• Journal of Korean Society of Coastal and Ocean Engineers
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• v.33 no.6
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• pp.383-390
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• 2021

The experiments in coastal engineering are very complex and a lot of components should be concerned. The experience has an important role in the successful execution. Hydraulic model experiments have been improved with the development of the wave generator and the advanced measuring apparatus. The hydraulic experiments have the advantage, that is, the stability of coastal structures and the hydraulic characteristics could be observed more intuitively rather than the numerical modelings. However, different experimental results can be drawn depending on the model scale, facilities, apparatus, and experimenters. In this study, two-dimensional hydraulic experiments were performed to suggest the guide of the test wave(random wave) generation, which is the most basic and important factor for the model test. The techniques for generating the random waves with frequency energy spectrum and the range for the incident wave height [(H_S)_M/(H_S)_T = 1~1.05] were suggested. The proposed guide for the test wave generation will contribute to enhancing the reliability of the experimental results in coastal engineering.

• The Journal of Engineering Geology
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• v.31 no.4
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• pp.493-506
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• 2021

Liquefaction refers to a phenomenon in which excessive pore water pressure occurs when a dynamic load such as an earthquake rapidly acts on a loose sandy soil saturated with soil, and the ground loses effective stress and becomes liquefied. The indoor repeated test for liquefaction evaluation can be confirmed through the repeated triaxial compression test and the repeated shear test. In this regard, this study tried to confirm the liquefaction resistance strength according to the relative density and particle size distribution of sand using the repeated triaxial compression test. As a result of the experiment, it was confirmed that the liquefaction resistance strength increased as the relative density increased regardless of the soil classification, and the liquefaction resistance strength according to the particle size distribution of the sand was confirmed that the liquefaction resistance strength of the SP sample close to SW was significantly higher. In addition, as a result of analyzing 30% of fine powder compared to 0% of fine powder, as the relative density increased to 40~70%, the liquefaction resistance strength decreased by 5~20%, and the domestic weathered soil ground had a fine liquefaction resistance strength compared to Jumunjin standard sand. When the minute was 10%, it was measured to be 30% or more, and when the fine particle was 30%, it was measured to be less than 50%.

• Journal of Environmental Impact Assessment
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• v.31 no.6
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• pp.378-387
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• 2022

Since air pollution has become a global issue to be managed, the Republic of Korea (ROC) is protecting air quality by predicting the air condition before a construction project starts through EnvironmentalImpact Assessment (EIA) and measuring the air condition afterwards the construction project ends through Post-environmental Impact Assessment (PEIA). The aim of this study consists on verifying the predicted and measured concentration data and analyzing their consistency in order to deduce improvement directions. Linear EIA projects which the investigation during operation period have been concluded between years 2017 and 2019 were used. As a result, the following improvement directions were suggested: reduction of EIA air quality standards, strengthen the management of projects with construction duration longer than 5 years, incorporation of first or second quarter (winter or spring) into the investigation period, consideration of construction equipment or conditions for better prediction. The strength of this study is that we arranged and utilized EIA predicted and PEIA measured data to understand the present EIA procedure and made meaningful suggestions through the consistency analysis contributing to air quality maintenance and investigation methodology enhancement.

• Applied Chemistry for Engineering
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• v.34 no.1
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• pp.23-29
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• 2023

Microfluidic reactors have been made to achieve significant development for the generation of new functional materials to apply in a variety of fields. Over the last decade, microfluidic reactors have attracted attention as a user-friendly approach that is enabled to control physicochemical parameters such as size, shape, composition, and surface property. Here, we develop a centrifugal microfluidic reactor that can control the flow of fluid based on centrifugal force and generate multifunctional particles of various sizes and compositions. A centrifugal microfluidic reactor is fabricated by combining microneedles, micro- centrifuge tubes, and conical tubes, which are easily obtained in the laboratory. Depending on the experimental control param- eters, including centrifuge rotation speed, alginate concentration, calcium ion concentration, and distance from the needle to the calcium aqueous solution, this strategy not only enables the generation of size-controlled microparticles in a simple and reproducible manner but also achieves scalable production without the use of complicated skills or advanced equipment. Therefore, we believe that this simple strategy could serve as an on-demand platform for a wide range of industrial and academic applications, particularly for the development of advanced smart materials with new functionalities in biomedical engineering.

• Journal of Korea Water Resources Association
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• v.55 no.2
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• pp.135-145
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• 2022

This study aims to verify the Drone utilization and the accuracy of the global navigation satellite system (GNSS), Drone RGB (Photogrammetry) (D-RGB), and Drone LiDAR (D-LiDAR) surveying performance in the downstream reaches of the local stream. The results of the measurement of Ground Control Point (GCP) and Check Point (CP) coordinates confirmed the excellence. This study was carried out by comparing GNSS, D-RGB, and D-LiDAR with the values which the hydraulic characteristics calculated using HEC-RAS model. The accuracy of three survey methods was compared in the area of the study which is the ownership station, to 6 GCP and 3 CP were installed. The comparison results showed that the D-LiDAR survey was excellent. The 100-year frequency design flood discharge was applied in the channel sections of the small stream. As a result of D-RGB surveying 2.30 m and D-LiDAR 1.80 m in the average bed elevation, and D-RGB surveying 4.73 m and D-LiDAR 4.25 m in the average flood condition. It is recommended that the performance of D-LiDAR surveying is efficient method and useful as the surveying technique of the geospatial information using the drone equipment in stream channel.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.84-84
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• 2023

