• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.9
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• pp.721-727
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• 2021

In this paper, aerodynamic characteristics of missile configuration with various grid fins in subsonic flow. To investigate the effects of grid fin shape, four types of experimental models were used. In addition, to examine aerodynamic characteristics of missile configurations with various grid fins according to effects of Reynolds numbers and configurations of grid fins, 6-components aerodynamic forces and moments were measured by internal balance in wind tunnel test.

• Proceedings of the KIPE Conference
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• 2020.08a
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• pp.461-462
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• 2020

본 논문은 LCL 필터를 사용하는 계통연계형 인버터의 병렬운전 조건에서 LCL 필터와 계통 임피던스 간의 상호간섭에 따른 공진특성을 분석하였으며, 시뮬레이션 및 실험을 통해 검증하였다. 인버터 병렬운전은 2대 조건을 고려하였으며, LCL 필터를 포함한 시스템 파라미터는 동일 조건으로 설정하였다. PCC 지점에 인버터 병렬운전 조건 시, 계통 임피던스 존재로 인해 각 인버터의 LCL 필터 간 상호간섭 영향이 발생하며 필터 공진주파수의 이동은 인버터 병렬연결 수와 계통 임피던스 크기와의 연관성을 분석하였다. PSIM을 통해 시뮬레이션하고, MATLAB/SIMULINK 2018a를 통해 검증한다. 실시간 디지털 시뮬레이터와 DSP 28377 제어보드 연동을 통해 2대 인버터 병렬운전 조건에서의 상호간섭 특성을 실험하였으며, 분석결과와 동일한 실험결과를 도출함으로써 해석의 타당성을 검증하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.6
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• pp.56-63
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• 2004

In this study, dynamic aeroelastic analyses of the canard with oscillating flap are conducted considering the effect of aerodynamic compressibility. The canard model considered herein is an all-movable type with a pitching axis on a canard-rotor-wing aircraft which was considered as one of the major UAV candidates under developing in Korea. The equivalent structural model is constructed based on the initial design data by the Korea smart UAV development center. Both the frequency and the time-domain aeroelastic analyses have been applied to practically conduct parametric studies on the effects of equivalent torsional stiffness. In the case of all-movable control surface with oscillating flap, the equivalent rotational stiffness of the pitch axes are important design parameters. The parametric results for the aeroelastic instability are practically presented.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.6
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• pp.83-91
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• 2006

An advanced method of Relaxed Static Stability (RSS) is utilized for improving the aerodynamic performance of modern version supersonic jet fighter aircraft. The flight control system utilizes RSS criteria in longitudinal axis to achieve performance enhancements and improve stability. The flight control law of T-50 advanced trainer employs RSS concept in order to improve the aerodynamic performance and guarantee aircraft stability. The longitudinal center of gravity(X-c.g) varies as a function of external stores, fuel state and gear position. Shifts in X-c.g relate directly to longitudinal static margin in aircraft stability. This paper deals the maximum aft X-c.g for critical aircraft loadings and checks static margin limits using sensitivity such as damping, natural frequency, gain and phase margin. And nonlinear analysis was conducted for such as short period input. And also, this paper shows the T-50 aircraft stability based on the result of high angle of attack flight such as upright and inverted departure.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.54-59
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• 2005

Nonlinear aeroelastic analyses of a missile control fin are performed considering backlash and dynamic stiffness of actuator. Doublet-Hybrid method is used for the calculation of subsonic unsteady aerodynamic forces, and aerodynamic forces are approximated by the minimum-state approximation. For nonlinear flutter analysis backlash is represented by a free-play and is linearized by using the describing function method. Also, dynamic stiffness is function of frequency and is calculated by solving equation of motion for actuator. The linear and nonlinear flutter analyses show that the aeroelastic characteristics are significantly dependent on the backlash and dynamic stiffness. From the nonlinear flutter analysis, various types of limit cycle oscillations are observed in a range of air speeds below the linear divergent flutter boundary. The nonlinear flutter characteristics and the nonlinear aeroelastic responses are also investigated in the time domain.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.2
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• pp.200-207
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• 2017

