• Computers and Concrete
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• 제20권5호
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• pp.583-593
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• 2017

Applications of fibre-reinforced polymer (FRP) composites for retrofitting, strengthening and repairing concrete structures have been expanded dramatically in the last decade. FRPs have high specific strength and stiffness compared to conventional construction materials, e.g., steel. Ease of preparation and installation, resistance to corrosion, versatile fabrication and adjustable mechanical properties are other advantages of the FRPs. However, there are major concerns about long-term performance, serviceability and durability of FRP applications in concrete structures. Therefore, structural health monitoring (SHM) and damage detection in FRP-retrofitted concrete structures need to be implemented. This paper presents a study on investigating the application of Rayleigh wave for detecting debonding defect in FRP-retrofitted concrete structures. A time-of-flight (ToF) method is proposed to determine the location of a debonding between the FRP and concrete using Rayleigh wave. A series of numerical case studies are carried out to demonstrate the capability of the proposed debonding detection method. In the numerical case studies, a three-dimensional (3D) finite element (FE) model is developed to simulate the Rayleigh wave propagation and scattering at the debonding in the FRP-retrofitted concrete structure. Absorbing layers are employed in the 3D FE model to reduce computational cost in simulating the practical size of the FRP-retrofitted structure. Different debonding sizes and locations are considered in the case studies. The results show that the proposed ToF method is able to accurately determine the location of the debonding in the FRP-retrofitted concrete structure.

• 한국군사과학기술학회지
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• 제14권4호
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• pp.639-647
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• 2011

In this paper, we have designed the Anti-Aircraft Artillery(AAA) model for the surface-to-air virtual engagement. The AAA model for the virtual combat simulation needs to detect the present target and estimate the target flight trajectory to find the aiming point. To find collision point of projectile fired from the artillery with the moving air target, we have presented the estimating technique for artillery aiming point. And we have analyzed the target probability of kill using Calton Hit function. Anti-air threat envelops are presented when the target velocity, position and the arrangement of four AAA are varying. Then we have compared the analyzed result using developed model with AEM model of MSA program.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 유기절연재료 전자세라믹 방전플라즈마 일렉트렛트 및 응용기술
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• pp.185-188
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• 2002

This paper describes the information for quantitative simulation of weakly ionized plasma. We should grasp the meaning of the plasma state condition to utilize engineering application and to understand materials of plasma state. In this paper, the drift velocity of electron in $SF_6+O_2$ mixture gas calculated for range E/N values l~900[Td] at the temperature is 300[$^{\circ}K$] and pressure is 1[Torr], using a set of electron collision cross sections determined by the authors and the values of drift velocity of electrons are obtained for TOF, PT, SST sampling method of Backward Prolongation by two term approximation Boltzmann equation method. It has also been used to predict swarm parameter using the values of cross section as input. The result of Boltzmann equation, the drift velocity of electrons, has been compared with pure $SF_6$, pure $O_2$ and mixture gas.

• 한국항공우주학회지
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• 제31권3호
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• pp.50-57
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• 2003

본 연구에서 헬리콥더의 궤적추종을 위한 제어기의 설계 및 평가를 수행하였다. 제어시스템의 알고리즘은 선형 되먹임 기법과 두 단계 시간분리 구조를 이용하여 구성하였다. 또한 헬리콥터 동특성에 대한 정확한 정보의 결핍으로 인한 모델 역변화 오차를 보상하기 위해 신경회로망을 이용한 실시간 적응제어 구조를 자세제어 시스템에 적용하였다. 제어 시스템의 궤적추종성능은 아파치 헬기의 동측성을 나타내는TMAN 시뮬레이션 프로그램의 단순형을 사용하여 평가하였다. 이를 통하여 실시간 신경회로망 적응제어 구조가 동특성 정보의 부족으로 이한 궤도 추종 제어의 성능 저하 문제에 매우 효과적으로 기여함을 보였다.

• International Journal of Aeronautical and Space Sciences
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• 제1권2호
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• pp.43-49
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• 2000

The Global Positioning System (GPS) is becoming more attractive navigation means for LEO (Low Earth Orbit) spacecraft due to the data accuracy and convenience for utilization. The anomalies such as serious variations of Dilution-Of-Precision (DOP), loss of infrequent 3-dimensional position fix, and deterioration of instantaneous accuracy of position and velocity data could be observed, which have not been appeared during the ground testing. It may cause lots of difficulty for the processing of the orbit control algorithm using the GPS data. In this paper, the characteristics of the GPS data were analyzed according to the configuration of GPS receiver such as position fix algorithm and mask angle using GPS navigation data obtained from the first Korea Multi-Purpose Satellite (KOMPSAT). The problem in orbit tracking using GPS data, including the infrequent deterioration of the accuracy, and an efficient algorithm for its countermeasures has also been introduced. The reliability and efficiency of the modified algorithm were verified by analyzing the effect of the results between algorithm simulation using KOMPSAT flight data and ground simulator.

