• 한국수소및신에너지학회논문집
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• 제17권2호
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• pp.141-148
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• 2006

This study was carried out to analyze the microstructure characteristics of electrolyte membrane through XRD, SEM and AC impedance measurement for using in high temperature steam electrolysis(HTE). It was investigated that thermal stability and electric characteristics by sintering condition using dry and wet process, and confirmed growth of particle and density change by sintering temperature. The sintering temperature and behavior had an effect on the relative density of the ceramic and the average grain size. The more amount of dispersant in organic compound increase, the more the density increased. But the binder was shown opposite phenomenon. It was analyzed that electrolyte resistance and electrical characteristics using AC impedance. The electrical properties of YSZ grain boundary changed with the sintering temperature.

• 한국해양학회지
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• 제16권1호
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• pp.12-23
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• 1981

A numerical experiment is made in order to clarify the mechanism of the upwelling phenomenon along the coast near the poleward edge of the western boundary current. The possibility of the upwelling is suggested from the analysis of the observational data in the east of Honshu, Japan, and in the south eastern coast of Korean Peninsula. This upwelling phenomenon is very deep and can be traced to the bottom layer. The upwelling phenomenon seems to be a general oceanic feature which characterizes the region along the west coast near the poleward edge of the western boundary current. This experiment is simulating the oceanic condition of the transition region between Kuroshio front and the Oyashio front in the east of Honshu, Japan. The possible explanations of the causes of the upwelling are as follows;In the interior of the modeled ocean the cold heavy water supplied from the north and the warm light water from the south make the north-south gradient of the pressure field and accelerate the eastward current to produce the h-orizontal divergence feld near the west coast. The divergence is compensated by the upwelling near the separation region. Another one is that the upwell-ed cold water strengthen constantly the pressure gradient which is balanced by the northward current and is weakened by the horizontal diffusion.

• 한국전산유체공학회지
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• 제16권3호
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• pp.8-14
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• 2011

Although the geometry of circular cylinder is simple, the flow is complicate because of the flow separation and vortex shedding. In spite of many numerical and experimental researches, the flow around a circular cylinder has not been clarified even now. It has been known that the unsteady vortex shedding from a circular cylinder can vibrate and damage a structure. Lock-on phenomenon is very important in the flow around an oscillating circular cylinder. The lock-on phenomenon is that when the oscillation frequency of the circular cylinder is at or near the frequency of vortex shedding from a stationary cylinder, the vortex shedding synchronizes with the cylinder motion. This phenomenon can be recognized by the spectral analysis of the lift coefficient history. At the lock-on region the vortex is shedding by the modulated frequency to the body frequency. However, the vortex is shedding by the mixed frequencies of natural shedding and forced body frequency in the region of non-lock-on. In this paper, it was analyzed the relation between the frequency of rotary oscillating circular cylinder and the vortex shedding frequency.

• 공업화학
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• 제9권5호
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• pp.698-703
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• 1998

실리콘고무 (polydimethylsiloxane, PDMS)막에 의한 trichloroethylene (TCE)과 chlorobenzene (CB)수용액의 투과증발실험을 수행하고 농도분극이 분리특성에 미치는 영향을 연구하였다. 경계층저항은 직렬저항모델을 사용하여 설명하였으며, 수용액으로부터 미량의 유기염화물을 제거하는 투과증발에서는 농도분극현상이 투과거동에 중요한 영향을 미치고 있음을 확인할 수 있었다. 같은 막두께에서, 막에 대한 친화력이나 선택투과성이 더 큰 TCE가 CB수용액보다 경계층저항의 영향이 더 크게 나타났다. 막두께가 증가할수록 경계층저항의 영향은 감소하고 막저항이 지배적이 되며, 겉보기분리계수는 증가하여 막의 고유분리계수에 가까워졌다.

• Wind and Structures
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• 제2권4호
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• pp.253-266
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• 1999

This paper presents the effects of free-stream turbulence on streamwise surface pressure fluctuations on two-dimensional rectangular cylinders. Particular attention is given to possible effects of turbulence integral scale on fluctuation and peak pressures. The mean, standard deviation, peak pressure coefficients, spectra and cross-correlation of fluctuating pressures were measured to investigate the nature of the separation and reattachment phenomenon in turbulent flows over a wide range of turbulence intensity and integral scale.

• 대한기계학회논문집B
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• 제41권7호
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• pp.481-487
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• 2017

충격파와 경계층의 간섭 현상은 경계층이 박리하고, shock train이 발생하며, 유동장은 매우 복잡한 형태로 된다. 이러한 현상은 반사 충격파와 비정상 경계층이 간섭하는 충격파관에서도 발생한다. 그러나 충격파관에서 발생하는 shock train 현상에 대한 연구는 미비한 실정이다. 본 연구에서는 2차원 축대칭 충격파관을 사용하여 수치해석을 수행하였으며, 충격파관에서 발생하는 shock train의 유동 특성을 상세히 조사하기 위하여 압축성 Navier-Stokes 방정식을 적용하였다. 본 연구의 수치해석 결과를 바탕으로 상세한 파동선도를 통해 실험 결과와 비교하였다.

