• 한국방재안전학회논문집
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• 제11권1호
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• pp.1-5
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• 2018

발전소는 선진 산업사회에서의 중요한 사회기반시설이다. 이러한 발전소가 해초, 물고기, 해파리, 새우 등과 같은 해양생물의 유입으로 정지 될 경우, 사회-경제적으로 심각한 문제가 발생하기도 한다. 따라서, 발전소 취수구 유입구 부분의 해양생물 침투로 인한 발전소 가동이 정지되는 것을 방지하기 위하여, 에어버블 차단막 기술이 활용되고 있다. 본 연구에서는 에어버블 차단막 기술의 기초연구인 에어버블의 거동을 분석하기 위하여 수직형 에어버블 실험장치를 개발 및 에어버블수직 거동 특성을 분석하였다. 에어버블 수직 거동 특성을 분석하기 위하여 수직형 에어버블 실험 장치를 이용하여 에어 분사량에 따른 수심별 에어버블의 상승 속도를 측정하였으며, 실험결과를 바탕으로 수심구간별 에어버블 상승속도 경험식을을 제시하였다. 제시된 경험식은 향후 에어버블 차단막 설계의 기초자료로 활용될 것이며, 발전시설 운영 부분에서의 안정성을 확보하는 데 크게 기여할 것으로 기대된다.

• Tribology and Lubricants
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• 제22권2호
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• pp.59-65
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• 2006

In hard disk drives as the head to disk spacing continues to decrease to facilitate recording densities, slider disk interactions have become much more severe due to direct contact of head and disk surfaces in both start/stop and flying cases. The slider disk interaction in CSS (contact-start-stop) mode is an important source of particle generation and tribocharge build-up. The tribocharge build-up in the slider disk interface can cause ESD (electrostatic discharge) damage. In turn, ESD can cause severe melting damage to MR or GMR heads. The spindle speed of typical hard disk drives has increased in recent years from 5400 rpm to 15000 rpm and even higher speeds are anticipated in the near future. And the increasing disk velocity leads to increasing disk acceleration and this might affect the tribocharging phenomena of the slider/disk interface. We investigated the tribocurrent/voltage build-up generated in HDD, operating at increasing disk accelerations. In addition, we examined the effects with relative humidity conditions and rest time. We found that the tribocurrent/voltage was generated during pico-slider/disk interaction and its level was about $3\sim16pA$ and $0.1\sim0.3V$, respectively. Tribocurrent/voltage build-up was reduced with increasing disk acceleration. Higher humidity conditions $(75\sim80%)$ produced lower levels tribovoltage/current. Therefore, a higher tribocharge is expected at a lower disk acceleration and lower relative humidity condition. Rest time affected the charge build-up at the slider-disk interface. The degree of tribocharge build-up increased with increasing rest time.

• 한국정보통신학회논문지
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• 제12권6호
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• pp.1120-1127
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• 2008

본 논문은 UWB 센서를 이용한 위치인식 시스템의 구현 및 실험결과와 상황인지형 서비스 구현에 대하여 기술한다. 정확한 위치측정을 위해 UWB 센서의 경사도(pitch), 편주(yaw), 센서 개수, tag 높이 등의 변화에 따른 위치인식 오차를 측정하여 각 변수의 설정 방법을 실험하였다. 이를 이용한 응용으로 상황인지 기술에 바탕한 지능형 헬스트레이닝 관리 시스템 구현하였다. 지능형 헬스 트레이닝 관리 시스템은 헬스장에서 피 훈련자의 위치와 장비의 사용 상태를 인식하여, 적절한 훈련 스케줄을 피 훈련자에게 제공하며, 그에 따른 훈련 장비들의 사용법을 PDA를 통해 안내한다. 상황인지형 서비스의 제공을 위해서는 사용자의 위치와 이동 정보에 대한 오차 보정이 요구되어 사용자의 이동하는 속도를 이용한 위치 보정 알고리즘을 제안하였다. 실험 결과는 제안된 보정 알고리즘을 적용함으로써 이 알고리즘이 적용하지 않았을 때에 비해 오류 데이터가 30% 정도 감소하였다.

