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    05 June 2025, Volume 46 Issue 6
    Nonlinear electromechanical coupling dynamics of a two-degree-of-freedom hybrid energy harvester
    Tingting CHEN, Kai WANG, Shengchao CHEN, Ziyu XU, Zhe LI, Jiaxi ZHOU
    2025, 46(6):  989-1010.  doi:10.1007/s10483-025-3264-7
    Abstract ( 35 )   HTML ( 8)   PDF (5582KB) ( 20 )  
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    Vibration energy harvesting presents a significant opportunity for powering wireless sensor networks and internet of things (IoT) devices, offering a sustainable alternative to traditional battery-based power sources. However, environmental vibrations are predominantly low-frequency, which presents a significant challenge to the efficient conversion of such energy. To address this challenge, this paper proposes a novel two-degree-of-freedom (2-DOF) energy harvester. The first layer of the harvester incorporates a piezoelectric composite beam (PCB) paired with permanent magnets to form a negative stiffness mechanism (NSM), which counteracts the stiffness of linear springs, thereby achieving quasi-zero stiffness (QZS) or bistable characteristics. The second layer integrates piezoelectric transduction units with triboelectric nanogenerator (TENG) units to further enhance the efficiency of low-frequency vibration energy conversion. By considering the modal characteristics of the PCB, this paper establishes the electromechanical coupling equations of the harvester from an energy perspective. The mechanical responses of the masses in both layers, as well as the electrical outputs of the PCB, are analytically solved. Furthermore, the effects of the system parameters on the efficiency of low-frequency vibration energy harvesting are thoroughly analyzed. This work provides a theoretical foundation for the development of self-powered IoT sensor nodes, enabling efficient energy harvesting from ambient low-frequency vibrations.

    Low-frequency vibration suppression of meta-beam withsoftening nonlinearity
    Weixing ZHANG, Dongshuo YANG, Xiangying GUO
    2025, 46(6):  1011-1028.  doi:10.1007/s10483-025-3258-9
    Abstract ( 23 )   HTML ( 3)   PDF (9662KB) ( 7 )  
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    In order to obtain a lower frequency band gap, this paper proposes a novel locally resonant meta-beam incorporating a softening nonlinear factor. An improved cam-roller structure is designed in this meta-beam to achieve the softening nonlinear stiffness of the local oscillators. Firstly, based on Hamilton's principle and the Galerkin method, the control equations for the coupled system are established. The theoretical band gap boundary is then derived with the modal analysis method. The theoretical results reveal that the band gap of the meta-beam shifts towards lower frequencies due to the presence of a softening nonlinear factor, distinguishing it from both linear metamaterials and those with hardening nonlinear characteristics. Then, the vibration attenuation characteristics of a finite size meta-beam are investigated through numerical calculation, and are verified by the theoretical results. Furthermore, parameter studies indicate that the reasonable design of the local oscillator parameters based on lightweight principles helps to achieve further broadband and efficient vibration reduction in the low-frequency region. Finally, a prototype of the meta-beam is fabricated and assembled, and the formations of the low-frequency band gap and the amplitude-induced band gap phenomenon are verified through experiments.

