• Wind and Structures
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• 제16권3호
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• pp.263-278
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• 2013

The fatigue load of a turbine blade has become more important because the size of commercial wind turbines has increased dramatically in the past 30 years. The reduction of the fatigue load can result in an increase in operational efficiency. This paper numerically investigates the load reduction of large wind turbine blades using active aerodynamic load control devices, namely trailing edge flaps. The PD and LQG controllers are used to determine the trailing edge flap angle; the difference between the root bending moment and its mean value during turbulent wind conditions is used as the error signal of the controllers. By numerically analyzing the effect of the trailing edge flaps on the wind turbines, a reduction of 30-50% in the standard deviation of the root bending moment was achieved. This result implies a reduction in the fatigue damage on the wind turbines, which allows the turbine blade lengths to be increased without exceeding the designed fatigue damage limit.

• Smart Structures and Systems
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• 제33권3호
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• pp.189-199
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• 2024

To properly extract the strain components under varying operational conditions is very important in bridge health monitoring. The abnormal sensor readings can be correctly identified and the expected operational performance of the bridge can be better understood if each strain components can be accurately quantified. In this study, strain components under varying load conditions, i.e., temperature variation and live-load variation are evaluated based on field strain measurements collected from a real concrete box-girder bridge. Temperature-induced strain is mainly regarded as the trend variation along with the ambient temperature, thus a smoothing technique based on the wavelet packet decomposition method is proposed to estimate the temperature-induced strain. However, how to effectively extract the vehicle-induced strain is always troublesome because conventional threshold setting-based methods cease to function: if the threshold is set too large, the minor response will be ignored, and if too small, noise will be introduced. Therefore, an autoencoder framework is proposed to evaluate the vehicle-induced strain. After the elimination of temperature and vehicle-induced strain, the left of which, defined as the model error, is used to assess the operational performance of the bridge. As empirical techniques fail to detect the degraded state of the structure, a clustering technique based on Gaussian Mixture Model is employed to identify the damage occurrence and the validity is verified in a simulation study.

• 한국항공우주학회지
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• 제31권6호
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• pp.110-117
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• 2003

착륙장치 시스템의 올림/내림 작동특성은 다양한 설계변수, 운용조건 및 환경조건에 따라 변화한다. 최소한의 작동공간 및 성능 요구조건을 만족하기 위하여, 착륙장치 시스템은 관련계통의 영향성을 고려하여 기구학적/동역학적 작동해석이 요구된다. 본 연구에서는 T-50 착륙장치를 모델로 ADAMS를 이용하여 착륙장치 작동에 따른 동적거동을 해석할 수 있는 프로그램을 개발하였다. 설계변수 설정, 유압 압력/유량의 관계 정의, 운동방정식을 유도하여 공력하중, 기동하중, 온도의 영향에 대한 착륙장치 및 덮개문의 정상/비상 작동 동적거동 해석결과를 제시하고 분석하였다. 이러한 해석결과를 바탕으로 향후 새로운 착륙장치 개발시 범용적인 해석이 용이할 뿐만 아니라 지상/비행시험의 문제점 발생시 고장탐구 해결에 활용할 수 있다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 D
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• pp.2825-2827
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• 2000

In electric power industry. load balance has been one of the most fundamental and important management goals. Therefore. the strategy to achieve high quality load management now includes load balance besides the stabilization of electricity supply and quality management of electricity. Amongst many techniques of load management. direct load management has been actively studied and utilized to increase power facility and peak load suppression. Higher peak load situation is appeared during summer than during winter in Korea. and approximately 20% of the peak load is due to the load for air-conditioning. To cope with this peak load problem during summer KEPCO is performing a research project to develop a system to remotely control air-conditioning load using wireless communication. Currently, applicable facilities are limited to small-scale air-conditioning facility that has less than 2KW power capacity. This paper described the 1st year of efforts made in the study.