The purpose in having a control surface on ships is to control the motion of the ship. The control surface may be composed entirely of a single movable surface or of a combination of fixed and movable portions. A control surface has one sole function to perform in meeting its purpose, and that is to develop a control force in consequence of its orientation and movement relative to the water. The forces and moments generated as a result of this rotation and angle of attack then determine the manoeuvring characteristics of the ship. In this paper, two-dimensional flow characteristics of a flapped rudder and a water-blowing control rudder were accomplished respectively by PIV method in a circulating water channel. Model test has been carried out with different angles of attack of main foil (NACA 0012) and flap's deflection angles to predict the performance of the flapped rudder and the water-blowing control rudder. The 2-frame particle tracking method has been used to obtain the velocity distribution in the flow field. $Re{\fallingdotseq}3.0{\times}10^4$ has been used during the whole experiments and measured results have been compared with each other.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.5
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• pp.621-626
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• 2019

The driver's steering wheel maneuver is a typical disturbance that causes excessive body motion and traveling instability of a vehicle. Abrupt and extreme operation can cause rollover depending on the geometric and dynamic characteristics, e.g., SUV vehicles. In this study, to cope with the performance limitation of conventional cars, fundamental research on the structurization of a control system was performed as follows. Mathematical modeling of the lateral behavior induced by driver input was carried out. A controller was designed to reduce the body motion based on this model. An algorithm was applied to secure robust control performance against modeling errors due to parameter uncertainty, $H_{\infty}$. Using the decoupled 1/4 car, a dynamic load simulating model considering the body moment was suggested. The simulation result showed the validity of the load-simulating model. The framework for a lateral behavior control system is proposed, including an experimental 1/4 vehicle unit, load simulating module, suspension control module, and hardware-in-the-loop simulation technology.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.30.1-30.1
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• 2009

PZT(Pb(Zr, Ti)$O_3$ 압전세라믹스는 뛰어난 압전 특성과 강유전 특성을 가지고 있어서 현재 널리 사용되고 있다. 하지만 PZT세라믹스는 큐리온도 이상에서 그 특성을 잃게 되고 높은 온도에서의 응용이 제한된다. 따라서 높은 큐리온도를 가지는 압전체를 개발하기 위한 연구가 많이 이루어지고 있다. $PbTiO_3$의 경우에는 $Bi(Zn_{0.5}Ti_{0.5})$, $BiFeO_3$등의 Bi계 세라믹스를 치환하면서 큐리온도가 올라가는 결과가 보고되고 있다. 하지만 이것은 PZT세라믹스 보다 압전 및 유전 특성이 상당히 낮다. 따라서 본 연구에서는 $(1-x)PbZrO_3-xPbTiO_3$조성에 Bi(Me)$O_3$(Me:Zn, Ti, Fe, Al)를 치환하여 압전특성 및 강유전 상전이 온도를 조사하였다. 모든 시편들은 고상반응법으로 제조하였고, 제조한 시편으로 조성에 따른 압전특성 및 유전특성의 변화를 측정하였다. 그리고 이를 통해 큐리온도는 PZT의 MPB조성근처에서 Bi계 세라믹의 치환은 $T_C$가 낮아 졌으나, Tetragonal 상을 가지고 있는 Ti-rich인 조성에서는 $T_C$가 높아지는 것을 관찰하였다.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.295-296
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• 2016

본 논문은 LCL 필터를 사용하는 계통연계형 인버터에 커패시터 전류 피드백 방식의 능동댐핑을 적용한 안정도 향상 방안를 분석하였다. 커패시터 전류 피드백 방식은 커패시터에 저항을 병렬 연결한 수동댐핑과 동일한 특성을 나타내며, 안정도 해석에 $1.5T_s$의 연산 및 PWM 시지연을 고려하였다. 주파수 응답 특성과 이산시간 영역에서 근궤적을 이용하여 안정도를 해석하며, 필터 공진을 저감시키기 위한 능동댐핑의 이득 $k_d$의 범위를 산정하였으며 PSIM 시뮬레이션과 5kW 계통연계형 실험을 통해 필터 공진에 대한 저감 효과를 검증하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.349-354
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• 2005

In this paper, a small supersonic wind tunnel is designed and built to study the flow characteristics of a supersonic impulse turbine cascade. The flow is visualized by means of a single pass Schlieren system. The supersonic cascade with 2-dimensional supersonic nozzle was tested for various blade leading edge shapes and gaps between the nozzle and cascade. Highly complicated flow patterns including shocks, nozzle-cascade interaction and shock boundary layer interactions are observed.