• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.3
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• pp.139-146
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• 2017

In order to understand the efficacy of submerged breakwater constructed for the beach protection, laboratory experiments were carried out by observing the characteristics of flow around a single shore-parallel submerged breakwater. The velocity field near the shoreline was measured by utilizing the LSPIV (Large-Scale Particle Image Velocimetry) technique, and mean surface and wave height distributions were observed around the submerged breakwater, according to various combinations of incident waves and submerged breakwaters. In this experiment, it was found that the mean flow pattern behind the submerged breakwater was determined by the balance among the gradients of mean water surface and excess wave-momentum flux (i.e., radiation stress tensors) which interact with the wave-induced current developed by the gradients on the rear and the side of the submerged breakwater. The divergent and convergent flow patterns behind the submerged breakwater (i.e., accretion and erosion response) of the numerical study of Ranasinghe et al.(2010) were observed in the measured velocity distributions, and their empirical formula mostly agreed with the experimental results. However, for some cases in this experiment, it was difficult to say that the flow pattern was one of them and was agreed with the empirical formula.

• The Journal of Engineering Geology
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• v.24 no.2
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• pp.273-281
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• 2014

In most current seismic design codes, design earthquake ground motions are defined by a reference spectrum, based on bedrock and site amplification factors that quantify the geotechnical dynamic conditions. Earthquake engineering bedrock is the fundamental geotechnical formation where the seismic waves are attenuated without amplification. To better define bedrock in an earthquake engineering context, shear wave velocity ($V_S$ ) data obtained from in-situ seismic tests were examined for several rock strata in Korea; these data were categorized by borehole drilling investigations. The $V_S$ values for most soft rock data in Korea are > 750 m/s, which is the threshold $V_S$ value for identifying engineering bedrock from a strong motion station. Conversely, VS values are < 750 m/s for 60% of $V_S$ data in weathered rock in Korea. Thus, the soft (or harder) rock strata below the weathered rock layer in Korea can be regarded as earthquake engineering bedrock.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.5
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• pp.315-321
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• 2023

Long-span bridges are flexible structures with low natural frequencies and damping ratios, making them susceptible to vibrational serviceability problems. However, the current design guideline of South Korea assumes a uniform threshold of wind speed or vibrational amplitude to assess the occurrence of harmful vibrations, potentially overlooking the complex vibrational patterns observed in long-span bridges. In this study, we propose a pointwise vortex-induced vibration (VIV) detection method using a deep-learning-based signalsegmentation model. Departing from conventional supervised methods of data acquisition and manual labeling, we synthesize training data by generating sinusoidal waves with an envelope to accurately represent VIV. A Fourier synchrosqueezed transform is leveraged to extract time-frequency features, which serve as input data for training a bidirectional long short-term memory model. The effectiveness of the model trained on synthetic VIV data is demonstrated through a comparison with its counterpart trained on manually labeled real datasets from an actual cable-supported bridge.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2022.05a
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• pp.288-290
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• 2022

As part of the SOC digitization for smart water management and flood prevention, the government reported that automatic and remote control system for drainage facilities (180 billion won) to 57% of national rivers and established a real-time monitoring system (30 billion won). In addition, they were also planning to establish a smart dam safety management system (15 billion won) based on big data at 11 regions. Therefore, research is needed for smart water management and flood prevention system that can accurately calculate the flow rate through real-time flow rate measurement of rivers. In particular, the most important thing to improve the system implementation and accuracy is to ensure the accuracy of real-time flow rate measurements. To this end, radar sensors for measuring the flow rate of electromagnetic waves in the United States and Europe have been introduced and applied to the system in Korea, but demand for improvement of the system continues due to high price range and performance. Consequently, we would like to propose an improved flow rate measurement and flood forecast system by developing a radar sensor for measuring the electromagnetic surface current meter for real-time flow rate measurement.

• Journal of Korean Port Research
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• v.11 no.2
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• pp.231-240
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• 1997

In the United States, a number of ocean outfalls discharge primary treated effluent into deep sea water and contribute for more efficient wastewater treatment. The long multiport diffuser connected by long pipe from a treatment plant discharge wastewater into deep water due to the steep slope of the sea bed. However, Plume discharged from the diffuser can have significant impacts on coastal communities and possibly immediate consequence on public health. Therefore, there have been growing interests about the dynamics of plume in the vicinity of the ocean outfalls. It is expected that the ocean outfall should be considered for more efficient and reliable wastewater treatments as soon as possible around coastal area in South Korea. A number of studies of plume ynamics have used various models to predict plume behavior. However, in many cases, the calculated values of plume behavior are in significantly poor agreement with realistic values. Therefore, in this study, it is recommended that improvements should be made in the application of the plume model to more simulate the actual discharge characteristics and ocean conditions. It should be noted that input parameters in plume models reflect realistic ocean conditions like waves as well as currents. In this study, as one of the new parameters, current and long wave-influenced plume rise and initial dilution have been taken into account by using simple linear wave theory under some specific assumptions for more reliable plume behavior description. Among the improved plume models approved by EPA (Environmental Protection Agency), the RSB(Roberts-Snyder-Baurngartner) and UM(Updated Merge) models were chosen for the calculation of plume behavior, and the variation calculated by both models on the basis of long period wave was compared in terms of plume rise and initial dilution.

