• Journal of the Korean Society of Propulsion Engineers
• /
• v.17 no.6
• /
• pp.20-29
• /
• 2013

Turbulent flow and combustion characteristics in a micro can combustor with a baffle plate are investigated by a Reynolds Stress Model. In order to examine the geometric effects on the turbulent combusting flow, several baffle configurations are selected. The interrelation between the flow structure and the thermal field are investigated by examing the variation of recirculation region, flame length and heat loss. For the flow mixing, the decreasing air hole is more efficient than the decrease of the fuel hole. As the fuel or air hole diameter decreases, combustion efficiency is enhanced and flame length is decreased. Additionally, as the diameter of air hole decreases, the heat loss and combustion temperature are increased, while they are reduced with decreasing the diameter of fuel hole.

• Korean Chemical Engineering Research
• /
• v.43 no.3
• /
• pp.412-418
• /
• 2005

The tube thickness map of water wall has been measured in a commercial circulating fluidized bed combustor (200 ton steam/hr, $4.97{\times}9.90{\times}28.98m$ height) with ultrasonic method and tube erosion has been discussed. Severe tube erosion took place in the splash region on all waterwalls including wingwalls. Erosion on the lower part of front and rear walls, close to both side walls, was more serious than other places. Erosion of some tubes around the gas exit was found to be noticible. Tube erosion increased on the wingwall as the position of the tube become closer to the center of the combustor crosssection.

• The Journal of the Acoustical Society of Korea
• /
• v.42 no.5
• /
• pp.395-401
• /
• 2023

Sound Event Detection (SED) aims to identify not only sound category but also time interval for target sounds in an audio waveform. It is a critical technique in field of acoustic surveillance system and monitoring system. Recently, various models have introduced through Detection and Classification of Acoustic Scenes and Events (DCASE) Task 4. This paper explored how to design optimal parameters of DenseNet based model, which has led to outstanding performance in other recognition system. In experiment, DenseRNN as an SED model consists of DensNet-BC and bi-directional Gated Recurrent Units (GRU). This model is trained with Mean teacher model. With an event-based f-score, evaluation is performed depending on parameters, related to model architecture as well as model training, under the assessment protocol of DCASE task4. Experimental result shows that the performance goes up and has been saturated to near the best. Also, DenseRNN would be trained more effectively without dropout technique.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.11 no.2
• /
• pp.145-152
• /
• 2023

In this study, microscopic observation was made on the surface of cement paste immersed in an aquatic environment for 100 days at electrochemical treatment to mitigate the leaching of alkali ions. To quantitatively rank the hydration products, unhydrated grains and porosity in the interfacial region, the backscattered electron(BSE) images were obtained by scanninng electron microscopy. As a result, it was found that the porosity on the surface was significantly reduced by the electrochemical treatment, while unhydrated grains were more or less increased presumably limited hydration reaction under electric charge. At electrochemical treatment, Ca²⁺ ions present in C-S-H gel could be precipitated with OH^- to form Ca(OH)₂ then to lower C-S-H gel and simultaneously to enhance Ca(OH)₂. Substantially, the risk of alkali leaching could be lowered by the limited ionized matrix under electrochemical treatment.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.29 no.3B
• /
• pp.247-257
• /
• 2009

In the present paper, turbulent open-channel flows with alternate vegetated zones are numerically simulated using threedimensional model. The Reynolds-averaged Navier-Stokes Equations are solved with the ${\kappa}-{\varepsilon}$ model. The CFD code developed by Olsen(2004) is used for the present study. For model validation, the partly vegetated channel flows are simulated, and the computed depth-averaged mean velocity and Reynolds stress are compared with measured data in the literature. Comparisons reveal that the present model successfully predicts the mean flow and turbulent structures in vegetated open-channel. However, it is found that the ${\kappa}-{\varepsilon}$ model cannot accurately predict the momentum transfer at the interface between the vegetated zone and the non-vegetated zone. It is because the ${\kappa}-{\varepsilon}$ model is the isotropic turbulence model. Next, the open channel flows with alternate vegetated zones are simulated. The computed mean velocities are compared well with the previously reported measured data. Good agreement between the simulated results and the experimental data was found. Also, the turbulent flows are computed for different densities of vegetation. It is found that the vegetation curves the flow and the meandering flow pattern becomes more obvious with increasing vegetation density. When the vegetation density is 9.97%, the recirculation flows occur at the locations opposite to the vegetation zones. The impacts of vegetation on the flow velocity and the water surface elevation are also investigated.

• Journal of The Korean Association For Science Education
• /
• v.28 no.4
• /
• pp.316-330
• /
• 2008

During the past two decades or so, science (or scientific or scientific & technological) culture has become one of the main themes not only of policy makers but also of science educators. Although, the idea of science culture has been taken as a desirable goal, there is little agreement about what it means and how to measure it. Particularly in Korea, there has been a rapid growth of science culture projects and programs, either by governmental or non-governmental, but with little systemic monitoring and evaluation for its practice. The purpose of this study is, thus, to explore a model of measuring science culture and develop a comprehensive indicator system for it. We reviewed many literatures on definitions of science culture and the surveys for related terms, particularly, of recent national and international surveys (e.g. US Science and Engineering Indicators, Eurobarometer, Japanese Science and Technology Indicators). Based on this review, a model for science culture is proposed and then used to define the Science Culture Indicators (SCI). This model encompasses two dimensions(i.e. individual and social), which are further divided into two aspects (i.e. potential and practice). Each dimension is expected to represent citizen literacy of and national infrastructure of science culture respectively. Each category in this $2{\times}2$ matrix is further divided into several sub-categories. The discussion concerning how the model and the indicators can be used to check the states of science culture at social as well as individual levels will be given with some concrete examples, such as indicators particularly related to science education.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.12 no.4
• /
• pp.248-254
• /
• 2009

