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Research on estimating roughness coefficient for 1-D hydraulic model using river flow measurement data and water surface slope (실측자료와 수면경사를 활용한 1차원 수리모형의 조도계수 산정 연구)

  • Seong Jun Kim;Chang Sung Kim;Geunsoo Son;Sunghyun Kwak;;;Hong Koo Yeo
    • Proceedings of the Korea Water Resources Association Conference
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    • 2023.05a
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    • pp.290-290
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    • 2023
  • 하천의 조도계수는 하천의 수리특성을 나타내는 대표적인 지표로써 수리모형의 모의를 수행하는데 중요한 매개변수 중 하나이다. 하지만 현재 수리모형의 조도계수는 하천정비기본계획시에 수립된 하나의 조도계수를 사용하여 모의를 수행하고 있어 유량 또는 수위에 따라 동일한 조도계수를 적용하게 되면 수위를 과대 또는 과소 모의 할 수 있는 문제가 있다. 따라서 다양한 유량 조건에 따른 모의결과의 신뢰성을 확보하기 위해서는 유량 규모에 따른 조도계수를 산정하여 검토할 필요가 있다. 이에 본 연구는 삼례교를 대상으로 하였으며, 실측된 유량자료를 활용하여 유량 또는 수위에 따른 조도계수를 산정하였고 HEC-RAS 모의 결과와 비교하였다. 분석결과, 삼례교 지점의 경우 일반적으로 수위가 증가할 수록 조도계수가 감소하다가 일정한 경향을 보이는 것과 상이하게 수위가 증가할수록 조도계수가 증가하는 경향을 보였다. 이는 하천 내에 관목이 형성되어있어 조도계수가 증가한 것으로 판단된다. 추후, 다양한 지점을 대상으로 분석을 통해 환경부 등 하천 관련 사업과 하천기본계획 수립 시 조도계수 표준화를 통한 합리적 설계에 기여할 수 있을 것으로 기대된다.

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Analyzing Effective Factors on Hydrogen Release Based on Response Surface Method and Analysis of Variance (반응표면법과 ANOVA 기반의 수소 누출에 대한 유효인자 분석)

  • JUNSEO LEE;SEHYEON OH;SEUNGHYO AN;EUNHEE KIM;BYUNGCHOL MA
    • Journal of Hydrogen and New Energy
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    • v.34 no.6
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    • pp.712-721
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    • 2023
  • While hydrogen is widely used, it has a low minimum ignition energy, raising safety concerns when using it. This research studied which parameters are the key variables in the hydrogen release and diffusion. These parameters were divided into six process variables in the initial release and two environmental variables in the dispersion. One hundred and twenty cases were selected through design of experiment, and the end-point in each case were analyzed using PHAST. Afterwards, an end-point prediction model was developed using RSM and ANOVA, and the impact of each variable on the endpoint was analyzed. As a result, the influence of eight variables was graded. The nozzle diameter had the greatest influence on the end-point, while the pipe roughness coefficient had no effect on the end-point. It is expected that these results will be used as basic data to improve safety across all fields of hydrogen handling facilities.

Molecular Simulation Study on Influence of Graphene Additives on Water Lubrication (물 윤활에 그래핀 첨가제가 미치는 영향에 대한 분자시뮬레이션 연구)

  • Hyun-Joon Kim
    • Tribology and Lubricants
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    • v.40 no.5
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    • pp.170-174
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    • 2024
  • This study investigates the lubrication enhancement effects and key mechanisms when graphene is used as an additive under water-lubricated conditions through molecular dynamics simulations. The study models two solid surfaces with a specific roughness values, with water molecules generated using a coarse-grained model placed between them. In cases in which an additive is included, one or three layers of graphene are inserted between the water molecules. The study applies a normal load by moving the two solid surfaces closer together and measures the friction force and atomic stress on the solid surfaces as the upper surface is moved horizontally. The results show that, compared with cases without an additive, both the friction force and friction coefficient are significantly reduced when graphene is added. In addition, the stress on the asperities of the solid surfaces is markedly reduced in the presence of the additive. We confirm that the primary reason for the improved lubrication performance is that graphene, when positioned at the interface, prevents direct contact between the solid surfaces and disperses the contact pressure. Notably, the lubrication performance is found to be nearly independent of the number of graphene layers at the interface.

