• International Journal of Aeronautical and Space Sciences
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• 제2권1호
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• pp.12-19
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• 2001

Study of turbulent mixing layers has been a popular subject from the point of view of both practical application and phenomenological importance in engineering field. Turbulent mixing layers can be applied in many fields where rapid transition to turbulence is desirable in order to prevent boundary layer separation or to enhance mixing. The ability to control mixing, structure and growth of the shear flow would obviously have a considerable impact on many engineering applications. In addition to practical applications, free shear flows are one of the simplest flows to understand the fundamental mechanism in the transition process to turbulence. After the discovery of large-scale vortical structure in free shear flows many researchers have investigated the physical mechanism of generation and dissipation processes of the vortical structure. This study investigated the role of the large-scale vortical structures in the turbulent mixing layer using LES(Large-Eddy Simulation). The result shows that the pairing interaction of the vortical structure plays an important role in the growth rate of a mixing layer. It is found that the turbulence quantities depend strongly on the velocity ratio. It is also found that the vorticity in the high-velocity-side can extract energy from the mean flow, while the vorticity in the low-velocity-side lose energy by the viscous dissipation. Finally the results suggest the guideline to obtain the desired flow by control of the velocity ratio.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 봄 학술발표회 논문집
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• pp.297-302
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• 2000

Pipe cooling method is widely used for reduction of hydration heat and control of cracking in mass concrete structures. However, in order to effectively apply pipe cooling systems to concrete structure, the coefficient of flow convection relating the thermal transfer between inner stream of pipe and concrete must be estimated. In this study, a device measuring the coefficient of flow convection is developed. Since a variation of thermal distribution caused by pipe cooling has a direct effect in internal forced flows, the developed testing device is based on the internal forced flow concept. Influencing factors on the coefficient of flow convection are mainly flow velocity, pipe diameter and thickness, and pipe material. finally a prediction model of the coefficient of flow convection is proposed using experimental results from the developed device. According to the proposed prediction model, the coefficient of flow convection increases with increase in flow velocity and decreases with increase in pipe diameter and thickness. Also, the coefficient of flow convection is largely affected by the type of pipe materials.

• 한국방재안전학회논문집
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• 제16권4호
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• pp.1-7
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• 2023

본 연구의 목적은 급경사지 사면에서 토석류 재해가 발생했을 때, 토석류 저감 구조물의 효과를 조사한 실험연구이다. 제어 구조물로는 베플 형태를 취하였고, 베플의 설치 기수와 각 제원에 따라서 하류에서의 토석류에 의한 토사퇴적면적과 토사도달거리를 조사한 것이다. 수로의 경사가 급할수록 토사의 퇴적면적과 도달거리가 증가하였고, 토사체적농도가 감소할수록 토사퇴적면적과 토사의 도달거리가 증가하였다. 토사농도가 작은 경우(Cv = 0.5)는 토석류의 액성이 크기 때문에 수로 경사에 따른 차이가 나타났고, 전반적으로 토사체적농도가 클수록 토사퇴적면적과 토사의 도달거리 감소율이 크게 나타났다. 베플의 수를 증가할수록 토사퇴적면적과 도달거리를 약 5~10% 이상 감소하는 것으로 나타남으로서 베플의 토석류 제어능력이 있음을 보여주고 있다. 본 연구의 결과는 급경사지에서 토사재해가 발생할 때 감쇠 또는 제어 구조물을 설치할 때 중요한 정보를 제공할 것이다.

• 대한기계학회논문집B
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• 제22권3호
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• pp.316-325
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• 1998

The objective of this study is to investigate the role of large-scale coherent structures in a spatially developing plane mixing layers. To achieve this, we have to look into the mutual interactions between three-dimensional large-scale coherent structures and the mean flow. Our attention will be focused on the energy exchange mechanism between the various modes, and the effects of the nonlinear evolution of the phases of the interacting modes. Linear stability of the three-dimensional viscous shear layer is formulated and solved as the basis for the solution of the nonlinear formulation based on the energy method. The importance of the initial conditions that may affect the evolution of the flow has been examined. It has been numerically calculated the nonlinear effects arising from the interactions among the three-dimensional large-scale coherent structures in a spatially developing plane mixing layers. The results of this study provide useful parametric information for the control of shear layer in practical applications in the mixing and transport augmentation.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2007년도 정기총회 및 학술발표대회
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• pp.603-607
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• 2007

Recently, the frequency of unexpecting heavy rains has been increased due to abnormal climate and extreme rainfall. There was a limit to analyze one dimension or two dimension stream flow of domestic rivers that was applied simple momentum equation and fixed energy conservation. Therefore, hydrodynamics flow analysis in rivers has been needed three dimensional numerical analysis for correct stream flow interpolation. In this study, CFD model on FLOW-3D was applied to stream flow analysis, which solves three dimension RANS(Reynolds Averaged Navier-Stokes Equation) control equation to find out physical behavior and the effect of hydraulic structures. Numerical simulation accomplished those results was compared by using turbulence models such as $k-{\backepsilon}$, RNG $k-{\backepsilon}$ and LES. Those numerical analysis results have been illustrated to bends and junctions by the turbulence energy effects, velocity of flow distributions, water level pressure distributions and eddy flows.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 D
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• pp.2640-2642
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• 2005

Servovalves are widely used in industrial areas in order to control the position of large steam valves which regulate steam flow to prime mover. We must control the position of large steam valves to regulate flow of working fluids in the process. The small pilot valves are used to regulate the large main valves in case that the pressure of control fluids supplied to servovalves is low about $12kg/cm^2$. But, in case that the pressure of control fluids supplied to servovalves is high enough about $110kg/cm^2$, the pilot valves are not needed and servovalves can control directly the large main valves due to its large working forces. Additionally, the basic structures of armature coil should be different according to the types of control system even in the same servovalve. This paper compares and describes some integral types of flow control.

