• 전자공학회논문지B
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• 제33B권8호
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• pp.15-21
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• 1996

This paper describes data placement schemes that provide uniform and balanced to multiple disks load for retrievals of VBR (variable bit rate) video at varying retrieval speeds. To support maximum concurent users at arbitrary-speed playbacks in a disk-arry based system, the hot spot disks should be carefully avoided. In this paper, we extend the proposed scheme, prime round-robin(PRR), for VBR video. In addition, we have compared the performance of PRR and PRR (PRR extension).

• 한국통신학회논문지
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• 제22권5호
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• pp.1036-1044
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• 1997

We modify the montgomery modeular multikplication to extract the common parts in common-multiplicand multi-plications. Since the modified method computes the common parts in two modular multiplications once rather than twice, it can speed up the exponentiations and reduce the amount of storage tables in m-ary or windowexponentiation. It can be also applied to an exponentiation mehod by folding the exponent in half. This method is well-suited to the memory limited environments such as IC card due to its speed and requirement of small memory.

• 대한안전경영과학회지
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• 제24권3호
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• pp.23-28
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• 2022

Rack is a place to store products. Workers pick products from rack storage. After picking up, workers move to another location by forklift. Driving speed, worker condition, and number/frequency of operation is responsible for forklift accidents. When an accident occurs, products get damaged. Therefore, it is important to prevent one. As the research result, To prevent forklift accidents, the minimum order quantity, the minimum number of operations, and low speed operation are required.

• Journal of Electrical Engineering and Technology
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• 제12권4호
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• pp.1442-1448
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• 2017

Recently, electric power systems have been operating with tight margins and have reached their operational limits. Many researchers consider a microgrid as one of the best solutions to relieve that problem. The microgrid is generally powered by renewable energies that are connected through power converters. In contrast to the rotational machines in the conventional power plants, the converters do not have physical rotors, and therefore they do not have rotational inertia. Consequently, a stand-alone microgrid has no inertia when it is powered by the only converter-based-generators (CBGs). As a result, the relationship between power and frequency is not valid, and the grid frequency cannot represent the power balance between the generator and load. In this paper, a superconducting flywheel energy storage system (SFESS) is applied to an inertia-free stand-alone (IFSA) microgrid. The SFESS accelerates or decelerates its rotational speed by storing or releasing power, respectively, based on its rotational inertia. Then, power in the IFSA microgrid can be balanced by measuring the rotor speed in the SFESS. This method does not have an error accumulation problem, which must be considered for the state of charge (SOC) estimation in the battery energy storage system (BESS). The performance of the proposed method is verified by an electromagnetic transient (EMT) simulation.

• 정보저장시스템학회논문집
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• 제1권2호
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• pp.169-174
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• 2005

Current information storage devices read/write data on the rotating disk. The axial vibration of a rotating disk should be suppressed for the successful operation of the device. Information storage devices widely used in these days adopt relatively thick disk which is stiff enough to suppress axial vibration under allowable limit. However, the thickness of the disk is going to be thinner and thinner as the small form factor of the devices is getting preferred by the consumer. In this study, a stabilizer system, which is composed with 8 air bearings, is proposed for suppressing the axial vibration of a $95{\mu}m$ thick PC disk in a non-contacting manner. The performance of the stabilizer system is simulated by numerical computation and then confirmed its results through a series of experiment. A thin and flexible disk has various vibration modes when it rotates in high speed. The stabilizer system generates positive as well as negative pressure due to the rotation of flexible disk so that the force due to the pressure distribution pushes and pulls rotating disk in a non-contacting manner. The balance between positive and negative pressure forces can be obtained by adjusting the area and the slope of the air bearing surface. The axial vibration of the flexible disk of 120mm diameter is suppressed successfully from over $1000{\mu}m$ to $30{\mu}m$ peak-to-peak value at the rotational speed of 5,000rpm.

