• 한국수자원학회논문집
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• 제43권1호
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• pp.41-49
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• 2010

본 연구의 계단형 보는 자연형 횡단 구조물의 한 형태로 제안되고 있다. 계단형 보 하류에서의 흐름은 기존 보(Round Crest Weir)에서 발생하는 도수와 달리 WTF(Wave Type Flow)라는 독특한 흐름이 발생한다. WTF는 계단형 보 하류에서 단차로 인해 발생되는 재순환영역(recirculation area)이 일정조건에서 발달하여 수면을 상승시키는 현상이다. WTF 조건에서의 파고는 하류수위(tailwater level) 보다 높아지고 WTF 구간에서의 최대유속발생이 수면에 가까운 곳에서 발생한다. 이와 같은 결과는 WTF 현상이 설계 시 접합부에 영향을 줄 수 있는 중요 인자임을 나타내는 것이다. 본 연구는 수리실험을 통해 WTF이 발생되는 수리조건과 WTF의 규모를 파악하였고 계단형 하류흐름조건에 따른 유속분포를 분석하였다. 본 연구의 결과는 계단형 보 설계 시 고려되지 못한 부분으로서 차후에 계단형 구조물 또는 계단식 변형 구조물 설계 시 주요 자료로 활용 될 것이다.

• 한국유체기계학회 논문집
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• 제11권3호
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• pp.22-29
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• 2008

Clean and renewable energy technologies using ocean energy give us non-polluting alternatives to fossil and nuclear-fueled power plants to meet establishment of countermeasures against the global warming and growing demand for electrical energy. Among the ocean energy resources, wave power takes a growing interest because of its enormous amount of potential energy in the world. Therefore, various types of wave power conversion system to capture the energy of ocean waves have been developed. However, suitable turbine type is not normalized yet because of relatively low efficiency of the turbine systems. The purpose of this study is to investigate the internal flow and performance characteristics of a cross-flow type hydro turbine, which will be built in a caisson for wave power generation. Numerical simulation using a commercial CFD code is conducted to clarify the effects of the turbine rotation speed and flow rate variation on the turbine characteristics. The results show that the output power of the cross-flow type hydro turbine with symmetric nozzle shape is obtained mainly from Stage 2. Turbine inlet configuration should be designed to obtain large amount of flow rate because the static pressure and absolute tangential velocity are influenced considerably by inlet flow rate.

• International Journal of Air-Conditioning and Refrigeration
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• 제10권1호
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• pp.50-63
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• 2002

The Karman boundary-layer has been numerically investigated for the disturbance wave number, wave velocity, azimuth angle and radius (Reynolds number, Re). The disturbed flow over rotating disk can lead to transition at a much lower Re than that of the well-known Type I instability. This early transition is due to the excitation of the Type II. Presented are the neutral stability results concerning these instabilities by solving newly formulated stability equations with consideration of whole convective terms. When the present numerical results are compared with the previously known results, the value of critical Re corresponding to Type I is moved from ${Re}_{c.1}$=285.3 to 270.2 and the value corresponding to Type II from ${Re}_{c.2}$=69.4 to 36.9, respectively. Also, the corresponding wave number is moved fro)m $k_1$=0.378 to 0.386 for Type I; from $k_2$=0.279 to 0.385 for Type II. For Type II, the upped limit of wave number and azimuth angle is $k_u$=0.5872, $\varepsilon_u$=$-17.5^{\circ}$, while its lower limit is near $k_u$=0, $\varepsilon_u$=$-28.4^{\circ}$. This implies that the disturbances will be relatively fast amplified at small Re and within narrow bands of wave number compared with the previous results.

• 설비공학논문집
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• 제12권8호
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• pp.771-781
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• 2000

The Karman boundary-layer, has been numerically investigated for the disturbance wave number, wave velocity, azimuth angle and radius (Reynolds number, Re). The disturbed flow over rotating disk can lead to transition at a much lower Re than that of the well-known Type 1 mode of instability. This early transition is due to the excitation of the Type II mode. Presented are the neutral stability results concerning these modes by solving new formulated vorticity equations with consideration of whole convective terms. When the present numerical results are compared with the previously known results, the value of critical Re corresponding to Type I is moved from Rec,! =285.3 to 270.2 and the value corresponding to Type II is from $Re_{c,2}$=69.4 to 36.9, respectively. Also, the corresponding wave number is moved from $k_1$ =0.378 to $k_1$ =0.389 for Type I; from $k_2$ =0.279 to $k_2$=0.385 for Type II. For Type II, the upper limit of wave number and azimuth angle is $k_U$=0.5872,$varepsilon_U=-18^{\circ}$ , while its lower limit is$k_L$ =0.05, $varepsilon_L=-27^{\circ}$ This implies that the disturbances will be relatively fast amplified at small Re and within narrow bands of wave number compared with the previous results.

• Journal of Magnetics
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• 제20권1호
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• pp.47-51
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• 2015

We measured radial arterial pulse signals using a prototype of a clip-type pulsimeter equipped with a permanent magnet and a Hall device, which produced signals through a voltage-detecting circuit. The systolic peak time and the reflective peak time for a temporally pulsed signal were analyzed for an arbitrary pulse wave at one position of a small permanent magnet. The measured value of the peripheral pulse wave velocity was about 1.25-1.52 m/s, demonstrating the accuracy of this new method. To measure the peripheral blood flow velocity, we simultaneously connected the radial artery pulsimeter to a photoplethysmography meter. The average value of the peripheral blood flow velocity was about 0.27-0.50 m/s.

