• The Journal of the Korea Contents Association
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• v.16 no.4
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• pp.614-623
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• 2016

Grid(pipe network) design is an important element of Smart Water Grid, which essential to estimate hydraulic parameters such as the pressure, friction factor, friction velocity, head loss and energy slope. Especially, friction velocity in a grid is an important factor in conjunction with energy gradient, friction coefficient, pressure and head loss. However, accurate estimation friction head loss, friction velocity and friction factor are very difficult. The empirical friction factor is still estimated by using theory and equation which were developed one hundred years ago. Therefore, in this paper, new equation from maximum velocity and friction velocity is developed by using integration relationship between Darcy-Weisbach's friction head loss equation and Schlichting equation and regression analysis. To prove the developed equation, smooth pipe data areis used. Proposed equation shows high accuracy compared to observed data. Study results are expected to be used in stability improvements and design in a grid.

• Journal of Korean Society of Steel Construction
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• v.14 no.5 s.60
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• pp.647-656
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• 2002

High-strength steel in steel bridges is the key to achieving cost-efficiency because it facilitates lightweight construction and rationalizes structure. The future of high-strength steel is bright, with its use projected to expand. As such, it is necessary to evaluate precisely various factors affecting the process of fabricating high-strength steel, i.e., welding heat, strain hardening, and weldability and performance of the welded joints. This study therefore performed the maximum hardness test and y-groove weld crack test using welding processes such as SAW, FCAW, and GMAW, in order to investigate the welding performance and characteristics of welded Joints or high-strength steel produced in Korea such as SM570, POSTEN60, and POSTEN80. In addition, a series of welding tests was carried out to estimate the tensile strength, bending characteristics, absorbed energy, and hardness in welded joints.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2003.05a
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• pp.157-164
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• 2003

Introduction of wave model, considered the effect of tide, wind and wave induced currents at the coastal waters of complex bathymetry, is a very important factor for most coastal engineering design and disaster protection problems. As the steady state spectral wave model could simulate depth induced wave shoaling and refraction, current induced refraction effect, steepness induced wave breaking, diffraction, wind wave growth, and wave-wave interaction that redistribute energy, this would support and compensate the gap in the real field of design where other wave models could not deal and cause wrong estimation. In this study, for that sense, we applied the spectral wave model t the large coastal waters near Gaduck Island where the Busan new port construction project is going on, for better understanding and analysis of wave transformation process. We also compared the simulation results with the calculated from the existing model. From such a trial of this study, we hope that broader and sager use of the spectral model in the area of port design and disaster prevention system come through in near future.

• Proceedings of the Korea Water Resources Association Conference
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• 1980.08a
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• pp.44-46
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• 1980

파의 에너지 감쇠기구의 관점에서 볼 때 분류손실방식인 유공벽식 방파제 중에서 원형공이 벽 전체에 균일하게 분포되어 있고 구멍 직경에 비해 벽 두께가 얇은 삼중 유공벽형 Caisson의 각 벽에 작용하는 파력에 고나해 이론적 접근과 실험을 통한 실증을 시도해 보았다. 이론적인 방법으로는 토굴구효남의 이론을 응용하였으며 주어진 파랑조건에 대해 각 유공벽 전 후면에 연속방정식과 Bernoulli 방정식을 이용하여, 각 영역별 연속 Potential의 진폭과 위상각에 대한 비선형 12원 연립방정식을 만들었고 Computer를 이용하여 반복법으로 각 속도 Potential을 확정하였다. 이렇게 구한 속도 Potential을 압력방정식에 대입하여 각 벽별 파력을 계산하였으며 동일한 파랑조건하의 실험에서 각 벽별 파력을 측정하여 양자를 서로 비교검토하였다. Bernoulli의 방정식중 에너지 손실항은 의사비선형으로 처리하였다. 유공율조합 0.25-0.3-0.2이고, 판두께가 1cm인 모형의 실험결과, 각 벽별 최대파력치의 특성으로서는 첫때, S-2, S-3등 간벽에 작용하는 파력이 전벽 및 후벽에 비해 두드러지게 작다는 사실과, 둘째 작용파력의 크기 순이 파형경사가 작을 때는 대략 S-4, S-1, S-2, S-3순이고 파형경사가 클 때에는 대략 S-1, S-4, S-2, S-3순이라는 점 등을 들 수 있겠다. 굴구효남이 가정한 f의 치 1.5를 사용하여 계산한 각 벽별 최대파력을 실험치와 비교해 본 결과, 파가 각 유공벽을 통과할 때의 손실수두를 실험에서의 양만큼 fr=1.5를 가정한 수학적 model이 설명해 주지 못한다고 볼 수 있으므로 두가지 방법에 의하여 본 실험에서 사용한 유공판의 손실계수를 근사적으로 추정하여 보았다. 추정한 f를 사용하여 다시금 각 벽별 최대파력을 계산하고 실험치와 비교해 보면 훨씬 서로 근접함을 알 수 있었다. 결국 본 논문의 이론을 사용하면 유공Caisson문제의 전체적인 윤곽 및 각 변수들의 파력에 대한 영향을 파악할 수 있겠다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.34 no.4
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• pp.119-127
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• 2022

