• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.257-262
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• 2004

A series of preliminary model tests are performed to find out the wave attenuating effect of the pneumatic breakwater of environment friendly type, which is a bubble screen generated by releasing compressed air from a submerged multiple parallel manifold Rising bubbles induce vertical current, which produces horizontal currents flowing away from the bubble-screen area in both directions. Near bottom, the corresponding currents flow toward the bubble screen, thus completing the circulation pattern. The surface current moving against the direction of wave propagation causes some attenuation of the waves. It becomes more effective as the relative depth (d/ L) increases (short-period waves in deep water). With the same air-discharge, the multiple parallel manifold can be more effective for the attenuation of longer waves through optimum arrangement of manifold number. installation depth, manifold gap, etc. The pneumatic breakwater will give a wide utilization as a device for protecting harbor facilities and as a simple, mobile breakwater.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.9
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• pp.14-24
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• 2009

Memory cell array and peripheral circuits are designed for system on panel style frame buffer. Moreover, a parallel test methodology to test multiple blocks of memory cells is proposed to overcome low yield of system on panel processing technologies. It is capable of faster fault detection compared to conventional memory tests and also applicable to the tests of various embedded memories and conventional SRAMs. The various patterns of conventional test vectors can be used to enhance fault coverage. The proposed testing method is also applicable to hierarchical bit line and divided word line, one of design trends of recent memory architectures.

• Proceedings of the IEEK Conference
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• 2000.06c
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• pp.97-100
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• 2000

As network resources have become faster and demands for multimedia service through network have increased, the demand for Media server system has increased. These kinds of media server solve their bottle neck problem of internal storage device by using parallel system which takes advantage of fast network resource. Many vendors have suggested each of their media server system to solve these problem radically, but most of them require major modification of infra component and additional drawback has added. For example, storage mechanism for specific media requires new file system which is totally different from traditional one, and algorithm for enhancing performance may not suit for traditional operating system environment. In this paper, we designed a parallel media server based on web interface of traditional system and implemented a program for media server. Implemented server system performs parallel processing through web interface without any modification of traditional system, and controls which is related to merging load by distributed data is charged only to client and control server and consequently load of storage server can be minimized. And also, data transfer protocol for streaming media includes Retransfer algorithm and client Admission control policy relevant to performance of whole system.

• Proceedings of the KIEE Conference
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• 1997.07f
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• pp.2234-2236
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• 1997

The SIT, a Static Induction Transistor, is a semiconductor switch that is also called the power junction field-effect transistor (power JFET). Its characteristics are similar to a MOSFET except that its power level is higher and its maximum frequency of operation is lower. The normal method to protect against internal circuit transients of the form of di/dt or dv/dt is the use of snubber circuits. However, the limits of di/dt and dv/dt are high enough for the SIT that it is possible to operate without snubber circuits. SITs can be connected in parallel in order to cope with higher load currents that the value of an individual device rating. The purpose of this study is to investigate the parallel operation of SITs. In this experiment, we used a half-bridge inverter, the output of inverter is up to almost 1MHz and 2kW. Experimental results show that the operation of parallel connected SITs are facilitated individually good current sharing. The reason is the positive temperature coefficient of resistance of the SIT.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.9A
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• pp.1101-1107
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• 2004

This paper presents an optimization algorithm and technique for designing parallel Cyclic Redundancy Check (CRC) circuit, which is most widely adopted for error detection A new heuristic algorithm is developed to find as many shared terms as possible, thus eventually to minimize the number and level of the exclusive-or logic blocks in parallel CRC circuits. 16-bit and 32-bit CRC generators are designed with different types of Programmable Logic Devices, and it has been found that our new algorithm and architecture significantly reduce the delay.

