PhD Oral Exam - Theodore Potsis, Building Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Moving towards a new era where structural engineering applications will rely more on Computational Fluid Dynamics as means to evaluate wind related characteristics, this thesis demonstrates a novel computational technique to model wind flow and wind-induced structural loads. During the last decades there have been continuous efforts in modelling efficiently turbulent flows by the practice and scientific community. Various methodologies have been discussed in the literature, but their applicability for structural design remains problematic, thus wind design standards and codes of practice hesitate to adopt computational procedures for structural loads. Therefore, a new tool that serves the engineering needs while respecting the scientific requirements has been developed.

The so-called Dynamic Terrain method utilizes velocity time series extracted from the Concordia Wind Tunnel as inlet conditions. A first target achieved was to model accurately the energy of the fluctuations of turbulence scales that are smaller than the building characteristic dimensions. This accomplishment covers a research gap in the state-of-the-art identified during a comprehensive review study. Another achievement is the ability of the method to model various exposure conditions, in addition to the characteristic standard open, suburban and urban exposures. Quasi-steady conditions are assumed for the inlet time series as to respect physical aspects such as the divergence-free criteria and numerical stability. The final pressure time series are extracted by filtering the numerical data to account for the inherent discontinuity of the inlet conditions and their propagation in the computational domain.

With this engineering tool, modelling of wind flow and peak pressures on building envelopes become possible via simple procedures and advantageous techniques, compared with similar approaches currently available. Validation of wind flow and pressure characteristics are presented for various structural applications. Mean, std and peak pressures have been validated for loads on low-rise buildings based on experiments from TPU, NIST and the Concordia Wind Tunnel. The accuracy is within acceptable margins established by comparisons among the experimental results from respective wind tunnel facilities. The tool is incorporated in an open database, where experimental data from the Concordia Wind Tunnel and OpenFOAM libraries are included for free usage by practitioners and scientific groups.