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노광우(Kwangwoo No),황세윤(Seyun Hwang),이권영(Kwonyeong Lee) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
Orifice is a device to generate pressure drop when the fluid passes through the narrow channel. In a kind of steam generator, helical coils are used as a heat transfer tubes. In this system, there will be a pressure deviation among helical coils. It will be difficult to generate high quality steam with this kind of unstable system with high deviation of pressure differences. To minimize the deviation, a multi-stage orifice with high pressure drop is suggested, and the characteristics of multi-stage orifice are investigated in this study. We performed not only single-phase flow pressure drop experiments with water, but also two-phase flow experiments with nitrogen/water for the multi-stage orifice. Also, the experimental data are compared with previous empirical correlations. Also, we study flow patterns about bubbly and slug in horizontal tube through visualizing the orifice.
CC 평가 · 인증 기술 ISO/IEC 국제 표준화 동향
이광우(Kwangwoo Lee),이수연(Lee Su Yeon),황현동(Hyundong Hwang),성정호(Jungho Sung),최희봉(Heebong Choi) 한국정보보호학회 2021 情報保護學會誌 Vol.31 No.4
공통평가기준(CC, Common Criteria)의 국제 표준인 ISO/IEC 15408, ISO/IEC 18045는 정보보호제품에 구현되어 있는 보안 기능의 보증과 안전성을 시험하기 위한 평가 기준을 제시하는 국제 표준으로 정보보호제품에 대한 국제적인 신뢰성을 보장할 수 있도록 기준을 제시하고 있다. 특히 ISO/IEC 15408, ISO/IEC 18045는 ISO/IEC 27000, ISO/IEC 19790과 함께 ISO/IEC JTC 1/SC 27을 대표하는 국제 표준이다. 본 논문에서는 ISO/IEC JTC 1/SC 27/WG 3 작업반에서 개정을 진행하고 올해 말에 출판 예정인 ISO/IEC 15408 및 ISO/IEC 18405의 주요 변경 내용 및 신규 개념에 대해 설명하고, 최근 WG 3 작업반에서 추진하고 있는 국제 표준화 활동 현황 및 주요 현황을 소개하고자 한다.
돔 분리형 연소관의 접착 길이에 따른 체결부의 구조해석
전광우(KwangWoo Jeon),신광복(KwangBok Shin),황태경(TeaKyung Hwang) 한국추진공학회 2011 한국추진공학회 학술대회논문집 Vol.2011 No.11
돔 분리형 복합재 연소관의 접합 체결부 최적의 설계 길이를 결정하기 위해 접합부 길이변화에 따른 구조해석을 수행하였다. 이때, 접착 체결부의 길이는 50mm에서 300mm의 범위를 갖는다. 무응력 상태의 초기 접합부 길이대비 응력구배가 발생하는 구간의 길이를 “응력구배 길이 비”로 정의하고 이를 목적함수로 선정하였다. 구조해석 결과 접착 체결부의 길이가 200mm 이상으로 증가할 경우 응력구배 길이 비의 증가가 서서히 나타남을 확인하였다. 이는, 접착 체결부에 적용되는 2,500psi 내압에서 구조적 안전성을 확보하는 최적화된 접착 체결부의 길이가 200mm임을 의미한다. In order to determine optimal design length of adhesive joint of a composite pressure vessel with separated dome, stress analysis of joint part according to changes of adhesive length was done. Adhesive length has a range of 50mm to 300mm as design variables. The ratio of adhesive length with any stress gradient to initial non-stressed adhesive length was called "stress gradient length ratio" and selected as objective function. The stress gradient length ratio of joint part with adhesive length of more than 200mm was increased very slowly with increase of adhesive length. It means that adhesive length of about 200mm could be the optimal value to ensure the structural safety of joint part against internal pressure of 2,500 psi.
전광우(KwangWoo Jeon),신광복(KwangBok Shin),황태경(TeaKyung Hwang) 한국추진공학회 2012 한국추진공학회지 Vol.16 No.3
In order to determine optimal design length of adhesive joint of a composite rocket motor case, stress analysis of joint part according to changes of adhesive length was done. Adhesive length has a range of 50 ㎜ to 300 ㎜ as design variables. The ratio of adhesive length without any stress gradient to initial non-stressed adhesive length was determined as evaluation criteria for selection of adhesive length, which called “stress gradient length ratio”. The numerical result showed that stress gradient length ratio of joint part with adhesive length of more than 200 ㎜ was increased very slowly with increase of adhesive length. It means that adhesive length of about 200 ㎜ could be the optimal dimension to ensure the structural safety of joint part against internal pressure of 2,500 psi.
