• Journal of Korean Society of Forest Science
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• v.107 no.2
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• pp.140-150
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• 2018

For the estimation of greenhouse gas dynamics in forests, it is useful to use a model which simulates both carbon (C) and nitrogen (N) cycle simultaneously. A forest C model, called FBDC, was developed and validated in Korea. However, studies on development of forest N model are insufficient. This study aimed to suggest a development process of a forest C and N model. We analyzed the general features, structures, ecological processes, input data, output data, and methods of integrating C and N cycles of the VISIT, Biome-BGC, Forest-DNDC, and O-CN. The structure and features of the FBDC were also analyzed. The VISIT was developed by integrating forest C model with a N cycle module, and the new model also could be designed by combining the FBDC with a N cycle module. The VISIT and Forest-DNDC could estimate soil $N_2O$ emissions, and the integrated model should include the processes shared by these models. Especially, the overseas models linked C and N cycles based on N absorption, C absorption, and decomposition of dead organic matter. Therefore, the integration of the FBDC with N cycle module should apply this linkage of structures between C and N cycles. Climate, soil texture, and species distribution data, which are essential for the model development, were available in Korea. However, parameter data associated with N cycle and validation data for soil $N_2O$ emissions need to be obtained by field studies.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.4
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• pp.500-507
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• 2010

Regard to the global warming, the shipping industries are progressed the dedicated endeavor to reduce greenhouse gas. As the study results of 2009 GHG study team, the $CO_2$ emission of shipping industries exceeded slightly 1.0 billion ton during one year(2007) and it is 3.3% of total $CO_2$ amount exhausted from all industries. This paper are introduced the energy efficiency design index / operation indicator monitoring system(EDiMS) which matched with EVAMOS software released by the dynamics laboratory of Mokpo maritime university. EDiMS can continuously be monitored amounts of $CO_2$, NOx, SOx, and PM emitted from ship and it can be applied as the useful tool of the inventory work of air pollution and the ship energy management plan for the mitigation or reduction of ship emission.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.3
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• pp.173-179
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• 2016

This is a numerical study on the curved channel type of hydrogen reformer using the commercial code of fluid dynamics. We numerically compared the numerical model in a previous study model and the modelling of a tube type curved channel. In the result of numerical analysis on 4 types of curved channel reformers, the methanol conversion efficiency of type 1~4 were 45.0%, 45.3%, 45.6%, 45.6% respectively, and there was hardly any difference by ${\pm}0.6%$. In light of flow characteristics, the rectangle type tube and the type 2 with $45^{\circ}$ turn showed most uniform flow characteristics and concentration distribution of methanol, and the circular type tube and the type 3 with $90^{\circ}$ turn had most un-uniform flow characteristics and concentration distribution of methanol. We concluded that the design for curved channel reformer has to have rectangle type tube with curve of almost $45^{\circ}$ as in the type of curved pipe with $45^{\circ}$ turn.

• Fire Science and Engineering
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• v.27 no.3
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• pp.1-7
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• 2013

The wildland fire intensity and scale are getting bigger owing to climate change in the world. In the case of domestic, the forest is distributed over approximately 63.7 % of country and the main facilities like a industrial facility or gas facility abuts onto it. Therefore there is potential that the wildland fire is developed to a large-scale disaster. In this study, the effect distances of the radiant heat flux from the crown fire are analysed according to the change of wind velocity. The safety criteria concerning the radiant heat flux to influence on the surrounding were researched to analyse the effect distances. The criteria of radiant heat flux were chosen $5kW/m^2$, $12.5kW/m^2$, $37.5kW/m^2$. WFDS, which is an extension of NIST's Fire Dynamics Simulator, was used to consequence analysis of the forest fire. In order to apply the analysis conditions, it is researched the forest conditions that is generally distributed in domestic region. As the result, the maximum effect distances by radiant heat were showed at the horizontal and vertical direction. When the wind velocity varied from 0 to 10 m/s, the maximum effect distance increased as the wind velocity increases. Interesting point is that the maximum effect distance were shown at the wind velocity of 8 m/s. The maximum effect distance was decreased according as the fuel moisture of trees increase. This study can contribute to analyse quantitative risk about the damage effect of the surrounding facilities caused by wildland fire.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.5
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• pp.563-569
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• 2012

