Analytical and numerical analyses of the micromechanics of soft fibrous connective tissues

State of the art research and treatment of biological tissues require accurate and efficient methods for describing their mechanical properties. Indeed, micromechanics motivated approaches provide a systematic method for elevating relevant data from the microscopic level to the macroscopic one. In this work the mechanical responses of hyperelastic tissues with one and two families of collagen fibers are analyzed by application of a new variational estimate accounting for their histology and the behaviors of their constituents. The resulting, close form expressions, are used to determine the overall response of the wall of a healthy human coronary artery. To demonstrate the accuracy of the proposed method these predictions are compared with corresponding 3-D finite element simulations of a periodic unit cell of the tissue with two families of fibers. Throughout, the analytical predictions for the highly nonlinear and anisotropic tissue are in agreement with the numerical simulations

Hybrid metamaterials combining pentamode lattices and phononic plates

We propose a design strategy for hybrid metamaterials with alternating phononic plates and pentamode units that produce complete bandgaps for elastic waves. The wave control relies on the simultaneous activation of two scattering mechanisms in the constituent elements. The approach is illustrated by numerical results for a configuration comprising phononic plates with cross-like cavities. We report complete bandgaps of tunable width due to variations of geometric parameters. We show that the wave attenuation performance of the hybrid metamaterials can be further enhanced through implementation of lightweight multiphase material compositions. These give rise to efficient wave attenuation in challenging low-frequency regions. The proposed design strategy is not limited to the analyzed cases alone and can be applied to various designs of phononic plates with cavities, inclusions or slender elements

Some aspects of the Liouville equation in mathematical physics and statistical mechanics

This paper presents some mathematical aspects of Classical Liouville theorem and we have noted some mathematical theorems about its initial value problem. Furthermore, we have implied on the formal frame work of Stochastic Liouville equation (SLE)

Power control of electric heating elements using thyristor voltage and resistance converters

  This article investigates the energy efficiency of thyristor converters with an active load. The conversion of electric energy in a “thyristor converter – electric heating element” installation is considered from the standpoint of electromagnetic theory. The energy characteristics of the considered installation was calculated in the MATLAB environment. When thyristor voltage converters are operated under the mode of controlling the power of active load, passive power was found to be generated at the input during the non-conductive state of the converter (thyristor is locked). The use of passive power allows additional thermal energy to be obtained by means of an extensive use of voltage, without increasing the current consumption. An increase in the depth of power control of electric heating elements by thyristor voltage converters leads to a significant increase in passive power. In the active power control range (50–100% of the nominal value), the factor accounting for variations in the total power in the converter due to an incomplete use of the voltage at the input of the considered installation decreases from 1.0 to 0.93. This reduces the power factor of the load converter from 0.97 to 0.925. Despite the high value of the load power factor (in the control interval 0–50% of the rated power value), the factor accounting for variations in the total power was found to be reduced to 0.66. As a result, the power factor of the converter with the load is reduced by ~ 33%. In order to increase the efficiency of converting electrical energy to control the active load power, it is proposed to use thyristor resistance converters that vary the electrical resistance of the load over time. It is shown that unsatisfactory operation of a thyristor voltage converter can be caused by inefficient use of voltage at the input of the “thyristor converter – electric heating element” installation. When using thyristor resistance converters, the current non-sinusoidality factor does not exceed 1.5 % and the voltage non-sinusoidality factor in a 0.38 kV network does not exceed 0.2 %.</jats:p

Multiscale instabilities in soft heterogeneous dielectric elastomers

The development of instabilities in soft heterogeneous dielectric elastomers is investigated. Motivated by experiments and possible applications, we use in our analysis the physically relevant referential electric field instead of electric displacement. In terms of this variable, a closed form solution is derived for the class of layered neo-Hookean dielectrics. A criterion for the onset of electromechanical multiscale instabilities for the layered composites with anisotropic phases is formulated. A general condition for the onset of the macroscopic instability in soft multiphase dielectrics is introduced. In the example of the layered dielectrics, the essential influence of the microstructure on the onset of instabilities is revealed. We found that: (i) macroscopic instabilities dominate at moderate volume fractions of the stiffer phase, (ii) interface instabilities appear at small volume fractions of the stiffer phase and (iii) instabilities of a finite scale, comparable to the microstructure size, occur at large volume fractions of the stiffer phase. The latest new type of instabilities does not appear in the purely mechanical case and dominates in the region of large volume fractions of the stiff phase

Problems and prospects of the Chinese construction industry

Abstract China’s economic growth is one of the most important sources of growth and stabilization of the world economy. Currently, the state has accelerated investment in new infrastructure programs. In addition to traditional infrastructure projects, the Chinese initiative is aimed at developing new technologies.Despite the new coronavirus pandemic, China’s GDP is growing quite fast today. The main support for various sectors of the economy is provided by the state and gives priority to domestic consumption demand, rather than external demand. In the construction industry, investments are increasing in infrastructure projects that contain the idea of modernizing the industry and introducing innovative technologies, including: Bcore CTS construction technology; BIM technologies; 3D printing construction technology; construction technologies using “green concrete”, and modular construction technologies continue to improve. The success of China’s economic reforms is facilitated by the fact that the state focuses on education, among other things, and this has resulted in many highly skilled workers who are able to effectively solve problems in the construction sector. Education reform and the use of new technologies contribute to the rapid development of the construction industry in China.</jats:p

Application of hydrodynamic simulation on the basis of a composite model to improve the efficiency of gas-condensate reservoir development

At the moment, the use of digital models in the development of oil and gas fields is an effective tool for making informed tactical and strategic decisions to maximize the extraction of hydrocarbon reserves in a field. At the same time, the permanent increase in the share of hard-to-recover reserves leads to an accelerated increase in the role of simulation of reservoir hydrocarbon systems in the development of oil and gas fields. Many gas-condensate fields in Eastern Siberia can be characterized as reservoirs with low permeability and porosity and difficult thermobaric conditions, and, as a result, the issue of improving the efficiency of the development of such reservoirs to increase the cumulative production of gas and condensate is relevant. If the initial reservoir pressure of a gas-condensate field corresponds to the dewpoint pressure, dropout of a significant amount of retrograde condensate is observed when the pressure in the reservoir decreases. Condensate dropout in the pore space of a reservoir leads to a decrease in both the condensate recovery factor (CRF) and the gas recovery factor (GRF). The predictive calculations of the development of a gas-condensate reservoir by vertical and horizontal wells were carried out with the use of the hydrodynamic simulator T-Navigator of a domestic manufacturer Rock Flow Dynamics. The calculations were performed under various process conditions on the example of a gas-condensate field, which is characterized by complicated thermobaric conditions (the initial reservoir pressure corresponds to the dewpoint pressure), while the target process parameter was the amount of condensate dropout in the reservoir. Based on the results of the study, the main conclusion can be drawn. The development of the reservoir by horizontal wells can significantly reduce the reservoir drawdown pressure compared to vertical wells, while the condensate dropout in the reservoir occurs in a larger volume; the condensate becomes immobile and prevents further gas production, reducing the total production of condensate. An increase in reservoir condensate recovery in the course of the development of a gas-condensate reservoir by vertical wells compared to horizontal wells is observed under certain reservoir conditions corresponding to the simulation performed in this study, namely, at low reservoir permeability and porosity and the presence of a saturated gas-condensate system