마름/젖음 천수흐름 해석을 위한 혼합격자기반 유한체적모형

김병현(Kim Byunghyun) 한국방재학회 2018 한국방재학회논문집 Vol.18 No.6

Godunov형 유한체적모형은 복잡한 유체의 흐름도 수치진동 없이 정확하게 해석할 수 있는 것으로 알려져 있다. 특히, 각 격자의 절점에서 지형고를 반영하는 격자기반 유한체적모형은 지형을 정확하게 반영할 수 있어 지형이 모형의 정확성에 중요한 역할을 하는 홍수모델링에 큰 이점이 있다. 하지만, 격자기반모형에서는 절점에서 반영한 지형고에 따라 부분적인 마름/젖음이 발생할 수도 있어, 2차원 수치모형에서 해결하기 어려운 문제 중에 하나인 마름/젖음 문제가 더 복잡해진다. 계산격자에서 발생하는 부분 마름/젖음 해석을 위해 Begnudelli and Sanders (2006)는 삼각격자 기반 체적-수위 관계(Volume-Free surface Relationships, VFRs)를 제안하였으며, Kim et al. (2014)은 혼합격자에 적용을 위해 제안 방법을 확장하였다. 본 연구에서는 삼각, 사각, 혼합격자를 포함한 3가지 유형의 격자를 생성하고 각 격자에 대해 해상도를 다르게 하여 혼합격자에 적용 가능한 VFRs (Kim et al., 2014)를 마름과 젖음이 발생하는 실험실 및 실제 발생한 댐 붕괴에 대해 정확성과 적용성을 검토하였다. 산정된 모형의 오차 및 계산시간은 합리적인 값을 보여주어, 본 연구에서 적용한 VFRs가 격자의 종류 및 해상도에 관계없이 잘 적용되고 있음을 확인하였다. The Godunov-type finite-volume model is able to accurately simulate complex fluid flows without numerical oscillation. In particular, the mesh-based finite-volume model can capture the feature geometry with precision at the nodes of the grid, and thus has a benefit in flood modeling. However, the mesh-based model may cause partial drying and wetting, which are challenges to solve in the 2D numerical model. Begnudelli and Sanders (2006) proposed a triangular mesh-based volume/free surface relationship (VFR) for resolving partial drying and wetting, and Kim et al. (2014) extended the method to mixed mesh. In this study the accuracy and applicability of VFRs extended by Kim et al. (2014) were examined by applying three mesh types, namely triangular, quadrilateral and mixed mesh, with various resolutions. Model errors and run times were acceptable and VFRs applied in this study performed well regardless of mesh type and resolution.

On Board 형 엔진제어기 형상설계

김태진(Taejin Kim),김영수(Youngsu Kim),김규동(Kyudong Kim),김재용(Jaeyong Kim),김병현(Byunghyun Kim),김창휘(Changhuy Kim) 항공우주시스템공학회 2017 항공우주시스템공학회 학술대회 발표집 Vol.2017 No.4

서울지역 유통한약재의 약용부위에 따른 유해중금속 분포

김동규(Donggyu Kim),김복순(Bogsoon Kim),한은정(Eunjung Han),한창호(Changho Han),김욱희(Oukhee Kim),최병현(Byunghyun Choi),황인숙(Insook Hwang),채영주(Youngzoo Chae),김민영(Minyoung Kim),박승국(Seungkook Park) 한국분석과학회 2009 분석과학 Vol.22 No.6

Observations of Short- and Long-Term Mechanical Properties of Glass Fiber Reinforced Polypropylenes with Post-Consumer Recycled Materials

Byunghyun Kang,Donguk Kim,Joo Seong Sohn,Nocheol Park,Kwangjoo Kim,Hyeong-Jun Kim,Youngdeog Koh,Byoung-Ho Choi 한국정밀공학회 2024 International Journal of Precision Engineering and Vol.11 No.2

