• Journal of Power Electronics
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• 제10권5호
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• pp.548-554
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• 2010

In this paper, a 1.5 kW Interior Permanent Magnet Synchronous Generator (IPMSG) with a power conditioner for the grid integration of a variable-speed wind turbine is developed. The power-conditioning system consists of a series-type 12-pulse diode rectifier powered by a phase shifting transformer and then cascaded to a PWM voltage source inverter. The PWM inverter is utilized to supply sinusoidal currents to the utility line by controlling the active and reactive current components in the q-d rotating reference frame. While the q-axis active current of the PWM inverter is regulated to follow an optimized active current reference so as to track the maximum power of the wind turbine. The d-axis reactive current can be adjusted to control the reactive power and voltage. In order to track the maximum power of the wind turbine, the optimal active current reference is determined by using a simple MPPT algorithm which requires only three sensors. Moreover, the phase angle of the utility voltage is detected using a simple electronic circuit consisting of both a zero-crossing voltage detecting circuit and a counter circuit employed with a crystal oscillator. At the generator terminals, a passive filter is designed not only to decrease the harmonic voltages and currents observed at the terminals of the IPMSG but also to improve the generator efficiency. The laboratory results indicate that the losses in the IPMSG can be effectively reduced by setting a passive filter at the generator terminals.

• Ocean and Polar Research
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• 제32권4호
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• pp.361-367
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• 2010

The principal objective of this paper was to evaluate the steering characteristics of a tandem tracked vehicle, each side of which features two tandem tracks, when crawling on extremely cohesive soft soil. The tandem tracked vehicle is assumed to be a rigid-body with 6-dof. The dynamic analysis program of the tandem tracked vehicle was developed via Newmark's method and the incremental-iterative method. A terra-mechanics model of extremely cohesive soft soil was implemented according to the relationships of normal pressure to sinkage, of shear resistance to shear displacement, and of dynamic sinkage to shear displacement. In order to simplify the characteristics of contact interaction between track segments and cohesive soft soil, the characteristics of soil are equated to the properties of intact soil. In an effort to evaluate the steering characteristics of a tandem tracked vehicle crawling on extremely cohesive soft soil, a series of dynamic simulations were conducted for a tandem tracked vehicle model with respect to the front and rear steering angle, the steering ratio, and the initial velocity.

• 한국초전도ㆍ저온공학회논문지
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• 제17권1호
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• pp.32-35
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• 2015

Many kinds of high temperature superconducting (HTS) devices are being developed due to its several advantages. In particular, the advantages of HTS devices are maximized under the DC condition. A line commutated converter (LCC) type high voltage direct current (HVDC) transmission system requires large capacity of DC reactors to protect the converters from faults. However, conventional DC reactor made of copper causes a lot of electrical losses. Thus, it is being attempted to apply the HTS DC reactor to an HVDC transmission system. The authors have developed a 8 mH class HTS DC reactor and a model-sized LCC type HVDC system. The HTS DC reactor was operated to analyze its operational characteristics in connection with the HVDC system. The voltage at both ends of the HTS DC reactor was measured to investigate the stability of the reactor. The voltages and currents at the AC and DC side of the system were measured to confirm the influence of the HTS DC reactor on the system. Two 5 mH copper DC reactors were connected to the HVDC system and investigated to compare the operational characteristics. In this paper, the operational characteristics of the HVDC system with the HTS DC reactor according to firing angle are described. The voltage and current characteristics of the system according to the types of DC reactors and harmonic characteristics are analyzed. Through the results, the applicability of an HTS DC reactor in an HVDC system is confirmed.

