• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.159-165
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• 2001

The fundamental fluid mechanics associated with the rotation of a smooth plane disk enclosed within a cylindrical chamber have been studied experimentally. In order to acquire systematic information pertinent to this problem torque and friction loss data were obtained over a wide range of disk Reynolds numbers for axial clearance-disk radius ratio H/R from 0.025 to 0.2 and radial tip gap-disk radius ratio s/R from 0.021 to 0.105. Loss analysis of hard disk drive(HDD) is presented to describe the contribution of windage loss of a rotating disk. The minimum loss from factor of HDD can be obtained from this analysis at each operation conditions.

• Journal of the Korea Society for Simulation
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• v.8 no.2
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• pp.29-43
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• 1999

As real-time processing of data with large storage space is required in the era of multimedia, disk arrays are generally used as storage subsystems which be able to provide improved I/O performance. To design the cost-effective disk array, it is important to develop performance models which evaluate the disk array performance. Both queueing theory and simulation are applicable as the method of performance evaluation through queueing modeling. But there is a limit to the analytical method using queueing theory due to the characteristics of disk array requests being serviced in the parallel and concurrent manner. So in this paper we evaluate the disk array performance using simulation method which abstract disk array systems in the low level. Performance results were evaluated through simulation, so that mean response time, mean queueing delay, mean service time, mean queue length for disk array requests and utilization, throughput for disk array systems, can be utilized for capacity planning in the phase of disk array design.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.25 no.1
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• pp.39-48
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• 2015

As a growing number of people are concerned about the protection of personal information, the use of encryption solution has been increased. In addition, with the end of support for Windows XP and the improvement of operating system, the use of the Full Disk Encryption solution like Bitlocker will be increased. Therefore, it is necessary to consider countermeasures against Full Disk Encryption for the future digital forensic investigation. This paper provides the digital evidence acquisition procedure that responds to the Full Disk Encryption environment and introduces the countermeasures and detection tool against Full Disk Encryption solutions that are widely used.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.1
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• pp.251-262
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• 1995

The goal of this study is to provide fundamental information on the design of a new diesel injector system. The cylindrical disk spray was made by an impinging disk insited below the exit of air-assist atomizor. The disintegration processes on a twin-fluid atomization by air-assist atomizor were investigated. Liquid jet was disintegrated at the condition that wavelength was equal and longer than the circumference of the liquid jet, .lambda. .geq. .pi.do. However, the wavelength and the diameter of the liquid jet were decreased according to the increasing of air velocity. The relative density distribution of droplets and pattern of spray by impinging disk were investigated with a C-CCD. Optimum design conditions for cylindrical disk spray were also achieved. The pattern of cylindrical spray can classified according to the size of the disk and the distance from the nozzle tip to the disk. When the space of the disk and the nozzle tip was narrow and the diameter of the disk was larger than that of the air orifice of the nozzle exit, the good distribution of spray could be achieved. When the air flowrate was constant, the spray width was decreased according to the increasing of the liquid flowrate. When the liquid flowrate was constant, the spray width was decreased according to the increasing of the air flowrate.

• Journal of computational fluids engineering
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• v.21 no.1
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• pp.64-71
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• 2016

This research is to numerically investigate the convective cooling performance in the Disk brake. Research concentrates on the heat transfer coefficient and cooling performance which are selected with cooling local locations. Cooling performance of the Hole disk has been compared by Ventilated Disk. According to the results of heat transfer on the disk brake, activated velocity distributions more appear in the Hole disk. This is due to the fact that a number of hole units have exactly 120 on the surface of the hole disk. Therefore, velocity distributions of hole disk brake is better activated than Ventilated disk. According to the calculations of Nusselt number between surface and atmosphere in the interested cooling area, average value of cooling effect has been increased 13.5% by the hole disk at driving of speed 65 km/h situation and grown 18% by the hole disk at driving speed of 100 km/h. Due to the flow of air through the hole route, cooling performance of the hole disk was very excellent. In addition, cooling effect on edge of the bottom is better than the vicinity of center.

