• International Journal of Aeronautical and Space Sciences
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• 제16권2호
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• pp.254-263
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• 2015

In this study, numerical simulations are carried out to investigate the dynamic SGS model effects in a Kerosene-LOx coaxial swirl injector under high pressure conditions. The turbulent model is based on large-eddy simulation (LES) with real-fluid transport and thermodynamics. To assess the effect of the dynamic subgrid-scale (SGS) model, the dynamic SGS model is compared with that of the algebraic SGS model. In a swirl injector under supercritical pressure, the characteristics of temporal pressure fluctuation and power spectral density (PSD) present comparable discrepancies dependant on the SGS models, which affect the mixing characteristics. Mixing efficiency and the probability density (PDF) function are conducted for a statistical description of the turbulent flow fields according to the SGS models. The back-scattering of turbulent kinetic energy is estimated in terms of the film thickness of the swirl injector.

• 에너지공학
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• 제21권3호
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• pp.228-236
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• 2012

큰 에디 모사(LES)는 복잡한 연소실 유동에서 RANS 모델과 비교해 난류 유동장에 대해 모델의 보편성과 더 정확한 결과를 제공하기 때문에 점차적으로 사용이 증대되고 있다. 내연 기관의 연소실 내 난류 유동장 해석을 큰 에디 모사를 사용하여 수행하였다. 이산화 방식, 초기 조건, 시간 간격과 SGS 모델과 같은 모델과 수치 인자에 따른 영향을 평가하였다. SGS 모델을 사용한 LES 모사는 실험치와 유사한 결과를 보여주었다.

• Journal of Advanced Marine Engineering and Technology
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• 제28권3호
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• pp.423-433
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• 2004

A large eddy simulation (LES) is performed for turbulent flow in a combustion device. The combustion device is simplified as a cylindrical chamber with sudden expansion. A flame holder is attached inside a cylindrical chamber in order to promote turbulent mixing and to accommodate flame stability. The turbulent sub-grid scale models are applied and validated. Emphasis is placed on the evaluation of turbulent model for the LES of complex geometry. The simulation code is constructed by using a general coordinate system based on the physical contravariant velocity components. The calculated Reynolds number is 5000 based on the bulk velocity and the diameter of inlet pipe. The predicted turbulent statistics are evaluated by comparing with the LDV measurement data. The Smagorinsky model coefficients are estimated and the utility of dynamic SGS models are confirmed in the LES of complex geometry.

• 대한한방부인과학회지
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• 제18권1호
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• pp.1-14
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• 2005

This study was performed to evaluate antithrombotic activities of Saegeumsan (瑞金散, SGS) which has effects of activating blood, removing thrombus. This study is designed to measure the effect which was given to blood flow rate through the regular volume of glass tube after the blood was diluted five times with ACD solution. Antithrombotic effect was calculated as a percentage of the experimental animal figure protected from the paralysis of hind legs or death of the mouse that is caused from the administration of platelet aggregation regent. We standardized the time when the experimental animals were incapable of functioning the hind legs more than 20 minutes or maintained trembling. Being classified one group of eight mice, each of them was divided into Normal, Control, and SGS. The normal group supplied a saline solution and the control group brought the dextran extravasated blood after an hour of administering the saline solution. Also, SGS was dissolved in $2m{\ell}$ saline solution and then we dosed it to the experimental mice with Oral Zonde one day before the experiment. After that, the mice were abstained from food. And then we gave a measured amount of it before an hour. Finally, it gave rise to dextran extravasated blood in the same way as the Control group. The results were obtained as follows, SGS significantly inhibited platelet aggregation induced by ADP and epinephrine when analyzed by the Sigmoid $E_{max}$ model in WinNonlin. $EC_{50}$ values of SGS were 4.61 mg/ml and 12.41 mg/ml for ADP and epinephrine respectively. SGS showed fibrinolytic activity insignificantly as compared with the control group. SGS increased blood flow rate significantly as compared with the control group in vitro. SGS inhibited pulmonary embolism induced by collagen and epinephrine(inhibitive rate is 37.5 %). SGS increased number of platelet and fibrinogen amount significantly, and shortened PT and APTT as compared with the control group in thrombus model induced by dextran. According to, SGS is effective antithrombotic activity from experimental result.

• 대한기계학회논문집B
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• 제24권11호
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• pp.1523-1534
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• 2000

The performance of a number of existing dynamic subgrid-scale(SGS) models is evaluated in large-eddy simulations(LES) of two prototype transitional and turbulent shear flows, a planar jet and a channel flow. The dynamic SGS models applied include the dynamic Smagorinsky model(DSM);Germano et al. 1991, Lully 1992), the dynamic tow-component model(DTM; Akhavan et al. 2000), the dynamic mixed model(DMM;Zang et al, 1993). and the dynamic two-parameter model(DTPM; Salvetti & Banerjee 1995). The results are compared with those for DNS for their evaluation. The LES results demonstrate the superior performance of DTM with use of a sharp cutoff filter and DMM with use of a box filter, as compared to their respect counterpart DSM, in predicting the mean statistics, spectra and large-scale structure of the flow, Such features of DTM and DMM derive from the construction of the models in which tow separate terms are included to represent the SGS interactions; a Smagorinsky edd-viscosity term to account for the non-local interactions, and a local-interaction term to account for the nonlinear dynamics between the resolved and subgrid scales in the vicinity of the LES cutoff. As well, overall the SGS models using a sharp cutoff filter are more successful than those using a box filter in capturing the statistics and structure of the flow. Finally, DTPM is found to be compatible or inferior to DMM.

