• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.2B
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• pp.163-171
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• 2009

Classical linear models have been generally used to analyze and forecast hydrologic time series. However, there is growing evidence of nonlinear structure in natural phenomena and hydrologic time series associated with their patterns and fluctuations. Therefore, the classical linear techniques for time series analysis and forecasting may not be appropriate for nonlinear processes. In recent, the BDS (Brock-Dechert-Scheinkman) statistic instead of conventional techniques has been used for detecting nonlinearity of time series. The BDS statistic was derived from the statistical properties of the correlation integral which is used to analyze chaotic system and has been effectively used for distinguishing nonlinear structure in dynamic system from random structures. DVS (Deterministic Versus Stochastic) algorithm has been used for detecting chaos and stochastic systems and for forecasting of chaotic system. This study showed the DVS algorithm can be also used for detecting nonlinearity of the time series. In this study, the stochastic and hydrologic time series are analyzed to detect their nonlinearity. The linear and nonlinear stochastic time series generated from ARMA and TAR (Threshold Auto Regressive) models, a daily streamflow at St. Johns river near Cocoa, Florida, USA and Great Salt Lake Volume (GSL) data, Utah, USA are analyzed, daily inflow series of Soyang dam and the results are compared. The results showed the BDS statistic is a powerful tool for distinguishing between linearity and nonlinearity of the time series and DVS plot can be also effectively used for distinguishing the nonlinearity of the time series.

• Journal of the Korean Society for Railway
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• v.15 no.2
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• pp.205-215
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• 2012

The purpose of this research is to identify the factors affecting the intention to adopt a transcontinental railway in Korea. We develop an empirically testable model that demonstrates the effects of factors including cost, service, and efficiency of railway transportation, on modal shift intention to railway, attitude of a Railway, and intention to adopt a Transcontinental Railway (KTAR) as a railway transportation mode in the end. A survey method enables us to analyze the model with a structural equation modeling. The empirical analysis reveals that two most influential factors-the modal shift to railway transportation and the attitude of a Railway-play roles in determining intention to adopt the Transcontinental Railway (KTAR). Of the factors of transportation mode, transportation cost has a greater impact than transportation service and transportation efficiency on the intention to adopt a Transcontinental Railway (KTAR).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.12
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• pp.1000-1006
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• 2009

Integrated Coal Gasification Combined Cycle (IGCC) power plants have been developed to reduce carbon dioxide emissions and to increase the efficiency of electricity generation. A devolatilization process of entrained coal gasification is predicted by CPD model which could describe the devolatilization behavior of rapidly heated coal based on the chemical structure of the coal. This paper is intended to compare the mass release behavior of char, tar and gas(CO, $CO_2,\;H_2O,\;CH_4$) for three different coals. The influence of coal structure on gas evolution is examined over the pressure range of 10${\sim}$30atm.

• 한국연소학회:학술대회논문집
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• 2012.04a
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• pp.231-233
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• 2012

Circulating Fluidized Bed (CFB) is a technically and economically proven technology for boiler systems and large CFB coal boilers are making inroads into the domestic power boiler market. For biomass gasification, it is also considered as a very promising technology for commercial. Due to the lack of experiences of a large scale CFB gasifier, however, any large scale CFB gasifiers are hard to in Korea in spite of fast-growing demand of domestic market. In this study, a 3 $MW_{th}$ CFB gasifier was developed for biomass gasification. The CFB gasifier consists of interconnected fast and bubbling fluidized bed reactors including unique features for in-situ tar removal. Various numerical and experimental approaches will be presented such as basic modeling works, investigation of hydrodynamics with a cold model, computational particle fluid dynamics and experiments in the 3 MWth gasifier.

