• The Journal of the Acoustical Society of Korea
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• v.34 no.1
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• pp.36-45
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• 2015

Recently, a lot of studies have been made about the methods used to generate turbulent velocity fields stochastically in order to effectively predict broadband flow noise. Among them, the FRPM (Fast Random Particle Mesh) method which generates turbulence with specific statistical properties using turbulence kinetic energy and dissipation obtained from the steady solution of the RANS (Reynolds Averaged Navier-Stokes) equations has been successfully applied. However, the FRPM method cannot be applied to the flow noise problems involving intrinsic unsteady characteristics such as centrifugal fan. In this paper, to effectively predict the broadband noise generated by centrifugal fan, U-FRPM (unsteady FRPM) method is developed by extending the FRPM method to be combined with the unsteady numerical solutions of the unsteady RANS equations to generate the turbulence considered as broadband noise sources. Firstly, an unsteady flow field is obtained from the unsteady RANS equations through CFD (Computational Fluid Dynamics). Then, noise sources are generated using the U-FRPM method combined with acoustic analogy. Finally, the linear propagation model which is realized through BEM (Boundary Element Method) is combined with the generated sources to predict broadband noise at the listeners' position. The proposed technique is validated to compare its prediction result with the measured data.

• KEPCO Journal on Electric Power and Energy
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• v.1 no.1
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• pp.181-188
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• 2015

The non-contact permanent magnet gear has advantages of high efficiency and improved reliability. It has other advantages of no mechanical friction loss, very little noise and vibration, and no need for lubricant. With these advantages, the non-contact permanent magnet gear that solves the physical contact problem of the mechanical gear has drawn attention. Due to this unique non-contact characteristic, the non-contact permanent magnet gear which is capable of non-contact torque transmission has replaced mechanical gear. The mechanical gears which is in many fields of the modern industry, is used mostly for power transmitting mechanical devices. However, it also has the problem of a low torque density, which requires improvement. In this paper, a novel pole piece shape is proposed in order to improve the problem of low torque density of the non-contact permanent magnet gear. The experiment data required for predicting the relationships among them are obtained using finiteelement Operating method based on two-dimensional (2-D) numerical analysis. Therefore, this paper derived an optimal model for thenon-contact permanent magnet gear with the novel pole piece using the Box-Behnken design, and the validity of the optimal design of the proposed pole piece shape through variance analysis and regression analysis demonstrated. In this paper, we performed the thransfer torque analysis in order to improve the torque density and power density, we have performed on optimal design of proposed pole piece shape using box-behnken.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.8
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• pp.64-71
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• 2017

A damage estimation method is presented for jacket-type support structure of offshore wind turbine using a change of modal properties due to damage and committee of neural networks for effective structural health monitoring. For more practical monitoring, it is necessary to monitor the critical and prospective damaged members with a limited number of measurement locations. That is, many data channels and sensors are needed to identify all the members appropriately because the jacket-type support structure has many members. This is inappropriate considering economical and practical health monitoring. Therefore, intensive damage estimation for the critical members using a limited number of the measurement locations is carried out in this study. An analytical model for a jacket-type support structure which can be applied for a 5 MW offshore wind turbine is established, and a training pattern is generated using the numerical simulations. Twenty damage cases are estimated using the proposed method. The identified damage locations and severities agree reasonably well with the exact values and the accuracy of the estimation can be improved by applying the committee of neural networks. A verification experiment is carried out, and the damage arising in 3 damage cases is reasonably identified.

• Journal of Digital Convergence
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• v.19 no.10
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• pp.195-202
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• 2021

The purpose of this study is to classify national ships into passenger ships, cargo ships, oil tankers, tugboats, barges, and other ships by use, and compare the rate of change and direction respectively. In this study, a total of 123 monthly data were searched from January 2011 to March 2021 in Statistics Korea's KOSIS "Traffic Logistics => Operating Vessel Statistics => Possesion State of National Vessels". To this end, we calculated the rate of change from the previous month for each ship and performed numerical analysis and model analysis. In the correlation analysis, the Total showed a high relationship in the order of Towing, Barge, Oil, Cargo and Ferry. In the regression analysis, each ship was found to be statistically significant and varied independently of each other. The increase rate was highest in the order of Ferry, Oil, Towing, Barge and Cargo during the last analysis period. In the analysis of Scatter Charts, Towing and Barge showed more than a certain level of synchronization with respect to the Total. The synchronization phenomenon for each ships was calculated to be rather low, indicating that the correlation between each ships was low. However, the correlation between Oil and Towing, Oil and Barge and Towing and Barge is relatively high, indicating a relatively large correlation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.142-149
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• 2019

