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채널 내에 부착된 정육면체 장애물 후류에서의 Vortex 구조에 대하여
황종연,양경수,Hwang, Jong-Yeon,Yang, Gyeong-Su 대한기계학회 2001 大韓機械學會論文集B Vol.25 No.12
Vortical structures in the near-wake region of a cubic obstacle are studied using numerical simulation. We consider flow between two parallel plates with a cube mounted on one of the plates. In the turbulent near-wake region of the flow, coherent structures such as hairpin vortices are found. Quasi-periodic behavior of the hairpin vortices is noticed; its dimensionless frequency at Re=1,000 is about 0.82 which is consistent with the result of Elavarasan of et al.'s experiment [Fluid Dyn. Research, 2000, 27] although their geometry is somewhat different from on. In the case of Re=3,500, the dimensionless frequency of the hairpin vortex is about 1.60. It is observed that the translating speed of the head of the hairpin vortex is lower than the streamwise mean velocity at that location. In the vicinity of the lower plate downstream of the cube, various length scales are identified thus less coherent. However, it is noticed that the vortical structures become gradually elongated downstream of the new reattachment.
황종연(Jong Yeon Hwang),한의정(Eui Jung Han),김태근(Tae Keun Kim),유순주(Soon Ju Yu),윤영삼(Young Sam Yoon),정용순(Yong Soon Chung) 한국환경영향평가학회 1998 환경영향평가 Vol.7 No.2
In order to study the general characteristics of reservoir and stream sediments, various analysis tests were conducted. Water contents and ignition loss were measured to know the primary sediment characteristics. The COD, total phosphorus and nitrogen were contained for the determination of organic substance content. For the purpose of establishing the contamination degree of heavy metals, some heavy metal contents were investigated. In heavy metal contents, reservoir sediments showed somewhat higer value than stream sediments. As a result, the reservoir sediment content of all analysis items were higher than stream sediment.
돌출된 표면위의 층류유동에 대한 전산 해석적 연구 (II) - 위상학적, 기구학적 연구 -
황종연,양경수,Hwang, Jong-Yeon,Yang, Kyung-Soo 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.11
Topological and kinematical studies of the singular points found in flows around a surface-mounted cube in a channel are presented. Numerical simulation was carried out using high-resolution grid systems. Singular points(saddles and nodes) were found around the cube, which satisfy the topological rules suggested by Hunt et al. As the Reynolds number increases, the structure of vortices around the cube becomes complex and the number of singular points increases. Nevertheless, the rule governing the numbers of singular points is still valid. This confirms that our simulation is correct from topological and kinematical point of view, and enables one to infer complex flow patterns in our simulation.
돌출된 표면 위의 충류유동에 대한 전산 해석적 연구 (I) -유동 해석-
황종연,양경수,Hwang, Jong-Yeon,Yang, Kyung-Soo 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.11
Flow over a protruding surface is investigated using numerical simulation. We consider flow between two parallel plates with a cube mounted on one side of the channel. As the flow approaches the cube, the adverse pressure gradient produces three-dimensional boundary-layer separation, resulting In the formation of horseshoe vortices. The objective of our study is to clarify both the steady and the unsteady characteristics of the vortex system. As the Reynolds number increases, the structure of the vortices near the cube becomes complex and the number of vortices increases. The distribution of skin friction on the cube-mounted wall reflects the effect of the horseshoe vortices. All these results are consistent with the experimental findings currently available.
영국의 시험 · 검사기관 정도관리 제도 중 현장평가 고찰
황종연 ( Jong Yeon Hwang ),이혜리 ( Hyeri Lee ),고상호 ( Sang Ho Go ),전수아 ( Sooa Jeon ),김지혜 ( Jeehye Kim ),이진주 ( Jin Joo Lee ),박창희 ( Park Chang Hee ),신선경 ( Sun-kyung Shin ),허유정 ( Ujeong Hur ) 한국환경분석학회 2021 환경분석과 독성보건 Vol.24 No.3
Withreferencetothequalitystandard,ISO/IEC17025,weconductedon-siteassessmentsofandcomparisonsbetweentestandinspectioninstitutionsinKoreaandtheUK.Thediversityofevaluationmethodsused‘inthefield’withintheUKisgreaterthantherangeinKorea.Nevertheless,whenassessingon-siteprocessesinbothcountries,itisclearthatmanyaspectsofthequalityassessment,includingtherolesoftheevaluationcommitteemembers,thepreparationofdocumentsforevaluation,theopeningmeeting,theevaluationprocessinthefield,andtheclosingmeeting,occurinasimilarorderintheUKasinKorea.However,oneimportantdifferencebetweentheon-siteevaluationsinKoreaandtheUKwasnoted;particularly,intheUK,thelevelofexcellenceachievedbytheevaluatedinstitutionishighlightedduringtheclosingmeeting.