• International Journal of Aeronautical and Space Sciences
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• 제11권4호
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• pp.338-344
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• 2010

This paper discusses the development of the control system of a mini quadrotor in Konkuk University for indoor applications. The attitude control system consists of a stability augmentation system, which acts as the inner loop control, and a modern control approach based on modeling will be implemented as the outer loop. The inner loop control was experimentally satisfied by a proportional-derivative controller; this was used to support the flight test in order to validate the modeling. This paper introduces the mathematical model for the simulation and design of the optimal control on the outer loop control. To perform the experimental tests, basic electronic hardware was developed using simple configurations; a microcontroller used as the embedded controller, a low-cost 100 Hz inertial sensors used for the inertial sensing, infra-red sensors were employed for horizontal ranging, an ultrasonic sensor was used for ground ranging and a high performance propeller system built on an quadrotor airframe was also employed. The results acquired from this compilation of hardware produced an automatic hovering ability of the system with ground control system support for the monitoring and fail-safe system.

• International Journal of Aeronautical and Space Sciences
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• 제12권4호
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• pp.365-370
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• 2011

This paper presents the air-to-air missile autopilot design for a $180^{\circ}$ heading reversal maneuver during boost-phase. The missile's dynamics are linearized at a set of operating points for which angle of attack controllers are designed to cover an extended flight envelope. Then, angle of attack controllers are designed for this set of points, utilizing a pole-placement approach. The controllers' gains in the proposed configuration are computed from aerodynamic coefficients and design parameters in order to satisfy designer-chosen criteria. These design parameters are the closed-loop frequency, damping ratio, and time constant; these represent the characteristics of the control system. To cope with highly nonlinear and rapidly time varying dynamics during boost-phase, the global gain-scheduled controller is obtained by interpolating the controllers' gains over variations of the angle of attack, Mach number, and center of gravity. Simulation results show that the proposed autopilot design provides satisfactory performance and possesses good [ed: or "sufficient" or "excellent"] capabilities.

• International Journal of Aeronautical and Space Sciences
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• 제11권1호
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• pp.49-57
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• 2010

Several pyrotechnic devices are employed over the course of satellite's missions, generally for the separation of structural subsystems and deployment of appendages. Firing of pyrotechnic devices results in impulsive loads characterized by high peak acceleration and high frequency content which can cause failures of various flight hardware elements and small components. Thus, accurate prediction of acceleration level in various components of spacecraft due to pyrotechnic devices is important. In this paper, two methods for pyroshock prediction, an empirical model and statistical energy analysis in conjunction with virtual mode synthesis, are applied to predict shock response of a low altitude earth observation satellite during launch vehicle separation. The predicted results are then evaluated through comparison with the shock test results.

• 한국항공우주학회지
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• 제48권8호
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• pp.573-580
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• 2020

다중개체를 제어하기 위해서 해결해야 되는 문제들 중 하나는 위치제어다. 위치와 속도를 제어하기 위한 모델로 augmented Cucker-Smale 모델이 존재했다. 하지만 기존 모델은 모든 개체에 동일한 시스템을 적용함에 따라서 개별개체의 특성을 살리지 못했다는 특징이 있다. 본 논문에서는 그 점을 보안하고 적절한 형태로 변형하기 위해서 초기 위치와 분포를 이용한 마할라노비스 거리를 계수와 통계학적 자유도를 적용해서, 모델의 수렴시간과 소모에너지를 동시에 줄이고자 한다. 모델의 성능 검증을 위해서 몬테카를로 시뮬레이션을 통해서 전체적인 경향성을 판단했고, 추가적으로 개별 개체의 움직임을 분석하여서 마할라노비스 거리 계수가 적절한 역할을 수행하고 있는지 확인했다.

• 항공우주기술
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• 제3권1호
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• pp.109-116
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• 2004

일반적으로 위성에 장착된 GPS 수신기는 GPS 위성으로부터 항법 신호를 받아서 위성의 위치, 시간 및 속도 정보를 제공하는 것을 주요 목적으로 하고 있다. 이러한 정보를 근거로 위성의 현재 위치정보 및 임무 수행을 위한 정보를 유도하게 된다. 2005년 발사예정인 아리랑 위성2호는 GPS 수신기에서 나오는 IPPS 신호를 위성체 각 프로세서의 기준시간으로 사용되며 DPLL, FEP회로 및 운용소프트웨어(FSW)에 의하여 동작된다. 본 논문에서는 아리랑 위성2호(KOMPSAT-2,이하 K2)의 시간동기구조에 대한 구조 및 설계에 대한 뿐 아니라 정밀도 분석 및 시험결과등 전 과정에 대한 내용을 기술하였다.