소하천의 유속계측을 위해 가장 많이 사용되고 있는 표면영상유속계는 표면유속을 계측하는데, 계측된 표면유속을 이용하여 유량을 산정하기 위해서는 수심 평균유속으로 변환할 필요가 있다. 이때 평균-표면유속 환산계수가 주로 사용되는데, 적정 환산계수를 산정하기 위해서는 수심별로 유속을 직접 계측하고 계측된 유속분포를 이용하여 평균-표면유속 환산계수를 산정하는 방법을 사용한다. 그러나 소하천은 홍수시 유속이 매우 빨라 물속에 직접 들어가는 것이 어렵고 장비를 이용하여 간접적인 방법으로 계측을 한다고 하더라도 소류사와 유송잡물 등으로 계측기가 파손되어 직접 계측에는 한계가 있다. 또한 직선구간 확보나 식생 등으로 부자를 이용한 계측도 어려워 계측 결과를 이용하여 환산계수를 산정하는 방법은 한계가 있다. 이런 이유로 대부분은 USGS가 제시한 0.85 ~ 0.95 범위 값 중에서 현장 여건을 고려하여 최적값을 결정·사용하고 있다. 본 연구에서는 홍수시 수심-유속분포를 직접 계측하기 어려운 소하천에서 표면영상유속계를 이용하여 계측한 수심별 표면유속분포를 이용하여 평균-표면유속 환산계수를 산정하는 방법을 개발하였다. 개발한 방법을 정량적으로 평가하기 위하여 건설기술연구원의 안동 하천실험시설에서 표면영상유속계로 수심상승에 따른 횡방향 유속분포를 계측하고 수위가 완전히 상승한 이후의 안정된 흐름 조건에서 플로우트래커를 이용하여 수심별 횡방향 유속분포를 계측하여 두 계측결과를 1:1로 비교하였다. 비교 결과 표면영상유속계로 계측한 수심별 표면유속분포와 플로우트래커로 계측한 수심-유속분포 결과는 유사한 분포를 보이는 것으로 나타나 표면영상유속계로 계측한 수심별 표면유속분포를 이용하여 평균-표면유속 환산계수를 산정하는 것이 가능하다는 결론을 도출하였다. 본 연구에서는 개발한 평균-표면유속 환산계수 산정방법의 적용성을 검토하기 위하여 표면영상유속계가 설치된 5개 시범소하천에서 7년(2016~2022)간 계측한 수심별 표면유속 자료를 수집하고 이 결과를 이용하여 평균-표면유속 환산계수를 산정하였다. 산정결과 대부분 USGS가 제시한 범위내의 값을 보이는 것으로 나타나 향후 본 연구의 개발 방법을 평균-표면유속 환산계수 산정에 활용할 수 있을 것으로 판단된다. 본 연구에서는 개발한 환산계수 산정방법은 향후 보다 많은 수리실험과 현장실험 등으로 정밀검증을 수행한다면 홍수시 수심-유속분포를 직접 계측하기 어려운 소하천에서 간편하면서도 적용성이 큰 신기술 확보가 가능할 것으로 기대된다.

• Journal of the Korean Geotechnical Society
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• v.22 no.11
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• pp.89-99
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• 2006

The PCRW (Precast Concrete Retaining Wall) has many advantages compared with cast in place concrete retaining wall : shorter construction period, excellency of quality and minimum interference with the adjacent structure and traffics. However, shallow foundation type of PCRW, which has comparatively better ground condition, has some disadvantages such as difficulty in transportation and higher cost due to the size of PCRW being expanded by resisting only with self-weight if there is no other supplementary reinforcement. The presented study, in order to complement such disadvantages of PCRW, have applied the micropile method. The micropile method has advantages like low-cost and high-efficiency and does not require huge space, because it can be executed with small size equipment. However, the mechanical behavior characteristics of the PCRW reinforced by micropile, which is installed to improve the reinforcement effect, is not yet clearly identified and there is no suggested standard as to the length, diameter, install angle and install position of micropiles. Hence, this method is yet being designed depend on engineer's experience. In this study, various laboratory model tests as to sliding and overturning were performed in order to identify and present the optimum type of reinforcement and reinforcement effect of the PCRW reinforced by micropiles. In addition, it also executed numerical analysis for the purpose of verifying the optimum type of reinforcement for micropiles based on the results of laboratory model tests. The optimum reinforcement type of micropiles was estimated by model test and numerical analysis. The length of micropiles is 0.4 times wall height and the diameter is 0.04 times wall length.