IRMS를 이용한 수소와 산소 안정동위원소의 정확도 및 정밀도 연구
황종연 ( Jong Yeon Hwang ),김보경 ( Bo Kyong Kim ),김민섭 ( Min Seob Kim ),이원석 ( Won Seok Lee ) 한국환경농학회 2013 한국환경농학회 학술대회집 Vol.2013 No.-
The isotope ratio mass spectrometer (IRMS) is an instrument that measures both of the elemental contents and isotope ratios of hydrogen, oxygen, carbon, nitrogen and sulfur in environmental samples at the same time. In this study, a recently introduced IRMS was used to analyze produced certified reference materials (CRMs), which helped establish analysis conditions of oxygen and hydrogen isotope ratios. It is important to ensure the reliability and present the accuracy and precision prior to applying environmental samples. In this study, three international standard materials such as VSMOW2, GISP and SLAP were employed. Among them, GISP was used for the calibration as it represents the intermediate hydrogen and oxygen isotope composition, while VSMOW2 and SLAP were applied to find the two end-points of δ D and δ18O values, respectively. In addition, the validation of accuracy and precision was performed with two CRMs indicating different isotope compositions. In analyzing δD and δ 18O values, the single analysis of each showed higher accuracy and precision than the simultaneous analysis of both during the calibration with GISP. The measured δ18O values of the two end-points were the same as the certified values of VSMOW (0 ‰) and SLAP (-55.5 ‰). However, the measured δD values, which were found-7.68 ‰ and-423.99 ‰, respectively, did not reach the certified values of VSMOW (0 ‰) and SLAP (-428 ‰). It is considered that the range (428 ‰) of hydrogen isotope ratios between the two international standards is quite wider than the range (55.5 ‰) of oxygen isotope ratios. Nonetheless, the gap between the two end-points was found to be narrowed from-0.57 ‰ of VSMOW to-420.87 ‰ of SLAP after calibration with VSMOW once H3 + factor correction was frequently performed every 1∼3 hours. The δ18O value of CRM certified as-19.64 ‰ fell within the certified value ±2σ in the range over around 39.9 nA, but the δD value of CRM certified as-152.02 ‰ was within the certified value ±4σ. In order to agree with the accepted values defined by VSMOW and SLAP, the measured δD values were switched over to the certified values through linear regression. As a result of normalization, the calculated δD values of CRM fell within the certified value ±2σ. In this study, the accuracy and precision of IRMS were assessed using CRMs, thereby establishing optimal analysis conditions for tracing environmental pollution sources.
회전하는 원형단면 실린더 주위의 난류유동 물질전달에 대한 직접수치모사 (Ⅰ) - 높은 Schmidt 수에 대하여 -
황종연(Jong-Yeon Hwang),양경수(Kyung-Soo Yang) 대한기계학회 2005 大韓機械學會論文集B Vol.29 No.7
In this paper, an investigation on high-Schmidt number (Sc=1670) mass transfer in turbulent flow around a rotating circular cylinder is carried out by Direct Numerical Simulation. The concentration field is computed for three different values of low Reynolds number, namely 161, 348 and 623 based on the cylinder radius and friction velocity. Statistical study reveals that the thickness of Nernst diffusive layer is very small compared with that of viscous sub-layer in the case of high Sc mass transfer. Strong correlation of concentration field with streamwise and vertical velocity components is observed. However, that is not the case with the spanwise velocity component. Instantaneous concentration visualization reveals that the length scale of concentration fluctuation typically decreases as Reynolds number increases. Statistical correlation between Sherwood number and Reynolds number is consistent with other experiments currently available.
황종연(Jong Yeon Hwang),한의정(Eui Jung Han),유순주(Soon Ju Yu),윤영삼(Young Sam Yoon),천세억(Se Eug Cheon),김태근(Tae Keun Kim) 한국환경영향평가학회 1999 환경영향평가 Vol.8 No.2
The organic contents of reservoir sediment can offer a good indicator to events in history of lake life. Reservoir sediment have many information of the past and future fingerprint about development direction of life cycle in biological animals. So, in this study we made an effort to know the distribution of organic contents in Daecheong reservoir sediment. Items for this investigations are such as follows: Loss on ignition, COD, Organic carbon, TN, TP, heavy metal contents. Loss on ignitions were determined in 6.44∼15.91% and COD were determined in 1.606∼6.859%, organic carbon in 1.077∼3.743%. Contents of TP and TN were in the range of 0.083∼0.757%, and 0.645∼0.926%, respectively.