• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.5
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• pp.391-399
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• 2005

Laser-generated ultrasonic inspection system is a non-contact scanning inspection device with high spatial resolution and wide bandwidth. The amplitude of laser-generated ultrasound is varied according to the energy of pulse laser and the surface conditions of an object where the CW measuring laser beam is pointing. In this paper, we correct the generating errors by measuring the energy of pulse laser beam and correct the measuring errors by extracting the gain information of laser interferometer at each time. h dynamic stabilizer is developed to stably scan on the surface of an object for an laser-generated ultrasonic inspection system. The developed system generates ultrasound after adaptively finding the maximum gain time of an laser interferometer and processes the signal in real time after digitization with high speed. In this paper, we describe hardware configuration and control algorithm to build a stable laser-generated ultrasonic inspection system. Also, we confirmed through experiments that the proposed correction method for the generating errors and measuring errors is effective to improve the performance of a system.

• Nuclear Engineering and Technology
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• v.25 no.1
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• pp.125-135
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• 1993

The safe and efficient operation of nuclear plants is recognized to be accomplished through the application of plant automation using digital technology, which is one of main targets of the next generation nuclear plants. For plant level automation, it is first required that each major subsystem be digitalized, and the steam generator water level control system is discussed in this study. The transfer functions between inputs and the level are derived by employing the thermal hydraulic model of the steam generator and are applied to the analysis of the current three-element control system. Since the control scheme in this study includes the steam generator itself as a process plant, the system order is high and the numerical instability arises in digitalizing. Together with this, the unreliability of the feedwater feedback signal at low power level leads to the proposal of a two-element control system with a proper digital controller. The digital PI controller developed for this system has the initial power adaptive gain and integration time constant. And it makes the overall system response satisfy the stability and other necessary control specifications simultaneously. Since the two-element control system using this controller depends on the initial power only, it is simple to define and it shows a similar level response behavior to that of its corresponding analog system.

• Smart Structures and Systems
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• v.20 no.1
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• pp.61-74
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• 2017

One of the most reliable and simplest tools for structural vibration control in civil engineering is Tuned Mass Damper, TMD. Provided that the frequency and damping parameters of these dampers are tuned appropriately, they can reduce the vibrations of the structure through their generated inertia forces, as they vibrate continuously. To achieve the optimal parameters of TMD, many different methods have been provided so far. In old approaches, some formulas have been offered based on simplifying models and their applied loadings while novel procedures need to model structures completely in order to obtain TMD parameters. In this paper, with regard to the nonlinear decision-making of fuzzy systems and their enough ability to cope with different unreliability, a method is proposed. Furthermore, by taking advantage of both old and new methods a fuzzy system is designed to be operational and reduce uncertainties related to models and applied loads. To design fuzzy system, it is required to gain data on structures and optimum parameters of TMDs corresponding to these structures. This information is obtained through modeling MDOF systems with various numbers of stories subjected to far and near field earthquakes. The design of the fuzzy systems is performed by three methods: look-up table, the data space grid-partitioning, and clustering. After that, rule weights of Mamdani fuzzy system using the look-up table are optimized through genetic algorithm and rule weights of Sugeno fuzzy system designed based on grid-partitioning methods and clustering data are optimized through ANFIS (Adaptive Neuro-Fuzzy Inference System). By comparing these methods, it is observed that the fuzzy system technique based on data clustering has an efficient function to predict the optimal parameters of TMDs. In this method, average of errors in estimating frequency and damping ratio is close to zero. Also, standard deviation of frequency errors and damping ratio errors decrease by 78% and 4.1% respectively in comparison with the look-up table method. While, this reductions compared to the grid partitioning method are 2.2% and 1.8% respectively. In this research, TMD parameters are estimated for a 15-degree of freedom structure based on designed fuzzy system and are compared to parameters obtained from the genetic algorithm and empirical relations. The progress up to 1.9% and 2% under far-field earthquakes and 0.4% and 2.2% under near-field earthquakes is obtained in decreasing respectively roof maximum displacement and its RMS ratio through fuzzy system method compared to those obtained by empirical relations.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.6
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• pp.633-641
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• 2015

Several complex processes that are employed in industries, such as shipping, power plants, and the petrochemical industry, involve time-varying behavior as well as strong nonlinear behavior during operation. The fixed-parameter proportional-integral-derivative (PID) controllers have difficulty in dealing with control problems that occur in such processes. In this paper, we propose a method of designing a nonlinear PID controller for industrial processes that exhibit a large number of nonlinearities and time-varying behavior. The gains of the nonlinear PID controller are characterized by a simple nonlinear function of the error and/or error rate depending on the process set-point and output. We tune the user-defined parameters using a genetic algorithm by minimizing the integral of time absolute error (ITAE) index. We verify the effectiveness of the proposed method by performing a comparison of the proposed method and two other nonlinear and adaptive methods that are employed for reference tracking, disturbance-rejection performances, and robustness to parameter changes on a continuously stirred tank reactor.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.1
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• pp.81-88
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• 2003