To investigate varying wave impact pressure exerting at the crest wall of rubble mound seawall, depending on breaking wave properties, regular waves with different wave periods were generated. Wave velocity fields and void fraction were measured using bubble image velocimetry and simple combined wave gauge system (Na and Son, 2021). For the waves with shorter wave period, maximum horizontal velocity was less reduced compared to incident wave speed while breaking-induced air entrainment was occurred intensely, leading to a significant reduction of wave impact pressure at the crest wall. For the waves with longer wave periods, less air wave entrained and the wave structure followed a flip-through mode (Cooker and Peregrine, 1991), resulting in an abrupt increase of the impact pressure.

• Journal of the Korean Wood Science and Technology
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• v.30 no.2
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• pp.108-114
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• 2002

Red pine(Pinus densiflora) square timbers with 14.0 cm and 16.5 cm of face size and 24 m long were dried in a vacuum-press kiln and in a radio-frequency/vacuum(RF/V) kiln to compare drying rate, moisture content(MC) distribution and specific energy. RF/V drying rate was higher than vacuum-press drying rate. The effect of size of cross section on the RF/V drying rates were more pronounced than those of vacuum-press drying. The longitudinal- and the transverse MC distribution of dried square timber showed convex profile for the vacuum-press drying and concave profile for the RF/V drying. Moisture gradient of width direction was similar to the thickness direction in vacuum-press dried square timber and was more slight than that of the thickness direction in the RF/V dried large square timber. The specific energy consumption curve increased as MC decreased. Specific energy(kWh/kg of water evaporated) of the vacuum-press process required more than that of the RF/V process.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.233-233
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• 2022

