Optimizing wind energy harvesting performance remains a significant challenge. Machine learning (ML) offers a promising approach for addressing this challenge. This study proposes an ML-based approach using the radial basis function neural network (RBFNN) and differential evolution (DE) to predict and optimize the structural parameters (the diameter of the spherical bluff body D, the total spring stiffness k, and the length of the piezoelectric cantilever beam L) of the wind energy harvester (WEH). The RBFNN model is trained with theoretical data and validated with wind tunnel experimental results, achieving the coefficient-of-determination scores R^2 of 97.8% and 90.3% for predicting the average output power P_{\text{avg}} and aero-electro-mechanical efficiency {\eta }_{\text{aem}}, respectively. The DE algorithm is used to identify the optimal parameter combinations for wind speeds U ranging from 2.5 m/s to 6.5 m/s. The maximum P_{\text{avg}} is achieved when D=57.5 mm, k=28.8 N/m, L=112.1 mm, and U=4.6 m/s, while the maximum {\eta }_{\text{aem}} is achieved when D=52.7 mm, k=29.2 N/m, L=89.2 mm, and U=4.7 m/s. Compared with that of the non-optimized structure, the WEH performance is improved by 28.6% in P_{\text{avg}} and 19.1% in {\eta }_{\text{aem}}.

In quadrupeds, the cervical and lumbar circuits work together to achieve the speed-dependent gait expression. While most studies have focused on how local lumbar circuits regulate limb coordination and gaits, relatively few studies are known about cervical circuits and even less about locomotor gaits. We use the previously published models by Danner et al. (DANNER, S. M., SHEVTSOVA, N. A., FRIGON, A., and RYBAK, I. A. Computational modeling of spinal circuits controlling limb coordination and gaits in quadrupeds. eLife, 6, e31050 (2017)) as a basis, and modify it by proposing an asymmetric organization of cervical and lumbar circuits. First, the model reproduces the typical speed-dependent gait expression in mice and more biologically appropriate locomotor parameters, including the gallop gait, locomotor frequencies, and limb coordination of the forelimbs. Then, the model replicates the locomotor features regulated by the M-current. The walk frequency increases with the M-current without affecting the interlimb coordination or gaits. Furthermore, the model reveals the interaction mechanism between the brainstem drive and ionic currents in regulating quadrupedal locomotion. Finally, the model demonstrates the dynamical properties of locomotor gaits. Trot and bound are identified as attractor gaits, walk as a semi-attractor gait, and gallop as a transitional gait, with predictable transitions between these gaits. The model suggests that cervical-lumbar circuits are asymmetrically recruited during quadrupedal locomotion, thereby providing new insights into the neural control of speed-dependent gait expression.

This study explores the nonlinear dynamics of a quasi-zero stiffness (QZS) vibration isolator coupled with a piezoelectric energy harvester connected to an RL-resonant circuit. The model of the system is formulated with the Lagrangian mechanics, representing a two-degree-of-freedom nonlinear electromechanical system subject to harmonic base excitation under a 1:1 internal resonance condition. The model is normalized, and the conditions dictating monostable and bistable oscillation modes are identified. The bifurcation characteristics of the coupled system are analyzed in both oscillation modes by means of harmonic balance and continuation methods. The vibration isolation performance, with and without the coupled harvester, is evaluated in terms of displacement transmissibility to assess its dual functionalities for vibration isolation and energy harvesting. Analytical results demonstrate that integrating a piezoelectric harvester into a monostable QZS isolator under 1:1 internal resonance does not compromise its vibration isolation capability while enabling efficient energy harvesting at extremely low-frequency base excitation. Furthermore, the system’s response under strong base excitation is investigated exclusively for energy harvesting in both monostable and bistable modes, leading to optimal structural parameter design. The conditions for intra-well and inter-well periodic oscillation modes, as well as chaotic responses, are analyzed analytically and validated numerically through stability charts, basins of attraction, bifurcation diagrams, time histories, and Poincaré maps. This work provides a comprehensive understanding of the oscillation dynamics of QZS isolators and offers valuable insights for optimizing their geometric parameters to function as high-performance vibration isolators and/or energy harvesters.

