are investigated. It is inferred that the disk drive model with air shroud results in a maximum of 44% and 10% less off-track and out-of-plane slider displacements, respectively.

Three dimensional finite element model for transient temperature prediction in hard disk drive

Hard disk drive (HDD) is often subjected to transient temperature during frequent seeking or due to the change of environmental conditions that causes HDD reliability problems. This paper presents a three dimensional (3D) finite element modelling technique that can be used to predict the transient temperatures of the HDD when it subjected to transient temperature during frequent seeking or due to the change of environmental conditions.

Numerical Investigation of Thermal Problems in Heat-Assisted Magnetic Recording System

This paper describes the numerical investigation of two thermal related problems in heat assisted magnetic recording: 1) the dependence of the recorded mark width on the laser power and 2) the temperature distribution of the lubricant layer and its variation with time and the change with and without the heat sink layer. It is found that the mark width increases with the increase of laser power, but the increase is not linear due to the Gaussian distribution of the laser intensity. It is also found that in certain power range, a smaller laser spot will generate a wider mark width at the same laser power. For lubricant cooling process, the temperature in lubricant layer decreases quickly after the laser is removed. Within 0.5 ns, the maximum temperature in lubricant layer drops 35.6degC when there is no heat sink layer applied under the recording media layer. With heat sink layer applied under the media layer, the temperature drop is even faster and decreases by 57.0degC in 0.5 ns. Hence, the heat sink layer is useful to quickly cool the lubricant layer to a thermally stable range.

Numerical investigation of thermal problems in HAMR system

The paper numerically investigated two thermal related problems in heat assisted magnetic recording: the dependence of the recorded mark width on the laser power and the temperature distribution and changes with time in lubricant layer at the condition without or with the heat sink layer. The results show that the mark width increases as the laser power increases and heat sink layer helps to reduce temperature in lubricant layer.

Structural Health Monitoring Using PZT Transducer Network and Lamb Waves

Structure health monitoring (SHM) using ultrasonic waves is an emerging technology that can be applied to real-time detect, locate and quantify the structural damages in aircraft structures. In this paper, the monitoring of crack growth at rivet holes in an aluminum test plate using a PZT transducer network and Lamb waves is investigated. The thin disc PZT transducers surface mounted at the test plate are used as actuators to transmit the windowed sinewave bursts and sensors to receive the ultrasonic Lamb waves. The symmetrical S0 mode and antisymmetrical A0 mode of the Lamb waves in the structures are studied with correlated theoretical, experimental and numerical analysis. The optimal excitation frequency is determined for the test plate. Finite element method (FEM) numerical models for simulations of the wave propagations and interactions with the holes and cracks in the plate are developed and verified with the experimental results. The wave responses modes and characteristics for detection of the cracks at the rivet holes are analyzed. The Lamb wave signals in the PZT transducer network are processed with the short time Fourier transform (STFT). It is demonstrated that the time of flight and the energy transmission ratio of the S0 wave are sensitive to the cracks in the structure.Copyright

Reduction of Flow Induced Vibration in Hard Disk Drive

In this paper, system level analysis is carried out for a functional HDD with two disks and four sliders operating at spindle speed of 15000 rpm. Full numerical models both for computational fluid dynamics (CFD) analysis and structural Finite Element Analysis (FEA) are developed. The flow induced vibrations of the sliders in all three directions, namely, off-track (X), down-track (Y) and out-of-plane direction (Z) are examined respectively. The numerical simulation results are compared and validated with the experimental results measured with a 3D laser Doppler vibrometer (LDV). Good agreements are observed for the vibrations in the three directions. The airflow patterns and characteristics of the flow induced vibration in HDD for three critical positions of the head gimbal assembly (HGA) parked at the disks identified as ID, MD and OD are investigated. The results reveal that the first slider from top has the highest flow induced vibrations in all the three directions due to the higher turbulent flow close to the top disk surface. Moreover, the results indicate that the slider vibration is interacted with the disk flutter in the HDD. Optimal designs of the HDD disk and air shroud are carried out to reduce the flow induced vibration of the slider, by suppressing the disk flutter and improving the turbulent flow in the HDD. It is demonstrated that significant reduction of flow induced slider vibration could be achieved with the optimal designs of the HDD.Copyright

Vibration characteristics of hard disk drives with different internal air pressures

Hard disk drive (HDD) performance and reliability at different environments are the interests and concerns of HDD researchers, engineers and consumers. This paper reports the experimental investigation of HDD vibration characteristics with different internal air pressures. Experiments are done by placing the HDD samples inside an altitude chamber and the vibrations are measured using a Laser Doppler vibrometer (LDV) and all-in-one (AIO) motor tester. The disk drive read/write test, vibration spectrum of actuator & suspension tip and disk flutter measurements reveal that the air pressure significantly affects the vibration behaviors of hard disk drive components and the system performances.

Flow induced slider vibration in a functional HDDI: Influence of air shroud

An air shroud is designed and placed within a commercially available hard disk drive operating at 15000 rpm. Turbulent air flow characteristics resulting from both the models, with and without air shroud, are compared and discussed. The wind blowing on the surfaces of the head gimbals assembly is converted into aerodynamic forces and the resulting positioning error due to off-track and out-of-plane displacements of various sliders are investigated. It is inferred the disk drive model with air shroud resulted in 21% and 40% less off-track and out-of-plane displacements respectively.

Modeling and prediction of structure-borne seek noise of HDDs

A numerical approach is presented for predicting the structure-borne seek noise in hard disk drives (HDDs) in time-domain. Rayleigh integral is adopted to relate the transient acceleration of top cover to its radiated sound pressure. A finite element modeling and simulation technique is employed to arrive at the transient vibration response, which is further used as the input for acoustic noise level calculation. The prediction results of a 1.8” HDD reveal the high dependency of structure-borne seek noise level on the current profile applied to VCM.

Feasibility of modeling air bearing as linear springs in hard disk drive

A model to predict the shock response of a 1.8-inch hard disk drive (HDD) is developed and verified by experiment. The feasibility of modeling the air bearing as linear springs is investigated. Result shows that when the vibration of the arm-suspension is concerned, the air bearing between the disk and slider can be modeled by linear springs to speed up the simulation.