• 한국유체기계학회 논문집
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• 제14권6호
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• pp.76-84
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• 2011

The effect of inlet velocity profile on the heat transfer coefficient in a rotating smooth channel was investigated experimentally. Three simulated inlet flow conditions of fully developed, uniform, and distorted inlet conditions were tested. The Reynolds number based on the channel hydraulic diameter was ranged from 10,000 to 30,000 and the transient liquid crystal technique was used to measure the distribution of the heat transfer coefficient in the rotating channel. Results showed that the overall heat transfer coefficient increased as the Reynolds number increased. Also, the distribution of the heat transfer coefficient was strongly affected by the inlet flow condition. Generally, the fully developed flow simulated condition showed the highest heat transfer coefficient.

• Journal of Communications and Networks
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• 제11권5호
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• pp.464-472
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• 2009

In this paper, we propose a packet scheduling algorithm for cellular relay networks by considering relay selection, variation of channel quality, and packet delay. In the networks, mobile users are equipped with not only cellular but also user relaying radio interfaces, where base station exploits adaptive high speed downlink channel. Our proposed algorithm selects a user with good cellular channel condition as a relay station for other users with bad cellular channel condition but can get access to relay link with good quality. This can achieve flexible packet scheduling by adjusting transmission rates of cellular link. Packets are scheduled for transmission depending on scheduling indexes which are calculated based on user's achieved transmission rate, packet utility, and proportional fairness of their throughput. The performance results obtained by using computer simulation show that the proposed scheduling algorithm is able to achieve high network capacity, low packet loss, and good fairness in terms of received throughput of mobile users.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2018년도 학술발표회
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• pp.149-149
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• 2018

Prediction on initial motion of sediment is crucial to evaluate sediment transport and channel stability. The condition of incipient movement of sediment is characterized by bed shear stress, which is generated from force of moving water against the bed of the channel, and by critical shear stress, which depends on force resisting motion of sediment due to the submerged weight of the grains. When the bed shear stress exceeds the critical shear stress, sediment particles begin rolling and sliding at isolated and random locations. In Mountain River, debris flow frequently occurs due to heavy rainfall and can lead some natural stones from mountain slope into the bed river. This phenomenon could add additional forces to sediment transport system in the bed of river and also affect or change direction and magnitude of sediment movement. In this paper, evaluations on incipient motion of uniform coarse gravel under falling spheres impacts using small scale flume channel were conducted. The drag force of falling spheres due to water flow and length movement of falling spheres were investigated. The experiments were carried out in flume channel made by glass wall and steel floor with 12 m long, 0.6 m wide, and 0.6 m deep. The bed slopes were selected with the range from 0.7% to 1.5%. The thickness of granular layer was at least 3 times of diameter of granular particle to meet grain placement condition. The sphere diameters were chosen to be 4cm, 6 cm, 8 cm, 10 cm. The spheres were fallen in to the bed channel for critical condition and under critical condition of motion particle. Based on the experimental results, the Shields curve of particles Reynold number and dimensionless critical shear stress were plotted. The relationship between with drag force and the length movement of spheres were plotted. The pathways of the bed material Under the impact of spheres falling were analyzed.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권1호
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• pp.61-77
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• 2017

The most challenging issues in the multi-channel MAC of the IEEE 1609.4 standard is how to handle the dynamic vehicular traffic condition with a high mobility, dynamic topology, and a trajectory change. Therefore, dynamic channel coordination schemes between CCH and SCH are required to provide the proper bandwidth for CCH/SCH intervals and to improve the quality of service (QoS). In this paper, we use a Markov model to optimize the interval based on the dynamic vehicular traffic condition with high mobility nodes in the multi-channel MAC of the IEEE 1609.4 standard. We evaluate the performance of the three-dimensional Markov chain based on the Poisson distribution for the node distribution and velocity. We also evaluate the additive white Gaussian noise (AWGN) effect for the multi-channel MAC coordination scheme of the IEEE 1609.4 standard. The result of simulation proves that the performance of the dynamic channel coordination scheme is affected by the high node mobility and the AWGN. In this research, we evaluate the model analytically for the average delay on CCHs and SCHs and also the saturated throughput on SCHs.

• 한국수자원학회논문집
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• 제49권7호
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• pp.635-644
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• 2016

본 연구에서는 2차원 수치모형을 이용하여 개수로 분류부에서 분류수로 폭과 유량비 변화에 따른 흐름특성을 파악하였다. 2차류 영향을 고려한 분류부 수치모의시 흐름분포를 실험결과에 더 정확하고 안정하게 모의가능하다. 분류수로내 통수능을 감소시키는 흐름분리구역과 2차류의 상호 작용에 의한 흐름정체 효과는 분류유량비를 감소시킨다. 분류부 상류 유입유량과 유속이 감소할수록 수로폭 변화에 따른 분류유량비 변화가 더 크다. 동일 하류단 경계조건에서 분류수로 폭을 감소시킬 때, 본류 하류부 프루우드 수-분류유량비 관계식의 변화율은 -2.4843~-2.6675로 유사하게 나타난다. 동일 분류유량비 조건에서 분류수로 폭이 감소할수록 수축계수는 증가하고, 흐름분리구역의 폭은 감소한다. 분류수로 폭을 증가시킬 경우 분류부 상류 유입유량이 적을수록, 그리고 분류부 상류 유입량을 증가시킬 경우 분류수로 폭이 좁을수록 흐름분리구역 폭 감소율이 더 크다. 동일 상류 유입유량 조건에서 분류수로 폭이 감소할수록 분류유량비, 흐름분리구역의 길이와 폭은 감소한다.

