• 한국가시화정보학회지
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• 제12권1호
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• pp.30-34
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• 2014

Bluff bodies under the external periodic force vibrate at their own natural or forced frequency. Rectangular bodies or similar structures such as high-rise towers and apartments, and recently a well-cited application - offshore floating bodies, usually needs to reduce these vibrations for stability and the mode control. Therefore, this study is aiming to reduce or control the vibration of a structure by a passive control method, i.e., TLCD (Tuned Liquid Column Damper). Controlling a moving body with a TLCD based on a variety of the orifice shape has been preliminary studied. In order to get a proper control, an optimized study is made on the design of the orifice shape, which has internal plates with the holes. The results show the force acting on the body due to the periodic movement highly depends on the number of holes on the plate and the height of the water level. Therefore, the optimum shape of the orifice and the height of the water level should be confirmed by a series of experiments.

• Wind and Structures
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• 제17권1호
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• pp.87-105
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• 2013

Modeling an equilibrium atmospheric boundary layer (ABL) in an empty computational domain has routinely been performed with the k-${\varepsilon}$ turbulence model. However, the research objects of structural wind engineering are bluff bodies, and the SST k-${\omega}$ turbulence model is more widely used in the numerical simulation of flow around bluff bodies than the k-${\varepsilon}$ turbulence model. Therefore, to simulate an equilibrium ABL based on the SST k-${\omega}$ turbulence model, the inlet profiles of the mean wind speed U, turbulence kinetic energy k, and specific dissipation rate ${\omega}$ are proposed, and the source terms for the U, k and ${\omega}$ are derived by satisfying their corresponding transport equations. Based on the proposed inlet profiles, numerical comparative studies with and without considering the source terms are carried out in an empty computational domain, and an actual numerical simulation with a trapezoidal hill is further conducted. It shows that when the source terms are considered, the profiles of U, k and ${\omega}$ are all maintained well along the empty computational domain and the accuracy of the actual numerical simulation is greatly improved. The present study could provide a new methodology for modeling the equilibrium ABL problem and for further CFD simulations with practical value.

• Wind and Structures
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• 제34권6호
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• pp.499-510
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• 2022

Computational Wind Engineering has rapidly grown in the last decades and it is currently reaching a relatively mature state. The prediction of wind loading by means of numerical simulations has been proved effective in many research studies and applications to design practice are rapidly spreading. Despite such success, caution in the use of simulations for wind loading assessment is still advisable and, indeed, required. The computational burden and the know-how needed to run high-fidelity simulations is often unavailable and the possibility to use simplified models extremely attractive. In this paper, the applicability of some well-known 2D unsteady RANS models, particularly the k-ω SST, in the aerodynamic characterization of extruded bodies with bluff sections is investigated. The main focus of this paper is on the drag coefficient prediction. The topic is not new, but, in the authors' opinion, worth a careful revisitation. In fact, despite their great technical relevance, a systematic study focussing on sections which manifest a fully detached flow configuration has been overlooked. It is here shown that the considered 2D RANS exhibit a pathological behaviour, failing to reproduce the transition between reattached and fully detached flow regime.

• 대한기계학회논문집B
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• 제32권10호
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• pp.791-799
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• 2008

We investigate the flow characteristics around a series of rectangular bodies ($40^d{\times}80^w{\times}80^h$, $80^d{\times}80^w{\times}80^h$ and $160^d{\times}80^w{\times}80^h$) placed in a deep turbulent boundary layer. The study is aiming to understand the surface pressure distribution around the bodies such as the suction pressure in the leading edge, when the flow is normal, which is responsible for producing extreme suction pressures on the roof. The experiment includes wind tunnel work by using HWA (Hot-Wire anemometry) and pressure transducers. The experiments are carried out at three different Reynolds numbers, based on the velocity U at the body height h, of $2.4{\times}10^4$, $4.6{\times}10^4$ and $6.7{\times}10^4$, and large enough that the mean flow is effectively Reynolds number independent. The results include the measurements of the growth of the turbulent boundary layer in the wind tunnel and the surface pressure around the bodies.