Multiple Albedo Variation Caused by the Shadow Effect of Urban Building and Its Impacts on the Urban Surface Heat Budget (도심 건축물 그림자효과에 의한 다중 반사도 변화와 도시지표면 열수지에 미치는 영향)

  • Lee, Soon-Hwan;Ahn, Ji-Suk;Kim, Sang-Woo;Kim, Hae-Dong
    • Journal of the Korean earth science society
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    • v.31 no.7
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    • pp.738-748
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    • 2010
  • In order to clarify the impact of variation of albedo on the atmospheric boundary layer caused by the density of building in urban areas, both satellite data analysis and numerical experiments were carried out. Utilized satellite data were multi-spectral visible data detected by the Korea Multi- Purpose Satellite -2 (KOMSAT-2), and the numerical models for the estimation of surface heat budget are Albedo Calculation Model (ACM) and Oregon State University Planetary Boundary Layer model (OSUPBL). In satellite data analysis, the estimated albedo in densely populated building area is lower than other regions by 17% at the maximum due to the shadow effect of skyscraper buildings. The surface temperature reached 43.5C in the highly dense and tall building area and 37.4C in the coarse density area of low buildings, respectively. However, the low albedo in densely integrated building area is not directly related to the increase of surface air temperature since the mechanical turbulence induced by the roughness of buildings is more critical in its impact than the decrease of albedo.

Analysis Method for Full-length LiDAR Waveforms (라이다 파장 분석 방법론에 대한 연구)

  • Jung, Myung-Hee;Yun, Eui-Jung;Kim, Cheon-Shik
    • Journal of the Institute of Electronics Engineers of Korea CI
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    • v.44 no.4 s.316
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    • pp.28-35
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    • 2007
  • Airbone laser altimeters have been utilized for 3D topographic mapping of the earth, moon, and planets with high resolution and accuracy, which is a rapidly growing remote sensing technique that measures the round-trip time emitted laser pulse to determine the topography. The traveling time from the laser scanner to the Earth's surface and back is directly related to the distance of the sensor to the ground. When there are several objects within the travel path of the laser pulse, the reflected laser pluses are distorted by surface variation within the footprint, generating multiple echoes because each target transforms the emitted pulse. The shapes of the received waveforms also contain important information about surface roughness, slope and reflectivity. Waveform processing algorithms parameterize and model the return signal resulting from the interaction of the transmitted laser pulse with the surface. Each of the multiple targets within the footprint can be identified. Assuming each response is gaussian, returns are modeled as a mixture gaussian distribution. Then, the parameters of the model are estimated by LMS Method or EM algorithm However, each response actually shows the skewness in the right side with the slowly decaying tail. For the application to require more accurate analysis, the tail information is to be quantified by an approach to decompose the tail. One method to handle with this problem is proposed in this study.

The Effect of Heat Sterilization on the Surface Topography and the Tensile Properties in Various Nickel Titanium Wires Including a Korean Product (열멸균과정이 nickel titanium호선의 기계적 성질과 표면상태에 미치는 영향)

  • Kim, Byoung-Ho;Nahm, Dong-Seok;Yang, Won-Sik
    • The korean journal of orthodontics
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    • v.28 no.6 s.71
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    • pp.927-935
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    • 1998
  • The purpose of this study is to investigate the changes of mechanical properties and surface topography of various nickel titanium wires after heat sterilization for recycling with quantitative method. The materials used were four kinds of nickel titanium orthodontic wires including a Korean product. Experimental specimens were treated with two kinds of heat sterilization methods ; dry heat (180C, 60min) and autoclave (121C, 15-20psi, 30min). Mechanical properties were evaluated by tensile test with Instron 4466 (load cell capacity:.1000 kg, cross head speed:5mm/min, grip distince:40mm in room temperature). Surface topography of various wires was compared with each other qualitatively by using scanning electron microscopy and quantitatively by using profilometer. The findings were analyzed statistically with student t-tests. The results were as follows; 1. Neither method of heat sterilization had any effects on tensile properties of the nickel-titanium wires used in this experiment. 2. Before heat sterilization, the surface smoothness was highest in Optimalloy, followed by Align and Sentalloy, with NiTi showing the lowest smoothness value. 3. In surface topography, Align and Optimalloy were not influenced by heat sterilization. NiTi, on the other hand, had increased roughness after dry heat sterilization and Sentalloy showed the same tendency after each of the two heat sterilization procedures.