The superheater and reheater tubes of a heavy-load fossil power plant boiler can be damaged by overheating, and therefore, the degree of overheating is assessed by measuring the oxide scale thickness inside the tube during outages. The tube temperature prediction from the oxide scale thickness measurement is necessarily accompanied by destructive tube sampling, and the result of tube temperature prediction cannot be expected to be accurate unless the selection of the overheated point is precise and the initial-operation tube temperature has been obtained. In contrast, if the tube temperature is to be predicted analytically, considerable effort (to carry out the analysis of combustion, radiation, convection heat transfer, and turbulence fluid dynamics of the gas outside the tube) is required. In addition, in the case of analytical tube temperature prediction, load changes, variations in the fuel composition, and operation mode changes are hardly considered, thus impeding the continuous monitoring of the tube temperature. This paper proposes a method for the short-term prediction of tube temperature; the method involves the use of boiler operation information and flow-network-analysis-based tube heat flux. This method can help in high-temperaturedamage monitoring when it is integrated with a practical tube-damage-assessment method such as the Larson-Miller Parameter.

• Korean Chemical Engineering Research
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• v.59 no.3
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• pp.417-428
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• 2021

The combustion characteristics of anthracite, which follow a complex process with low reactivity, must be considered through the dynamic behavior of circulating fluidized bed (CFB) boilers. In this study, computational fluid dynamics (CFD) simulation was performed to analyze the combustion characteristics of anthracite in a pilot scale 0.1 MW_th Oxy-fuel circulating fluidized bed (Oxy-CFB) boiler. The 0.1MW_th Oxy-CFB boiler is composed of combustor (0.15 m l.D., 10 m High), cyclone, return leg, and so on. To perform CFD analysis, a 3D simulation model reactor was designed and used. The anthracite used in the experiment has an average particle size of 1,070 ㎛ and a density of 2,326 kg/m³. The flow pattern of gas-solids inside the reactor according to the change of combustion environment from air combustion to oxygen combustion was investigated. At this time, it was found that the temperature distribution in air combustion and oxygen combustion showed a similar pattern, but the pressure distribution was lower in oxygen combustion. addition, since it has a higher CO₂ concentration in oxygen combustion than in air combustion, it can be expected that carbon dioxide capture will take place actively. As a result, it was confirmed that this study can contribute to the optimized design and operation of a circulating fluidized bed reactor using anthracite.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.4
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• pp.468-475
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• 2019

An end-line flame arrester allows free venting in combination with flame protection for vertical vent applications. End-line flame arresters are employed in various fields, especially in shipping. In flame arresters, springs are essential parts because the spring load and the spring's elasticity determine the hood opening moment. In addition, the spring has to work under a high-temperature condition because of the burning gas flame. Therefore, it is necessary to analyze the mechanical load and elasticity of the spring when the flame starts to appear. Based on simulations of the working process of a specific end-line flame arrester, a thermal and structural analysis of the spring is performed. A three-dimensional model of a burned spring is built using computational fluid dynamics (CFD) simulation. Results of the CFD analysis are input into a finite element method simulation to analyze the spring structure. The research team focused on three cases of spring loads: 43, 93, and 56 kg, correspondingly, at 150 mm of spring deflection. Consequently, the spring load was reduced by 10 kg after 5 min under a $1,000^{\circ}C$ heat condition. The simulation results can be used to predict and estimate the spring's load and elasticity at the burning time variation. Moreover, the obtained outcome can provide the industry with references to optimize the design of the spring as well as that of the flame arrester.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.2
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• pp.406-413
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• 2022

The subsea pipeline pre-commissioning stage consists of the following processes: Flooding, Venting, Hydrotesting, Dewatering, Drying, and N2 Purging. Among these processes, drying and nitrogen purging processes are stipulated to reduce and maintain the relative humidity below dew point to prevent the generation of hydrate and the risk of gas explosion in the pipeline during operation. The purpose of this study is to develop an analysis method for the air drying and nitrogen purging process during pre-commissioning of the subsea pipeline, and to evaluate the applicability of the analysis method through comparison with on-site measurement results. An analysis method using Computational Fluid Dynamics (CFD) was introduced and applied as a method for evaluating the relative humidity inside a subsea pipeline, and it was confirmed that analysis results were in good agreement with the on-site measurement results for the air drying and nitrogen purging process of the offshore pipeline. If the developed air drying and nitrogen purging analysis method are used as pre-engineering tools for pre-commissioning of subsea pipelines in the future, it is expected to have a significant impact on the improvement of work productivity.

