• Wind and Structures
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• 제18권5호
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• pp.567-598
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• 2014

In this paper, wind induced aerodynamic loads on a standard tall building have been evaluated through large-eddy simulation (LES) technique. The flow parameters of an open terrain were recorded from the downstream of an empty boundary layer wind tunnel (BLWT) and used to prescribe the transient inlet boundary of the LES simulations. Three different numerically generated inflow boundary conditions have been investigated to assess their suitability for LES. A high frequency pressure integration (HFPI) approach has been employed to obtain the wind load. A total of 280 pressure monitoring points have been systematically distributed on the surfaces of the LES model building. Similar BLWT experiments were also done to validate the numerical results. In addition, the effects of adjacent buildings were studied. Among the three wind field generation methods (synthetic, Simirnov's, and Lund's recycling method), LES with perturbation from the synthetic random flow approach showed better agreement with the BLWT data. In general, LES predicted peak wind loads comparable with the BLWT data, with a maximum difference of 15% and an average difference of 5%, for an isolated building case and however higher estimation errors were observed for cases where adjacent buildings were placed in the vicinity of the study building.

• Wind and Structures
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• 제29권3호
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• pp.177-194
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• 2019

While establishing adequate load paths in the light-frame wood structures is critical to maintain the overall structural integrity and avoid significant damage under extreme wind events, the understanding of the load paths is limited by the high redundant nature of this building type. The objective of the current study is to evaluate the system effects and investigate the load paths in the wood structures especially the older buildings for a better performance assessment of the existing building stock under high winds, which will provide guidance for building constructions in the future. This is done by developing building models with configurations that are suspicious to induce failure per post damage reconnaissance. The effect of each configuration to the structural integrity is evaluated by the first failure wind speed, amajor indicator beyond the linear to the nonlinear range. A 3D finite-element (FE) building model is adopted as a control case that is modeled using a validated methodology in a highly-detailed fashion where the nonlinearity of connections is explicitly simulated. This model is then altered systematically to analyze the effects of configuration variations in the model such as the gable end sheathing continuity and the gable end truss stiffness, etc. The resolution of the wind loads from scaled wind tunnel tests is also discussed by comparing the effects to wind loads derived from large-scale wind tests.

• Wind and Structures
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• 제30권4호
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• pp.379-392
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• 2020

The paper presents a Life-Cycle Cost-based optimization framework for wind-excited tall buildings equipped with Tuned Mass Dampers (TMDs). The objective is to minimize the Life-Cycle Cost that comprises initial costs of the structure, the control system and costs related to repair, maintenance and downtime over the building's lifetime. The integrated optimization of structural sections and mass ratio of the TMDs is carried out, leading to a set of Pareto optimal solutions. The main advantage of the proposed methodology is that, differently from the traditional optimal design approach, it allows to perform the unified design of both the structure and the control system in a Life Cycle Cost Analysis framework. The procedure quantifies wind-induced losses, related to structural and nonstructural damage, considering the stochastic nature of the loads (wind velocity and direction), the specificity of the structural modeling (e.g., non-shear-type vibration modes and torsional effects) and the presence of the TMDs. Both serviceability and ultimate limit states related to the structure and the TMDs' damage are adopted for the computation of repair costs. The application to a case study tall building allows to demonstrate the efficiency of the procedure for the integrated design of the structure and the control system.

• Wind and Structures
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• 제23권6호
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• pp.523-542
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• 2016

Snowdrift formation on roofs should be considered in snowy and windy areas to ensure the safety of buildings. Presently, the prediction of snowdrifts on roofs relies heavily on field measurements, wind tunnel tests and numerical simulations. In this paper, a new snowdrift modeling method by using CFD (Computational Fluid Dynamics) coupled with DEM (Discrete Element Method) is presented, including material parameters and particle size, collision parameters, particle numbers and input modes, boundary conditions of CFD, simulation time and inlet velocity, and coupling calculation process. Not only is the two-way coupling between wind and snow particles which includes the transient changes in snow surface topography, but also the cohesion and collision between snow particles are taken into account. The numerical method is applied to simulate the snowdrift on a typical stepped flat roof. The feasibility of using coupled CFD with DEM to study snowdrift is verified by comparing the simulation results with field measurement results on the snow depth distribution of the lower roof.

• 국제초고층학회논문집
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• 제2권3호
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• pp.193-212
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• 2013

The Endless Column by Constantin Brâncuşi is "the most radical sculpture in the history of classic modernism", "the only one of modern times that can be compared with the great Egyptian, Greek and Renaissance monuments". It "is not only an artistic masterpiece, but also an extraordinary feat of engineering", the greatest example of collaboration between a sculptor and an engineer. This article illustrates the path that led the artist to conception of the column, its planning and construction, the investigations on preservation of the monument and its restoration, the aerodynamic tests in the wind tunnel, the modeling of the wind and the structure in virtue of which the aeroelastic instability, dynamic response and fatigue life were investigated. The conclusions discuss the column's role in the panorama of the great works of modern engineering.

