복합적층구조 해석을 위한 개선된 쉘요소

최창근,유승운,Choi, Chang Koon,Yoo, Seung Woon 대한토목학회 1991 대한토목학회논문집 Vol.11 No.3

The paper is concerned with the analysis of laminated composite shell structures using an improved degenerated shell element. In the formulation of the element stiffness, the combined use of three different techniques was made. They are; 1) an enhanced interpolation of transverse shear strains in the natural coordinate system to overcome the shear locking problem; 2) the reduced integration technique in in-plane strains to avoid the membrane locking behavior; and 3) selective addition of the nonconforming displacement modes to improve the element performances. This element is free of serious shear/membrane locking problems and undesirable compatible/commutable spurious kinematic deformation modes. An incremental total Lagrangian formulation is presented which allows the calculation of arbitrarily large displacements. The resulting non-linear equilibrium equations are solved by the Newton-Raphson method. The versatility and accuracy of this improved degenerated shell element are demonstrated by solving several numerical examples. 본 논문에서는 개선된 감절점(degenerated) 쉘 유한요소의 복합적충을 갖는 쉘구조에의 적용성을 고찰하였다. 본 논문의 개선된 쉘 요소는 shear locking 해결에 우수한 결과를 보인 가정된 전단변형도를 대치사용하고, membrane locking 현상을 제거하기 위해 평면내 변형도의 구성시 감차적분을 행하며, 쉘요소 자체의 거동을 보완하기 위해 비적합변위형을 선택적으로 추가하였다. 본 요소는 shear/membrane locking이 발생하지 않으며, 전달가능한 거짓 영에너지모드도 나타나지 않는다. 유한변형을 고려한 기하학적 비선형 방정식을 total Lagrangian 수식화를 시용하여 정형화 하였고, 비선형 수치해석은 Newton-Raphson 반복법으로 반복 계산한다. 여러 예제해석을 통하여 본 개선된 쉘 유한요소의 유용성과 정확도를 고찰하였다.

사변형 요소를 이용한 추계론적 유한요소해석

최창근,노혁천,Choi, Chang Koon,Noh, Hyuk Chun 대한토목학회 1993 대한토목학회논문집 Vol.13 No.5

본 논문은 추계론적 유한요소해석의 한 방법인 가중적분법의 확장에 대해서 논하였다. 가중적분법의 사용은 Deodatis에 의해서 삼각형요소로 확장되었다. 이에 의해서 2차원 문제에 대한 응답변화도를 수치적인 해석에 의해서 얻을 수 있게 되었다. 본 논문에서는 가중적분법을 일반 평면요소를 사용할 수 있도록 확장한다. 제안된 방법에 의해서 확정론적 유한요소해석에서 사용된 요소망은 추계론적 유한요소해석에서도 그대로 사용할 수 있도록 되었다. 나아가서, CST요소는 상수만을 그 요소로 가지는 변위-변형률 행렬을 가지는 특수한 경우이므로 제안된 방법을 사용할 경우 CST요소와 일반 평면 사변형 요소를 혼용하여 사용할 수 있을 것이다. The extension of the weighted integral method in the area of stochastic finite element analysis is presented. The use of weighted integral method in numerical analysis was extended to CST(constant strain triangle) element by Deodatis to calculate the response variability of 2D stochastic systems. In this paper, the extension of the weighted integral method for general plane-elements is represented. It has been shown that the same mesh used in the deterministic FE analysis can be used in the stochastic FE analysis. Furthermore, because the CST element is a special case which has constant strain-displacement matrix the mingling of CST elements with the other quadrilateral elements in the analysis may also be possible.

한국 연안 해조류 생물량의 연간 변동 양상: 경상남도 욕지도 지역

최창근,김정하,정익교,Choi, Chang-Geun,Kim, Jeong-Ha,Chung, Ik-Kyo 한국조류학회(藻類) 2008 ALGAE Vol.23 No.4

