• Structural Engineering and Mechanics
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• 제82권5호
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• pp.571-585
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• 2022

As a vital component of power grids, long-span transmission tower-line systems are vulnerable to wind load excitation due to their high flexibility and low structural damping. Therefore, it is essential to reduce wind-induced responses of tower-line coupling systems to ensure their safe and reliable operation. To this end, a shape memory alloy-bidirectional tuned mass damper (SMA-BTMD) is proposed in this study to reduce wind-induced vibrations of long-span transmission tower-line systems. A 1220 m Songhua River long-span transmission system is selected as the primary structure and modeled using ANSYS software. The vibration suppression performance of an optimized SMA-BTMD attached to the transmission tower is evaluated and compared with the effects of a conventional bidirectional tuned mass damper. Furthermore, the impacts of frequency ratios and SMA composition on the vibration reduction performance of the SMA-BTMD are evaluated. The results show that the SMA-BTMD provides superior vibration control of the long-span transmission tower-line system. In addition, changes in frequency ratios and SMA composition have a substantial impact on the vibration suppression effects of the SMA-BTMD. This research can provide a reference for the practical engineering application of the SMA-BTMD developed in this study.

• 대한지역사회영양학회지
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• 제2권4호
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• pp.605-615
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• 1997

The job characteristics and competencies of 285 dietitians in employee foodservices were investigated by worker-oriented job analysis methodology. The purposes of this study were to : a) determine the knowledge, abilities, skills and other characteristics(KASO) needed for dietitians in two types of employee foodservice groups(self-operated vs. contracted), b) categorize KASO items by factor analysis and c) provide job information and job descriptions for dietitians in employee foodservices. The job analysis questionnaire was consisted of questions concerning the 134 KASO items. The questionnaire was mailed to 250 dietitians who are members of The Korean Dietetic Association Practice Group in self-operated foodservices(group A) and 250 dietitians who are employed in contracted foodservice companies(group B). Completed questionnaires were received from 285 dietitians(121 in self-operated, 164 in contracted) ; with response rate of 57%. Statistical data analysis was completed using the SPSS/win and the SAS/win packages. The results of this study can be summarized as follows. 1) Through factor analysis, the 134 KASO items were regrouped into 6 categories :‘primary dietetic tasks concerning menu management and administrative work regarding merchants’, ‘primary dietetic tasks concerning procurement and purchasing of food and supplies and meal production and service control’, ‘primary dietetic tasks concerning facility, sanitation and safety control’, ‘secondary dietetic tasks concerning nutrition education and research’, ‘secondary dietetic tasks concerning foodservice operation management’and‘human attributes’. 2) Analysis of the total scores(average scores of degree of frequency, importance and entry requirements of KASO items within 6 categories), group A showed high priorities placed on‘human attributes’, ‘procurement and purchasing of food and supplies and meal production and service control’, ‘menu management and administrative work regarding merchants’, ‘whereas group B showed high priorities placed on’‘human attributes’, ‘foodservice operation management’. (Korean J Community Nutrition 2(4) : 605-615, 1997)

• 한국정보통신학회논문지
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• 제26권7호
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• pp.1026-1031
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• 2022

인지무선 에드혹 네트워크 (CRAHN : Cognitive Radio Ad-Hoc Networks)는 무선 서비스의 증가에 따른 주파수 자원부족을 극복할 수 있는 네트워크 기술이다. CRANH에서 주 사용자에 대한 간섭을 회피하기 위해 유휴채널을 확인하는 채널센싱이 필요하며, 주 사용자 출현시 빠른 유휴 채널선택을 통해 핸드오버로 인한 시간지연을 최소화 해야한다. 본 연구에서는 강화학습을 이용하여 CRANH에서 부 사용자의 채널 센싱의 대상을 축소하고 유휴채널의 가능성이 높은 채널을 우선적으로 센싱하도록함으로써 전송효율을 개선하였다. 또한 주기적인 센싱을 수행하지 않고 데이터의 전송시점에 채널을 센싱함으로써 센싱시점과 데이터 전송시점간의 차이로 인한 주 사용자와의 충돌가능성을 최소화할 수 있는 멀티채널 매체접근제어(MAC: Medium Access Control) 프로토콜을 제안하고 시뮬레이션을 통해 그 성능을 분석하였다.

• 조명전기설비학회논문지
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• 제22권7호
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• pp.7-15
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• 2008

A single active capacitor snubber-assisted soft-switching sinewave pulse modulation utility-interactive power conditioner with a three-winding flyback high frequency transformer link and a bidirectional active power switch in its secondary side has been proposed. With the aid of the switched-capacitor quasi-resonant snubber cell, the high frequency switching devices in the primary side of the proposed DC-to-AC sinewave power inverter can be turned-off with ZVS commutation. In addition to this, the proposed power conditioner in the DCM can effectively take the advantages of ZCS turn-on commutation. Its output port is connected directly to the utility AC power source grid. At the end, the prototype of the proposed HF-UPC is built and tested in experiment. Its power conversion conditioning and processing circuit with a high frequency flyback transformer link is verified and the output sinewave current is qualified in accordance with the power quality guidelines of the utility AC interactive power systems.

