Coupled heat-fluid-solid numerical study on heat extraction potential of hot dry rocks based on discrete fracture network model

Fracture networks within hot dry rock(HDR)geothermal reservoirs are complex,and heat extraction via water injection is thus a coupled process of heat-fluid-solid multifield.In this paper,utilizing the theory of normally distributed random functions,we develop a corresponding pre-processing subprogram to establish a discrete network model of complex fracture distribution in HDR reservoirs;then construct a heat-fluid-solid finite element model for heat extraction via water injection and compare the numerical solution with the analytical solution of the one-dimensional non-isothermal consolidation problem for verification.The numerical simulation results show that the main factors affecting the heat extraction efficiency of HDR reservoirs include fracture width,fracture density,fracture permeability,and matrix permeability.When a HDR reservoir is injected with water for heat extraction,there is a certain threshold value of these influential parameters,beyond which the outlet temperature drops significantly,resulting in an obvious thermal breakthrough.When injecting water for heat extraction,the values of these parameters should be controlled and kept at a reasonable level,otherwise,the HDR reservoir may enter a thermal breakthrough stage in advance,which is not conducive for long-period heat extraction.Influenced by the random distribution of complex fractures,the leading edge of the cold front may present an irregular distribution.During the process of heat extraction,the stress gradually changes from a compressional state to a tensile state,which induces further damage to the HDR reservoir.

Multiscale Finite Element Method for Coupling Analysis of Heterogeneous Magneto-Electro-Elastic Structures in Thermal Environment

Magneto-electro-elastic (MEE) materials, a new type of composite intelligent materials, exhibit excellent multifield coupling effects. Due to the heterogeneity of the materials, it is challenging to use the traditional finite element method (FEM) for mechanical analysis. Additionally, the MEE materials are often in a complex service environment, especially under the influence of the thermal field with thermoelectric and thermomagnetic effects, which affect its mechanical properties. Therefore, this paper proposes the efficient multiscale computational method for the multifield coupling problem of heterogeneous MEE structures under the thermal environment. The method constructs a multi-physics field with numerical base functions (the displacement, electric potential, and magnetic potential multiscale base functions). It equates a single cell of heterogeneous MEE materials to a macroscopic unit and supplements the macroscopic model with a microscopic model. This allows the problem to be solved directly on a macroscopic scale. Finally, the numerical simulation results demonstrate that compared with the traditional FEM, the multiscale finite element method (MsFEM) can achieve the purpose of ensuring accuracy and reducing the degree of freedom, and significantly improving the calculation efficiency.

Some recent advances in 3D crack and contact analysis of elastic solids with transverse isotropy and multifield coupling

Significant progress has been made in mixed boundary-value problems associated with three-dimensional（3D） crack and contact analyses of advanced materials featuring more complexities compared to the conventional isotropic elastic materials.These include material anisotropy and multifield coupling,two typical characteristics of most current multifunctional materials.In this paper we try to present a state-of-the-art description of 3D exact/analytical solutions derived for crack and contact problems of elastic solids with both transverse isotropy and multifield coupling in the latest decade by the potential theory method in the spirit of V.I.Fabrikant.whose ingenious breakthrough brings new vigor and vitality to the old research subject of classical potential theory.We are particularly interested in crack and contact problems with certain nonlinear features.Emphasis is also placed on the coupling between the temperature field（or the like） and other physical fields（e.g.,elastic,electric,and magnetic fields）.We further highlight the practical significance of 3D contact solutions,in particular in applications related to modern scanning probe microscopes.

A review of the strengthening–toughening behavior and mechanisms of advanced structural materials by multifield coupling treatment

The application of an external field is a promising method to control the microstructure of materials, leading to their improved performance. In the present paper, the strengthening and toughening behavior of some typical high-performance structural materials subjected to multifield coupling treatment, including electrostatic field, electro-pulse current, thermal field, and stress field, are reviewed in detail. In addition to the general observation that the plasticity of materials could be increased by multi-external fields, strength enhancement can be achieved by controlling atomic diffusion or phase transformations. The paper is not limited to the strengthening and toughening mechanisms of the multifield coupling effects on different types of structural materials but is intended to provide a generic method to improve both the strength and ductility of the materials. Finally, the prospects of the applications of multi-external fields have also been proposed based on current works.