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강재의 저온 특성을 고려한 선체 보강판과 빙하의 충격 상호 작용에 대한 수치 해석
남웅식 한국해양공학회 2019 韓國海洋工學會誌 Vol.33 No.5
It is essential to design crashworthy marine structures for operations in Arctic regions, especially ice-covered waters, where the structures must have sufficient capacity to resist iceberg impact. In this study, a numerical analysis of a colliding accident between an iceberg and stiffened plates was carried out employing the commercial finite element code ABAQUS/Explicit. The ice material model developed by Liu et al. (2011) was implemented in the simulations, and its availability was verified by performing some numerical simulations. The influence of the ambient temperature on the structural resistance was evaluated while the local stress, plastic strain, and strain energy density in the structure members were addressed. The present study revealed the risk of fracture in terms of steel embrittlement induced by ambient temperature. As a result, the need to consider the possibility of brittle failure in a plate-stiffener junction during operations in Arctic regions is acknowledged. Further experimental work to understand the structural behavior in a plate-stiffener junction and HAZ is required.
Experimental and Theoretical Study on the Prediction of Axial Stiffness of Subsea Power Cables
남웅식,채광수,임영석 한국해양공학회 2022 韓國海洋工學會誌 Vol.36 No.4
Subsea power cables are subjected to various external loads induced by environmental and mechanical factors during manufacturing, shipping, and installation. Therefore, the prediction of the structural strength is essential. In this study, experimental and theoretical analyses were performed to investigate the axial stiffness of subsea power cables. A uniaxial tensile test of a 6.5 m three-core AC inter-array subsea power cable was carried out using a 10 MN hydraulic actuator. In addition, the resultant force was measured as a function of displacement. The theoretical model proposed by Witz and Tan (1992) was used to numerically predict the axial stiffness of the specimen. The Newton–Raphson method was employed to solve the governing equation in the theoretical analysis. A comparison of the experimental and theoretical results for axial stiffness revealed satisfactory agreement. In addition, the predicted axial stiffness was linear notwithstanding the nonlinear geometry of the subsea power cable or the nonlinearity of the governing equation. The feasibility of both experimental and theoretical framework for predicting the axial stiffness of subsea power cables was validated. Nevertheless, the need for further numerical study using the finite element method to validate the framework is acknowledged.
조준현,남웅식,김선주,이두현,민경훈,이태호,이상규 사단법인 한국질량분석학회 2016 Mass spectrometry letters Vol.7 No.3
High-resolution quadrupole-Orbitrap mass spectrometry (HRMS), with high-resolution (> 10,000 at full-width at half-maximum) and accurate mass (< 5 ppm deviation) capabilities, plays an important role in the structural elucidation of drug metabolites in the pharmaceutical industry. ML106, a derivative of imidazobenzimidazole, decreased melanin content and tyrosinase activity in a dose-dependent manner. Here, we investigated the phase 1 metabolic pathway of ML106 using HRMS in human liver microsomes (HLMs) and recombinant cDNA-expressed cytochrome P450 (CYP). After the incubation of ML106 with pooled HLMs and recombinant cDNA-expressed CYP in the presence of NADPH, five phase 1 metabolites, including three mono-hydroxylated metabolites (M1-3) and two di-hydroxylated metabolites (M4 and M5), were investigated. The metabolite structures were postulated by the elucidation of protonated mass spectra using HRMS. The CYP isoforms related to the hydroxylation of ML106 were studied after incubation with recombinant cDNA-expressed CYP. Here, we identified the phase 1 metabolic pathway of ML106 induced by CYP in HLMs.
Selective Inhibitory Effect of Osthenol on Human Cytochrome 2C8
조필중,남웅식,이두현,이태호,이상규 대한화학회 2018 Bulletin of the Korean Chemical Society Vol.39 No.6
Osthenol is a furanocoumarin with anti?tumor, anti?inflammatory, and anti?viral activity. It is present in various citrus juices and fruits; however, its inhibitory effects on cytochrome P450 (CYP) enzyme activity, in the context of herb?drug interaction (HDI) prediction, have not been previously studied. In this study, osthenol was chemically synthesized in order to identify potential HDIs. Its inhibitory effect on eight CYP isoforms and the underlying mechanism of inhibition were investigated by using cocktail assays and liquid chromatography?tandem mass spectrometry in pooled human liver microsomes. The inhibitory effect of osthenol on CYP2C8?catalyzed paclitaxel hydroxylation was selective and dose?dependent, but not time?dependent. The IC50 value was 2.8 ?M. Additionally, osthenol displayed mixed mode inhibition with a relatively low Ki value of 0.96 ?M, which is indicative of the potential for HDIs with co?administered CYP2C8 substrates. To the best of our knowledge, this is the first report of selective inhibition of CYP2C8 by osthenol.
심주희,남웅식,이두현,이수연,오현찬,주정민,유광현,한재윤,기성환,정태천,이태호,이상규 대한약학회 2015 Archives of Pharmacal Research Vol.38 No.5
Cytochrome P450 (CYP) is an importantenzyme that can act on xenobiotic substances such as toxicchemicals or drugs. Phenobarbital (PB) has been widelyused to induce CYP2B activity to investigate the drug–druginteraction of CYP2B substrate drugs. Leelamine is aditerpene compound, and is the current focus of efforts todevelop a treatment for diabetes. In this study, we identifiedthe selective and potent inductive effect of leelamineon CYP2B at doses of 5, 10, or 20 mg/kg in male ICR micefor 1 or 3 days. In liver, the activity of CYP2B significantlyincreased 3.6-fold after treatment with leelamine, comparedto vehicle-treated group. Activities of benzyloxyresorufinO-dealkylase and pentoxyresorufin O-dealkylasesignificantly increased 6.3- and 5.3-fold, respectively, witha single treatment of 20 mg/kg leelamine for 1 day. Furthermore,immunoblot analysis showed that significantlyand dose-dependently increased CYP2B10 protein levels inliver. However, PCR results showed that there were nosignificant changes in the CAR and CYP2B mRNA levelsafter leelamine treatment. Accordingly, we suggest thatleelamine is a novel substitute of PB for the selectiveinduction of CYP2B activity in vivo.
상용 유한요소코드 사용자-서브루틴을 이용한 저온용 고장력강 (EH36)의 파단 시뮬레이션
정준모(Joonmo Choung),남웅식(Woongshik Nam),김영훈(Younghun Kim) 한국해양공학회 2014 韓國海洋工學會誌 Vol.28 No.1
This paper discusses a new formulation for the failure strain in the average stress triaxiaility domain for a low-temperature high-strength steel (EH36). The new formula available at a low average stress triaxiality zone is proposed based on the comparison of two results from tensile tests of flat type specimens and their numerical simulations. In order to confirm the validity of the failure strain formulation, a user-subroutine was developed using Abaqus/Explicit, which is known to be one of the most popular commercial finite element analysis codes. Numerical fracture simulations with the user-subroutine were conducted for all the tensile tests. A comparison of the engineering stress-strain curves and engineering failure strain obtained from the numerical simulation with the user-subroutine for the tensile tests revealed that the newly developed user-subroutine effectively predicts the initiation of failure.