• Journal of Advanced Marine Engineering and Technology
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• v.22 no.4
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• pp.451-459
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• 1998

THe influence of internal acoustic exitation through a square prism on the turbulent wake flow characteristics was investigated. The intermediate wake region where is about ten times the respective length of the body was experimentally investigated using a conditional phase average technique. At first the static base pressures of square prism and the shedding frequencies have been measured at various internal acoustic exciation frequencies. The experiment were performed under the four cases of internal acoustic excitation frequencies 0Hz 30Hz($St_e$=0.09) 65Hz($St_e$=0.20) 120Hz($St_e$=0.38) And velocity vector fields were presented and discussed. The influence of acoustic exvitation frequencies on the structure of intermediate turbulent wake region is evident. As the internal acoustic frequency increased shedding frequency gradually increased and aerodynamic force decreased. Also it was found that the vortex shedding occurs dratically well and shedding frequency reached nearly the same value as the internal acoustic frequency. but above Strouhal number 0.3 the influence disappeared.

• Proceedings of the Korean Society of Computer Information Conference
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• 2014.07a
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• pp.467-468
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• 2014

본 논문에서는 컴퓨터 보안 강화를 위해 WOL(Wake On LAN) 기능을 출입문 제어시스템에 탑재하여 RFID 카드를 소지한 사용자만이 컴퓨터에 일차적으로 접근 가능한 전략을 제안한다. 이러한 전략은 컴퓨터 사용을 위해 단순히 비밀번호를 이용해 로그온 하는 기존의 방법과 비교해 사전에 자신의 RFID 카드를 이용한 물리보안 인증 단계를 전처리 과정으로 포함함으로써 컴퓨터 보안이 한층 강화되었다고 볼 수 있다. 뿐만 아니라 출입문 제어시스템에 탑재된 WOL 기능에 의해 사용자가 자신의 컴퓨터에 실질적으로 접근하기 이전에 일부 부팅과정에 완료됨에 따라 사용자가 컴퓨터 부팅 과정동안 기다려야하는 대기시간을 줄임으로써 업무효율을 기대할 수 있다. 본 논문에서는 RFID 리더기와 라즈베리파이(Rasqberry Pi)사용해 WOL 기능을 탑재한 출입문 제어시스템을 직접 구현하고 실제 컴퓨팅 환경을 구현해 실험을 실시하였다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2017.05a
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• pp.441-443
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• 2017

Modern people who have been busy in their busy daily life tend to reduce outside activities and activities in their homes are increasing. As a result, the frequency of use of electronic products such as computers is increasing and products are being developed. However, the remaining inconvenience of using a computer is that you have to sit in front of a computer when you are tired and want to watch movies, browse the internet and do simple tasks. This is why the penetration rate of smartphones is increasing. In order to solve the inconvenience of such a computer, we have designed a program that enables Wake on LAN function, which is a function for booting a remote shutdown computer, and mouse control and keyboard control by communicating with a smartphone application and a computer.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.4 s.247
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• pp.298-305
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• 2006

The flow around a circular cylinder which oscillates rotationally with a relatively high forcing frequency has been investigated experimentally using flow visualization and hot-wire measurements. Dominant parameters are Reynolds number (Re), oscillation amplitude $({\theta}_A)$, and frequency ratio $F_R=f_f/f_n$, where $f_f$ is the forcing frequency and $f_n$ is the natural frequency of vortex shedding. Experiments were carried out under the conditions of $Re=4.14{\times}10^3,\;{\theta}_A={\pi}/6$, and $0{\leq}F_R{\leq}2$. The effect of frequency ratio $F_R$ on the flow structure of wake was evaluated by measuring wake velocity profile and spectral analysis of hot-wire signal. Depending on the frequency ratio $F_R$, the cylinder wake has 5 different flow regimes. The vortex formation length and vortex shedding frequency are changed significantly before and after the lock-on regime. The drag coefficient was reduced under the condition of $F_R<1.0$ and the maximum drag reduction is about 33% at $F_R=0.8$. However, the drag is increased as $F_R$ increases beyond $F_R=1.0$. This active flow control method can be effective in aerodynamic applications, if the forcing parameters are selected optimally.

• Journal of Electrical Engineering and Technology
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• v.9 no.3
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• pp.827-834
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• 2014

In order to meet the low voltage ride-through requirement in a grid code, a wind power plant (WPP) has to stay connected to a grid, supporting the voltage recovery for a grid fault. To do this, a plant-level controller as well as a wind generator (WG) controller is essential. The dynamic response of a WPP should be analyzed in order to design a plant-level controller. The dynamic response of a WPP for a grid fault is the collective response of all WGs, which depends on the wind speed approaching the WG. Thus, the dynamic response of a WPP should be analyzed by taking the wake effect into consideration, because different wind speeds at WGs will result in different responses of the WPP. This paper analyzes the response of a doubly fed induction generator (DFIG)-based offshore WPP with a grid fault taking into account the wake effect. To obtain the approaching wind speed of a WG in a WPP, we considered the cumulative impact of multiple shadowing and the effect of the wind direction. The voltage, reactive power, and active power at the point of common coupling of a 100 MW DFIG-based offshore WPP were analyzed during and after a grid fault under various wind and fault conditions using an EMTP-RV simulator. The results clearly demonstrate that not considering the wake effect leads to significantly different results, particularly for the reactive power and active power, which could potentially lead to incorrect conclusions and / or control schemes for a WPP.

