**4. POD analysis of surface pressure**

The rectangular building with AOA of 0°and 90°represents two different side ratio cases, in which the twisted wind can exert remarkably different effects on the pressure pattern. As a result, to better understand the fluid–structure interaction mechanism, POD was employed to identify the pressure patterns hidden in the fluctuating pressure field on the building surface.

## **4.1 Mode energy distribution**

The energy contributions of the dominant modes and the normalized cumulative number of modes are presented in **Figure 7**. Affected by twisted flow, the fluctuating energy of each pressure mode was reduced to a certain degree, especially for the dominant modes. The energy proportion of the first mode in the case of 0°AOA was larger than that in the case of 90°AOA for the two different flow types CWP and TWP30. Moreover, the difference in the energy percentage between the dominant modes for the case 0° AOA was much more significant in comparison with that of 90° AOA. For example, the fluctuating energy occupied by the first mode of CWP with 0° AOA was around 33%, more than twice that of the second mode. This observation can be attributed to the fact that a tall building with a larger side ratio can produce more complicated flow motion, topology, and behavior. As a result, to reach 90% of the total energy, only the first 5% modes were needed for case 0°AOA, but much larger modes of 24% were needed for the 90° AOA case.
