• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.1011-1015
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• 2005

본 실험에서는 부력 조건이 달라질 때 단공방류구에서 정체수역으로 수평방류되는 부력제트의 거동을 규명하였다. LIF (Laser Induced Fluorescence) 시스템을 이용하여 수행하였는데, LIF 시스템은 고해상도의 이미지를 취득할 수 있어 데이터의 정확도가 높으며, 동시에 한 평면상의 농도장을 일시에 측정할 수 있는 장점이 있는 기술이다. LIF 시스템은 크게 세부분으로 구성되어 있는데 방출시스템, 포착시스템, 처리시스템이 그것이다. 실험 조건을 고려해서 온수를 이용하여 주변수와의 밀도차를 재현하였으며, LIF 시스템의 추적입자로 형광염료 Rhodamine B를 사용하였다. 또한, 실험 데이터 취득과정에서 필요한 검정과정을 수행하였는데, LIF 시스템에서 검정과정은 레이저 입사광의 강도가 불균등한 분포를 가지는 점과 주변수의 매질에 의한 근의 감쇠가 발생하는 문제를 해결하기 위한 것이다. LIF 시스템은 부력제트의 농도장을 매우 정밀하게 측정할 수 있는데, 방류밀도 Froude 수가 변함에 따라 측정된 순간이미지를 통해 제트의 진화과정을 상세하고 가시적으로 확인할 수 있었다. 검정과정을 거친 농도 종단면에서 중심선의 연장선이 LIF 시스템에 의해 측정된 순간이미지의 중심선 궤적과 거의 일치하는 것도 알 수 있었다. 또한 LIF 시스템을 통해서 취득된 단일수평부력제트의 궤적과 중심선 희석률을 기존의 상용모형인 VISJET과 CORMIX1에 의해 예측된 결과와 비교$\cdot$분석한 결과, 제트 중심선 궤적의 경우, LIF 시스템을 이용한 측정값은 대체로 VISJET 모형의 결과와 일치하는 것으로 밝혀졌다. 중심선 희석률의 경우, LIF 측정값은 대체로 CORMIX1 모형, Cederwall(1968)의 경험식과 일치하는 경향을 보였다.0\%$일 때가 밸브를 $60\%$와 $80\%$ 개폐시켰을 때보다 $0.3kg/cm^2,\;0.29kg/cm^2$ 낮게 나타나 밸브를 전체 개방 했을 때 관로내의 수압이 상수설계기준에 적합한 수압을 유지함을 알 수 있다. 상수관로 설계 기준에서는 관로내 수압을 $1.5\~4.0kg/cm^2$으로 나타내고 있는데 $6kg/cm^2$보다 과수압을 나타내는 경우가 $100\%$로 밸브를 개방하였을 때보다 $60\%,\;80\%$ 개방하였을 때가 더 빈번히 발생하고 있으므로 대상지역의 밸브 개폐는 $100\%$ 개방하는 것이 선계기준에 적합한 것으로 나타났다. 밸브 개폐에 따른 수압 변화를 모의한 결과 밸브 개폐도를 적절히 유지하여 필요수량의 확보 및 누수방지대책에 활용할 수 있을 것으로 판단된다.8R(mm)(r^2=0.84)$로 지수적으로 증가하는 경향을 나타내었다. 유거수량은 토성별로 양토를 1.0으로 기준할 때 사양토가 0.86으로 가장 작았고, 식양토 1.09, 식토 1.15로 평가되어 침투수에 비해 토성별 차이가 크게 나타났다. 이는 토성이 세립질일 수록 유거수의 저항이 작기 때문으로 생각된다. 경사에 따라서는 경사도가 증가할수록 증가하였으며 $10\% 경사일 때를 기준으로 $Ro(mm)=Ro_{10}{\times}0.797{\times}e^{-0.021s(\%)}$로 나타났다.천성 승모판 폐쇄 부전등을 초래하는 심각한 선천성 심질환이다. 그러나 진단 즉시 직접 좌관상동맥-대동맥 이식술로 수술적 교정을 해줌으로써 좋은 성적을 기대할 수 있음을 보여주었다.특히

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2004.04a
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• pp.179-186
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• 2004

Introduction of wave model, considered the effect of shoaling, refraction, diffraction, partial reflection, bottom friction, breaking at the coastal waters of complex bathymetry, is a very important factor for most coastal engineering design and disaster prevention problems. As waves move from deeper waters to shallow coastal waters, the fundamental wave parameters will change and the wave energy is redistributed along wave crests due to the depth variation, the presence of islands, coastal protection structures, irregularities of the enclosing shore boundaries, and other geological features. Moreover, waves undergo severe change inside the surf zone where wave breaking occurs and in the regions where reflected waves from coastline and structural boundaries interact with the incident waves. Therefore, the application of mild-slope equation model in this field would help for understanding of wave transformation mechanism where many other models could not deal with up to now. The purpose of this study is to form a extended mild-slope equation wave model and make comparison and analysis on variation of harbor responses in the vicinities of Pohang Old Harbor and Pohang New Port, etc. due to construction of New Port in Youngil Bay. This type of trial might be a milestone for port development in macroscale, where the induced impact analysis in the existing port due to the developemnt could be easily neglected.

