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Geometry-dependent MITC method for a 2-node iso-beam element
Lee, Phill-Seung,Noh, Hyuk-Chun,Choi, Chang-Koon Techno-Press 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.29 No.2
In this paper, we present an idea of the geometry-dependent MITC method. The simple concept is exemplified to improve a 2-node iso-beam (isoparametric beam) finite element of varying section. We first study the behavior of a standard 2-node iso-beam finite element of prismatic section, which has been widely used with reduced integration (or the equivalent MITC method) in order to avoid shear locking. Based on analytical studies on cantilever beams of varying section, we propose the axial strain correction (ASC) scheme and the geometry-dependent tying (GDT) scheme for the 2-node iso-beam element. We numerically analyze varying section beam problems and present the improved performance by using both ASC and GDT schemes.
이필승(Lee Phill-Seung),노혁천(Noh Hyuk-Chun) 대한토목학회 2007 대한토목학회논문집 A Vol.27 No.3A
본 논문에서는 최근 주요 연구들을 토대로 쉘 구조물의 유한요소해석에 대하여 중요한 개념들과 그 연관관계를 고찰한다. 감절점 쉘 유한요소의 수학모델인 기본쉘수학모델을 살펴본다. 쉘 구조물의 두께가 얇아짐에 따라 일어나는 쉘 구조문제의 세가지 극한거동들(휨지배거동, 막지배거동, 혼합지배거동)에 대한 쉘의 점근거동 이론을 소개하고 점근거동을 유한요소해석을 통해 찾아내는 방법을 알아본다. 유한요소해의 오차를 s-norm으로 평가하는 방법을 소개하고 이를 이용하여 쉘 유한요소의 잠김현상이 유한요소해의 수렴곡선에 어떻게 나타나는지 살펴본다. 쉘 구조물의 유한요소해석에서 균일최적수렴의 개념을 논의한다. 마지막으로 이상적인 쉘 유한요소의 조건을 알아보고 쉘 유한요소의 성능평가를 위한 방법론을 제시한다. Based on recent research works, important concepts on the finite element analysis of shell structures and the relations among them are presented in this paper. We review the basic shell mathematical model, which is the underlying mathematical model of the continuum mechanics based shell finite elements. The asymptotic theory of shell structures then is reviewed and we present how to evaluate the asymptotic behavior in finite element solutions. S-norm is introduced as an error measure of finite element solutions and we show "locking" in the convergence curves of shell finite element solutions. We discuss the concept of "uniform optimal convergence" in finite element analysis of shells. We finally summarize requirements on ideal shell finite elements and propose how to perform benchmark tests of shell finite elements.
Dong-Hwa Lee,Hyo-Jin Kim,Phill-Seung Lee 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.80 No.5
In this paper, we present a new method to calculate interface warping functions for the analysis of beams with geometric and material discontinuities in the longitudinal direction. The classical Saint Venant torsion theory is extended to a three-dimensional domain by considering the longitudinal direction. The interface warping is calculated by considering both adjacent cross-sections of a given interface. We also propose a finite element procedure to simultaneously calculate the interface warping function and the corresponding twisting center. The calculated interface warping functions are employed in the continuum-mechanics based beam formulation to analyze arbitrary shape cross-section beams with longitudinal discontinuities. Compared to the previous work by Yoon and Lee (2014a), both geometric and material discontinuities are considered with fewer degrees of freedom and higher accuracy in beam finite element analysis. Through various numerical examples, the effectiveness of the proposed interface warping function is demonstrated.
Lee, Sang-Min,Oh, Dong-Joon,Jung, Im-Deok,Bae, Kong-Myeong,Jung, Phill-Gu,Chung, Kwang-Hyo,Cho, Seung-Jin,Ko, Jong-Soo 한국정밀공학회 2009 International Journal of Precision Engineering and Vol.10 No.3
Nickel micromesh sheets were designed and fabricated and their water-repellent and water-proof abilities were characterized. The network-type microstructures of the micromesh sheets functioned as micro-protrusions of lotus leaves, which allowed the sheets to superhydrophobic. The micromesh enabled the material waves, including sound and light waves, to pass through the microholes, but repelled water. Because of the effects of the micromesh and plasma polymerized fluorocarbon(PPFC) coating, the contact angle of the micromesh sheets was drastically jumped up from $63^{\circ}$ of the non-coated nickel flat film to $140^{\circ}$ of the PPFC-coated nickel micromesh, which modified the nickel sheet from hydrophilic to superhydrophobic. The narrower lattice width in the micromesh was more effective at enhancing the water-repellency. On the other hand, the narrow lattice width weakened the water-proof ability. Reducing the hole size and increasing the lattice width of the micromesh are necessary to improve the water-proof ability.
