• Journal of Wetlands Research
• /
• v.23 no.1
• /
• pp.27-34
• /
• 2021

In this study, the main influencing factors of the occurrence of cyanobacteria at each of the eight Multifunctional weirs were derived using a random forest, and a categorical prediction model based on a Algal bloom warning system was developed. As a result of examining the importance of variables in the random forest, it was found that the upstream points were directly affected by weir operation during the occurrence of cyanobacteria. This means that cyanobacteria can be managed through efficient security management. DO and E.C were indicated as major influencers in midstream. The midstream section is a section where large-scale industrial complexes such as Gumi and Gimcheon are concentrated as well as the emissions of basic environmental facilities have a great influence. During the period of heatwave and drought, E.C increases along with the discharge of environmental facilities discharged from the basin, which promotes the outbreak of cyanobacteria. Those monitoring sites located in the middle and lower streams are areas that are most affected by heat waves and droughts, and therefore require preemptive management in preparation for the outbreak of cyanobacteria caused by drought in summer. Through this study, the characteristics of cyanobacteria at each point were analyzed. It can provide basic data for policy decision-making for customized cyanobacteria management.

• Journal of the Korea Convergence Society
• /
• v.12 no.8
• /
• pp.31-37
• /
• 2021

As the size of buildings increases due to urbanization due to the development of industry, the need to purify the air and maintain a comfortable indoor environment is also increasing. With the development of monitoring technology for refrigeration systems, it has become possible to manage the amount of electricity consumed in buildings. In particular, refrigeration systems account for about 40% of power consumption in commercial buildings. Therefore, in order to develop the refrigeration system failure diagnosis algorithm in this study, the purpose of this study was to understand the structure of the refrigeration system, collect and analyze data generated during the operation of the refrigeration system, and quickly detect and classify failure situations with various types and severity . In particular, in order to improve the classification accuracy of failure types that are difficult to classify, a three-step diagnosis and classification algorithm was developed and proposed. A model based on SVM and LGBM was presented as a classification model suitable for each stage after a number of experiments and hyper-parameter optimization process. In this study, the characteristics affecting failure were preserved as much as possible, and all failure types, including refrigerant-related failures, which had been difficult in previous studies, were derived with excellent results.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.24 no.5
• /
• pp.43-55
• /
• 2020

The effect of cutted pin in front of pin-fin array was analyzed for increasing the cooling performance of gas turbine blade. The numerical simulations were conducted to figure out the flow and thermal characteristics. The base case which is staggered pin-fin array, cut pin case 1 which has X₂/D_p=1.25 cut pin and cut pin case 2 which has X₃/D_p=1.75 cut pin were compared. The results showed that cut pin increases the strength of the horseshoe vortex which occurred at the leading edge of pin-fin array. Furthermore, the wake effect is reduced at the trailing edge of pin-fin array. As a result, the heat transfer distribution on the endwall increases. However, the friction factor increases owing to the installation of cut pin, but the thermal performance factor is increased maximum 23.8% in cut pin case 2. Therefore, installation of cut pin will be helpful for increasing the cooling performance of pin-fin array of gas turbine blade.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.41 no.6
• /
• pp.697-705
• /
• 2021

Currently, roadway operation agencies provide interior zones of tunnels with emergency information including crash, fire, and vehicles' stop, through state-of-the-art technologies such as variable message signs and radio-based broadcast systems. However, when coping with an emergency in tunnel interior zones, such information could be too late for drivers to access. A radio-based emergency alert system at the access zones of freeway tunnels, on the other hand,could be a good alternative for solving this problem. Therefore, the objective of this study is to assess user acceptability of such an alternative system. To carry out this study, an online survey was conducted on 762 drivers, and the survey results were analyzed using a structural equation modeling to identify factors affecting acceptability of the proposed system. As a result, driver characteristics such as age group, driving frequency, and driving career, utilization of conventional traffic information, and usefulness of conventional traffic information have a positive impact on acceptability. It is expected that the findings of the study will be a basis to effectively address and deploy a new emergency alert system at the access zones of freeway tunnels.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.20 no.6
• /
• pp.14-25
• /
• 2021

With the spread of COVID-19 and the government policy of social distancing, the demand for subways and buses is decreasing, whereas the demand for public bicycles and personal transportation is increasing. Hence, research is needed to understand the characteristics of this phenomenon and to prove the statistical reliability of the correlation between the subway and shared bicycle demands. In this study, the correlation between the number of confirmed COVID-19 cases and the replacement rate of subway and public bicycle demands was examined, but the statistical significance was not significant. However, during the period of September to December 2020, in which the number of confirmed COVID-19 cases in Seoul started to increase rapidly, there was a correlation between the number of confirmed COVID-19 cases and the replacement ratio. If the number of confirmed COVID-19 cases increases by more than a certain number, public bicycles are expected to play a significant role as alternates to the subways. It is expected that the role of public bicycles will increase, and that it is possible to suggest the direction of transportation operation and policy establishment for the continuation of COVID-19 countermeasures in field demonstration after elementary technology development. It is also expected that this study will suggest a direction for future development and policymaking.

