• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.223-227
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• 2010

하천의 수위와 유량에 대한 정확한 정보는 이수, 치수와 같은 수자원 관리에 있어서 가장 기본적인 기초자료가 된다. 하천 수위와 유량 자료를 확보하기 위한 지속적인 직접 계측 방법은 많은 시간과 비용이 소모되며, 홍수 시에는 위험성이 존재하여 자료 확보가 불가능하다. 따라서 수치모형을 이용한 수위-유량 자료의 예측과 활용이 필요하며, 2차원 수치모형의 경계조건을 설정할 경우에도 활용할 필요성이 있다. 본 연구에서는 복단면 개수로 및 불규칙한 하상을 보이는 횡단면 상에서의 단위유량 예측을 위한 유한요소모형을 개발한다. 지배방정식은 Wark 등 (1990)이 제시한 운동량방정식을 이용하며, 단면형상과 Manning 조도계수, 그리고 수위를 알면, 결과적으로 흐름방향 단위유량의 횡방향 분포를 얻을 수 있다. 개발된 모형의 검증을 위해 실측 자료와 비교하며, 또한 Darcy-Weisbach 마찰계수를 이용하는 Darby와 Thorne (1996)의 모형 결과와도 비교한다. 검증된 모형의 알고리즘을 2차원 모형의 상류단 경계조건 설정에 활용하여, 절점별 유입유량을 차등분배 시켰을 때와 그렇지 못했을 때의 결과를 비교한다. 또한 수위를 경계조건으로 입력하였을 때 개발 모형을 활용하여 유입유량을 예측하는 활용방안을 제시한다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.10a
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• pp.598-598
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• 2010

와이퍼 작동 중에 발생하는 진동소음 중 1000Hz 이상의 스퀼 소음은 발생 메커니즘이 정확하게 알려지지 않았으며 발생하는 조건도 불규칙하다. 이 스퀼 소음의 발생 빈도 및 주파수를 변경하는 설계를 위하여 스퀼 진동 소음의 발생 메커니즘의 원인분석이 우선적으로 이루어져야 한다. 이 논문에서는 자동차 와이퍼 시스템에서 워셔액을 분사하였을 때 발생하는 스퀼 소음을 측정하고 인자 별로 분석하였다. 스퀼 소음이 발생하는 인자들을 마찰계수와 연관이 있는 인자, 기하학적인 인자, 와이퍼의 운동과 관련된 인자들로 나누어 분석하였다. 실제 와이퍼 시스템을 구현하기 위하여 모터와 원판 지지대 등을 이용하였고, 마이크로폰, 레이저 바이브로미터, 노이즈북, 아르테미스를 이용하여 측정 및 분석하였다.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.8 s.173
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• pp.57-63
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• 2005

Development of a locomotive mechanism fer the capsule type endoscopes will largely enhance the ability to diagnose disease of digestive organs. In connection with it, most of researches have focused on an installable locomotive mechanism in the capsule. In this paper, it is introduced that the movement of a capsule type endoscope in digestive organ can be manipulated by magnetic force produced outside human body. Since the magnetic force is provided by permanent magnets, no additional power supply to the capsule is required. Using a robotic manipulator for locating the external magnet, the capsule motion control system can cover the whole human digestive organs. This study is particularly concentrated on dither motion effect to improve the mobility of capsule type endoscope. It was experimentally found out that the friction coefficient between the capsule and digestive organ can be remarkably reduced by superposing yawing or rolling dither motion on the translatory motion. In this paper, the experimental results obtained with the direction, amplitude and frequency of sinusoidal dither motion changed is reported.