( Phill Seung Jung ),( Yeon Sik Na ),( Shin Wha Lee ),( Jeong Yeol Park ),( Jong Hyeok Kim ),( Young Man Kim ),( Joo Hyun Nam ),( Young Tak Kim ),( Dae Yeon Kim ) 대한산부인과학회 2012 대한산부인과학회 학술대회 Vol.98 No.-
To correlate pathologic findings on conization specimens and other clinical parameters with residual disease in radical hysterectomy specimens in patients with cervical cancer to determine which subgroup of patients may be eligible for less radical surgery Between 2003 and 2011, we perfomed 472 conizations before treating cervical cancer patients. The exclusion criteria were the patients who were given neoadjuvant chemotherapy and/or definitive CCRT and/or radical trachelectomy and the patients whose pathologic reports were missing or unclear. A total of 292 patients who underwent radical hysterectomy after conization were included in this retrospective study. Mean age of this patients were 51.7 years (28-85) and mean size of residual tumor was 1.3cm (0-7.3 cm). FIGO stage distribution were 17 patients in IA1, 21 in IA2, 233 in IB1, 10 in IB2 and 11 in others. At radical hysterectomy, 87 patients (30%) had no residual cancer, while 205 patients (70%) had residual cancer. Univariate analysis showed that positive resection margin and tumor size more than 2cm were significant factors for predicting residual disease. These factors also significant in a multivariate analyisis (positive resection margin OR 6.869, 95% CI 2.734-17.262, p<0.001; tumor size >2cm OR 3.090, 95% CI 1.744-5.474, p<0.001). Of the resection margin status, Positive endocervical and deep margin were significant but not significant in exocervical margin. The patients with negative resection margin and small tumor (< 1 cm) had no residual disease and no recurrences in the median FU of 32 months. Positive resection margin on conization and large tumor size (>2c m) were significant factors for predicting residual cancer after radical hysterectomy. Using these factors, we can develop the predicting models for detecting subgroup of patients who are eligible for less radical surgery.
( Phill Seung Jung ),( Shin Wha Lee ),( Dae Yeon Kim ),( Jong Hyeok Kim ),( Yong Man Kim ),( Young Tak Kim ),( Joo Hyun Nam ) 대한산부인과학회 2014 대한산부인과학회 학술대회 Vol.100 No.-
목적: The aim of this study is to evaluate diagnostic accuracy of combined 18F-fluoro-2-deoxyglucose-positron emission tomography/computed tomography (18F-FDG-PET/CT) imaging in suspected recurrence of epithelial ovarian cancer with non-disseminated lesions by correlating with pathologic report after secondary cytoreduction. 방법: We retrospectively reviewed patients with recurrent epithelial ovarian cancer after primary treatment at Asan Medical Center from January, 2004 to December, 2013. Among those, 130 patients underwent secondary cytoreduction after imaging studies such as combined 18F-FDG-PET/CT or CT. We evaluated the sensitivity and positive predictive value (PPV) of combined 18F-FDG-PET/CT imaging and compared with those of CT correlating with the pathologic result of the secondary cytoreduction. 결과: A total of 63 patients with a median age of 46 (range: 21-68) were enrolled in this study. 46 patients underwent combined 18F-FDG-PET/CT and 61 did CT imaging before their secondary cytoreduction. The distribution of the cell type is as followed; 44 papillary serous adenocarcinomas, 5 clear cell carcinomas, 6 serous carcinomas, 2 mucinous adenocarcinomas, 3 endometrioid adenocarcinomas, 3 other types. The median level of CA-125 before the secondary cytoreduction was 22.3 (range: 2.4-1380.0) U/mL, and the mean max standardized uptake value of 18F-FDG-PET in the study cohort was 6.2 (range: 1.6-26.7). After the secondary cytoreduction, 54 (85.7%) patients were confirmed to have recurred with a median maximal tumor diameter of 3.5 (range: 0.1-10.0) cm on the pathologic report. Combined 18F-FDG-PET/CT showed a sensitivity of 70.4% and a PPV of 82.6% with false positive rate of 17.4% in detecting recurrent epithelial ovarian cancer. 결론: Our study demonstrated a discrepancy from previous studies in respect of a diagnosis value of combined 18F-FDG-PET/CT imaging in recurrent epithelial ovarian cancers with non-disseminated lesions. A prospective study with larger cohort would be needed.