• Wind and Structures
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• 제6권6호
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• pp.485-498
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• 2003

This paper presents a mechanical model of Rain-Wind Induced Vibration (RWIV) of stay cables. It is based on the physical interpretation of the phenomenon as given in Cosentino, et al. (2003, referred as Part I). The model takes into account all the main forces acting on cable, on the upper water rivulet (responsible of the excitation) and the cable-rivulet interaction. It is a simplified (cable cross-sectional and deterministic) representation of the actual (stochastic and three-dimensional) phenomenon. The cable is represented by its cross section and it is subjected to mechanical and aerodynamic (considering the rivulet influence) forces. The rivulet is supposed to oscillate along the cable circumference and it is subjected to inertial and gravity forces, pressure gradients and air-water-cable frictions. The model parameters are calibrated by fitting with experimental results. In order to validate the proposed model and its physical basis, different conditions (wind speed and direction, cable frequency, etc.) have been numerically investigated. The results, which are in very good agreement with the RWIV field observations, confirm the validity of the method and its engineering applicability (to evaluate the RWIV sensitivity of new stays or to retrofit the existing ones). Nevertheless, the practical use of the model probably requires a more accurate calibration of some parameters through new and specifically oriented wind tunnel tests.

• Wind and Structures
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• 제27권5호
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• pp.293-309
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• 2018

The prediction of multimode flutter relies, to a larger extent than bimodal flutter, on accurate modeling of the self-excited forces since it is challenging to perform experimental validation by using aeroelastic tests for a multimode case. This paper sheds some light on the accuracy of predicted self-excited forces by comparing numerical predictions of self-excited forces with measured forces from wind tunnel tests considering the flutter vibration mode. The critical velocity and the corresponding flutter vibration mode of the Hardanger Bridge are first determined using the classical multimode approach. Then, a section model of the bridge is forced to undergo a motion corresponding to the flutter vibration mode at selected points along the bridge, during which the forces that act upon it are measured. The measured self-excited forces are compared with numerical predictions to assess the uncertainty involved in the modeling. The self-excited lift and pitching moment are captured in an excellent manner by the aerodynamic derivatives. The self-excited drag force is, on the other hand, not well represented since second-order effects dominate. However, the self-excited drag force is very small for the cross-section considered, making its influence on the critical velocity marginal. The self-excited drag force can, however, be of higher importance for other cross-sections.

• 한국항공우주학회지
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• 제50권7호
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• pp.497-505
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• 2022

본 연구에서는 회전익기 통합 해석 코드인 CAMRAD II를 이용하여 풍동 시험용 Lift-offset 동축 반전 로터의 성능 및 허브 진동 하중 해석을 수행하였다. 본 논문에서는 전체 로터의 추력을 트림 목표 값으로 사용하는 트림 조건 및 상/하 로터 각각의 추력을 트림 목표 값으로 이용하는 트림조건을 사용하였다. 두 종류의 트림 기법에 대하여 다양한 전진비 및 Lift-offset 값을 고려하여 해석을 수행하였고, 계산된 결과를 선행연구의 풍동 시험 및 해석 결과와 상호 비교하였다. 두 종류의 트림 기법을 이용한 연구 결과에서 모두 다양한 전진비 및 Lift-offset 값에 대하여 상/하 로터 각각의 양력, 토크 및 전체 로터의 로터 유효 양항비가 선행연구의 풍동 시험 결과와 유사함을 확인하였다. 또한 로터의 2P 허브 진동 하중 해석 결과를 기반으로 Lift-offset 동축 반전 로터 허브의 진동 하중 특성을 확인하였다. 본 연구를 통하여 CAMRAD II를 이용한 풍동 시험용 Lift-offset 동축 반전 로터의 모델링 및 해석 기법을 적절히 구축하였으며, 성공적으로 검증하였다.

• 한국전산구조공학회논문집
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• 제33권1호
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• pp.1-7
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• 2020

트윈 빌딩의 풍응답은 풍하중의 공력 특성과 트윈 빌딩 구조 시스템의 동적 특성에 영향을 받는다. 본 논문에서는 트윈 빌딩의 두 빌딩의 간격이 다른 두 경우에 대해서 풍응답에 영향을 주는 풍압의 특성을 풍동 실험과 적합 직교 분해 기법을 이용해 파악하고, 3차원 구조 시스템 모델링을 통해 동특성을 파악하였다. 그리고 이중 모달 변환 기법을 이용해서 각 풍압의 특성과 구조물의 동특성이 풍응답에 미치는 영향을 파악하였다. 적합 직교 분해 기법을 통해서 채널링과 와류 효과에 대해서 파악할 수 있었다. 풍 직각 방향의 풍하중은 두 빌딩의 간격에 영향을 많이 받았으며, 풍 방향의 풍하중은 간격에 영향을 적게 받았다. 마찬가지로, 이중 모달 변환 기법에서 교차 참여 계수는 풍 직각 방향에서는 두 빌딩의 간격에 따라 크게 달라진 반면, 풍 방향은 영향이 적었다. 이에 따라 두 빌딩의 간격이 풍 방향의 풍응답 보다 풍 직각 뱡향의 풍응답에 중요한 역할을 하는 것을 알 수 있었다.

• International Journal of Aeronautical and Space Sciences
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• 제14권3호
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• pp.229-236
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• 2013

This paper presents the experimental investigation of a biplane micro air vehicle. The effects of geometric parameters, gap, stagger, and decalage angle are investigated at low Reynolds number (~150,000) in a low-speed wind tunnel. A rigid flat plate with an aspect ratio of one and square planform shape is used to evaluate all three geometric parameters. The side dimension of the single flat plate is 0.15 m. The goal is to find an optimal biplane configuration that should exceed monoplane performance by generating high lift and flying as slow as possible, in order to capture high-quality visual recordings. This configuration will directly help to fly at a lower velocity and to make tighter turns that are advantageous in restricted environments. The results show that the aerodynamic performance of the biplane MAV is significantly enhanced through the combination of gap and stagger effects. A performance comparison demonstrates the superiority of the optimal biplane configuration compared to a monoplane in cruise and glide phases. Moreover, no significant compromise is found for the range, endurance, and climb performance.