• 대한기계학회논문집B
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• 제35권2호
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• pp.169-178
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• 2011

격자볼츠만 방법(LBM)을 이용하여 난류 경계층에서의 오염물질 확산에 대하여 수치계산을 수행 하였다. 난류 경계층 내의 유동을 모사하기 위하여 격자볼츠만 방법에 Smagorinsky 아격자 모델을 적용한 LB-SGS 모델을 사용하였으며, 오염물질의 확산을 모사하기 위하여 Passive-scalar 방법을 적용하였다. LB-SGS 모델의 신뢰성 검증을 위하여 Fackrell & Robins(1982)과 Raupach & Legg(1983)의 실험 조건과 동일한 조건하에서 수치계산을 수행하였고, 수치계산으로 얻어진 농도 분포를 실험값과 비교하였다. 이 결과로부터 LB-SGS 모델이 난류 경계층 내에서의 오염물질의 농도분포를 예측하는데 적합한 모델임을 알 수 있었다.

• 대한기계학회논문집B
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• 제23권1호
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• pp.82-91
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• 1999

A numerical analysis based on the three-dimensional Reynolds-averaged Navier-Stokes equation has been conducted to investigate the flow within a NASA rotor 67 transonic fan. General coordinate transformations are used to represent the complex blade geometry and an H-type grid is used. The governing equations are solved using implicit LU-SGS scheme for the time-marching integration and a standard ${\kappa}-{\varepsilon}$ model is used with wall functions for the turbulence modeling. The computations are compared with the experimental data and a detailed study of the flow structures near peak efficiency and near stall is presented. The calculated overall aerodynamic efficiency and three-dimensional shock system agree well with the laser anemometer data.

• Wind and Structures
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• 제13권6호
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• pp.557-580
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• 2010

A new inflow turbulence generation method and a combined dynamic SGS model recently developed by the authors were applied to evaluate the wind effects on 508 m high Taipei 101 Tower. Unlike the majority of the past studies on large eddy simulation (LES) of wind effects on tall buildings, the present numerical simulations were conducted for the full-scale tall building with Reynolds number greater than $10^8$. The inflow turbulent flow field was generated based on the new method called discretizing and synthesizing of random flow generation technique (DSRFG) with a prominent feature that the generated wind velocity fluctuations satisfy any target spectrum and target profiles of turbulence intensity and turbulence integral length scale. The new dynamic SGS model takes both advantages of one-equation SGS model and a dynamic production term without test-filtering operation, which is particular suitable to relative coarse grid situations and high Reynolds number flows. The results of comparative investigations with and without generation of inflow turbulence show that: (1) proper simulation of an inflow turbulent field is essential in accurate evaluation of dynamic wind loads on a tall building and the prescribed inflow turbulence characteristics can be adequately imposed on the inflow boundary by the DSRFG method; (2) the DSRFG can generate a large number of random vortex-like patterns in oncoming flow, leading to good agreements of both mean and dynamic forces with wind tunnel test results; (3) The dynamic mechanism of the adopted SGS model behaves adequately in the present LES and its integration with the DSRFG technique can provide satisfactory predictions of the wind effects on the super-tall building.

• Journal of Advanced Marine Engineering and Technology
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• 제34권8호
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• pp.1084-1093
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• 2010

화염 전파 특성을 나타내는 G 방정식에 기초한 Sub-grid Scale연소 모델을 이용하여 보염기 주위의 난류 예혼합 연소 해석에 관한 대 와동 모사를 수행하였다. Dynamic SGS 모델이 G방정식에 도입되었으며, 삼각형의 보염기 배면의 예혼합 연소 유동에 의해 검증되었다. 해석결과는 실험결과와의 비교를 통해 속도와 온도분포를 잘 예측하고 있음을 확인하였다.

• Journal of Acupuncture Research
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• 제36권2호
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• pp.92-99
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• 2019

Background: This study was conducted to evaluate the effects of pharmacopuncture and dermal application of Sebalgukhwa-san extracts on hair growth in an alopecia mouse model. Methods: Twenty-one C57BL/6 mice were divided into 3 groups; control group-normal saline injection or vehicle solution application, positive control group-minoxidil (MNXD), experimental group-pharmacopuncture and applied Sebalgukhwa-san (SGS) extract. The effects of the treatment on hair growth, were determined through photographs, and phototrichogram analysis by folliscope. Hair follicle morphometry by hematoxylin-eosin staining was performed, and hair growth-related protein expression of vascular endothelial growth factor, insulin like growth factor-1, and transforming growth factor-beta 1 were monitored by Western blotting. Serum levels of aspartate aminotransferase and alanine aminotransferase were measured for liver function test. Results: Body weight increased consistently in all groups. Hair growth was improved in the MNXD and SGS groups compared with the control. Hair density and thickness improved statistically significantly in the MNXD and SGS groups compared with the control p < 0.05. The number of hair follicles improved in the MNXD and SGS groups compared with the control but the size did not. The expression of vascular endothelial growth factor and insulin like growth factor-1 increased, and there was a decrease in the expression of transforming growth factor-beta 1 in the MNXD and SGS groups compared with the control, however, there was no significant difference. Sebalgukhwa-san treatment had no toxicity in liver function tests. Conclusion: Pharmacopuncture and dermal application of Sebalgukhwa-san extract may be therapeutically beneficial for the treatment of alopecia.