In this study, the past erosion history and current status in the CHUNG-UI beach of Eulwang-dong, Jung-gu, Incheon-Si, South Korea were investigated and analyzed the wave with wave-induced current to investigate the causes of coastal erosion. As a result, the significant wave height ($H_{1/3}$) was in the range of 0.07~1.57 m and the mean value was 0.21 m. The maximum wave height ($H_{max}$) was in the range of 0.02-4.76m and the mean value was 0.27m. The vertical wave height and cycles were estimated through numerical model experiments of wave transformation. The 50-year frequency design wave height ranged from 0.82m to 3.75m. As a result of the experiment of wave-induced current, wave-induced current in the CHUNG-UI beach was decreased after the installation of the Detached breakwater and the Jetty. On the other hand, when the crest elevation was increased up to 5 m, there was no significant change, but when the crest elevation was increased to 8m, strong wave-induced current occurred around the submerged breakwaters due to lowered depth of water. In addition, the main erosion of the CHUNG-UI beach is due to the intensive invasion of the wave characteristics coming from the outer sea into the white sandy beach. The deformation of the wave centered on the front of the sandy beach caused additional longshore currents flowing parallel to the sandy beach and rip currents in the transverse direction, thus confirming that the longshore sediment was moved out of the front and out of the sea. The results of this study can be used as preliminary data for the recovery of the sand and the selection of efficient erosion prevention facilities.

• Journal of Climate Change Research
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• v.3 no.1
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• pp.13-24
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• 2012

CCGIS (Climate Change Adaptation Toolkit based on GIS) was developed to use as a tool for the climate change assessment and any relevant tasks involving climate change adaptation policy over Korean peninsula. The main objective of CCGIS is to facilitate an efficient and relevant information for the estimation of climate change vulnerability index by providing key information in the climate change adaptation process. In particular, the atmospheric modeling system implemented in CCGIS, which is composed of climate and meteorological numerical model and the atmospheric environmental models, were used as a tool to generate the climate and environmental IPCC SRES (A2, B1, A1B, A1T, A1FI, and A1 scenarios) climate data for the year of 2000, 2020, 2050, and 2100. This article introduces the components of CCGIS and describes its application to the Korean peninsula. Some examples of the CCGIS and its use for both climate change adaptation and estimation of vulnerability index applied to Korean provinces are presented and discussed here.

• Ecology and Resilient Infrastructure
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• v.7 no.4
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• pp.327-335
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• 2020

The method of selecting an existing flood hazard area via a numerical model requires considerable time and effort. In this regard, this study proposes a method for selecting flood vulnerable areas through topographic analysis based on a surface runoff mechanism to reduce the time and effort required. Flood vulnerable areas based on runoff mechanisms refer to those areas that are advantageous in terms of the flow accumulation characteristics of rainfall-runoff water at the surface, and they generally include lowlands, mild slopes, and rivers. For the analysis, a digital topographic map of the target area (Seoul) was employed. In addition, in the topographic analysis, eight topographic factors were considered, namely, the elevation, slope, profile and plan curvature, topographic wetness index (TWI), stream power index, and the distances from rivers and manholes. Moreover, receiver operating characteristic analysis was conducted between the topographic factors and actual inundation trace data. The results revealed that four topographic factors, namely, elevation, slope, TWI, and distance from manholes, explained the flooded area well. Thus, when a flood vulnerable area is selected, the prioritization method for various factors as proposed in this study can simplify the topographical analytical factors that contribute to flooding.

• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.6
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• pp.1137-1144
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• 2022

In this study, an artificial intelligence(AI) was developed to help with facial expression practice in order to express emotions. The developed AI used multimodal inputs consisting of sentences and facial images for deep neural networks (DNNs). The DNNs calculated similarities between the emotions predicted by the sentences and the emotions predicted by facial images. The user practiced facial expressions based on the situation given by sentences, and the AI provided the user with numerical feedback based on the similarity between the emotion predicted by sentence and the emotion predicted by facial expression. ResNet34 structure was trained on FER2013 public data to predict emotions from facial images. To predict emotions in sentences, KoBERT model was trained in transfer learning manner using the conversational speech dataset for emotion classification opened to the public by AIHub. The DNN that predicts emotions from the facial images demonstrated 65% accuracy, which is comparable to human emotional classification ability. The DNN that predicts emotions from the sentences achieved 90% accuracy. The performance of the developed AI was evaluated through experiments with changing facial expressions in which an ordinary person was participated.

• 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.

• The Journal of Engineering Geology
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• v.32 no.1
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• pp.157-171
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• 2022

Electrical resistivity tomography (ERT) is a traditional and representative geophysical method for determining the resistivity distributions of surrounding soil and rock volumes. Depth resolution profiles and sensitivity distribution sections of the resistivities with respect to various electrode configurations are calculated and investigated using numerical model data. Shallow vertical resolution decreases in the order of Wenner, Schlumberger, and dipole-dipole arrays. A high investigable depth in homogeneous medium is calculated to be 0.11-0.19 times the active electrode spacing, but is counterbalanced by a low vertical resolution. For the application of ERT depth resolution profiles and sensitivity distributions, we provide subsurface structure models for two types of land-creping failure (planar and curved), subvertical fracture, and weathered layer over felsic and mafic igneous rocks. The dipole-dipole configuration appears to be most effective for mapping land-creeping failure planes (especially for curved planes), whereas the Wenner array gives the best resolution of soil horizons and shallow structures in the weathered zone.