Extended spectral proper orthogonal decomposition for analysis of correlated surrounding flow structures and wind load components of a building

Proper orthogonal decomposition (POD) has been used in numerous studies in wind engineering to extract key features of a building's surrounding flow field and surface pressure, the connections between which, however, remain difficult to quantify. This study combined the extended POD with spectral POD (SPOD) method into a new method called extended SPOD (ESPOD) to correlate flow structures with surface pressure. SPOD wind force spectra were defined to quantify how much each pair of velocity and pressure modes contribute to the wind force on a building. The method was validated by a case study on a typical isolated high-rise building, in which periodic coherent structures were extracted to reveal the main mechanisms of the wind forces, including the influences from approaching turbulence, wake vortices, and conical vortices. Phase synchronization, which is utilized in ESPOD, is an effective criterion for distinguishing the multiple physical mechanisms at the same frequency. Additional information provided by the correlated velocity mode helps interpret the physical meanings of the relatively less informative pressure modes. Finally, compared to velocity-based approaches, the pressure-based approach can capture the wind force fluctuations more completely, and the velocity modes are not distorted too much by the non-optimal decomposition.