• Journal of the Korean Society of Industry Convergence
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• v.17 no.3
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• pp.84-92
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• 2014

In this paper, a novel 5-axis hybrid-kinematic machine tool is introduced and the research results on accuracy improvement of the prototype machine tool are presented. The 5-axis hybrid machine tool is made up of a 3-DOF parallel manipulator and a 2-DOF serial one connected in series. The machine tool maintains high ratio of stiffness to mass due to the parallel structure and high orientation capability due to the serial-type wrist. In order to acquire high accuracy, the methodology of measuring the output shafts by additional sensors instead of using encoder outputs at the motor shafts is proposed. In the kinematic view point, the hybrid manipulator reduces to a serial one, if the passive joints in the U-P serial chain at the center of the parallel manipulator are directly measured by additional sensors. Using the method of successive screw displacements, the kinematic error model is derived. Since a ball-bar is less expensive than a full position measurement device and sufficiently accurate for calibration, the kinematic calibration method of using a ball-bar is presented. The effectiveness of the calibration method has been verified through the simulations. Finally, the calibration experiment shows that the position accuracy of the prototype machine tool has been improved from 153 to $86{\mu}m$.

• The Journal of Korea Robotics Society
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• v.10 no.2
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• pp.119-132
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• 2015

Two novel parallel mechanisms (PMs) employing two or three PaPaRR subchains are suggested. Each of those two PMs has translational 3-DOF motion and employs only revolute joints such that they could be adequate for haptic devices requiring minimal frictions. The position analyses of those two PMs are conducted. The mobility analysis, the kinematic modeling, and singularity analysis of each of two PMs are performed employing the screw theory. Then through optimal kinematic design, each of two PMs has excellent kinematic characteristics as well as useful workspace size adequate for haptic applications. In particular, by applying an additional redundantly actuated joint to the 2-PaPaRR type PM which has a closed-form position solution, it is shown that all of its parallel singularities within reachable workspace are completely removed and that its kinematic characteristics are improved.

• Journal of Power Electronics
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• v.19 no.2
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• pp.519-528
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• 2019

The unified power quality conditioner (UPQC) is an effective custom power device that is used at the point of common coupling to protect loads from voltage and current-related PQ issues. Currently, most researchers have studied series unit and parallel unit models and an idealized transformer model. However, the interactions of the series and parallel converters in AC-link are difficult to analyze. This study utilizes an equivalent transformer model to accomplish an electric connection of series and parallel converters in the AC-link and to establishes a precise unified mathematical model of the UPQC. The strong coupling interactions of series and parallel units are analyzed, and they show a remarkable dependence on the excitation impedance of transformers. Afterward, a feed-forward decoupling method based on a unified model that contains the uncertainty components of the load impedance is applied. Thus, this study presents an adaptive method to estimate load impedance. Furthermore, simulation and experimental results verify the accuracy of the proposed modeling and decoupling algorithm.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.11
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• pp.1621-1627
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• 2013

This paper compares power losses between voltage controlled before and after using power conversion device in AC feeding system. For this purpose we present voltage control procedures and criteria and model high speed line and train using PSCAD/EMTDC to compare power losses in various feeding condition. Power losses of the simulation result in power control before and after in single point feeding system was reduced maximum 0.37 MW(23.8 %) and average 0.23 MW(20.5 %) when one vehicle load operates maximum load condition. When three vehicles operate maximum load condition in one feeder section, power losses after voltage control was reduced 1.03 MW(49.5%) compared to before voltage control. And, power loss of parallel feeding system is reduced the average 0.08 MW(7.2 %) compared to the single feeding system. In conclusion, adaptive voltage control method using power conversion device can reduce power losses compared with existing method.

• Journal of Industrial Technology
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• v.40 no.1
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• pp.19-23
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• 2020

In this paper, we proposed a PC-based CNC control system using EtherCAT-based servo drive and I/O device. The default communication of LinuxCNC is a parallel port, and data processing with high bandwidth is impossible. However, it is possible to apply various bandwidth devices through the application of EtherCAT, one of the industrial Ethernet communications with high bandwidth. Therefore, the hardware control method of LinuxCNC was applied through EtherCAT communication from the existing parallel port. Finally, through HAL configuration, I/O device operation check and 3-axis motion control proved the LinuxCNC system with EtherCAT.