• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.168-168
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• 2015

자연하천의 주요한 특징 중 하나인 하천의 사행은 직선수로에서 예측되는 유속분포를 왜곡시키며 매우 복잡한 흐름구조를 형성한다. 이는 하상 경계면에서 발생하는 전단응력 분포의 변화를 야기하는데 하상 경계면에서의 전단응력은 다양한 경험적 관계에 의존하는 유사이동의 한계 소류력 산정 및 오염물질 거동해석의 분산계수 산정에 많은 영향을 미치게 된다. 물리적인 관측을 통한 하상 경계면에서의 전단응력의 관측은 다소 제한적이며 많은 비용을 요구한다. 따라서 하상 경계면에서 발생하는 전단응력의 경우 수심의 20% 이하의 연직 유속분포를 벽법칙에 적용하여 추정하는 방법이 주로 이루어지고 있다. 벽법칙을 이용한 하상 경계면의 전단응력을 계산하는 경우 대수중복층의 유속 분포 $u/u^*=(1/{\kappa})ln(zu^*/{\nu})+B$에서 무차원상수 ${\kappa}$와 B의 적절한 추정이 요구되어 진다. 일반적으로 무차원상수 ${\kappa}$와 B는 수리학적으로 매끄러운 벽면에서 대략 ${\kappa}=0.4$, B=5.5로서 경험적으로 이용되고 있다. 본 연구에서는 직선수로 및 다양한 사행수로의 3차원 흐름장 모의를 수행하여 벽법칙의 대수 중복층을 따르는 주흐름 방향 유속의 연직분포를 비교하였다. 수치모의 소프트웨어로서 Linux 기반의 OpenFOAM이 사용되었으며 모델의 검증을 위해 Chang(1971)에 의해 수행 된 사행수로에서의 유속장 관측 결과와 비교하였고 수치모의 결과가 실험 관측치와 잘 일치하는 것으로 판단되었다. 수치모의에 적용 된 사행수로의 형상은 Hey(1976)에 의해 제안 된 사행하천의 지형학적 인자들 간에 관계를 이용하여 사행도 1.03에서 2.42까지 총 7개의 사행수로 지형을 생성하였다. 사행도의 변화에 따라 만곡부 정점에서 대수중복층 구간의 주흐름 방향 유속의 연직분포를 비교한 결과, 본 연구에서 생성 된 모든 사행수로에서 대수중복층 구간의 무차원 유속 $u^+$와 무차원 거리 $z^+$가 로그 분포를 따르는 것으로 나타났으나 경험적으로 사용되었던 무차원상수 B의 경우 사행도가 증가 할수록 대수적으로 감소하는 경향이 나타났다. 본 연구에서는 이러한 관계가 무차원 상수 B값에 미치는 영향을 반영하여 수리학적으로 매끄러운 벽면에서 적용이 가능한 수정된 대수중복층 식을 제시하고자 한다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.3
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• pp.540-546
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• 1992

Turbulent Couette flow between coaxial cylinders with inner one rotating has been investigated experimentally and numerically. The radius ratio of the coaxial cylinders is 0.43. Mean velocity and turbulent stresses have been measured by hot-wire anemometer in the range of Reynolds number based on the velocity at rotating wall and the radial distance between walls, 60,900-187,000. For the numerical computation, the Reynolds stress model has been used as a turbulence closure model. Measurements of mean velocity show that the velocity profile of wall layer largely deviates from universal logarithmic law due to the effect of streamline curvature, especially in the region near the stationary outer cylinder. The results computed with the Reynolds stress model agree well with the experimental data in the prediction of circumferential intensity of turbulent fluctuations. However, the computed level of radial intensity is much higher than the measurement. Curvature-corrected versions of the Reynolds stress model improves the prediction of turbulent intensities, but the results are not fully satisfactory.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.18 no.2
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• pp.111-120
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• 2000

Water, waste, electric and gas facilities are urban based facilities that needed in our life and are often located in underground. Therefore, underground facilities are more difficult to manage efficiently than ground facilities. It is needed to carry out survey/probe into underground facilities and to build database in order to prevent city-misfortunes being occurred because of negligent management and in order to minimize budget-waste and a traffic jam according to repetition of road excavation constructions. Also, the development of application system is required to manage efficiently underground facility. Chonju city has launched underground water supply facility computerizing project as a part of National Geographic Information System project until December 1998 and executed survey/probe into 402.89 km water supply that is 80 mm up inside central town area 39.6 $km^2$. Also, chonju city built database into 537 km water supply that is 80 mm below based on water supply card without other survey/probe works. Also, existing work process each department is changed into GIS applied work process and underground water supply facility management system is developed by its work process basis. Water supply underground facility management system that is developed is composed of sub-system like base-map management, water supply inspect, water supply management and water supply inquiry, construction work management, administration management and map management. This research presents the procedure and method of underground water supply facility survey/probe and problem being occurred during survey/probe procedure and also show the functions of each sub-systems composing underground water supply facility management system.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.1
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• pp.66-73
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• 2010

