• Korean Chemical Engineering Research
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• v.47 no.3
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• pp.344-348
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• 2009

One-dimensional modeling was carried-out to predict the capacity loss of a lithium-ion polymer battery during cycling. The model not only accounted for electrochemical kinetics and ionic mass transfer in a battery cell, but also considered the parasitic reaction inducing the capacity loss. In order to validate the modeling, modeling results were compared with the measurement data of the cycling behaviors of the lithium-ion polymer batteries having nominal capacity of 5Ah from LG Chem. The cycling was performed under the protocol of the constant current discharge and the constant current and constant voltage charge. The discharge rate of 1C was used. The range of state of charge was between 1 and 0.2. The voltage was kept constant at 4.2 V until the charge current tapered to 50 mA. The retention capacity of the battery was measured with 1C and 5C discharge rates before the beginning of cycling and after every 100 cycles of cycling. The modeling results were in good agreement with the measurement data.

• Korean Chemical Engineering Research
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• v.45 no.3
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• pp.242-248
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• 2007

For an optimal design of automotive electric system, it is important to have a reliable modeling tool to predict the charge-discharge behaviors of the automotive battery. In this work, a two-dimensional modeling was carried out to predict the charge-discharge behaviors of a 12-V automotive lead-acid battery. The model accounted for electrochemical kinetics and ionic mass transfer in a battery cell. In order to validate the modeling, modeling results were compared with the experimental data of the charge-discharge behaviors of a lead-acid battery. The discharge behaviors were measured with three different discharge rates of C/5, C/10, and C/20 at operating temperature of $25^{\circ}C$. The batteries were charged with constant current of 30A until the charging voltage reached to a predetermined value of 14.24 V and then the charging voltage was kept constant. The discharge and charge curves from the measurements and modeling were in good agreement. Based on the modeling, the distributions of the electrical potentials of the solid and solution phases, the porosity of the electrodes, and the current density within the electrodes as well as the acid concentration can be predicted as a function of charge and discharge time.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.5
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• pp.71-80
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• 2012

To improve the $NO_X$ conversion over a SCR (selective catalytic reduction) catalyst, the DOC (diesel oxidation catalyst) is usually placed upstream of the SCR catalyst to enhance the fast SCR reaction ($4NH_3+2NO+2NO_2{\rightarrow}4N_2+6H_2O$) using equimolar amounts of NO and $NO_2$. Here, a ratio of $NO_2/NO_X$ above 50% should be avoided, because the reaction with $NO_2$ only ($4NH_3+4NO+O_2{\rightarrow}4N_2+6H_2O$) is slower than the standard SCR reaction ($4NH_3+4NO+O_2{\rightarrow}4N_2+6H_2O$). In order to accurately predict the performance characteristics of SCR catalysts, it is therefore desired to develop a more simple and reliable mathematical and kinetic models on the oxidation kinetics of nitric oxide over a DOC. In the present work, the prediction accuracy and limit of three different chemical reaction kinetics models are presented to describe the chemicophysical characteristics and conversion performance of DOCs. Steady-state experiments with DOCs mounted on a light-duty four-cylinder 2.0-L turbocharged diesel engine then are performed, using an engine-dynamometer system to calibrate the kinetic parameters such as activation energies and preexponential factors of heterogeneous reactions. The reaction kinetics for NO oxidation over Pt-based catalysts is determined in conjunction with a transient one-dimensional (1D) heterogeneous plug flow reactor (PFR) model with diesel exhaust gas temperatures in the range of 115~$525^{\circ}C$ and space velocities in the range of $(0.4{\sim}6.5){\times}10^5\;h^{-1}$.