• Journal of Korea Society of Waste Management
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• v.34 no.7
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• pp.685-696
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• 2017

This study focuses on computational particle fluid dynamics (CPFD) modeling for the fast pyrolysis of biomass in a conical spouted bed reactor. The CPFD simulation was conducted to understand the hydrodynamics, heat transfer, and biomass fast pyrolysis reaction of the conical spouted bed reactor and the multiphase-particle in cell (MP-PIC) model was used to investigate the fast pyrolysis of biomass in a conical spouted bed reactor. A two-stage semi-global kinetics model was applied to model the fast pyrolysis reaction of biomass and the commercial code (Barracuda) was used in simulations. The temperature of solid particles in a conical spouted bed reactor showed a uniform temperature distribution along the reactor height. The yield of fast pyrolysis products from the simulation was compared with the experimental data; the yield of fast pyrolysis products was 74.1wt.% tar, 17.4wt.% gas, and 8.5wt.% char. The comparison of experimental measurements and model predictions shows the model's accuracy. The CPFD simulation results had great potential to aid the future design and optimization of the fast pyrolysis process for biomass.

• Korean Journal of Food Science and Technology
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• v.5 no.2
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• pp.89-94
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• 1973

Discoloration by heating and gamma-radiation of aqueous solutions of two coal-tar food dyes used in meat products was observed. Tartrazin with sodium tri-polyphosphate or cinnamon oil was slightly discolorized by heating at $75^{\circ}C$, but Amaranth was comparatively resistant. Effect of gamma rays of coal-tar food dyes was generally increased with irradiation doses, and especially by the addition of sodium tri-polyphosphate and cinnamon oil. This tendency was higher in Tartrazin than Amaranth. The addition of sodium nitrate and ascorbic acid, and storage at low temperature, however, seems to be effective in decreasing the discoloration of irradiated solutions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.8
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• pp.613-621
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• 2009

Coal is the energy resource which is important with the new remarking energy resource. Coal combustion produces more NOx per unit of energy than any other major combustion technology. Pollutant emission associated with coal combustion will have a huge impact on the environment. Coal conversion has three processes which are drying, coal devolatilization and char oxidation. Coal devolatilization process is important because it has been shown that HCN which is converted from volatile N contributes 60 to 80% of the total NOx produced. This paper addresses mass release behavior of char, tar, gas and HCN in an experiment of Laminar Flow Reactor with two coals such as Roto middle coal (Sub-bituminous) and Anglo coal (Bituminous). The experiment is compared with the data predicted by CPD model for mass release of HCN about Roto south, Indominco, Weris creek and China orch coals. The results show that HCN increases as a function of decreasing the ratio of fixed carbon(FC)/ volatile matter(VM of the coals contain.)

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2898-2903
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• 2008

The coal considerably is the energy resource which is important with the new remarking energy resource. The coal conversion has two processes which are coal devolatilization and char oxidation. Coal devolatilization is important because it describes up to 70% weight loss and has been shown that nitrogen contribute 60 to 80% of the total NOx produced. The chemical percolation devolatilization(CPD) model is used here to describe coal devolatilization. The model was developed to describe coal devolatilization behavior of rapidly heated coal based on characteristics of the chemical structure of the parent coal. This paper describes CPD model in detail and makes an analysis of Shenhua coal(bituminous) which is used calculated 13-C NMR(carbon-nuclear magnetic resonance).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.11a
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• pp.85-88
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• 1995

In this report the large-signal RF performance of GaN MESFETs at different operating temperatures is investigated using a harmonic balance modeling technique. The predicted device performance calculated by the large-si anal model of a GaN FET is shown to be in good agreement with experimen tar data. It is demonstrated that the optimal RF performance of a GaN MESFET amplifier is achieved by balancing the input impedence for a optimized de sign. A GaN MESFET with the optimized design is predicted to produce maximum RF output power of about 4W/mm and 1W/mm at room temperature and 773 K, respectively. The device produces a peak Power-Added Efficiency (PAE) of 52% and 32% at the two temperatures.

• 연구논문집
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• s.27
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• pp.109-118
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• 1997

Kerosene Burner has widely used in domestic heating appliance. Higher combustion efficiency is required to save fuel and clean exhaust gas. The combustion characteristics in kerosene burner highly depends on the performance of evaporating liquid kerosene. And performance of evaporating effect on generation of tar. In this study, flow and heat transfer of kerosene burner is simulated by FLUENT/UNS using unstructured mesh system and discrete phase model to analyze performance of evaporating kerosene liquid. The simulated results show very complicated flow pattern and back flow at the exit of burner.