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콘크리트 재료의 동적 물성 변화를 모사하기 위한 유변학적(Rheological)모델 개발 및 평가
황영광,임윤묵,Hwang, Young Kwang,Lim, Yun Mook 대한토목학회 2015 대한토목학회논문집 Vol.35 No.4
본 연구에서는 속도 의존성을 나타내는 콘크리트의 인장거동을 모사하기 위하여 유변학적(rheological) 모델을 개발하였고 이를 평가하였다. 일반적으로 외부에서 가해지는 하중 속도가 증가할수록 콘크리트의 물성(강도, 탄성계수, 파괴에너지 등)은 그 크기가 증가한다. 콘크리트의 강도는 다른 물성에 비하여 큰 속도의존성을 나타내고, 압축 하중인 경우보다 인장 하중을 받는 경우 그 속도의존성이 크게 나타난다. 이러한 콘크리트의 속도 의존성을 모사하기 위하여, 기존 RBSN(Rigid-Body-Spring-Network) 모델의 거동을 나타내는 스프링 세트에 대쉬포트(Dashpot)와 같은 점성 요소와 Coulomb 마찰 요소를 조합하였다. 요소의 조합에 따라 세 가지 모델( 1)점탄성, 2)점소성, 3)점탄소성 손상(Damage 모델)을 고려하였고, 이에 대한 구성관계식을 유도하였다. 개발된 해석모델은 직접인장 실험의 응력-변형률 관계곡선과 비교 검증되었고, 이중 점탄소성 손상 모델은 실험결과를 잘 모사할 수 있음을 확인하였다. In this study, the rheological models were introduced and developed to reflect rate dependent tensile behaviour of concrete. In general, mechanical properties(e.g. strength, elasticity, and fracture energy) of concrete are increased under high loading rates. The strength of concrete shows high rate dependency among its mechanical properties, and the tensile strength has higher rate dependency than the compressional strength. To simulate the rate dependency of concrete, original spring set of RBSN(Rigid-Body- Spring-Network) model was adjusted with viscous and friction units(e.g. dashpot and Coulomb friction component). Three types of models( 1) visco-elastic, 2) visco-plastic, and 3) visco-elasto- plastic damage models) are considered, and the constitutive relationships for the models are derived. For validation purpose, direct tensile test were simulated, and characteristics of the three different rheological models were compared with experimental stress-strain responses. Simulation result of the developed visco-elasto-plastic damage(VEPD) model demonstrated well describing and fitting with experimental results.
외연적 시간적분법 활용 동적 구조해석 속도 향상을 위한 적합직교분해 기반 침습적 차수축소모델 적용 연구
황영광,김명일 한국전산구조공학회 2024 한국전산구조공학회논문집 Vol.37 No.1
일반적으로 적합직교분해(proper orthogonal decomposition, POD) 기반의 침습적(intrusive) 차수축소모델(reduced order model, ROM)을 활용하면 구조 시스템의 전체 자유도를 크게 줄이고 외연적 시간 적분법에서 해의 안정성을 만족하는 임계 시간 간격을 증가시킬 수 있다. 따라서 본 연구에서는 POD-ROM을 활용하여 Voronoi-cell 격자 요소로 이산화된 구조 시스템의 축소와 이에 따른 외연적 시간 적분법의 임계 시간 간격 및 해석 정확도 변화를 살펴보았다. 또한 지진하중과 같은 불규칙한 하중 이력을 받는 구조물 응답해석에 POD-ROM을 적용하였다. 해석 결과 ROM을 통해 해의 정확도를 충분히 확보하면서 연산 시간을 크게 단축할 수 있음을 확인하였다. 또한 POD-ROM과 VCLM의 연계 방안의 적절성을 확인하였다. 향후 해당 연구는 고정밀 대용량 동적 구조해석의 실용성을 높이고, 설계 변수에 따른 구조물 동적 거동의 실시간 예측을 위한 기반 연구로 활용될 수 있다. Using the proper orthogonal decomposition (POD) based intrusive reduced order model (ROM), the total degrees of freedom of the structural system can be significantly reduced and the critical time step satisfying the conditional stability increases in the explicit time integrations. In this study, therefore, the changes in the critical time step in the explicit time integrations are investigated using both the POD-ROM and Voronoi-cell lattice model (VCLM). The snapshot matrix is composed of the data from the structural response under the arbitrary dynamic loads such as seismic excitation, from which the POD-ROM is constructed and the predictive capability is validated. The simulated results show that the significant reduction in the computational time can be achieved using the POD-ROM with sufficiently ensuring the numerical accuracy in the seismic analyses. In addition, the validations show that the POD based intrusive ROM is compatible with the Voronoi-cell lattice based explicit dynamic analyses. In the future study, the research results will be utilized as an elemental technology for the developments of the real-time predictive models or monitoring system involving the high-fidelity simulations of structural dynamics.
주위장기에 유착된 대장암의 수술에서 복강경 주위장기 병합절제술이 적합한가?
