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    01 September 2024, Volume 45 Issue 9
    Articles
    Chien-physics-informed neural networks for solving singularly perturbed boundary-layer problems
    Long WANG, Lei ZHANG, Guowei HE
    2024, 45(9):  1467-1480.  doi:10.1007/s10483-024-3149-8
    Abstract ( 237 )   HTML ( 12)   PDF (6023KB) ( 113 )  
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    A physics-informed neural network (PINN) is a powerful tool for solving differential equations in solid and fluid mechanics. However, it suffers from singularly perturbed boundary-layer problems in which there exist sharp changes caused by a small perturbation parameter multiplying the highest-order derivatives. In this paper, we introduce Chien's composite expansion method into PINNs, and propose a novel architecture for the PINNs, namely, the Chien-PINN (C-PINN) method. This novel PINN method is validated by singularly perturbed differential equations, and successfully solves the well-known thin plate bending problems. In particular, no cumbersome matching conditions are needed for the C-PINN method, compared with the previous studies based on matched asymptotic expansions.

    Swimming velocity of spherical squirmers in a square tube at finite fluid inertia
    Tongxiao JIANG, Deming NIE, Jianzhong LIN
    2024, 45(9):  1481-1498.  doi:10.1007/s10483-024-3146-9
    Abstract ( 150 )   HTML ( 2)   PDF (4519KB) ( 42 )  
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    The three-dimensional lattice Boltzmann method (LBM) is used to simulate the motion of a spherical squirmer in a square tube, and the steady motion velocity of a squirmer with different Reynolds numbers (Re, ranging from 0.1 to 2) and swimming types is investigated and analyzed to better understand the swimming characteristics of microorganisms in different environments. First, as the Reynolds number increases, the effect of the inertial forces becomes significant, disrupting the squirmer's ability to maintain its theoretical velocity. Specifically, as the Reynolds number increases, the structure of the flow field around the squirmer changes, affecting its velocity of motion. Notably, the swimming velocity of the squirmer exhibits a quadratic relationship with the type of swimming and the Reynolds number. Second, the narrow tube exerts a significant inhibitory effect on the squirmer motion. In addition, although chirality does not directly affect the swimming velocity of the squirmer, it can indirectly affect the velocity by changing its motion mode.

    On an isotropic porous solid cylinder: the analytical solution and sensitivity analysis of the pressure
    H. ASGHARI, L. MILLER, R. PENTA, J. MERODIO
    2024, 45(9):  1499-1522.  doi:10.1007/s10483-024-3144-7
    Abstract ( 111 )   HTML ( 2)   PDF (932KB) ( 49 )  
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    Within this work, we perform a sensitivity analysis to determine the influence of the material input parameters on the pressure in an isotropic porous solid cylinder. We provide a step-by-step guide to obtain the analytical solution for a porous isotropic elastic cylinder in terms of the pressure, stresses, and elastic displacement. We obtain the solution by performing a Laplace transform on the governing equations, which are those of Biot's poroelasticity in cylindrical polar coordinates. We enforce radial boundary conditions and obtain the solution in the Laplace transformed domain before reverting back to the time domain. The sensitivity analysis is then carried out, considering only the derived pressure solution. This analysis finds that the time t, Biot's modulus M, and Poisson's ratio ν have the highest influence on the pressure whereas the initial value of pressure P0 plays a very little role.

    Natural vibration and critical velocity of translating Timoshenko beam with non-homogeneous boundaries
    Yanan LI, Jieyu DING, Hu DING, Liqun CHEN
    2024, 45(9):  1523-1538.  doi:10.1007/s10483-024-3148-7
    Abstract ( 152 )   HTML ( 1)   PDF (1929KB) ( 45 )  
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    In most practical engineering applications, the translating belt wraps around two fixed wheels. The boundary conditions of the dynamic model are typically specified as simply supported or fixed boundaries. In this paper, non-homogeneous boundaries are introduced by the support wheels. Utilizing the translating belt as the mechanical prototype, the vibration characteristics of translating Timoshenko beam models with non-homogeneous boundaries are investigated for the first time. The governing equations of Timoshenko beam are deduced by employing the generalized Hamilton's principle. The effects of parameters such as the radius of wheel and the length of belt on vibration characteristics including the equilibrium deformations, critical velocities, natural frequencies, and modes, are numerically calculated and analyzed. The numerical results indicate that the beam experiences deformation characterized by varying curvatures near the wheels. The radii of the wheels play a pivotal role in determining the change in trend of the relative difference between two beam models. Comparing the results unearths that the relative difference in equilibrium deformations between the two beam models is more pronounced with smaller-sized wheels. When the two wheels are of equal size, the critical velocities of both beam models reach their respective minima. In addition, the relative difference in natural frequencies between the two beam models exhibits nonlinear variation and can easily exceed 50%. Furthermore, as the axial velocities increase, the impact of non-homogeneous boundaries on modal shape of translating beam becomes more significant. Although dealing with non-homogeneous boundaries is challenging, beam models with non-homogeneous boundaries are more sensitive to parameters, and the differences between the two types of beams undergo some interesting variations under the influence of non-homogeneous boundaries.