• Journal of Navigation and Port Research
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• v.28 no.5
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• pp.421-428
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• 2004

Introduction of wave model, considered the effect of shoaling, refraction, diffraction, partial reflection, bottom friction, breaking at the coastal waters of complex bathymetry, is a very important factor for most coastal engineering design and disaster prevention problems. As waves move from deeper waters to shallow coastal waters, the fundamental wave parameters will change and the wave energy is redistributed along wave crests due to the depth variation, the presence of islands, coastal protection structures, irregularities of the enclosing shore boundaries, and other geological features. Moreover, waves undergo severe change inside the surf zone where wave breaking occurs and in the regions where reflected waves from coastline and structural boundaries interact with the incident waves. Therefore, the application of mild-slope equation model in this field would help for understanding of wave transformation mechanism where many other models could not deal with up to now. The purpose of this study is to form a extended mild-slope equation wave model and make comparison and analysis on variation of harbor responses in the vicinities of Pohang Old Harbor and Pohang New Port, etc. due to construction of New Port in Youngil Bay. This type of trial might be a milestone for port development in macroscale, where the induced impact analysis in the existing port due to the development could be easily neglected.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.11
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• pp.180-187
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• 2013

The dinger in solar generation is the amount of sunlight which the solar cells absorb. Various types of solar trackers, which rotate themselves in order to make the solar cells face the sun as much as possible, have been developed, and especially the method of tracking with two axes has greatly contributed in increasing the generation amount at work sites. Among theses 2-axis solar trackers, the inclination-dependent 2-axis solar tracker are widely utilized for its advantages of requiring less initial investment and easy maintenance due to a solid structure. However, the drawback is that the generation efficiency is relatively low because of the structural restriction that limits the rotation angle, thus making it less efficient when tracking the sun. This paper proposes a method to increase the generation efficiency of the inclination-dependent 2-axis solar tracker. It also contains the derived equations needed for precise controlling along with a method to keep tracking with the other axis even when one has reached its angle limit. To confirm that the proposed method increases the amount of incidence onto the solar cells, formulas needed for operation on the proposed method and tracking the exact position of the sun are derived, and applying this to the quarterly data of Korea Astronomy and Space Science Institute it shows maximum over 11.1% more incidence compared to existing methods.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.6
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• pp.374-386
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• 2010

Recently, the theoretical and experimental research is being made actively in control character of waves of perforated-wall caisson breakwater like the slit caisson. This study showed that the character of reflection coefficient and the wave pressure acting on the front and inner of slit caisson were estimated in two and three dimensional numerical wave flume and compared each other. The numerical experiment was set and conducted by various cases as to a variety of wave steepness under 7 sec, 9 sec, 11sec and 13 sec period condition. In this study using a 2 and 3 dimensional numerical wave flume, it applied the Model for the immiscible two-phase flow based on the Naveir-Stokes Equations. This technique can easily reproduce a complicated physical phenomenon more than others and organize the program simply. According to the results of the experiment, the reflection coefficient was estimated high in short-period waves. However, 2-dimensional numerical experiment and 3-dimensional numerical experiment were the same in case of the long-period waves and high wave steepness. And to conclude in case of short-period waves the pressures were a relatively small difference between the two, but there was a big gap in longperiod waves and high wave steepness.

• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.1
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• pp.33-41
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• 1998

The response characteristics of the PZT transducers during glass capillary breakage were studied at the epicenter of the glass plate. The PZT transducers had been made by using EC-65 PZT ceramics(supplied by Edo co.) with a constant area and a various thickness. The theoretical displacement and velocity at the epicenter of glass plate with an air boundary condition were calculated by assuming the point load of 1N force strength and a rise time of 280 ns with a ramped functional dependence, and the 1st pulses of the PZT transducer may be considered as the vertical velocity incident on the electrode of the PZT ceramic. The responses of the PZT transducer may be depended on the thickness mode of the PZT ceramic below 0.33 in the ratio of the thickness to the diameter of PZT ceramic, but the reponse of the PZT transducer may be depended on the other modes of PZT transducer in the addition of the thickness mode of the PZT ceramic above 0.33. The full time of half maximum at the 1st pulse was nearly 280 ns without a variation of applied breakage load and the resonant frequency of the PZT transducer, and then may be considered as the rise time of a AE source. The maximum amplitude of the 1st pulse depended on the incident vertical velocity and capacitance of the PZT transducer. Therefore, the full time of half maximum and maximum amplitude of the 1st pulse may be considered as the rise time and strength of acoustic emission source respectively.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.2
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• pp.333-342
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• 2017