박영광,이호석,윤호근,박창균,노상익,황덕원 대한내시경복강경외과학회 2009 Journal of Minimally Invasive Surgery Vol.12 No.2
Purpose: The aim of this study was to assess the feasibility and safety of laparoscopic multivisceral resection of colorectal cancer adherent to adjacent organs. Methods: We reviewed retrospectively 32 patients undergoing elective laparoscopic multivisceral resection for colorectal cancer adherent to adjacent organs between June 2003 and May 2009. Survival curves were generated by Kaplan-Meier method. Results: The median age of 32 patients was 73 years. In 10 of 17 rectal cancer patients (59%), neoadjuvant chemoradiation was performed. All the surgeries were completed laparoscopically. The postoperative complications occurred in 21.9% and there was no operative mortality. The median length of hospital stay was 15.5 days. In 23 of 32 patients (72%), the resection was considered curative. Median follow-up period of all patients and curatively resected patients was 22 (range, 2∼65) months, 34 (range, 4∼65) months respectively. Local recurrence rate, the 3-year overall survival rate and the 3-year disease free survival rate of 23 curatively resected patients was 4.3%, 92.9% and 84.4%, respectively. Conclusion: Laparoscopic multivisceral resection is feasible and safe in highly selected patients with colorectal cancer adherent to adjacent organs. Further validation is needed.
심영광,Jeong-Tae Kim,Mun-Hyuk Seong,Yeon-Jeong Kim,Tae-Jin Shim,Sang Min Kim,Sang Yeub Lee,배장환,김기석,황경국,김동운,조명찬 대한의학회 2012 Journal of Korean medical science Vol.27 No.10
Thioredoxin-1 (Trx-1) is one of important anti-oxidative molecules to overcome the oxidative stress. The aim of the present study is to investigate the clinical relationship between serum concentration of Trx-1 on the pre-percutaneous coronary intervention (prePCI) and myocardial damage amount in the patients with acute myocardial infarction with the culprit lesion in only the left anterior descending artery on coronary angiography (n = 100). Initial value of creatine kinase (CK) was 368.3 ± 531.4 U/L, and MB isoenzyme of CK (CK-MB) level was 22.92 ± 33.8 ng/mL, and cardiac specific troponin T (cTnT) level was 0.61 ± 1.6 ng/mL. Positive correlations were observed between prePCI Trx-1 level and initial CK (P = 0.005, r = 0.281), and cTnT (P < 0.001, r = 0.453), peak CK (P = 0.001,r = 0.316) in all patients, but the statistical relation was observed only in ST segment elevation myocardial infarction (STEMI) patients (P = 0.008, r = 0.329 for initial CK,P = 0.001, r = 0.498 for initial cTnT, P = 0.005, r = 0.349 for peak CK), not in Non-STEMI patients. Conclusively, we consider prePCI serum Trx-1 as a predictor for myocardial damage amount in patients with STEMI.
폴리감마글루탐산을 함유하는 생분해성 나노섬유의 제조 및 생의학적 응용
고영광,김원일,김철주,권오경,황진상,권오형,Ko, Young-Gwang,Kim, Won-Il,Kim, Cheol-Joo,Kwon, Oh-Kyoung,Hwang, Jin-Sang,Kwon, Oh-Hyeong 한국섬유공학회 2010 한국섬유공학회지 Vol.47 No.2
One of the serious complications that have not been solved yet in modern medicine is a postoperative tissue adhesion of internal organs. Tissue adhesions are associated with numerous postoperative complications, including pain, functional obstruction and difficult re-operative surgery. In this study, poly($\gamma$-glutamic acid)($\gamma$-PGA) based nanofiber sheets were prepared by using electrospinning technique to evaluate the ability of the prevention of postoperative tissue adhesion. The anti-adhesion membranes were prepared from $\gamma$-PGA and poly(D,L-lactic-co-glycolic acid)(PLGA) with different compositions by electrospinning. Also non-steroidal anti-inflammatory drug (ibuprofen) was incorporated during fabrication of nanofibers. Various electrospun nanofibers were characterized by SEM, FTIR, water contact angle measurement, biodegradability test, in vitro drug release profile, cell culture test, and in vivo animal study using Sprague Dawley rat model. The average diameter of the nanofibers electrospun from the various biodegradable polymer solutions ranged from 300 nm to 900 nm, approximately. From in vivo animal study, it was observed that ibuprofen-incorporated $\gamma$-PGA nanofiber sheet (crosslinked) was significantly effective in preventing post-surgical tissue adhesion and wound healing, probably due to the appropriate hydrophilicity preventing shrinkage of the sheet. On the other hand, PLGA nanofibrous mat was dramatically contracted in vivo due to its high hydrophobicity and resulted in insufficient coverage of wound.
EYECANE: 시각 장애인을 위한 지능형 상황 인식기
황지혜(Jihye Hwang),지영광(Yeounggwang Ji),김경태(Kyung-tai Kim),김은이(Eun Yi Kim) 한국정보과학회 2013 정보과학회 컴퓨팅의 실제 논문지 Vol.19 No.7
제안된 EYECANE 시스템은 시각 장애인용 cane에 카메라가 장착된 보조 내비게이션 시스템이다. EYECANE은 시각장애인이 익숙하지 않은 상황에서 안전하게 보행하도록 상황을 인식해 주는 시스템이다. 본 시스템은 세 가지 환경 정보를 사용자에게 제공 한다: 1) 사용자가 서있는 현재의 상황, 2) 사용자를 중심으로 있는 장애물의 크기와 위치, 3) 추출된 장애물을 안전하게 피하기 위한 방향. 제안된 시스템의 효율성을 증명하기 위해 다양한 환경에서 실험했다. In this paper, the navigating system with camera embedded whitecane, which is called EYECANE, is presented to help the visually impaired in safely traveling on unfamiliar environments. It provides three environmental information to the user: 1) the current situation (place type) where a user stands on, 2) the positions and sizes of obstacles around a user, and 3) the viable paths to prevent the collisions of such obstacles. The experimental results demonstrated the effectiveness of the proposed method.