• Nuclear Engineering and Technology
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• 제14권2호
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• pp.78-85
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• 1982

정상상태의 플라즈마의 이론적 해석을 통해서 플라즈마의 회전과 동위원소 분리기로서의 적합성을 분석하였다. 이 장치는 두개의 동심원통형 전극과 이들 사이의 원통형 공동으로 구성되었으며, 축 방향으로 외부자장이 걸려 있다. 두 전극사이에 생성되는 전류밀도는 전기방전의 형태로 동위원소 혼합물로부터 플라즈마를 생성하고, 자장과 교차되어 발생하는 Lorentz힘에 의해서 플라즈마를 회전시킨다. 자기 유체역학 방정식을 바탕으로 이 계를 설명하는 두개의 연립편미분방정식을 얻었고, 네 경계조건을 사용하여 Fourier-Bessel로 표현된 이차원적 전류밀도와 속도분포의 해를 얻었다. 실제로 가능한 조건하에서 플라즈마 회전속도는 $10^4$m/sec 정도에 달하고, Hartmann수가 커짐에 따라 플라즈마회전 속도도 커진다. 이 같은 고속의 회전속도를 감안해 볼때 플라즈마 원심분리기는 기계적으로 회전되는 가스원심분리기보다 훨씬 높은 효율을 가지게 될 것이다.

• Current Optics and Photonics
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• 제2권2호
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• pp.195-202
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• 2018

A Scanning Rayleigh Doppler lidar for wind profiling based on a non-polarized beam splitter cube optically contacted FPI is developed for wind measurement from high troposphere to low stratosphere in 5-35 km. Non-polarized beam splitter cube optically contacted to the FPI are used for a stable optical receiver. Zero Doppler shift correction is used to correct for laser or FPI frequency jitter and drift and the timing sequence is designed. Stability of the receiver for Doppler shift discrimination is validated by measuring the transmissions of FPI in different days and analyzed the response functions. The maximal relative wind deviation due to the stability of the optical receiver is about 4.1% and the standard deviation of wind velocity is 1.6% due to the stability. Wind measurement comparison experiments were carried out in Jiuquan ($39.741^{\circ}N$, $98.495^{\circ}E$), Gansu province of China in 2015, showing good agreement with radiosonde result data. Continuous wind field observation was performed from October 16th to November 12th and semi-continuous wind field of 19 nights are presented.

• 한국물환경학회지
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• 제34권6호
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• pp.602-620
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• 2018

Korean benthic macroinvertebrate community from 959 sites and 14 environmental factors that could affect the biological distribution were surveyed and analyzed. The 438 taxa were divided into six groups according to TWINSPAN. Based on the environmental factor values corresponding to each taxon, the average and range of environmental factors for each biological group tended to increase or decrease in eight environmental factors (altitude, slope, current velocity, fraction of fine particles in substrates, turbidity, $BOD_5$, T-N and T-P). As a result of discriminant analysis (hit ratio: 69.6 %), environmental factors that significantly influence the distribution of each biological group were $BOD_5$, altitude, catchment area, T-N, T-P and fraction of fine particles in substrates. The discriminant functions 1 and 2 classified the existing six biological groups (clustered by TWINSPAN) into five (group 1: highland highly sensitive group; group 2: lowland sensitive group, group; 3 and 4: lowland slightly tolerant group; group 5: lowland tolerant group; group 6: lowland highly tolerant group). Most of the benthic macroinvertebrates were identified in the species level. However, a few others were identified in genus or family level, too. Even the organisms belonging to the same genus or family may prefer different environmental factors in the species level, the identification of characteristic of the habitat environment preferred by organism and species level identification of these organisms are utmost. The results of this study may be used as basic information on environmental factors which can be considered in preservation and restoration research for biodiversity.

• 한국물환경학회지
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• 제27권4호
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• pp.542-550
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• 2011

Changes of suspended sediment concentration in the Seomjin river estuary located in south sea of the Korea peninsula were investigated during the spring tide in autumn (i.e. 25 hours in October) 2000 and winter (i.e. 25 hours in February) 2001. The changes of temperature and salinity during the spring tide in October 2000 showed larger variations than the those in February 2001. During the spring tide in October 2000, currents at bottom layer were observed to be stronger than during the spring tide in February 2001, showing that both of the two periods had ebb currents-predominant tide asymmetries. The suspended sediment concentrations in October 2000 were larger than the those in February 2001. At the time of the maximum of tide currents or after about one hour of the maximum during the autumn months, the suspended sediment turbidity was observed to be maximum. Another observation station at Hadong upstream from the Seomjin river estuary showed about one hour delay in tide phase, Thereby, the suspended sediment concentration showed high turbidity after two hours at bottom and three hours at surface layer, in particular, in October 2000. This results can be explained by the facts that river discharge increased significantly after the summer rainy season, causing also increase of erosion processes by strong current velocity at bottom layer.

