• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.10
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• pp.1737-1743
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• 2008

A weather radar extracts the weather information from the return echoes which consist of scattered electromagnetic wave signals from rain, cloud and dust particles, etc. The characteristics of Doppler weather signal and ground clutter should be analyzed to extract the accurate weather information. However, the conventional symmetric weather Doppler model is somewhat inappropriate in representing various weather situations. Therefore, the improved model is suggested to describe the skewness in the Doppler spectrum model. Using the suggested model, many various weather signals can be simulated efficiently in time and spectral domain according to weather situations, operation environment and system characteristics. This simulation method may be very helpful in verifying the accuracy of the weather information extraction algorithms and developing the new system for further performance improvement.

• Atmosphere
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• v.31 no.4
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• pp.377-394
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• 2021

The recent largest forest fire in the Yeongdong region, Goseung/Okgae fires of 2019 occurred during YangGang wind event. The wind can be locally gusty and extremely dry, particularly in the complex terrain of Yeongdong. These winds can cause and/or rapidly spread wildfires, the threat of which is serious during the dry spring season. This study examines the spatial variability of the surface wind and its coupling with the upper atmospheric wind using the data during the IOP of the Gangwon Yeongdong Wind Experiments (G-WEX) conducted in 2020 and the data during YangGang wind event on 4~5 April 2019. In the case of IOPs, strong wind at the surface with a constant wind direction appears in the mountain area, and weak wind with large variability in wind direction appears from foothill to the coast in the vicinity of Gangneung region. However, in the 2019 event, strong wind at the surface with a constant wind direction appears in the entire region from the mountain to the coast, even with the stronger wind in the coast than in some part of the mountain area. The characteristics of the upper atmospheric wind related with the spatial distribution of surface wind show that during IOPs of G-WEX, a strong downdraft exists near the mountaintop in the level of about 1 to 4 km. However, in the 2019 event a strong downdraft is reinforced, when its location moves toward the coast and descends close to the ground. These downdrafts are generated by the breaking of mountain waves.

• Geomechanics and Engineering
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• v.25 no.2
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• pp.143-157
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• 2021

Expansive soil is the most predominant geologic hazard which shows a large amount of shrinkage and swelling with changes in their moisture content. This study investigates the macro-mechanical and micro-structural behaviours of dredged natural expansive clay from coal mining treated with ordinary Portland cement or hydrated lime addition. The stabilised expansive soil aims for possible reuse as pavement materials. Mechanical testing determined geotechnical engineering properties, including free swelling potential, California bearing ratio, unconfined compressive strength, resilient modulus, and shear wave velocity. The microstructures of treated soils are observed by scanning electron microscopy, x-ray diffraction, and energy dispersive spectroscopy to understand the behaviour of the expansive clay blended with cement and lime. Test results confirmed that cement and lime are effective agents for improving the swelling behaviour and other engineering properties of natural expansive clay. In general, chemical treatments reduce the swelling and increase the strength and modulus of expansive clay, subjected to chemical content and curing time. Scanning electron microscopy analysis can observe the increase in formation of particle clusters with curing period, and x-ray diffraction patterns display hydration and pozzolanic products from chemical particles. The correlations of mechanical properties and microstructures for chemical stabilised expansive clay are recommended.

• Journal of the Korea Society for Simulation
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• v.28 no.2
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• pp.81-88
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• 2019

Since the AESA radar scans and tracks a distant targets or ground, it requires a test field which meets far-field condition before flight test. In order to test beam foaming, targeting, and availability from cluttering and jamming, it is general to build a outdoor roof-lab test site at tens of meters high. However, the site is affected by surrounding terrain, weather, and noise wave and is also requires time, space, and a lot of costs. In order to solve this problem, theoretical near-field beam foaming method has proposed. However, it requires modification of associated hardware in order to construct near-field test configuration. In this paper, we propose near-field beam foaming method which use single LUT in order to calibrate the variation of TRM(transmit-receive module) which consists AESA radar without modification of associated hardware and software. It requires less costs than far-field test and multiple LUT based near-field test, nevertheless it can derives similar experimental results.

