Porous and cracked rocks elasticity: Macroscopic poroelasticity and effective media theory

Macroscopic poroelasticity and effective medium theory are two independent approaches which can be used to analyze the role of pores, cracks, and fluid on elastic properties. Macroscopic poroelasticity belongs to the macroscopic framework of thermodynamics whereas effective medium theory expresses the medium properties in terms of microstructural characteristics (pore and crack shape, etc.) and component properties (fluid properties, solid grain properties, etc.). In this paper, we review the fundamental assumptions and results of both approaches, and show that they are complementary but do not apply over the same range of conditions. A compilation of data is reported, in various dry and saturated rocks, to show the validity of the Gassmann equation and the dispersion between unrelaxed modulus –where effective medium model applies- and relaxed modulus –where poroelasticity applies.

Efficient Techniques for Solution of Complex Computational Tasks in Building Physics

Various simplification or optimization techniques are sought that reduce demands of computational modeling on time or computing power while keeping a sufficient level of accuracy. In this paper, determination of hygrothermal performance of a brick block is presented using two homogenization techniques based on different principles. While the computational homogenization technique uses a multiscale method realized on the master/slave computer system, the materials homogenization comes out from the effective media theory (EMT), and after the determination of effective material properties, the whole isotropic problem can be transformed to one dimension. Contrary to most applications of EMT, free parameters of mixing formulas are not determined based on an experimental measurement of a single material property but on a complex hygrothermal performance of the element where the distribution of moisture and temperature over a reference year is taken into account. The calculated results from both techniques are compared with results obtained by high-performance computing without any computational simplifications. For materials homogenization, the best results are achieved when k = 0.9 in Lichtenecker’s mixing rule is assumed, which corresponds to a nearly parallel arrangement of the block. The root mean square error (RMSE) of relative humidity (RH) and temperature distribution is only 0.992% and 0.566°C, respectively. This is even better than the results of computational homogenization (RMSE: 1.502% of RH and 0.629°C). Besides obtaining sufficiently precise results, a significant time-saving is achieved, accounting for more than 99%, while being solved on a single-processor computer.

High Permeability of Z-Type Ferrite Sheets Directional Array

Z-type ferrite sheets were prepared by chemical precipitation method to investigate influences of directional arrays from the Z-type ferrite sheets on magnetic properties. The permeability of the ferrite directional arrays was obviously improved in the specific direction. Assuming that the intrinsic permeability of Z-type ferrite was existed, the magnetic permeability in array was calculated by the Maxwell-Garnett equation of effective media theory. The reason for the large difference between the theoretical calculation and measured value was also discussed.

Property Analysis for Microwave Absorbing Material Based on Effective Medium Model

In order to predict the absorbing properties of absorbing material effectively in theory, effective media theory was applied to reduce the effective electromagnetic parameters of several composite absorbing agents under different volume ratio. The comparison with experimental data shows that this method can well forecast the absorbing properties of absorbing material. For practical absorbing agent and penetrating agent, this method can compute the optimal proportioning and material thickness.

Analysis of Thermal Conductivity of Lime Plaster with Pozzolanic Addition by Different Homogenization Techniques

Thermal conductivity of lime-pozzolan plaster is analyzed in the paper. At first, determination of basic physical properties of tested material is done for its basic characterization, as well as for the assessment of input parameters in the subsequent analysis of measured data by different homogenization techniques. The measurements of thermal conductivity are performed in dependence on moisture content from the dry state to the fully water saturated state using transient pulse method. Among the homogenization techniques based on effective media theory, Lichtenecker’s and Dobson’s models are used. The measured data presented in this paper can find utilization in practical applications of the studied plaster. The analyzed homogenization techniques are found to be applicable for a rapid evaluation of moisture dependent thermal conductivity.