기도가 막혔을 때 / 기도는 항상 하라

임희창 기독교대한성결교회 활천사 1994 활천 Vol.490 No.-

NACA0015 익형의 공력특성에 대한 수치해석적 연구

임희창,이수정,정의철 한국풍공학회 2012 한국풍공학회지 Vol.16 No.4

In this study, a numerical simulation is made to understand the effect of the angle of attack on a NACA airfoil, which will be used for a basic shape to apply for making the vertical axis Darius wind turbine. The near-wall y+ value which is less than 1 is known to be most desirable for a near-wall modeling. Therefore, this study is aiming to observe the variation and find the optimized value of y+. The Reynolds number used in this study was 360,000, where the chord length and the velocity were 0.12m and 43.8m/s, respectively. Generally, the lift coefficient of the airfoil tends to increase as the angle of attack increases and it decreases substantially at the stall angle and then it decreases. As expected, the lift coefficient increases rapidly from 0 to 10 degs and then after the sudden drop of the lift (i.e., the stall) at around 10 to 16 degs depending on the y+ value. In this paper, it seems to be reliable and appropriate to use y+ value close to 1. From the surface pressure distribution, the maximum and minimum peaks were obtained at the C/Cm 1.89, and these peaks move forward or backward as the angle of attack increases. 본 연구에서는, NACA 익형의 받음각의 변화에 따른 영향을 파악하기 위한 연구로서, 수직축 다리우스 풍력 발전기를 만들기 위한 기본적 형상을 이용하였다. 특히 수치해석에 있어 근접벽면 모델링에서 y+값이 1에 가까울수록 수치결과값이 정확해진다고 알려져 있다. 따라서 본 연구에서는, y+값의 변화를 통하여 최적의 y+값을 찾는 것을 목표로 하고 있다. 본 연구에서 사용한 레이놀즈 수는 360,000로 익형길이, 입구 유속은 각각 0.12m, 43.8m/s으로 설정하였다. 수치해석결과 익형의 양력계수는 받음각이 증가함에 따라 증가하는 경향을 보이며, 실속각 이후에 급격히 감소하는 것을 확인하였으며 양력계수는 받음각이 0° ∼ 10°까지 증가하였고 이후, y+값에 따라 다르지만 대략 10° ∼ 16°에서 급격히 떨어졌다. 본 논문에서 실험결과에 근거하여 수치해석에 y+값이 1에 가까운 것이 적절하다고 판단된다. 표면 압력 분포에서 최대값과 최소값 C/Cm은 1.89, 그리고 최대값의 변화는 받음각의 증가에 따라 앞쪽, 혹은 뒤쪽으로 이동되었다.

다공성 방풍펜스의 방풍효과에 관한 수치해석적 연구

임희창,이상준 한국풍공학회 2000 한국풍공학회지 Vol.4 No.1

신재생 및 유체공학 연구실

임희창 한국가시화정보학회 2012 한국가시화정보학회지 Vol.10 No.3

균일 유동 속에 놓인 산지지형을 지나는 유동에 관한 풍공학적 연구

임희창,박기철,이상준 한국풍공학회 1999 한국풍공학회지 Vol.3 No.1

Orifice shape effect of the TLCD system under a low frequency

임희창,Lim, HeeChang The Korean Society of Visualization 2014 한국가시화정보학회지 Vol.12 No.1

Bluff bodies under the external periodic force vibrate at their own natural or forced frequency. Rectangular bodies or similar structures such as high-rise towers and apartments, and recently a well-cited application - offshore floating bodies, usually needs to reduce these vibrations for stability and the mode control. Therefore, this study is aiming to reduce or control the vibration of a structure by a passive control method, i.e., TLCD (Tuned Liquid Column Damper). Controlling a moving body with a TLCD based on a variety of the orifice shape has been preliminary studied. In order to get a proper control, an optimized study is made on the design of the orifice shape, which has internal plates with the holes. The results show the force acting on the body due to the periodic movement highly depends on the number of holes on the plate and the height of the water level. Therefore, the optimum shape of the orifice and the height of the water level should be confirmed by a series of experiments.

