• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.797-800
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• 2006

The power flow analysis(PFA) can be effectively used to predict structural vibration in medium-to-high frequency ranges. In this paper, vibration experiment has been performed to observe the analytical characteristics of the power flow analysis of the vibration of a plate. In the experiment, the loss factor of the plate and the input mobility at a source point have been measured. The data for the loss factor has been used as the input data to predict the vibration of the plate with PFA. The frequency response functions have been measured over the surface of the plate. The comparison between the experimental results and the predicted results for the frequency responsefunctionshasbeenperformed.

• Bulletin of the Korean Chemical Society
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• 제21권9호
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• pp.875-881
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• 2000

We study the rheological properties of concentrated polymer solution and the melt under simple shear and elon-gational flow using Brownian dynamicssimulation. In order to describe the anisotropic molecular motion, we modifiedthe Giesekus' mobility tensor by incorporating the finitely extensible non-linear elastic (FENE) spring force into dumbbell model. To elucidate the nature of this model, our simulation results are compared with the data of FENE-P ("P"standsfor the Perterin) dumbbell model and experiments. While in steady state both original FENE and FENE-P models exhibit a similar viscosity response,the growthof viscosity becomes dissimilar as the anisotropy decreases and the flowrate increases. The steady state viscosity obtained from the simulation well describes the experiments including the shear-thinning behavior in shear flow and viscosity-thinning behavior in elongational flow. But the growth of viscosity oforiginal FENE dumbbell model cannot describe the experimental results in both flow fields.

• 대한교통학회지
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• 제33권2호
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• pp.204-213
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• 2015

지하철 역사 공간 내 보행교통류의 혼잡 상황은 역사의 이용효율을 저해시킨다. 특히 방향별 동선의 미분리로 인한 보행자간 상충은 보행자의 이동저항을 증가시키며 통행시간과 안전사고에 부정적인 영향을 끼치게 된다. 본 연구에서는 미시적 움직임에 기반한 양방향 보행교통류의 통행 특성을 분석하였으며, 동선 분리로 인한 운영상의 효과를 분석하는 모형을 개발하였다. 이산요소법에 따라 역사 공간을 2차원 grid 구조로 해석하였으며, 각 grid에 존재하는 cell 별로 보행자의 움직임이 이루어진다고 보았다. 그 결과 양방향 보행교통류가 상충하는 상황에서는 동선을 분리시키고, 우측통행을 유도하여 보행자들의 진행 방향을 정돈시키는 경우가 가장 효율이 좋은 것으로 분석되었다. 이에, 동선 분리 시스템을 적용하여 보행편의 및 이동성을 증진시키기 위한 시사점을 제시하고자 한다.

• 한국통신학회논문지
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• 제27권12C호
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• pp.1245-1250
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• 2002

최근 몇 년간 인터넷 사용 환경이 주로 유선 접속에서 점차 무선으로 접속하는 경우가 증가하고 있으며 또한 실시간 응용 데이터의 사용이 늘어나고 있다. 이에 따라 사용자의 이동성을 제공하고 동시에 QoS를 제공하기 위한 무선 네트워크의 연구 및 개발이 필수적이다. IETF는 이미 이러한 이동성 지원을 위한 차세대 프로토콜인 Mobile IPv6와 QoS를 위한 RSVP를 각각 개발하였으며 이것은 앞으로 유선 네트워크뿐만 아니라 무선 네트워크에도 적용되리라 예상된다. 그러나 이 두 가지 메커니즘의 통합과 효율적 연동은 아직까지 제시되지 않았다. 본 논문에서는 우선 빠른 이동성을 지원할 수 있는 무선 네트워크 모델로 최근 IETF에서 제안하고 있는 Mobile IPv6 기반의 셀룰러 IP를 사용하였으며 셀룰러 IP와 기존 RSVP의 적용에 있어서의 문제점으로 이동 호스트의 잦은 핸드오프로 발생하는 RSVP 시그널링 오버헤드 증가 문제와 네트워크 내에서 동일한 응용 데이터에 대한 자원 예약에 있어서의 문제점을 해결하면서 두 가지 프로토콜의 효율적 연동을 위해 IPv6 헤더의 플로우 레이블 필드(flow label field)를 이용하는 개선된 RSVP 메커니즘을 제안하였다.

