FPSO Riser 지지구조의 설계최적화에 대한 근사화 기법의 비교 연구

심천식,송창용,Shim, Chun-Sik,Song, Chang-Yong 한국전산구조공학회 2011 한국전산구조공학회논문집 Vol.24 No.5

본 논문에서는 해양작업 상태의 하중조건을 고려한 부유식 원유생산 저장 하역장치에 설치된 라이져 보강구조의 강도설계에 관련하여 다양한 근사화 기법 기반 설계최적화 및 그 성능을 비교하고자 한다. 설계최적화 문제는 하중조건별 구조강도의 제한조건 하에서 중량을 최소화하여 설계변수인 구조 부재치수가 결정되도록 정식화된다. 비교 연구를 위해 사용된 근사화 기법은 반응표면법 기반 순차적 근사최적화(RBSAO), 크리깅 기반 순차적 근사최적화(KBSAO), 그리고 개선된 이동최소자승법(MLSM) 기반 근사최적화 기법인 CF-MLSM와 Post-MLSM이다. RBSAO와 KBSAO의 적용을 위하여 상용프로세스 통합 설계최적화(PIDO) 코드를 사용하였다. 본 연구에 적용한 MLSM 기반 근사최적화 기법들은 제한조건의 가용성을 보장할 수 있도록 새롭게 개발되었다. 다양한 근사화 모델 기반 설계최적화 기법에 의한 결과는 설계 해의 개선 및 수렴속도 등의 수치적 성능을 기준으로 실제 비근사 설계최적화 결과와 비교 검토하였다. The paper deals with the comparative study of design optimization based on various approximation techniques in strength design of riser support structure installed on floating production storage and offloading unit(FPSO) using offshore operation loading conditions. The design optimization problem is formulated such that structural member sizing variables are determined by minimizing the weight of riser support structure subject to the constraints of structural strength in terms of loading conditions. The approximation techniques used in the comparative study are response surface method based sequential approximate optimization(RBSAO), Kriging based sequential approximate optimization(KBSAO), and the enhanced moving least squares method(MLSM) based approximate optimization such as CF(constraint feasible)-MLSM and Post-MLSM. Commercial process integration and design optimization(PIDO) tools are employed for the applications of RBSAO and KBSAO. The enhanced MLSM based approximate optimization techniques are newly developed to ensure the constraint feasibility. In the context of numerical performances such as design solution and computational cost, the solution results from approximate techniques based design optimization are compared to actual non-approximate design optimization.

연관 피드백과 퍼지 함의 연산자를 이용한 스니핏 추출 방법

박선,심천식,이성로,Park, Sun,Shim, Chun-Sik,Lee, Seong-Ro 한국정보통신학회 2012 한국정보통신학회논문지 Vol.16 No.3

정보 검색 시 검색엔진은 사용자에게 웹페이지 순위와 웹페이지의 요약정보를 제공한다. 이중 웹 페이지를 대표 할 수 있는 요약된 정보를 스니핏(snippet)이라한다. 스니핏은 사용자의 웹페이지 방문에 큰 영향을 준다. 정확한 방문 페이지의 정보를 모르고 단지 스니핏 만을 이용할 때에 가끔 사용자의 의도와는 다른 잘못된 웹 페이지를 방문할 수 있다. 이것은 검색엔진에서 지원하는 스니핏에 사용자의 의도를 정확하게 반영하는 것이 어렵기 때문이다. 본 논문은 이러한 문제를 해결하기 위해 연관 피드백과 퍼지 함의 연산자를 이용한 새로운 스니핏 추출 방법을 제안한다. 제안방법은 연관 피드백을 이용하여 사용자의 질의를 확장하고, 확장된 질의와 웹 페이지 사이에 퍼지 함의 연산자를 이용하여 질의와 확장된 질의의 포함관계가 반영된 스니핏을 추출함으로써 사용자의 의도를 스니핏에 더 잘 반영할 수 있다. 실험결과에서 제안방법이 다른 방법보다 스니핏 추출에 더 좋은 성능을 보인다. In information retrieval, search engine provide the rank of web page and the summary of the web page information to user. Snippet is a summaries information of representing web pages. Visiting the web page by the user is affected by the snippet. User sometime visits the wrong page with respect to user intention when uses snippet. The snippet extraction method is difficult to accurate comprehending user intention. In order to solve above problem, this paper proposes a new snippet extraction method using fuzzy implication operator and relevance feedback. The proposed method uses relevance feedback to expand the use's query. The method uses the fuzzy implication operator between the expanded query and the web pages to extract snippet to be well reflected semantic user's intention. The experimental results demonstrate that the proposed method can achieve better snippet extraction performance than the other methods.