    Modeling and mechanism of vibration reduction of pipes by visco-hyperelastic materials
    Jie JING, Xiaoye MAO, Hu DING, Honggang LI, Liqun CHEN
    2025, 46(6):  1029-1048.  doi:10.1007/s10483-025-3263-6
    Abstract ( 20 )   HTML ( 3)   PDF (4185KB) ( 3 )  
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    Pipes have been extensively utilized in the aerospace, maritime, and other engineering sectors. However, the vibrations of pipes can significantly affect the system reliability and even lead to accidents. Visco-hyperelastic materials can enhance the dissipative effect, and reduce the vibrations of pipes. However, the mechanism based on the constitutive model for visco-hyperelastic materials is not clear. In this study, the damping effect of a visco-hyperelastic material on the outer surface of a plain steel pipe is investigated. The nonlinear constitutive relation of the visco-hyperelastic material is introduced into the governing equation of the system for the first time. Based on this nonlinear constitutive model, the governing model for the forced vibration analysis of a simply-supported laminated pipe is established. The Galerkin method is used to analyze the effects of the visco-hyperelastic parameters and structural parameters on the natural characteristics of the fluid-conveying pipes. Subsequently, the harmonic balance method (HBM) is used to investigate the forced vibration responses of the pipe. Finally, the differential quadrature element method (DQEM) is used to validate these results. The findings demonstrate that, while the visco-hyperelastic material has a minimal effect on the natural characteristics, it effectively dampens the vibrations in the pipe. This research provides a theoretical foundation for applying vibration damping materials in pipe vibration control.

    Theoretical and experimental investigation on vibration of bolted-flange-joined conical-cylindrical shells
    Chunhao ZHANG, Qingdong CHAI, Changyuan YU, Wuce XING, Yanqing WANG
    2025, 46(6):  1049-1068.  doi:10.1007/s10483-025-3261-8
    Abstract ( 9 )   HTML ( 3)   PDF (86645KB) ( 1 )  
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    This study investigates the vibration characteristics of bolted-flange-joined conical-cylindrical shells (BFJCCSs) through both theoretical analysis and experimental testing. The proposed model incorporates the pressure distribution within the bolted joint and accounts for the flange effect. The energy expressions for the conical and cylindrical shells are derived from Donnell's shell theory, while those for the flanges are obtained from the Euler-Bernoulli beam theory. The Lagrange equation is used to derive the dynamic equation, and the experimental studies on the BFJCCS are conducted to validate the accuracy of the model. Subsequently, the comprehensive effects of bolt loosening and bolt number on the frequency parameters are analyzed. Additionally, the effects of the flange dimensions and cone angle on the vibration behavior of the BFJCCS are discussed. In particular, the dynamic differences between the welded conical-cylindrical shell (WCCS) and BFJCCS are investigated. It is found that compared with the WCCS, the fundamental frequency of the BFJCCS is reduced by 7.6%, and the corresponding modal damping ratio is reduced by 21.0%. However, the high-order frequencies of the BFJCCS are higher than those of the WCCS, accompanied by a higher modal damping ratio. Compared with the bolt loosening degree, the bolt number has a more significant effect on frequencies. As the bolt number decreases, the impact of the bolt loosening degree diminishes gradually.

    Rayleigh wave propagation in an elastic half-space with an attached piezoelectric semiconductor layer considering flexoelectricity and size-effects
    Linyao WANG, Aibing ZHANG, Chuanzeng ZHANG, Jianke DU, Z. M. XIAO, Jia LOU
    2025, 46(6):  1069-1088.  doi:10.1007/s10483-025-3265-8
    Abstract ( 22 )   HTML ( 4)   PDF (2056KB) ( 5 )  
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    To address the urgent demand for the miniaturization and multifunctional integration of high-frequency Rayleigh surface wave devices in 5G communication technology, the propagation characteristics of Rayleigh surface waves in an elastic half-space attached by a nanoscale piezoelectric semiconductor (PSC) thin layer with flexoelectricity and size-effects are systematically investigated. Based on the Hamiltonian principle, the elastic dynamic equations and Gauss's theorem of electrostatics are obtained. The eigenvalue problem is numerically solved with a genetic algorithm in MATLAB, and the dispersion properties are obtained. The effects of various key factors, including the flexoelectricity, inertia gradients, strain gradients, electric field gradients, PSC layer thickness, steady-state carrier concentration, and bias electric fields, on the propagation and attenuation characteristics of Rayleigh surface waves are analyzed. The results demonstrate that the increases in the flexoelectric coefficient and strain gradient characteristic length lead to an increase in the real part of the complex phase velocity, while the increases in the inertia gradient characteristic length, electric field gradient characteristic length, PSC layer thickness, and steady-state carrier concentration result in a decrease. Additionally, the bias electric fields significantly influence the Rayleigh surface wave attenuation. The present findings are crucial for the accurate property evaluation of miniaturized high-frequency Rayleigh wave devices, and provide valuable theoretical support for their design and optimization.

