• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.33 no.1
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• pp.9-26
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• 1997

Stokes drift(SD) and Lagrangian discharge(LD) are important factors for analysis of flushing time, tidal exchange, solute transport and pollutant dispersion. The factors should be calculated using the approached method to flow phenomena. The aim of this paper re-examines the previous procedures for computing the SD and LD, and is to propose the new method approached to stratified flow field in the cross-section of coastal region, e.g. Masan Bay. The intensity of velocity near the bottom boundary layer(BBL) depends on the sea-bed irregularity in the coastal estuaries. So we calculated the depth mean velocity(DMV) considering that of BBL omitted in Kjerfve's calculation method. It revealed that BBL effect resulting in application of the bay acts largely on DMV in half more among 1l stations. The new expression of SD and LD per unit width in the cross-section using the developed DMV and proposed decomposition procedure of current were derived as follow : $$Q=u_0+\frac{1}{2}H_1{U_1cos(\varphi_h-\varphi_u)+U_3cos(\varphi_h-\varphi{ud})} LD ED SD$(Q_{skim}+Q_{sk2}) The third term, $Q_{sk2}$, on the right-hand of the equation is showed newly and arise from vertical oscillatory shear. According to the results applied in 3 cross-sections including 11 stations of the bay, the volume difference between proposed and previous SD was founded to be almost 2 times more at some stations. But their mean transport volumes over all stations are 18% less than the previous SD. Among two terms of SD, the flux of second term, $Q_{skim}$, is larger than third term, $Q_{sk2}$, in the main channel of cross-section, so that $Q_{skim}$ has a strong dependence on the tidal pumping, whereas third term is larger than second in the marginal channel. It means that $Q_{sk2}$ has trapping or shear effect more than tidal pumping phenomena. Maximum range of the fluctuation in LD is 40% as compared with the previous equations, but mean range of it is showed 11% at all stations, namely, small change. It mean that two components of SD interact as compensating flow. Therefore, the computation of SD and LD depend on decomposition procedure of velocity component in obtaining the volume transport of temporal and spacial flow through channels. The calculation of SD and LD proposed here can separate the shear effect from the previous SD component, so can be applied to non-uniform flow condition of cross-section, namely, baroclinic flow field.

• Journal of Korea Water Resources Association
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• v.39 no.6 s.167
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• pp.487-494
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• 2006

The flood discharge on the rising limb of a hydrograph at Hwawon station greatly differs from the flood discharge on the falling limb for the same stage. When there is such a big hysteresis, there can be a significant amount of errors in the rated discharge obtained from a simple rating curve. To reduce errors in rated discharges, a looped rating curve was established for Hwawon station in the Nakdong River. In order to compute the deviation between real discharges and simply rated discharges, a simple rating curve was established using the stage and discharge data from the results of a hydraulic channel routing. The relationship between the discharge deviation ${\Delta}Q$ and a product of B and ${\Delta}h/{\Delta}t$ was analysed, where B is the channel topwidth; ${\Delta}h$ is the stage increment; At is the time increment. Strong relation between ${\Delta}Q$ and $B{\Delta}h/{\Delta}t$ was found. The discharges calculated from the relationship show differences by 10 % or less for the 7 observations out of 11 observations in 1997 whose stages exceeds 7 m. The observed discharges for the stages over 9 m in 1998 also show small difference with the discharges estimated from the loop rating curve. Looped rating curve is recommended, instead of the simple rating curve to reduce the errors of rated discharges for gauging stations like Hwawon, which has relatively large loop width.

• Journal of the Korean Society of Safety
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• v.32 no.4
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• pp.46-52
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• 2017

