Flexural-wave-generation using a phononic crystal with a piezoelectric defect

This paper proposes a method to amplify the performance of a flexural-wave-generation system by utilizing the energy-localization characteristics of a phononic crystal(PnC)with a piezoelectric defect and an analytical approach that accelerates the predictions of such wave-generation performance.The proposed analytical model is based on the Euler-Bernoulli beam theory.The proposed analytical approach,inspired by the transfer matrix and S-parameter methods,is used to perform band-structure and time-harmonic analyses.A comparison of the results of the proposed approach with those of the finite element method validates the high predictive capability and time efficiency of the proposed model.A case study is explored;the results demonstrate an almost ten-fold amplification of the velocity amplitudes of flexural waves leaving at a defect-band frequency,compared with a system without the PnC.Moreover,design guidelines for piezoelectric-defect-introduced PnCs are provided by analyzing the changes in wave-generation performance that arise depending on the defect location.

Numerical study of edge waves using extended Boussinesq equations

An edge wave numerical model was developed based on extended Boussinesq equations with the internal wave-generation method. The form of edge waves near a seawall was chosen as the input signal in order to avoid treatment of the moving shoreline on a sloping beach. As there was an energy transfer between different edge wave modes, not only the target mode but also other modes appeared in the simulations. Due to the nonlinear effect, the simulation results for mode-0 edge waves were slightly modulated by mode-1 and mode-2 waves. As the magnitudes of these higher-mode waves are not significantly related to those of the target mode, the internal wave-generation method in Boussinesq equations can produce high-quality edge waves. The numerical model was used to investigate the nonlinear properties of standing edge waves, and the numerical results were in strong agreement with theory.

Analytical estimation of mixing coefficient induced by surface wave-generated turbulence based on the equilibrium solution of the second-order turbulence closure model

Based on the equations of motion and the assumption that ocean turbulence is of isotropy or quasi-isotropy, we derived the closure equations of the second-order moments and the variation equations for characteristic quantities, which describe the mechanisms of advection transport and shear instability by the sum of wave-like and eddy-like motions and circulation. Given that ocean turbulence generated by wave breaking is dominant at the ocean surface, we presented the boundary conditions of the turbulence kinetic energy and its dissipation rate, which are determined by energy loss from wave breaking and entrainment depth respectively. According to the equilibrium solution of the variation equations and available data of the dissipation rate, we obtained an analytical estimation of the characteristic quantities of surface-wave-generated turbulence in the upper ocean and its related mixing coefficient. The derived kinetic dissipation rate was validated by field measurements qualitatively and quantitatively, and the mixing coefficient had fairly good consistency with previous results based on the Prandtl mixing length theory.

A 2-D NUMERICAL IRREGULAR WAVE TANK AND ITS VERIFICATION

A two-dimensional numerical irregular wave tank based on the potential wave theory was developed. A source term was used inside the domain to generate waves, and outgoing waves were dissipated by sponge layers and transmitted by radiation boundary. The σ-coordinate transformation was introduced to map the time-dependent irregular physical domain to a fixed regular computational domain, and thus the free surface and bottom boundary conditions could be implemented precisely. The model was verified by simulating the nonlinear regular and irregular wave propagation on constant-depth water, as well as regular waves reflected from a vertical wall, and satisfactory agreement between numerical results and analytical solutions was obtained. The present numerical model is proved to be an effective tool for a long-duration simulation of coastal wave dynamics where the wave reflection is significant.

Experimental investigation of regular wave propagation over an idealized reef model

The wave transformation over the deep-sea coral reefs is an essential issue in the analysis of the reef ecosystem and the design of large reef-top structures.Extensive wave flume experiments are conducted to investigate the wave transformation processes over an idealized reef model.Detailed measurements of the wave height,the wave set-up and the wave-generated flow on the reef-top are made with and without the reef-top structure at various submerged depths and under different wave conditions.It is found that the reef-top structure has a significant influence on the wave breaking,the wave set-up and the wave-generated flow.The wave set-up increases with the increasing wave height and the decreasing submergence depth.However,the relationship between the wave set-up and the wave period is complex,influenced by the reef-top structure.