문장군집의 응집도와 의미특징을 이용한 포괄적 문서요약

박선,이연우,심천식,이성로,Park, Sun,Lee, Yeonwoo,Shim, Chun Sik,Lee, Seong Ro 한국정보통신학회 2012 한국정보통신학회논문지 Vol.16 No.12

지식 기반의 포괄적 문서요약은 문장집합의 구성이 요약 결과에 영향을 받는다. 이러한 문제를 해결하기 위해서 본 논문은 의미특징에 의한 군집과 문장군집의 응집도를 이용하여 포괄적 문서요약을 하는 새로운 방법을 제안한다. 제안 방법은 비음수행렬분해에서 유도되는 의미특징을 이용하여 문장을 군집하고, 문서의 내부구조를 잘 표현하는 문장군집들로 문서의 주제 그룹을 분류할 수 있다. 또한 문장군집의 응집도와 재군집에 의한 군집의 정재를 이용하여 중요한 문장을 추출함으로써 요약의 질을 향상시킬 수 있다. 실험결과 제안방법은 다른 포괄적 문서요약 방법에 비하여 좋은 성능을 보인다. The results of inherent knowledge based generic summarization are influenced by the composition of sentence in document set. In order to resolve the problem, this papser propses a new generic document summarization which uses clustering of semantic feature of document and coherence of document cluster. The proposed method clusters sentences using semantic feature deriving from NMF(non-negative matrix factorization), which it can classify document topic group because inherent structure of document are well represented by the sentence cluster. In addition, the method can improve the quality of summarization because the importance sentences are extracted by using coherence of sentence cluster and the cluster refinement by re-cluster. The experimental results demonstrate appling the proposed method to generic summarization achieves better performance than generic document summarization methods.

조선 해양 구조물용 강재의 파단 변형률

정준모(Joonmo Choung),심천식(Chun-Sik Shim) 대한조선학회 2011 대한조선학회 학술대회자료집 Vol.2011 No.11

This is the third of several companion papers dealing with derivation of material constants for ductile failure criterion under hydrostatic stress. It is observed that ultimate engineering stresses and elongations at fracture from tensile tests for round specimens with various notch radii tend to increase and decrease, respectively, due to stress triaxiality. The engineering stress curves from tests are compared with numerical simulation results, and it is proved that curves from two approaches are very closely coincide each other. Failure strains are obtained from equivalent plastic strain histories from numerical simulations at the time when the experimental engineering stress falls down suddenly. After introducing a new concept of average stress triaxiality and accumulated average strain energy, material constants of Johnson-Cook failure criterion for critical energies of 100%, 50%, and 15% are presented. Experimental results conducted for EH-36 steel are relatively good agreement with 100% critical energy whereas literature states that aluminum fits with 15% critical energy. Therefore it is expected that a unified failure criterion, available for most kinds of ductile materials, of critical energy according to the used materials can be provided.

조선 해양 구조물용 강재의 소성 및 파단 특성 Ⅰ

정준모(Joonmo Choung),심천식(Chun-Sik Shim),김경수(Kyung Su Kim) 한국해양공학회 2011 韓國海洋工學會誌 Vol.25 No.2

In this paper, the global study trends for material behaviors are investigated regarding the static and dynamic hardenings and final fractures of marine structural steels. In particular, after reviewing all of the papers published at the 4th and 5th ICCGS (International Conference on Collision and Grounding of Ship), the used hardening and fracture properties are summarized, explicitly presenting the material properties. Although some studies have attempted to employ new plasticity and fracture models, it is obvious that most still employed an ideal hardening rule such as perfect plastic or linear hardening and a simple shear fracture criterion with an assumed value of failure strain. HSE (2001) presented pioneering study results regarding the temperature dependency of material strain hardening at various levels of temperature, but did not show strain rate hardening at intermediate or high strain rate ranges. Nemat-Nasser and Guo (2003) carried out fully coupled tests for DH-36 steel: strain hardening, strain rate hardening, and temperature hardening and softening at multiple steps of strain rates and temperatures. The main goal of this paper is to provide the theoretical background for strain and strain rate hardening. In addition, it presents the procedure and methodology needed to derive the material constants for the static hardening constitutive equations of Ludwik, Hollomon, Swift, and Ramberg-Osgood and for the dynamic hardening constitutive equations of power from Cowper-Symonds and Johnson-Cook.