• The Journal of the Korea Contents Association
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• v.18 no.11
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• pp.222-235
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• 2018

This study explores the factor which effects user's viewing on online in the situation of increasing viewing via OTT. After analyzing how the amount of news coverage and viewing rate affects user's active viewing, higher the number of views, In case of groundwave programs, if number of news coverage is high, hits of view and the number of comments is also high. While viewing rate, the number of views, the number of comments are independent of each other. In case of TV channels of comprehensive programming and cable TV, there is a interaction effect of viewing rate and the amount of news coverage. This study highlights the importance of the amount of news coverage when viewers is watching video on web.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.11
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• pp.1518-1523
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• 2018

A method for designing a DDQYA fed by a CPW is proposed in this paper. The proposed CPW-fed DDQYA consists of two series-connected strip dipoles, a ground reflector, and a strip-pair director. Instead of the conventional microstrip feed line in which the signal line is located on the substrate opposite to the antenna, a CPW is used because CPW is located on the same side with the antenna, and so the fabrication is easy. The strip-pair director is composed of two horizontally-separated strips, and it is added above the second dipole to enhance the gain in the high frequency region. A prototype of the proposed CPW-fed DDQYA is fabricated on an FR4 substrate. The fabricated antenna has a frequency band of 1.66-3.38 GHz(68.3%) for a voltage standing wave ratio < 2, and measured gain ranges 5.0-7.3 dBi over a frequency band of 1.60-2.90 GHz.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.10a
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• pp.61-62
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• 2016

In this paper, a design method for a compact stepped open slot antenna for an operation in the UWB band is studied. The proposed antenna is miniaturized by inserting L-shaped slots on the ground plane of the stepped open slot antenna through the creation of a resonance in the low frequency, and a strip director is appended to the antenna in order to increase the gain in the middle and high frequency regions. The effects of varying the length of the L-shaped slots, the distance between the director and the slot antenna, and the director length on input reflection coefficient and realized gain characteristics of the proposed antenna are analyzed. The optimized antenna with the size of $30mm{\times}30mm$ is fabricated on an FR4 substrate, and the experiment results show that the antenna has a frequency band of 3.02-11.04 GHz for a VSWR < 2, which assures the operation in the UWB band.

• Korean Journal of Applied Biomechanics
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• v.29 no.2
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• pp.105-112
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• 2019

Objective: The main purpose of this study was to investigate the effects of wearing an ankle weight belt while performing gait in water by focusing on the effect of using ankle weights have on the gait kinematics and the muscle activities for developing optimum training strategies. Method: A total of 10 healthy male university students were recruited for the study. Each participant was instructed to perform 3 gait conditions; normal walking over ground, walking in water chest height, and walking in water chest height while using ankle weights. All walking conditions were set at control speed of $4km/h{\pm}0.05km/h$. The depth of the swimming pool was at 1.3 m, approximately chest height. The motion capture data was recorded using 6 digital cameras and the EMG was recorded using waterproof Mini Wave. From the motion capture data, the following variables were calculated for analysis; double and single support phase (s), swing phase (s), step length (%height), step rate (m/s), ankle, knee, and hip joint angles ($^{\circ}$). From the electromyography the %RVC of the lower limb muscles medial gastrocnemius, rectus femoris, erector spinae, semitendinosus, tibialis anterior, vastus lateralis oblique was calculated. Results: The results show significant differences between the gait time, and step length between the right and left leg. Additionally, the joint angular velocities and gait velocity were significantly affected by the water resistance. As expected, the use of the ankle weights increased all of the lower leg maximum muscle activities except for the lower back muscle. Conclusion: In conclusion, the ankle weights can be shown to stimulate more muscle activity during walking in chest height water and therefore, may be useful for rehabilitation purposes.

• Journal of the Korean Geotechnical Society
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• v.38 no.1
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• pp.5-15
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• 2022

Due to the Pohang earthquakes in 2017, concerns are increasing that Korea is no longer safe from liquefaction, and needs the research to take proper measures for liquefaction. Liquefaction is defined as the loss of shear strength of the ground. In order to solve this problem, many studies, such as composing a liquefaction hazard map using Liquefaction Potential Index (LPI), have been conducted. However, domestic researches on the comparative analysis of liquefaction prediction results are not sufficient. Therefore, in this study, liquefaction hazard maps were composed using the standard penetration test results, shear wave velocity values, and cone penetration test results. After that, the precision was determined by comparing the calculated LPI using the geotechnical information and predicted LPI via spatial interpolation target. Based on the analysis results, the predicted LPI value using geotechnical information is more precise than using calculated LPI value.

• Journal of the Korean Geosynthetics Society
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• v.20 no.4
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• pp.105-112
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• 2021

In the case of harbor structures, it is important to understand the characteristics of structures that are subjected to repeated loads as they are structures that receive repetitive loads such as wave pressure as well as static loads. In this study, the lateral resistance according to the pile embeded depth of the block breakwater reinforced with piles by cyclic lateral loads was obtained through an model experiment. As the depth of embedment of the pile increased, the lateral resistance showed a tendency to increase. As the load was repeated, the gradient of the lateral resistance gradually appeared to be gentle. The bending moment of the rear pile was larger than that of the front pile. The bending moment of piles in the ground was similar to that when the pile head was free in the cohesionless of Broms (1964).