Breaking bore roller characteristics: Turbulence statistics using optical techniques

Air–water properties of unsteady breaking bores part 1: Novel Eulerian and Lagrangian velocity measurements using intrusive and non-intrusive techniques

“…Shi et al (2020) considered the breaking bore quasi-steady, combining synchronisation and optical flow to obtain dense velocity contours in the breaking bore roller. Their subsequent work (Shi et al, 2021) further quantified two-dimensional turbulence in the breaking bore roller.…”

“…The OF velocity data were calculated in the Eulerian frame of reference. Following the synchronisation technique by Shi et al (2021), the ensemble-averaged longitudinal (𝑉 𝑥,𝐸𝐴 ) and vertical (𝑉 𝑧,𝐸𝐴 ) velocities were obtained from 50,000 instantaneous OF values, as shown in Fig. 12, where 𝑥 𝑡𝑜𝑒 is the longitudinal coordinate of the roller toe.…”

“…The instantaneous velocity data were further derived from these trajectories, and were mapped into a structured grid using a data restructuring method modified from Aleixo et al (2011). The data restructuring method consisted in (1) dividing the image plane in a 𝑚 × 𝑛 grid, (2) relocating the instantaneous velocity data into the grid based on the relative location from the roller toe (Shi et al, 2021) and ( 3) averaging instantaneous velocity data in each grid bin. Care must be taken for the selection of grid size.…”

Air–water properties of unsteady breaking bore part 2: Void fraction and bubble statistics

“…The contour maps of instantaneous void fraction using EBDT were ensemble-averaged, based on 71,556 frames from 80 ultra-high-speed videos, denoted as 𝐶 𝐸𝐴 . The implementation of a synchronisation technique e spatially shifted the data using the reference position of the roller toe, assuming that the breaking bore translated as quasi-steady flow (Shi et al, 2021a). The contour plot of the ensemble-averaged void fraction using EBDT is presented in Fig.…”

Experimental research on the impact pressure of tidal bore fronts

“…Breaking bores, characterized by a single breaking roller followed by a few secondary waves (weak breaking bore) or violent aeration flow (strong breaking bore), exhibit different hydrodynamic characteristics from undular bore. Pierre et al [12] present numerical simulation of a weak breaking bore, while Leng et.al [13] and Shi et.al [14] studied the roller characteristics of breaking bore, revealing a strongly three-dimensional turbulent flow motion. Pan et al [15] deduced a relationship between the tidal bore propagation velocity and the height of the upper and ebb stream based on the one-dimensional continuity equation and momentum equation.…”