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백승철,권순범,김희동,Baek, Seung-Cheol,Kwon, Soon-Bum,Kim, Heuy-Dong 대한기계학회 2002 大韓機械學會論文集B Vol.26 No.7
Rapid expansion of a moist air or a stream through a supersonic nozzle often leads to non-equilibrium condensation shock wave, causing a considerable energy loss in flow field. Depending on amount of latent heat released due to non-equilibrium condensation, the flow is highly unstable or a periodical oscillation accompanying the condensation shock wave in the nozzle. The unsteadiness of the condensation shock wave is always associated with several kinds of instabilities as well as noise and vibration of flow devices. In the current study, a passive control technique using a porous wall with a plenum cavity underneath is applied for the purpose of alleviation of the condensation shock oscillations in a transonic nozzle. A droplet growth equation is coupled with two-dimensional Navier-Stokes equation system. Computations are carried out using a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. An experiment using an indraft wind tunnel is made to validate the present computational results. The results show that the oscillations of the condensation shock wave are completely suppressed by the current passive control method.
백승철,권순범,김희동,Baek, Seung-Cheol,Kwon, Soon-Bum,Kim, Heuy-Dong 대한기계학회 2002 大韓機械學會論文集B Vol.26 No.7
The current study describes experimental and computational works on the passive control of the steady and unsteady condensation shock waves, which are generated in a transonic nozzle. The bleed slots are installed on the contoured wall of the transonic nozzle in order 10 control the magnitude of the condensation shock wave and its oscillations. For computations, a droplet growth equation is copuled with two-dimensional Navier-Stokes equation systems. Computations are carried out using a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. Baldwin-Lomax turbulence model is employed to close the governing equations. An experiment using an indrafi transonic wind tunnel is made to validate the computational results. The current computations represented well the experimental flows. From both the experimental and computational results it is found that the magnitude of the condensation shock wave in the bleed slotted nozzle is signi ficantly reduced, compared with no passive control of solid wall. The oscillations of the condensation shock wave are successfully suppressed by a bleed slot system.
백승철(Seung-Chul Baek),홍준식(Jun-Sik Hong) 한국정보기술학회 2011 한국정보기술학회논문지 Vol.9 No.10
When measuring a distance between two-dimensional images in a multi-resolution using a well-known GBD(Gray Block Distance) algorithm, it is not easy to discriminate a relative classification of images because the vividness in the region whose gray level has rapidly changed, particularly at the boundary of an image, becomes indistinct. In this paper, an image classification method using the normalization based on its multi-resolution environments is proposed. The proposed method taken here preserves the information about such a rapidly changed region and at the same time measures the distance between images. From our simulation results, image classification in the GBD algorithm is not performed well when k=4, where k is the number of rectangles of gray block side. However, the proposed method works well independent of the value of k. Our method gives a better characteristic for image classification as k decreases due to its smaller deviation compared to the GBD algorithm. The images used in the in this experiments can be ordered by least square error(LSE) with relatively regardless of differences in the intensity. Therefore, compared to the GBD algorithm, it is more easily discriminated to classify such images.
스트레스 관련 피부질환 환자의 혈장내 β - endorphin의 변화
백승철 ( Seung Churl Baek ),김정원 ( Chung Won Kim ) 대한피부과학회 1995 대한피부과학회지 Vol.33 No.5
Background : Stress has long been known to play a role in many dermatologic disorders ard can affect the onset and course of the disorder in some patients. Stress-induced exacerbation or onset of symptoms has been reported in chronic urticaria, alopecia areata, berpes simplex, herps zoster, and psoriasis vulgris, and these diseases can be classified as stress-associated dermatoses. Beta p-endorphin is one if the most important mediators of stress, which is known to be generat ed upon stimulation of t.he pituitary adrenal axis, and its secretion increases during periods of stress. Objective : In order t,o see wheather p-endorphin might be related to the onset or recurrence of stress-associated dermatses, we compared the plasma concentration of p-endorphin in patients with stress associated dematoses with those of healthy subjects. Methods : The concentation of p-endorphin in sera was quantified by radioimmunoassay, usirg the INCSTAR 'IRIA Kit for plasma p-endorphin. Each patient was asked to indicate if they be lieved that their skin proilem began after an important stressful event in their lives. Results : There was no significant difference in plasma p-endorphin levels between patient,s with chronic urticaria, alopeciareata, herpes simplex, and herpes zoster and healthy subjects(p>0.05), whereas in patients witi psoriasis vulgaris, plasma level of p-endorphin was significantly in creased(p<0.001). There was no relationship between the stressful events and plasma pendorphin concentrations. Conclusions : The plasma p-endorphin level is not correlated with the onset or recurrence of stress-associated dermatuses such as chronic urticaria, alopecia areata, herpes simplex, and herp.s zoster. The increase in p-endorphin in psoriasis vulgaris is more likely that this peptide is generted by the lymphocyte irliltrate in the skin and/or by lymphocytes when they recirculate rath:.r than by the activation of the pituitary-adrenal axis by stress. (Kor J Dermatol 1995;33(5): 841-846)
Prandtl-Meyer 유동에서 발생하는 응축충격파의 피동제어
백승철(Seung-Cheol Baek),권순범(Soon-Bum Kwon),김희동(Heuy-Dong Kim) 한국항공우주학회 2004 韓國航空宇宙學會誌 Vol.32 No.1
Prandtl-Meyer 유동에서 발생하는 웅축충격파를 제어하기 위한 피동제어법의 유효성을 조사하기 위해 계산과 실험을 수행하였다. 본 연구에서 사용된 제어법은 균질 응축을 수반하는 다공벽과 공동을 사용한 피동제어법이다. 실험결과와 비교하기 위해 액적성장방정식과 완전히 결합된 2차원 압축성 Navier-Stokes 방정식은 3차 오더 MUSCL 타입 TVD 유한차분법을 사용하여 풀었다. 본 연구의 피동제어법은 응축충격파의 강도감소에 유효하며, 또 응축충격파의 비정상 운동이 다공벽/공동 시스템을 이용한 제어법으로 완전히 억제되었다. Both computational and experimental works are performed to clarify the effectiveness of a passive control method applied to the condensation in Prandtl-Meyer flow. The present study makes use of the passive control strategy employing a porous wall and cavity system with homogeneous condensation. Two-dimensional compressible Navier-Stokes equations, fully coupled with a droplet growth equation, are solved to reproduce the experimental results using a third-order MUSCL type TVD finite-difference scheme. It was found that the strength of condensation shock wave in Prandtl-Meyer flow were weakened. Furthermore, the unsteady motion of condensation shock wave was effectively suppressed using the passive cavity/porous system.