This study introduces an advanced analytical-numerical framework to examine the free vibration characteristics of a rotating auxetic sandwich annular plate, featuring three-phase nanocomposite face sheets supported by a Kerr-type elastic foundation. A sophisticated zig-zag displacement theory is utilized to accurately represent interlaminar kinematics and transverse shear effects, while the Generalized Differential Quadrature Method (GDQM) provides an efficient and precise numerical solution to the governing equations across diverse boundary conditions. The suggested formulation takes into account the effects of rotation, non-uniform radial loading, auxetic core geometry, and nanocomposite material gradation all at once. This makes it a single, efficient way to model the dynamics of multifunctional rotating structures. The findings indicate that the auxetic core substantially improves vibration suppression via its negative Poisson’s ratio mechanism, whereas the nanocomposite face sheets enhance stiffness and stability without augmenting structural weight. Also, the Kerr foundation parameters, especially the shear stiffness, are very important for adjusting the frequency response. The model shows that the best angle for auxetic cells (30°–45°) and the best ratio of fibers to interphases are the ones that give the most dynamic stiffness. The suggested method is a powerful way to predict how to design lightweight, high-speed rotating parts like aerospace panels, turbomachinery blades, and adaptive metamaterial-based structures that need stiffness, stability, and vibration control all at the same time.

The internal water pressure (IWP) in hydropower house substructures should be not seen merely as a static loading that acts on the substructure all at once, but rather as a cyclic one that repeatedly acts on the substructure for many times over its life cycle. Previous work has only focused on the static structural performance of hydropower house substructures. A neglected area is how cyclic IWP loadings would degenerate the structural performance of a hydropower house substructure. The aim of this work is thus to investigate the crack propagation behavior in mass concrete of hydropower house substructures with cyclic IWP loadings considered. The extended finite element method based on the ABAQUS code is used to model the crack propagation behavior. The intake c-cross-section of the Laxiwa hydropower house substructure is numerically modeled with axisymmetric elements. A major finding is the blocking effect of the slope on the upward-sliding behavior of the steel liner. The blocking effect should lead to concentrated steel-to-concrete IWP loading transfers at the slope-cutting constructions, which allow the initial cracks to propagate into the mass concrete under the cyclic IWP loadings. Another major finding is concerning the crack propagation from the turbine floor down into the mass concrete adjacent to the generator pedestal when a relatively stiff membrane (e.g. E m=3 MPa) is employed. This study has found noticeable stiffness degradation of the hydropower house substructure as the IWP loading repeats. The insights gained from this study may be of assistance to hydroelectric power plant designers and operators.

To investigate the dynamic characteristics of blade with dampers, this paper proposed a nonlinear vibration calculation and analysis method for blade with the planar Under Platform Dampers (UPDs) based on the bristle friction theory. A LuGre friction model under uniformly distributed load conditions was established and incorporated into the dynamic model construction of the blade. The dynamic model of the blade structure was established by using the Assumed modal method and orthogonal polynomials. The harmonic balance method with alternating time-frequency domain (HBM-AFT) was employed to solve the dynamic model, addressing the strong nonlinearity of friction. The Newmark-Beta numerical integration method was employed to validate the accuracy and superiority of the proposed method. Finally, the nonlinear vibration characteristics of the blade were analyzed under varying preloads and installation positions. The periodic solution and amplitude frequency curve of the nonlinear vibration of the blade indicate that increasing the preload of UPD can to some extent enhance the resonance frequency of the blade. The installation position of the damper significantly affects the resonance amplitude of the blade. This study holds significant implications for the practical design of blades.

This study investigates the buckling behavior of laminated composite structures by employing a mixed finite element formulation based on a higher-order shear deformation theory that incorporates transverse stretching effects. The displacement field is defined through higher-order polynomial variations across the thickness, enabling accurate representation of both transverse shear and normal deformations without requiring shear correction factors. The mixed approach is derived using the Hellinger–Reissner variational principle, allowing both displacement and stress resultants to be treated as independent variables for improved numerical stability and convergence. Governing equations are developed and implemented in a C0 finite element framework suitable for rectangular laminates under mechanical loading. Benchmark comparisons demonstrate strong agreement with available analytical and three-dimensional elasticity solutions, validating the precision of the proposed model. Parametric analyses further reveal the significant influence of transverse stretching and stacking sequence on the critical buckling loads of laminated plates. The main novelty lies in extending the mixed finite element framework to include transverse stretching effects within the HSDT for buckling analysis, offering higher accuracy and efficiency compared with existing plate theories.