For driver's convenience, the ACC(Adaptive Cruise Control) requires a system which determines the direction of vehicles and controls the vehicle to keep the distance among the automobiles constant. This paper describes the microstrip array antennas designed to operate at 24 GHz, and used as a direction indicator of moving vehicles. 8${\times}$2 transmit array antenna with wide beamwidth, 8${\times}$4 receive center array antenna, and two 8${\times}$8 receive array antennas with narrow beamwidth were designed and fabricated. Measurement results for the arrays showed that the azimuthal beamwidth is 50$^{\circ}$and the gain is 16.7 dBi for the transmit array antenna. For the receive array antenna, the center, the left, and the right array antenna have beamwidths of 20$^{\circ}$, 13$^{\circ}$, 13$^{\circ}$respectively, and have gains of more than 20 dBi. The left and right array antenna have the beam tilt angle of ${\pm}$18$^{\circ}$. The measured radiation patterns showed a good agreement with the simulated patterns, and the designed array antennas are suitable fur detecting 3 directions of the vehicle within the scan angle area.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.85-85
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• 2011

홍수기에 안전하고 정확한 유량측정을 통하여 물관리에 필요한 기초수문자료를 확보하고자 한국수자원공사에서 1993년도부터 홍수유량측정기술 확보를 위한 연구를 시작하였다. 그간의 연구성과를 바탕으로 1999년도에 하천의 유속을 비접촉식으로 측정할 수 있는 홍수용 전자파표면유속계를 개발하여 특허등록하였고 그와 동시에 이의 상품화를 추진하여 2010년도까지 75대를 보급하여 실무에서 이용하고 있다. 이동식인 홍수용 전자파표면유속계를 바탕으로 2001년도에는 고정식 실시간 홍수유량측정측정시스템을 개발하여 특허등록하였고, 이 시제품을 현재 용담 수자원시험유역의 동향지점에서 시험운영하고 있다. 또한, 현장 유량측정실무자들의 홍수용 전자파표면유속계 개선요구에 따라 편각용 전자파표면유속계 시제품을 개발하였으며, 이는 임의의 한 지점에 설치한 한 대의 장비로 좌우 여러 측선의 유속을 동시에 측정할 수 있는 다점 측정기능을 갖도록 성능을 개선하였다. 이에 따라 홍수시 유량측정에 소요되는 시간이 줄어들어 신속하게 유량측정을 완료할 수 있는 계기를 마련하였다. 이와 더불어 유속측정 범위를 확장하여 홍수시의 고유속 뿐만 아니라 0.5 m/s 이하의 저유속까지 측정할 수 있는 범용 전자파표면유속계의 시제품을 추가로 개발하였다. 이 장비는 최저유속 0.03 m/s의 측정을 실내시험을 통하여 입증하였다. 범용 전자파표면유속계는 상품화 시제품의 개발을 목표로 기존 시제품의 현장시험을 통하여 현장적용상의 문제점에 대한 해결에 주력하였다. 첫째, 평갈수용 전자파표면유속계의 사용편의를 개선하기 위하여 소형화 및 경량화를 추진하였고, 이를 위하여 사용주파수를 기존의 10 GHz에서 24 GHz로 변경함으로써 $35{\times}35\;cm$ 크기의 기존안테나를 $22{\times}22\;cm$ 크기로 소형화하였으며 송수신부의 무게는 기존 18 kg에서 3.3 kg으로 혁신적으로 줄이는데 성공하였다. 이를 위하여 안테나는 기존의 반사형안테나에서 도파관슬롯배열안테나로 변경하였다. 둘째, 측정값의 안정화를 위하여 안테나의 특성을 개선하여 부엽(side-lobe) 레벨 30 dB 이하 그리고 전후방비(front-back ratio) 50 dB 이하로 개선하여 안테나가 지향하는 방향 이외의 위치에서 반사되는 불필요한 신호를 줄였다. 또한 적응형 이득제어(adaptive gain control)기법의 채택으로 미소 신호에 대한 안정적 측정 및 과다 신호에 대한 능동적 감쇄를 할 수 있도록 시스템을 구성하여 전 유속범위에 대한 안정적 측정을 가능토록 설계 및 제작하였다. 셋째, 자가점검 기능을 탑재하여 유속측정 전에 기기의 상태에 대한 self test기능을 통하여 측정자가 기기의 상태를 사전에 파악 가능토록함으로써, 기기 오작동에 대한 능동 대처할 수 있도록 하였다. 이외에도 저전력 회로설계를 통하여 배터리 사용시간을 확장하였고, 기존의 전자파표면유속계가 가지고 있던 방습 및 방수에도 내성을 갖는 제품으로 설계하였으며 스마트기기를 이용한 무선측정 및 세련된 디자인 등 사용자의 요구사항을 충분히 반영하였다.