• Transactions of Materials Processing
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• v.13 no.7
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• pp.570-579
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• 2004

정상상태 압연공정의 오일러리안 공정해석 모델에 관한 연구들을 종합 정리하였다 본 연구의 유한요소해석 모델은 집합조직의 발전에 따른 이방성과 미세기공의 성장에 따른 기계적 성질의 열성화를 평형방정식에 직접 결합하였다 따라서 집합조직의 발전 및 기공률의 변화를 예측하고 동시에 이방성과 기계적성질의 열성화를 해석에 반영할 수 있다. 더불어 오일러리안 해석에서 형상예측을 위하여 자유곡면 수정법과 유선추적법을 유한요소해석 모델에 결합하였다 본 연구의 공정해석 모델을 평판 압연, 클래드압연, 삼차원 사각단면봉의 압연 및 형상압연에 적용하여 집합 조기의 발전, R-값, 항복곡면, 결함성장 등의 기계적성질의 변화 예측과 클래드 압연시에 이중재 접촉면 형상, 배불림, 형상압연 시의 단면변화 등의 형상변화 예측을 보여주었다.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.803-810
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• 2007

An analytical method capable of predicting various stress-strain responses in axially loaded concrete confined with FRP (fiber reinforced polymers) composites in a rational manner is presented. Its underlying idea is that the volumetric expansion due to progressive microcracking in mechanically loaded concrete is an important measure of the extent of damage in the material microstructure, and can be utilized to estimate the load-carrying capacity of concrete by considering the corresponding accumulated damage. Following from this, an elastic modulus expressed as a function of area strain and concrete porosity, the energy-balance equation relating the dilating concrete to the confining device interactively, the varying confining pressure, and an incremental calculation algorithm are included in the solution procedure. The proposed method enables the evaluation of lateral strains consecutively according to the related mechanical model and the energy-balance equation, rather than using an empirically derived equation for Poisson's ratio or dilation rate as in other analytical methods. Several existing analytical methods that can predict the overall response were also examined and discussed, particularly focusing on the way of considering the volumetric expansion. The results predicted by the proposed and Samaan's bilinear equation models correlated with observed results with a reasonable degree, however it can be judged that the latter is not capable of predicting the response of lateral strains correctly due to incorporating the initial Poisson's ratio and the final converged dilation rate only. Further, the proposed method seems to have greater benefits in other applications by the use of the fundamental principles of mechanics.

• Membrane Journal
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• v.10 no.3
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• pp.139-147
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• 2000

Non-Fickian (or anomalous) diffusion was observed in transient sorption of aromatic solvents(such as benzene, toluene, and chlorobenzene) in fluoropolymers (such as ETFE, ECTFE and PVDF). In this study, five other transient sorption models (Crank, Long ＆ Richman, Berens ＆ Hopfenberg, Neogi, Li) based on Fick's law were employed to fit the anomalous sorption data for aromatic solvents. The adjustable parameters were determined by least square analysis of the measured and predicted fractional uptake. For ETFE sorption data slightly deviating from Fickian behavior, all the models exhibited satisfactory results in fitting the anomalous sorption data. In particular, Neogj model predicted intrinsic diffusivity (0.4～0.8$\times$10$^{-5}$ $\textrm{cm}^2$/day) and equilibrium diffusivity (0.13～0.31$\times$10$^{-4}$ $\textrm{cm}^2$/day) as well as relaxation kinetics related to non-Fickain diffusion. For a typical sigmoidal sorption behavior in PVDF, only Crank's model could give the reasonable evaluation on transport properties. The ratio of intial diffusivity (D$_{i}$) to final equilibrium diffusivity (D$_{\infty}$) was ranged from 80 to 200. For the final stage of uptake In ECTFE with drastic acceleration, all the models exhibited significant deviations from the sorption data. New diffusion models based on thermodynamics and continuum mechanics should be employed to get valuable information on transport properties as well as relaxation kinetics coupled with non-Fickian diffusion.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.12
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• pp.1919-1927
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• 1993

A new MAC protocol has been proposed and analysed to relieve the unfairness problems exhibited by the basic version of the DQDB standard. DQDB MAC protocol has the unfairness problems in throughputs. message delay and so or. And when the slots are reused or the file transmissions takes long, the unfairness problems in the system become worse. The new access protocol proposed here, which of called the Balanced DQDB, guarantees a fair bandwidth distribution by using one bit of the dual bus network protocol and keeps up all characteristics of DQDB. the DQDB analysis model introduced by Wen Jing, et al, was considered to analyse a sequential balance distribution of solts. And the probabilities of the empty in operation mode were represented to determine the probabilities for busy bits to generate on each node of the bus using the Markov chain. Through the simulations. the performances of the proposed Balanced DQDB and that of the standard DQDB of the BWB mechanism were compared at the state that the values of the RQ or CD counter on each node varied dynamically. As the results, it is shown that the Balanced DQDB has the decrement of throughputs in upstream, but the numbers of the used empty slots at each node of the Balanced DQDB had more than that of the others because the Balanced DQDB has over 0.9 throughputs in the 70~80% nodes of total node and it has constant throughputs at each node. And there results were analogous to that of the analytical model.

