Doctor of Philosophy
Civil and Environmental Engineering
Bitsuamlak, Girma T.
Driven by the burgeoning growth of computing power over the last few decades, the capability of computational fluid dynamics (CFD) to simulate turbulent flows of practical interest has progressed rapidly. In the past, a notable research effort has been dedicated to applying CFD for modeling wind loads on structures, particularly for tall buildings. However, the current state of CFD for wind load evaluation of tall buildings using Large-Eddy Simulation (LES) has several critical challenges, including the treatment of atmospheric boundary layer (ABL) flow conditions, turbulence modeling of separated flows around buildings, and simulation of wind-structure interaction for dynamically sensitive buildings. For CFD to be a practically useful wind engineering tool, these challenges must be addressed adequately meeting the rigors of the current wind engineering practice. This thesis presents the development of a CFD-based framework for accurate aerodynamic and aeroelastic modeling of tall buildings with the objective of overcoming these key limitations. The capabilities of the framework are demonstrated using a series of case studies.
The CFD-based framework is developed in three major phases. In the first phase, computationally efficient methods were developed for modeling the characteristics of the approaching ABL turbulence. A novel synthetic inflow turbulence generation method is proposed that satisfies two-point flow statistics coupled with an implicit ground roughness modeling technique to represent the local terrain effect. In the next phase of the framework, aerodynamic wind loads on tall buildings having different surrounding configurations are simulated and validated against wind tunnel results. Initially, the cladding and overall loads, as well as responses of an isolated standard tall building, are investigated. Then, the framework is applied to a more realistic case involving a complex-shaped tall building located in a city center. In the final phase of research, the capability of the framework is extended by implementing a high-fidelity fluid-structure interaction (FSI) procedure to model the aeroelastic response of tall buildings. The implemented FSI algorithm uses a partitioned approach that couples a transient fluid solver with a multi-degree-of-freedom model of the building. Then the FSI procedure is applied to simulate the aeroelastic response of a tall flexible building. Overall, comparing the results from each phase of the study with wind tunnel measurements showed an encouraging level of agreement. It is expected that the framework presented in this thesis is of practical importance to the wind-resistant design of tall buildings.
Summary for Lay Audience
Over the last few decades, the power of computers has shown rapid growth, making it possible to simulate complex wind flow using numerical models. This development attracted interest in modeling wind loading on structures, particularly tall buildings, that are more susceptible to wind effects. However, computational modeling of wind load on tall buildings accurately has several critical challenges. To mention some, replicating the natural wind around the building site, capturing its complex behavior around buildings, and simulating its interaction with the motion of the building. To make computational methods practical design tools, these challenges must be resolved by adhering to the rigor of established experimental testing practices. This thesis presents the development of a high-fidelity computational framework for accurately modeling wind loads on tall buildings. The capabilities of the framework are demonstrated using a series of case studies.
The computational framework is developed in three major phases. In the first phase, a new technique was developed to mimic the natural wind approaching a building with minimal computational cost. In the next step of the framework, wind effects on tall buildings situated in different surrounding configurations are simulated and compared with experimental measurements. At this stage of development, the structure is modeled by neglecting its swaying motion. The primary wind effects simulated on the building are the pressure exerted on its façades and the cumulative force on the entire building structure. The final research phase expands the framework to model the two-way interaction between the building and the wind. The wind blows on the structure causing it to sway, and the tower disturbs the air around it while swinging. Such kind of simulation was achieved by integrating two computational entities: the wind flow model and the structural model of the building. Then, this technique is applied to simulate the swaying motion of a tall building under strong wind conditions. Finally, comparing the results from each phase of the study with experimental measurements showed an encouraging level of agreement. The framework presented in this thesis is expected to have practical relevance for designing tall buildings that can withstand wind effects.
Melaku, Abiy Fantaye, "A Computational Framework for Aerodynamic and Aeroelastic Modeling of Wind Loads on Tall Buildings" (2023). Electronic Thesis and Dissertation Repository. 9277.
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