The seasonal variation of marine algal biomass and community were studied with nondestructive sampling and quadrat method during May 2006 to April 2008 in the intertidal and subtidal zone at Yokjido. As result, total 120 species, 13 Chlorophyta, 34 Phaeophyta, 71 Rhodophyta and 2 Spermatophyta were identified in this study. The major species which contributed significantly to the total biomass were Ulva pertusa, Undaria pinnatifida, Ecklonia stolonifera, Sargassum horneri, S. serratifolium, Gelidium amansii and Prionitis cornea. The mean biomass was 235.5 g wet wt m$^{-2}$ in intertidal, 1,038.9 g wet wt m$^{-2}$ in 1 m, 1,013.1 g wet wt m$^{-2}$ in 5 m, and 19.7 g wet wt m$^{-2}$ in 10 m depths of mean sea level. Seasonal biomass change in intertidal zone, the peak season was in spring, while the lowest was in autumn. The vertical distribution of marine vegetation was characterized by Ulva pertusa - Gelidium divaricatum - Gloiopeltis furcata - Sargassum thunbergii - Hizikia fusiformis at intertidal zone, and Caulerpa okamurae - Gelidium amansii - Chondrus ocellatus - Ecklonia stolonifera - Sargassum horneri - Gracilaria textorii at subtidal zone. These result indicates that the marine algal species and biomass of 1 m and 5 m depths in subtidal zone are greater than intertidal zone, and Ecklonia stolonifera and Sargassum spp. are the dominant species of Yokjido.

부산시 기장군 연안의 해조상 및 군집 특성

최창근,최인영,홍용기,Choi, Chang-Geun,Chowdhury, M.T.H.,Choi, In-Young,Hong, Yong-Ki 한국해양학회 2010 바다 Vol.15 No.3

기장 연안 해조류의 해조상 및 군집 구조를 분석하기 위해서 2006년 8월과 2009년 8월에 연구를 수행하였다. 해조류는 녹조류 6종, 갈조류 10종, 홍조류 38종 등 총 54종의 서식이 확인되었다. 이 중 35종의 해조류가 각각의 조사 시기에 공통적으로 출현하였다. 평균 현존량은 2006년에 $616.0\;g\;m^{-2}$에서 $1,462.4\;g\;m^{-2}$였고, 2009년에는 $354.8\;g\;m^{-2}$에서 $965.6\;g\;m^{-2}$이었다. 현존량이 가장 높은 지역은 문동이었고, 가장 낮은 곳은 서암(2006년)과 동백(2009년)이었다. 출현 해조류를 6개의 기능형으로 구분하면, 성긴분지형이 58.7%와 58.1%, 다육질형이 10.9%와 11.6%, 사상형이 13.0%와 9.3%, 각상형이 6.5%와 9.3%, 엽상형이 6.5%와 7.0%, 유절산호말형이 4.3%와 4.7%로 나타났다. 생태지수인 R/P, C/P, (R+C)/P 값은 2006년에 4.00, 0.75, 4.75와 2009년에 5.17, 1.00, 6.17로 나타났다. 2006년과 2009년의 자료를 분석했을 때, 기장 연안의 해조류 출현 종 수와 현존량은 유사하였다. 이러한 자료로 볼 때, 기장 연안에서 시행된 소규모 공사 전, 후인 2006년과 2009년의 해조류 종 다양성에는 변화가 나타나지 않은 것으로 분석되었다. Marine algal flora and community structure were investigated at four sites in Kijang area on the southern east coast of Korea in August 2006 and August 2009, respectively. A total of 54 seaweeds including 6 green, 10 brown, 38 red were collected and identified. Of 54 seaweeds, 35 species were found throughout the survey period. Mean biomass in wet weight was from $616.0\;g\;m^{-2}$ to $1,462.4\;g\;m^{-2}$2 in 2006, and $354.8\;g\;m^{-2}$ to $965.6\;g\;m^{-2}$ in 2009. Maximum biomass was recorded at Mundong site, and minimum was recorded at Seoam (2006) and Dongbaek (2009) sites. The flora investigated (2006, 2009) could be classified into six functional groups such as coarsely branched form (58.7%, 58.1%), thick leathery form (10.9%, 11.6%), filamentous form (13.0%, 9.3%), crustose form (6.5%, 9.3%), sheet form (6.5%, 7.0%) and jointed calcareous form (4.3%, 4.7%) during survey period. The R/P, C/P and (R+C)/P values reflecting flora characteristics were 4.00, 0.75 and 4.75 at 2006, and 5.17, 1.00 and 6.17 at 2009, respectively. Therefore, the number of marine algae species and biomass in Kijang area were similar when they were comparing with the previous data. It suggest that any changes of seaweed diversity have not been observed in Kijang coastal area before and after the anthropogenic construction between 2006 and 2009.