• 정보처리학회논문지:컴퓨터 및 통신 시스템
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• 제2권8호
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• pp.317-326
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• 2013

본 논문에서는 바이너리 프로그램의 정적인 구조를 표현하는 제어 흐름 그래프를 비교하는 방법을 제안한다. 제어 흐름 그래프를 비교하기 위해서 기본 블록에 포함된 프로그램의 명령어 및 구문 정보를 비교한 후 기본 블록 사이의 유사한 정도를 측정한다. 또한, 에지 확장을 통해 기본 블록들 간의 제어 흐름을 표현하는 그래프 에지의 유사성을 함께 반영한다. 각 기본 블록 사이의 유사도 결과를 기반으로 기본 블록을 서로 매칭하고, 기본 블록 사이의 매칭 정보를 이용해서 전체 제어 흐름 그래프의 유사도를 측정한다. 본 논문에서 제안한 방법은 자바 프로그램으로부터 추출한 제어 흐름 그래프를 대상으로 제어 흐름 구조의 유사성에 따라 두 가지 기준으로 실험을 수행하였다. 그리고, 성능을 평가하기 위해서 기존의 구조적 비교 방법을 함께 실험하였다. 실험 결과로부터 에지 확장 방법은 서로 다른 프로그램에 대해 충분한 변별력을 가지고 있음을 확인할 수 있다. 프로그램 비교에 좀 더 많은 시간이 소요되지만, 구조가 유사한 프로그램에 대한 매칭 능력에서 기존의 구조적 비교 방법에 비해 우수한 결과를 보였다. 제어 흐름 그래프는 프로그램의 분석에 다양하게 활용될 수 있으며, 제어 흐름 그래프의 비교 방법은 프로그램의 유사성 비교를 통한 코드의 최적화, 유사 코드 검출, 코드의 도용 탐지 등 다양한 분야에서 응용될 수 있을 것이라 기대된다.

• 한국수산과학회지
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• 제30권1호
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• pp.139-147
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• 1997

Sediment transport around artificial habitat which is induced by the change ol flow due to installation of the structure plays a role not only as a defect function of subsidence and burial but also bottom-environment control function. This study examined the characteristics of local scouring and deposition with sediment sizes, current velocities and installation direction of artificial habitat in flow field. Resultant subsidence and burial processes are investigated and discussed with Reynolds number. Together with sediment number and dimensionless time elapse, prediction formulas are established by combining these relationships. Bottom control function as cultivating effects is discussed with installation direction, and applicability of countermeasures is compared and stone pavement method is recommended.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2007년도 학술발표회 논문집
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• pp.1287-1292
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• 2007

Recently, the frequency of unexpecting heavy rains has been increased due to abnormal climate and extreme rainfall. There was a limit to analyze 1D or 2D stream flow that was applied simple momentum equation and fixed energy conservation. Therefore, hydrodynamics flow analysis in rivers has been needed 3D numerical analysis for correct stream flow interpretation. In this study, CFD model on FLOW-3D was applied to stream flow analysis, which solves three dimenson RANS(Reynolds Averaged Navier-Stokes Equation) control equation to find out physical behavior and the effect of hydraulic structures. Numerical simulation accomplished those results was compared by using turbulence models such as ${\kappa}-{\varepsilon}$, RNG ${\kappa}-{\varepsilon}$ and LES. Those numerical analysis results have been illustrated by the turbulence energy effects, velocity of flow distributions, water level pressure distributions and eddy flows around the piers at Jangwall bridge in urbarn stream.

• Smart Structures and Systems
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• 제32권5호
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• pp.281-295
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• 2023

The purpose of this study is to demonstrate and verify the application of phase-control absolute-acceleration-feedback active tuned mass dampers (PCA-ATMD) to multiple-degree-of-freedom (MDOF) building structures. In addition, servo speed control technique has been developed as a replacement for force control in order to mitigate the negative effects caused by friction and inertia. The essence of the proposed PCA-ATMD is to achieve a 90° phase lag for a structure by implementing the desired control force so that the PCA-ATMD can receive the maximum power flow with which to effectively mitigate the structural vibration. An MDOF building structure with a PCA-ATMD and a real-time filter forming a complete system is modeled using a state-space representation and is presented in detail. The feedback measurement for the phase control algorithm of the MDOF structure is compact, with only the absolute acceleration of one structural floor and ATMD's velocity relative to the structure required. A discrete-time direct output-feedback optimization method is introduced to the PCA-ATMD to ensure that the control system is optimized and stable. Numerical simulation and shaking table experiments are conducted on a three-story steel shear building structure to verify the performance of the PCA-ATMD. The results indicate that the absolute acceleration of the structure is well suppressed whether considering peak or root-mean-square responses. The experiment also demonstrates that the control of the PCA-ATMD can be decentralized, so that it is convenient to apply and maintain to real high-rise building structures.