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이정상,Lee, Jung-Sang 한국기술사회 2010 技術士 Vol.43 No.2
Immersed tunnel had been a rather new term in Korea before Busan-Geoje fixed link project was started and became known through the media. Although Korean is unfamiliar with the immersed tunnel, this construction method has a long history in the world. Busan-Geoje Fixed Link immersed tunnel consist of 18 elements and each element is approximately 180m long. These tunnel elements are prefabricated of reinforced concrete in a temporary dry dock and are towed to the site and lowered into final position in a dredged trench and are placed on a screeded gravel bed directly without temporary support.
이정상(Jung-Sang Lee),김진호(Jin-ho Kim),김종암(Chongam Kim) 한국항공우주학회 2007 韓國航空宇宙學會誌 Vol.35 No.1
검정금파리 날개의 “8자 운동”에 의한 공기역학적 힘의 발생에 관해 수치해석을 수행하였다. 날개운동은 자유류가 있는 tethered flight 실험에서 관찰된 결과에서 인용하였다. 해석결과 양력은 downstroke 중일 때 주로 발생하였고 추력은 upstroke 끝에서 갑작스럽게 발생하였다. 본 연구에서는 양력과 추력 발생의 이러한 특성을 후류에서의 와류구조와 에어포일 주위의 압력장을 통해 물리적으로 이해하고자 하였다. 결과적으로 양력발생은 유효받음각의 증가에 따른 앞전와류와 관계있었으며, 추력발생은 유동장 형태의 측면에서 와류 짝(vortex pairing)현상과 압력장 측면에서 와류정지 현상으로 설명할 수 있었다. Numerical simulation is conducted to investigate aerodynamic force generation mechanism for the figure-of-eight motion of Dipteran fly, Phormia-Regina. Wing trajectory is referred to experimental result, which was observed from the tethered flight under free stream condition. Numerical simulation shows that the lift is mainly generated during downstroke motion and the large amount of thrust is generated abruptly at the end of upstroke motion. In the present work, vortical structure in the wake and the pressure field around the airfoil are examined to understand the generation of lift and thrust. Consequently, the lift generation is related with the leading edge vortex which is developed by an effective angle of attack. And the thrust generation can be explained by vortex pairing in the flow field and by vortex staying in the pressure field.
동적 실속을 이용한 Flapping-Airfoil의 추력 발생
이정상(Jung Sang Lee),김종암(Chongam Kim),노오현(Oh-Hyun Rho) 한국전산유체공학회 2002 한국전산유체공학회 학술대회논문집 Vol.2002 No.-
This paper deals with a thrust generation on flapping-airfoil by dynamic stall. Dynamic stall refers to a series of complicated aerodynamic phenomena accompanied by a stall delay in unsteady motion. In most cases, once it occurs, the dynamic stall may lead to an abrupt fluctuation of aerodynamic forces. An inverse Karman vortex has been considered as a main reason for a thrust generation. In this paper, however, we have found out that a thrust is closely related to reduced frequency and leading edge vortex in addition to inverse Karman vortex. In order to certify our opinion, piching and plunging motions were calculated with the parameter of amplitude and frequency by using the unsteady, incompressible Navier-Stokes flow solver with a two-equation turbulence model. For more efficient computation, it is parallelized by MPI programming method.
이정상(Jung-Sang Lee),김진호(Jin-ho Kim),김종암(Chongam Kim) 한국항공우주학회 2007 韓國航空宇宙學會誌 Vol.35 No.1
Part 1에서 수행된 검정금파리의 “8자 운동”에 대한 해석결과는 와류들이 양력과 추력발생에 중요한 역할을 하는 것으로 나타났다. 곤충날개에서 발생되는 공기역학적 힘은 레이놀즈수와 같은 공기역학적 요소와 더불어 진동수, 운동진폭, 운동성분 등과 같은 운동학적적 요소들 또 날개의 형태 및 개수등과 같은 형태학적 요소들에 따를 것으로 생각된다. 본 연구에서는 레이놀즈수, 진동수 그리고 운동성분에 따른 양력과 추력발생을 고찰함으로써 이들이 공기역학적으로 어떤 영향을 미치는가를 조사하였다. 이로써 part 1의 결과를 물리적으로 좀 더 상세하게 설명할 수 있는 근거를 찾고자 하였다. 해석결과 “8자 운동”을 구성하는 운동성분 중 회전운동이 추력발생에 지배적인 역할을 하고 있었으며, 또한 추력발생은 반시계 방향의 회전순환과 깊은 관련이 있었다. Numerical results from the figure-of-eight motion of Phormia-Regina in Part 1 indicate that vortical structure and vortex dynamics do play a critical role in lift and thrust generation. The aerodynamic force generation of insects' wing could be governed by aerodynamic parameters such as Reynolds number; kinematic parameters such as frequency, amplitude, and component of the figure of eight motion; and morphological parameters such as wing shape and the number of wing. In the present work, the effects of Reynolds number, reduced frequency and motion component are investigated in detail to clarify aerodynamic characteristics of insect wing. Through numerical results and their physical interpretation, the mechanism of aerodynamic force generation is presented more clearly. Rotation turns out to be the most important component in thrust generation and subsequent counterclockwise rotational circulation is closely related with thrust generation.