Sediment exchange in river has been affected by artificial changes such as dredging and abnormal climate changes like intense rainfall. Over last decades in Korea, there were many constructions, restoration or rehabilitation in rivers. Therefore, deposition and erosion become more actively occurred than before, which may threaten the river safety such as flood defense. For safety's sake, the dredging of river bed, which is considered as the most typical measure, has been increased to extend hydraulic conveyance compared with previous conditions. However, since it might change the sediment mechanism, there would be another risk at which unexpected side effects such as headward erosion could be occurred. Particularly, sedimentation at abrupt expansion region is able to lead to hydraulic characteristics like water elevation in the upstream region in the beginning of dredging, which, however, has been barely studied in this field. Therefore in this study, the relationship between sediment mechanism at dredging section and hydraulic characteristics in upstream region were presented through numerical simulations in the idealized abruptly widen channel using Delft3D. The ideal channel of 2,000 m length with each side angle of 45 degrees at abruptly widen expansion region was employed to consider the sediment angle of repose. The sensitivity analysis was performed on the dimensionless factors consisted of upstream and downstream depths($h_u$, $h_d$), width($w_u$, $w_d$), water level(H), flow rate(Q) and discharge of sediment($Q_s$). And the sedimentation amount at dredging and the upstream hydraulic characteristics were investigated through that analysis. It showed that $h_d/h_u$, $H/h_u$ and $w_d/w_u$ were more influential in sequence of effect on sedimentation amount, while $h_d/h_u$, $w_d/w_u$ and $H/h_u$ on upstream region. It means that $h_d/h_u$ was revealed as the most significant factors on sedimentation, also it would most highly affect the rising of water level upstream.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.897-908
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• 2008

황강에는 1989년 합천다목적댐과 본댐 하류 6.5km 지점에 조정지댐이 건설되었는데 조정지댐의 건설 목적은 본댐에서 피크 발전에 의해 방류되는 유량을 하류로 조절방류하기 위한것이다. 황강은 두댐의 건설후 하천폭, 하상재료, 식생 및 하천구간내 사주의 형성 등 많은 하천 지형학적 변화가 있었다. 이러한 변화는 댐 건설후 흐름 및 유사이송의 변화에 기인한다. 2002년 합천댐 저수지 퇴사량 조사에 의하면 합천댐은 연간 약 600천$m^3$의 유사를 차단한 것으로 파악되었다. 조정지댐은 연최대피크 방류량을 654.7$m^3/s$에서 126.3$m^3/s$로 감소시켰는데 이는 댐건설전의 19.3%에 해당하는 양이다. 댐건설로 인한 하류 하천의 지형적인 변화를 파악하기 위하여 합천조정지댐 하류로부터 낙동강 합류점까지 45 km에 대하여 조사하였다. 1982, 1993 및 2004년의 항공사진을 분석한 결과 비식생하도폭(non-vegetated active channel width)은 평균 152m 감소되었는데 이는 1982년의 약 53%에 해당한다. 비식생하도의 면적 역시 평균 6.6$km^2$가 감소하였다. 평균 중앙하상재료(D50)의 크기는 1983년 1.07mm에서 2003년 5.72mm로 증가한 반면 평균 하상구배는 1983년 0.000943에서 2003년 0.000847로 감소하였다. 총 하상 세굴깊이는 조정지댐 하류 20km 구간에서 평균 약 2.6m였다. 1차원 유사모형인 GSTAR-1D를 이용하여 예측된 최심하상고는 2013-2015년 사이 (댐건설후 약 25년 후)에 안정된 상태에 도달하는 것으로 나타났다. 합천 조정지댐이 본 댐에서의 피크 방류량을 상당히 감소시키고 있지만 홍수기에 조정지댐 수문의 급격하고 주기적인 개폐로 인하여 하류에 흐름의 펄스를 발생시키고 있다. 이러한 펄스가 하류 하천 지형변화에 미치는 영향을 파악하기 위하여 유사모형과 해석적인 방법을 개발 적용하여 구한 값과 비교 검토 하였다. 결과에 따르면, 일 흐름의 펄스(daily pulse)와 홍수피크(flood peak)는 각각의 평균값이 흐를 때와 비교하여 하천지형변화에 훨씬 큰 영향을 미치는 것으로 나타났다. 일 흐름 펄스와 홍수피크는 각각의 평균값의 21%와 15%의 토사 이송량 (tons/day) 증가를 보여주었다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.4
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• pp.1335-1342
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• 2014

