ABSTRACT
This paper presents laboratory results in which the free surface oscillations that are caused by the interaction between an open-channel flow and a lateral cavity are measured. For a square cavity with a side length equal to the width of the main stream, this oscillation phenomenon, named seiching, can result in standing waves in both the transverse and longitudinal direction for the same flow case. This bidirectional aspect of seiching is confirmed by the current results using a Fourier transform of the surface registrations in both the cavity and the main channel area. More importantly, a wavelet analysis in the time and frequency domains shows that bidirectional seiching is not a stationary phenomenon since the wavelet power of the two observed seiching modes varies significantly in time. Therefore, a more time-localised approach is used, which reveals that the entire measurement period can be subdivided in time windows where only one of the two seiching modes is considerably excited.
