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유용훈(Yong Hoon Yoo),장두환(Doo Hwan Jang),박훈철(Hoon Cheol Park),변영환(Yong Hwan Byun),변도영(Doyoung Byun) 한국항공우주학회 2008 韓國航空宇宙學會誌 Vol.36 No.1
본 연구에서는 딱정벌레목 곤충의 비행특성을 알아보기 위해 유동가시화가 수행되었고, 겉날개의 날갯짓의 영향에 대해 고찰하였다. 또한 고속 카메라를 이용하여 겉날개와 속날개의 움직임을 분석하였다. 실험 결과 날갯짓 하는 곤충의 세 가지 양력발생 원리를 확인 할 수 있었다. 그리고 겉날개의 미세한 날갯짓을 확인할 수 있었으며, 겉날개의 효과를 예상할 수 있었다. A flow visualization is conducted to investigate a flight characteristics of a Coleoptera and an effect of flapping elytra was considered in this study. Also the movements of outer wing(elytra) and inner wing is analyzed using High Speed Camera. As a result of this experiment, in case of flapping insect, three mechanisms to generate lift is confirmed. A small movement of outer wing(elytra) is confirmed and the effect of outer wing(elytra) is estimated.
전용희(Yong-Hee Jeon),이재우(Jae-Woo Lee),변영환(Yung-Hwan Byun) 한국전산유체공학회 1999 한국전산유체공학회 학술대회논문집 Vol.1999 No.-
Numerical design optimization techniques are implemented for the improvement of the ram accelerator performance. The design object is to find the minimum ram tube length required to accelerate projectile from initial velocity V0 to target velocity Ve. The premixture is composed of H₂, O₂, N₂ and the mole numbers of these species are selected as design variables. The objective function and the constraints are linearized during the optimization process and gradient-based Simplex method and SLP(Sequential Linear Programming}have been employed. With the assumption of two dimensional inviscid flow for internal flow field, the analyses of the nonequilibrium chemical reactions for 8 steps 7 species have been performed. To determined the tube length, ram tube internal flow field is assumed to be in a quasi-steady state and the flow velocity is divided into several subregions with equal interval. Hence the thrust coefficients and accelerations for corresponding subregions are obtained and integrated for the whole velocity region. With the proposed design optimization techniques, the total ram tube length had been reduced 19% within 7 design iterations. This optimization procedure can be directly applied to the multi-stage, multi-premixture ram accelerator design optimization problems.
전용희(Yong-Hee Jeon),전권수(Kwan-Su Jeon),이재우(Jae-Woo Lee),변영환(Yung-Hwan Byun) 한국전산유체공학회 2000 한국전산유체공학회 학술대회논문집 Vol.2000 No.5
In this paper, numerical study has been done for the improvement of the superdetonative ram accelerator performance and for the design optimization of the system. The objective function to optimize the premixture composition is the ram rube length required to accelerate projectile from initial velocity V_0 to target velocity Ve. The premixture is composed of H₂, O₂, N₂ and the mole numbers of these species are selected as design variables. RSM(Response Surface Methodology) which is widely used for the complex optimization problems is selected as the optimization technique. In particular, to improve the non-linearity of the response and to consider the accuracy and efficiency of the solution, design space stretching technique has been applied. Separate sub-optimization routine is introduced to determine the stretching position and clustering parameters which construct the optimum regression model, Two step optimization technique has been applied to obtain the optimal system. With the application of stretching technique, we can perform system optimization with a small number of experimental points, and construct precise regression model for highly non-linear domain. The error to compared with analysis result is only 0.01% and it is demonstrated that present method can be applied more practical design optimization problems with many design variables.
유용훈(Yong Hoon Yoo),변도영(Doyoung Byun),박훈철(Hoon Cheol Park),변영환(Yung Hwan Byun) 한국가시화정보학회 2008 한국가시화정보학회 학술발표대회 논문집 Vol.- No.2
A visualization using Particle Image Velocimetry is conducted to investigate flight characteristics of a beetle and an effect of flapping was considered in this study. The smoke wire visualization in previous research is shown the qualitative flapping characteristics of a beetle. Using the PIV method, we can obtain quantitative values which are the velocity around wings. PIV experiment is carried out on streamwise plane and spanwise plane. Using velocity field obtained by PIV, vorticity field is calculated by simple program as well as pressure field. Positions of vortices are not clear in the velocity fields, but vortices fields show the positions are easy to observe leading edge vortex (LEV) and trailing edge vortex (TEV) as well as wing tip vortex.
전권수(Kwon-Su Jeon),전용희(Yong-Hee Jeon),이재우(Jae-Woo Lee),변영환(Yung-Hwan Byun) 한국전산유체공학회 2000 한국전산유체공학회지 Vol.5 No.2
In this paper, the numerical study has been done for the improvement of the superdetonative ram accelerator performance and for the design optimization of the system. The objective function to optimize the premixture composition is the ram tube length, required to accelerate projectile from initial velocity Fa to target velocity Ve. The premixture is composed of H₂, O₂, N₂ and the mole numbers of these species are selected as design variables. RSM(Response Surface Methodology) which is widely used for the complex optimization problems is selected as the optimization technique. In particular, to improve the non-linearity of the response and to consider the accuracy and the efficiency of the solution, design space stretching technique has been applied. Separate sub-optimization routine is introduced to determine the stretching position and clustering parameters which construct the optimum regression model. Two step optimization technique has been applied to obtain the optimal system. With the application of stretching technique, we can perform system optimization with a small number of experimental points, and construct precise regression model for highly non-linear domain. The error compared with analysis result is only 0.01% and it is demonstrated that present method can be applied to more practical design optimization problems with many design variables.
김상진(Sang-Jin Kim),전용희(Yong-Hee Jeon),이재우(Jae-Woo Lee),변영환(Yung-Hwan Byun) 한국전산유체공학회 2000 한국전산유체공학회 학술대회논문집 Vol.2000 No.10
To improve the performance at all design points, multi -point optimization method is implemented for the nose fairing shape design of space launcher. The response surface method is used to effectively reduce the huge computational loads during the optimization process. The drag is selected as the objective function, and the surface heat transfer characteristics, and the internal volume of the nose fairing are considered as design constraints. Fun Navier-Stokes equations are selected as governing equations. Two points drag minimization, and two points drag / heat flux optimization were successfully performed and configurations which have good performance for the wide operation range were derived. By considering three design points, the space launcher shape which undergoes the least drag during whole flight mission was designed. For all the design cases, the constructed response surfaces show good confidence level with only 23 design points with the proper stretching of the design space.