This work presents a piezoelectric vibration energy harvester (PVEH) featuring a pre-shaped curved beam with clamped boundaries to investigate its energy harvesting mechanism based on the intrinsic snap-through behavior. Since the ability of the beam to exhibit meta-stable and bi-stable states strongly depends on its geometric parameters, the potential energies of models with varying thicknesses and initial apex heights are analyzed, followed by the derivations of electromechanical coupled equations for both meta-stable and bi-stable systems. The effects of the geometric parameters of the curved beam on the nonlinear dynamic behaviors and energy harvesting efficiencies under different external excitations are examined. Series of experiments are tested to validate the theoretical analyses. The research findings show that the separation between the potential wells in the bi-stable beam is mainly governed by the thickness and initial apex height, while the potential barrier height is affected by both the geometric and material properties. The optimal energy harvesting efficiencies in the transition analyses of meta-stable and bi-stable states are achieved by tuning specific geometric parameters. Design guidelines are provided to maximize the bandwidth and efficiency for energy harvesting applications.

This study uses numerical and analytical schemes to consider the wave propagation behavior of a triply periodic minimal surface sandwich cylindrical system (TPMS-SCS) for the first time. Although these structures exhibit outstanding physical and mechanical properties, their dynamic and acoustic features have not been reported yet. This study addresses this gap by calculating the sound transmission loss (STL) coefficient within the framework of the wave approach across various architectures, including the primitive (P), Schoen gyroid (G), and wrapped package-graph (IWP) of a TPMS lattice structure. To determine an analytical STL, a third-order approach is used to precisely capture the stress-strain distribution based on the thickness coordinate, thereby providing a simultaneous solution to the general characteristic relations along with fluid-structure coupling. Given the lack of studies for frequency and STL comparisons, the structure is modeled considering a finite element (FE) design, which is a challenging and time-consuming process because of the complex topological TPMS configurations incorporated within a sandwich cylinder. In fact, achieving convincing computational accuracy requires fine mesh discretization, which significantly increases computational costs during vibroacoustic analysis. Using the numerical results from the COMSOL software Multiphysics, the accuracy of the analytical STL spectrum is verified for different configurations, including P, G, and IWP. The effective acoustic specifications of a TPMS-SCS in the frequency domain are examined by the comparison of the STL with that of a simple cylinder of the same mass. In this context, it would also be beneficial to examine the effect of TPMS thickness, which can demonstrate the importance of the present results. The findings of this approach can be beneficial for scholars working on the numerical and analytical sound insulation characteristics of metamaterial-based cylindrical systems.

An analytical method is proposed with the “stiffness gradient of the response” as a sensitivity metric, and the relationships between the vibration responses and stiffness changes are established. First, a 2-degree-of-freedom (DOF) system is used as an example to propose a stiffness gradient-based evaluation method, taking the effective control bandwidth ratio as a metric of effectiveness. The results show that there is an optimal mass ratio in both variable mass and variable stiffness cases. Then, a typical 16-DOF system is used to investigate the frequency domain characteristics of the stiffness gradient values in the complex system. The distributions of stiffness gradient values show multiple peak intervals corresponding to the sensitive regions for vibration control. By assigning random mass parameters, a significant exponential decay relationship between the subsystem’s mass and effective control is identified, emphasizing the importance of the optimal mass ratio. The finite-element simulation results of solid plate models with springs and oscillators further validate the theoretical results. In short, the gradient value of stiffness effectively quantifies the effects of subsystems on vibration control, providing an analytical tool for active control in complex systems. The identified exponential decay relationship offers meaningful guidance for implementation strategies.

Moving-load induced vibrations can, in certain instances, exceed those caused by equivalent static loads, especially at the critical velocity of moving loads. Suppressing these vibrations is of critical practical importance in various engineering fields, including the design of precision robotics and advanced aerospace structures where components are subject to moving loads. In this paper, an inertial nonlinear energy sink (NES) is used for the first time to reduce the vibration response of graphene platelet (GPL)-reinforced nanocomposite beams with elastic boundaries under moving loads. Based on the von Kármán nonlinear theory, the governing equations of the beam-NES system are derived using the Lagrange equation. The Newmark-Newton method, in conjunction with the Heaviside step function, is used to obtain the nonlinear responses of the beam under moving loads. The effects of the boundary spring stiffness, the GPL parameters, as well as the velocity and frequency of the moving loads on the beam response and the performance of the NES are thoroughly studied. The results of this work provide insights into applying NESs to suppress the nonlinear vibrations induced by moving loads in composite structures with elastic boundaries.

Current studies on carbon nanotube (CNT) size effects predominantly employ Eringen’s differential nonlocal model, which is widely recognized as ill-suited for bounded domains. This paper investigates the free vibration of multi-walled CNTs (MWCNTs) with mathematically well-posed two-phase strain-driven and stress-driven nonlocal integral models incorporating the bi-Helmholtz kernel. The van der Waals (vdW) forces coupling MWCNT layers are similarly modeled as size-dependent via the bi-Helmholtz two-phase nonlocal integral framework. Critically, conventional pure strain-driven or stress-driven formulations become over-constrained when nonlocal vdW interactions are considered. The two-phase strategy resolves this limitation by enabling consistent coupling. Each bi-Helmholtz integral constitutive equation is equivalently transformed into a differential form requiring four additional constitutive boundary conditions (CBCs). The numerical solutions are obtained with the generalized differential quadrature method (GDQM) for these coupled higher-order equations. The parametric studies on double-walled CNTs (DWCNTs) and triple-walled CNTs (TWCNTs) elucidate the nonlocal effects predicted by both formulations. Additionally, the influence of nonlocal parameters within vdW forces is systematically evaluated to comprehensively characterize the size effects in MWCNTs.

