단독 원기둥 주위의 후류유동에 관한 연구

승삼선(Samsun Seung),이재성(Jaesung Lee),김상일(Sangil Kim) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.춘계 No.-

This experimental study is investigated the wake flow around a elastically supported circular cylinder. In this study, the Reynolds Numbers are varied in the region of 1.4×10<SUP>4</SUP>≤Re≤3.2×10<SUP>4</SUP>. Under these conditions we have figured out the process of wake mechanism and moving path of the vortex by measuring the velocity at each position in the wake around a cylinder. Also these facts from wind tunnel test are proved by flow visualization test through water channel. As a result, we have concluded as followings : i) The process(formation→growth→collapse) of vortex in the wake around a cylinder is observed, ii) The vortex efflux angle is about 16~17 degrees under the experimental conditions. These degrees have no concern with velocity change and the existence of flow-induced vibration of a cylinder. iii) The moving path of vortex center is inferred by spectrum analysis of fluctuating velocity behind the cylinder. These are confirmed by doing visualization test.

회전하는 하나의 내부 원통에서 서로 다른 반경비가 Taylor-Couette 유동에 미치는 영향

승삼선(Samsun Seung),김상일(Sangil Kim) 대한기계학회 2018 大韓機械學會論文集B Vol.42 No.12

회전하는 하나의 내부 원통이 서로 다른 반경비를 갖는 경우에 Taylor vortex형성에 미치는 영향에 대해 수치해석을 수행하였다. 서로 다른 반경비는 내부 원통 중앙을 기준으로 동일한 폭에 깊이를 달리한 것으로 먼저 반경비가 0.83인 매끈한 내부 원통에 대한 수치계산 결과를 기존의 실험결과와 비교하여, 타당성을 검토하였다. 그런 다음, 내부 원통 중앙에 동일한 홈의 폭에 깊이를 각각 3, 6, 9, 12 mm 달리한 내부 원통에 회전수 25, 100 rpm인 경우의 수치계산 결과와 비교하였다. 그 결과, Taylor vortex는 층류인 경우 내부 원통 양끝에서 생성되기 시작하지만 홈이 있는 경우에는 홈 모서리에서도 이루어짐을 확인하였다. 홈의 깊이와 내부 원통의 회전수에 따라 쌍으로 이루어진 Taylor vortex셀의 폭이 달라졌으며, 회전수가 큰 경우에는 작은 경우보다 Taylor vortex 셀의 폭이 넓어져 개수가 감소하였다. 또한 각각의 Taylor vortex 쌍의 vortex 중심은 이웃하고 있는 vortex 쌍 사이의 vortex 중심보다 더 가깝게 자리하고 있음을 확인하였다. The Taylor-Couette flow in a rotating inner cylinder with different radius ratios has been studied numerically to show the effects of Taylor vortices formation, where different radius ratios refer to the varied depths having the same width based on the center of the inner cylinder. The numerical calculations results are compared with those of the straight inner cylinder. In order to examine the feasibility of the numerical calculations, the numerical results are compared with existing experimental results for a straight inner cylinder. Then, we compare the numerical results in the case of inner cylinders with different radius ratios. Initially, laminar Taylor vortices form at the end walls and corners of the groove. Results show that the widths of pairs of Taylor vortex cells are varied according to the depth and rotational speed of the inner cylinder. In the case involving a higher rotational speed of inner cylinder widths, and the number of pairs of Taylor vortex cells are wide and decreasing than low rotational speed of it. In addition, the vortex centers of each Taylor vortex pair are closer together than the vortex centers between neighboring vortex pairs.

T.A.B 실시 유무에 따른 대공간의 열환경 특성

승삼선 ( Sam Sun Seung ),이승철 ( Seung Chul Lee ) 대한설비관리학회 2010 대한설비관리학회지 Vol.15 No.2

It is important to evaluate thermal environmental characteristics and the amenities in a large space such as a building with a performance hall. Because there are sometimes occurred inefficient HVAC system operation and excessive energy consumptions. Especially in a thermal environmental view, people feel thermal displeasure because of temperature differences between vertical and horizontal directions. We have performed thermal environmental characteristics analysis for N Korean performance arts center by using CFD techniques. Consequently we confirmed that supply flow balancing after T.A.B decreased thermal stratification locally and increased people`s thermal comfort. So it is necessary to carry out T.A.B for HVAC system in a large space. And it can be used as a fundamental design data for large space design.