Bionic X-shaped vibration isolators have been widely employed in aerospace and other industrial fields, but the stiffness properties of classic X-shaped structures limit the vibration isolation ability for low frequencies. An innovative bionic quasi-zero stiffness (QZS) vibration isolator (BQZSVI), which can broaden the QZS range of a classic X-shaped isolator and can bring it closer to the equilibrium position, is proposed. The BQZSVI consists of an X-shaped structure as the bone fabric of lower limbs and a nonlinear magnetic loop device simulating the leg muscle. Based on static calculation, the stiffness characteristic of the structure is confirmed. The governing equations of motion of the BQZSVI structure are established in the framework of the Lagrange equation, and the harmonic balance method (HBM) is adopted to obtain the transmissibility responses. The results show that the BQZSVI can provide a more accessible and broader range of QZS. In the dynamic manifestation, the introduction of the BQZSVI can reduce the amplitude of a classic X-shaped vibration isolator by 65.7%, and bring down the initial vibration isolation frequency from 7.43 Hz to 2.39 Hz. In addition, a BQZSVI prototype is designed and fabricated, and the exactitude of the theoretical analysis method is proven by means of experiments.

In this paper, we theoretically study the Lamb wave in a multilayered piezoelectric semiconductor (PSC) plate, where each layer is an n-type PSC with the symmetry of transverse isotropy. Based on the extended Stroh formalism and dual-variable and position (DVP) method, the general solution of the coupled fields for the Lamb wave is derived, and then the dispersion equation is obtained by the application of the boundary conditions. First, the influence of semiconducting properties on the dispersion behavior of the Lamb wave in a single-layer PSC plate is analyzed. Then, the propagation characteristics of the Lamb wave in a sandwich plate are investigated in detail. The numerical results show that the wave speed and attenuation depend on the stacking sequence, layer thickness, and initial carrier density, the Lamb wave can propagate without a cut-off frequency in both the homogeneous and multilayer PSC plates due to the semiconducting properties, and the Lamb wave without attenuation can be achieved by carefully selecting the semiconductor property in the upper and lower layers. These new features could be very helpful as theoretical guidance for the design and performance optimization of PSC devices.

The acoustic wave propagation in gas-saturated double-porosity materials composed of a microporous matrix and mesopores with arrays of plate-type resonators is investigated. A macroscopic description, established with the two-scale asymptotic homogenization method, evidences the combined effect of inner resonances on the acoustic properties of the respective effective visco-thermal fluid. One type of resonance originates from strong pore-scale fluid-structure interaction, while the other one arises from pressure diffusion. These phenomena respectively cause weakly and highly damped resonances, which are activated by internal momentum or mass sources, and can largely influence, depending on the material’s morphology, either the effective fluid’s dynamic density, compressibility, or both. We introduce semi-analytical models to illustrate the key effective properties of the studied multiscale metamaterials. The results provide insights for the bottom-up design of multiscale acoustic metamaterials with exotic behaviors, such as the negative, very slow, or supersonic phase velocity, as well as sub-wavelength bandgaps.

With the miniaturization of devices and the development of modern heating technologies, the generalization of heat conduction and thermoelastic coupling has become crucial, effectively emulating the thermodynamic behavior of materials in ultrashort time scales. Theoretically, generalized heat conductive models are considered in this work. By analogy with mechanical viscoelastic models, this paper further enriches the heat conduction models and gives their one-dimensional physical expression. Numerically, the transient thermoelastic response of the slim strip material under thermal shock is investigated by applying the proposed models. First, the analytical solution in the Laplace domain is obtained by the Laplace transform. Then, the numerical results of the transient responses are obtained by the numerical inverse Laplace transform. Finally, the transient responses of different models are analyzed and compared, and the effects of material parameters are discussed. This work not only opens up new research perspectives on generalized heat conductive and thermoelastic coupling theories, but also is expected to be beneficial for the deeper understanding of the heat wave theory.

