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531 results on '"Kwon, Tae‐Hyuk"'

130. Effect of rheological properties on debris-flow intensity and deposition in large scale flume experiment

Author

Nguyen, Ba-Quang-Vinh, Lee, Ji-Sung, Kim, Yun-Tae, Lee, Seung-Rae, and Kwon, Tae-Hyuk

Subjects
rheological properties, debris-flow deposition, flume test, debris-flow intensities
Abstract

Debris flows are one of the most serious hazards in the mountainous areas. To assess and mitigate the debris-flow hazard, debris- flow intensities and deposition on fans must be estimated. Rheological properties including yield stress and viscosity are major parameters to describe and predict behaviors of debris flow. In the present study, the effect of rheological properties on debris-flow intensities and deposition on fans of natural clay was investigated using large scale flume experiments. The experimental device employed in the tests consists of a tilting ���ume with an inclination 17��, on which a steel tank with a removable gate was installed. A ���nal horizontal plane works as the deposition area. Natural soil samples of different water contents were tested. Rheological properties of soil mixtures were obtained from vane-rheometer tests. Non-linear regression analysis was used to assess the effect of yield stress and viscosity on debris-flow velocity, runout distance, deposited area and deposited volume. We found that the relationship between surface velocity profile and horizontal distance was complicated and could be expressed by sixth order polynomial function. Mean velocity, runout distance, deposited area decreased following a power law with an increase in yield stress and viscosity. Empirical equations were proposed to estimate these properties. The results of laboratory tests compared reasonably well with the results from numerical analysis. The results indicated that yield stress and viscosity play a significant role in the behavior of debris flow.

Published
2019
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131. Roles of barrier location for effective debris flow mitigation: assessment using DAN3D

Author

Choi, Shin-Kyu, Kwon, Tae-Hyuk, Lee, Seung-Rae, and Park, Joon-Young

Subjects
velocity, volume, debris flows, entrainment, debris-flow barrier, location
Abstract

Debris flows can travel at rapid velocities and can cause economic and societal damages. Accordingly, barriers that can dissipate the energy of debris flows are frequently installed as a mitigation measure. However, the effect of barriers on debris-flow behavior is not fully understood. In this study, we used DAN3D to investigate the interactions between a debris flow and barriers, and evaluate the effect of barrier location on debris-flow velocity and volume. We chose a study site in Seoul, Korea, where a debris- flow event occurred in 2011. At the site, we numerically installed a closed-type barrier at four different locations along the flow path in the watershed. We then simulated the debris flow while monitoring debris-flow velocity and volume. The barriers decreased the velocity and volume of the debris flow compared to a simulation with no barrier. In particular, installation of the barrier at the upstream portions of watersheds resulted in the greatest reduction in velocity. Installation of the barrier at downstream portions of watersheds resulted in the greatest deposition of volume. These results contribute to a better understanding of debris-flow behavior associated with the installed barriers as a mitigation measure, and can be used for optimum and efficient design of the debris-flow barriers.

Published
2019
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132. Hillslope evaluation in the vicinity of the Wolsong nuclear power plant after 12th September 2016 Gyeongju earthquake, South Korea

Author

Pradhan, Ananta Man Singh, Lee, Ji-Sung, Lee, Seung-Rae, Kwon, Tae-Hyuk, and Kim, Yun-Tae

Subjects
landslide, hillslope evaluation, Gyeongju earthquake
Abstract

Landslides result not only from the environmental background conditions of slopes but also from triggering factors, such as rainfall and earthquake. Severe landslides and debris flows are common natural disasters in South Korea since it is characterized by high rainfall and rugged topography. A secondary effect of an earthquake could be slope instability. A 5.8-magnitude (ML) earthquake, the most powerful seismic activity since the nation started measuring tremors, struck the historic city of Gyeongju, North Gyeongsan Province, at 20:32:54 KST. The Wolsong nuclear power plant is situated in the foothills of a mountainous area about 26 km SE of the earthquake epicenter. South Korea���s biggest historical earthquake raised the nuclear safety concerns. To assess regional landslide hazard under the conditions of heavy rainfall and after 5.8 ML Gyeongju earthquake, this study, a coupled hydrological model with infinite slope model was used to find the hillslope stability under the roles of rainfall and earthquake.