Riblet 홈을 가진 원주의 저항감소에 관한 연구 ( An Experimental Study on Drog Reduction of Grooved Cylinders )

임희창,이상준 대한기계학회 2000 대한기계학회 춘추학술대회 Vol.- No.-

Wind flow around rectangular obstacles with aspect ratio

임희창 한국풍공학회 2009 Wind and Structures, An International Journal (WAS Vol.12 No.4

It has long been studied about the flow around bluff bodies, but the effect of aspect ratio on the sharp-edged bodies in thick turbulent boundary layers is still argued. The author investigates the flow characteristics around a series of rectangular bodies (40d × 80w × 80h, 80d × 80w × 80h and 160d × 80w × 80h in mm) placed in a deep turbulent boundary layer. The study is aiming to identify the extant Reynolds number independence of the rectangular bodies and furthermore understand the surface pressure distribution around the bodies such as the suction pressure in the leading edge, when the shape of bodies is changed, responsible for producing extreme suction pressures around the bluff bodies. The experiments are carried out at three different Reynolds numbers, based on the velocity U at the body height h, of 24,000, 46,000 and 67,000, and large enough that the mean boundary layer flow is effectively Reynolds number independent. The experiment includes wind tunnel work with the velocity and surface pressure measurements. The results show that the generation of the deep turbulent boundary layer in the wind tunnel and the surface pressure around the bodies were all independent of Reynolds number and the longitudinal length, but highly dependent of the transverse width.

Detached eddy simulation of flow around rectangular bodies with different aspect ratios

임희창,Masaaki Ohba 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.20 No.1

As wind flows around a sharp-edged body, the resulting separated flow becomes complicated, with multiple separations and reattachments as well as vortex recirculation. This widespread and unpredictable phenomenon has long been studied academically as well as in engineering applications. In this study, the flow characteristics around rectangular prisms with five different aspect ratios were determined through wind tunnel experiments and a detached eddy simulation, that placed the objects in a simulated deep turbulent boundary layer at Re=4.6 X 10 ^4. A series of rectangular prisms with the same height (h = 80 mm), different longitudinal lengths (l = 0.5h, h, and 2h), or different transverse widths (w = 0.5h, h, and 2h) were employed to observe the effects of the aspect ratio. Furthermore, five wind directions (0, 10, 20, 30, and 45) were selected to observe the effects of the wind direction. The simulated results of the surface pressure were compared to the wind tunnel experiment results and the existing results of previous papers. The vortex and spectrum were also analyzed to determine the detailed flow structure around the body. The paper also highlights the pressure distribution around the rectangular prisms with respect to the different aspect ratios. With an increasing transverse width, the surface suction pressure on the top and side surfaces becomes stronger. In addition, depending on the wind direction, the pressure coefficient experiences a large variation and can even change from a negative to a positive value on the side surface of the cube model.

Short-term observation of wind energy potentiality in the Wol-Ryong wind site

임희창 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.11

Accurate analysis of the atmospheric wind profiles and climate characteristics in a certain area is a prerequisite for providing reliable information on a wind energy site. Two 2-D ultrasonic anemometers and one cup anemometer, arranged perpendicularly to the prevailing wind direction, were used to measure the atmospheric wind environment at a height of 4.5 m in the coastal region of Wol-Ryong, Jeju,South Korea. This study aims to estimate future wind resources with various estimation methods. The wind energy is theoretically estimated at 75 m, the hub height of 800 kW and 1500-kW-class wind turbines, at the Wol-Ryong site. Methods using three equations, a logarithmic profile, a modified logarithmic profile, and a power law, are applied for accurate prediction of the atmospheric wind profile. In addition, yearly wind power can be calculated by using the probability distribution from Weibull and Rayleigh profiles. It is found that the predicted wind speed is strongly affected by surface atmospheric conditions such as the friction velocity, atmospheric stability, and averaged roughness length. The Rayleigh profile gives more power generation than the Weibull distribution, especially under low–windspeed conditions. The logarithmic profile method seems to be the proper method for estimating the energy production at the Wol-Ryong site for neutral atmospheric conditions. On the other hand, the other two methods - the modified logarithmic profile method and the power law method - seem to be improper for neutral conditions.