Applied Mathematics and Mechanics-English Edition最新文献

An explicit form of the elastic strain-energy function for direction-dependent large elastic strain behaviors of soft fiber-reinforced composites is first presented based upon a decoupled approach for simulating complex nonlinear coupling effects. From this form, the exact closed-form solutions are then obtained for the uniaxial tension responses in the fiber and cross-fiber directions. With such exact solutions, the issue of simultaneously simulating strongly coupling nonlinear responses in the fiber and cross-fiber directions may be reduced to the issue of separately treating each decoupled uniaxial stress-strain response, thus bypassing usual complexities and uncertainties involved in identifying a large number of strongly coupled adjustable parameters. The numerical examples given are in good agreement with the experimental data for large strain responses.

Understanding and modeling flows over porous layers are of great industrial significance. To accurately solve the turbulent multi-scale flows on complex configurations, a rescaling algorithm designed for turbulent flows with the Chapman-Enskog analysis is proposed. The mesh layout and the detailed rescaling procedure are also introduced. Direct numerical simulations (DNSs) for a turbulent channel flow and a porous walled turbulent channel flow are performed with the three-dimensional nineteen-velocity (D3Q19) multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) to validate the accuracy, adaptability, and computational performance of the present rescaling algorithm. The results, which are consistent with the previous DNS studies based on the finite difference method and the LBM, demonstrate that the present method can maintain the continuity of the macro values across the grid interface and is able to adapt to complex geometries. The reasonable time consumption of the rescaling procedure shows that the present method can accurately calculate various turbulent flows with multi-scale and complex configurations while maintaining high computational efficiency.

By means of Muskhelishvili’s method and the technique of generalized conformal mapping, the physical plane problems are transformed into regular mathematical problems in quasicrystals (QCs). The analytical solution of an elliptical orifice problem with asymmetric cracks in one-dimensional (1D) orthorhombic QCs is obtained. By using the Dugdale-Barenblatt model, the plastic simulation at the crack tip of the elliptical orifice with asymmetric cracks in 1D orthorhombic QCs is performed. Finally, the size of the atomic cohesive force zone is determined precisely, and the size of the atomic cohesive force zone around the crack tip of an elliptical orifice with a single crack or two symmetric cracks is obtained.

Surface tension plays a central role in the mechanical behavior of soft materials such as gels. Elastocapillary deformation of elastic graded substrates is ubiquitous in soft materials. In this work, the effect of a partially wetting sessile liquid droplet on the elastocapillary deformation of a soft elastic graded substrate is studied. The modulus is assumed to have an exponential form along the thickness direction. By applying the Fourier transformation, a mixed boundary-value problem is reduced into a dual integral equation. The numerical results show that the surface displacement is strongly affected by the inhomogeneity of the material. The study of the wetting properties of gel substrates is essential for both understanding the wetting phenomena of gels and developing gels for applications as soft actuators and sensors that can be used in wearable electronics and soft robotics.

The investigations of surface waves in the piezoelectric medium bring out great possibility in designing smart surface acoustic wave (SAW) devices. It is important to study the dispersion properties and manipulation mechanism of surface waves in the semi-infinite piezoelectric medium connected with periodic arrangement of shunting circuits. In this study, the extended Stroh formalism is developed to theoretically analyze the dispersion relations of surface waves under different external circuits. The band structures of both the Rayleigh wave and the Bleustein-Gulyaev (BG) wave can be determined and manipulated with proper electrical boundary conditions. Furthermore, the electromechanical coupling effects on the band structures of surface waves are discussed to figure out the manipulation mechanism of adjusting electric circuit. The results indicate that the proposed method can explain the propagation behaviors of surface waves under the periodic electrical boundary conditions, and can provide an important theoretical guidance for designing novel SAW devices and exploring extensive applications in practice.

Sandwiched functionally-graded piezoelectric semiconductor (FGPS) plates possess high strength and excellent piezoelectric and semiconductor properties, and have significant potential applications in micro-electro-mechanical systems. The multi-field coupling and free vibration of a sandwiched FGPS plate are studied, and the governing equation and natural frequency are derived with the consideration of electron movement. The material properties in the functionally-graded layers are assumed to vary smoothly, and the first-order shear deformation theory is introduced to derive the multi-field coupling in the plate. The total strain energy of the plate is obtained, and the governing equations are presented by using Hamilton’s principle. By introducing the boundary conditions, the coupling physical fields are solved. In numerical examples, the natural frequencies of sandwiched FGPS plates under different geometrical and physical parameters are discussed. It is found that the initial electron density can be used to modulate the natural frequencies and vibrational displacement of sandwiched FGPS plates in the case of nano-size. The effects of the material properties of FGPS layers on the natural frequencies are also examined in detail.