In this study, the change in the mechanical properties of glass fiber-reinforced thermoplastic (GFRTP) according to the recycled material content was evaluated. The recycled material was polypropylene, with short glass fiber reinforcement, dry blended with virgin polypropylene and additional glass fiber, and injected into its final shape. It is known that during the recycling process, the length of the glass fibers decreases, which leads to the deterioration of the mechanical properties. Therefore, to compensate for the fiber length shortening, long glass fibers were introduced, and changes of the length distribution of the glass fiber and mechanical properties were investigated. Variation of key short- and long-term mechanical properties by introducing long fibers was measured and investigated by performing tensile test, Izod impact test, essential work of fracture (EWF) test, and fatigue test. Most of the mechanical properties showed a linear relationship with the long glass fiber content, but the percent elongation at break and the resistance to the crack initiation were significantly improved immediately after the long fiber was introduced. In addition, the distribution of fiber length was measured and analyzed, and it was found that significant fiber breakage occurred during the injection process and the recycling process including the chopping of recycled material. Finally, through the observation of fracture surfaces, it was validated that the ductile-to-brittle fracture mechanism transition was mainly caused by the poor compatibility between virgin and recycled materials.

Autoencoder ODEs for Time Series Anomaly Detection

Byunghyun Kim(김병현),Jihye Na(나지혜),Yeongsin Byeon(변영신),Sejin Kim(김세진),Jae-Gil Lee(이재길) 한국정보과학회 2022 한국정보과학회 학술발표논문집 Vol.2022 No.12

Experimental and Computational Study on Separation Control Performance of Synthetic Jets with Circular Exit

Kim, Minhee,Lee, Byunghyun,Lee, Junhee,Kim, Chongam The Korean Society for Aeronautical and Space Scie 2016 International Journal of Aeronautical and Space Sc Vol.17 No.3

This paper presents experimental and computational investigations of synthetic jets with a circular exit for improving flow control performance. First, the flow feature and vortex structure of a multiple serial circular exit were numerically analyzed from the view point of flow control effect under a cross flow condition. In order to improve separation control performance, experimental and numerical studies were conducted according to several key parameters, such as hole diameter, hole gap, the number of hole, jet array, and phase difference. Experiments were carried out in a quiescent condition and a forced separated flow condition using piezoelectrically driven synthetic jets. Jet characteristics were compared by measuring velocity profiles and pressure distributions. The interaction of synthetic jets with a freestream was examined by analyzing vortical structure characteristics. For separation control performance, separated flow over an airfoil at high angles of attack was employed and the flow control performance of the proposed synthetic jet was verified by measuring aerodynamic coefficient. The circular exit with a suitable hole parameter provides stable and persistent jet vortices that do beneficially affect separation control. This demonstrates the flow control performance of circular exit array could be remarkably improved by applying a set of suitable hole parameters.

Efflorescence assessment using hyperspectral imaging for concrete structures

Kim, Byunghyun,Cho, Soojin Techno-Press 2018 Smart Structures and Systems, An International Jou Vol.22 No.2

Efflorescence is a phenomenon primarily caused by a carbonation process in concrete structures. Efflorescence can cause concrete degradation in the long term; therefore, it must be accurately assessed by proper inspection. Currently, the assessment is performed on the basis of visual inspection or image-based inspection, which may result in the subjective assessment by the inspectors. In this paper, a novel approach is proposed for the objective and quantitative assessment of concrete efflorescence using hyperspectral imaging (HSI). HSI acquires the full electromagnetic spectrum of light reflected from a material, which enables the identification of materials in the image on the basis of spectrum. Spectral angle mapper (SAM) that calculates the similarity of a test spectrum in the hyperspectral image to a reference spectrum is used to assess efflorescence, and the reference spectral profiles of efflorescence are obtained from theUSGS spectral library. Field tests were carried out in a real building and a bridge. For each experiment, efflorescence assessed by the proposed approach was compared with that assessed by image-based approach mimicking conventional visual inspection. Performance measures such as accuracy, precision, and recall were calculated to check the performance of the proposed approach. Performance-related issues are discussed for further enhancement of the proposed approach.

Monomorphic ventricular tachycardia due to protease inhibitor intoxication by atazanavir

Byunghyun Kim,김경수 대한응급의학회 2018 Clinical and Experimental Emergency Medicine Vol.5 No.2

Atazanavir is a protease inhibitor approved for use in combination with other antiretroviral drugs for the treatment of human immunodeficiency virus infection. Atazanavir and other protease inhibitors can sometimes induce corrected QT prolongation and ventricular arrhythmia. A 40-year-old man with no comorbidities, except human immunodeficiency virus 1 infection, presented with palpitations 3 days after an overdose of 150 caps of atazanavir, with suicidal intent. His initial electrocardiogram showed monomorphic ventricular tachycardia, and hyperbilirubinemia was observed in his initial blood test. Immediately after magnesium sulfate infusion, his ventricular tachycardia was converted into junctional bradycardia with prolonged corrected QT. After 3 days of close observation in the intensive care unit, the corrected QT prolongation and hyperbilirubinemia were normalized.