• Journal of electromagnetic engineering and science
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• v.1 no.1
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• pp.73-77
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• 2001

We studied the fabrication of GaAs-based pseudomorphic high electron mobility transistors(PHEMT`s) for the purpose of millimeter- wave applications. To fabricate the high performance GaAs-based PHEMT`s, we performed the simulation to analyze the designed epitaxial-structures. Each unit processes, such as 0.1 m$\mu$$\Gamma$-gate lithography, silicon nitride passivation and air-bridge process were developed to achieve high performance device characteristics. The DC characteristics of the PHEMT`s were measured at a 70 $\mu$m unit gate width of 2 gate fingers, and showed a good pinch-off property ($V_p$= -1.75 V) and a drain-source saturation current density ($I_{dss}$) of 450 mA/mm. Maximum extrinsic transconductance $(g_m)$ was 363.6 mS/mm at $V_{gs}$ = -0.7 V, $V_{ds}$ = 1.5 V, and $I_{ds}$ =0.5 $I_{dss}$. The RF measurements were performed in the frequency range of 1.0~50 GHz. For this measurement, the drain and gate voltage were 1.5 V and -0.7 V, respectively. At 50 GHz, 9.2 dB of maximum stable gain (MSG) and 3.2 dB of $S_{21}$ gain were obtained, respectively. A current gain cut-off frequency $(f_T)$ of 106 GHz and a maximum frequency of oscillation $(f_{max})$ of 160 GHz were achieved from the fabricated PHEMT\\`s of 0.1 m$\mu$ gate length.h.

• Korean Journal of Social Welfare Studies
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• v.47 no.1
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• pp.151-178
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• 2016

The primary goal of the current study was to investigate the longitudinal relationship between household income, main caregiver depression, and youth aggression from the interactionist perspective. The data were derived by combining the 2006, 2009 and 2012 survey waves from the Korean Welfare Panel Study. This data set covered the full span of adolescence from elementary to high school. The study utilized 561 families as the final sample and conducted autoregressive cross-lagged analysis. As a result, the early income status, main caregiver depression and youth aggression were likely maintained over time. Second, the results provided support for a reciprocal relationship between income and main caregiver depression. On the other hand, the reciprocal relationship between main caregiver depression and youth aggression was not found in the current study. Finally, the mediating effect of main caregiver depression between income and youth aggression was not found in the present study. In conclusion, the results of this study support the interactionist model in that the association between family income and main caregiver depression involves reciprocity and mutual influence across time. These findings have major implications for policy and interventions in regards to low-income families.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.3
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• pp.624-629
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• 2018

The current study was conducted to develop a portable composite gas detector allowing the detection of both $CO_2$ and $CH_4$ gases by means of the Non Dispersive Infra-Red (NDIR) method. The gas detector is configured to radiate infrared waves using infrared lamps, where the wavelength of the infrared light is reduced due to absorption throughout the chamber, and this reduction (absorption) is detected by the absorption detector, before being converted and amplified to a 3.5V~6V electrical signal, providing as accurate a measurement as possible. The conventional singe sensor method measures the relative measurement by absorbing only specified wavelengths of infrared radiation, which in the case of gas detection leads to problems with accuracy due to the lack of a reference sensor when detecting light with a wavelength of only $4.26{\mu}m$. The dual sensor employed in this study provides a comparative measurement between the reference value derived from the wavelength of $3.91{\mu}m$, which is not influenced by other gas sources, and the measurement value derived from the wavelength of $4.26{\mu}m$, in order to reduce the errors and enhance the reliability, thereby allowing low power consumption for portable devices and multi-gas detection for both $CO_2$ and $CH_4$ gases. The portable composite gas detector developed herein provides a measurement rage of 0ppm~5,000ppm for $CO_2$ gas, and 0.5%vol for $CH_4$, which allows the determination of whether the $CO_2$ and $CH_4$ contents in indoor air are less than 1,000ppm or not. The current study established that the composite gas detector can be interlinked with firefighting appliances through portable devices or home automation, and is anticipated to be very effective in fire prevention.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.6
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• pp.561-568
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• 2020

Wave measurements using X-band radar have many advantages compared to other wave gauges including wave-rider buoy, P-u-v gauge and Acoustic Doppler Current Profiler (ADCP), etc.. For example, radar system has no risk of loss/damage in bad weather conditions, low maintenance cost, and provides spatial distribution of waves from deep to shallow water. This paper presents new methods for estimating significant wave heights of X-band marine radar images using Artificial Neural Network (ANN). We compared the time series of estimated significant wave heights (Hs) using various estimation methods, such as signal-to-noise ratio (${\sqrt{SNR}}$), both and ${\sqrt{SNR}}$ the peak period (TP), and ANN with 3 parameters (${\sqrt{SNR}}$, TP, and Rval > k). The estimated significant wave heights of the X-band images were compared with wave measurement using ADCP(AWC: Acoustic Wave and Current Profiler) at Hujeong Beach, Uljin, Korea. Estimation of Hs using ANN with 3 parameters (${\sqrt{SNR}}$, TP, and Rval > k) yields best result.

• Journal of Wetlands Research
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• v.15 no.3
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• pp.423-430
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• 2013

An algorithm to allow shoreline movement during numerical experiment on sediment transport, deposition or resuspension for general coastal morphology is proposed here. The bed slope near shoreline, i.e. mean sea level, is influenced by bed material, tidal current, waves, and wave-induced current, but has been reported to remain within a stable range. Its annual variation is not large, either. The algorithm is adjusting the bathymetry, if the largest bed slope within shoreline band exceeds a given bed slope due to continuous erosion at zones below the shoreline. This algorithm automatically describes retreat of shoreline caused by erosion, when used within a numerical system. The algorithm was tested to a situation which includes a continuous dredging at a point, and showed satisfactory development of concentric circle contours. Next, the algorithm was tested to another situation which includes sinking of eroded part of bed plate, and produced satisfactory results, too. Finally, the algorithm was tested to a movable-bed laboratory experimental conditions. The shoreline movement behind detached breakwater was reasonably reproduced with this algorithm.