Abstract
In this paper, we use laboratory wave tank experiments to study the effect of asymmetry and defects on the bandgaps of surface water waves and use the finite element numerical method to validate our results. We demonstrate here that breaking the mirror symmetry around the midplane of a periodic structure introduces multiple bandgaps in the spectrum caused by the involvement of high-order transverse modes. The results show that the presence of a defect in the structure leads to the formation of a strong defect mode in the Bragg gap, which is localized around the defect element and a weak mode in the induced non-Bragg gap. The results show that the bandgap excited by symmetry breaking is much narrower due to the weak mode coupling. In addition, at the non-Bragg resonance frequency in the defect state, the transverse water surface wavefield distribution around the defect is asymmetric about the midplane of the channel. The multiple transmission modes in the spectrum of the structure can be applied in the design of Bragg reflection-based wave attenuation structures that can help protect shorelines and coastal infrastructure. The asymmetry of the surface wavefield in the non-Bragg gap can be applied in the development of energy harvesting technologies. Due to the generality of wave phenomena in periodic structures, the findings of this research provide a basis for more research in physical acoustics and optics and may lead to the development of cutting-edge appliances, such as bandpass filters.
Highlights
Analysis of surface water wave propagation in periodic structures is a subject of intense research due to its potential applications in oceanic water wave engineering technologies
The results show that the presence of a defect in the structure leads to the formation of a strong defect mode in the Bragg gap, which is localized around the defect element and a weak mode in the induced non-Bragg gap
We have performed experiments to investigate the influence of the sidewall symmetry on the bandgaps of surface water waves in a rectangular periodic structure and validated our results using finite element method simulations
Summary
Analysis of surface water wave propagation in periodic structures is a subject of intense research due to its potential applications in oceanic water wave engineering technologies. To the author’s knowledge, the problem of surface water waves in square wallcorrugated asymmetric structures, despite its potential application in practical water wave control and coastal protection, has yet to be considered experimentally and numerically. Primarily motivated by the observation of interesting phenomena in electromagnetic, acoustic, and elastic waves, and further, by the success of the use of Bragg reflections for water wave control and practical engineering application in shoreline protection, we use a rectangular water trough having a periodic array on its sidewalls of rectangular glass blocks to demonstrate the existence of multiple stopbands in the asymmetric structure. The existence of multiple bandgaps in the same structure that was initially symmetric will provide an enhanced opportunity to better control surface water waves and merit reference in the design of more efficient Bragg reflection-based wave attenuation structures in ocean environments. V, a summary of the study and its findings are presented under the conclusion
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