• 대한조선학회논문집
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• 제33권4호
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• pp.22-31
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• 1996

임의의 형상을 갖는 몽뚝한 물체에 작용하는 압력을 효율적으로 계산할 수 있는 방법을 확립하여, 조류중 유벽의 부유 성능을 스커트의 변형을 고려해 예측할 수 있는 방법을 개발하였다. 물체 전면의 압력은 반류영역을 박리유선을 경계로한 가상의 강체로 놓고 포텐샬 유동을 해석하여 구하였고, 후면의 압력은 기존의 실험 결과를 바탕으로 결정하였다. 압력 계산 방법의 검증을 위해 몇 가지 뭉뚝한 물체의 무한 수심에서의 압력 저항을 계산하여 기존의 실험 결과와 잘 일치한다는 것을 확인하였다. 유벽의 변형은 유동장과 연계되어 있어서 순차반복법을 통하여 구하였다. 여러 조류속도와 추의 질량에 대한 유벽의 변형된 형상과 홀수의 감소를 구하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2731-2736
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• 2007

In this paper, incompressible flow over a cylinder near a plane wall using the Immersed Boundary. Finite Difference Lattice Boltzmann Method (IB-FDLBM) is implemented. In this present method, FDLBM is mixed with IBM by using the equilibrium velocity. We introduce IBM so that we can easy to simulate bluff-bodies. With this numerical procedure, the flow past a circular cylinder near a wall is simulated. We calculated the flow patterns about various Reynolds numbers and gap ratios between a circular cylinder and plane wall. So these are enabled to observe for vortex shedding. The numerical results are found to be in good agreement with those of previous studies.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.148-153
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• 2001

A computational investigation of the effect of the electromagnetic force(or Lorentz force) on the flow behavior around a circular cylinder, a typical model of bluff bodies, is conducted. Two-dimensional unsteady flow computation for $Re=10^2$ is carried out using a numerical method of finite difference approximation in a curvilinear body-fitted coordinate system by solving the momentum equations including the Lorentz force as a body force. The effect of the spatial variations of the Lorentz forcing region and forcing direction along the cylinder circumference is investigated. The numerical results show that the Lorentz force can effectively suppress the flow separation and oscillation of the lift force of the circular cylinder cross-flow, leading to the reduction of the drag.

• 한국전산유체공학회지
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• 제4권1호
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• pp.34-40
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• 1999

Drag reduction on vehicles are the main concern for the body shape designers in order to lower the fuel consumption rate and to aid the driving stability. The drag of bluff bodies like transportation vehicles is mostly pressure drag due to the flow separation, which can be minimized by controlling the location and size of the separation bubble. In the present study, the TURBO-3D code is incorporated with optimal algorithm based on analytical approximation method to obtain an optimal afterbody shape of the MIRA Model corresponding to the lowest drag coefficient. For this purpose three mutually independent afterbody angles are chosen as design variables, while the drag coefficient is chosen as an objective function. It is demonstrated in the present study that an optimal body shape having the lowest drag coefficient which is about 6% lower than that of the original shape has been successfully obtained within number of iterations of tile optimal design loop.

• 한국음향학회지
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• 제17권2호
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• pp.71-78
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• 1998

와(vortex) 박리는 고형물체가 유동내에서의 유체의 흐름을 방해할 때 발생하는 전 형적인 주기적 진동 현상이다. 본 연구에서는 삼각주형 실린더가 유동내에 유발하는 와 발 리 특성을 가시화 기법, 와에 의해 변조된 초음파의 파워 스펙트럼 및 유동관에서의 진동측 정 등을 통해 연구하였다. 가시화 관찰과 유동측정 실험 결과, 발생 와는 발생체 전면으로부 터 3d와 5d 사이에서 가장 안정성이 유지됨을 발견하였다. 넓은 레이놀즈 수(104≤Re≤106) 의 유동영역에서 액체와 기체원형유동의 측정 실험결과로부터 스트로우할(Strouhal) 수가 와발생체 폭(d)과 형상비(d/D)의 증가함수이며, 삼각주 단면의 높이에 반비례함을 알 수 있 었다. 또한 실험 결과로부터 실린더의 기하학적 치수로 삼각주형 실린더의 스트로우할 수를 예측할 수 있는 경험식을 제시하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 춘계 학술대회논문집
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• pp.67-74
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• 1998

Reducing drag of vehicles are the main concern for the body shape designers in order to lower fuel consumption rate and to aid the driving stability. The drag of bluff bodies like transportation vehicles is mostly pressure drag due to the flow separation, which can minimized by controlling the location and size of the separation bubble. In the present study, the TURBO-3D code is incorporated with optimal algorithm based on analytical approximation method to obtain optimal afterbody shape of the MIRA Model corresponding to the lowest drag coefficient. For this purpose three mutually independent afterbody angles are chosen as design variables, while the drag coefficient is chosen as an objective function. It is demonstrated in the present study that an optimal body shape having lowest drag coefficient which is about $6\%$ lower than that of the original shape has been successfully obtained within number of iterations of the optimal design loop.