• 한국지반환경공학회 논문집
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• 제11권9호
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• pp.5-14
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• 2010

본 연구는 성토지반이나 사면에서의 강우 침투 시 포화도 변화에 따른 전단강도 특성을 규명하고자 대전지역 도로공사현장을 대상으로 성토재로 쓰이는 화강풍화토에 대하여 포화도 변화에 따른 전단강도특성을 분석하였다. 다짐함수비를 달리한 시료에 대해 직접전단시험을 실시하여 분석한 결과 최적함수비와 건조측 다짐함수비에서 점착력과 전단저항각이 가장 크게 나타났으며, 다짐함수비가 습윤측으로 갈수록 점착력이 감소하는 경향을 보였다. 또한, 다짐함수비별 시료에 대하여 포화도 변화에 따른 전단특성을 연구한 결과 침투한 물에 의해 포화도가 증가할수록 점착력은 50% 이상 감소하는 경향을 보였으나, 상대적으로 전단저항각의 감소폭은 $1{\sim}2^{\circ}$정도로 작았다. 또한, 잔류전단강도정수에 대한 포화도 변화의 영향은 실용적 차원에서 효과를 기대하기가 어려울 것으로 판단된다. 즉, Mohr-Coulomb의 파괴규준에서 포화도 변화가 잔류전단강도 변화에 미치는 영향은 미미한 것으로 판단된다.

• 한국생활과학회지
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• 제14권2호
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• pp.303-312
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• 2005

The purpose of this research is to analyze the lower part of dress forms with different sectional rotation-angles ($e.g.\;9^{\circ},\;15^{\circ},\;30^{\circ},\;45^{\circ}$) using three-dimensional measurement system and to investigate measurement properties for dress making. The dress forms used in this experiment were size 8 and six types: four from Korea and two from Japan. The instrument and tools for three-dimensional measurement was Whole Body 3D scanner (Exyma-WBS2H). The analysis program used in this experiment was Rapid Form 2004 PP1 (INUS technology, Inc, Korea). The measurement of dress forms was done three times with different sectional rotation-angles and its data were analyzed using SPSS WIN 10.0 Package. The following results were obtained: 1. With mean and standard deviation of each measured part, it was found out that the dress forms from two countries were different in size per each part. For example, the Japanese one was relatively large in middle hip and hip, compared to the Korean one. 2. The 3D analysis of the sectional rotation-angles revealed some differences between the two dress forms in sectional length per each part. 3. With cluster analysis results, it was found that there were definite differences among measurements per each part, especially in $30^{\circ}\;and\;45^{\circ}$ sections. 4. The proportion of the dress forms showed significant differences in the curvature between center and side section of the lower parts. In addition, the shapes on the horizontal section map of the four levels (waist, middle hip, hip, and bottom) were analyzed.

• 천문학회보
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• 제35권1호
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• pp.34.1-34.1
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• 2010

Solar proton events, whose fluxes are larger than 10 particles cm-2 sec-1 ster-1 for >10 MeV protons, have been observed since 1976. NOAA proton event list from 1997 to 2006 shows that most of the events are related to both flares and CMEs but a few fraction of events (5/93) are only related with CMEs. In this study, we carefully identified the sources of these events. For this, we used LASCO CME catalog and SOHO MDI data. First, we examined the directions of CMEs related with the events and the CMEs are found to eject from the western hemisphere. Second, we searched a major active region in the front solar disk for several days before the proton events occurred by taking into account two facts: (1) The location of the active region is consistent with the position angle of a given CME and (2) there were several flares in the active region or the active region is the largest among several candidates. As a result, we were able to determine active regions which are likely to produce proton events without ambiguity as well as their longitudes at the time of proton events by considering solar rotation rate, $13.2^{\circ}$ per day. From this study, we found that the longitudes of five active regions are all between $90^{\circ}W$ and $120^{\circ}W$. When the flare peak time is assume to be the CME event time, we confirmed that the dependence of their rise times (proton peak time - flare peak time) on longitude are consistent with the previous empirical formula. These results imply that five events should be also associated with flares which were not observed because they occurred from back-side.

