• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.2
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• pp.479-492
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• 2014

In this study, was proposed a numerical scheme imposing exact solutions as the internal boundary conditions for the shallow-water flows over a discontinuous transverse structure such as a step. The HLLL approximate Riemann solver with the MUSCL was used for the test of the proposed scheme. Very good agreement was obtained between simulations and exact solutions for various problems of the shallow-water flows over a step. In addition, results by the numerical model showed good agreement with those of dam-break experiments over a step and stepped chute one. Developed model can simulate the shallow-water flows over discontinuous bottom such as a drop structure without additional rating curve or topography smoothing. Given the proper evaluations for the flow resistance by a step and the energy loss by the nappe flow in the future, could be simulated flooding and drying of the shallow-water flows over discontinuous topography such as a weir or the river road with retaining wall.

• Korean Chemical Engineering Research
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• v.58 no.2
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• pp.190-196
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• 2020

The step to obtain a process dynamic model through process experiments is very important because it needs times and expenditures. Step response method is one of the standard methods to have long been used for understanding process dynamics, obtaining dynamical models and designing control systems. For the step response, it is usually required to measure process output for a step input change in the open-loop manner. Its disadvantage criticized is the long open-loop operation. For this, a method based on the time-optimal control technique to minimize the test time for obtaining the step response has been recently presented. However, the method requires iterative computations for the minimization of test times. Here, a method where iterative computations are not required is proposed. Simulation results are presented to show that test times to obtain step responses are reduced considerably and an autotuning method based on the proposed method is compared with the relay feedback autotuning method accepted widely for the autotuning of controllers.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.6
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• pp.1237-1246
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• 2015

A novel technique was proposed to calculate fluxes accurately by separation of flow area into a part of step face which is dominated by flow resistance of it and an upper part which is relatively less affected by the step face in analyzing shallow-water flows over discontinuous topography. This technique gives fairly good agreement with exact solutions, 3D simulations, and experimental results. It has been possible to directly analyze shallow-water flows over discontinuous topography by the technique developed in this study. It is expected to apply the developed technique to accurate evaluation of overflows over weirs or retaining walls (riverside roads) and areas flooded by the inundation in the city covered in discontinuous topography.

• Journal of the Korean Institute of Telematics and Electronics
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• v.20 no.3
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• pp.33-39
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• 1983

New Schottky devices with thin stepped oxide layer (about 1000 ${\AA}$) along the edge of metal-semiconductor junction have been designed and fabricated. The breakdown voltages of these diodes have been compared with those of conventional metal overlap and P guard ring Schottky diode structures. Thin stepped oxide layer has been grown by the process of T.C.E. oxidation. In order to compare and demonstrate the improved down phenomena of these devices, conventional metal overlap diode and P guard ring which have the same dimension with new devices have also been integrated in a same New Schottty devices structured with thin stepped oxide layer have shown significant improvement in breakdown phenomena compared with conventional diodes.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.3
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• pp.575-583
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• 2017

Various types of flow patterns around the stepped weir and spillway, such as the skimming flow over such structures and the wave-type flow with a standing undular hydraulic jump and roller downstream of the structures, are developed in open channels. Unsteady three-dimensional numerical simulations are carried out using a hybrid RANS-LES turbulence modeling approach and the volume of fluid method for resolving free surface fluctuations to represent the turbulent flow including the skimming flow and wave-type flow over a stepped weir installed in a rectangular channel. The comparison of numerical results with an existing experimental measurement reveals that the present numerical simulations reasonably well reproduce the turbulent flow passing the stepped weir, in terms of time-averaged velocity profiles at selected locations downstream of the weir, flow topology characterized by the wave-type and skimming flows, the maximum height and length of the standing wave and the length of reattachment of recirculating zone. The numerical result further elucidates the distinct flow behaviors of the wave-type and skimming flow by presenting instantaneous intense variations of free surface and velocity vectors, the distributions of Reynolds shear stress and turbulent kinetic energy and three-dimensional complex features of coherent structures and total pressure distribution.

