Influence Of Media Properties Research Articles

Accelerating microwave tomography based on generalized analytical singular value decomposition

In this paper, a 2-D microwave tomography system with circular observation domain is proposed. By means of Analytical Singular Value Decomposition (ASVD) object reconstruction process significantly accelerated. The spectral expansion of the Green’s function is employed to derive generalized SVD of scattering integral operator. The analytical formulation of singular values and vectors is straightforward without considerable computation cost. Influence of medium properties and configuration on singular values are studied numerically. Also, the performance of the proposed method is validated against experimental data. Thanks to the spectral representation, truncation parameter for singular values can be determined in a closed form. As a result, small singular values can be filtered out to ensure stability.

参与性介质中脉冲激光回波信号的角度特性

To improve the echo signal-to-noise ratio and temporal-spatial resolution of active detection systems further, the two-way transient radiative transfer model of ultrashort pulse laser in participating medium is established using Monte Carlo method. Based on the model above, the influence of medium properties and target reflective characteristic on the angular characteristic of Gaussian pulse laser echo signal in isotropic scattering medium is analyzed. Research shows that the incident zenith angles of target echo signal have reached its steady state in optically thick medium, with the peak angle interval of 30~40 and the energy concentration range of 30~50, but the temporal broadening characteristic is irrelevant to angle intervals; the spectral attenuation coefficient affects the energy attenuation and pulse width of echo signal strongly, but the scattering albedo embodies in the energy attenuation of post-echo signal mainly; high intensity pre-echo signal caused by specular reflection weakens, and the absolute difference of target echo signal is extremely small between specular reflection and diffuse reflection, with weaker relevance. The reference for gated-camera design selection and pulsed laser wavelength is provided. , 2015, Science Press. All right reserved.

Challenges in the Application of Fractional Derivative Models in Capturing Solute Transport in Porous Media: Darcy-Scale Fractional Dispersion and the Influence of Medium Properties

Heterogeneous media consisting of segregated flow regions are fractional-order systems, where the regional-scale anomalous diffusion can be described by the fractional derivative model (FDM). The standard FDM, however, first, cannot characterize the Darcy-scale dispersion through repacked sand columns, and second, the link between medium properties and model parameters remains unknown. To fill these two knowledge gaps, this study applies a tempered fractional derivative model (TFDM) to capture bromide transport through laboratory repacked sand. Column transport experiments are conducted first, where glass beads and silica sand with different diameters are repacked individually. Late-time tails are observed in the breakthrough curves (BTC) of bromide even in relatively homogeneous glass beads. The TFDM can capture the observed subdiffusion, especially the late-time BTC with a transient declining rate. Results also show that both the size distribution of repacked sand and the magnitude of fluid velocity can affect subdiffusion. In particular, a wider sand size distribution or a smaller flow rate can enhance the subdiffusion, leading to a smaller time index and a higher truncation parameter in the TFDM. Therefore, the Darcy-scale dispersion follows the tempered stable law, and the model parameters might be related to the soil size and flow conditions.

Influence of Media Properties on Fluid Flow in Faulted and Fractured Anisotropic Media: A Study Using a Modified Flux-Vector-Based Green Element Method

This article illustrates the use of the modified ‘q-based’ GEM for complex geological problems in anisotropic media involving faults/fractures, by adopting various values of the permeability for both the faults/fractures and the media. The bulk permeabilities are compared and illustrated for different cases. Examples based on generating randomly positioned faults for which the number of faults can vary, but the sum of their lengths is fixed, are investigated. Situations are presented for a number of different total fault lengths and for various physical properties of the faults within a fixed total fault length. For some of the cases, particle traces are shown to better illustrate the behaviour of the flow.

NUMERICAL ANALYSIS OF THE STRESS JUMP INTERFACE CONDITION FOR LAMINAR FLOW OVER A POROUS LAYER

A number of natural and engineering systems can be characterized by some sort of porous structure through which a working fluid permeates. Boundary layers over tropical forests and spreading of chemical contaminants through underground water reservoirs are examples of important environmental flows that can benefit form appropriate mathematical treatment. For hybrid media, involving both a porous structure and a clear flow region, difficulties arise due to the proper mathematical treatment given at the interface. The literature proposes a jump condition in which stresses at both sides of the interface are not of the same value. The objective of this article is to present a numerical implementation for solving such a hybrid medium, considering here a channel partially filled with a porous layer through which fluid flows in laminar regime. One unique set of transport equations is applied to both regions. Numerical results are compared with available analytical solutions in the literature for two cases, namely, with and without the nonlinear Forchheimer term. Results are presented for the mean velocity across both the porous structure and the clear region. The influence of medium properties, such as porosity and permeability, is discussed.