실험에 의한 직교류홴의 유량 및 소음 분석

안철오,류호선,Ahn, Cheol-O,Rew, Ho-Seon 한국유체기계학회 1998 한국유체기계학회 논문집 Vol.1 No.1

This study was carried out to investigate the effect of design parameters on the volume flow-rate and the noise level and to finally find the optimal design variables. Eighteen cross-flow fans were designed by the method of orthogonal array, and the flow-rate and the noise level were measured. These data were analyzed by the neural network system. The effects of eight design variables(scroll exit angle, scroll arc length et al.) on the fan performance and the noise level were valuated and discussed. This experiment shows that the design solutions suggested by neural network system may increase its volume flow-rate and reduce noise simultaneously.

실험에 의한 CROSS FLOW FAN 소음 분석

안철오(Cheol-O Ahn),류호선(Ho-Seon Rew) 한국소음진동공학회 1997 한국소음진동공학회 학술대회논문집 Vol.1997 No.5

3차원 입자와법을 위한 병렬화 기법

안철오(Cheol-O Ahn),서인수(In Soo Seo),이상환(Sang Hwan Lee) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10

Astrophysics, fluid dynamics, molecular dynamics or many other physical problems can be considered as a system composed of many particles, so called N-body system. Because these simulations are prohibitively expensive for large N, the fast algorithms and the parallel schemes must be employed. In this study, the performance effects of three domain decomposition schemes(Orthogonal Recursive Bisection, Morton order, Peano-Hilbert Order) and the locally essential tree are examined. We simulated a spherical vortex sheet problem and a flow past a sphere at Re=100 using the vortex element method with the 128-node linux cluster. The performance difference was found according to different particle distributions. In the case of computational domain with large aspect ratio, the orthogonal recursive bisection shows more efficient than others. However, using the locally essential tree, the performance differences between domain decomposition schemes are decreased.

분자동역학을 위한 두가지 고속화 기법의 비교

안철오(Cheol O Ahn),서인수(In Soo Seo),이상환(Sang Hwan Lee) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10

In this study, we compared two different fast algorithms for molecular dynamics simulations. One algorithm partitions simulation domain into several cells and assigns molecules to these cells by their positions. Using this cell-molecule relationship, this method is efficient to find the nearby molecules. We propose another algorithm which uses a hierarchical tree data structure. The tree structure is adaptive to the distribution of molecules. And both algorithms can be applied to make 'neighbor list' to reduce the number of unnecessary inter-atomic distance calculations in molecular simulations. However, the effectiveness of the neighbor list algorithm, it is useless when the number of molecules and simulation domain are increased with time. Results show that proposed algorithm is effective due to the adaptiveness to the distribution of molecules.

와사법을 이용한 타원판 후류의 전산 가시화

안철오(Cheol-O Ahn),이상환(Sang-Hwan Lee) 한국가시화정보학회 2002 한국가시화정보학회 학술발표대회 논문집 Vol.- No.-

대규모 중력장 다체계 전산모사를 위한 새로운 트리코드

안철오(Cheol O Ahn),이상환(Sang Hwan Lee) 한국정보과학회 2007 한국정보과학회 학술발표논문집 Vol.34 No.1A

나노 채널에서의 표면 거칠기와 경계 습윤의 효과

추연식(Yun-Sik Choo),안철오(Cheol-O Ahn),이상환(Sang-Hwan Lee) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10

The nanochannels are characterized by a large surface-to-volume ratio, so that the surface properties strongly affect the flow resistance. We present here the results showing that the effect of wetting properties and the surface roughness may considerably reduce the friction of fluid past the boundaries. For a simple fluid flowing over hydrophilic and hydrophobic surfaces, the influences of surface roughness are investigated by the nonequilibrium molecular dynamics (NEMD) simulations. The solid surfaces with embossed squares were considered as the rough surface. It was found that the fluid slip at near a solid surface highly depends on the wall-fluid interaction and the surface roughness. For the fluids over hydrophobic surfaces, the snapshots of fluid molecules show that an air gap or nanobubble exists at the fluid-solid interface. Due to the increase of drag resistance at the solid-fluid interface, the fluid slip on rough surfaces is smaller than that on smooth surface walls.

미소 T 채널의 혼합 특성에 관한 연구

이상현(Sang hyun Lee),안철오(Cheol-O Ahn),서인수(In Soo Seo),이상환(Sang Hwan Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11

We simulated the mixing characteristics in micro T-channel using Lattice Boltzmann Method. We studied the relation a mixing length and pressure-drop due to inlet and outlet ration in Reynolds number 0.5, Peclet number 500 and Schmidt 1000. The ratio of a down-inlet to up-inlet was 0.5~1.5 times, up-inlet to outlet was 1~3 times and outlet length was 250 times to up-inlet. The mixing length decrease linearly as outlet ratio decreased, and pressure-drip increase non-linearly. Initial stage of micro channel mixture was fast by downinlet ratio, however, the mixing length is not influence.