• Journal of the Korean Geotechnical Society
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• v.23 no.2
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• pp.47-60
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• 2007

Conventional active surface wave measurements performed using a transient or continuous source are often limited in the maximum depth of penetration due to the difficulty of generating low-frequency energy with reasonably portable sources. This limitation may inhibit accurate seismic site response calculations because of the inability to define deeper subsurface structure. By measuring surface wave generated by passive sources including microtremors and cultural noise, it is possible to overcome this problem and develop soil stiffness profiles to much larger depth. Reliability of dispersion estimates from the passive surface wave measurements is critical to present reliable shear wave velocity profiles and can be improved by the measurements and analyses of passive surface waves based on correct understanding of systematic errors included in passive dispersion data. In this study, the systematic errors caused by poor wavenumber resolution and energy leakage into sidelobes in passive tests are mainly explored. Recommendations for reliable passive surface wave measurements and dispersion estimates are presented and illustrated at a site in San Jose, California, U.S.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.33-33
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• 2021

예측하기 어려운 복잡한 기후 변화로 인해 수자원 관리측면에서 다양한 방법을 도입하여 해결할 수 있는 방안이 국가적 주요 관심사로 다루어지고 있다. 따라서 투입인력과 소요시간 절감, 장비와 인력진입 불가지역에 대한 정보획득, 높은 공간해상도, 항공측량 대비 높은 경제성 등 다양한 장점의 드론을 이용한 하천지형 특성별 수리특성 분석방안이 필요하다. 본 연구에서는 성연천 하류부지역을 대상으로 위성항법시스템(Global Navigation Satellite System, GNSS) 측량 지형성과와 드론측량(Drone) 지형성과를 지상에 설치된 CHP(Check Point) 좌표 값을 확인하여 두 지형의 정확도를 비교하였으며 HEC-RAS 모형을 이용하여 빈도별 수리특성을 비교 산정하였다. 본 연구는 성연천 하류 480m구간을 선정하고 GNSS를 이용한 실측지형자료와 GCP(Ground Control Point)를 얻기 위해 정확도 검증을 실시하였으며 위성항법시스템(GNSS) 측량과 DRONE RGB측량의 CHP(Check Point) 오차를 비교하여 정확도를 검증하였다. 오차 값이 확인된 위성항법시스템(GNSS)을 이용하여 가상기준점을 선정하고 RTK 모바일스테이션을 설치하여 DRONE LIDAR측량을 통해 지형자료를 취득하였으며 얻어진 지형자료를 HEC-RAS를 통해 입력 후 성연천 하천기본계획에 제시되어진 조도계수와 빈도별 홍수위를 적용하여 연구구간 480m에 대해 100년 빈도의 결과 값을 비교 검토하였다. 100년 빈도 계획 홍수량 조건의 하상과 한계수위의 차에서 위성항법시스템(GNSS) 측량 지형자료를 기준으로 평균수위 측정오차는 드론 RGB 측량 지형자료 0.460m, 드론 LIDAR 측량 지형자료 0.260m의 결과를 얻었으며 동일 조건 흐름하의 평균유속에서 위성항법시스템(GNSS) 측량 지형자료를 기준으로 평균유속 측정오차는 드론 RGB 측량 지형자료 0.40m/s, 드론 LIDAR 측량 지형자료 0.36m/s의 결과를 얻었다. 통수 단면적의 비교 결과는 위성항법시스템(GNSS) 측량 지형자료를 기준으로 드론 RGB 측량 지형자료 전체 단면의 평균오차는 20.20m², 드론 LIDAR 측량 지형자료 전체 단면의 평균오차는 21.68²의 결과를 얻었으며 이상에서와 같이 홍수위와 평균유속, 통수 단면적의 측정오차 비교 결과를 종합할 때 통수 단면적 측정결과는 위성항법시스템(GNSS) 측량과 드론 RGB 측량의 차이가 적었으나 계획 홍수량 조건의 하상과 한계수위 차이와 동일조건 흐름하의 평균유속에서 위성항법시스템(GNSS) 측량과 드론 LIDAR 측량의 차이가 적은 것으로 나타났다. 그리고 통수용량(capacity)(m³) 비교에서는 위성항법시스템(GNSS) 측량을 기준으로 드론 RGB 측량은 약 7644m³, 드론 LIDAR 측량은 약 7547m³의 차이를 보여 드론 LIDAR를 이용한 결과가 가장 정확한 측정방법으로 추천할 수 있음을 확인하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5D
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• pp.611-617
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• 2009

With advanced technologies applied to transportation, realtime traffic information has been necessary for not only drivers but also agencies. In normal, traffic conditions have been represented to three levels according to congestion: "free", "slow", and "jammed". Those categories and criteria are set up for traffic management even though traffic information is provided for drivers. This study examines how drivers feel current congestion levels and delves into traffic categories and criteria which they recognize. To collect data for drivers' recognition, a survey of freeway travellers is conducted answering the question about traffic flow speed from video image on a freeway section. In the result of the survey, the surveyee preferred a 4-level traffic condition including "delayed" to 3-level traffic condition. As its criteria, 20 km/h, 50 km/h, and 75 km/h were obtained. These results are expected to contribute to building more appropriate traffic information for drivers and providing an operational guideline for Traffic Monitering Centers.