• 한국ITS학회 논문지
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• 제20권4호
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• pp.13-27
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• 2021

본 연구에서는 영동고속도로 용인IC~양지IC구간을 대상으로 2020년 데이터를 활용하여 자율주행자동차의 시장점유율 변화가 교통류에 미치는 영향을 추정하였다. 교통류에 미치는 영향 정도를 추정하기 위해 미시교통시뮬레이션 모형인 VISSIM을 활용하였다. 자율주행자동차의 종방향 제어를 반영하기 위해서 intelligent driver model(IDM)을 구축 후 VISSIM에 적용하여 일반차와 비교를 수행하고 주행행태를 검증하였다. 자율주행자동차의 시장점유율에 따른 이동성 및 안전성 분석 결과, 자율주행자동차 도입 시 시장점유율이 높아질수록 네트워크의 이동성은 향상되지만, 안전성의 경우 차종이 혼재되었을 때 교통류가 불안정해지므로 더욱 안전 관리에 집중해야 한다는 것을 확인하였다.

• 한국수소및신에너지학회논문집
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• 제34권5호
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• pp.456-464
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• 2023

In this study, a compact hydrogen liquefaction system was constructed with the aim of creating a data storage and monitoring program for liquid hydrogen production. This program was designed to receive and record signals from diverse control equipment through the LabVIEW software. A range of measurement instruments were devised to collect data, encompassing variables such as flow rate, pressure, temperature, and liquid level. As a result, it was possible to directly check the production of liquid hydrogen by obtaining various data of condensed liquid hydrogen. In addition, it was confirmed that long-term storage of liquid hydrogen is possible by developing automatic ON/OFF through the LabVIEW program.

• 한국수소및신에너지학회논문집
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• 제35권3호
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• pp.280-289
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• 2024

In this study, a cryogenic vessel was constructed to maintain and control the safe pressure of liquid hydrogen boil-off gas (BOG), and the numerical analysis was conducted on the development of computational fluid dynamics model inside the high-pressure vessel. An evaluation system was constructed using cryogenic inner and outer containers, pre-cooler, upper flange, and internal high-pressure container. We attempted to analyze the performance of the safety valve by injecting relatively high temperature hydrogen gas to generate BOG gas and quickly control the pressure of the high-pressure vessel up to 10 bar. As a results, the liquid volume fraction decreased with a rapid evaporation, and the pressure distribution increased monotonically inside a high pressure vessel. Additionally, it was found that the time to reach 10 bar was greatly affected by the filling rate of liquid hydrogen.

• 한국수소및신에너지학회논문집
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• 제35권4호
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• pp.384-391
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• 2024

In this study, a fuel cell with a single stack of 100 cm² was manufactured and a superconducting coil driving experiment was conducted. Fuel cell activation and performance evaluation were performed, and a method of applying current to a superconducting coil using a fuel cell was considered by controlling the flow rate of gas supplied to the fuel cell. A scenario was created using a specific program to change the amount of gas supplied to the fuel cell over time. As a result of analyzing the voltage and magnetic field of the superconducting coil according to the applied current, it was confirmed that the performance of fuel cell was almost the same with that of power supply.

• 한국수소및신에너지학회논문집
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• 제35권4호
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• pp.392-400
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• 2024

In this study, 3-cell stack fuel cell power technology was developed for charging superconducting coil. It was found that the performance of the fuel cell stack increased depending on the number of activation. In addition, the flow rates of hydrogen and air supplied to 3-cell stack was adjusted because of a large difference in membrane electrode assembly (MEA) characteristics depending on its location. As a result, it was confirmed that it was possible to apply current to the superconducting coil from about 15 to 33 A by changing the variable resistance, and it was confirmed that the voltage difference between fuel cell cells could be overcome through sufficient control of fuel supply.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.66-69
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• 2001

Effect of $N_2$ flow rate on properties of GaN thin films grown by plasma-enhanced molecular beam epitaxy(PEMBE) was discussed to optimize the quality of thin films. It was found that at low $N_2$ flow rate indicating high III/V flux ratio, the growth rate of GaN thin films was controlled by $N_2$ flux, and at high $N_2$ flow rate the growth rate was not controlled by $N_2$ flux any longer. It was also found that III/V flux ratio affected film quality. The film grown at higher $N_2$ flow rate showed low background carrier concentration, higher carrier mobility, and narrow FWHM in band-edge emission of low temperature PL. It is thought that the film in more Ga flux region was grown by 2-dimensional layer-by-layer growth mode, and the film in more nitrogen region was grown by 3-D island growth mode. All samples exhibited a good crystallinity.