• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1993년도 한국자동제어학술회의논문집(국제학술편); Seoul National University, Seoul; 20-22 Oct. 1993
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• pp.218-223
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• 1993

In this paper, we present a full digital control scheme which controls currents and speed of the permanent magnet AC servo motor with large range of bandwidth and high performance. The current equations of the permanent magnet AC servo motor are linearized by feedback linearization technique. Both acceleration feedforward terms and IP controllers, whose gains are functions of motor speed, are used in order to control motor currents. In addition the phase delays in current control loops are compensated by placing phase lead-lag compensators after current commands, which make it possible to avoid high gains in the current controllers. Unity power factor can be achieved by the proposed current controller. Pulsewidth modulation is performed by way of the well-known comparison with a triangular carrier signals. The velocity controller is designed on the basis of the linearized model of the permanent magnet AC servo motor by the proposed current controller. The performance of the entire control system is analyzed in the presence of uncertainty in the motor parameters. The proposed control scheme is implemented using the digital signal processor-based controller composed of an Analog Device ADSP 2111 and a NEC78310. The pulsewidth modulation (PWM) signals are generated through a custom IC, SAMSUNG-PWM1, which has the outputs of current controllers as input. The experimental results show that the permanent magnet AC servo motor can be always driven with high dynamic performance by the proposed full digital control scheme of motor speed and motor current.

• 한국해양공학회지
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• 제28권4호
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• pp.314-323
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• 2014

In this study, a gearbox and blade were modeled in the MASTA program, and the housing and carrier components were modeled using a finite element method. Using substructure synthesis, all the components were combined and used to establish a vibration model of a 2.5-MW wind turbine gearbox. In addition, the safety displacement factor was evaluated using an AGMA data sheet about bearing's outer race for the input shaft and output shaft. As a result, the bearing's outer race for the input shaft, and the radial and axial responses were satisfied by the $1^{st}$ and $2^{nd}$ planetary gears and the $3^{nd}$ helical gear transmission error(TE), respectively. However, the output shaft support bearing's outer race responses were not satisfied with the radial response by the $2^{nd}$ TE and axial response by the $3^{rd}$ TE. To reduce the vibration, tooth modification was needed. After profile tooth modification, at the outer race of the output shaft support bearing, the radial response was reduced by approximately $20{\mu}m$, and the axial response was reduced by approximately $6{\mu}m$.

• 대기
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• 제29권4호
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• pp.429-438
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• 2019

Organic carbon (OC) and elemental carbon (EC) in PM_2.5 were measured with Sunset Laboratory Model-5 Semi-Continuous OC/EC Field Analyzer by NIOSH/TOT method at Anmyeondo Global Atmosphere Watch (GAW) Regional Station (37°32'N, 127°19'E) in July and August, 2017. The mean values of OC and EC were 3.7 ㎍ m^-3 and 0.7 ㎍ m^-3, respectively. During the study period, the concentrations of reactive gases and aerosol compositions were evidently lower than those of other seasons. It is mostly due to meteorological setting of the northeast Asia, where the influence of continental outflow is at its minimum during this season under southwesterly wind. While the diurnal variation of OC and EC were not clear, the concentrations of O₃, CO, NOx, EC, and OC were evidently enhanced under easterly wind at night from 20:00 to 8:00. However, the high concentration of EC was observed concurrently with CO and NOx under northerly wind during 20:00~24:00. It indicates the influence of thermal power plant and industrial facilities, which was recognized as a major emission source during KORUS-AQ campaign. The diurnal variations of pollutants clearly showed the influence of land-sea breeze, in which OC showed good correlation between EC and O₃ in seabreeze. It is estimated to be the recirculation of pollutants in land-sea breeze cycle. This study suggests that in general, Anmyeondo station serves well as a background monitoring station. However, the variation in meteorological condition is so dynamic that it is primary factor to determine the concentrations of secondary species as well as primary pollutants at Anmyeondo station.

