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A numerical study on the flow characteristics in the mixing region of the catalytic combustor
Dongjin Hong,Chongmin Kim,Man Young Kim,Sang Min Lee,Kook Young Ahn 대한기계학회 2007 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.21 No.11
Catalytic combustion is usually accomplished by a chemical reaction at the catalyst surface. Therefore, it is important that the fuel and air stream be well mixed and supplied uniformly. In this study, a perforated plate is used to enhance the mixing and flow uniformity for stable catalytic combustion. Also, a numerical simulation is performed to investigate the variation of flow characteristics according to various parameters. The results show that the uniformity of mixing and flow can be effectively improved for most of the cases by using a well-designed perforated plate.
홍동진(Dongjin Hong),김종민(Chongmin Kim),김만영(Man Young Kim) 한국항공우주학회 2007 韓國航空宇宙學會誌 Vol.35 No.9
촉매 연소는 통상의 연소 방식과는 달리 촉매 표면에서 연료와 산화제의 화학 반응에 의한 연소 방식이다. 따라서 연소 영역 이전에 연료와 공기가 잘 혼합되어야 하며, 균일한 공급이 이루어져야 한다. 만약 불균일한 유동 분포가 발생하게 되면, 국부적인 고온 지역이 발생하게 되고 이는 촉매와 지지체에 손상을 초래하게 된다. 본 연구에서는 촉매 연소기의 혼합 및 유동 균일도를 향상시키기 위해 다공판을 사용하였으며, 다양한 파라메터의 변화에 따른 유동 특성의 변화를 조사하기 위해 수치적인 방법을 사용하였다. 각각의 조건하에서 촉매부의 입구에서 유동의 균일도를 조사하고 평가하였으며, 그 결과 적절히 설계된 다공판을 사용하였을 경우 대부분의 해석 조건에 대해 효과적인 균일도 향상을 나타냄을 확인할 수 있었다. A catalytic combustion is accomplished by the chemical reaction between fuel and oxidizer at the catalyst surface, different from conventional combustion. Therefore, it is important that the fuel and air stream are well mixed and supplied uniformly prior to the combustion region. If the flow is maldistributed, a hot spot may occur that can lead to subsequent catalyst and substrate damage. Therefore, in order to enhance the mixing and flow uniformity, in this study, the perforated plate is used. A numerical simulation is performed to investigate the variation of flow characteristics by changing various parameters. Under each condition, the uniformity of the flow stream at the entrance of the catalyst section is evaluated and compared. The results show that the uniformity can be effectively improved for most of the case by using the well-designed perforated plates.
망 관리 정보를 포함한 X.500 DIB의 객체 지향 모델링
홍동진(Dongjin Hong),이재호(Jaeho Lee),임해철(Haechull Lim) 한국정보과학회 1994 한국정보과학회 학술발표논문집 Vol.21 No.2B
디렉토리 서비스(X.500)는 일반 통신망과 관련된 정보만을 객체-클래스의 정보 집합인 DIB(Directory Information Base)내에 저장하고 있다. 본 논문은 여기에 디렉토리가 망 관리 기능까지 수행할 수 있도록 하기 위해, 망 관리의 여러 표준안(X.700, CCITT의 M.3100, RFC)을 분석하여 디렉토리가 담당할 수 있는 망 관리 기능을 정의하고, 이러한 관리 기능을 위한 필수 정보를 추출하였다. 그리고, DIB의 논리적구조인 DIT(Directory Information Tree)를 확장하였으며, 확장된 DIB를 객체 지향 개념으로 모델링하였다. 특히 망 관리 기능은 메소드(method)형식으로 새롭게 정의하였다.
Stress analysis of high-temperature superconducting wire under electrical/magnetic/bending loads
Dongjin Seo,Yunjo Jung,Hong-Gun Kim,Hyung-Seop Shin,Young-Soon Kim 한국초전도저온학회 2023 한국초전도저온공학회논문지 Vol.25 No.4
The Second-generation high-temperature superconducting (HTS) Rare-Earth Barium Copper Oxide (REBCO) wire is a composite laminate having a multi-layer structure (8 or more layers). HTS wires will undergo multiple loads including the bending-tension loads during winding, high current density, and high magnetic fields. In particular, the wires are subjected to bending stress and magnetic field stress because HTS wires are wound around a circular bobbin when making a high-field magnetic. Each of the different laminated wires inevitably exhibits damage and fracture behavior of wire due to stress deformation, mismatches in thermal, physical, electrical, and magnetic properties. Therefore, when manufacturing high-field magnets and other applications, it is necessary to calculate the stress-strain experienced by high-temperature superconducting wire to present stable operating conditions in the product's use environment. In this study, the finite element model (FEM) was used to simulate the strain-stress characteristics of the HTS wire under high current density and magnetic field, and bending loads. In addition, the result of obtaining the neutral axis of the wire and the simulation result was compared with the theoretical calculation value and reviewed. As a result of the simulation using COMSOL Multiphysics, when a current of 100 A was applied to the wire, the current value showed the difference of 10-9. The stress received by the wire was 501.9 MPa, which showed a theoretically calculated value of 500 MPa and difference of 0.38% between simulation and theoretical method. In addition, the displacement resulted is 30.0012 μm, which is very similar to the theoretically calculated value of 30 μm. Later, the amount of bending stress by the circular mandrel was received for each layer and the difference with the theoretically obtained the neutral axis result was compared and reviewed. This result will be used as basic data for manufacturing high-field magnets because it can be expanded and analyzed even in the case of wire with magnetic flux pinning.
Reasoning Ability of Deep Learning Models on Tautological Expressions in Korean
( Hong Seung-hye ),( Shin Unsub ),( Lee Gyu-min ),( Hwang Dongjin ),( Song Sanghoun ) 서강대학교 언어정보연구소 2023 언어와 정보 사회 Vol.49 No.-
The purpose of this paper is to evaluate the abductive reasoning capability of deep learning-based language models, with a specific focus on their ability to infer the meaning of tautological expressions. To achieve this, we conducted two experiments that required language models to understand the meaning of tautological expressions in different contexts. The first experiment was a binary classification task in which the models were presented with preceding sentences as contexts along with a tautological expression, and evaluated the adequacy of the tautological sentence. We employed three BERT-based models and assessed their capability based on the results of human evaluation. The second experiment involved having ChatGPT generate a coherent sentence that followed the preceding sentence and tautological expression. We categorized certain types of errors from the generated sentences that were deemed inappropriate. This study is significant in revealing the limitations of contemporary deep learning-based language models in terms of abductive reasoning and suggests a new task for standardized model evaluation.