• Journal of the Korean Society for Marine Environment & Energy
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• v.19 no.4
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• pp.266-273
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• 2016

Two-dimensional hydraulic experiments were performed to assess the impact of artificial seaweed on wave energy attenuation, and coastal erosion prevention. In this experimental study, erosion geometry and wave reflection coefficients were determined for normal and stormy incident waves, with and without artificial seaweed. The coastline of beaches without artificial vegetation was observed to retreat, and the longshore bar height increased in normal and stormy conditions. Through the introduction of artificial seaweed (of widths 0.8 m, and 1.6 m), the coastline was found to advance in the offshore direction due to material deposition. From these results, it is shown that artificial seaweed alters the cross-section of beaches, such that it is possible to prevent coastline erosion.

• Journal of the Korean Geophysical Society
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• v.2 no.2
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• pp.100-110
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• 1999

In order to find a good seismic source for high-resolution reflection surveys on a tidal flat, characteristic features of several sources were examined through test recording by the walkaway configuration. The sources comprise portable vibrator, 1.2 kg monkey spanner, 4.7 kg sledge hammer, and weight drops with a 30 kg and a 100 kg iron ball, respectively. We analyzed raw and filtered seismic data for the resolution of individual events, then compared various seismic sources to define suitable one for the high-resolution survey in terms of energy level and frequency contents. The study reveals that the portable vibrator is the most suitable source for the detection of and imaging geologic structures less than 20-30 m deep in a tidal flat. We ascribe this to the wide frequency band and high-frequency contents of the portable vibrator. In contrast, the hammer may be an alternative where the target depth increases up to 100 m.

• Economic and Environmental Geology
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• v.38 no.6 s.175
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• pp.623-631
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• 2005

We applied the seismic method to investigate the site characteristics around the Circular Pond (top diameter 7.3 m, bottom diameter 3 m, and depth 4.78 m) at the Ssangsujung Park within the Gongsansung in Gongju. Previous excavations for the cultural assets beneath the Ssangsujung Park disclosed the assumed site of the Palace of the Beakje Dynasty and the Circular Pond containing the Bakje relics. We demonstrated that the seismic prospecting can be applicable to delineate the underground structure around the cultural properties by the three kinds of seismic approaches: walk-away test, conventional refraction method, and equal-distance refraction survey. The last method which is designed by this work ran detect the I-W variations of seismic velocity in the subsurface medium across the Circular Pond on the basis of the difference of the P-wave arrival times between the 1-m-spacing 24 geophones and the corresponding 24 shots parallel with the geophone profile. From the combined results, prominent three-layer velocity structure is observed around the Circular Pond. The bottom layer is interpreted as the basement rock which is exposed near the Ssangsujung whereas the upper layer with relatively lower velocities is interpreted to be the artificial covering. The basement depth beneath the Circular Pond is deeper than the norhern area. The western basement of Circular Pond has the thicker weaker layer compared with the eastern part. Thus, the middle layer could be constructed as the artificial foundation during the Beakje Dynasty. Consequently, the Kong-sansung Circular Pond is possibly built upwardly rather than digging.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.207-218
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• 2013

One of the input parameters in the evaluation of seismic performance of rockfill dams is shear-wave velocity of rock debris and clay core. Reliable evaluation of shear-wave velocity by surface-wave methods requires overcoming the problems of rock-debris discontinuity, material inhomogeneity and sloping boundary. In this paper, for the shear-wave velocity investigation of rockfill dams, SBF (Short-Array Beamforming) technique was proposed using the principles of conventional beamforming technique and adopted to solve limitations of the conventional surface-wave techniques. SBF technique utilizes a 3- to 9-m long measurement array and a far-field source, which allowed the technique to eliminate problems of near-field effects and investigate local anomalies. This paper describes the procedure to investigate shear-wave velocity profile of rockfill dams by SBF technique and IRF (Impulse-response filtration) technique with accuracy and reliability. Validity of the proposed SBF technique was verified by comparisons with downhole tests and CapSASW (Common-Array-Profiling Spectral-Analysis-of-Surface-Waves) tests at a railroad embankment compacted with rock debris.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.237-240
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• 2000