• International Journal of Aeronautical and Space Sciences
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• 제18권4호
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• pp.807-815
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• 2017

For liquid rocket engine(LRE)-based space launch vehicles, longitudinal instability, often referred to as the pogo phenomenon in the literature is predicted. In the building block of system-level task, accurate dynamic modeling of a fluid-filled tank is an essential. This paper attempts to apply the virtual mass method that accounts for the interaction of the vehicle structure and the enclosed liquid oxygen to LOX-filled tanks. The virtual mass method is applied in a modal analysis considering the hydroelastic effect of the launch vehicle tank. This method involves an analysis of the fluid in the tank in the form of mass matrix. To verify the accuracy of this method, the experimental modal data of a small hemispherical tank is used. Finally, the virtual mass method is applied to a 1/8-scale space shuttle external tank. In addition, the LOX tank bottom pressure in the external tank model is estimated. The LOX tank bottom pressure is the factor required for the coupling of the LOX tank with the propulsion system. The small hemispherical tank analysis provides relatively accurate results, and the 1/8-scale space shuttle external tank provides reasonable results. The LOX tank bottom pressure is also similar to that in the numerical results of a previous analysis.

• Wind and Structures
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• 제20권3호
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• pp.449-468
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• 2015

Current wind-resistance designs of large-scale indirect dry cooling towers (IDCTs) exclude an important factor: the influence of the ventilation rate for radiator shutter on wind loads on the outer surfaces of the tower shell. More seemingly overlooked aspects are the effects of various ventilation rates on the wind pressure distribution on the tower surfaces of two IDCTs, and the feature of the flow field around them. In order to investigate the effects of the radiator shutter ventilation rates on the aerodynamic interference between IDCTs, this paper established the numerical wind tunnel model based on the Computational Fluid Dynamic (CFD) technology, and analyzed the influences of various radiator shutter ventilation rates on the aerodynamic loads acting upon a single and two extra-large IDCTs during building, installation, and operation stages. Through the comparison with the results of physical wind tunnel test and different design codes, the results indicated that: the influence of the ventilation rate on the flow field and shape coefficients on the outer surface of a single IDCT is weak, and the curve of mean shape coefficients is close to the reference curve provided by the current design code. In a two-tower combination, the ventilation rate significantly affects the downwind surface of the front tower and the upwind surface of the back tower, and the larger positive pressure shifts down along the upwind surface of the back tower as the ventilation rate increases. The ventilation rate significantly influences the drag force coefficient of the back tower in a two-tower combination, the drag force coefficient increases with the ventilation rate and reaches the maximum in a building status of full ventilation, and the maximum drag coefficient is 11% greater than that with complete closure.

• 한국습지학회지
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• 제18권1호
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• pp.84-93
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• 2016

해양과 육지 사이에 있는 연안습지는 연안의 수질을 개선하고 다양한 생물의 자연적인 서식처로 이용될 뿐 아니라 연안침식을 억제하는 기능을 가지고 있다. 연안식생은 외해에서 입사하는 파에너지 또는 폭풍해일을 감소하며 해저 안정화를 통해 습지를 유지하는 기능을 가지고 있다. 식생에 의한 파랑감쇠의 특성을 위해서는 식생과 파랑의 역학적 과정의 검토가 필수적이며 이를 통해 연안과정이나 연안의 동수역학적 특성을 이해할 수 있다. 본 연구에서는 파랑조건 이외에 식생형태에 따른 파랑감쇠 특성을 정량화하기 위해 수리실험을 통해 검토하였으며, 식생모형은 강성식생을 대상으로 규칙파가 작용하는 경우에 대해 파악하였다. 파형경사 ak와 상대수심 kh에 따른 수면위로 돌출된 식생에 대한 파랑감쇠를 검토하기 위하여 수리실험과 수치해석을 수행하였다. 실험결과에 대한 파고감쇠는 Dalrymple et al.(1984)의 파고감쇠식을 통해 식생에 의한 파고전달율, 감쇠율 및 항력계수를 해석하였다. 실험결과 식생에 작용하는 항력계수는 Reynolds수 보다는 Keulegan-Carpenter 수와 상관성이 있고, 파형경사가 증가할수록 파고감쇠율이 증가하고 있음을 확인하였다.

• 한국전자거래학회지
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• 제14권1호
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• pp.143-160
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• 2009

대용량의 데이타를 다루는 OLAP 데이타베이스 환경에서는 기반 디스크 시스템의 구조와 효율적 접근방법이 전체적인 성능을 좌우하는 중요한 요소가 된다. 최근 들어 하드 디스크들은 여러 개의 물리적 존을 갖는 구조로 설계되고 있는데, 각 존들은 그 위치에 따라 다양한 탐색시간과 데이타 전송률을 갖는 특징을 갖고 있다. 그러나 기존 연구에서는 다중 존을 고려하지 않은 하나의 탐색시간과 데이타 전송률을 갖는 단순한 디스크 모델에 기반을 두고 진행되어 왔다. 본 논문에서는 대용량의 데이타를 다루는 OLAP 환경에서 주어진 실체뷰 집합을 다중 존에 효율적으로 저장하는 기법을 제안한다. 이를 위해 각 실체뷰를 접근확률에 따라 디스크 존에 배치하는 알고리즘을 제시하고, 데이타 지속적으로 갱신되는 동적 환경에서의 저장 방법에 대해서도 살펴본다. 마지막으로 실험을 통하여 본 논문에서 제시된 알고리즘을 효율성을 증명한다.