    A semi-analytical model and mechanism analysis for force-frequency effect and coefficient of square quartz
    Lixia MA, Qiang ZHOU, Lijun YI, Ji WANG
    2025, 46(6):  1089-1106.  doi:10.1007/s10483-025-3255-6
    Abstract ( 19 )   HTML ( 2)   PDF (3214KB) ( 0 )  
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    This study presents a closed-form solution for central stress, a semi-analytical model, and a modified anisotropic semi-analytical model to efficiently calculate the force-frequency coefficients (FFCs) of square quartz crystal resonators (QCRs) with different side lengths and azimuth angles under eccentrically concentrated and distributed loads. The semi-analytical model is validated by comparisons between the experimental results and the nonlinear finite element method (FEM) simulation results. Based on the semi-analytical model for the FFC and nonlinear FEM simulations, the FFC variations of square QCRs under external loads and the related mechanisms are investigated. Among the initial stresses caused by external loads, the central stress parallel to the x-crystallographic axis is the primary factor influencing the FFC of quartz. Our findings can provide practical tools for calculating the FFC, and help the design and development of square quartz force sensors.

    Thermal radiation impact on hybrid nanocomposite flow in stretchable channels: a Darcy-Forchheimer model with the Taylor wavelet approach
    B. J. GIREESHA, K. J. GOWTHAM
    2025, 46(6):  1107-1124.  doi:10.1007/s10483-025-3260-7
    Abstract ( 24 )   HTML ( 1)   PDF (1096KB) ( 2 )  
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    The study of stretching surfaces has garnered significant attention due to its importance in a wide range of industrial and engineering functions, including the drawing of wires and plastic films, shrink film production, polymer sheet extrusion, the manufacturing of glass fibers, and the manufacturing of polyester heat-shrink tubing. This research incorporates a Darcy-Forchheimer porous medium to account for the effects of porosity. The governing equations are transformed into a boundary value problem and solved semi-analytically using the Taylor wavelet method. The effects of various parameters are depicted through graphical analyses. The results show that for both converging and diverging stretching surfaces, an increase in the porosity parameter causes a decrease in the velocity field. Additionally, higher Reynolds numbers enhance inertial effects, leading to more pronounced velocity fluctuations. Stretching causes a consistent drop in velocity toward the center and an increase close to the walls in both types of channels, indicating that the volume percentage of nanoparticles influences the heat distribution. Notably, stretching induces a marked temperature drop at the channel's center.

    Neural network solution based on the minimum potential energy principle for static problems of structural mechanics
    Jiamin QIAN, Lincong CHEN, J. Q. SUN
    2025, 46(6):  1125-1142.  doi:10.1007/s10483-025-3257-8
    Abstract ( 19 )   HTML ( 2)   PDF (5220KB) ( 14 )  
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    This paper presents the variational physics-informed neural network (VPINN) as an effective tool for static structural analyses. One key innovation includes the construction of the neural network solution as an admissible function of the boundary-value problem (BVP), which satisfies all geometrical boundary conditions. We then prove that the admissible neural network solution also satisfies natural boundary conditions, and therefore all boundary conditions, when the stationarity condition of the variational principle is met. Numerical examples are presented to show the advantages and effectiveness of the VPINN in comparison with the physics-informed neural network (PINN). Another contribution of the work is the introduction of Gaussian approximation of the Dirac delta function, which significantly enhances the ability of neural networks to handle singularities, as demonstrated by the examples with concentrated support conditions and loadings. It is hoped that these structural examples are so convincing that engineers would adopt the VPINN method in their structural design practice.

