• Structural Engineering and Mechanics
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• 제12권4호
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• pp.449-457
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• 2001

In the design of industrial chimneys and towers, structural engineers must assume a level of the inherent damping in the structures. In order to better estimate the dynamic response of those structures, actual damping was measured from wind-induced vibration signals of chimneys and towers and its characteristics with respect to the response levels, the structural systems, and the wind direction were discussed. Damping ratio and natural frequency for three chimneys and two towers were calculated using random decrement technique.

• Wind and Structures
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• 제1권3호
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• pp.255-269
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• 1998

Second-order moments of considerable magnitude arise in tall and slender RC chimneys and towers subject to along-wind loading, on account of eccentricities in the distributed self-weight of the tower in the deflected profile. An accurate solution to this problem of geometric nonlinearity is rendered difficult by the uncertainties in estimating the flexural rigidity of the tower, due to variable cracking of concrete and the 'tension stiffening' effect. This paper presents a rigorous procedure for estimating deflections and second-order moments in wind-loaded RC tubular towers. The procedure is essentially based on a generalised formulation of moment-curvature relationships for RC tubular towers, derived from the experimental and theoretical studies reported by Schlaich et al. 1979 and Menon 1994 respectively. The paper also demonstrates the application of the proposed procedure, and highlights those conditions wherein second-order moments become too significant to be overlooked in design.

• Wind and Structures
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• 제16권5호
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• pp.477-490
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• 2013

This paper presents results of calculations performed according to our own semi-empirical mathematical model of critical vortex excitation. All calculations are carried out using own computer program, which allows the simulation of both the across-wind action caused by vortices and the lateral response of analysed structures. Vortex excitation simulations were performed in real time taking into account wind-structure interaction. Several structures of circular cross-sections were modelled using a FEM program and calculated under the action of critical vortex excitation. Six steel chimneys, six concrete chimneys and two concrete towers were considered. The method of selection and estimation of the experimental parameters describing the model are also presented. Finally, the results concerning maximum lateral top displacements of the structures are compared with available full-scale data for steel and concrete chimneys.

• Wind and Structures
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• 제16권5호
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• pp.457-476
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• 2013

This paper presents theoretical background for a semi-empirical, mathematical model of critical vortex excitation of slender structures of compact cross-sections. The model can be applied to slender tower-like structures (chimneys, towers), and to slender elements of structures (masts, pylons, cables). Many empirical formulas describing across-wind load at vortex excitation depending on several flow parameters, Reynolds number range, structure geometry and lock-in phenomenon can be found in literature. The aim of this paper is to demonstrate mathematical background of the vortex excitation model for a theoretical case of the structure section. Extrapolation of the mathematical model for the application to real structures is also presented. Considerations are devoted to various cases of wind flow (steady and unsteady), ranges of Reynolds number and lateral vibrations of structures or their absence. Numerical implementation of the model with application to real structures is also proposed.

• Journal of Advanced Research in Ocean Engineering
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• 제4권2호
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• pp.86-95
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• 2018

The fluid flow over structures has been widely investigated by many researchers because its extensive application in offshore structures, skyscrapers, chimneys and cooling towers, brides. In the viewpoint of reducing the drag for offshore structure, it becomes challenging problem in the field of hydrodynamic of offshore structure. The purpose of this study is to investigate a flow over a square cylinder with an attached splitter plate using RANS method. First, RANS turbulent models such as a standard $k-{\omega}$ model, SST $k-{\omega}$ model, RNG $k-{\varepsilon}$ model, realizable $k-{\varepsilon}$ model, standard $k-{\varepsilon}$ model were used for choosing suitable turbulent model which has the best agreement with available experimental result. Drag of single cylinder estimated by using standard $k-{\omega}$ has a good agreement with published experimental result. Therefore, the stand $k-{\omega}$ was selected for simulation for flow over a square cylinder with an attached plate. Second, the numerical results of drag of square cylinder with an attached splitter plate in various length of an attached plate were performed using RANS method in ANSYS Fluent. In this paper, the numerical simulations were conducted at a Reynolds number of 485 and the thickness of the splitter plate is chosen as a constant value about 10% of cylinder width. The numerical results of drag coefficient of square cylinder are compared with experimental result published by other researchers. Finally, the effect of the splitter plate attached to the rear side of the square cylinder has been investigated numerically with a focus on the drag coefficient and flow characteristic. As a result, the drag coefficient decreases with an increase in splitter plate length.

• 한국과학예술포럼
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• 제37권5호
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• pp.119-133
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• 2019

본 연구는 초고층 건물의 치열한 높이 경쟁이 지속되면서 더 이상 높이만으로는 다른 건물과의 차별성이 부족하다는 인식이 팽배하면서 비정형적 형태에서 경쟁력이 새롭게 부각되고 있다. 또한 비정형 초고층 건물은 높이뿐만 아니라 그 형태로도 국가, 도시, 기업의 경제적 경쟁력을 표출하는 상징성을 드러내고 있다. 디지털 미디어가 도입되기 이전에는 건축물의 구조와 형태사이에 간극이 존재했으며 이를 해결하기 위한 별도의 구조적인 매개물이 요구되었다. 1980년대 후반부터 디지털 기반의 비정형재현 과정이 실험적으로 활용하기 시작하였고 2000년 이전에는 사무공간의 초고층건축으로 사용하거나 산업용 굴뚝, 통신탑 등의 용도가 대부분이었다. 2000년 이후 대다수 글로벌 브랜드호텔 또는 상·주거공간으로 복합·다양한 용도의 초고층건축이 증가하는 추세에 의해 최근의 건축사례들은 이전의 한계를 벗어나고 있음을 분명하게 확인된다. 복잡한 비정형형상으로부터 직접적인 구조체계를 도출하고 사선형, 곡면형이 지닌 조형적인 표현성을 실현할 수 있는 디지털 기반의 형성을 통해 구조와 형태사의 새로운 관계설정에 대한 필요성이 요구된다. 이에 2000년 이후 신축된 건축 가운데 국제초고층협의회(CTBUH)의 데이터를 기준에 의해 초고층 100위의 빌딩을 대상으로 정형 및 사선형, 곡면형 등으로 구분하여 조형적 형태를 인지하는 실질적인 설계가 이루어지는 설계 프로세스를 근거로 한다. 본 연구의 목적은 복잡·다양한 비정형 건축형태를 구축하기 위한 형태의 상호관련성을 유추하는데 목적이 있다. 따라서 연구 결과는 다음과 같다. 첫째, 복합된 용도의 건물에 따른 다양한 형태구성의 고층부의 외관이 보인다. 둘째, 접힘은 내부방향으로 반복적 접힘이 적용되어 나타난다. 셋째, 2방향 곡면은 twist의 속성을 가지는 pure, helix, spiral twist 유형의 대부분 나타난다. 그러므로 향후 본 연구를 기반으로 미래 초고층건축의 형태분류 및 양상을 예측하는데 기초적 데이터로서 활용하고자 한다.