• 한국정보과학회논문지:컴퓨팅의 실제 및 레터
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• 제12권1호
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• pp.78-89
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• 2006

정보가전기기를 개발하는데 있어서 가장 어려운 일 중 하나는 네트워크 성능을 최적화하거나 성능상의 특이 현상을 극복하는 일이다. 본 논문에서는 상용 홈 네트워크 게이트웨이를 개발하면서 이런 네트워크 성능 최적화의 한 문제를 발견하고 정의하며, 그 원인을 규명하고, 이를 해결한 연구를 기술한다. 본 논문의 흠 게이트웨이는 비대칭 링크인 ADSL 을 사용하는데 업링크로의 패킷 전송 속도가 다운링크로의 패킷 전송 유무에 간섭을 받는 특이 현상인 속도 간섭 현상을 보인다. 이러한 현상은 보통 receive livelock 문제로 생각되어 입력 큐에서의 패킷 경쟁이 그 원인이라고 분석된다. 그러나 본 논문에서는 실험적 검증을 통해 이 현상이 receive livelock과는 그 원인이 다른 새로운 문제임을 밝혀낸다. 추가적인 분석과 실험의 결과 출력 큐에서의 패킷 경쟁과 TCP 프로토콜의 메커니즘이 이 현상의 원인임을 밝힌다. 우리는 이 문제를 해결하기 위해 패킷 스케줄링 메커니즘을 제안하며 이를 흠 게이트웨이에 구현한다. 그 결과 개선된 흠 게이트웨이에서는 속도 간섭 현상이 완전히 해결됨을 보인다.

• 대한치과기공학회지
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• 제12권1호
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• pp.15-21
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• 1990

This research was to investigate and study on 92 Dental Technicians who had had some experience of working or being employed at dental craft-shops or craft-rooms in Seoul area and had transferred to other types of occupation, with regard to their reasons for changing their profession. For an approach to the study, some questionnaires and interview including 3 aspects of in quiriesmental, economic and social backgrounds-were administered, and major findings are as follows ; 1. The ages in which transferring to other kinds of job happened occurred mostly from 20 to 30(78.26%) an a group of subjects whose ages ranged from 20 to 30 years old. And, with regard to their experience of working or being employed at dental craft-shops or craftrooms, the transfer of their profession to the other kinds mosty happened in a group of subjects(94.56%) whose experience of working in the dental field is less than 4 years. 2. The reason of transfer with reference to the mental background was mostly mattered in a group that expressed "Excessive Work Duties"(34.78%), and most lowly mattered in a group of subjets who had "Certain Relations with Dentists"(8.70%). Thus, it appeared that the biggest reason of transfer by the mental background was, due to the excessive duty work, not to have Sufficient time to be usualized by dental technicians for their own purpose. 3. With reference to the economical background, a group that declared there was "No Wage Standards in Ratio to Their Labor" was the most in the separation rate as shown 45.56%. And, a group suspecting "No Guarantee for Their Living after Retirement" Showed a separation rate, 9.78%. In other words, the reason for transfer was that they did not receive due wage according to their amount of labor. 4. With reference to the social background, a group making a subject for no good working environments or conditions had a separation rate, 41.30%, which was the most among others, and a group with a subject of "The Rarity of Employment because of Excessive Supply of Dental Technicians" had the rate, 10.87%, which was the lowest. This meant that the major cause of transfer by the social background was a phenomenon for dental technicans to escape from unclean working places.

• 한국전산유체공학회지
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• 제8권2호
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• pp.24-32
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• 2003

In this work, we propose a new idea of flapping airfoil design for optimal aerodynamic performance from detailed computational investigations of flow physics. Generally, flapping motion which is combined with pitching and plunging motion of airfoil, leads to complex flow features such as leading edge separation and vortex street. As it is well known, the mechanism of thrust generation of flapping airfoil is based on inverse Karman-vortex street. This vortex street induces jet-like flow field at the rear region of trailing edge and then generates thrust. The leading edge separation vortex can also play an important role with its aerodynamic performances. The flapping airfoil introduces an alternative propulsive way instead of the current inefficient propulsive system such as a propeller in the low Reynolds number flow. Thrust coefficient and propulsive efficiency are the two major parameters in the design of flapping airfoil as propulsive system. Through numerous computations, we found the specific physical flow phenomenon which governed the aerodynamic characteristics in flapping airfoil. Based on this physical insight, we could come up with a new kind of airfoil of tadpole-shaped and more enhanced aerodynamic performance.

• 한국응용과학기술학회지
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• 제30권3호
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• pp.551-559
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• 2013

To investigate the adhesion effect of sodium bisulfite content in making blocked isocyanate, wood adhesive PB-1, PB-2, PB-3 and PB-4 containing sodium bisulfite content of 15%, 22.5%, 30% and 37.5% were synthesized respectively. As a result, when the amount of sodium bisulfite increased in adhesives, the tensile strength was found to be proportionally increased. The final adhesive mixtures were manufactured using a two-components system which are prepared by mixing two separate protein and BI solutions due to the precipitate in the adhesives. As PVA was added to adhesives to increase tenacity, the plywood dehiscence phenomenon after cold pressing process was declined. By addition of PVA, the tensile strength was improved up to $6.5{\sim}7kgf/cm^2$ with BI/protein ratio from 1:6 up to 1:8. Phase separation between milk fat and aqueous layer was disappeared after addition of emulsifier, Tween 20. Additon of Tween 20 showed tensile strength up to $5{\sim}6.5 kgf/cm^2$ at NCO/protein ratio of 1:12 ~ 1:14 without phase separation.