• 한국건설관리학회:학술대회논문집
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• 한국건설관리학회 2004년도 제5회 정기학술발표대회 논문집
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• pp.526-530
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• 2004

산업설비 분야는 건설 산업의 고도화에 따라 산업시설의 비중이 증대되고 있으며, 첨단기술의 접목을 통한 고부가 가치를 창출할 수 있는 역동적인 분야임에도 단계별 정보 흐름의 관리와 지식 집약적인 업무 수행이 미흡한 실정이다. 향후 국제 산업설비 시장에서 건설 프로젝트 수요증대, 유지관리 분야의 확대가 예상되며, 이에 대응하여 국내에서는 지속적인 설계기술 및 노하우 축적이 시급하다. 본 연구에서는 국내 산업설비의 미흡한 부분을 객관적으로 파악하고, 주요 단계의 업무 모델을 제시하기 위하여 국내 산업설비 현행 업무프로세스로부터 프로젝트 관리 핵심요소를 도출하였다. 이를 해외 산업설비 수준과 비교해 봄으로써 국내공사 기술수준을 파악하고, 산업설비 주요 업무단계에 대한 업무모델을 구축하여 향후 개선된 업무모델을 제시하고자 한다.

• 대한토목학회논문집
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• 제32권2C호
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• pp.61-68
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• 2012

일반적으로 해양 말뚝기초의 경우 해양 환경적 영향 및 시공상의 오차로 인해 수직도 오차가 필연적으로 발생한다. 해양구조물의 경우 수평하중이 아닌 수직하중에 의해 설계가 지배적이나, 해상풍력발전기 기초의 경우 수평하중이 지배적이며, 블레이드 회전에 의한 동적인 운동을 하는 구조형식으로 수직도 오차가 구조적으로 중요한 영향을 끼칠 수 있다. 이에 본 연구에서는 5MW급 해상풍력발전기 모노파일 기초의 수직도 오차에 따른 기초와 지반의 구조응답 특성을 분석하였다. 해양환경하중은 ISO 기준에 의해 산정하였으며, 수직도 오차 범위는 $L/{\infty}$(=0), L/300, L/200 및 L/100로 선정하였다. 해석결과 수직도 오차가 없는 모노파일에 비해 L/100 오차를 갖는 지반의 부재력 최대 값이 약 7.2%정도 더 증가되는 것으로 분석되었다.

• Earthquakes and Structures
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• 제11권5호
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• pp.741-777
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• 2016

A simplified approach of assessing torsionally balanced (TB) and torsionally unbalanced (TU) low-medium rise buildings of up to 30 m in height is presented in this paper for regions of low-to-moderate seismicity. The Generalised Force Method of Analysis for TB buildings which is illustrated in the early part of the paper involves calculation of the deflection profile of the building in a 2D analysis in order that a capacity diagram can be constructed to intercept with the acceleration-displacement response spectrum diagram representing seismic actions. This approach of calculation on the planar model of a building which involves applying lateral forces to the building (waiving away the need of a dynamic analysis and yet obtaining similar results) has been adapted for determining the deflection behaviour of a TU building in the later part of the paper. Another key original contribution to knowledge is taking into account the strong dependence of the torsional response behaviour of the building on the periodic properties of the applied excitations in relation to the natural periods of vibration of the building. Many of the trends presented are not reflected in provisions of major codes of practices for the seismic design of buildings. The deflection behaviour of the building in response to displacement controlled (DC) excitations is in stark contrast to behaviour in acceleration controlled (AC), or velocity controlled (VC), conditions, and is much easier to generalise. Although DC conditions are rare with buildings not exceeding 30 m in height displacement estimates based on such conditions can be taken as upper bound estimates in order that a conservative prediction of the displacement profile at the edge of a TU building can be obtained conveniently by the use of a constant amplification factor to scale results from planar analysis.