• Advances in nano research
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• 제10권2호
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• pp.151-163
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• 2021

The main target of this study is to investigate nonlinear transient responses of moving polymer nano-size plates fortified by means of Graphene Platelets (GPLs) and resting on a Winkler-Pasternak foundation under a transverse pressure force and a temperature variation. Two graphene spreading forms dispersed through the plate thickness are studied, and the Halpin-Tsai micro-mechanics model is used to obtain the effective Young's modulus. Furthermore, the rule of mixture is employed to calculate the effective mass density and Poisson's ratio. In accordance with the first order shear deformation and von Karman theory for nonlinear systems, the kinematic equations are derived, and then nonlocal strain gradient scheme is used to reflect the effects of nonlocal and strain gradient parameters on small-size objects. Afterwards, a combined approach, kinetic dynamic relaxation method accompanied by Newmark technique, is hired for solving the time-varying equation sets, and Fortran program is developed to generate the numerical results. The accuracy of the current model is verified by comparative studies with available results in the literature. Finally, a parametric study is carried out to explore the effects of GPL's weight fractions and dispersion patterns, edge conditions, softening and hardening factors, the temperature change, the velocity of moving nanoplate and elastic foundation stiffness on the dynamic response of the structure. The result illustrates that the effects of nonlocality and strain gradient parameters are more remarkable in the higher magnitudes of the nanoplate speed.

• 한국기계가공학회지
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• 제21권9호
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• pp.78-84
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• 2022

An air circuit breaker (ACB) is an electrical protection device that interrupts abnormal fault currents that result from overloads or short circuits in a low-voltage power distribution line. The ACB consists of a main circuit part for current flow, mechanism part for the opening and closing operation of movable conductors, and arc-extinguishing part for arc extinction during the breaking operation. The driving mechanism of the ACB is a spring energy charging type. The faster the contact opening speed of the movable conductors during the opening process, the better the breaking performance. However, there is a disadvantage that the durability of mechanism decreases in inverse proportion to the use of a spring capable of accumulating high energy to configure the breaking speed faster. Therefore, to simultaneously satisfy the breaking performance and mechanical endurance of the ACB, its driving mechanism must be optimized. In this study, a dynamic model of the ACB was developed using the MDO(Mechanism Dynamics Option) module of CREO, which is widely used in multibody dynamics analysis. To improve the opening velocity, the Taguchi design method was applied to optimize the design parameters of an ACB with many linkages. In addition, to evaluate the improvement in the operating characteristics, the simulation and experimental results were compared with the MDO model and improved prototype sample, respectively.

• 한국전자통신학회논문지
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• 제17권5호
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• pp.767-774
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• 2022

본 논문에서는 우리나라에서 운용 중인 4개 제조사 윈드프로파일러의 성능 평가 및 품질관리의 방향성을 제시하기 위해 원시 스펙트럼 자료를 분석하였다. 계절별로 평균한 스펙트럼의 프로파일과 파워 스펙트럼 밀도(PSD, Power Spectrum Density)로 산출한 4가지 통계값(최소, 평균, 중앙, 최댓값)의 프로파일을 활용하였다. 스펙트럼 자료의 품질은 LAP-3000이 가장 우수하였고, YKJ3, PCL-1300, CLC-11-H가 뒤를 이었다. 철원과 추풍령에 설치된 PCL-1300은 지형과 비기상 신호로 인한 스펙트럼의 변동성이 커서 지형 클러터 제거와 이동평균, 멀티피크 등의 신호처리 과정이 요구되었다. 군산과 파주에 설치된 CLC-11-H는 직류 치우침과 전파거리 접힘 현상이 발견되어 직류 치우침 제거와 관측 유효 고도 제한이 선행될 필요가 있다.