본 연구에서는 한국 동해 대륙붕 해역에서의 주요 해양현상인 수직 수온구조의 단기변동, 수온전선, 그리고 내부파의 변동을 분석하고 이들 변화에 따른 음파의 음장변화를 고찰하였다. 한국 동해항 근해에서 수온의 수직적 변화는 계절적인 변화 이외에 약 2주간의 짧은 기간에도 매우 극적인 변화가 존재함이 실측자료를 통해 밝혀졌다. 1999년 관측된 CTD 자료를 바탕으로 음장 변화를 살펴본 결과 주파수 1kHz, 음원수심 $30{\cal}m$ 인 경우 수신기 수심에 따라 최소 3dB, 최대 10dB까지 차이를 가져올 수 있음을 알 수 있었다. 한국 동해에서 연안과 외해 사이에는 수온전선이 매우 자주 발달하며 여름에 가장 강한 것으로 알려져 있다. 동해항 근해에는 대표적인 수괴인 대마난류수와 북한한류수가 공존하며 이들의 상대적인 세력 변화 때문에 수은(음속)이 거리에 따라 급격하게 변하는 수온전선이 발달할 수 있다. 저주파수 대역 (200Hz)에 대한 간단한 시뮬레이션 결과는 수온전선이 정상적인 분포에 비해서 거리에 따라 7dB 정도의 큰 전파손실을 초래할 수 있음을 보인다. 한국 동해 연안에도 내부파가 존재한다는 사실이 최근 3년간의 연구 결과 밝혀졌다. 내부파는 외해에서 발생하여 대륙단을 거쳐 대륙붕으로 진행해 오면서 내부파 군 (Packets)으로 분산된다. 수직적 변화가 전체 수층의 $14\%$를 차지하는 간단한 형태의 내부파를 가정하여 음장변화를 시물레이션 한 결과 주파수 1 kHz, 음원수심 $20{\cal}m$인 경우 내부파는 수렴구역 형성을 현저하게 방해하여 최대 5dB까지의 차이를 유발하였다. 추후 이에 대한 연구는 내부파 전체의 시,공간적 분포 특성이 구체적으로 규명되면 보다 정확한 음장변화 추정이 이뤄져야 할 것으로 보인다. 또한 내부파와 음파의 상대적인 진행 방향에 따라 음장변화가 크게 다를 것이 예상되므로 이를 규명하기 위해서는 궁극적으로 3차원적인 음장분포 연구가 필요하다. 음향센서를 해저면에 매설할 경우 수충의 수온변화와 센서 주변의 수온변화 사이에는 어느 정도의 시간지연이 존재하게 되므로 이에 대한 영향을 규명하는 것도 센서의 성능예측을 위해서 필요하리라 사료된다.

• Journal of the Korean earth science society
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• v.25 no.4
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• pp.270-276
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• 2004

Multi-channel Analysis of Surface Waves (MASW) and Seismic Cone Penetration Test (SCPT) have been recently developed to obtain S-wave velocity profiles which were conventionally investigated by a down-hole seismic survey. For unconsolidated sedimentary sites, we studied these three methods, and compared the results with a drilling log. All the methods showed that the changes in the S-wave velocities were consistent with the changes in the sedimentary facies. In addition, the SCPT was most sensitive to changes in sedimentary facies among the three profiles. The results of the SCPT showed that there exists a low velocity zone, which is mainly composed of clayey sand, at the depth of 8${\sim}$12m in the sediments.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.20
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• pp.152-162
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• 1975

Five barley varieties were compared under six 1evels of nitrogen fertilization and two methods of cultural management, conventional and drill seeding. The increase in grain yield and nitrogen content of the leaves showed a significant linear regression from added increaments of nitrogen in Haganemugi and Olbori, particulary under drill seeding. The other varieties resulted in various degrees of lodging and no significant increases in yield. The spike number per square meter was the major component of yield, but when the spike number per square meter was sufficient, 1000 grain weight was equally as important as a component of yield.

• Korean Journal of Optics and Photonics
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• v.19 no.3
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• pp.229-236
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• 2008

The optimum conditions of second harmonic generation (SHG) can be successfully achieved experimentally using single pass and double pass methods of a pumping beam. The beam has a power of several Watts radiated by a DOFA (Diode Laser Oscillator & Fiber Amplifier) system, which is a high power CW wavelength tunable infrared laser system, in a PPLN (Periodically Poled MgO doped Lithium Niobate) nonlinear crystal. In the case of a single pass method, the parameters are the wavelength of 535 nm for SHG and the output power of 245 mW generated from the pumping input beam with wavelength of 1070 nm and the power of 2.45 W at phase matching temperature of $108.9^{\circ}C$. The conversion efficiency of SHG was 10%. In order to enhance the output of SHG, the double pass method of the SHG system of a PPLN using a concave mirror for the retroreflection and a pair of wedged flat windows for phase compensation was also presented. In this double pass system, we obtained the SHG output beam with the wavelength of 535 nm and the maximum power of 383 mW at optimum phase matching temperature of $108.5^{\circ}C$ by using an incident pumping beam with wavelength of 1070 nm and the power of 2.45 W. The maximum conversion efficiency is 15.6%, which is more than that of the single pass method.

• Explosives and Blasting
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• v.23 no.3
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• pp.27-42
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• 2005

An explosion modeling technique was developed by using the spherical discrete element code, $PFC^{3D}$, which can be used to model the dynamic stress wave propagation phenomenon. The modeling technique is simply based on an idea that the explosion pressure should be applied to a $PFC^{3D}$ particle assembly not in the form of an external force (body force), but in the form of a contact force (surface force). The stress wave propagation modeling was conducted by simulating the experimental approach based on the Hopkinson's effect combined with the spatting phenomenon that had previously been developed to determine the dynamic tensile strength of Inada granite. As a result, the stress wave velocity obtained by the proposed modeling technique was 4167 m/s, which is merely $3\%$ lower than the actual wave velocity of 4300 m/s for an Inada granite.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.6
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• pp.154-159
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• 2010

In this paper, the magnetically shielded room for low magnetic field shielding is designed and measured by fabricated. The size of magnetically shielded room was 3.0[m](W)$\times$3.0[m](L)$\times$3.0[m](H) to enter the industrial measuring instruments and analyzed DC and AC shielding characteristics of magnetic materials with a high permeability and AC shielding characteristics by eddy current of conductive materials. As a results, shielded room dimensions were obtained. To verify the analysis results, magnetically shielded room is fabricated and the calculated results are compared with the measured results. The Measured results show good agreement with calculated results. According to measurements, 5 times of 0.1[Hz] and 86 times of 60[Hz] is achieved at low frequency. The fabricated shielding room can be used as the magnetically shielding room for low magnetic field shielding.