Bojing Zhu

Finite element investigation of the poroelastic effect on the Xinfengjiang Reservoir-triggered earthquake

Coulomb failure stress changes (ΔCFS) are used in the study of reservoir-induced seismicity (RIS) generation. The threshold value of ΔCFS that can trigger earthquakes is an important issue that deserves thorough research. The Ms6.1 earthquake in the Xinfengjiang Reservoir in 1962 is well acknowledged as the largest reservoir-induced earthquake in China. Therefore, it is a logical site for quantitative calculation of ΔCFS induced by the filling of the reservoir and for investigating the magnitude of ΔCFS that can trigger reservoir seismic activities. To better understand the RIS mechanism, a three-dimensional poroelastic finite element model of the Xinfengjiang Reservoir is proposed here, taking into consideration of the precise topography and dynamic water level. We calculate the instant changes of stress and pore pressure induced by water load, and the time variation of effective stresses due to pore water diffusion. The ΔCFS on the seismogenesis faults and the accumulation of strain energy in the reservoir region are also calculated. Primary results suggest that the reservoir impoundment increases both pore pressure and ΔCFS on the fault at the focal depth. The diffusion of pore pressure was likely the main factor that triggered the main earthquake, whereas the elastic stress owing to water load was relatively small. The magnitude of ΔCFS on seismogenesis fault can reach approximately 10 kPa, and the ΔCFS values at the hypocenter can be about 0.7–3.0 kPa, depending on the fault diffusion coefficient. The calculated maximum vertical subsidence caused by the water load in the Xinfengjiang Reservoir is 17.5 mm, which is in good agreement with the observed value of 15 mm. The accumulated strain energy owing to water load was only about 7.3×1011 J, even less than 1% of the seismic wave energy released by the earthquake. The reservoir impoundment was the only factor that triggered the earthquake.

Arbitrary 3D flaws in electromagnetothermoelastic composites under coupled multiple fields

The arbitrary 3D flaws in fully electromagnetothermoelastic coupled multiphase composites (EMTE-CMCs) under extended electromagnetothermoelastic coupled loads are turned into a set of extended hypersingular integral equations. Analytical solutions for the extended singular stresses, the extended stress intensity factors and the extended energy release rate near the crack fronts are provided. A numerical method is put forward in which the extended displacement discontinuities are approximated by the product of basic density functions and polynomials. In addition, the relationships between the extended stress intensity factors and the shapes of cracks, the distance between two interface flaws, the properties of the materials and the electromagnetoelastic coupling effects are discussed. The effects of flaw orientation, interaction and shielding are analyzed.

Submicron size-scale mapping of carbonate effective elastic properties from FIB-SEM images and finite element method

In this paper, an automatic unstructured focused ion beam (FIB) and scanning electron microscopy (SEM) images induced representative volume element (RVE) finite element (FE) method is developed to predict submicron scale carbonate rock effective Young’s and bulk moduli and Poisson’s ratio on parallel CPU-GPU platform. Based on high resolution-contrast surface morphology and internal fabric-texture structure images from carbonate rock specimen (covered 0.12–64 μm2 area and 8000 μm3 domain), the cubic RVE FE models are constructed from different sites through Avizo with user-defined parameters Matlab coding. The effective Young’s and bulk moduli and Poisson’s ratio of the different RVEs and porosity and pore size are computed by using periodic boundary condition in the well-known FE software Abaqus. FE mesh sensitivity analysis has been conducted where all moduli converge to a certain constant value at larger FE mesh density. The effect of fabric-texture (pore size, shape, and distribution) on the elastic properties is discussed. The correlations between the computed effective elastic properties and pore size, porosity, RVE size have been established. The simulation results show that the effective Young’s and bulk moduli and Poisson’s ratio have strong anisotropic behavior and depend on RVE size, porosity and pore size. The RVE size, porosity and pore size are three independent factors in affecting of the effective elastic moduli, the effect mechanism of porosity and pore size is same while the effect mechanism of RVE size is difference.

Submicron volume roughness & asperity contact friction model for principle slip surface in flash heating process

Based on focused ion beam and shear friction apparatus data, the multi-resolutions (0.2 nm-5 μm) volume roughness & asperity contact (VR & AC) three-dimensional structure on principle slip surface interface-surface (PSS-IS) is measured on high performance computational platform; and physical plastic-creep friction model is established by using hybrid hyper-singular integral equation & lattice Boltzmann & lattice Green function (BE-LB-LG). The correlation of rheological property and VR & AC evolution under transient (10 μs) macro-normal stress (18–300 MPa) and slip rate (0.25–7.5 m/s) are obtained; and the PSS-IS friction in co-seismic flash heating is quantitative analyzed for the first time.

Numerical Simulation on the Effective Thermal Conductivity of Porous Material

The thermal conductivity of porous material is an important basic parameter, but it is not easy to study, due to the complexity of the structure of porous material. In the present work, we show a numerical simulation method to study the thermal conductivity of the porous material. We generate 200 material models with random distribution of solid skeleton and air for a fixed porosity, then we get the effective thermal conductivity of the porous material by Monte Carlo statistical analysis. The results are in good agreement with the previous empirical formula. The numerical results show that the effective thermal conductivity of porous material depends on the thermophysical properties of solid skeleton and air, the pore distribution and pore structure, the numerical error decreases with the increase in the number of grids, this finite element method can be used to estimate the effective thermal conductivity of composites and maybe has broad application prospects in terms of computing the effective thermal conductivity and other physical properties of composite material with known components.