Budgets of fresh water, salt, DIP and DIN in the Youngsan river estuary were estimated seasonally in order to clarify the characteristics of material cycling and flux of nutrients with a simple box model. Inflow volumes of freshwater into system was approximately $36.481{\times}10^6{\sim}663.634{\times}10^6m^3/month$ and existing water mass of freshwater in system calculated by salt budget was approximately $2.515{\times}10^6{\sim}5.812{\times}10^6m^3$. Mean residence time of freshwater was calculated to be about 0.26~2.03 day. water exchange $1,248{\times}10^6{\sim}9,489{\times}10^6m^3/month$ assumed with salinity between estuary and adjacent ocean. Inflow mass of DIN and DIN were approximately 76.63~1,149.91 ton/month and 2.91~61.22 ton/month, respectively. Residence times of DIP and DIN were calculated to be 0.45~1.10 day and 0.28~1.92 day, respectively. The ratio of water residence time versus DIP, DIN residence time was calculated that freshwater residence time was longer than DIP, DIN residence time except for summer season. Thus, We assume that circulation of Nutrients in the system will happen rapidly except for summer season. Specially DIP in Winter could assume to outer input source existence because of seawater inflow in system and high DIP concentration in open sea.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.10
• /
• pp.178-184
• /
• 2017

This study was performed on 16 patients diagnosed with tsutsugamushi disease and cerebral infarction from January 2007 to December 2015. An acute cerebral infarction was diagnosed by brain MRI and MRA. Tsutsugamushi disease was diagnosed using a polymerase chain reaction. To distinguish the difference between the generalized cerebral infarction and infarction with tsutsugamushi disease, the blood pressure and body temperature were measured uponadmission. In general, the blood pressure increases during an acute cerebral infarction. Interestingly, in this study, 12 patients showed a systolic blood pressure less than 130 mmHg uponadmission. The location of the cerebral infarction and whether single or multiple cerebral infarction were examined. Thirteen patients had a cerebral infarction in anterior circulation and 3 patients developed in posterior circulation. To evaluate the coagulation disorders, prothrombin time (PT), activated partial thromboplastin time (aPTT), D-dimer, fibrinogen, fibrin degradation product (FDP). D-dimer, which is generally known to increase in an acute cerebral infarction, showed a significant increase in the 13 patients. Fibrin degradation products (FDP) showed a significant increase in 15 patients. The pathophysiological mechanism of tsutsugamushi disease is known as vasculitis, which may result in an endothelial cell injury and proliferation of the endothelial wall, which may lead to a cerebral infarction accompanied by coagulopathy. Without endothelial cell damage and proliferation, a vasospasm caused by vasculitis may cause vasoconstriction and cerebral infarction.

• Journal of Energy Engineering
• /
• v.6 no.1
• /
• pp.58-67
• /
• 1997

In this study numerical computations were performed to predict reacting flow fields of gasification processes of pulverized subbituminous coal in a cylindrical coal gasifier. To check the size effects of particles on flow fields in the gasifier, simulations were performed for five cases with four sizes of particles such as 40 $\mu\textrm{m}$, 60 $\mu\textrm{m}$, 80 $\mu\textrm{m}$ and 100 $\mu\textrm{m}$. Each case has a unique size of particles with one more case that has evenly mixed four sizes of particles. Predictions showed that the gasification which uses coals of the mixed sizes reveals more preferable gas velocity and temperature distributions than that uses coals of a unique size. Predicted gas temperature at the exit of the gasifier ranged 1,400 to 1580$^{\circ}C$, 1,480 to 1,700$^{\circ}C$, 1,600 to 1740$^{\circ}C$, 1630 to 1790$^{\circ}C$ and 1500 to 1680$^{\circ}C$ for particle sizes of 40 $\mu\textrm{m}$, 60 $\mu\textrm{m}$, 80 $\mu\textrm{m}$, 100 $\mu\textrm{m}$ and the evenly mixed four sizes, respectively.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.17 no.1
• /
• pp.200-214
• /
• 1993

This paper presents the results of fluidelastic instability analysis performed for the U-tube bundle of a Westinghouse model 51 steam generator, one of the recirculating types designed at an early stage, in which the principal region of external cross-flow is associated with the U-bend portion of tube. The prerequisites for this analysis are detailed informations of the secondary side flow conditions in the steam generator and the free vibration behaviours of the U-tubes. In this study, the three-dimensional two-phase flow field in the steam generator has been calculated employing the ATHOS3 steam generator two-phase flow code and the ANSYS engineering analysis code has been used to calculate the free vibration responses of specific U tubes under consideration. The assessment of the potential instability for the suspect U-tubes, which is the final analysis process of the present work, has been accomplished by combining the secondary side velocity and density distributions obtained from the ATHOS3 prediction with the relative modal displacement and natural frequency data calculated using the ANSYS code. The damping of tubes in two-phase flow has been deduced from the existing experimental data by taking into account the secondary side void fraction effect. In operation of the steam generator, the tube support conditions at the tube-to-tube support plate intersections due to either tube denting degradation or deposition of tube support plate corrosion products or ingression of dregs. Thus, various hypothetical cases regarding the tube support conditions at the tube-to-tube support plate intersections have been considered to investigate the clamped support effects on the forced vibration response of the tube. Also, the effect of anti-vibration bars support in the curved portion of tube has been examined.