Shallow water depths were estimated using Compact Airborne Spectrographic Imager (CASI)-1500 and mapped to analyze the bottom bathymetry changes due to the rip currents in Haeundae beach, South Korea for the first time. The depths were estimated empirically using the maximum reflectances from 420nm to 597nm wavelength of CASI and 47 in situ water depth measurements, which were compared with ground-truth bathymetry measurements. The comparisons showed that the RMSE was 1.1m with a correlation coefficient of 0.76. In addition, CASI imagery showed remarkably detailed bottom features, especially those resulting from the rip currents within the beach. Two different channels carved by the rip current were analyzed and characterized with respect to the width and slope compared to surrounding regions. While the west side of the channel showed a wide and gentle slope, the east side of the channel showed a narrow and steep slope. The estimated bathymetry map revealed that the uneven offshore bottom features were related to the transport and accumulation of sediments by the rip current, which reaches hundreds of meters offshore. Accordingly, the accumulated sediments were estimated by adding topography changes compared to the depths of the non-rip current regions. The sediments were accumulated in off channels as much as almost twice the amount of annual sand supplements along the Haeundae beach.

• Journal of Global Scholars of Marketing Science
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• v.13
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• pp.71-88
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• 2004

Although the factors that affect the width of latitude of price acceptance is well documented, the attempt to develop a practice-oriented methodology to calibrate the region of price insensitivity (i.e., a latitude of price acceptance) for a given individual brand has been relatively rare. The researcher aims to try to full this gap by developing a conjoint analysis-based procedure that can be applied to many industries. Furthermore, we examine the difference in the latitude of price acceptance between on- and off-line transaction in stock industry in Korea. The conjoint analysis-based procedure was applied to measure the disaggregate price response curve for individual stock investment both on- and off line transaction channel. The curves from the samples enable us to estimate the individual choice probabilities corresponding to applied price points. Using t-test the differences in mean choice probabilities between the list price and another price point were tested, through which we can get the latitude of price acceptance for a given brand in stock market. These procedures were tested in on- and off-line stock market in South Korea. The results showed that investors on off-line channel have wider latitudes of price acceptance than the investors on on-line transaction system.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.2
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• pp.56-61
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• 2015

The effects of the growth temperature on the properties of a-plane GaN epi-layer on r-plane sapphire by HVPE were studied, when the constant V/III ratio and the flow rate of HCl for the Ga source channel was fixed at 10 and 700 sccm, respectively. Additionally the effects of V/III ratios for source gasses were studied when growth temperature and the flow rate of HCl for the Ga source channel was fixed at $1000^{\circ}C$ and 700 sccm, respectively. As the growth temperature was increased, the values of Full Width Half Maximum (FWHM) for Rocking curve (RC) of a-plane GaN (11-20) epi-layer were decreased and thickness of a-plane GaN epi-layer were increased. As V/III ratios were increased at $1000^{\circ}C$, the values of FWHM for RC of a-plane GaN (11-20) were declined and thickness of a-plane GaN epi-layer were increased. The a-plane GaN (11-20) epi-layer grown at $1000^{\circ}C$ and V/III ratio = 10 showed the lowest value FWHM for RC of a-plane GaN (11-20) for 734 arcsec and the smallest dependence of Azimuth angle for FWHM of (11-20) RCs.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.3
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• pp.576-581
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• 2005

In this paper. the a-Si:H TFT using ferroelectric of $SrTiO_3$ as a gate insulator is fabricated on glass. High k gate dielectric is required for on-current, threshold voltage and breakdown characteristics of TFT Dielectric characteristics of ferroelectric are superior to $SiO_2$ and $Si_3N_4$. Ferroelectric increases on-current and decreases threshold voltage of TFT and also ran improve breakdown characteristics.$SrTiO_4$ thin film is deposited by e-beam evaporation. Deposited films are annealed for 1 hour in N2 ambient at $150^{\circ}C\~600^{\circ}C$. Dielectric constant of ferroelectric is about 60-100 and breakdown field is about IMV/cm. In this paper, the TFT using ferroelectric consisted of double layer gate insulator to minimize the leakage current. a-SiN:H, a-Si:H (n-type a-Si:H) are deposited onto $SrTiO_3$ film to make MFNS(Metal/ferroelectric/a-SiN:H/a-Si:H) by PECVD. In this paper, TFR using ferroelectric has channel length of$8~20{\mu}m$ and channel width of $80~200{\mu}m$. And it shows that drain current is $3.4{\mu}A$at 20 gate voltage, $I_{on}/I_{off}$ is a ratio of $10^5\~10^8,\;and\;V_{th}$ is$4\~5\;volts$, respectively. In the case of TFT without having ferroelectric, it indicates that the drain current is $1.5{\mu}A$ at 20gate voltage and $V_{th}$ is $5\~6$ volts. If properties of the ferroelectric thin film are improved, the performance of TFT using this ferroelectric thin film can be advanced.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.537-541
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• 2003