• 한국가스학회지
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• 제18권2호
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• pp.48-54
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• 2014

본 논문에서는 알코올 측정용 센서의 광학적 특성 향상을 위한 고유한 광학적 구조를 제안하였으며, 모의해석을 실시하였다. 광 도파관은 한쪽에 공통초점을 갖는 두 개의 타원형 광 도파관으로 구성되었으며, 각 광 도파관의 서로 다른 초점에 적외선 광원과 적외선 센서를 갖는다. 두 타원형 광 도파관의 각도가 30도에서 90도로 증가시켰을 때, 단위면적당 최대 입사광량은 $2.23{\times}10^6W/m^2$에서 $5.74{\times}10^5W/m^2$로 감소하였다. 그러나 조사 빔의 반지름은 1.86 mm로 최소값을 나타내었고, 전체 입사 에너지는 90도 각도를 갖는 구조와 비교하여 약 10 % 작은 값을 보였다. 모의해석 결과로부터 본 논문에 제안한 구조는 긴 흡수파장을 갖는 광학적 가스센서의 감도향상에 기여할 것으로 판단된다.

• 한국수자원학회논문집
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• 제38권3호
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• pp.189-198
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• 2005

본 연구에서는 조력발전소 배수갑문의 형상과 배치에 따른 방류능력을 해석하는데 3차원 수치모의가 효과적으로 이용될 수 있음을 보였다. 3차원 수치모형은 RANS를 지배방정식으로 하는 FLOW-3D 모형을 이용하였다. 본 연구결과 배수갑문의 방류능력은 물받이길이와 도류벽의 접근각도에 큰 영향을 받는 것으로 나타났다. 그리고 이의 개선 여부에 따라 $10\%$ 이상의 방류량 차이가 발생하였다. 또한 방류량은 배수문과 수차구조물을 연결하는 구조물의 형상과 물받이 끝 사면경사의 영향을 받는 것으로 나타났다. 본 연구에서는 배수갑문의 설계시 방류능력 개선을 위해서는 수리학적 검토가 필요하며, 수치모형실험이 수리모형실험과 더불어 유용한 해석도구로 이용될 수 있음을 보였다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2019년도 학술발표회
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• pp.152-152
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• 2019

This study demonstrates a novel approach of remotely sensed estimates of stream flow at fifteen hydrological station in the Han River Basin, Korea. Multi-temporal data of the European Space Agency's Sentinel-1 SAR satellite from 19 January, 2015 to 25 August, 2018 is used to develop and validate the flow estimation model for each station. The flow estimation model is based on a power law relationship established between the remotely sensed surface area of water at a selected reach of the stream and the observed discharge. The satellite images were pre-processed for thermal noise, radiometric, speckle and terrain correction. The difference in SAR image brightness caused by the differences in SAR satellite look angle and atmospheric condition are corrected using the histogram matching technique. Selective area filtering is applied to identify the extent of the selected stream reach where the change in water surface area is highly sensitive to the change in stream discharge. Following this, an iterative procedure called the Optimum Threshold Classification Algorithm (OTC) is applied to the multi-temporal selective areas to extract a series of water surface areas. It is observed that the extracted water surface area and the stream discharge are related by the power law equation. A strong correlation coefficient ranging from 0.68 to 0.98 (mean=0.89) was observed for thirteen hydrological stations, while at two stations the relationship was highly affected by the hydraulic structures such as dam. It is further identified that the availability of remotely sensed data for a range of discharge conditions and the geometric properties of the selected stream reach such as the stream width and side slope influence the accuracy of the flow estimation model.

• 한국지반공학회논문집
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• 제15권4호
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• pp.235-246
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• 1999

지하철 터널 등의 지하구조물을 개착식으로 시공할 때에는 먼저 지반을 굴착하고 구조물을 설치한 후에 굴착공간을 되메움한다. 이때 굴착면과 구조물사이의 되메움 공간이 협소하여 되메움지반의 자중에 의하여 지하구조물에 작용하는 토압은 고전적인 방법으로 구한 토압과 상이하다. 개착식으로 시공한 구조물의 상부슬래브와 측벽에 작용하는 연직 및 수평토압은 되메움공간의 형상에 따라 영향을 받을수 있으며 이를 규명하기 위하여 되메움공간의 형상과 벽마찰각을 변화시키면서 실내모형시험을 실시하여 그 결과를 기존의 토압이론과 비교분석하였다. 그 결과 되메움공간의 형상 즉 되메움폭과 원지반 굴착면 경사 및 구조물의 벽마찰각에 의한 영향이 관찰되었다.