Efflorescence assessment using hyperspectral imaging for concrete structures

Byunghyun Kim,Soojin Cho 국제구조공학회 2018 Smart Structures and Systems, An International Jou Vol.22 No.2

Efflorescence is a phenomenon primarily caused by a carbonation process in concrete structures. Efflorescence can cause concrete degradation in the long term; therefore, it must be accurately assessed by proper inspection. Currently, the assessment is performed on the basis of visual inspection or image-based inspection, which may result in the subjective assessment by the inspectors. In this paper, a novel approach is proposed for the objective and quantitative assessment of concrete efflorescence using hyperspectral imaging (HSI). HSI acquires the full electromagnetic spectrum of light reflected from a material, which enables the identification of materials in the image on the basis of spectrum. Spectral angle mapper (SAM) that calculates the similarity of a test spectrum in the hyperspectral image to a reference spectrum is used to assess efflorescence, and the reference spectral profiles of efflorescence are obtained from theUSGS spectral library. Field tests were carried out in a real building and a bridge. For each experiment, efflorescence assessed by the proposed approach was compared with that assessed by image-based approach mimicking conventional visual inspection. Performance measures such as accuracy, precision, and recall were calculated to check the performance of the proposed approach. Performance-related issues are discussed for further enhancement of the proposed approach.

Tissue reactions to Implanted Intracanal Medicaments in Rats

Kim, Miri,Kim, Byunghyun,Kim, Wonkyung 大韓齒科保存學會 2004 Restorative Dentistry & Endodontics Vol.29 No.1

최근 근관나 치료 영역에서는 적절한 기계적 근관 성형과 근관 세척으로만 효과적으로 근관 내 미생물의 숫자를 감소시킬 수 있어 다른 약제의 사용은 권장되고 있지 않다. 그럼에도 불구하고 수 종의 근관내 약제는 감염된 근관에서 미생물의 숫자를 줄이고 근관 내용물의 불활성화와 삼출액을 줄이기 위해 사용되고 있다. 그 중 포름 알데하이드를 함유하고 있는 Depulpin®과 근관 치료학에서 오랫동안 널리 사용되어온 수산화 칼슘을 포함하고 있는 Tempcanal®과 Vitapex®등에 대한 세포 독성은 충분한 연구가 이루어지지 모한 상태이다. 이에 본 연구에서는 이들 약제가 백서에서의 세포 독성에 미치는 영향에 관하여 고찰하고자 하였다. Sprague-Dawley계 백서 숫놈 20마리를 사용하여, 각 각의 쥐는 케타민과 럼푼을 근육내 주사하여 마취하였고, 복부의 피하 부위를 절개한 뒤 3개씩의 Teflon-coating된 매식체를 삽입하였다. 매식체 안에는 각각 Tempcanal®, Vitapex®, Depulpin®을 넣고, 백서 20마리를 6개군으로 나누어 매식체 삽입 후 1주 뒤, 4주 뒤에 희생시켜 매식체 주위 조직을 잘라내고 10% 포르말린에 고정 후 파라핀에 포매 하였다. 미세 절단기로 4㎛로 연속 절단 후, hematoxy-line-eosin 염색 후 3명의 관찰자가 광학 현미경으로 관찰하여 염증의 정도를 4단계로 평가한 뒤 Kruskall-Wallis test(P<0.05)로 통계처리하였다. 그 결과 제 1군(Tempcanal® 7일후 군), 제 2군(Vitapex® 7일후 군), 제 3군 (Depulpin® 7일후 군)모두 중등도의 염증도를 보였으나, 세 군간에 통계학적 유의성은 없었다. 그러나 제 4군(Tempcanal®30일후 군), 제 5군(Vitapex® 30일후 군)의 경우에서는 약한 염증도를 보여주었으나, 제 6군 (Depulpin® 30일후 군)은 가장 심한 염증 반응과 함께 조직 괴사의 양상을 보여주었으며, 4,5군과 6군간에 통계학적 유의성을 보였다. 본 실험 결과, Depulpin®은 Tempcanal®와 Vitapex® 에 비해 높은 세포 독성을 보여주고 있으나, 좀 더 많은 임상적 검증이 필요할 것으로 사료된다.