수치해석 격자 및 화원 위치가 도로 터널 임계속도 산정에 미치는 영향

이승철(Seung-Chul Lee),전우철(Woo-Chul Jeon),박영록(Young-Rock Park),승삼선(Sam-Sun Seung) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.5

To estimate the critical velocity in road tunnel fire, this study calculated one-dimensional equation and conducted three-dimensional computational fluid dynamics, varying the grid number and the location of the fire source. 8 kinds of numerical analysis were carried out. The critical velocity in the target tunnel by one-dimensional way, 2.22 ㎧ was calculated, when hydraulic diameter was applied instead of the tunnel height. According to six numerical analysis, each grid number has different position, temperature, and CO concentration of backlayering. In the Case of the subject, 0.8 million grid was found to be the most ideal. According to three numerical analysis, the location of the fire source affect the critical velocity, through the different air velocity, temperature, and CO concentration distribution of each Case. This solution is considered to be caused by the different buoyancy force according to the density gradient of stratification.

스프링클러 설비의 배관방식에 따른 유량 분배 특성

이승철(Seung-Chul Lee),승삼선(Sam-Sun Seung) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.5

The flow distribution characteristics in piping arrangements of sprinkler system have been investigated in this paper by the numerical simulation. While the exit flow rates of loop type piping arrangements predicted by the three-dimensional CFD calculation and those given by the design flow rate show a close agreement, the results of the general type piping arrangement are found to differ from the design flow rate by -19.1% to 27.3% for the various exits. These discrepancies may be attributed to the underlying limitation concerning the fitting loss coefficients, which assume that the flow in front of the fittings is fully developed. Consequently, loop type piping arrangement of sprinkler system must be selected in order that the flow rate may be balanced.

CFD를 이용한 정수장의 환기특성

이승철(Seung-Chul Lee),김상일(Sang-Il Kim),승삼선(Sam-Sun Seung),조영진(Young-Jin Cho) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.5-3

In this paper, the ventilation characteristics of a filter basin of the purification plant were investigated for different windows size and the locations by numerical simulation. It has been found that the maximum concentration of chlorine gas in the filter basin with original windows was predicted about 0.13ppm. It means that an additional required amount of ventilation is needed to maintain good indoor air quality. For the filter basin with double sized windows and relocations, the maximum concentration of chlorine gas was predicted 0.11ppm. It is known that the window size and its locations in a filter basin of the purification plant are important factors to reduce the concentration of chlorine gas in the indoor.

버스전용 지하주차장의 환기 특성에 관한 수치해석적 연구

이승철(Lee, Seung-Chul),승삼선(Seung, Sam-Sun) 한국산학기술학회 2007 한국산학기술학회논문지 Vol.8 No.2

본 연구에서는 전산유체역학 기법을 도입하여 17대 버스가 주차된 지하주차장의 환기특성을 분석하였다. 그 결과 지하주차장내 버스 4대가 운행할 때 CO와 NO의 평균농도는 각각 1.3과 0.3 ppm으로 나타났다. 또한 15대 버스가 공회전할 때 지하주차장내의 CO와 NO_x의 평균농도는 2.9와 0.8 ppm으로 각각 나타났다. 따라서 두 가지 경우의 결과가 허용기준을 충족하여 지하주차장에 설치될 환기설비의 용량 및 위치는 적정한 것으로 판단된다. In this paper, the ventilation characteristics of an underground parking lot with 17 buses has been investigated for two cases by computational fluid dynamics. It has been found that the average concentration of CO and NO_x gas in the parking lot were 1.3 and 0.3 ppm respectively, when four buses operated. When the fifteen vehicles stopped in the parking lot, the average concentration of CO and NO_x gas was 2.9 and 0.8 ppm respectively. The average concentration of two pollutants(CO, NO_x) are lower than the standard values. Therefore the facilities and its location is proper to ventilation.

서로 다른 두 개의 와류방출 주파수간의 비선형간섭

김상일(Sang Il Kim),승삼선(Sam Sun Seung),이승철(Seung-Chul Lee) 대한기계학회 2014 大韓機械學會論文集B Vol.38 No.3

