![]() Generic variants of the measured rough profiles are generated by the Weierstrass-Mandelbrot function through altering the fractal dimension D and length-scale parameter G. The rough surface is characterized by a 3D-Laser profiler and the fractal dimension of the cleat surface is quantified. In this paper, we develop a numerical model of coal seam gas diffusion and adsorption considering surface roughness based on fractal statistics and the lattice Boltzmann method. Direct studies on the effects of surface roughness for methane migration in coal by experimental methods are difficult to perform because the micro-scale heterogeneous pore structure and methane sorption properties are difficult to observe and therefore robust numerical simulations provide the most comprehensive method of investigation. Roughness plays an important role because adsorption is very sensitive to the change in the area. The main mode of gas flow is supported by the cleat network pattern for which the surface roughness is a very significant property of gas transport. The problem has attracted interest from many fields such as microstructural characterization, permeability-, porosity-, fluid flow-, diffusion-, adsorption/desorption- and adsorption-induced deformation studies. Of particular interest is the mode of microscale gas transport through so-called coal cleats which form a network of micro-channels/fractures and allow for gas transfer through impermeable coal seams. Unconventional energy such as coal seam gas is trapped in a low porosity/permeability environment and poses challenges for production. ![]() ![]() Besides, nonlinear GARPFrMT, color space rotation, together with 3D scrambling and bitwise XOR operation make the proposed color image encryption algorithm have good performance.The simulation results have shown that the proposed encryption schemes are capable of resisting different common attacks and robust against noise and occlusion attacks. In this encryption scheme, for gray image, the Arnold transform and the bitwise XOR operation are also adopted to encrypt the image in order to enhance the security.Finally, the encryption algorithm based on Gaussian apertured reality-preserving FrMT (GARPFrMT) used for color image is proposed. With the Gaussian apertured FrMT in diffraction domain, a reality-preserving transform is proposed and used for image encryption. This hard aperture is not only used to control the amount of light passing the lens by adjusting its size, but also reduces the leakage of light, which will, to some extent, enhance the robustness against direct attacks.Secondly, the Gaussian aperture, as a soft aperture for balancing between hard aperture and no aperture, is introduced into the apertured FrMT. The side-lengths of the hard aperture serve as a key to improve the security and further increase the key space of the encryption system. The apertured fractional Mellin transform (apertured FrMT) can be performed through the log-polar transform and the apertured fractional Fourier transform in diffraction domain. The main work is as follows:Firstly, an optical image encryption scheme based on the fractional Mellin transform with a hard aperture has been proposed. Inverse fourier transform calculator series#The feasibility of the proposed encryption schemes is verified by a series of numerical simulations. This thesis focuses on the study of introducing the aperture into FrMT in diffraction domain (FrMT) and its application in optical image encryption system. ![]()
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