• Korean Chemical Engineering Research
• /
• v.60 no.2
• /
• pp.313-319
• /
• 2022

AlGaN/GaN based HfO₂ MOSHEMT (metal oxide semiconductor high electron transistor) with different gate recess depth was simulate to demonstrate a successful normally-off operation of the transistor. Three types of the HEMT structures including a conventional HEMT, a gate-recessed HEMT with 3 nm thick AlGaN layer, and MIS-HEMT without AlGaN layer in the gate region. The conventional HEMT showed a normally-on characteristics with a drain current of 0.35 A at V_G = 0 V and V_DS = 15 V. The recessed HEMT with 3 nm AlGaN layer exhibited a decreased drain current of 0.15 A under the same bias condition due to the decrease of electron concentration in 2DEG (2-dimensional electron gas) channel. For the last HEMT structure, distinctive normally- off behavior of the transistor was observed, and the turn-on voltage was shifted to 0 V.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.35 no.2
• /
• pp.109-117
• /
• 2022

There has been an increasing number of studies on photovoltaic energy generation system in an offshore site with the largest energy generation efficiency, as increasing the researches and developments of renewable energies for use of offshore space and resources to replace existing fossil fuels and resolve environmental challenges. For installation and operation of floating photovoltaic systems in an offshore site with harsher environmental conditions, a stiffness of structural members comprising the total system must be reinforced to inland water spaces as dams, reservoirs etc., which have relatively weak condition. However, there are various limitations for the reinforcement of structural stiffness of the system, including producible size, total mass of the system, economic efficiency, etc. Thus, in this study, a floating breakwater is considered for reducing wave loads on the system and minimizing the reinforcement of the structural members. Wave reduction performances of floating breakwaters are evaluated, considering size and distance to the system. The wave loads on the system are evaluated using the higher-order boundary element method (HOBEM), considering the multi-body effect of buoys. Stresses on structural members are assessed by coupled analyses using the finite element method (FEM), considering the wave loads and hydrodynamic characteristics. As the maximum stresses on each of the cases are reviewed and compared, the effect of floating breakwater for floating photovoltaic system is checked, and it is confirmed that the size of breakwater has a significant effect on structural responses of the system.

• Transactions of the Korean hydrogen and new energy society
• /
• v.32 no.6
• /
• pp.442-454
• /
• 2021

The porous transport layer (PTL) is essential to effectively remove oxygen and hydrogen gas from the electrode surface at high current density operation conditions. In this study, the effect of PTL with different characteristics such as pore size, pore gradient, interfacial coating was investigated by multi-layered sintered mesh. A water electrolysis single cell of active area of the 34.56 cm² was constructed, and IV performance and impedance analysis were conducted in the range of 0 to 2.0 A/cm². It was confirmed that the multi-layered sintered mesh PTL, which have an average pore size of 25 to 57 ㎛ and a larger pore gradient, removed bubbles effectively and thus seemed to improve IV performance. Also, it was confirmed that the catalytic metals such as Ni, NiMo coating on the PTL reduced activation overpotential, but increased mass transport overpotential.

• Journal of the Korea Society of Computer and Information
• /
• v.27 no.3
• /
• pp.71-77
• /
• 2022

In this paper, we propose 1×2 array antenna with dual linear polarization characteristics for mmWave band operation. The proposed antenna is designed two microstirp feeding structure and FR-4 substrate, which is thickness 0.4 mm, and the dielectric constant is 4.3. The size of 1×2 array antenna is 2.33 mm×2.33 mm, and total size of array antenna is 13.0 mm×6.90 mm. From the fabrication and measurement results, bandwidths of 1.13 GHz (28.52~29.65 GHz) for port 1 and 1.08 GHz (28.45~29.53 GHz) for port 2 were obtained based on the impedance bandwidth. Cross polarization ratios are obtained from 7.68 dBi to 16.90 dBi in case of vertical polarization, and from 7.46 dBi to 15.97 dBi in case of horizontal polarization for input port 1, respectively. Also, cross polarization ratios are obtained from 8.59 dBi to 13.72 dBi in case of vertical polarization and from 9.03 dB to 14.0 dB in case of horizontal polarization for input port 2, respectively.

• Journal of the Korean Institute of Landscape Architecture
• /
• v.50 no.2
• /
• pp.102-115
• /
• 2022

The purpose of this study is to present types of design concept based on the specificity of landscape design, and to derive a theoretical framework for the landscape design concepts by analyzing the design concepts appearing in urban park design competitions. Through literature review, five types of landscape design concepts were categorized into value and vision, analysis and interpretation, form and structure, program and element, and process and operation. Using this framework, the design concepts shown in 96 works submitted to 18 domestic and overseas urban park design competitions were analyzed. The results of the analysis are summarized as follows. First, due to the complexity of contemporary urban parks, design concepts are presented as mixtures of main concepts and secondary concepts in multiple layers. Second, it was identified that design concepts of 'form and structure' were used the most in urban park designs, followed by the 'program and element' concepts. The 'value and vision' and 'analysis and interpretive' concepts are introduced as third and fourth. Third, the reason that the 'form and structure' concept is widely used as main and secondary concepts is judged to be because the form of a space, which is the key result of the design, has an important influence on the identity of the design. Fourth, the reason that the 'program and element' concept type is widely introduced is that urban park design has a stronger planning aspect to produce programs during the design process, compared with other design fields where programs are usually given in advance. Lastly, it is difficult to see that the properties of the site solely affect the type of design concept, because a design concept is the result of a complex and creative process in which a designer subjectively interprets the objective characteristics of the site and project, and given design guidelines can affect the type of design concept.