• 한국산학기술학회논문지
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• 제22권4호
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• pp.140-149
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• 2021

기업 기밀과 고객 정보를 적절하게 보호하고 유지하기 위해, 조직은 정보보호 관리체계(ISMS), 개인정보보호 관리체계(PIMS), 비즈니스연속성 관리체계(BCMS)와 같은 경영시스템을 도입하여 운영하기 시작하였다. 본 연구는 정보보안을 고려하는 모든 조직이 정보보호 관리체계를 유지하는 것이 바람직하며 ISMS는 정보보안 문화, 실무 및 가이드라인을 고려하는 다양한 조직 안에 각기 다른 형태를 가질 수 있다는데서 출발하였다. 산업분야에 상관없이 적용 가능하고 보편적으로 널리 알려진 국제 정보보호 관리체계 ISO27001을 도입한 조직을 대상으로, 인증 심사에 따른 부적합 사례를 통해 산업별, 조직규모별, 심사유형별 정보보호 관리체계의 주요 통제 영역을 도출하려 하였다. 국내의 경우 산업분야별 인증을 유지하고 있는 곳이 많지 않아 실증 연구를 위한 자료 확보에 어려움이 있지만, 탐색적 연구 대상으로서의 의미가 있는 것으로 보인다. 분석을 통해, 대상 업체들에서 ISO27001:2013이 발표된 2013년부터 2020년까지 각 형태별로 부적합 빈도수가 가장 높았던 요구사항을 주요 통제영역으로 도출하였다. 이를 바탕으로 3개 산업분야, 조직규모, 심사유형에 따라 ISMS의 주요 통제항목에 차이가 있다는 것을 발견하였다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1990년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 26-27 Oct. 1990
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• pp.1316-1321
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• 1990

Molten steel level information of ladle is very important for process control in steelmaking process. At secondary refining process, measuring lance and snokel have to keep constant thier depth from molten steel surfaces. But, there is much slag on the molten steel surface. Besides, not only the thickness of slag is varied with refining condition, but also molten steel level is largely affected by firebrick errosion. Then, optical measuring method and/or by human eyes cannot detect true molten steel surface, but slag surface. This slag thickness is 300mm at maximum, then huge diameter eddy current sensor will be needed if that type sensor is applied. In addition to, cooling system is necessary because the molten steel and slag temperature is high. This is not practically. To solve this problem, immersion type levelmeter is developed. This sensor is made up from primary and secondary cylindrical coils. High frequency current is applied to primary coil. Electro-motive force from secondary coil is measured, which is varied with molten steel level. This complete set is installed within stainless steel long capsule and attached to top of lance. This sensor is immersed into molten steel bath of ladle or tundish with protection of expendable paper sleeve.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.310-315
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• 2008

Authors design a rotary-type small-scaled linear induction motor(LIM) and a performance test machine before manufacturing a real-scaled LIM for a railway transit. The designed LIM is a single-sided, short primary type and its primary has 4 poles. The rated power is 10(kW). In order to analyze characteristics of the LIM, authors use a mixed 2D-3D FEM analysis. 3-D FEM analysis is used for calculating a distribution of eddy-current on the semi-caped AL-sheet of the secondary reaction. Authors calculate a correction factor of conductivity and an equivalent conductivity on the secondary AL-sheet using a normalized eddy-current. The equivalent conductivity which is calculated in this way includes a transverse edge-effect of the LIM. Authors apply the equivalent conductivity on the secondary AL-sheet of 2D-FEM model and get performance characteristics of the LIM. Basic characteristics such as thrust and normal force, input current, efficiency and power factor of the LIM have been analyzed with the variation of frequency and speed. In order to apply an air-gap control system, the variation of the basic characteristics have been analyzed with the air-gap length variation of the LIM. Finally, authors introduce an operation mode using the air-gap control system and conduct a research on feasibility of the system.

• Smart Structures and Systems
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• 제10권6호
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• pp.573-591
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• 2012

In this study, a procedure to design an optimal LCVA that maximizes the equivalent damping ratio added to the primary structure subjected to along-wind excitation is proposed. That design procedure does not only consider the natural frequency and damping ratio of the LCVA, but also the proportion of the U-shaped liquid, which is closely related to the participation ratio of the liquid mass in inertial force. In addition, constraints to ensure the U-shape of the liquid are considered in the design process, so that suboptimal solutions that violate the optimal tuning law partly are adopted as a candidate of the optimal LCVA. The proposed design procedure of the LCVA is applied to the control of the 76-story benchmark building, and the optimal proportions of the liquid shape under various design conditions are compared.

• 전기학회논문지
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• 제68권1호
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• pp.8-12
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• 2019

Combined Cycle Unit(CC) generates the primary power from the Gas Turbine(GT) and supplies the remaining heat of the GT to the Steam Turbine(ST) to generate the secondary power from the ST. It plays a major role in terms of energy efficiency and Load Frequency Control(LFC). Incremental Heat Rate(IHR) curves of economic dispatch(ED) of CC is applied differently by GT/ST combination. But It is practically difficult because of performance test by all combinations. This paper suggests a reasonable method for estimating IHR curves for partial combinations(1:1~(N-1):1) using IHR curves when operating with GT alone(1:0) and with all(N:1) combinations of CC.

• 한국주조공학회지
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• 제26권5호
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• pp.205-210
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• 2006

여러 전자기 재료 프로세싱 연구 중에서 연구 되어지지 않았던 Al-Si 합금의 조직제어를 직류 자기장과 교류 전류장을 사용하여 시도 하였다. 본 연구의 목적은 Al-Si 합금에서의 새로운 거시, 미시 조직제어를 하기 위해 사용된 전자기 진동의 영향을 조사하는 것이다. 전자기 진동이 초정 알루미늄의 형상 변화를 위해 낮은 진동수 (>60Hz)로 주어질 경우, 수지상의 형상이 구상화 형상으로 변해갔다. 전자기 진동이 공정 실리콘 형상 변화를 위해 주어졌을 경우, 높은 진동수 (>500Hz)에서 조대한 판상 조직이던 실리콘이 미세한 섬유상 조직으로 변화하고, 기계적 성질도 우수해졌다.