Investigation of Multiply Composite Artificial Bars for Bragg Scattering of Water Waves

Abstract

The Bragg scattering of water waves by multiply composite artificial bars was investigated both theoretically and experimentally. Miles' theory is first employed to derive general formulae to calculate Bragg reflection coefficients for multiply composite artificial bars with different shapes, spacings, bar heights, bar footprint, and the number of bars. The theory provides explicit expressions in estimating Bragg reflections over multiply composite bars in practical engineering applications. The undulating oscillation components expanded with respect to the bottom slope and curvature components in the numerical model can increase the accuracy for the simulation of Bragg scattering. Experiments of Bragg reflection over multiply rectangular artificial bars were also conducted in a wave flume. Analytical solutions are in good agreement with numerical simulations of evolution equation of mild-slope equation (EEMSE) and laboratory experiments. Influence parameters that may lead to the optimal combination of a multiple artificial bar to increase the bandwidth of Bragg resonance were studied.

Wave reflection and vortex evolution in Bragg scattering in real fluids

“…Notably, both the numerical and theoretical predictions of Bragg scattering neglect the role of the viscosity; most studies focus on the wave profile transformation of waves propagating over bottom undulations (e.g., Dalrymple and Kirby, 1986;Kirby and Anton, 1990;Hsu et al, 2003;Hsu et al, 2007;Tsai et al, 2011). The level of viscosity, however, can be important and in some situations the numerical results gathered when neglecting its influence fail to describe the real flow interaction process.…”

Experimental study on the hydrodynamic characteristics of a Bragg breakwater with triple vertical plates

“…Hsu et al [30] numerically investigated the Bragg scattering of multiply composite artificial bars by varying the relative bar height and the number of bars with different intervals, and showed that the bandwidth of high-performance region was increased. Tsai et al [31] investigated theoretically and experimentally the Bragg scattering of water waves by multiple composite artificial bars with different shapes, spacings, bar heights, bar footprint, and the number of bars, and the increased bandwidth was observed. Recently, in the respect of free surface breakwater, Ding et al [32] numerically studied the interaction of water waves with multiple composite flexible membranes by changing the relative group spacing, the end condition, the number, the tension, the draft and the protrusion of the membranes, and found that the bandwidth of Bragg reflection was increased compared to the multiple uniform-spacing flexible membranes.…”

Viscous numerical wave tank for Bragg resonance by cnoidal and Stokes waves

“…Hsu et al (2007) used a second-order fully non-linear Boussinesq type model to explore Bragg reflection of irregular waves. Tsai, Kuo, Lan, Hsu, and Chen (2011) investigated the Bragg scattering of multiply composite artificial bars and validated their results by using the EEMSE model (Hsu, Tsai, & Huang, 2003). However, linear theoretical and numerical predictions are limited to the potential assumptions used.…”