The bolted flange structure finds significant applications in fields such as aerospace, shipbuilding, and pipeline transportation. The investigation of its dynamic characteristics has consistently been a focal point for researchers; however, there remains a deficiency in the development of robust analytical models. This paper introduces a novel analytical model based on the finite element methods and the Timoshenko beam theory to accurately simulate the bolted flange structure. The stiffness, mass, damping, and inertia matrices of the rotor system are individually derived, and the dynamic equation is subsequently formulated. The model’s validity and accuracy are validated through both the experimental testing and the finite element analysis. This study aims to elucidate the relationship between the external loads and the influence of the geometric configuration on the stiffness and contact behavior of the bolted flange structure, thereby enabling a thorough and precise prediction of the static and dynamic load transfer pathways, as well as the distribution of vibrational energy within the structure, while also facilitating the incorporation of friction and slip effects. Simultaneously, this work provides a foundational framework for the optimization design of bolted flange structures, addressing the factors such as the number, size, and geometric distribution of bolts.

When the size of a magneto-electro-elastic cylindrical shell (MEECS) is reduced to micro-/nano-scale, the size-dependent flexomagnetic effect (FME) and flexoelectric effect (FEE) significantly influence their multi-physical coupling behaviors. To investigate these effects on the post-buckling behaviors of an MEECS, a nonlinear post-buckling model is developed based on the higher-order shear deformation theory (HSDT) and magneto-electro-elastic (MEE) constitutive relations with the FME and FEE. The equilibrium path and the corresponding shell deformations are obtained with a set of newly developed generalized displacement functions within the framework of the Galerkin approach. These displacement functions are established based on the trigonometric series expansions, which accurately satisfy the clamped boundary conditions (BCs). The effects of geometry, flexomagnetic/flexoelectric coefficients, and external electromagnetic fields on the post-buckling behaviors of an MEECS with the FME and FEE are analyzed. Numerical results indicate that the FME decreases the upper critical load of an MEECS, whereas the FEE exhibits an opposite effect by increasing it.

Anisogrid composite lattice conical shells, which exhibit varying stiffness along their cone generators, are widely used as interstage structures in aerospace applications. Buckling under axial compression represents one of the most hazardous failure modes for such structures. In this paper, the smeared stiffness method, which incorporates the effect of component torsion, is used to obtain the equivalent stiffness coefficients for composite lattice conical shells with triangular and hexagonal patterns. A unified framework based on the variational differential quadrature (VDQ) method is established, leveraging its suitability for asymptotic expansion to determine the critical buckling loads and the b-imperfection sensitivity parameter of lattice conical shells with axially varying stiffness due to rib layout. The influence of pre-buckling deformation is taken into account to enhance the accuracy of predictions on the linear buckling loads. The feasibility of the present equivalent continuum model is verified, and the differences in buckling behaviors for composite lattice conical shells with both triangular and hexagonal unit cells are numerically evaluated through the finite element (FE) simulations and the VDQ method.

Curved beams with complex geometries are vital in numerous engineering applications, where precise vibration analysis is crucial for ensuring safe and effective designs. Traditional finite element methods (FEMs) often struggle to accurately represent the dynamic characteristics of these structures due to the limitations in their shape function approximations. To overcome this challenge, the current study introduces an innovative finite element (FE)-based technique for the undamped vibrational analysis of curved beams with arbitrary curvature, employing explicitly derived interpolation functions. Initially, the exact interpolation functions are developed for circular arc elements with the force method. These functions facilitate the creation of a highly accurate stiffness matrix, which is validated against the benchmark examples. To accommodate arbitrary curvature, a systematic transformation technique is established to approximate the intricate curves with a series of circular arcs. The numerical findings indicate that increasing the number of arc segments enhances accuracy, approaching the exact solutions. The analysis of free vibrations is conducted for both circular and non-circular beams. Mass matrices are derived using two methods: lumped mass and consistent mass, where the latter is based on the interpolation functions. The effectiveness of the proposed method is confirmed through the comparisons with the existing literature, demonstrating strong agreement. Finally, several practical cases involving beams with diverse curvature profiles are analyzed. Both natural frequencies and mode shapes are determined, providing significant insights into the dynamic behavior of these structures. This research offers a dependable and efficient analytical framework for the vibrational analysis of complex curved beams, with promising implications for structural and mechanical engineering.

The present work analyzes the linear and weakly nonlinear stability of double-diffusive convection (DDC) in a Navier-Stokes-Voigt (NSV) fluid, considering a chemical reaction and an internal heat source. The lower fluid layer is salted and heated. The quiescent state and dimensionless variables yield dimensionless parameters for the governing partial differential equations (PDEs). A two-dimensional scenario is investigated using the stream function. Stationary and oscillatory convection can be analyzed using the linear approach. The nonlinear equations are numerically solved using the Runge-Kutta Fehlberg (RKF-45) technique. Additionally, the physics-informed neural network (PINN) validates the mathematical outcomes. The Kelvin-Voigt parameter and the Prandtl number do not affect stationary convection. Thhe neutral stability diagrams show that the ratios of diffusivity, solute Rayleigh, and Kelvin-Voigt parameters stabilize oscillatory convection. However, internal heat and chemical reactions cause instability. The Kelvin-Voigt, internal heat, and chemical reaction parameters increase mass and heat transfer (MHT), while the solute Rayleigh number and the ratio of diffusivity decrease MHT.