• Transactions of the Society of Information Storage Systems
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• v.2 no.4
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• pp.245-250
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• 2006

Organizations such as broadcasting stations and libraries which deal with huge amount of information require high-capacity storage systems for archiving their materials and information. It is necessary and urgent for the storage people to develop a compact, high capacity, and low-cost data storage systems. Even though the Blue-ray technology is commercialized and now it is on the market, demand for the compact and low-cost system is still increasing. A flexible disk system has been introduced recently to satisfy above mentioned requirements. The system uses multiple of thin disks and is expected to achieve technical requirements. However, decreasing the disk thickness makes it difficult to read and write data because it decreases the disk rigidity so that the transverse vibration of the rotating disk increases easily due to both the interaction with surrounding air and the vibration characteristics of thin flexible disk itself. In this study, flat-type stabilizer is proposed to suppress the transverse vibration of a $95{\mu}m$-thick polycarbonate disk. Characteristics of disk vibration have been studied through the results of numerical analysis from the fluid mechanics point of view. Numerical simulation is verified through the experiment by measuring the gap between the rotating disk and the stationary flat stabilizer. The axial deflections of the disk are computed for various rotating speeds and reference gap sizes and then a method of regression is applied to those data. As a result, an empirical relation is proposed for the steady deformation shape of the rotating disk.

• Journal of The Korean Society of Agricultural Engineers
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• v.60 no.2
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• pp.25-36
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• 2018

Drip irrigation system is a low energy cost method which can efficiently save and supply water by dropping water slowly on the crop's root zone during crop growth. In the drip irrigation system, disk filters take an important role to physically remove impurity (inorganic and suspended organic) particles present in agricultural water which can cause emitter clogging. For the purpose, both top-and-bottom surfaces of the disk are grooved in micron size flowing from outside to inside. However, many congested flow paths in disk filter media incur higher head loss of inflow water resulting in relatively decreasing velocities depending on operation time than sand and mesh filters. Therefore, it is important to optimize the structure of disk filter in micro irrigation system. The head loss of disk filter media takes also charge of more than 60 % of total head loss in whole disk filter. This study is to find the appropriate cross-sectional shape of the disk groove to minimize the head loss by executing the experiment. The experiment used three disk filters that have similar filter body but have a half-elliptic and two kinds of triangular cross sections. The experimental results showed that the disk filter with half-elliptic cross sections of disk grooves have less head loss than the disk filter with regular triangular one.

• Tribology and Lubricants
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• v.17 no.1
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• pp.1-9
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• 2001

Hard disk drives operate in various environmental conditions. Thus, it is necessary to assess the reliability of the head/disk interface under these conditions. In this work, stiction and acoustic emission signals were investigated under different temperature, humidity, and ambient pressure conditions. Also, track average amplitude was observed for disk failure in N$_2$environment. It is shown that failure of the head/disk interface occurs more readily at high temperature and low ambient pressure conditions.

• Journal of Institute of Control, Robotics and Systems
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• v.10 no.2
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• pp.153-163
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• 2004

The control objective in hard disk drives is to move head as fast as possible to target track and position the head over the center of target track in the presence of external disturbances. The external shock or disk clamping error in manufacturing process causes the disk center to deviate from the disk rotation center. The disk shift acts on the control system as disturbance and degrades severely the performance of disk drives. In this paper, we present a new controller that compensates for the periodic disturbances very fast. The disturbance compensator is arranged in parallel with the state feedback controller. To avoid the interference with the state feedback controller, the compensator creates compensation signal without the feedback of system output until steady state. The pulse type controller is included additionally for improving the transient performance due to initial state. Finally, in order to demonstrate the superior performance of the proposed compensator. we present some experimental results using a commercially available disk drive.

• Journal of Sensor Science and Technology
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• v.22 no.1
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• pp.49-53
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• 2013

In this paper, we proposed a laser-based non-contact temperature measuring method for high speed rotating polycarbonate (PC) disk using transparency change of thermocolor. The thermocolor has abilities to change color and transparency due to a change in temperature. The thermocolor is applied on one side of polyvinylidene fluoride (PVDF) membrane. The thermocolor applied membrane is attached to inside of reaction chamber in disk. An optical system consisted of a laser beam radiator and a laser photometer is installed. Laser is irradiated at the bottom side of disk and the transmitted laser beam is detected by the laser photometer at the opposite side of disk. During the disk is rotating, laser is irradiated and detected simultaneously. The laser photometer senses the transmitted laser power and generates voltage as output. The temperature of disk can be detected during the disk is rotating up to 3000 RPM.