Double Voids Research Articles

Micro–Macro Assessment of the Pile Bearing Capacity Interaction with Single and Double Voids in Different Soil Densities Using the Discrete-Element Method

Micro–Macro Assessment of the Pile Bearing Capacity Interaction with Single and Double Voids in Different Soil Densities Using the Discrete-Element Method

Analysis of dynamic characteristics and influencing factors of CO2 low-permeability coal reservoir sequestration

ABSTRACT Abandoned coal seams can be an important carrier for CO2 geological storage. Considering the gas seepage-diffusion and physical adsorption coupling characteristics in the process of CO2 adsorption and storage in coal and rock, a two-dimensional model of coupled flow-solidity for geological storage of CO2 in low-permeability reservoir with double voids was established by introducing the Zhang Hongbin model algorithm and adding the Klinkenberg effect and the compression effect of the rock skeleton in coal reservoirs in the controlling equation for rock deformation. The coupled flow-solid model was solved by using the PDE equation of COMSOL Multiphics program, and the simulation results difference between the new model and the traditional model in terms of sequestration dynamics were compared. The dynamic characteristic of reservoir gas pressure, formation stress, permeability and sequestration density in the process of CO2 geologic sequestration and injection were analyzed, and the influences of injection pressure and injection well diameter on the amount of CO2 sequestration were explored. The results show that the new model is more reasonable for calculating reservoir gas pressure and permeability compared with the Palmer-Mansoori model (PM model), and can simulate the free-state seepage movement of CO2 in the fracture system as well as its physical adsorption process compared with the single-heavy pore medium model. With continuous CO2 injection, the maximum sequestration density was raised to a limit value of about 1000 kg/m3 after 1 year. The date of reaching the limit of the sequestration volume was advanced by about 45 d when the positive pressure of the injected gas was increased from 10 kPa to 50 kPa. This model can reproduce the main parameters including, when affecting the effect, and realize the calculation of parameters such as CO2 density reaching the limit value, sealing limit day, sealing limit amount, which can provide a theoretical basis for further deep understanding of CO2 geological sealing law and scientific development of gas injection scheme.

Thermoelastic diffusion based on a nonlocal three-phase-lag diffusion model with double porosity structure

This work aims to develop a new diffusion-elasticity-based model using Eringen’s nonlocal elasticity theory under the purview of the three-phase-lag (TPL) model of hyperbolic thermoelasticity. This problem is treated in the context of a double porosity structure in a homogeneous, isotropic thermoelastic medium. By considering the phase laggings of the diffusion flux vector and using nonlocal continuum mechanics, new constitutive and field equations are derived. The problem is solved by employing the normal mode analysis technique which gives the exact results of all the physical variables. To illustrate the theoretical results, different physical quantities are calculated numerically and presented graphically with respect to distance and time. The influences of different thermoelastic models like TPL (three-phase-lag model), GN-III (Green-naghdi model), DPL (dual-phase-lag model), LS (Lord-Shulman model), and CT (coupled thermoelasticity) on the physical quantities are shown graphically. Additionally, the effects of nonlocal parameters, double voids, and diffusion on the physical quantities are represented graphically. Some limiting and particular cases are also derived from the governing equations and those results have been compared with the existing results available in the literature. Some 3D surface curves are also presented to study the impact of diffusion, nonlocality, and double voids on various physical quantities.

Size-dependent effect on the interaction of surface waves in micropolar thermoelastic medium with dual pore connectivity

This research tackles a critical knowledge gap in Rayleigh surface wave propagation. It offers a comprehensive analysis that surpasses previous limitations. A size-dependent micropolar medium with unique void distributions and thermal effects is considered in this work. The constitutive relations and equations of motion for a nonlocal micropolar thermoelastic medium with double voids (MTMWDV) have been established by using Eringen’s nonlocal elasticity theory. Employing the three-phase-lag thermoelasticity theory (TPLTE), the study utilizes a wave-mode method to derive analytical solutions for Rayleigh waves in a nonlocal MTMWDV. To gain a comprehensive understanding of wave behavior, we solve the characteristic equation and analyze its roots, applying a filter based on the surface wave decay condition. A medium with stress-free and isothermal boundaries is explored through computational simulations to determine the attenuation coefficient and phase velocity. Furthermore, particle motion analysis is conducted to complement the analytical and computational approaches. Moreover, the influence of the nonlocal parameter and various thermoelastic models on these wave phenomena is investigated. The validity of the current mathematical model is confirmed through the derivation of particular scenarios.

Analytical solutions for bolted tunnel structures with voids behind the lining

Understanding the mechanical behaviour of tunnels reinforced by end-anchored bolts and lining with voids behind the lining is crucial in determining the appropriate supporting measures. In this study, we constructed a geometric model for a tunnel with a single or double void. We used the substructure method and point matching method to obtain the elastic analytical solutions for the model. We examined the stress, internal force, and deformation characteristics of the tunnel and support structure under the influence of single and double voids. To validate the analytical model, we established a numerical model using the finite difference method. Additionally, we compared and analyzed the mechanical behaviour of tunnels reinforced by bolts and lining versus lining-only, and determined the contribution factor of the bolts.

Dynamic problems for elastic bodies with double voids

AbstractIn this paper, in a general formulation, we solve the initial‐boundary value problems of dynamics for an isotropic elastic body with a double voids. Using the Laplace transform, these problems are reduced to pseudo‐oscillation boundary value problems the solutions of which are represented explicitly as absolutely and uniformly converging series. It is proved that inverse transforms yield solutions of the initial dynamic problems. The uniqueness of regular solutions of the considered problems is investigated.