부산 영도의 해조상과 곰피(Ecklonia stolonifera Okamura) 군락

최창근,Choi, Chang-Geun 한국조류학회(藻類) 2007 ALGAE Vol.22 No.4

Studies have been made of the species composition and community structure of benthic marine algae at intertidal zone and subtidal zone of Youngdo at Busan. In this area, a total of 69 marine algal species including 10 Chlorophyta, 17 Phaeophyta and 42 Rhodophyta was identified. Dominant species in coverage were Enteromorpha linza, Ulva pertusa, Gelidium divaricatum, Hildenbrandtia rubra and Chondrus ocellatus throughout the year. Enteromorpha linza, Ulva pertusa, Porphyra yezoensis, Gelidium divaricatum, Corallina pilulifera, Grateloupia elliptica and Chondrus ocellatus vertically distributed in intertidal zone, while Ecklonia stolonifera, Gelidium amansii, Prionitis cornea, Gracilaria textorii, Acrosorium polyneurum and Phycodrys fimbriata in subtidal zone. The vertical distribution of subtidal zone were characterized by Ecklonia stolonifera at 1 to 5 m depths. During a year, biomass and length of Ecklonia stolonifera gradually decreased from March to January, but increased from February. Zoosporangial sori were observed from September to December. In conclusion, number of species in this area was remarkably reduced as compared to the previous data at Busan and it’s vicinity.

교량의 예비설계를 위한 전문가 시스템의 개발

최창근,최인혁,Choi, Chang Koon,Choi, In Hyuk 대한토목학회 1992 대한토목학회논문집 Vol.12 No.1

본 논문에서는 교량의 예비설계 단계중에서 상부구조 형식의 선정에 대한 전문가 시스템을 구축하는 것을 나타낸다. 본 시스템을 구축하기 위한 도구로는 전진추론방식 및 생산시스템으로 지식표현되는 전문가 시스템 개발용 도구인 K-CLIPS가 이용되었으며, 이 도구 위에서 구성된 지식 모듈, 데이터 베이스 및 지식 베이스로 시스템이 구성되었다. 지식 모듈은 주로 교량의 형식 선정과정을 관리하는 설계순서에 관한 지식이고, 지식 베이스 내에 있는 각 부 시스템이 심볼처리에 의해 수행되는 과정에서 데이타 베이스는 이를 지원해 주는 역할을 한다. This paper represents the expert system for selecting the superstructure types of bridges in the part of a preliminary bridge design. The system is implemented with the expert system tool called K-CLIPS which uses the production system for knowledge representation and provides the mechanism of forward chaining. This expert system is composed of a knowledge base, data base and a knowledge module built by the tool which consists of the knowledges on design procedures. During symbolic processing the data base supports the sub system in knowledge base.

근접한 세 원형구조물의 공기역학적 거동에 대한 연구

최창근,김윤석,Choi, Chang Koon,Kim, Yun Seok 대한토목학회 1992 대한토목학회논문집 Vol.12 No.4

본 연구에서는 횡열(橫列)배치된 두 원형구조물의 하류측(下流側)에 위치하는 원형구조물의 공기역학적 거동에 대하여 고찰하였다. 세 구조물의 배치에 따라, 하류측(下流側) 구조물에는 4가지 종류의 진동이 발생하는 복잡한 거동이 나타난다. 상류측(上流側) 구조물의 존재에 의하여 vortex induced oscillation은 큰 진폭증가를 보이며, wake buffeting으로 판단되는 한정(限定)지동이 발생한다. 또한 $1.4{\leq}S/D{\leq}3.6$ 간격에서는 풍속증가에 관계없이 일정한 진폭을 유지하는 진동이 발생하며, 이 진동의 진폭이 어느 한계점을 넘게 되면, 풍속증가에 따라 진폭이 증가하는 발산형(發散型) 진동으로 발달하게 된다. It this study, the aerodynamic responses of circular cylinder behind a pair of circular cylinders arranged side by side in a uniform flow were investigated. We confirmed that four types of oscillation are occured on downstream cylinder in such an arrangement. Influenced by upstream cylinders, the amplitude of vortex induced oscillation is increased and wake buffeting occured when S/D(S: distance between the centers of upstream cylinders, D: diameter of cylinder) is smaller than 1.2. When S/D is larger than 1.2, gap flow introduces to oscillation which maintains a uniform amplitude in spite of increasing wind speed. This oscillation is reduced to "wake galloping" if its amplitude exceeds the limit point.

