Filtering Characteristics of Phonon Polaritons Waves Based on Dielectric-h-BN-Dielectric Structure in Mid-Infrared Band

Hyperbolic materials can be used to excite hyperbolic phonon polaritons in specific frequency bands, which causes abrupt interfaces with fluctuations of permittivity and different transmission characteristics at different incident wavelengths. Using the quasi-static approximation, the filtering characteristics of hexagonal Boron nitride (h-BN) and the transmission characteristics of phonon polaritons waves on a dielectric-h-BN-dielectric structure were studied in the paper. The results show that a smaller relative permittivity of the materials above and below h-BN and a thicker h-BN (ε1 = 1 (air), ε2 = 3.9 (SiO2), d = 100 nm) will lead to better filtering characteristics for different wavenumbers’ incident waves (propagation length from 0.0028 μm to 1.9756 μm). Simulation results in COMSOL validated the previous theoretical calculations. Moreover, the transmissivity and 3dB bandwidth of the type-II band were calculated with different structure widths. The maximum transmissivity of ~99% appears at a width of 100 nm, and the minimum 3dB bandwidth reaches 86.35 cm−1 at a structure width of 1300 nm. When the structure width meets or exceeds 1700 nm, the 3dB bandwidth is equal to 0, and its structure length is the limit for the filter application. These characteristics reveal the excellent filtering characteristics of the dielectric-h-BN-dielectric structure, and reveal the great potential of using the dielectric-h-BN-dielectric structure to design optical filter devices with excellent performance in mid-infrared bands.

Performance Analysis of a Semicircular Free Surface Ocean Structure under the Different Water Depths

The increasing importance of the sustainability challenge in o engineering has led to the development of free surface ocean structure of various configurations. In this study, the hydrodynamic characteristics of a perforated free surface, semicircular breakwater (SCB) are investigated for irregular wave conditions under the different water depths. The performance of the breakwaters was evaluated in the form of coefficients of transmission (CT), reflection (CR) and energy dissipation (CL). The measured wave modification in front of the structure and in the structure’s chamber were quantified and presented in the form of a ratio relative to the incident wave height, respectively, which are then presented as a function of the relative immersion depth (D/d) and the relative structure width (B/Lp), where D = the depth of immersion, d = the water depth, B = the structure width and Lp = the wavelength corresponding to the peak wave period. The measured wave modification in front of the structure and in the breakwater’s chamber were quantified and presented in the form of a ratio relative to the incident wave height, respectively. It is found that the wave attenuation ability of the SCB model improves with the increase of D/d and B/Lp. The SCB performs better as an energy dissipater than as a wave reflector.

Ice loads from first-year ice ridges and rubble fields

A method for estimating global loads from consolidated first-year ice ridges and rubble fields on wide Arctic offshore vertical-sided structures is presented. The method utilizes full-scale global ice load measurements in the Arctic to represent the failure behavior of the consolidated layer and a Mohr-Coulomb approach for the remaining layers. By including full-scale data, the model can take into account the effects of scale and non-simultaneous failure of the consolidated ice layer across the structure width. The results are compared with those obtained from several other first-year ice ridge and rubble field load models.Key words: first-year ice ridges, rubble fields, ice load and pressure measurements, Arctic structures, ice load models.

Third Canadian Geotechnical Colloquium: Ice forces on wide structures

Successful use of artificial islands as exploration drilling platforms in the southern Beaufort Sea requires an understanding of the interactions of ice sheets with wide structures. Ice forces exerted on wide structures arise from the mechanical processes inherent in particular ice failure modes as environmental stresses move an ice sheet past a structure. Four primary ice failure modes occur against wide structures: flexure, rubble formation, buckling, and crushing. The horizontal forces associated with these modes differ by more than two orders of magnitude depending on structure geometry, ice sheet properties, and ice movement rates. Structure width influences the occurrence of ice failure modes, the ice failure stresses, and the total forces that can be exerted on a structure by an ice sheet. The relative inability to clear failed ice around wide structures (compared with narrow structures) leads to rubble formation when ice movement is continuous. After consolidation, the resulting rubble field can amplify forces exerted on the structure. Increased structure width generally results in decreased expected forces per unit width of structure. For crushing, the most serious ice failure mode for island design, increased structure width generates the possibility of nonsimultaneous failure. The resulting averaging of statistical variations across the width leads to reduced expected stresses for wide compared to narrow structures.