최근 기후변화로 인해 집중호우 및 돌발홍수의 증가로 침수피해가 빈번하게 발생하고 있다. 마찬가지로 해안지역의 피해 또한 증가하고 있으나, 해안지역의 특성을 고려한 연구가 미비한 실정이다. 따라서 본 연구에서 해안지역의 특성을 고려해 폭풍해일로 인한 월파뿐만 아니라 강우도 고려하여 해안지역의 범람 양상을 확인하고자 하였다. 본 연구에서는 국내 해안지역에 대한 빈도별 폭풍해일과 강우로인한 범람 모의를 진행하였다. 우선, 수치해석 모형의 경계조건을 산정하기 위해 EurOtop(2018)의 경험식을 이용하여 월파량을 산정하였다. EurOtop의 월파량 산정 시 암석 옹벽이 아닌 콘크리트 옹벽으로된 경사식 단면으로 고려하여 계산하였고 산책로와 벽까지 고려하여 계산하였다. 경험식 계산을 위해 매개변수(유의파고, 여유고, 구조물의 조도계수, 구조물의 기울기 및 경사 등)를 조정하여 계산하였다. 이 중, 계산에 사용된 유의파고는 시나리오별 강우에 대해 SWAN(Simulating WAves Nearshore)으로 계산된 값을 활용하였고, 해안선을 두 부분으로 나누어 해안지역 각 지점별 파고값의 평균을 사용해 월파량 계산을 진행했다. 이때, 파고의 종류로 5% 확률의 파고, 평균 파고, 중앙값 파고, 95% 확률의 파고로 분류해 월파량 계산을 진행했고, 그 중, 평균 파고를 이용해 계산한 월파량을 수치해석 모델의 입력자료로 활용하였다. 시나리오별로 계산된 월파량만을 이용해 2차원 침수모형인 FLO-2D의 경계조건 입력값으로 사용하여 침수 양상을 표출하기 위해 Mapper와 ArcGIS를 이용하여 침수와 범람 양상을 확인하였다. 또, 다른 조건으로 시나리오별 계산된 월파량, 연구유역 해안 반대편에 위치한 산으로부터 유입되는 물의 양 그리고 해안지역 전체에 내리는 강우를 입력자료로 사용해 모의를 진행한 후 Mapper와 ArcGIS로 표출하여 침수 및 범람 양상을 확인하였다.

• Journal of the Korean Solar Energy Society
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• v.38 no.6
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• pp.51-63
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• 2018

Nowadays the bifacial PV system market and its applications are increasing rapidly. The performance of the bifacial PV system take advantage of its rear surface irradiance. Also, the ground albedo, PV module tilt and azimuth, PV module installation height, shading effect and module temperature are factors of bifacial PV system performance. This paper investigates how the performance of bifacial PV system is influenced by above factors. First, we analyzed the energy yield depending on PV module installation by simulation. Secondly, we compare energy performance evaluation of monofacial and bifacial module on different weather condition by experiment. Thirdly, we tested the albedo effect and checked operating characteristics using Dupont Tyvek material for the bifacial PV module. Fourthly, we check the shading effect of bifacial PV module on bypass diode operating. Finally, we applied the bifacial PV module in the nearby subway station for the noise reduction barrier using a qualified simulation program. In summary, we confirm that the energy performance superiority of the bifacial PV module has a lot of application use including road. Also, we have confirmed the bifacial module and inverter design should be considered by rear surface irradiance.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.460-468
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• 2021

A TBM is an equipment that excavates a tunnel with a full face by rotating a circular cutter head and its advantages are fast excavation rate and safe construction. A TBM, which is primarily used for tunnel excavation on civil construction sites, is easily adaptable to information and communication technology. Research related to unmanned and automated technology is being actively pursued. TBM applications for mining and energy resource development in other countries were investigated in this study. The difference of TBM applications between the mining and energy resource development and civil construction sites was examined. Technical factors such as geological conditions, depth, site access, TBM launching, alignment and inclination, TBM size, and others that should be considered when choosing a TBM were investigated. Finally, the advantages and disadvantages of TBM application in mines and the technical requirements for TBM for successful mine application are summarized.

• The Journal of the Acoustical Society of Korea
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• v.43 no.2
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• pp.168-177
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• 2024

When designing an underwater Piezoelectric Energy Harvester (PEH), Vortex Induced Vibration (VIV) is generated throughout the cantilever through a change in curvature, and the generation of VIV increases the vibration displacement of the curved cantilever PEH, which is an important factor in increasing actual power. The material of the curved PEH selected a Polyvinyline Di-Floride (PVDF) piezoelectric film, and the flow velocity is set at 0.1 m/s to 0.50 m/s for 50 mm, 130 mm, and 210 mm with various curvatures. The strain energy change of PEH by VIV was observed. The smaller the radius of curvature, the larger the VIV, and as the flow rate increased, more VIV appeared. Rapid shape transformation due to the small curvature was effective in generating VIV, and strain energy, normalized voltage, average power, etc. To increase the amount of power of the PEH, it is considered that the average power will increase as the number of curved PEHs increases as well as the steep curvature is improved.