    A coupled Legendre-Laguerre polynomial method with analytical integration for the Rayleigh waves in a quasicrystal layered half-space with an imperfect interface
    Bo ZHANG, Honghang TU, Weiqiu CHEN, Jiangong YU, L. ELMAIMOUNI
    2024, 45(9):  1539-1556.  doi:10.1007/s10483-024-3145-8
    Abstract ( 163 )   HTML ( 1)   PDF (3378KB) ( 140 )  
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    The Laguerre polynomial method has been successfully used to investigate the dynamic responses of a half-space. However, it fails to obtain the correct stress at the interfaces in a layered half-space, especially when there are significant differences in material properties. Therefore, a coupled Legendre-Laguerre polynomial method with analytical integration is proposed. The Rayleigh waves in a one-dimensional (1D) hexagonal quasicrystal (QC) layered half-space with an imperfect interface are investigated. The correctness is validated by comparison with available results. Its computation efficiency is analyzed. The dispersion curves of the phase velocity, displacement distributions, and stress distributions are illustrated. The effects of the phonon-phason coupling and imperfect interface coefficients on the wave characteristics are investigated. Some novel findings reveal that the proposed method is highly efficient for addressing the Rayleigh waves in a QC layered half-space. It can save over 99% of the computation time. This method can be expanded to investigate waves in various layered half-spaces, including earth-layered media and surface acoustic wave (SAW) devices.

    Critical current degradation in an epoxy-impregnated rare-earth Ba2Cu3O7-x coated conductor caused by damage during a quench
    Donghui LIU, Huadong YONG, Youhe ZHOU
    2024, 45(9):  1557-1572.  doi:10.1007/s10483-024-3141-8
    Abstract ( 101 )   HTML ( 0)   PDF (1445KB) ( 24 )  
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    High-temperature superconducting (HTS) rare-earth Ba2Cu3O7-x (REBCO) coated conductors (CCs) have significant potential in high-current and high-field applications. However, owing to the weak interface strength of the laminated composite REBCO CCs, the damage induced by the thermal mismatch stress under a combination of epoxy impregnation, cooling, and quenching can cause premature degradation of the critical current. In this study, a three-dimensional (3D) electromagnetic-thermal-mechanical model based on the H-formulation and cohesive zone model (CZM) is developed to study the critical current degradation characteristics in an epoxy-impregnated REBCO CC caused by the damage during a quench. The temperature variation, critical current degradation of the REBCO CC, and its degradation onset temperature calculated by the numerical model are in agreement with the experimental data taken from the literature. The delamination of the REBCO CC predicted by the numerical model is consistent with the experimental result. The numerical results also indicate that the shear stress is the main contributor to the damage propagation inside the REBCO CC. The premature degradation of the critical current during a quench is closely related to the interface shear strength inside the REBCO CC. Finally, the effects of the coefficient of thermal expansion (CTE) of the epoxy resin, thickness of the substrate, and substrate material on the critical current degradation characteristics of the epoxy-impregnated REBCO CC during a quench are also discussed. These results help us understand the relationship between the current-carrying degradation and damage in the HTS applications.

    Bending strength degradation of a cantilever plate with surface energy due to partial debonding at the clamped boundary
    Zhenliang HU, Xueyang ZHANG, Xianfang LI
    2024, 45(9):  1573-1594.  doi:10.1007/s10483-024-3140-7
    Abstract ( 126 )   HTML ( 0)   PDF (365KB) ( 38 )  
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    This paper investigates the bending fracture problem of a micro/nanoscale cantilever thin plate with surface energy, where the clamped boundary is partially debonded along the thickness direction. Some fundamental mechanical equations for the bending problem of micro/nanoscale plates are given by the Kirchhoff theory of thin plates, incorporating the Gurtin-Murdoch surface elasticity theory. For two typical cases of constant bending moment and uniform shear force in the debonded segment, the associated problems are reduced to two mixed boundary value problems. By solving the resulting mixed boundary value problems using the Fourier integral transform, a new type of singular integral equation with two Cauchy kernels is obtained for each case, and the exact solutions in terms of the fundamental functions are determined using the Poincare-Bertrand formula. Asymptotic elastic fields near the debonded tips including the bending moment, effective shear force, and bulk stress components exhibit the oscillatory singularity. The dependence relations among the singular fields, the material constants, and the plate's thickness are analyzed for partially debonded cantilever micro-plates. If surface energy is neglected, these results reduce the bending fracture of a macroscale partially debonded cantilever plate, which has not been previously reported.