Failure behavior and reinforcing design of degraded tunnel linings based on the three-dimensional numerical evaluation

Void diseases behind the lining can commonly occur in tunnel structures. In this research, the failure behavior and reinforcing design of degraded tunnel linings with double void diseases were investigated. The effect of void disease on the three-dimensional distribution of inner force was explored. Subsequently, the stress distribution and plastic failure behavior of degraded tunnel linings with void diseases were studied. Then, the reinforcing behavior of the fiber-reinforced plastic (FRP)-polymer cement mortar (PCM) method was concerned. Finally, the distribution of potential cracking zone was discussed. The main results in this research indicated that the three-dimensional distribution of bending moment is greatly affected by the voids behind the lining, and the lining exhibits obvious bending outwards phenomenon within the void-affected zone. Concerning the failure characteristics between the double voids, plastic shear failure is prone to occur at the outer surface, but tensile-shear failure is likely to generate at the inner surface. In addition, the failure rate can be significantly affected by the spatial distribution of voids. Furthermore, the FRP-PCM method can significantly reduce the failure rate of the tunnel linings. Moreover, the distribution of potential cracking zone including the tensile cracking zone (TCZ), shear cracking zone (SCZ), and tensile-shear cracking zone (TSCZ) was determined.

Steady vibration problems in the theory of elasticity for materials with double voids

In the present paper, the linear theory of elasticity for materials with double voids is considered. Some basic properties of plane harmonic waves of this theory are established. The internal boundary value problems (BVPs) of steady vibrations are formulated. On the basis of Green’s tensors, the internal BVPs are reduced to the equivalent Fredholm’s integral equations of the second kind with symmetrical kernel. The existence of eigenfrequencies of the internal BVPs of steady vibrations is proved. Finally, the formula of the asymptotic distribution of these eigenfrequencies is obtained.

Phase field modelling on the growth dynamics of double voids of different sizes during czochralski silicon crystal growth

To investigate their dynamics and interaction mechanisms, the growth process of the two voids with different sizes during Czochralski silicon crystal growth were simulated by use of an established phase field model and its corresponding program code. On the basis of the several phase field numerical simulation cases, the evolution laws of the double voids were acquired as follows: the phase field model is capable to simulate the growth process of double voids with different sizes; there are two modes of their growth, that is, either mutual integration or competitive growth; the exact moment of their fusion can be also captured, and it is τ of 7.078 (simulation time step of 14156) for the initial vacancy concentration of 0.02 and the initial space between two void centers of 44Δx.

Sensitivity of gold nano-conductors to voids, substitutions, and electric field: ab initio results

Gold nanowires are good candidates for nano-electronics devices. A previous study has shown that the beryllium-terminated BeO (0001) surface may be a useful platform for supporting gold nano-conductors, since it preserves the nano wire configuration and does not restrict its conductivity. Here, we used ab initio simulations to determine the sensitivity of potential gold nano-conductors to the presence of point defects, O2 substitutions and to an applied perpendicular electric field, as in field effect transistors. We found that the presence of the point defects causes only small changes in the atomic bond lengths of the NW, does not alter the NW configuration, but may affect the overall conductivity. Single or double voids on the same channel reduce the conductance by 28 % at most, but when the voids arrange in a way that only one channel remains for conductance, it reduces by factor of two to ≈1 G0 (G0 = 2e2/h). The presence of a single O2 molecule as a substitution reduces the electron availability in the neighboring Au atoms, in most cases reducing the conductance. The perpendicular electric field, which is typical for field effect transistors, affects the electron density distribution, shifts and changes the conductance spectra profile, but does not decrease the conductivity.

Impact of heavy doping with donors on CZ silicon properties

This work reports a detailed characterization of 200 mm silicon wafers heavily doped with antimony, arsenic or phosphorus, in the range 1–50 mΩ•cm, corresponding to 7 × 1019 – 2 × 1017 at·cm−3. Grown‐in voids (revealed as light‐scattering objects on the wafer surface) are shown to be controlled by the dopant concentration. For As‐doped wafers the voids show a pronounced increase in their density up to [As] = 1.7 × 1019 cm−3, but at higher concentration the void density drops sharply. The same behaviour was found for P‐doped wafers where a sharp drop occurs at [P] > 2.9 × 1019 cm−3. In the case of antimony, the explored concentration range was sufficient only to reveal the increasing side of the curve. AFM characterization confirmed the morphology of voids as also seen in lightly‐doped silicon. Both single and double voids were observed. The oxygen precipitate density (BMD) was measured after submitting the wafers to a stabilization and growth thermal cycle. Overall it ranges from 1 × 106 ( = detection limit) to 1.5 × 1010 counts/cm3. The relationship between BMD density and oxygen concentration follows the classical S‐shaped curve, indicating that also for heavily doped N+ type wafers the oxygen content plays a major role on BMD formation.

Void formation in melt-grown silicon studied by molecular dynamics simulations: From grown-in faulted dislocation loops to vacancy clusters

Molecular dynamics simulations of a dislocation based mechanism for void formation in silicon are presented. By studying a moving solid-liquid interface in Si, we observe the formation of dislocation loops on (111) facets consisting of coherency and anticoherency dislocations, which disband within nanoseconds into vacancy clusters of 10 or more vacancies. These vacancy clusters can act as nucleation seeds for the experimentally observed octahedral single and double voids.