Investigation of Human Body Sensitivity to Local Cooling

Ju-Youn Lee(이주연),Cheol-O Ahn(안철오),Baik-Young Chung(정백영),Kwan-Shik Cho(조관식) 한국생활환경학회 2002 한국생활환경학회지 Vol.9 No.3

서열(暑熱)환경에 있어서 인체가 가장 빨리 쾌적감을 느끼기 위해서는 국부적으로 냉 온열자극을 주는 것이다. 그 중에서 대류, 복사, 전도에 의한 국부 냉방을 들 수 있지만, 기류에 의한 냉방이 가장 효과적 이라고 할 수 있다. 본 연구는 고온 고습의 서열환경에서 피험자(대학생 남녀6명)를 대상으로 인체 생리실험을 실험하였다 . 실험조건은, 실온 2조건(Ta = 30℃, 33℃), 기류 토출온도 2조건 (Tdc = 15℃, 20℃) 상대습도 2조건 (RH = 50%,80%) 으로 하였다. 전실조건은 기온 33℃, 상대습도 50% 정온기류로, 착의량은 0.5 clo였다. 피부온은 피부표면 7부위를 측정하였고, 혈압,맥박은 실험전후에 측정하였다. 평균피부온은 Hardy & DuBois의 7점법으로 측정하였고, 본 연구에서는 두부(頭部)에 기류를 주었기 때문에 두부에서의 생리적인 반응을 다른 부위와 비교하여 평가하였다. 그 결과, 생리적인 반응에서 토출온도 15℃의 조건에서는 다른 부위에서는 피부온의 영향은 그다지 나타나지 않았으나, 기류노출 부위인 두부에서 기류를 노출시킨 후 급격히 피부온이 하강하면서 두부가30℃ 이하로 냉각되었다. 토출온도 20℃의 경우에는 15℃의 조건과 같이 신체 각 부위 의 피부온은 두부 이외 에는33℃~35℃의 안정된 피부온을 나타내었으나, 실온30℃의 환경에서는 팔, 손, 대퇴부에서 낮은 피부온을 나타내었다. 평균 피부온은 33.8℃~34.5℃의 범위였고, 두부의 피부온이 31.5℃~33.3℃의 범위로(일반적 34℃~35℃) 고습한 환경에서는 땀이 기류로 인해 냉각됨으로 인해, 초기에 급격한 피부온의 저하를 가져오고, 점차로 건조되면서 피부온이 상승하는 현상을 나타내었다[Fig. 2참조]. 신체 각 부위 온열감 평가에서는 전체적으로 [-1: 약간 서늘하다~+1: 약간 따뜻하다]의 쾌적측 의 온열감 평가를 나타내었다. 부위 가운데 두부에서 [-2:서늘하다~-1:약간 서늘하다]의 가장 낮은 온열감 평가를 나타내었고, 머리부위가 다른 부위에 비해 냉각됨을 알 수 있다. 또, 낮은 피부온에 비해 높은 온열감 평가를 나타낸 것은 다른 부위에서 느끼는 따뜻함을 두부를 냉각시킴으로 인해 온열감 평가가 약간 완화되었음을 알 수 있었다. 위 결과로 평균 피부온이 35℃ 정도까지는 Spot기류를 인체에 가함으로 인해 서열(暑熱) 환경을 완화가능하고, 어느 정도 쾌적감을 향상 시킬 수 있다는 결과를 얻었다. The purpose of this study was to clarify the effects of localized cool airflow on thermal comfort in muggy condition. The experiment was conducted in summer. The subjects (6 young females & males) were exposed to the following conditions: combinations of air temperatures (Ta = 30℃, 33℃), discharge temperature (Tdc = 15℃, 20℃) and relative humidity (RR = 50%, 80%) The following results were obtained: For the whole parts of the body thermal sensation were voted [-1: slightly cool]~[+l: slightly warm]. The skin temperature of the head in contact with the airflow was affected by the low discharge temperature (15℃). The skin temperature mentioned was from 3 1. 5℃ to 33.3℃. The mean skin temperature ranged from 33.8℃ to 34.5℃. We prove that localized airflow could relieve muggy conditions even to 35℃ of mean skin temperature.

유전자 알고리즘을 이용한 축류 송풍기 설계최적화

유인태(In-Tae Yoo),안철오(Cheol-O Ahn),이상환(Sang-Hwan Lee) 한국유체기계학회 2003 유체기계 연구개발 발표회 논문집 Vol.- No.-

In an attempt to solve multiobjective optimization problems, weighted sum method is most widely used for the advantage that a designer can consider the relative significance of each object functions by weight values but it can be highly sensitive to weight vector and occasionally yield a deviated optimum from the relative weighting values designer designated because the multiobjective function has the form of simple sum of the product of the weighting values and the object functions in traditional approach.<br/> To search the design solution well agree to the designer's weighting values, we proposed new multiobjective function which is the functional of each normalized objective functions and considered to find the design solution comparing the distance between the characteristic line and the ideal optimum. In this study, proposed multiobjective function was applied to design high efficiency and low noise axial flow fan and the result shows this approach will be effective for the case that the quality of the design can be highly affected by the designer's subjectiveness represented as weighting values in multiobjective design optimization process.