• 한국전산유체공학회:학술대회논문집
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• 2005.04a
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• pp.51-56
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• 2005

A new feedback control system based on system identification is proposed and preliminarily tested on Van der Pol equation which has a similar characteristic to circular cylinder. The same principle is applicable to circular cylinder in a uniform flow for suppresing the vortex shedding. The feedback controller is designed to impose feedback signal at the phase which is located outside the range of lock-on. The lift coefficient (CL) is employed as a feedback signal and the control forcing is given by a rotational oscillation of the cylinder. By applying the feedback control system, the lift coefficient is reduced.

• 한국가시화정보학회:학술대회논문집
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• 2007.11a
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• pp.134-137
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• 2007

The temporal evolution of wake behind a circular cylinder oscillating rotationally with a relatively high forcing frequency has been investigated experimentally using a dynamic PIV technique. Experiments were carried out with varying the frequency ratio $F_R\;(=f_f/f_n)$ in the range from 0.0 (stationary) to 1.6 at oscillation amplitude of ${\theta}_A=30^{\circ}$ and Reynolds number of $Re=4.14{\times}10^3$. Depending on the forcing condition ($F_R$), the flow was divided into three regimes; non-lock-on ($F_R=0.4$), transition ($F_R=0.8$, 1.6) and lock-on regimes ($F_R=1.0$) with markedly different flow structure in the near-wake region behind the cylinder. When the frequency ratio was less than 1.0 ($F_R{\le}1.0$), the rotational oscillatory motion of the cylinder decreased the length of the vortex formation region and enhanced the mutual interaction between large-scale vortices across the wake centerline. The entrainment of ambient fluid seemed to play an important role in controlling the near-wake flow and shear-layer instability. However, the flow characteristics changed markedly beyond the lock-on flow regime ($F_R=1.0$) due to high-frequency forcing. At $F_R=1.6$, the mutual interactions between the vortices shed from both sides of the cylinder were not so strong. Thereby, the flow entrainment and momentum transfer into the wake center region were reduced. In addition, the size of the large-scale vortices decreased since the lateral extent of the wake was suppressed.

• Journal of Trauma and Injury
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• v.36 no.4
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• pp.421-424
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• 2023

This case report presents the case of a 49-year-old man who presented to our level I trauma center after sustaining injuries in an altercation with local law enforcement in which he was shot with a less lethal bean bag and tased. In a primary survey, a penetrating left supraclavicular wound was noted in addition to a taser dart lodged in his flank. No other traumatic findings were noted in a secondary survey. Given hemodynamic stability, completion imaging was obtained, revealing a foreign body in the left lung, a left open clavicle fracture, a C5 tubercle fracture, a possible grade I left vertebral injury, and a left first rib fracture. Soft tissue gas was seen around the left subclavian and axillary arteries, although no definitive arterial injury was identified. The bean bag projectile was embedded in the parenchyma of the left lung on cross-sectional imaging. The patient underwent thoracotomy for removal of the projectile and hemostasis. A thoracotomy was chosen as the operative approach due to concerns about significant bleeding upon foreign body removal. A chest tube was placed and subsequently removed on postoperative day 5. The patient was discharged on postoperative day 7. At a 2-week outpatient follow-up visit, the patient was doing well. This case report is the first to describe this outcome for a drag-stabilized bean bag. Although law enforcement officers utilize bean bag projectiles as a "less lethal" means of crowd control and protection, these ballistics pose significant risk and can result in serious injury.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.265-270
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• 2001

This study presents a feedback control methodology for suppression of the vortex shedding from a circular cylinder in a uniform flow. A rotational oscillation is applied as a controlled forcing and the lift coefficient ($C_L$) is used as a feedback signal. A feedback control concept is made based on the phase relation between the rotation velocity and $C_L$ at 'lock-on', The phase between the forcing and the vortex formation is changed $180^{\circ}$ from the phase of enhancing the lock-on state. This concept is examined by solving the Van del Pol equation. The results are satisfactory.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.6
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• pp.860-873
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• 1998

In a low speed open-type wind tunnel, a group of parallel wakes downstream of two dimensional grid model consisting of several circular cylinders were experimentally investigated to study the response of the wake flows to the acoustic excitation, in hoping to promote the understanding of the underlying mechanism behind the gross flow change due to artificial excitation. In the unexcited wake flows, the development of the individual wakes behind cylinders was almost uniform for the ratio of the spacing to the cylinder diameter of s/d.geq.1.5. For smaller s/d, however, the jet streams issued through the gaps between the cylinders became biased in one side and the cylinders had wakes of different sizes. At s/d=1.25, the gap flow directions change in time, leading to unstable wake patterns. Further reduction in s/d made this unstable flip-flopping of the jets stable. The most effective excitation frequency was found to be in the Strouhal number range of St=0.5-0.6. This frequency was related to the vortex shedding. At s/d=1.75, the excitation frequency was 2 or 4 times the vortex shedding frequency. When the flow was excited at this frequency, the vortex sheddings were energized, and pairings between neighboring vortices were generated. Also, the merging process between individual wakes was accelerated. The unstable and unbalanced wake patterns at s/d=2.15 were made stable and balanced. The unstable and unbalanced wake patterns at s/d=2.15 were made stable and balanced. For smaller spacing of s/d .leq,1.0, the acoustic excitation became less effective in controlling the flow.