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- 저자 : 이승재(Lee, Seung Jae) (검색결과 1,601 건)
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이승재,조인성,Lee, Seung-Jae,Cho, In-Sung 한국주조공학회 2018 한국주조공학회지 Vol.38 No.2
The lack of industrial manpower that Korean companies have been suffering in 21st century is largely responsible for the low-fertility phenomenon. This research suggests an alternative solution with a program for fostering foreign laborers with technical skills in casting industry. Industrial manpower growth is feasible through accepting migrants who have had official education on the fundamental industrial technologies provided by Korean government. These technically trained migrants who can keep economical self-perpetuating ability are can help to effectively address the problem of the declining working-age population and the decreasing potential growth rate in Korea.
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이승재,이근동,나상일,제성관,정다운,오원근,서영호,손욱호,Lee, S.J.,Lee, K.D.,Na, S.I.,Je, S.K.,Jung, D.U.,Oh, W.G.,Seo, Y.H.,Son, W.H. 한국전자통신연구원 2014 전자통신동향분석 Vol.29 No.1
모바일 비주얼 검색(MVS: Mobile Visual Search) 기술은 스마트폰 환경에서 질의 영상의 특징을 검출하고 그 주변 영역의 정보를 이용하여 추출한 서술자를 미리 구축된 영상정보 DB와 비교하여 검색하는 기술로 스마트폰의 보급과 네트워크 환경발달에 따라 응용서비스의 범위와 가능성이 확대되고 있다. 본 동향에서는 기존의 텍스트, 음성, QR코드 등의 검색을 넘어 인간이 보는 그대로를 검색하고자 하는 모바일 비주얼 검색의 기술 및 표준화 동향을 분석하고 향후 전망에 대해서 살펴보고자 한다.
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초기 불완전성을 고려한 공간 트러스의 분기좌굴과 라이즈-스팬 비에 따른 임계하중 특성
이승재,손수덕,Lee, Seung-Jae,Shon, Su-Deok 한국강구조학회 2012 韓國鋼構造學會 論文集 Vol.24 No.3
본 연구는 초기조건에 민감한 공간 트러스를 대상으로 불완전성으로 인한 분기거동 및 불안정 특성에 대해서 연구하였으며, 접선강성행렬의 행렬식과 고유치해석으로 임계점과 좌굴하중을 구하였다. 고유모드의 민감성에 의한 불안정 현상을 고찰하기 위해서 2-자유절점공간 트러스와 스타 돔 및 3링 돔 모델을 예제로 채택하였으며, 라이즈-스팬 비 및 하중 파라메타에 따른 좌굴하중의 영향을 분석하였다. 2-자유절점 모델의 초기 형상불완전성에 따른 민감성은 고유모드에 따라 임계 후 평형경로가 바뀌었으며, 좌굴하중은 불완전 량의 증가에 따라 감소하는 결과를 얻었다. 예제에서 나타난 두 가지 민감한 좌굴패턴은 자유절점의 변위 위치를 살펴봄으로서 설명할 수 있었고, 형상 불완전성에 따른 거동은 비대칭 고유모드가 가장 큰 영향을 주었다. 민감한 고유모드는 단순화한 모델의 비신장 메커니즘 기저와 유사하였다. 스타 돔 모델은 라이즈-스팬 비가 높을수록 전체좌굴보다는 국부좌굴이 우세하며, 하중 파라메타 값이 클수록 평형경로 상에 분기점이 발생하였다. 또한 스타돔과 3링 모델의 좌굴하중은 각각 극한점 하중레벨의 약 50-70% 및 80-90%로 나타났다. This study investigated the characteristics of bifurcation and the instability due to the initial imperfection of the space truss, which is sensitive to the initial conditions, and the calculated buckling load by the analysis of Eigen-values and the determinant of tangential stiffness. A two-free nodes model, a star dome, and a three-ring dome model were selected as case studies in order to examine the unstable phenomenon due to the sensitivity to Eigen mode, and the influence of the rise-span ratio and the load parameter on the buckling load were analyzed. The sensitivity to the imperfection of the two-free nodes model changed the critical path after reaching the limit point through the bifurcation mode, and the buckling load level was reduced by the increase in the amount of imperfection. The two sensitive buckling patterns for the model can be explained by investigating the displaced position of the free node, and the asymmetric Eigen mode was a major influence on the unstable behavior due to the initial imperfection. The sensitive mode was similar to the in-extensional mechanism basis of the simplified model. Since the rise-span ratio was higher, the effect of local buckling is more prominent than the global buckling in the star dome, and bifurcation on the equilibrium path occurring as the value of the load parameter was higher. Additionally, the buckling load levels of the star dome and the three-ring model were about 50-70% and 80-90% of the limit point, respectively.