This work was focused on the material parameter extraction for the isothermal cyclic deformation analysis for which Chaboche(Combined Nonlinear Isotropic and Kinematic Hardening) and Overlay(Multi Linear Hardening) models are normally used. In this study all the parameters were driven especially based on Overlay theories. A simple method is suggested to find out best material parameters for the cyclic deformation analysis prior to the isothermal LCF(Low Cycle Fatigue) analysis. The parameter extraction was done using 400 series stainless steel data which were published in the reference papers. For simple and quick review of the parameters extracted by suggested method, 1D FORTRAN program was developed, and this program could reduce the time for checking the material data tremendously. For the application to FE code ABAQUS user subroutine for the material models was developed by means of UMAT(User Material Subroutine), and the stabilized hysteresis loops obtained by the numerical analysis were in good harmony with test results.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.1
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• pp.12-23
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• 1995

Currents driven by irregular waves are modelled using numerical model with various empirical relations improved. Kitaigorodskii's equilibrium equation is refined to account for shoaling effect and used for checking the breaking condition. In order to compute the bottom friction realistically. equivalent roughness blights are estimated considering the ripple shape and bed load transport which may be significant the surf zone. Two sets of equations are employed to evaluate the ripple shape: one is suggested by Nielsen and the other by Madsen and Rogengaus. Both equations give similar shape of ripples. but Madsen et al. give lower value of ripple factor than Swart suggesting that the equivalent roughness becomes relatively small. Optimization technique is used to determine the proper values for the empirical parameters of $\kappa$-ι equations, and the longshore current velocity is computed using the values of empirical parameters determined by the optimization technique.

• Journal of the Korean Chemical Society
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• v.30 no.5
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• pp.456-464
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• 1986

The complex formation of branched poly(ethylene imine) (BPEI) with bivalent transition metal ions, such as Fe(II), Co(II), Ni(II) and Cu(II), have been investigated in terms of visible absorption and pH titration methods in an aqueous solution in 0.1M KCl at 30${\circ}$. The stability constants for M(II)-BPEI complexes was calculated with the modified Bjerrum method. The formation curves of M(II)-BPEI complexes showed that Fe(II), Co(II), Ni(II) and Cu(II) ions formed coordination compounds with four, two, two, and two ethylene imine group, respectively. In the case of Cu(II)-BPEI complex at pH 3.4 ∼ 3.8, ${\lambda}_{max}$ was shifted to the red region with a decrease in the acidity. The overall stability constants (log $K_2$) increased as the following order, Co(II) < Cu(II) < Ni(II) < Fe(II).

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.1
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• pp.154-159
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• 1987

In the previously reported Part I, the behavior of the flank wear for carbide tool was studied as a preceeding step to present a simple method for Quick Tool-Life Testing, and the following general equation was obtained $W_{f}$ =(a+bt) $V^{m}$ . In this study the following step-cutting formula for the constants a, b and m in the above general model is derived by using step-cutting data [a numerical formula] To check the validity of the above formula, the comparison is made between the tool-life equation inferred in this method and that inferred in the conventional tool-life testing method, when the wear criterion is 0.3mm. The equation obtained in the present method is V(T')$^{0.57}$=1763 whereas the equation obtained in the conventional tool-life testing method is V(T)$^{0.56}$=1605 The results of the above two formula are satisfactory and also verify the validity of the present research.earch.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.123-123
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• 2021