• Journal of Korean Society of Water and Wastewater
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• v.33 no.2
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• pp.111-119
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• 2019

Electro-coagulation process has been gained an attention recently because it could overcome the membrane fouling problems in MBR(Membrane bio-reactor). Effect of the key operational parameters in electro-coagulation, current density(${\rho}_i$) and contact time(t) on membrane fouling reduction was investigated in this study. A kinetic model for ${\rho}_i$ and t required to reduce the membrane fouling was suggested under different MLSS(mixed liquor suspended solids) concentration. Total 48 batch type experiments of electro-coagulations under different sets of current densities(2.5, 6, 12 and $24A/m^2$), contact times(0, 2, 6 and 12 hr) and MLSS concentration(4500, 6500 and 8500mg/L) were carried out. After each electro-coagulation under different conditions, a series of membrane filtration was performed to get information on how much of membrane fouling was reduced. The membrane fouling decreased as the ${\rho}_i$ and t increased but as MLSS decreased. Total fouling resistances, Rt (=Rc+Rf) were calculated and compared to those of the controls (Ro), which were obtained from the experiments without electro-coagulation. A kinetic approach for the fouling reduction rate (Rt/Ro) was carried out and three equations under different MLSS concentration were suggested: i) ${\rho}_i^{0.39}t=3.5$ (MLSS=4500 mg/L), ii) ${\rho}_i^{0.46}t=7.0$ (MLSS=6500 mg/L), iii) ${\rho}_i^{0.74}t=10.5$ (MLSS=8500 mg/L). These equations state that the product of ${\rho}_i$ and t needed to reduce the fouling in certain amounts (in this study, 10% of fouling reduction) is always constant.

• Proceedings of the Korea Society for Simulation Conference
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• 2004.05a
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• pp.7-12
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• 2004

공개키 기반 구조(PKI; Public Key Infrastructure)에 필수적인 요소인 인증서의 상태 검증에 있어서 인증서 상태 검증 서버인 OCSP (Online Certificate Status Protocol) 서버는 실시간 상태 검증을 제공한다. 그러나, 서버와 클라이언트의 메시지 인증을 위해 전자 서명을 수행해야 하며, 이 때 사용되는 공개 암호 연산 과정의 복잡성은 동시에 많은 클라이언트의 요청이 발생할 경우에 응답 시간을 크게 지연시킨다는 단점을 가지고 있다. 본 논문에서는 이러한 문제를 해결하기 위한 인증서 상태 검증 서버의 시뮬레이션 모델을 DEVS (Discrete Event system Specification) 방법론을 이용하여 설계하였다. 이 모델은 인증서의 상태 검증을 요청하는 영역에 위치하여 해쉬 함수를 적용한 인증을 수행하도록 구성되었으며, 시뮬레이션 결과는 제시한 방법이 인증서 상태 검증 속도를 증대시켜 결과적으로 사용자의 응답 시간이 감소되는 것을 보여준다.

• Proceedings of the Korean Society of Computer Information Conference
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• 2024.01a
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• pp.339-341
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• 2024

본 논문에서는 전기 자동차 배터리 팩 설계에서 성능 예측을 위해 전산유체해석 및 Long Short-Term Memory (LSTM)를 활용한다. 두 계산 모두의 예측이 상당한 유사성을 나타내며, 전산유체해석은 시스템 유체 역학을 고려한 상세한 물리 모델을 제공하고, LSTM은 시계열 데이터를 기반으로 한 딥러닝 모델로 효과적으로 패턴을 파악, 향후 온도 상승을 예측한다. 결과는 두 접근 모두가 효과적인 예측을 제공하며 향후 전기 자동차 배터리 팩 설계 및 최적화에서 종합적인 접근의 필요성을 강조한다. 특히, LSTM 기반 예측에 소요되는 시간은 계산 유체 역학의 약 25%로, 약 일주일 정도로 빠르게 확인 가능하다. 이는 현대 산업 환경에서 시간적 효율성이 중요한 측면을 강조하며, 계산 유체 역학의 상세한 물리 모델링과 LSTM의 빠른 예측 속도를 결합한 설계 방법론을 제안한다.