    Surface effects on double-ended dislocation sources in single-crystal micropillars: implications for size-dependent and stochastic yield strength
    Xu ZHANG, Dayang DENG, M. YE, T. SUMIGAWA, H. R. MA, Xuewei HUANG
    2025, 46(6):  1143-1166.  doi:10.1007/s10483-025-3256-7
    Abstract ( 10 )   HTML ( 1)   PDF (5221KB) ( 2 )  
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    This study investigates the surface effects on the operation of double-ended dislocation sources in single-crystal micropillars under compression. A comprehensive theoretical framework is formulated to derive the stress field of the source segment and the corresponding Peach-Koehler (PK) forces acting on this segment near the free surfaces. An analytical formulation is then developed to compare the source strength with and without the influence of the surface stress. The results reveal that the surface effects on the dislocation source strength are highly sensitive to the interplay between the source length and its distance from the free surface. These surface effects can either enhance or reduce the critical stress required for the source operation by up to 50%, leading to significant fluctuations in yield strength, as commonly observed in discrete dislocation dynamics simulations and experimental studies. These findings provide different interpretations for the size-dependent and stochastic yield stress behavior in face-centered cubic (FCC) micropillars.

    Analysis of the electromechanical coupling characteristics of piezoelectric semiconductor PN junction shell structures
    Tiqing WANG, Feng ZHU, Peng LI, Zelin XU, Tingfeng MA, I. KUZNETSOVA, Zhenghua QIAN
    2025, 46(6):  1167-1186.  doi:10.1007/s10483-025-3259-6
    Abstract ( 18 )   HTML ( 2)   PDF (4271KB) ( 4 )  
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    Based on the nonlinear drift-diffusion (NLDD) model, the coupled behavior between the mechanical and electrical fields in piezoelectric semiconductor (PS) PN junctions under two typical loading conditions is investigated. The governing equations for the general shell structure of the PS PN junction are derived within the framework of virtual work principles and charge continuity conditions. The distributions of the electromechanical coupling field are obtained by the Fourier series expansion and the differential quadrature method (DQM), and the nonlinearity is addressed with the iterative method. Several numerical examples are presented to investigate the effects of mechanical loading on the charge carrier transport characteristics. It is found that the barrier height of the heterojunction can be effectively modulated by mechanical loading. Furthermore, a nonlinearity index is introduced to quantify the influence of nonlinearity in the model. It is noted that, when the concentration difference between the two sides is considerable, the nonlinear results differ significantly from the linear results, thereby necessitating the adoption of the NLDD model.

    Numerical investigation on a comprehensive high-order finite particle scheme
    Yudong LI, Yan LI, Chunfa WANG, P. JOLI, Zhiqiang FENG
    2025, 46(6):  1187-1214.  doi:10.1007/s10483-025-3262-9
    Abstract ( 17 )   HTML ( 2)   PDF (19922KB) ( 5 )  
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    In the field of discretization-based meshfree/meshless methods, the improvements in the higher-order consistency, stability, and computational efficiency are of great concerns in computational science and numerical solutions to partial differential equations. Various alternative numerical methods of the finite particle method (FPM) frame have been extended from mathematical theories to numerical applications separately. As a comprehensive numerical scheme, this study suggests a unified resolved program for numerically investigating their accuracy, stability, consistency, computational efficiency, and practical applicability in industrial engineering contexts. The high-order finite particle method (HFPM) and corrected methods based on the multivariate Taylor series expansion are constructed and analyzed to investigate the whole applicability in different benchmarks of computational fluid dynamics. Specifically, four benchmarks are designed purposefully from statical exact solutions to multifaceted hydrodynamic tests, which possess different numerical performances on the particle consistency, numerical discretized forms, particle distributions, and transient time evolutional stabilities. This study offers a numerical reference for the current unified resolved program.

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