• 대한기계학회논문집B
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• 제30권12호
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• pp.1228-1235
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• 2006

PEMFC(Proton Exchange Membrane Fuel Cell) is a low temperature fuel cell and has many probabilities of commercial use. However, water management is one of the serious technical problems for commercialization. It is necessary to understand the relationship between operation conditions and water behavior in PEMFC channel because it affects fuel cell performance. In this paper, the distribution of current density according to inlet humidity condition is mainly observed and discussed. If the anode inlet is well humidified, electro-osmotic drag is very active. For this reason, current density is very high at inlet side and the distribution is non-uniform.

• 한국통신학회논문지
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• 제30권10A호
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• pp.896-905
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• 2005

본 논문에서는 N-채널 SAW(Stop and Wait) ARQ 재전송 기법을 채택하고 있는 HSDPA 시스템에서 HS-DSCH 채널의 성능 향상을 목적으로 선택적 패킷 지연(SPD :Selective Packet Delay) 기법을 제안한다. SPD 기법은 무선 채널 상태에 따라 적응적으로 패킷 전송을 제어하는 방법으로 채널 상태가 나쁜 경우에는 해당 패킷 전송을 일정시간 동안 강제 지연하고 대신에 해당 타임 슬롯을 채널 상태가 양호한 다른 사용자에게 할당해 주는 기법이다. 따라서 제안하는 기법은 버스트 에러 환경에서 연속적인 패킷 손실로 인해 발생하게 되는 긴 재전송 지연을 효과적으로 줄일 수 있는 특징을 가진다. 또한 SPD 기법에 효율적으로 적용될 수 있는 SPD-LDPF(Long Delayed Packet First)와 SPD-DCRR(Deficit Compensated Round Robin)의 두 종류의 패킷 스케줄링 기법을 제안한다. 시뮬레이션 결과, 제안한 기법은 패킷 평균지연 특성, 처리량 성능, 그리고 사용자간 공평성에서 모두 우수한 성능을 보임을 확인하였다.

• 감성과학
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• 제6권2호
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• pp.9-16
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• 2003

본 연구는 인간의 물리적인 요소(머리너비, 가슴너비, 팔길이 등)에 따른 반응속도의 변화에 대해 다룬다. 본 연구에 따르면, 머리 앞뒤 너비나 팔길이 등의 요소들은 반응속도에 영향을 미치지 않았으나, 너비에 해당하는 요소들은 인간의 반응속도에 영향을 미치는 것으로 평가되었다. 본 연구의 결과는 특수상황에 보다 우수한 작업자를 선정하거나, 운동선수를 테스트 없이 우선적으로 선정하는 데 사용될 수 있다. 또한, 본 연구의 결과는 인간정보전달 경로상의 노이즈라고 명명된 채널 노이즈와 시간과의 관계를 규명하기 위한 채널 노이즈 타임분석을 위해 사용될 수 있다.

• International Journal of Computer Science & Network Security
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• 제23권5호
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• pp.121-127
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• 2023

A 500 km/h linear motor high speed terrestrial transportation service is planned to launch 2027 in Japan. In order to support 5G service in the train, the Sub-carrier spacing frequency of 30 kHz is planned to be used instead of common 15 kHz sub-carrier spacing to mitigate Doppler effect in such high-speed transportation. In addition, to increase the cell size of 5G mobile system, plural Base Station antenna will transmit the identical Down Link (DL) signal to form the expanded cell size along the train rail. In this situation, forward and backward antenna signals will be Doppler shifted by reverse direction respectively and the receiver in the train might suffer to estimate accurate Channel Transfer Function (CTF) for its demodulation. In this paper, Delay and Doppler Profiler (DDP) based Channel Estimator is proposed and it is successfully implemented in signal processing simulation system. Then the simulated performances are compared with the conventional Time domain linear interpolated estimator. According to the simulation results, QPSK modulation can be used even under severe channel condition such as 500 km/h, 2 path reverse Doppler Shift condition, although QPSK modulation can be used less than 200 km/h with conventional Channel estimator.

• 한국의류산업학회지
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• 제12권3호
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• pp.318-326
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• 2010

The advantages of the multi-channel retailing have been widely discussed but empirical research on fashion multi-channel retailing has been limited. In this study, multi-channel concept was discussed and then, channel choosing condition of apparel shopper and channel choosing criteria for information search and buying were investigated as a empirical study. Drawing on a sample of 298 customers of apparel products in Korea, the result demonstrated that some differences in the perception of experience goods and search goods among apparel products. And, according to buying channel, consumers were different from each other in information search time and clothing expenses. Some suggestion for the future research of multi-channel retailing was given.