조선 해양 구조물용 강재 변형률 경화 및 변형률 속도 경화의 이론적 배경

정준모(Joonmo Choung),심천식(Chun-Sik Shim),김경수(Kyung Su Kim) 대한조선학회 2011 대한조선학회 학술대회자료집 Vol.2011 No.6

In this paper, global study trends of material behaviors are investigated regarding static and dynamic hardenings and final fractures of marine structural steels. Especially, after reviewing all papers published in the 4th and 5th ICCGS (International Conference on Collision and Grounding of Ship), the used hardening and fracture properties are summarized explicitly presenting material properties. Although some papers have tried to employ new plasticity and fracture models, it is obvious that most papers still employed ideal hardening rule such as perfect plastic or linear hardening and simple shear fracture criterion with assumed value of failure strain. HSE (2001) presented pioneering study results regarding temperature dependency of material strain hardening at the various level of temperatures, but did not show strain rate hardening at intermediate or hight strain rate ranges. Nemat-Nasser and Guo (2003) carried out fully coupled tests for DH-36 steel: strain hardening, strain rate hardening, and temperature hardening and softening at multiple steps of strain rates and temperatures. Main pillars of this paper are to provide theoretical backgrounds of strain and strain rate hardening. In addition, the procedure and methodology to derive material constants for static hardening constitutive equations of Ludwik, Hollomon, Swift, and Ramberg-Osgood and for dynamic hardening constitutive equations of power, Cowper-Symonds and Johnson-Cook.

조선 해양 구조물용 강재 파단 변형률에 관한 실험적 연구

정준모(Joonmo Choung),심천식(Chun-Sik Shim),김경수(Kyung Su Kim) 대한조선학회 2011 대한조선학회 학술대회자료집 Vol.2011 No.6

This is the third of several companion papers dealing with derivation of material constants for ductile failure criterion under hydrostatic stress. It is observed that ultimate engineering stresses and elongations at fracture from tensile tests for round specimens with various notch radii tend to increase and decrease, respectively, due to stress triaxiality. The engineering stress curves from tests are compared with numerical simulation results, and it is proved that curves from two approaches are very closely coincide each other. Failure strains are obtained from equivalent plastic strain histories from numerical simulations at the time when the experimental engineering stress falls down suddenly. After introducing a new concept of average stress triaxiality and accumulated average strain energy, material constants of Johnson-Cook failure criterion for critical energies of 100%, 50%, and 15% are presented. Experimental results conducted for EH-36 steel are relatively good agreement with 100% critical energy whereas literature states that aluminum fits with 15% critical energy. Therefore it is expected that a unified failure criterion, available for most kinds of ductile materials, of critical energy according to the used materials can be provided.

조선 해양 구조물용 강재 파단의 이론적 배경

정준모(Joonmo Choung),심천식(Chun-Sik Shim),김경수(Kyung Su Kim) 대한조선학회 2011 대한조선학회 학술대회자료집 Vol.2011 No.6

Main pillars of this paper are to provide theoretical backgrounds of fracture phenomena in marine structural steels. In this paper, various fracture criteria are theoretically investigated: shear failure criteria with constant failure strain and stress triaxiality-dependent failure strain (piecewise failure and Johnson-Cook criteria), forming limit curve failure criterion, micromechanical porosity failure criterion, and continuum damage mechanics failure criterion. It is obvious that stress triaxiality is a very important index to determine failure phenomenon for ductile materials. Assuming an piecewise failure strain curve as a function of stress triaxiality, the numerical results are well coincided with test results for smooth and notched specimens where low and high stress triaxialities are observed. Therefore it is proved that a failure criterion with reliable material constants presents plastic deformation process as well as fracture initiation and evolution.

빙해선박용 강재의 저온특성에 관한 연구

민덕기(Dug-Ki Min),심천식(Chun-Sik Shim),신동완(Dong-Wan Shin),조상래(Sang-Rai Cho) 대한조선학회 2011 大韓造船學會 論文集 Vol.48 No.2

멤브레인 LNG 선박용 강화 폴리우레탄폼의 극저온 거동 연구

장철웅(Cheol-Woong Jang),심천식(Chun-Sik Shim),송하철(Ha-Cheol Song),송창용(Chang Yong Song) 한국해양공학회 2013 韓國海洋工學會誌 Vol.27 No.1

In the context of the structural performance of an LNG hold, the mechanical characteristics of the insulation material are considered to be a critical design factor under cryogenic temperatures. This paper presents the thermal elasto-plastic behavior of the reinforced polyurethane foam(RPUF) adapted for the insulation material of a membrane type LNG carried via both experiments and numerical simulations realizing the cryogenic condition. The experiments are carried out to investigate the thermal transfer and thermal elasto-plastic deformation characteristics of an actual RPUE specimen. The heat transfer simulations based on the finite element method(FEM) include a forced convection analysis. The results of heat transfer analyses are compared with the experimental results. Reasonable cryogenic conditions for RPUF are reviewed based on both the analysis and experimental results.