• 대한조선학회논문집
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• 제59권6호
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• pp.439-446
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• 2022

Efforts to reduce carbon dioxide(CO₂) emissions are being carried out due to climate environmental problems. Eco-friendly ships are also being developed, and various energy saving measures have been developed and applied. In ships, researches have been conducted in various fields such as electric propulsion system and energy saving devices. In addition, the development of ships using various renewable energy, such as kite using wind power and wind power generation, has been carried out. This paper proposes a plan to use renewable energy for ships by applying wave generators to small ships. In 2016, 130 small domestic ships drifted by sea due to discharge of starting storage batteries, and discharge cases accounted for the largest portion of the causes of domestic ship accidents. This is due to the excessive use of storage batteries for starting the main engine by departing in a weak storage battery state for small ships. Accordingly, two type wave power generators - opened flow wave power generator and enclosed vibrator type wave power generator - are developed for charging a starting storage battery when the ships are stationary at sea or port. Opened flow wave power generator utilizes the flow of fluid in the ship by using wave induced ship motion. Enclosed vibrator type wave power generator utilizes the pendulum kinetic energy located in a ship due to wave induced ship motion.

• 한국재료학회지
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• 제14권7호
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• pp.522-528
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• 2004

Heat analysis of the plate type and wave type heat sink were carried out by using computational simulation. The heat resistance and air flow of two heat sink models were analysed according to natural and forced convection condition and positions of fan. When a fan was at the position of z-axis and y-axis in forced convection, the heat resistances of plate type heat sink were $0.17^{\circ}C/W$, and $0.28^{\circ}C/W$ respectively. In the case of wave type heat sink, they were $0.18^{\circ}C/W$ and $0.53^{\circ}C/W$. As the air flow velocities were averagely $0.386\;m/s\~3.269\;m/s$, air flow velocity of plate type heat sink was faster than that of wave type. In this experiment, it was observed that the plate type heat sink showed a good ability of heat radiation comparing with wave type one.

• 대한토목학회논문집
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• 제37권3호
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• pp.575-583
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• 2017

계단형 보와 여수로 같은 수공구조물의 상부에서는 스키밍 흐름 그리고 직하류부에서는 정상파를 포함하는 도수 현상인 파형흐름과 같이 다양한 형태의 흐름이 발생한다. 연구에서는 하이브리드 RANS-LES 난류 모델링 기법과 자유수면 변동을 해석하기 위한 VOF (volume of fluid)기법을 병합한 3차원 부정류 수치모형을 이용하여 계단형 보가 설치된 사각형 개수로에서 발생하는 파형흐름과 스키밍 흐름을 포함하는 난류흐름을 수치모의 하였다. 시간평균 수치모의 결과와 기존 수리모형 실험 결과를 비교분석한 결과, 수치모의는 보 하류부에서의 평균유속분포의 변화, 정체파와 수면와류를 포함하는 파형흐름의 전반적인 수면 변화, 파형흐름의 파고와 길이, 정체파 하부에서 발생하는 재순환 흐름 영역의 길이 등을 양호하게 잘 재현하는 것으로 나타났다. 수치모의를 통해서 자유수면과 순간 유속 벡터의 변동, 전단응력과 난류에너지의 분포 그리고 3차원 난류조직구조와 총압력분포의 형태와 변동 자료를 제시하여 스키밍 흐름과 파형흐름 영역에서의 독특한 흐름 거동 특성을 규명하였다.

• 한국산업융합학회 논문집
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• 제24권6_2호
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• pp.801-808
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• 2021

In this paper, a numerical analysis was conducted on the effect of the flow control valve of a oscillation water column(OWC) type wave power generator turbine. The OWC wave power turbine operates with compressed air in the air chamber according to the change of wave height. When the wave height changes rapidly, a flow control valve is required due to overload of the turbine and reduced efficiency. Therefore, in this paper, a flow control valve with an opening angle of 60 degrees was installed in the front of the turbine, and the pressure drop, torque, and overall performance were calculated according to the change of turbine RPM and flow rate of turbine inlet. In conclusion, the flow control valve with an opening angle of 60 degrees affects when the turbine rotates at low rotation and the inlet flow rate is large. But it does not have a significant effect on overall turbine performance and it is necessary to find the optimal angle in the future works.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2016년도 학술발표회
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• pp.65-65
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• 2016

위어나 낙차공 같은 수공구조물 직하류부에서는 다양한 형태의 흐름조건이 발생한다. 낙차공 하류에서 발생하는 독특한 흐름형태 중 하나는 정상파형도수를 갖는 파형흐름이다. 이 연구에서는강 등(2010)이 수리실험을 수행한 바 있는 계단형 위어 하류부에서의 형성되는 파형흐름을 3차원 수치해석을 수행한다. 위어 구조물 위를 통과하는 난류흐름을 해석하기 위해서 Spalart-Allamaras 1방정식 모형을 이용한 URANS 수치모의와 DES (detached eddy simulation)을 실시하였다. 위어 주변에서의 자유수면 변동, 파상도수, 자유수면에서의 와류 그리고 바닥부근에서의 재순환 영역의 형상과 크기, 선정된 종방향 위치들에서의 흐름방향유속분포 등의 항으로 수치해석결과를 실험값과 비교하여 수치모의의 적절성과 난류모델들의 성능을 평가한다.