• Water for future
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• v.27 no.2
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• pp.73-83
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• 1994

The unproper development of the nearshore zone can enhance the diffusion of pollutant in the nearshore zone resulting in unbalanced sediment budget of beach which causes alteration of beach topography. Therefore, it is required to predict the effects of the envirnmental change quantitatively. In this paper, the depth-averaged and time-averaged energy balance equation is selected to acount for the wave transformation such as refraction, shoaling effect, the surf zone energy disipation, wave breaking index and bore, due to wave breaking in the shore region.(Numerical solutions are obtained by a finite difference method, ADI and Upwind. For the calculation of the wave-induced current, the unsteady nonlinear depth-averaged and time-averaged governing equation is derived based on the continuity and momentum equation for imcompressible fluid.) Numerical solutions are obtained by finite difference method considering influences of factors such as lateral mixing coefficient, bed shear stress, wave direction angle, wave steepness, wave period and bottom slope. The model is applied to the computation of wave transformation, wave-induced current and variation of mean water leel on a uniformly sloping beach.

• Tribology and Lubricants
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• v.25 no.4
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• pp.243-249
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• 2009

A magnetic clutch consists of pulley and disk. It delivers and isolates the power needed for the operation of the compressor used in automotive air conditioning system. To improve the performance, efficiency and durability of automotive air conditioning system, appropriate design of pulley, disk and system working parameters(the magnitude of magnetic force, and so on) is necessary. For that goal, it is required to understand the friction characteristics of magnetic clutch for the initial operating time. In this study, friction tests were carried out in order to investigate the effect of sliding velocity on the friction characteristics of magnetic clutch using pin-on-disk type friction and wear tester. For experiments, pulley and disk used in real automotive air conditioning system were considered. Friction experiments were conducted under various sliding velocities, and coefficients of kinetic friction were obtained. Under the experimental conditions considered in this study, the coefficients of kinetic friction increased with the increase of test number(sliding distance) and decreased with the increase of sliding velocity.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.91-91
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• 2017

트라이볼로지란? 상대운동을 하면서 서로 영향을 미치는 두면 및 이와 관련된 문제로 마찰, 마모, 윤활에 대한 것을 말한다. 트라이볼로지는 1960대에 조사 연구되기 시작하면서 학문적으로 많은 정리가 이루어졌고, 현재 현대사회에서 문제가 되고 있는 에너지 및 환경 문제를 해결할 수 있는 핵심 요소로 떠오르고 있다. 특히 4차 산업혁명시대를 맞이하여 많은 부분에서는 인공지능, 클라우딩, 빅 데이터 및 로봇 등을 이야기하고 이에 대한 투자 및 개발을 이야기하고 있지만, 이 4차 산업을 뒷받침할, 강인한 제조업이 없으면 불가능한 혁명이라고 말 할 수 있다. 특히 트라이볼로지는 제조업의 무인 자동화 및 무인 로봇 등 이를 필요로 하는 산업 기기와 같은 전반적인 부품 및 소재의 마모를 감소시켜, 기계 장치의 신뢰성을 증가시킬 수 있다. 마찰은 두 물체 상호간의 열 발생을 억제 시키고, 마모는 물체의 표면 경도가 높으면 높을수록 마모량이 적어진다고 알려져있다. 따라서 트라이볼로지와 관련한 표면 처리의 경우, 고온 환경에서의 사용성 증대 및 고경도화 그리고 저마찰을 위한 방향으로 개발 발전되어져 왔다. 트라이볼로지 코팅 중 내마모 코팅의 경우, 티타늄 원소를 기본으로 알루미늄(Al) 및 실리콘(Si)를 합금화하면서, 고경도화 및 내열성을 증대시키는 방향으로 발전되어 왔다. 그에 따라 표면경도의 경우, 4000 Hv, 내열성 $1200^{\circ}C$에 도달였다. 하지만 여전히 철계와의 마찰계수는 0.3 이상으로 이를 낮추는 방법이 요구되고 있다. 최근 트라이볼로지 코팅 중 카본을 함유한 비정질 다이아몬드상 카본 막 (Diamond like Carbon Film : DLC) 이나, Diamond 막의 수요 증가는 마찰을 낮추어 융착마모를 줄이려는 노력으로 볼 수 있다. 특히 수소를 포함하지 않는 고경도 탄소막인 ta-C(tetrahedral amorphous-Carbon)의 수요는 증대되고 있으며, 이에 대한 후막화 및 양산화 기술의 개발의 현재 isssu로 대두되고 있다.