• Animal Bioscience
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• v.35 no.11
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• pp.1698-1710
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• 2022

Objective: Raw potato starch (RPS) is resistant to digestion, escapes absorption, and is metabolized by intestinal microflora in the large intestine and acts as their energy source. In this study, we compared the effect of different concentrations of RPS on the intestinal bacterial community of weaned piglets. Methods: Male weaned piglets (25-days-old, 7.03±0.49 kg) were either fed a corn/soybean-based control diet (CON, n = 6) or two treatment diets supplemented with 5% RPS (RPS5, n = 4) or 10% RPS (RPS10, n = 4) for 20 days and their fecal samples were collected. The day 0 and 20 samples were analyzed using a 16S rRNA gene sequencing technology, followed by total genomic DNA extraction, library construction, and high-throughput sequencing. After statistical analysis, five phyla and 45 genera accounting for over 0.5% of the reads in any of the three groups were further analyzed. Furthermore, short-chain fatty acids (SCFAs) in the day 20 fecal samples were analyzed using gas chromatography. Results: Significant changes were not observed in the bacterial composition at the phylum level even after 20 d post feeding (dpf); however, the abundance of Intestinimonas and Barnesiella decreased in both RPS treatment groups compared to the CON group. Consumption of 5% RPS increased the abundance of Roseburia (p<0.05) and decreased the abundance of Clostridium (p<0.01) and Mediterraneibacter (p< 0.05). In contrast, consumption of 10% RPS increased the abundance of Olsenella (p<0.05) and decreased the abundance of Campylobacter (p<0.05), Kineothrix (p<0.05), Paraprevotella (p<0.05), and Vallitalea (p<0.05). Additionally, acetate (p<0.01), butyrate (p<0.05), valerate (p = 0.01), and total SCFAs (p = 0.01) were upregulated in the RPS5 treatment group Conclusion: Feeding 5% RPS altered bacterial community composition and promoted gut health in weaned piglets. Thus, resistant starch as a feed additive may prevent diarrhea in piglets during weaning.

• Advances in aircraft and spacecraft science
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• v.9 no.5
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• pp.415-431
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• 2022

Secondary flows have a huge impact on losses generation in modern low pressure gas turbines (LPTs). At design point, the interaction of the blade profile with the end-wall boundary layer is responsible for up to 40% of total losses. Therefore, predicting accurately the end-wall flow field in a LPT is extremely important in the industrial design phase. Since the inlet boundary layer profile is one of the factors which most affects the evolution of secondary flows, the first main objective of the present work is to investigate the impact of two different inlet conditions on the end-wall flow field of the T106A, a well known LPT cascade. The first condition, labeled in the paper as C1, is represented by uniform conditions at the inlet plane and the second, C2, by a flow characterized by a defined inlet boundary layer profile. The code used for the simulations is based on the Discontinuous Galerkin (DG) formulation and solves the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the Spalart Allmaras turbulence model. Secondly, this work aims at estimating the influence of viscosity and turbulence on the T106A end-wall flow field. In order to do so, RANS results are compared with those obtained from an inviscid simulation with a prescribed inlet total pressure profile, which mimics a boundary layer. A comparison between C1 and C2 results highlights an influence of secondary flows on the flow field up to a significant distance from the end-wall. In particular, the C2 end-wall flow field appears to be characterized by greater over turning and under turning angles and higher total pressure losses. Furthermore, the C2 simulated flow field shows good agreement with experimental and numerical data available in literature. The C2 and inviscid Euler computed flow fields, although globally comparable, present evident differences. The cascade passage simulated with inviscid flow is mainly dominated by a single large and homogeneous vortex structure, less stretched in the spanwise direction and closer to the end-wall than vortical structures computed by compressible flow simulation. It is reasonable, then, asserting that for the chosen test case a great part of the secondary flows details is strongly dependent on viscous phenomena and turbulence.