• Journal of the Korean earth science society
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• v.41 no.3
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• pp.238-247
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• 2020

This study simulated strong ground motion waveforms in the southern Korean Peninsula, based on the physical earthquake modeling of the Southern California Earthquake Center (SCEC) BroadBand Platform (BBP). Characteristics of intensity attenuation were investigated for M 6.0-7.0 events, incorporating the site effects. The SCEC BBP is software generates broadband (0-10 Hz) ground-motion waveforms for earthquake scenarios. Among five available modeling methods in the v16.5 platform, we used the Song Model. Approximately 50 earthquake scenarios each were simulated for M 6.0, 6.5, and 7.0 events. Representative metrics such as peak ground acceleration (PGA) and peak ground velocity (PGV) were obtained from the synthetic waveforms that were simulated before and after the consideration of site effects (V_S30). They were then empirically converted to distribution of instrumental intensity. The intensity that considers the site effects is amplified at low rather than high V_S30 zones.

• Spatial Information Research
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• v.18 no.5
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• pp.133-142
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• 2010

Many pedestrian or fire evacuation models have been studied last decades for modeling evacuation behaviors or analysing building structures under emergency situations. However, currently developed models do not consider the differences of visibility of pedestrians by obstacles such as furniture, wall, etc. The visibility of pedestrians is considered one of the important factors that affect the evacuation behavior, leading to making simulation results more realistic. In order to incorporate pedestrian's visibility into evacuation simulation, we should be able to give different walking speeds according to differences of visibility. We improved the existing floor field model based on cellular automata in order to implement the visibility. Using the space syntax theory, we showed how we split the indoor spaces depending on the different visibilities created by different levels of structural depths. Then, we improved the algorithm such that pedestrians have different speeds instead of simultaneous movement to other cells. Also, in order for developing a real time simulation system integrated w ith indoor sensors later, we present a process to build a 3D simulator using a spatial DBMS. The proposed algorithm is tested using a campus building.

• Applied Chemistry for Engineering
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• v.9 no.7
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• pp.1079-1084
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• 1998

Reaction kinetics between 4,4'-dihexyl methane diisocyanate($H_{12}MDI$) and n-hexanol in toluene with dibutyltin dilaurate(DBTDL) as catalyst was studied by experimental measurements and mathematical modeling. Experiments were carried out at various temperatures, catalyst concentrations and [NCO]/[OH] ratios, and the reaction kinetics were described by two second-order reactions, the one between NCO and OH leading to urethane and the other between urethane and NCO leading to allophanate. The rate constants were estimated by the Runge-Kutta 4th-order method. Experiments and mathematical simulations showed a good agreement for various experimental conditions. The [allophanate]/[urethane] ratios at 90% conversion of initial NCO were estimated to be over 20% for most conditions employed in the present study, indicating that allophanate formation might significantly affect the properties of urethane polymers.

• Journal of Korean Society of Water and Wastewater
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• v.34 no.3
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• pp.183-190
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• 2020

Although membrane bio-reactor (MBR) has been widely applied for wastewater treatment plants, the membrane fouling problems are still considered as an obstacle to overcome. Thus, many studies and commercial developments on mitigating membrane fouling in MBR have been carried out. Recently, high voltage impulse (HVI) has gained attention for a possible alternative technique for desalting, non-thermal sterilization, bromate-free disinfection and mitigation of membrane fouling. In this study, it was verified if the HVI could be used for mitigation of membrane fouling, particularly the internal pore fouling in MBR. The HVI was applied to the fouled membrane under different conditions of electric fields (E) and contact time (t) of HVI in order to investigate how much of internal pore fouling was reduced. The internal pore fouling resistance (R_f) after HVI induction was reduced as both E and t increased. For example, R_f decreased by 19% when the applied E was 5 kV/cm and t was 80 min. However, the R_f decreased by 71% as the E increased to 15 kV/cm under the same contact time. The correlation between E and t that needed for 20% of R_f reduction was modeled based on kinetics. The model equation, E^1.54t = 1.2 × 10³ was obtained by the membrane filtration data that were obtained with and without HVI induction. The equation states the products of En and t is always constant, which means that the required contact time can be reduced in accordance with the increase of E.