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Open Channel Characteristics on Different Land Cover for Neponset River, Boston, MA (상이한 토지이용에서 나타나는 하천의 특성에 관한 연구 : 메사추세츠 보스턴의 네폰셋강의 사례연구)

  • Lee, Ja-Won
    • Journal of the Korean association of regional geographers
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    • v.16 no.2
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    • pp.100-109
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    • 2010
  • The study examines two different sites to analyze the difference of stream channel profile between two different landuse areas on Neponset River, Boston, MA. Landuse represents the current status of land in terms of human, agricultural or forest, industry and environmental activity types. According to the previous research, forest and urban area are significantly distinguished in chemical characteristic, shape and bed load of the stream. On the chosen sites, I look at the cross-section profile, the slope, velocity, and roughness of the channels. With the data collected at the site I determined the value for the channel bed material using Manning's equation, and compared with the result of HEC-RAS model with the cross-section profile data I measured. In the forest area, water surface elevation and bed material obtained through Manning's equation are very close to HEC-RAS model result. However, in the resident area the Manning's 'n' value calculated much higher than assumption which was considered as cobble whose 'n' value is 0.03-0.06. The difference could be caused by unusual steep elevation on the site and the dam present down further. With the steep elevation upside of dam, there is critical-depth condition occurs. The difference of Manning's 'n' value reflects the difference of depth. HEC-RAS model was run to analyze the difference and the result shows that depth is 0.36 much less than 0.688 what I computed when the Manning's n value is 0.03(cobble) instead of the result of the study (0.13292). Beside, dam is a major source of fragmentation and degradation of stream, and it's possibly inferred upstream water levels are increased and stream velocity is decreased. This study is meaningful for introduction of HEC-RAS in geography field to analyze different sites with channel bed material, and it is going to be used more actively to manage river and river side.

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Fabrication and Modeling of Microlens Array by a Modified LIGA Process

  • Kim Dong Sung;Lee Hyun Sup;Yang Sang Sik;Lee Bong-Kee;Lee Sung-Keun;Kwon Tai Hun;Lee Seung S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2003.04a
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    • pp.7-13
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    • 2003
  • Microlens arrays were fabricated using a novel fabrication technology based on the exposure of a PMMA (Polymethylmethacrylate) sheet to deep X-rays and subsequent thermal treatment. X-ray irradiation causes the decrease of molecular weight of PMMA, which in turn decreases the glass transition temperature and consequently causes a net volume increase during the thermal cycle resulting in a swollen microlens. A new physical modeling and analyses for micro lens formation were presented according to experimental procedure. A simple analysis based on the new model is found to be capable of predicting the shapes of micro lens which depend on the thermal treatment. For the replication of micro lens arrays having various diameters with different foci on the same surface, the hot embossing and the microinjection molding processes has been successfully utilized with a mold insert that is fabricated by Ni-electroplating based on a PMMA microstructure of micro lenses. Fabricated microlenses showed good surface roughness with the order of 1nm.

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The Behavior of the Mobility Degradation in Pocket Implanted MOSFETS (Halo 구조의 MOSFET에서 이동도 감소 현상)

  • Lee Byung-Heon;Lee Kie-Young
    • Journal of the Institute of Electronics Engineers of Korea SD
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    • v.42 no.4 s.334
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    • pp.1-8
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    • 2005
  • The increased effective impurity due to the pocket ion implantation is well blown to give rise to a reduction of the effective mobility of halo MOSFETs. However, further decrease of the effective mobility can be observed in pocket implanted MOSFETs above the mobility reduction due to the Coulomb impurity scattering and the gate bias dependency of the effective mobility can also differ from the simple model describing the mobility behavior in terms of the effective impurity. Phonon scattering and surface scattering as well as impurity Coulomb scattering are also shown to be effective in the degradation of the carrier mobility of pocket implanted MOSFETs. Using the 1-D regional approximation the effect of the distribution of the inversion charge density along the channel on the drain current is investigated. The inhomogeneous channel charge distribution due to pocket implantation is also shown to contribute to the further reduction of the effective mobility in halo MOSFETs.

A Real Scale Experimental Study for Evaluation of Permissible Shear Stresses on Vegetation Mats (식생매트 허용 소류력 평가를 위한 실규모 실험 연구)

  • Lee, Du Han;Kim, Dong-Hee;Kim, Myounghwan;Rhee, Dong Sop
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.13 no.12
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    • pp.6151-6158
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    • 2012
  • By the activation of environment-friendly river works, application of vegetation mats is increasing, however, evaluation techniques for hydraulic stability of vegetation mats are not presented. This study is conducted to develop the objective test method for vegetation mats. Two kind of vegetation mats are tested by the real scale experiments, and hydraulic quantities are measured and analyzed to evaluate acting shear stresses. Roughness and shear stress are evaluated by 1 D non-uniform model. After each tests, changes in mat surfaces and sub-soil are evaluated, and from these evaluation, 3 types of mat surface damages and 2 types of sub-soil damages are presented. In the study, the case in which some damages in mat surface don't cause loss of sub-soil, is presented to be in the stable condition. Appling this stable condition and acting shear stresses, permissible shear stresses of vegetation mats are evaluated, and the results show that the reinforced mat with wire netting has more permissible shear stress.