• Korean Chemical Engineering Research
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• v.56 no.2
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• pp.191-203
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• 2018

This study was investigated the effect of the morphology change of copper (Cu) powders under the different rotational speed and milling time by using three kinds of grinding media with different size and materials, and performed DEM simulations of ball behavior. In order to clarify the mechanism of grinding by three - dimensional simulations of the ball behavior in a traditional ball mill, the force, kinetic energy, and medium velocity of the grinding media were calculated. In the simulation, the amount of change of the input energy was also calculated by adjusting the rotational speed, ball material, kinetic velocity, and friction coefficient in the same as the actual experimental conditions. The scanning electron microscope results show that the particle morphology changes from irregular to spherical when the ball size is small.

• 한국해양학회지
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• v.30 no.6
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• pp.565-583
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• 1995

We have used a nonlinear quasi-geostrophic model to study effects of lateral friction and bottom topography on the motion of warm eddies. The two empirical orthogonal functions of the stream function, accounting for the vertical structure, represent the barotropic and first baroclinic dynamic modes. This model is integrated 360 days on a 1000 km ${\times}$ 1000 km domain with a resolution of 10 km ${\times}$ 10 km including both the thermocline and idealized topography of the East Sea. Prescribed inflow through the Korea Strait is compensated by outflow through the Tsugaru Strait. The balance between the nonlinear advection term and the planetary ${\beta}$-effect tends to make northward movement of warm eddy over a flat bottom. The motion of a warm eddy over a sloping topography can be dominated by the nonlinear advection, while nonlinearity plays a secondary role over a flat topography. For eddies dispersing over topography, the nonlinear tendency is a function of time. For a strong warm eddy, northward propagation can occur. For intermediate strength of eddies one might expect a balance between the nonlinear term and the topographic ${\beta}$-effect. As nonlinearity decreases with eddy dispersion, southward motion along the slope may occur by such as a topographic Rossby wave. Our numerical simulations have confirmed the importance of lateral friction on eddy motions, in such a way that the northward penetration of the warm eddy increases drastically by the decrease of the lateral friction. The northward motion of warm eddy can be prevented by reducing the Reynolds number sufficiently. We have also demonstrated the crucial role of topographic effects in the eddy motion process.

• The KSFM Journal of Fluid Machinery
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• v.5 no.1 s.14
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• pp.20-26
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• 2002

This study reports the analysis of the pressure drop characteristics for the air-particle flow in powder transport piping system. The pressure drop characteristics of air-particle flow in piping system is not well understood due to the complexity of particles motion mechanism. Particles or powders suspended in air flow cause the increase of the pressure drop and affect directly the transportation efficiency. In this study, the pressure drop in powder transport piping system with straight and curved pipes is analyzed for the interactions of air flow and particle motion. The total pressure drop increases with increasing of the pipe length, the mixture ratio, and the friction factor of particles due to the increasing friction loss by air and particles in a coal piping system. For the coal powders of $74{\mu}m$ size and powder-to-air mass mixture ratio of 0.667, the total pressure drop by the consideration of powders and air flow is $30\%$ higher than that of air flow only.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2002.11a
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• pp.139-145
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• 2002

The flow zone through propeller jets are used in evaluating the environmental and constructional effects of navigation on the waterway. It relies on the characteristics of ships and water depth. A numerical model using the momentum theory of the propeller and Shield's diagram was developed in a restricted waterway. Equations for discharge are presented based on thrust coefficients and propeller speed and are the most accurate means of defining discharge. Approximate methods for discharge are developed based on applied ship's power. Equations for discharge are as a function of applied power, propeller diameter, and ship speed. Water depth of the waterway and draft of the shop are also necessary for the calculation of the grain size of the initial motion. The velocity distribution of discharge from the propeller was simulated by the Gaussian normal distribution function. The shear velocity and shear stress were from the Sternberg's formula. Case studies to show the influence of significant factors on sediment movement induced by the ship's propeller at the channel bottom are presented.