The incorporation of the quasicrystalline phase into the metal matrix offers a wide range of potential applications in particle-reinforced metal-matrix composites. The analytic solution of the piezoelectric quasicrystal (QC) microsphere considering the thermoelectric effect and surface effect contained in the elastic matrix is presented in this study. The governing equations for the QC microsphere in the matrix subject to the external electric loading are derived based on the nonlocal elastic theory, electro-elastic interface theory, and eigenvalue method. A comparison between the existing results and the finite-element simulation validates the present approach. Numerical examples reveal the effects of temperature variation, nonlocal parameters, surface properties, elastic coefficients, and phason coefficients on the phonon, phason, and electric fields. The results indicate that the QC microsphere enhances the mechanical properties of the matrix. The results are useful for the design and understanding of the characterization of QCs in micro-structures.

This paper presents an integrated study from fracture propagation modeling to gas flow modeling and a correlation analysis to explore the key controlling factors of intensive volume fracturing. The fracture propagation model takes into account the interaction between hydraulic fracture and natural fracture by means of the displacement discontinuity method (DDM) and the Picard iterative method. The shale gas flow considers multiple transport mechanisms, and the flow in the fracture network is handled by the embedded discrete fracture model (EDFM). A series of numerical simulations are conducted to analyze the effects of the cluster number, stage spacing, stress difference coefficient, and natural fracture distribution on the stimulated fracture area, fractal dimension, and cumulative gas production, and their correlation coefficients are obtained. The results show that the most influential factors to the stimulated fracture area are the stress difference ratio, stage spacing, and natural fracture density, while those to the cumulative gas production are the stress difference ratio, natural fracture density, and cluster number. This indicates that the stress condition dominates the gas production, and employing intensive volume fracturing (by properly increasing the cluster number) is beneficial for improving the final cumulative gas production.

We propose a novel symplectic finite element method to solve the structural dynamic responses of linear elastic systems. For the dynamic responses of continuous medium structures, the traditional numerical algorithm is the dissipative algorithm and cannot maintain long-term energy conservation. Thus, a symplectic finite element method with energy conservation is constructed in this paper. A linear elastic system can be discretized into multiple elements, and a Hamiltonian system of each element can be constructed. The single element is discretized by the Galerkin method, and then the Hamiltonian system is constructed into the Birkhoffian system. Finally, all the elements are combined to obtain the vibration equation of the continuous system and solved by the symplectic difference scheme. Through the numerical experiments of the vibration response of the Bernoulli-Euler beam and composite plate, it is found that the vibration response solution and energy obtained with the algorithm are superior to those of the Runge-Kutta algorithm. The results show that the symplectic finite element method can keep energy conservation for a long time and has higher stability in solving the dynamic responses of linear elastic systems.

The deformations and stresses of a rotating cylindrical hollow disk made of incompressible functionally-graded hyper-elastic material are theoretically analyzed based on the finite elasticity theory. The hyper-elastic material is described by a new micro-macro transition model. Specially, the material shear modulus and density are assumed to be a function with a power law form through the radial direction, while the material inhomogeneity is thus reflected on the power index m. The integral forms of the stretches and stress components are obtained. With the obtained complicated integral forms, the composite trapezoidal rule is utilized to derive the analytical solutions, and the explicit solutions for both the stretches and the stress components are numerically obtained. By comparing the results with two classic models, the superiority of the model in our work is demonstrated. Then, the distributions of the stretches and normalized stress components are discussed in detail under the effects of m. The results indicate that the material inhomogeneity and the rotating angular velocity have significant effects on the distributions of the normalized radial and hoop stress components and the stretches. We believe that by appropriately choosing the material inhomogeneity and configuration parameters, the functionally-graded material (FGM) hyper-elastic hollow cylindrical disk can be designed to meet some unique requirements in the application fields, e.g., soft robotics, medical devices, and conventional aerospace and mechanical industries.