Corporate Governance and Payout Policy : Evidence from Korean Business Groups
Lee-Seok Hwang,Hakkon Kim,Kwangwoo Park,Raesoo Park 한국재무학회 2012 한국재무학회 학술대회 Vol.2012 No.09
Using a unique, comprehensive data set from a survey on corporate governance practices among Korean listed firms, we find that firms with sound governance practices are associated with both high firm value and high dividend payout ratios. Although high in firm value, firms in major business groups (or chaebol) have lower dividend payouts on average than independent firms do. This relationship is driven primarily by the corporate governance sub-components of poor shareholder protection and the relatively weak role of chaebol firms’ boards of directors. Our evidence suggests that the entrenched control by chaebol firm owners stemming from the control rights much above the cash flow rights puts less weight on protecting the minority shareholders and distributes less corporate wealth to shareholders.
Kim, Jaewook,Hong, Kwangwoo,Choi, Sunghwan,Hwang, Sang-Yeon,Youn Kim, Woo The Royal Society of Chemistry 2015 Physical chemistry chemical physics Vol.17 No.47
<P>We developed a program code of configuration interaction singles (CIS) based on a numerical grid method. We used Kohn-Sham (KS) as well as Hartree-Fock (HF) orbitals as a reference configuration and Lagrange-sinc functions as a basis set. Our calculations show that KS-CIS is more cost-effective and more accurate than HF-CIS. The former is due to the fact that the non-local HF exchange potential greatly reduces the sparsity of the Hamiltonian matrix in grid-based methods. The latter is because the energy gaps between KS occupied and virtual orbitals are already closer to vertical excitation energies and thus KS-CIS needs small corrections, whereas HF results in much larger energy gaps and more diffuse virtual orbitals. KS-CIS using the Lagrange-sinc basis set also shows a better or a similar accuracy to smaller orbital space compared to the standard HF-CIS using Gaussian basis sets. In particular, KS orbitals from an exact exchange potential by the Krieger-Li-Iafrate approximation lead to more accurate excitation energies than those from conventional (semi-) local exchange-correlation potentials.</P>
최적화 해석 기법을 이용한 복합재 압력용기의 스커트 치수 선정에 관한 연구
김준환(Junhwan Kim),전광우(Kwangwoo Jeon),신광복(Kwangbok Shin),황태경(TaeKyung Hwang) 한국추진공학회 2012 한국추진공학회 학술대회논문집 Vol.2012 No.5
본 연구의 목적은 최적화 해석 기법을 이용하여 복합재 압력용기의 스커트 치수를 도출하는 것이다. 복합재 압력용기의 스커트 최적화 해석은 부분문제 근사법(sub-problem approximation method)알고리즘을 사용하였으며, APDL(ANSYS Parametric Design Language)을 이용하여 해석의 모든 과정을 일괄처리(batch processing)하였다. 설계변수로는 압력용기 스커트 부위의 두께와 길이를 선정하였으며, 내압에 의해 발생하는 변위와 무게를 각각 목적함수로 하여 최적화 해석을 통해 최적의 스커트 치수를 도출하였다. 그 결과 복합재 압력용기의 스커트 무게를 최대 4.38% 절감할 수 있었다. The purpose of this study is to find the optimum skirt size for a composite pressure vessel using optimum analysis technique. The size optimization for skirt shape of a composite pressure vessel was conducted using sub-problem approximation method and batch processing codes programmed by APDL(ANSYS Parametric Design Language). The thickness and length of skirt part were selected as design variables for the optimum analysis. The objective function and constraints were chosen as weight and displacement of skirt part, respectively. The numerical results showed that the weight of skirt of a composite pressure vessel would be saved by maximum 4.38% through the size optimization analysis for the skirt shape.
( Yohan Nam ),( Seokmin Yoon ),( Jihye Baek ),( Jong-hwa Kim ),( Miri Park ),( Kwangwoo Hwang ),( Wonyong Kim ) 한국미생물 · 생명공학회 2022 Journal of microbiology and biotechnology Vol.32 No.3
The incidence of stress-related type 2 diabetes (stress-T2D), which is aggravated by physiological stress, is increasing annually. The effects of Lactobacillus, a key component of probiotics, have been widely studied in diabetes; however, studies on the effects of postbiotics are still limited. Here, we aimed to examine the mechanism through which heat-killed Lactiplantibacillus plantarum LRCC5314 (HK-LRCC5314) alleviates stress-T2D in a cold-induced stress-T2D C57BL/6 mouse model. HK-LRCC5314 markedly decreased body weight gain, adipose tissue (neck, subcutaneous, and epididymal) weight, and fasting glucose levels. In the adipose tissue, mRNA expression levels of stress-T2D associated factors (NPY, Y2R, GLUT4, adiponectin, and leptin) and pro-inflammatory factors (TNF-α, IL-6, and CCL-2) were also altered. Furthermore, HK-LRCC5314 increased the abundance of Barnesiella, Alistipes, and butyrate-producing bacteria, including Akkermansia, in feces and decreased the abundance of Ruminococcus, Dorea, and Clostridium. Thus, these findings suggest that HK-LRCC5314 exerts protective effects against stress-T2D via gut microbiome modulation, suggesting its potential as a supplement for managing stress-T2D.