    Optimization for sound insulation of a sandwich plate with a corrugation and auxetic honeycomb hybrid core
    Fenglian LI, Yiping WANG, Yuxing ZOU
    2024, 45(9):  1595-1612.  doi:10.1007/s10483-024-3139-6
    Abstract ( 101 )   HTML ( 1)   PDF (2254KB) ( 39 )  
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    A sandwich plate with a corrugation and auxetic honeycomb hybrid core is constructed, and its sound insulation and optimization are investigated. First, the motion governing equation of the sandwich plate is established by the third-order shear deformation theory (TSDT), and then combined with the fluid-structure coupling conditions, and the sound insulation is solved. The theoretical results are validated by COMSOL simulation results, and the effects of the structural parameter on the sound insulation are analyzed. Finally, the standard genetic algorithm is adopted to optimize the sound insulation of the sandwich plate.

    Radiative heat transfer analysis of a concave porous fin under the local thermal non-equilibrium condition: application of the clique polynomial method and physics-informed neural networks
    K. CHANDAN, K. KARTHIK, K. V. NAGARAJA, B. C. PRASANNAKUMARA, R. S. VARUN KUMAR, T. MUHAMMAD
    2024, 45(9):  1613-1632.  doi:10.1007/s10483-024-3143-6
    Abstract ( 122 )   HTML ( 2)   PDF (3214KB) ( 109 )  
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    The heat transfer through a concave permeable fin is analyzed by the local thermal non-equilibrium (LTNE) model. The governing dimensional temperature equations for the solid and fluid phases of the porous extended surface are modeled, and then are nondimensionalized by suitable dimensionless terms. Further, the obtained non-dimensional equations are solved by the clique polynomial method (CPM). The effects of several dimensionless parameters on the fin's thermal profiles are shown by graphical illustrations. Additionally, the current study implements deep neural structures to solve physics-governed coupled equations, and the best-suited hyperparameters are attained by comparison with various network combinations. The results of the CPM and physics-informed neural network (PINN) exhibit good agreement, signifying that both methods effectively solve the thermal modeling problem.

    Analytical modeling and approaches of multihelix cables incorporating with interwire mutual contacts
    Zhichao ZHANG, Xingzhe WANG
    2024, 45(9):  1633-1654.  doi:10.1007/s10483-024-3147-6
    Abstract ( 128 )   HTML ( 3)   PDF (2466KB) ( 12 )  
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    This study aims to develop an analytical model based on the curve beam theory to capture the mechanical response of a multihelix cable considering the internal contact displacements. Accordingly, a double-helix cable subjected to axial tension and torsion is analyzed, and both the line and point contacts between the neighboring wires and strands are considered via an equivalent homogenized approach. Then, the proposed theoretical model is extended to a hierarchical multihelix cable with mutual contact displacements by constructing a recursive relationship between the high- and low-level multihelix structures. The global tensile stiffness and torsional stiffness of the double-helix cable are successfully evaluated. The results are validated by a finite element (FE) model, and are found to be consistent with the findings of previous studies. It is shown that the contact deformations in multihelix cables significantly affect their equivalent mechanical stiffness, and the contact displacements are remarkably enhanced as the helix angles increase. This study provides insights into the interwire/interstrand mutual contact effects on global and local responses.

    Study on the effective elastic performance of composites containing decagonal symmetric two-dimensional quasicrystal coatings
    Yurun WU, Lu LI, Lianhe LI
    2024, 45(9):  1655-1664.  doi:10.1007/s10483-024-3142-9
    Abstract ( 116 )   HTML ( 3)   PDF (730KB) ( 32 )  
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    On account of the Mori-Tanaka approach, the effective elastic performance of composites containing decagonal symmetric two-dimensional (2D) quasicrystal (QC) coatings is studied. Explicit expressions for the effective elastic constants of rare-earth QC reinforced magnesium-based composites are provided. Detailed discussion is presented on the effects of the volume fraction of the inclusions, the aspect ratio of the inclusions, the coating thickness, and the coating material parameters on the effective elastic constants of the composites. The results indicate that considering the coating increases the effective elastic constants of the composites to some extent.

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