This paper presents a novel lattice Boltzmann (LB) model for neutron transfer and a block-structured adaptive-mesh-refinement (SAMR) technique for proposed LB model. By discretizing the general Boltzmann equation, the LB model for neutron transfer is established and the corresponding parameters are obtained. The SAMR technique removes the requirement of tree-type data structure in traditional adaptive-mesh-refinement technique and adjusts the time step adaptively and identically in all blocks. By applying the node-type distribution function, the needs for rescaling the distribution functions is eliminated. To solve the discontinuities of scalar flux at fine-coarse blocks interface, a novel technique is presented which treats the inner boundary condition by streaming process of LB method. Simulation results show good accuracy and efficiency of the proposed neutron LB model with SAMR technique. This paper may provide a powerful technique for large engineering calculation.
The ability to tune the emission wavelength of infrared emitter while maintaining wavelength‐selectivity remains a challenge. By incorporating the nonvolatile phase‐changing material Ge2Sb2Te5 (GST), a nonvolatile tunable wavelength‐selective emitter (gold (Au)‐GST‐Au structure) based on Fabry–Perot (FP) resonance theory is demonstrated. An algorithm based on Bayesian optimization (BO) and transfer matrix method (TMM) for optimal design is proposed. First, the influence of amorphous proportion on tunability is investigated. It is found that the peak emission wavelength shifts from 5.3 to 3.8 μm and peak emissivity increases from 0.75 to 0.98 with an increase of the amorphous proportion. Second, the influence of the thickness of the top and middle layer on the emission spectrum is studied. It is illustrated that the thickness of each layer has a significant impact on the emission spectrum. Finally, an objective function considering wavelength‐selectivity in atmospheric and nonatmospheric windows as well as tunability is proposed. The optimal structure can be realized within calculations for less than 0.027% of total candidate structures. When the weight w = 0, the optimal structural parameters are dAu = 0.0018 μm and dGST = 0.4318 μm; and the effect of the weight factor in objective function is also investigated.
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