• 대한기계학회논문집A
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• 제34권3호
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• pp.283-289
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• 2010

친환경기술과 신재생 에너지 자원에 대한 세계적인 관심이 증가하면서, 플라이휠 에너지 저장 장치는 화학전지나 연료전지와 같은 기존의 에너지 저장 시스템의 대안 중 하나로 부상하고 있다. 플라이휠 에너지 저장장치의 에너지 저장 용량은 극질량 관성모멘트와 회전속도의 제곱에 비례하기 때문에, 가능한 높은 회전속도와 높은 극질량 관성모멘트를 갖도록 설계하는 것이 중요하다. 하지만, 시스템의 운전안정성 확보가 최적설계의 구속조건으로 작용할 수 있다. 본 논문에서는 에너지 저장 용량을 최대화하고 운전안정성 및 외란에 대한 강인성을 확보하는 플라이휠 시스템의 최적설계를 제안한다. 그리고, 기존의 PD 제어에 비교하여 교차궤환제어법이 자이로스코프효과를 줄이고, 에너지 저장밀도를 높이는데 필수적임을 확인하였다.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2015년도 춘계학술대회
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• pp.643-645
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• 2015

스토리지의 발달로 자동차 항공분야 등 실생활 어디에서든 스토리지가 활발히 활용되고 있다. 최근 빅데이터가 대두됨에 따라 많은 데이터를 스토리지에 저장하고 데이터를 처리하는 데이터 분산처리 연구가 활발히 진행되고 있다. 하지만 많은 사람들이 데이터를 동시에 요청할 때 병목현상이나 처리 속도가 느려지는 문제가 발생한다. 본 논문에서는 많은 데이터를 저장하고 처리해야하는 빅 데이터 분야에 사용될 것을 고려하여, 데이터 요청 시 보다 효율적으로 데이터를 처리하고 많은 데이터를 효율적인 관리가 가능한 데이터 경량화 처리 시스템 알고리즘을 제안한다.

• 전력전자학회논문지
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• 제5권6호
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• pp.610-619
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• 2000

본 논문에서는 현재 전력저장시스템으로써 가장 많이 사용하고 있는 배터리를 대체할 목적의 5MB (Superconductive Magnetic Bearing)를 이용한 off-line UPS에 관해 연구하였다 영구자석의 덩어리형 고온 초전도 체위에서의 부상득성을 이용하여 베어링 문제의 해결방안에 접근함으로써 고효율의 FES찰 구성하여 단상 off-line UPS에 적용하였으며 제어회로에는 80C 1 96KC 마이크로프로세서를 사용하였고 빠픈 응답윤 요구하는 부분 은 아날로그회로를 사용하여 구성하였다. 에너지 저장모드에서 컨버터 입력천류는 전원전압과 동상의 정현파로 제어하였으며 에너지 회생모드에서는 출력잔압윤 정현파로 제어하기위해 필터커패시터전류릎 직접 제어하였다. 시작 품제작을 통해 시스템의 안장된 동작특성을 확인함으로써 제안된 FES가 Off-line UPS 에서의 에너지 저장매체로써 우수함을 입증하였다.

• 정보저장시스템학회논문집
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• 제2권4호
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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.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권7호
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• pp.3583-3598
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• 2019

In order to improve the reliability and repair efficiency of distributed storage systems, minimum bandwidth regenerating (MBR) codes based on cyclic variable fractional repetition (VFR) codes are constructed in this thesis, which can repair failed nodes accurately. Specifically, in order to consider the imbalance of data accessed by the users, cyclic VFR codes are constructed according to that data with different heat degrees are copied in different repetition degrees. Moreover, we divide the storage nodes into groups, and construct MBR codes based on cyclic VFR codes to improve the file download speed. Performance analysis and simulation results show that, the repair locality of a single node failure is always 2 when MBR codes based on cyclic VFR codes are adopted in distributed storage systems, which is obviously superior to the traditional MBR codes. Compared with RS codes and simple regenerating codes, the proposed MBR codes based on cyclic VFR codes have lower repair locality, repair complexity and bandwidth overhead, as well as higher repair efficiency. Moreover, relative to FR codes, the MBR codes based on cyclic VFR codes can be applicable to more storage systems.