• Journal of the Korean Society for Advanced Composite Structures
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• v.3 no.4
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• pp.38-44
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• 2012

This paper presents experimental studies aiming at evaluation of structural behaviors of RC (Reinforced Concrete) beams externally strengthened with taper ended CFRPs(Carbon Fiber Reinforced Polymers). Experiments are performed with RC beams having different numbers of CFRP layers and length of each layer. The beams are subjected to four point-bending with simply supported condition. Test results of taper ended CFRPs and non-tapered CFRPs are compared and the better strengthening effect is observed from tapered ended CFRPs.

• Water for future
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• v.51 no.11
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• pp.84-89
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• 2018

• Proceedings of the KAIS Fall Conference
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• 2008.11a
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• pp.101-104
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• 2008

일반적으로 연속경간을 가지는 강합성 I-형강 교량에 있어서 내부 지점 부근에서 상대적으로 큰 부모멘트가 발생하므로, 이에 경제적인 단면 활용을 위하여 변단면을 적용하여 휨강도를 증가시킨다. 본 연구에서는 기존 강도계산식에 관한 연구를 토대로 하여 비탄성 구간에 있는 변단면 I형보의 횡-비틀림 좌굴강도를 유한요소해석프로그램 ABAQUS(2007)를 이용하여 산정하고, 간편한 설계식을 제안하고 있다. 지간 한쪽 끝에 계단식 단면변화를 가지는 보에 대해서 고려하였으며, 플랜지 길이방향 비, 너비방향 비, 두께의 비로 계단식 I형보를 나타내었다. 해석에 사용된 단면매개변수는 36가지 조합이며, 비탄성 횡-비틀림 거동을 고려하기위하여 잔류응력 및 초기결함을 고려한 비선형해석을 실시하였는데, Pi(1995)등이 고려한 잔류응력의 형상과 국내 I형강 표준 치수 허용치에 근거하여 부재 길이의 0.1%를 초기제작오차로 고려하였다. 해석모델의 양쪽 끝단에는 모멘트하중을 재하하였다. 개발 제한된 식은 선형 모멘트 하중이 작용할 때 적용가능한 식으로 경제적이고 합리적인 설계에 적극 활용될 수 있을 것이다.

• Journal of Korea Water Resources Association
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• v.49 no.12
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• pp.961-969
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• 2016

Due to the recent requirement of installing low-head structures considering environmental aspects, various types of fixed weir have been suggested. However, the design guideline of transverse structures for practical application is very limited. The purpose of the present study is to analyze the hydraulic properties of the fixed weirs installed at the small and middle sized rivers of Korea depending on the physical specifications to provide fundamental data that may be reflected to the design of a low-head fixed weir considering the relevant environmental aspects. The basic discharge coefficient of slope-type and step-type weirs depending on change of crest was estimated, and a stage-discharge curve was developed. In addition, the flow properties under free flow and submerged flow conditions were analyzed by varying the hydraulic conditions such as discharge and crest.

• Journal of Korean Society of Transportation
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• v.35 no.5
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• pp.396-408
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• 2017

In Korea, the number of elderly has been increasing rapidly. So it is also expected that the economic activity and the trip frequency of the elderly will increase. On the other hand, elderly related accidents such as falls during walking are steadily increasing and the satisfaction about pedestrian environment of elderly is very low. In this paper, we found one of the reasons for these dissatisfaction in pedestrian facility, which is not considering the walking ability (about 75% of non-elderly person) of the elderly. So, we analyze the kinematic walking characteristics of the elderly with the motion analysis system, when the elderly use stairs. As a result of analysis of various walking variables, the current standard for stairway height in Korean law (18cm) requires excessive force to elderly so it was difficult for elderly to keep the balance of the body in ascending and descending walk of stairs. In this paper, we propose the stair design criteria through the cluster analysis of walking parameters reflecting the gait characteristics of the elderly. This change is not a big for non-elderly person, but it can promote more socioeconomic activities for the elderly.