This paper theoretically investigates the influence of a cylindrical PN junction on the propagation characteristics of shear cylindrical waves (SCWs) in an infinitely long piezoelectric semiconductor (PS) concentric cylinder structure. This PS concentric cylinder structure is composed of three regions: an inner PS cylinder, an outer PS cylindrical shell, and a cylindrical PN junction at the interface between the two aforementioned regions. First, the basic equations of the PS concentric cylinder structure are derived, taking into account the coupling of the mechanical displacement, electric potential, and charge carrier perturbation in the cylindrical coordinate system. Next, a mathematical model for the SCWs in this PS concentric cylinder structure is established, utilizing the spectral method and considering the physical characteristics of the cylindrical PN junction. Finally, the dispersion and attenuation curves of the SCWs are numerically calculated to discuss the influence of the interface effect resulting from the cylindrical PN junction. It is found that the existence of a cylindrical PN junction can either reduce or enhance the mechanical-to-electrical energy conversion, which is closely related to the doping mode, doping concentration, and curvature radius of the cylindrical interface. A reasonable design of the aforementioned parameters can optimize the wave motion in acoustic equipment formed by PS media with different frequencies or wavelengths. The construction and resolution of the mathematical model as well as the analysis of physical mechanisms can offer theoretical guidance for improving the efficiency of energy conversion from mechanical energy to electrical energy and optimizing the acoustic performance of energy harvesting devices.

Sandwich piezoelectric semiconductor (PS) structures have significant applications in multi-functional semiconductor devices. The analysis of multi-field coupling behaviors of PS structures is of fundamental importance in developing novel PS devices. In this paper, we develop a general temperature-deformation-polarization-carrier (TDPC) coupling model for sandwich-type PS beams involving pyroelectricity under thermal loadings, based on three-dimensional (3D) basic equations of the thermo-piezoelectric semiconductor (TPS). We derive analytical solutions for extensional, bending, and buckling deformations of simply-supported sandwich n-type PS beams subjected to open-circuit and electrically isolated boundary conditions. The accuracy of the proposed model in this paper is verified through finite element simulations implemented in the COMSOL software. Numerical results show that the initial electron concentration and the thickness ratio of the PS layer to the beam’s total thickness have a significant effect on thermally induced extensional and bending responses, as well as critical buckling mechanical and thermal loadings. This study provides a theoretical framework and guidance for designing semiconductor devices based on sandwich PS beam structures.

A dimensionless load-displacement model based on the energy-density equivalence principle is proposed to obtain the stress-strain relationships of metallic materials under monotonic indentations with various diameters of spherical indenters. Finite element simulations are carried out to verify the constitutive relations from the new model, involving indentations made with various spherical indenters. For each indenter, some quasi-static spherical indentation tests are conducted on the materials with 40 preset constitutive relationships. The results indicate that the stress-strain curves predicted by the model align with the preset curves under 200 loading conditions. Moreover, the goodness-of-fit between the predicted stress-strain curves and the preset curves exceeds 0.96 for all indenters and materials. In the end, the indentation tests are conducted by the spherical indenters with the diameters of 1.587 mm for fifteen metallic materials and 1 mm for eight metallic materials. The results show that the stress-strain curves obtained by the spherical indentation based on the new model closely match those obtained from the uniaxial tensile tests. The relative errors for both the proof strength at 0.2% plastic extension and the tensile strength are below 5%.

Fins are extensively utilized in heat exchangers and various industrial applications as they are lightweight and can benefit in various systems, including electronic cooling devices and automotive components, owing to their adaptable design. Furthermore, spine fins are introduced to improve performance in applications such as automotive radiators. They can be shaped in different ways and constructed from a collection of materials. Inspired by this, the present model examines the effects of internal heat generation and radiation-convection on the thermal distribution in a wetted convex-shaped spine fin. Using dimensionless terms, the proposed fin model involving a governing nonlinear ordinary differential equation (ODE) is transformed into a dimensionless form. The study uses the operational matrix with the Charlier polynomial collocation method (OMCCM) to ensure precise and computationally efficient numerical solutions for the dimensionless equation. In order to aid in the analysis of thermal performance, the importance of major parameters on the temperature profile is graphically illustrated. The main outcome of the study reveals that as the radiation-conductive, wet, and convective-conductive parameters increase, the heat transfer rate progressively improves. Conversely, the ambient temperature and internal heat generation parameters show an inverse relationship.