도시하천유역이나 복합유역 등 지역적 성향을 고려한 도달시간 산정에 관한 연구는 현재까지도 미흡한 실정이다. 소규모 유역의 홍수량을 산정할 경우 유하시간보다 유입시간 비중이 상대적으로 크다. 그러나 유하시간만을 고려하여 도달시간을 산정할 때, 소규모 유역의 경우 하도가 없고 유역면적이 5km² 내외 또는 하도의 저류 효과를 기대할 수 없는 경우 도달시간이 짧아 홍수량이 과대 산정된다. 이를 극복하고자 재해영향성평가등의 협의 실무지침에서는 도달시간 이외에 매개변수인 저류상수를 인위적으로 증가시키는 방법을 제안하고 있다. 하지만 이 방법 역시 유역의 물리적인 특성을 나타내는 변수를 왜곡한다는 근복적인 문제를 완전히 해결하지 못하였다. 이에 본 연구에서는 기존 중·대규모 하천을 대상으로 수행된 연구결과를 바탕으로 제안된 홍수 도달시간 산정방법의 한계를 극복하고, 유입시간이 지배적인 소규모 복합유역에 적용 가능한 도달시간 산정방안을 제시하고자 한다. 이를 위해 실증실험을 통해 기존 유입시간 산정식을 개선하고, 도시수문 모니터링 시범유역에 적용하여 정확성을 평가하고자 하였다. 먼저, 홍수도달 시간 측정을 위한 강우유출 실내 실험장치를 제작하였다. 실험장치는 본체(길이3m×폭1.2m×높이0.8m)와 경사조절 장치(0~15도)를 포함하고 있다. 본체 전면부를 타공(ø10mm)하고 상·하단에서 지표와 기저유출을 집수하여 티핑버킷으로 유량을 측정하였고, 토체 내에는 토양수분센서를 설치하여 강우유출 발생시간 동안 토양수분 변화를 측정하였다. 본 연구에서는 하도흐름인 유하시간(Kraven 공식)을 계산하여 도달시간을 산정하기 보다 지표면 흐름인 유입시간(Kerby 공식)에 보정계수를 도입하여 도달시간을 산정하는 방안을 검토하였다. 실험 결과, 불투수 면적비율이 증가함에 따라 도달시간은 감소하고, 불투수 유역이 하류에 위치할수록 유출발생시간이 빨라졌다. 실증실험 결과를 바탕으로 도시수문 모니터링 시범유역에 적용하여 기존 유하시간과 저류상수를 보정하는 도달시간 산정방식(연속형 Kraven)과 유입시간을 보정한 도달시간 산정(수정 Kerby)으로 도출된 유출량을 실측 유량과 비교하였다. 그 결과 제안된 홍수도달시간 산정식에서 모의된 홍수량이 기존 방식과 유사하거나 우수한 첨두홍수량을 보였으며, 설계자 임의성이 배제된 일관성있는 해석값을 제시해 줄 것으로 판단된다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6B
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• pp.399-406
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• 2012

The objective of this research is to develop greenhouse gas generation models and estimation method of their parameters for solid waste landfills. Two models obtained by differentiating the Modified Gompertz and Logistic models were employed to evaluate two parameters of a first-order decay model, methane generation potential ($L_0$) and methane generation rate constant (k). The parameters were determined by the statistical comparison of predicted gas generation rate data using the two models and actual landfill gas collection data. The values of r-square obtained from regression analysis between two data showed that one model by differentiating the Modified Gompetz was 0.92 and the other model by differentiating the Logistic was 0.94. From this result, the estimation methods showed that $L_0$ and k values can be determined by regression analysis if landfill gas collection data are available. Also, new models based on two models obtained by differentiating the Modified Gompertz and Logistic models were developed to predict greenhouse gas generation from solid waste landfills that actual landfill generation data could not be available. They showed better prediction than LandGEM model. Frequency distribution of the ratio of Qcs (LFG collection system) to Q (prediction value) was used to evaluate the accuracy of the models. The new models showed higher accuracy than LandGEM model. Thus, it is concluded that the models developed in this research are suitable for the prediction of greenhouse gas generation from solid waste landfills.

• Journal of the Korean GEO-environmental Society
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• v.4 no.2
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• pp.77-91
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• 2003

The Hoek-Brown failure criterion for rock masses developed first in 1980 is widely accepted and has been applied in a variety of rock engineering problems including slope analyses. The failure criterion was modified over the years because rock mass strength by the original failure criterion in 1980 was overestimated. The modified failure criterion, named Generalized Hoek-Brown Failure Criterion, was proposed with a new classification called the Geological Strength Index(GSI) in 1994. Generally, Hoek-Brown failure criterion is applied in numerical analyses of rock mass behaviors using equivalent Mohr-Coulomb parameters estimated by linear regression method. But these parameters estimated by this method have some inaccuracies to be applied and to be incorporated into numerical models and limit equilibrium programs. The most important issue is that this method cannot take account of non-linear characteristics of Hoek-Brown criterion, therefore, equivalent Mohr-Coulomb parameters is used as constant values regardless of field stress distribution in rock masses. In this study, the numerical analysis on rock slope stability considering non-linear characteristics of Hoek-Brown failure criterion was carried out. Futhermore, by the latest Hoek-Brown failure criterion in 2002, the revised estimating method of equivalent Mohr-Coulomb parameters was applied and rock mass damage criterion is introduced to account for the strength reduction due to stress relaxation and blast damge in slope stability.