The a-Si:H TFTs using ferroelectric of SrTiO$_3$, as a gate insulator is fabricated on glass. Dielectric characteristics of ferroelectric is better than SiO$_2$, SiN. Ferroelectric increases ON-current, decreases threshold voltage of TFT and also breakdown characteristics. The a-Si:H deposited by PECVD shows absorption band peaks at wavenumber 2,000 $cm^{-1}$ /, 635 $cm^{-1}$ / and 876 $cm^{-1}$ / according to FTIR measurement. Wavenumber 2,000 $cm^{-1}$ /, 635 $cm^{-1}$ / are caused by stretching and rocking mode SiH1. The wavenumber of weaker band, 876 $cm^{-1}$ / is due to SiH$_2$ vibration mode. The a-SiN:H has optical bandgap of 2.61 eV, refractive index of 1.8 - 2.0 and resistivity of 10$^{11}$ - 10$^{15}$ aim respectively. Insulating characteristics of ferroelectric is excellent because dielectric constant of ferroelectric is about 60 - 100 and breakdown strength is over 1 MV/cm. TFT using ferroelectric has channel length of 8 - 20 $\mu$m and channel width of 80 - 200 $\mu$m. And it shows drain current of 3 $\mu$A at 20 gate voltages, Ion/Ioff ratio of 10$^{5}$ - 10$^{6}$ and Vth of 4 - 5 volts.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.133-144
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• 2009

Incheon Bridge, 18.4 km long sea-crossing bridge, will be opened to the traffic in October 2009 and this will be the new landmark of the gearing up north-east Asia as well as the largest & longest bridge of Korea. Incheon Bridge is the integrated set of several special featured bridges including a magnificent cable-stayed girder bridge which has a main span of 800 m width to cross the navigation channel in and out of the Port of Incheon. Incheon Bridge is making an epoch of long-span bridge designs thanks to the fully application of the AASHTO LRFD (load & resistance factor design) to both the superstructures and the substructures. A state-of-the-art of the geotechnologies which were applied to the Incheon Bridge construction project is introduced. The most Large-diameter drilled shafts were penetrated into the bedrock to support the colossal superstructures. The bearing capacity and deformational characteristics of the foundations were verified through the world's largest static pile load test. 8 full-scale pilot piles were tested in both offshore site and onshore area prior to the commencement of constructions. Compressible load beyond 30,000 tonf pressed a single 3 m diameter foundation pile by means of bi-directional loading method including the Osterberg cell techniques. Detailed site investigation to characterize the subsurface properties had been carried out. Geotextile tubes, tied sheet pile walls, and trestles were utilized to overcome the very large tidal difference between ebb and flow at the foreshore site. 44 circular-cell type dolphins surround the piers near the navigation channel to protect the bridge against the collision with aberrant vessels. Each dolphin structure consists of the flat sheet piled wall and infilled aggregates to absorb the collision impact. Geo-centrifugal tests were performed to evaluate the behavior of the dolphin in the seabed and to verify the numerical model for the design. Rip-rap embankments on the seabed are expected to prevent the scouring of the foundation. Prefabricated vertical drains, sand compaction piles, deep cement mixings, horizontal natural-fiber drains, and other subsidiary methods were used to improve the soft ground for the site of abutments, toll plazas, and access roads. Light-weight backfill using EPS blocks helps to reduce the earth pressure behind the abutment on the soft ground. Some kinds of reinforced earth like as MSE using geosynthetics were utilized for the ring wall of the abutment. Soil steel bridges made of corrugated steel plates and engineered backfills were constructed for the open-cut tunnel and the culvert. Diverse experiences of advanced designs and constructions from the Incheon Bridge project have been propagated by relevant engineers and it is strongly expected that significant achievements in geotechnical engineering through this project will contribute to the national development of the longspan bridge technologies remarkably.