Biblio

From the perspective of time domain, the propagation characteristics of sound waves in seawater can be seen more intuitively. In order to study the influence and characteristics of seamount on low frequency acoustic propagation, the research of this paper used the Finite Element Method (FEM) based on time domain to set up a full-waveguide low-frequency acoustic propagation simulation model, and discussed the influencing laws about acoustic propagation on seamount. The simulation results show that Seamounts can hinder the propagation of sound waves, weaken the energy of sound waves. The topographic changes of seamounts can cause the coupling and transformation of acoustic signals during the propagation which can stimulate the seabed interface wave.

Each year, large ground motions from earthquakes cause infrastructure damage and loss of life worldwide. Here we present a novel concept that redirects and attenuates hazardous seismic waves using an engineered seismic-muffler acting as a cloaking device. The device employs vertically-oriented, sloping-opposing boreholes or trenches to form muffler walls and is designed to: 1) reflect and divert large amplitude surface waves as a barrier, while 2) dissipating body and converted waves traveling from depth upward into the muffler duct. Seismic wave propagation models suggest that a seismic-muffler can effectively reduce broadband ground motion directly above the muffler. 3D simulations are also compared for validation with experimental data obtained from bench-scale blocks containing machined borehole arrays and trenches. Computer models are then scaled to an earth-sized model. Results suggest a devastating seismic energy magnitude 7.0-\$\textbackslashtextbackslashmathrm M\_\textbackslashtextbackslashmathrm E\$ earthquake can be reduced to less damaging magnitudes experienced in the muffler vicinity, 4.5- \$\textbackslashtextbackslashmathrm M\_\textbackslashtextbackslashmathrm E\$ (surface wave) and 5.7- \$\textbackslashtextbackslashmathrm M\_\textbackslashtextbackslashmathrm E\$ (upgoing coupling into the muffler). Our findings imply that seismic-muffler structures significantly reduce the impact of the peak ground velocity of dangerous surface waves, while, seismic transmission upward through the muffler base at depth has marginal effects.

A novel method for computation of modal reflectivity at optical waveguide end-facet is presented. The method is based on the characteristic Green's function (CGF) technique. Using separability assumption of the structure and rational function fitting method (RFFM), a closed-form field expression is derived for optical planar waveguide. The uniform derived expression consists of discrete and continuous spectrum contributions which denotes guided and radiation modes effects respectively. An optimization problem is then defined to calculate the exact reflection coefficients at the end-facet for all extracted poles obtained from rational function fitting step. The proposed CGF-RFFM-optimization offers superior exactness in comparison with the previous reported CGF-complex images (CI) technique due to contribution of all components of field in the optimization problem. The main advantage of the proposed method lies in its simple implementation as well as precision for any refractive index contrast. Excellent numerical agreements with rigorous methods are shown in several examples.