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스텝 하중을 받는 공간 트러스 시스템의 멀티스텝 테일러 급수 해석과 동적 불안정
이승재,손수덕,Lee, Seung-Jae,Shon, Su-Deok 한국강구조학회 2012 韓國鋼構造學會 論文集 Vol.24 No.3
The goal of this paper is to apply the multi-step Taylor method to a space truss, a non-linear discrete dynamic system, and analyze the non-linear dynamic response and unstable behavior of the structures. The accurate solution based on an analytical approach is needed to deal with the inverse problem, or the dynamic instability of a space truss, because the governing equation has geometrical non-linearity. Therefore, the governing motion equations of the space truss were formulated by considering non-linearity, where an accurate analytical solution could be obtained using the Taylor method. To verify the accuracy of the applied method, an SDOF model was adopted, and the analysis using the Taylor method was compared with the result of the 4th order Runge-Kutta method. Moreover, the dynamic instability and buckling characteristics of the adopted model under step excitation was investigated. The result of the comparison between the two methods of analysis was well matched, and the investigation shows that the dynamic response and the attractors in the phase space can also delineate dynamic snapping under step excitation, and damping affects the displacement of the truss. The analysis shows that dynamic buckling occurs at approximately 77% and 83% of the static buckling in the undamped and damped systems, respectively. 본 연구의 목적은 비선형 불연속 시스템인 공간 트러스에 멀티스텝 테일러 해법을 적용하는 것과 비선형 동적 응답 및 불안정 특성을 분석하는 것이다. 해석적 접근에 기초한 보다 정밀한 해는 공간 구조물의 역 문제나 또는 불안정 문제를 다루는데 매우 필요하며, 이는 지배방정식의 비선형성에 기인한다. 따라서 기하학적 비선형을 고려하여 지배 운동 방정식을 유도하였으며, 테일러 해법을 이용하여 정밀한 해석적 해를 구하였다. 해석 방법의 정밀도 검증을 위해서 단일자유도 모델을 채택하였으며, 테일러 해법을 이용한 결과를 4차 룬게-쿠타 법과 비교하였다. 또한, 스텝 하중을 받는 모델의 동적 불안정과 좌굴 특성을 고찰하였다. 두 해석 방법의 비교 결과는 매우 잘 일치하였고, 동적 응답과 위상공간에서의 끌개는 스텝하중 아래에서의 동적 좌굴 현상과, 모델에 감쇠가 미치는 영향을 잘 설명할 수 있음을 보여주었다. 해석결과에서 비감쇠 시스템과 감쇠 시스템의 동적 좌굴 하중 레벨은 각각 정적 좌굴 하중 레벨의 약 77%와 83%의 범위로 나타났다.
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천장 브래킷형 모듈러 시스템의 접합부 내진 성능과 설계 프로세스
이승재,강창훈,박재성,곽의신,손수덕,Lee, Seungjae,Kang, Changhoon,Park, Jaeseong,Kwak, Euishin,Shon, Sudeok 한국공간구조학회 2020 한국공간구조학회지 Vol.20 No.3
This paper examines the seismic performance and structural design of the ceiling bracket-type modular connection. The bracket-type system reduces the cross-sectional area loss of members and combines units using fitting steel plate, and it has been developed to be fit for medium-story and higher-story buildings. In particular, this study conducted the cyclic loading test for the performance of the C-type and L-type brackets, and compared the results. The test results were also compared with the commercial FEA program. In addition, the structural design process for the bracket-type modular connection was presented. The two connections, proposed as a result of the test results, were all found to secure the seismic performance level of the special moment steel frame. In the case of initial stiffness, the L-type bracket connection was found to be great, but in the case of the maximum moment or fully plastic moment, it was different depending on the loading direction.
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일방향 철근 콘크리트 슬래브의 폭발 피해 분석을 위한 최적의 비파괴검사법에 관한 연구
이승재,오태근,박종일,김희식,Lee, Seoung-Jae,Oh, Tae-Keun,Park, Jong-Yil,Kim, Hie Sik 한국안전학회 2017 한국안전학회지 Vol.32 No.5
It is necessary to analyze on the compressive strength among material properties of concrete for confirming damages of architectures due to large explosion. A non destructive test is known as the representative methods estimating compressive strength and ultrasonic pulse velocity, rebound hardness test are widely used because of their simplicity, convenience. But combined method supplementing two types is applied at now as they are affected by the characteristics of test specimen. In this research to check damages on the members of structure before and after explosion, the characteristics of compressive strength are compared and analyzed through a real explosion test prior to full scale structures. The test results showed that the larger the TNT powder and the shorter the distance, the greater the decrease in strength before and after the explosion and that the largest displacement and moment for the explosive load and the greatest decrease in the strength at the central part. Due to the surface condition and the thickness variation of the concrete specimens, the standard deviation value is the smallest in the combining method of fusion of the ultrasonic method and rebound hardness method. Thus, the combining method can be one of appropriate methods to evaluate the strength in the reinforced concrete structures damaged by the explosion.
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이승재,김효진,주천기,Seung-Jae Lee,Hyo-Jin Kim,M,S,Choun-Ki Joo 대한안과학회 2005 대한안과학회지 Vol.46 No.11
Purpose: To evaluate the changes in ocular high-order aberration after wavefront-guided laser in situ keratomileusis (LASIK) and wavefront-guided laser-assisted subepithelial keratectomy (LASEK). Methods: Twenty-four eyes of 14 patients who underwent wavefront-guided LASIK, and ten eyes of six patients who underwent wavefront-guided LASEK were retrospectively reviewed. Uncorrected visual acuity, best corrected visual acuity, manifest refraction and high order aberration were evaluated before the operation and at 1 week, 1 month, 2 months and 6 months after the operation. Aberrations were measured using a WaveScan Wavefront System (VISX, Santa Clara, CA). We analyzed the total high-order aberration, coma aberration and spherical aberration before and after surgery. Results: There were no statistically significant differences in total high-order aberration or coma aberration between preoperative and postoperative 6 month measurements in either group. However the spherical aberration showed a statistically significant increase between the preoperative and postoperative 6 month measurements in the wavefront-guided LASEK group (p=0.037). The total high order aberration showed no correlation with the preoperative spherical equivalent (p=0.55), and the change in total high-order aberration did not correlate with the amount of surgically achieved correction in either group at all follow-up periods. Conclusions: Wavefront-guided LASIK and wavefront-guided LASEK showed no statistically significant changes in total high-order aberration at postoperative 6 months.
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