Published
2019
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140. MOF × Biopolymer: Collaborative Combination of Metal–Organic Framework and Biopolymer for Advanced Anticancer Therapy

Author

Kim, Kibeom, primary, Lee, Sungmin, additional, Jin, Eunji, additional, Palanikumar, L., additional, Lee, Jeong Hyeon, additional, Kim, Jin Chul, additional, Nam, Jung Seung, additional, Jana, Batakrishna, additional, Kwon, Tae-Hyuk, additional, Kwak, Sang Kyu, additional, Choe, Wonyoung, additional, and Ryu, Ja-Hyoung, additional

Published
2019
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146. Characteristics of steady-state propagation of hydraulic fractures in ductileelastic and two-dimensionally confined plate media

Author

Ham, Soo-Min, Kwon, Tae-Hyuk, Ham, Soo-Min, and Kwon, Tae-Hyuk

Abstract

This study explores the steady-state propagation of hydraulic fractures in ductile and elastic media, with anemphasis on time-varying fracture geometry. A series of well-controlled experiments was performed, in whichthe hydraulic fracture propagation behaviors in two-dimensionally confined gelatin plates were monitored whilevarying the gelatin stiffness, fracturingfluid viscosity, and injectionflow rate. In all cases, comet-shaped, bi-wingfractures were initiated, and thefluid pressure responses and fracture geometry, including propagation velocity,length, width, and opening area were analyzed using the acquired time-lapsed images. The fracture propagationinitiated before the peak pressure value, and the initiation pressure increased with the gelatin stiffness, injectionflow rate, and viscosity, however, mainly governed by the elastic stiffness. Contrary to theoretical models, twostates were identified over the course of comet-shaped hydraulic fracture propagation: a transient state in whichthe fracture propagation velocity and fracture width gradually increased, and thereafter, a steady state where thevelocity and width became consistent. As a result, the steady-state propagation velocity was primarily de-termined by theflow rate, and the fracture width in a steady state was proportional to thefluid pressure nor-malized by the medium stiffness, owing to the elastic response. Based on experimental observations, simple butrobust semi-empirical models were suggested to predict the fracture width and propagation velocity in a steadystate.

Published
2019
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147. Non-destructive Monitoring of Dye Depth Profile in Mesoporous TiO2Electrodes of Solar Cells with Micro-SORS

Author

Botteon, Alessandra, Kim, Wang-Hyo, Colombo, Chiara, Realini, Marco, Castiglioni, Chiara, Matousek, Pavel, Kim, Byung-Man, Kwon, Tae-Hyuk, and Conti, Claudia

Abstract

The dye distribution within a photo-electrode is a key parameter in determining the performances of dye-sensitized photon-to-electron conversion devices, such as dye-sensitized solar cells (DSSCs). A traditional, depth profiling investigation by destructive means including cross-sectional sampling is unsuitable for large quality control applications in manufacturing processes. Therefore, a non-destructive monitoring of the dye depth profile is required, which is the first step toward a non-destructive evaluation of the internal degradation of the device in the field. Here, we present a conceptual demonstration of the ability to monitor the dye depth profile within the light active layer of DSSCs by non-destructive means with high chemical specificity using a recently developed non-destructive/non-invasive Raman method, micro-spatially offset Raman spectroscopy (micro-SORS). Micro-SORS is able to probe through turbid materials, providing the molecular identification of compounds located under the surface, without the need of resorting to a cross-sectional analysis. The study was performed on the photo-electrode of DSSCs. This represents the first demonstration of the micro-SORS concept in the solar cell area as well as, more generally, the application of micro-SORS to the thinnest layer to date. A sample set has been prepared with varying concentrations of the dye and the thickness of the matrix consisting of a titanium dioxide layer. The results showed that micro-SORS can unequivocally discriminate between the homogeneous and inhomogeneous dye depth profiles. Moreover, micro-SORS outcomes have been compared with the results obtained with destructive time-of-flight secondary ion mass spectrometry measurements. The results of the two techniques are in good agreement, confirming the reliability of micro-SORS analysis. Therefore, this study is expected to pave the way for establishing a wider and more effective monitoring capability in this important field.

Published
2022
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