Algal Succession on Different Substrata Covering the Artificial Iron Reef atIkata in Shikoku, Japan

최창근,손철현,Choi, Chang-Geun,Ohno, Masao,Sohn, Chul-Hyun The Korean Society of Phycology 2006 ALGAE Vol.21 No.3

Succession of artificial seaweed communities in an artificial iron reef at Ikata, southern Japan was studied based on monthly or bimonthly observations from February 1999 to August 2000. Communities were associated with different substrata (40 cm x 60 cm: steel, concrete, wood and stone) as the cover on artificial iron reefs (4.5 m x 4.1 m x 2.5 m, 45.38 m3 and 3.2 ton), which were placed on a sandy substratum at 8 m depth. Within one month diatoms dominated on all substrata with cover of approximately 100%. Enteromorpha intestinalis and Colpomenia sinuosa dominated on the reef within three months after the placement in the spring. Seaweed communities on the reef decreased during the summer. In the winter, the seaweeds on the reef recovered. Sargassum spp., Ecklonia kurome and Padina arborescens dominated on each substratum after one year. Seaweed communities on the artificial reef were similar to those on the rocky substratum around the artificial reef and also similar on different substrata covering the iron artificial reef. These results indicate that seaweed succession was impacted by season and the recruitment of spores and propagules from mature algae around the artificial reefs.

동해안 울진 연안 조하대 저서 해조류의 군집구조

최창근,곽석남,손철현,Choi, Chang-Geun,Kwak, Seok-Nam,Sohn, Chul-Hyun 한국조류학회(藻類) 2006 ALGAE Vol.21 No.4

Studies have been made of the species composition and variation of benthic marine algae at subtidal zone of Uljin on the east coast of Korea. Destructive method was employed to measure biomass over four seasons (2000-2002). Of 87 marine algae species identified, 11 were Chlorophyta, 29 were Phaeophyta and 47 were Rhodophyta. Dominant species in biomass were Ulva pertusa, Undaria pinnatifida and Sargassum piluliferum in summer, Laminaria religiosa, Sargassum fulvellum and Gigartina tenella in autumn, Codium fragile, Undaria pinnatifida, Sargassum horneri, S. piluliferum and S. ringgoldianum in winter, and Undaria pinnatifida, Dictyopteris divaricata, Sargassum confusum and S. horneri in spring. In general, green algae (Ulva pertusa, Codium fragile) and brown algae (Undaria pinnatifida, Sargassum fulvellum, S. horneri, S. piluliferum) appeared predominantly in the 3, 6 m depths and red algae (Gelidium amansii, Plocamium telfairiae) in the 9, 12 m depths. The barren ground of the rocky shore might provide the decrease of benthic marine algae biomass and species.

평판구조물의 해석을 위한 개선된 유한요소모델의 개발

최창근,김선훈,Choi, Chang Koon,Kim, Sun Hoon 대한토목학회 1987 대한토목학회논문집 Vol.7 No.4

본 연구에서는 Mindlin 평판요소의 개선을 위하여 사용되고 있는 감차적분방법과 비적합 변위형의 추가방법에 대한 재검토가 이루어졌으며, 이 두방법을 혼합 사용하여 개발한 새로운 평판유한요소가 제시되었다. 요소는 2차 Mindlin 평판이론에 의하여 수식화되었다. 개발된 평판요소를 이용하여 구한 수치해석 결과는 이론치에 매우 빨리 수렴하여, 요소의 찌그러짐(distortion)에 관계없이 신뢰성 있는 결과를 보여주었다. 또한 개발된 요소들은 강체운동(rigid body motion)에 필요한 최소의 zero eigenvalue를 가지며, 두꺼운 평판은 물론 아주 얇은 평판의 해석에서도 항상 좋은 결과를 보여주었다. The applications of reduced integration technique, addition of nonconforming modes, and their coupling to the Mindlin plate elements to improve their basic behavior are reviewed and the establishment of a series of new plate elements by combined use of these schemes are presented in this paper. The element formulation is based upon quadratic Mindlin plate concept. The results obtained by new elements converged to the exact solutions very rapidly as the mesh is refined and showed reliable solutions even for severely distorted meshes. The new elements have the requisite numbers of zero eigenvalues associated with rigid body modes to avoid the spurious zero energy modes. These elements are shown to be applicable to the wide range of plate problems, giving a high accuracy for both thick and thin plates.