• 한국대기환경학회지
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• 제33권6호
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• pp.605-615
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• 2017

Efficient simultaneous reduction conditions for $NO_x$ and $NH_3$-slip was investigated in SCR (Selective Catalytic Reduction) process with load variation by applying dual catalysts (SCR catalyst, $NH_3$ decomposition catalyst) system. $N_2O$ formation characteristics were analyzed to look into possible undesirable reaction pathways. In the experiments of catalyst characteristics, various operational variables were tested for the combined catalytic system, such as $NH_3/NO_x$ ratio, temperature, oxygen concentration and $H_2O$. The reaction characteristics of $NO_x$, $NH_3$ and $N_2O$ were analyzed and optimal conditions could be evaluated for the combustion facility with varied load. In terms of $NO_x/NH_3$ simultaneous reduction and $N_2O$ formation suppression, optimal condition was considered NSR 1.2 and temperature $300^{\circ}C$. At this operational condition, $NO_x$ conversion was 98%, $NH_3$ reduction efficiency was 95%, generated $N_2O$ concentration 9.5 ppm with inlet $NO_x$ concentration of 100 ppm. In $NH_3-SCR$ process with $NH_3$ decomposition catalyst, $NO_x$ and $NH_3$ can be considered to be reduced simultaneously at limited conditions. The results of this study may be utilized as basic data at facilities requiring simultaneous $NO_x$ and $NH_3$ reduction for facilities with load variation.

• Journal of Power Electronics
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• 제11권6호
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• pp.793-800
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• 2011

This paper investigates the operational modes of buck dc-dc converters and their energy transmission methods. The operational modes of such converters are classified in two types, discontinuous conduction mode (DCM) and continuous conduction mode (CCM). In this paper, the critical inductance relation of DCM and CCM is determined. The equations of the output voltage ripple (OVR) for each mode are obtained for a specific input voltage and load resistance range. The maximum output voltage ripple (MOVR) is also obtained for each mode. The filter size is decreased and the minimum required inductance value is calculated to guarantee the minimization of the MOVR. The experimental and simulation results in PSCAD/EMTDC prove the correctness of the presented theoretical concepts.

• JSTS:Journal of Semiconductor Technology and Science
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• 제15권3호
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• pp.326-333
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• 2015

This paper reports an adaptive positive feedback bias control technique for operational transconductance amplifiers to adjust the bias current based on the output current monitored by a current replica circuit. This technique enables operational transconductance amplifiers to quickly adapt their power consumption to various analog workloads when they are configured with negative feedback. To prove the concept, a test voltage follower is fabricated in $0.5-{\mu}m$ CMOS technology. Measurement result shows that the power consumption of the test voltage follower is approximately linearly proportional to the load capacitance, the signal frequency, and the signal amplitude for sinusoidal inputs as well as square pulses.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 A
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• pp.95-97
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• 1995

A superconducting current generator, or a superconducting rectifier(SCR) is used as a current source to energize a superconducting magnets in SMES, MRI. We selected a full-wave SCR among various SCR models and analyzed its operational characteristics by computer simulation. In process of pumping the current, the improvement of performance is dependent on how much bigger the open resistance of the switch is in comparison to load coil impedance when one of two switches become active. Faster transfer can he seen in resistive commutation mode by shortening the time elapsed for the resistance to arrive at certain level from zero state. Although recovery time for the switch has no direct effect on current pumping, optimal switch design is needed to increasing operational frequency.

• 전기학회논문지
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• 제61권11호
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• pp.1578-1583
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• 2012

There are 3 systems in incentive-based normal load management in Korea; day or hour-ahead, week-ahead, months-ahead. These are originally similar in their operational implementation, but differ in their pre-notification period. Therefore the incentive of these systems should be different according to prenotification period. This is the key problem in implementing these load managements. Customers participating in these load managements feel their economic differences, depending on the risk by prenotification dates. The shorter prenotification period, the more risk take the customers. This paper proposes the method of incentive variation in prenotification difference, by using the theory of financial yield curve, which is used in analysing short and long duration bond interesting rates and is reflecting risk premium in their period.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2006년도 추계학술대회 논문집
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• pp.1082-1087
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• 2006

Human factors still plays a significant role in railway accidents. The accidents often resulted from multiple causes of hardware failures and human errors. So to ensure the safety of railway operations, human error should be effectively prevented and managed. Among several factors influencing human performance, task load (or task complexity) is well known as a major contributor to human error. In order to reduce the potential of human error, a systematic analysis should be undertaken to evaluate task load and to reduce it by modifying task process and/or education&training. In this paper, we proposed a systematic framework for railway industry to perform task analysis and to evaluate task load, and applied it to KTX operational tasks. According to the application study, we identified 14 generic task types of KTX operation. And also this paper shows the quantitative task load of those generic tasks which were analyzed by NASA-TLX method.