본 연구는 서로 다른 두 개의 직경을 가지는 원기둥으로부터 나오는 두 개의 와류방출주파수간의 비선형간섭에 관한 것이다. 두 개의 서로 다른 주파수는 두 개의 직경을 가지는 원기둥에 의해 인위적으로 만들어졌고, 원기둥 후류의 속도 변동은 3 차원으로 측정되었다. 그리고 원기둥 표면에는 압력공이 설치되어 원기둥 표면의 압력도 측정하였다. 이 압력 신호를 기준 신호로 사용하였다. TSC 해석을 병행하여 두 주파수간의 비선형간섭의 세기를 조사하였다. 그 결과, 다음과 사실을 알았다. i)원기둥 후류의 주파수 분포, ii)위상집합평균법에 의한 원기둥 후류의 3 차원적인 흐름 상태, iii)두 개의 직경을 가지는 원기둥에서 나오는 두 개의 주파수간의 비선형간섭과 저주파의 종와류과의 관계. This study analyzes the nonlinear interaction between two different vortex shedding frequencies from a cylinder with two diameters. In particular, two different vortex shedding frequencies are generated by preparing a cylinder having two diameters artificially. Flow velocity fluctuations behind the cylinder are measured threedimensionally. Additionally, we fabricated a hole and placed a pressure transducer for measuring the pressure on the cylinder surface. The pressure signal from the pressure transducer is used as basic signal. A TSC(Trans Spectrum Coherence) is used for checking the strength of the nonlinear interaction between two different vortex shedding frequencies. As a result, the following are clarified: i) frequency distribution behind the cylinder, ii) three-dimensional flow state behind the cylinder through calculation of ensemble average, and iii) close relationship between the vertical vortex and change of low frequency by nonlinear interaction between two different vortex shedding frequencies from the cylinder with two diameters.

OBD에 기초한 승용차 엔진의 고장유형 분석과 진단 사례 연구

민종식(Min, Jong-Sik),승삼선(Seung, Sam-Sun) 한국산학기술학회 2006 한국산학기술학회논문지 Vol.7 No.6

본 논문은 OBD(On-Board Diagnostics)를 통해 얻은 데이터(직접 취득 128대, 관련 사이트 획득 데이터 1,114대)를 토대로 승용차 엔진의 고장 유형별 분포를 분석하고, 이를 다시 승용차 엔진의 계통별 및 복잡한 경우의 고장 현상으로 구분하여 그에 따른 대표적인 진단 사례 방안을 제시하고 있다. 그 결과, 고장 유형별 분포는 공회전시 부조가 32%(394대), 가속 불량이 21% (261대), 주행중 시동 꺼짐이 19%(234대), 시동 불량이 11 %(133대), 연비 불량이 9%(116대), 출력 부족이 8%(104대)의 순으로 나타났다. 또한 고장 현상을 입력, 제어, 출력, 기계적인 계통으로 나누어 분석하여본 결과, 계통별 고장현상 및 진단에서는 단순 부품에 의한 고장은 진단하는데 크게 어렵지 않으나 제어 계통에서는 복합적인 문제가 발생되면 OBD와 연계된 전용장비로 해당구간을 취하여 데이터를 얻어 파형을 겹쳐보는 등의 방법을 이용하여 분석함으로써 대표적인 진단사례 방안을 제시할 수 있었다. In this study, we have performed a systematic case study on troubles and diagnoses of passenger car’s engine based on OBD. We have acquired 1,242 data in order to analysis accurate troubles’ causes and apposite diagnoses. 128 data of them are got using OBD apparatus, and the rest of them are collected on related website. As results, distribution on trouble cases shows bad idling(32%), poor acceleration(21 %), stop in running(l9%), faulty start(11%), inferior fuel economy(9%), and insufficient power(8%) in order of magnitude. And in the systematic cases, it is not difficult to detect troubles in a single part. But we know that special apparatus such as multichannel scanner is needed in complicated troubles. Furthermore we think that the survey is continued in various ways for more systematic case study on troubles and diagnoses.

서로 다른 두 개의 와류방출 주파수간의 조화형 비선형 간섭

김상일(Sangil Kim),승삼선(Samsun Sueng),이승철(Seung-Chul Lee),김효준(Hyojun Kim) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.5

This study is on the nonlinear interaction between two different vortex shedding frequencies from the cylinder having two diameters. In particular, two different vortex shedding frequencies are made by making the cylinder having two diameters artificially. And the flow velocity fluctuations behind the cylinder are measured three dimensionally. Also, we made a hole of pressure transducer for measuring the pressure on the cylinder surface and measured the pressure of cylinder surface. The pressure signal from the pressure transducer is used as basic signal. The TSC is used for checking the strength of nonlinear interaction between two different vortex shedding frequencies. As a result, it is clarified that; I) frequency distribution behind the cylinder. ii) three dimensional flow state behind the cylinder by calculation of ensemble average. iii) a close connection between the vertical vortex and change of low frequency by nonlinear interaction between two different vortex shedding frequencies from the cylinder having two diameters.