In order to understand the mechanism of the cross-shore evolution of storm (barred) and normal (nonbarred) profiles of a sandy beach, the vertically two-dimensional laboratory experiment was performed with a movable bed. The beach profiles and free surface motion were measured under monochromatic wave conditions evolving the storm and normal beach profiles. The observation was conducted in the surf zone during the alternation of the two wave conditions to reach its quasi-equilibrium state. The sandbar-crest and trough and the steep berm were evolved due to the plunging breakers in the storm case, and the bar-trough was decayed due to the spilling breakers in the normal case. From the measurements, it was found that the storm wave case was in an erosion state and the normal wave case was in an accretion state. The strong undertow, which is a dominant factor of the offshore migration mechanism, was developed in the storm wave case, and the weak undertow was developed in the normal wave case. The skewness and the asymmetry of the nonlinear wave motion, which is a dominant factor of the onshore migration mechanism, was measured similarly in both cases.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.6
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• pp.482-488
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• 2011

Seadike is a coastal structure constructed in the rear region of the foreshore to maximize its usability by preventing direct effect of wave. The expected construction field is determined under the design wave and tidal condition where minor wave overtopping is anticipated. Thus, the location of seadike is generally fixed at the highest site of the surrounding area with seadike crest height controlling the permissible range of wave overtopping volume. But a lot of times, frontal sand beach of the seadike continuously deforms due to incident waves, resulting failure in maintaining its initial slope. The erosion and deposition of the seadike front cause changes in the crest height and volume of wave overtopping and decrease in the setting depth of the seadike, which endangers seadike region as a result. In this study, the relation of local scouring and setting depth of the seadike front in the run-up region is examined by using 2D hydraulic model tests and numerical simulations by modified SBEACH model. As a result, the study learned that if appropriate boundary condition is applied to the modified SBEACH model, it is possible to create practical estimations on the local scouring at the seadike foot when erosive waves flow into the region.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.4
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• pp.240-249
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• 2016

In this study, we investigated wave force distribution at points on a vertical structure of semi-infinite breakwater considering diffraction. Wave forces of monochromatic and random waves on a vertical structure are studied considering diffractions in front and lee side of the breakwater for non-breaking wave condition. We selected width of breakwater are 0 for reference condition. In monochromatic wave case, relative wave force becomes 0 on the head of the breakwater by acting incident wave force and diffracting wave force simultaneously and oscillating patterns of relative wave force occurs based on 1.0 as distance from the head increases. Relative wave force of monochromatic waves decreases as incident wave angle increases. Relative wave force of random waves is defined by using ratio of root mean square and wave force spectrum in this study. The case considering random phase of each wave components are compared to the case which don't consider random phase and both results are almost similar. Relative wave force of random waves is also 0 near the head of the breakwater likewise monochromatic wave. Oscillating pattern of relative wave force of random waves becomes relatively weaker for composition of each wave components as distance from the head increases.

• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.2
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• pp.247-258
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• 2014

To evaluate the influence of the external force components on the littoral currents in the Gusipo beach, Jeonbuk, West Coast of Korea where a wide tidal sand flat developed, a coupled hydrodynamic model considered real time tidal currents and wave-induced currents was constructed in which the EFDC for tides and tidal currents, the SWAN for waves and the SHORECIRC for wave-induced currents were used as the hindcasting models. A series of field observations for tides, tidal currents and incident waves were carried out and especially to observe the littoral currents in the tidal sand flat, the GPS mounted and light weight drogues were used. Also wind data were collected from the adjacent weather station. To analyze the littoral current components, the numerical drogue tracking results considered real time winds, tides and waves were compared with the field drogue data. The drift speed of numerical drogues was reproduced as the range of 68.0~105.2% compared with the field data and the velocity error of main direction component showed a good result as -16.7~10.0%. As a result, in the mild slope tidal flat including wide surf zone, the tides and winds were the major affection component of the littoral currents, on the other hand, the wave-induced currents seemed the minor component when the incident wave heights were relatively small.