K. Sundaravadivelu

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.

Blood Flow in an Out-of-Plane Aorto-left Coronary Sequential Bypass Graft

Coronary artery bypass graft (CABG) is a major therapy for ischemic heart disease which if left untreated can progress to failure of the heart. Restenosis, a leading cause of CABG, can be correlated with the geometric configuration and the hemodynamics of the graft. In this chapter we use computational fluid dynamics (CFD) to investigate the hemodynamics in a 3D out-of-plane sequential bypass graft model. Using a finite volume approach, quasi-steady flow simulations are performed at mid-ejection and at mid-diastole. Plots of velocity vectors, wall shear stress (WSS), and spatial WSS gradient (WSSG) distribution are presented in the aorto-left coronary bypass graft domain. Simulation results reveal a more uniform WSS and spatial WSSG distribution in the side-to-side (sequential graft) anastomosis configuration over the end-to-side (multiple graft) anastomosis. Results for the multiple bypass graft model show the peak magnitudes of the spatial WSSG are higher compared to the sequential bypass graft model. These findings suggest that sequential bypass grafting may be preferable over multiple bypass grafting to avoid non-uniformities of WSS.

A numerical simulation of particle trajectory in thin hard disk drive

This work numerically investigates the particle trajectory in a turbulent flow field and its trapped status in 2.5 inch thin hard disk drives (HDDs). The trajectory of particle is calculated and the particle trapped status is studied by statistical analysis of the behavior of massive particles. Two air filter designs are compared and evaluated. The effects of particle release position, particle size and density on the trapped status are examined. The results indicate that the filter should be arranged far from the read/write head, and the particle trapped status depends on the particle size and particle release position. The simulation results provide useful information and can be used as a guideline in the design of particle removal system inside thin HDDs.

A new fluid structure coupling approach for high frequency/small deformation engineering application

The present work introduces an engineering approach to investigate the coupled fluid-structure interactions for high-frequency and small displacement problems. A new sequential coupling method is developed to investigate the fluid-structure interactions in high-frequency and small displacement systems. The new method is based on the idea that the structure immersed in the fluid vibrates due to the flow force, and in turn the vibrating structure also imposes a reaction power to the surrounding flow. The reaction power is interpreted by a boundary vibrating velocity. The new developed fluid-structure coupling approach is applied to a model disk drive and the results indicate that the dominant coupling effect is induced by the first frequency boundary vibration in out-of-plane direction. Without consideration of coupling effects, the arm vibration amplitude is overestimated in the out-of-plane direction, and underestimated in the in-plane direction. The turbulent flow behavior and the characteristics around vibrating boundary are revealed under the influence of the coupling approach. The simulation results are examined and verified by LDV measurements, which confirm that the newly developed approach is feasible for predicting the vibration amplitude of immersed vibration boundaries.

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.

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

Air Flow Analyses in an Ultra-Thin Hard Disk Drive

Turbulent air flow analysis is carried out in an ultra-thin hard disk drive using the large eddy simulation (LES). Aerodynamic force acting on various structural components is obtained for about 40 ms and analyzed in detail. Using one set of full scale simulation data, aerodynamic force data for other different sets of operating conditions is obtained using scaling methods thus minimizing the computational time significantly. Validation of the scaling methods is discussed and concluded.

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.

Numerical Simulation of Turbulent Air Flow in Hard Disk Drives

Turbulent air flow characteristics in a hard disk drive (HDD) model are simulated through a novel non-linear two-equation turbulence model. Simulated numerical results are validated by comparing against a higher order model (RSM) predictions. Comparisons in terms of mean flow characteristics are found to agree well with the RSM model predictions than that of the linear model predictions. The computational time taken by the nonlinear model is found to be significantly less than that of the RSM model and hence can be used effectively for engineering analysis