• Journal of the Korean Society of Groundwater Environment
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• v.4 no.1
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• pp.14-19
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• 1997

Laboratory experiments were conducted to study the effects of pH and salt level on the soil sorption equilibrium of pentachlorophenol (PCP) which is hydrophobic and ionogenic. Experimental results indicated that the sorption equilibrium constant (Kp) of PCP increased with decreasing pH. A quantitative sorption model involving linear isotherms was estabilished to predict the pH effect on the PCP sorption equilibrium over the pH range from 3 to 8. The model prediction was in good agreement with the experimental data. Also, the Kp increased with salt concentration over the entire pH range. At added salt levels less than 0.1M, increase in Kp was larger than when the added levels were higher than 0.1M. Salt might increase the PCP sorption by inducing 'salting out-effect' or by forming deprotonated PCP-cation ion pairs such as PCP$\^$-/K$\^$＋/. Taking the pH range (5-8) and the salt content (up to 50 g/L) in the groundwater of Metropolitan landfill sites into consideration, the results indicated that the retardation factor of PCP in this area might range from 3 to 550 depending upon pH and salt content.

• Applied Chemistry for Engineering
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• v.26 no.4
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• pp.483-488
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• 2015

This study examined the adsorption characteristics of $Cr^{6+}$ and $As^{3+}$ in the aqueous solution by Hizikia susiformis biochar which was collected from Jeju Island. The optimal pH for $Cr^{6+}$ and $As^{3+}$ adsorption were 2 and pH 6, respectively. Kinetic data showed that the adsorption occurred during the first 100 min, and the most of heavy metals were bound to biochars within 300 min. Moreover, the kinetic data presented that the course of adsorption follows the Pseudo first and second order models. The equilibrium data were well fitted by the Langmuir model and the $Cr^{6+}$ adsorption capacity (25.91 mg/g) was higher than that of $As^{3+}$ (16.54 mg/g). From these results, the seaweed biochar was shown to be a efficient adsorbent for $Cr^{6+}$ and $As^{3+}$ metals in a contaminated environment.

• Polymer(Korea)
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• v.24 no.2
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• pp.182-193
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• 2000

Molar cyclization equilibrium constant (K$_{x}$) of poly(alkylene terephthalate) (PAT) cyclics was calculated by the Monte Carlo simulation on the basis of rotational isomeric state (RIS) model. The experimental $K_{x}$ of PAT cyclics, which was not clearly explained by the Jacobson-Stockmayer theory and the method of Flory, Suter, and Mutter however, was explained well by the direct computational method with the reaction radius ${\gamma}$=0.5 < ${\gamma}^{2}$> $^{1/2}$. The effect of PAT conformation on $K_{x}$ of PAT cyclics was investigated by changing its statistical weight parameters, ${\sigma}_{1}$ and ${\sigma}_{2}{\cdot}K_{x}$ of PAT cyclics obtained by the direct computation method with various radii and the radius ${\gamma}$=0.5 < ${\gamma}^{2}$> $^{1/2}$ was slightly changed with ${\sigma}_{1}$ and ${\sigma}_{2}$. Consequently, it was concluded that $K_{x}$ of PAT cyclics is strongly dependent on the configuration of each PAT and affected by the change of its conformation to some extent.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.9
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• pp.814-821
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• 2015

The STEP Cube Lab. classified as a pico-class satellite has been successfully developed as a flight model(FM) to be launched in 2015. Its mission objective is to perform the on-orbit verification of fundamental space core-technologies. In this study, a thermal design concept based on the passive method to achieve the mission objective is introduced. The effectiveness of the thermal design and performance of the satellite has been verified through the acceptance level thermal vacuum test. In addition, to improve the reliability of thermal mathematical model, correlation was performed using the results of thermal balance test. This paper describes a series of process for the thermal vacuum test on the STEP Cube Lab. FM.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.11
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• pp.95-105
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• 2005

The HAUSAT-2 nanosatellite which is scheduled to launch in 2008 is being developed by SSRL(Space System Research Lab.). The HAUSAT-2 STM(Structural-Thermal Model) was developed as the first system model to verify structural and thermal design margin. The qualification level vibration and thermal tests have been conducted on STM. This paper addresses the comparison of structural analysis and test results of HAUSAT-2 STM. It was shown that the natural frequency of HAUSAT-2 STM satisfies the stiffness requirements without structural damage in the random vibration test. The assembly and integration validity were also checked out through STM.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2007.04a
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• pp.48-51
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• 2007

본 논문에서는 비선형 상호 결합 시스템의 출력 궤환 제어기 설계에 대해서 연구한다. 먼저 퍼지 모델 기법을 이용하여 비선형 상호 연결된 시스템을 Takagi-Sugeno (T-S) 퍼지 모델로 모델링한다. 그 각각의 하위 시스템에 대한 출력 궤한 제어기를 동적 병렬 분산 보상 (DPDC) 기법을 이용하여 퍼지 출력 궤환 제어기로 설계한다. 하위 시스템들의 평형점이 안정화 되는 선형 행렬 부등식 (LMI)를 구하고, 그 부등식을 만족하는 값들로부터 하위 시스템의 제어기 이득을 구한다.