This paper presents a method for generating an obstacle-avoiding trajectory in optimal time and addresses the control problem of double-pendulum cranes, accounting for external disturbances and system constraints. Firstly, the double pendulum crane system is demonstrated to be a flatness system, with the flat outputs corresponding to the positions of the loads. Subsequently, by analyzing and incorporating various constraints, an optimization problem is formulated to determine the reference trajectory from the initial position to the final position of the load, minimizing travel time while ensuring obstacle avoidance. To mitigate the effects of disturbances and sensor limitations, a fixed-time extended-state observer is employed to estimate the output signal velocities and the total disturbance. These estimated signals and the derivative from the Lyapunov function of the proposed Nonsingular Hierarchical Fixed-Time Sliding Mode Control are utilized to design a Lyapunov-based Model Predictive Controller, enabling the load to track the reference trajectory while minimizing the swing angle and adhering to system constraints. Furthermore, the stability of the Lyapunov-based Model Predictive Controller is established based on the stability properties of the Nonsingular Hierarchical Fixed-Time Sliding Mode Control. Finally, simulation results and comparisons demonstrate the effectiveness of the proposed methods under various conditions.

This study investigates the bending behavior of auxetic doubly-curved nanoshells featuring a butterfly-shaped honeycomb (BSH) lattice configuration. The research specifically examines the unique mechanical response of these architectured nanostructures under flexural loading, with emphasis on their negative Poisson’s ratio characteristics stemming from the BSH geometry. The investigation was initiated by applying higher-order shear deformation theory (HSDT), which provides a refined framework for analyzing the bending behavior of such complex geometries. Following this, the equations of motion were derived by sequentially applying Nonlocal Strain Gradient Theory (NSGT) to capture nanoscale size effects, then employing Hamilton’s equation to obtain the energy-based dynamic formulation. By employing these advanced theoretical frameworks, the intricate dynamics of the BSH structures were captured. Ultimately, Navier’s method was utilized to systematically examine the bending properties of the BSH nanoshells through the careful resolution of the derived equations. The numerical results obtained from this systematic investigation were critically validated against benchmark solutions available in the existing literature, thus confirming the accuracy and reliability of the results obtained. Furthermore, an in-depth analysis was conducted to explore how various factors, including the Nonlocal nanoscale phenomena, Strain gradient stiffening effects, Shell curvature kinematics, and Topological design variables of the BSH, significantly affect the deflection of the BSH nanoshell during bending. This multifaceted approach enhances our understanding of the mechanical behavior of advanced nanostructures.

This article investigates the free vibration behavior of a stiffened sandwich plate subjected to combined hygrothermal, electrical, and magnetic fields and resting on a Pasternak elastic foundation. The porous functionally graded magneto-electro-elastic sandwich plates (PoFG-MEES) consists of three layers: a top layer made of PoFGMEE (porous magneto-electro-elastic functionally graded materials), a core of functionally graded material with porosity (PoFGM), and a bottom layer, which incorporates stiffeners made from the same perfect functionally graded material. The through-thickness variation of material properties is modeled using a modified power-law function with two porosity distribution patterns, while the electric potential and magnetic field in the PoFGMEE layer follow combined cosine–linear profiles. The proposed model employs a higher-order shear deformation theory (HSDT-4), the pb2-Ritz method, and Lekhnitskii’s smeared stiffener technique to account for material gradation, porosity distribution, and stiffener reinforcement under various boundary conditions. Numerical results, validated against existing literature, reveal that porosity distribution, material volume fractions, foundation stiffness, external fields, and stiffener configuration significantly influence the natural frequencies. Specifically, a Pasternak foundation and optimized stiffener arrangements enhance structural stiffness, while electric and magnetic fields can either increase or decrease frequencies depending on their polarity. The findings provide valuable insights for designing smart structures and stiffened sandwich plates operating under coupled hygrothermal, electrical, and magnetic fields.

To fully realize the potential of tubular structures in lightweight design, a variable-thickness rolled blanks (VRB) and variable strength (VS) hot-stamping forming process is proposed to produce the VRB-VS tubes with circular cross-section, which demonstrate significant promise for a broad spectrum of engineering applications, such as automotive seat frames and mobile elevating work platforms, among others. The complicated interacting mechanisms between multiple design variables and crashworthiness indices introduce great challenges during substantial optimization design of VRB-VS tubular structures to balance design efficiency and crashworthiness performance under transverse impact. The inherent conflict arises from a dual-aspect paradox in crashworthiness design: the ambiguous relationships between design variables and crashworthiness responses, and the sensitivity gradient divergence observed across different design schemes, collectively necessitating prolonged design iterations that substantially escalate the development cycle duration and associated costs of automotive components. To overcome these challenges, a dual-field quantification framework, comprising the normalized internal energy density ( IED ) and its spatial gradient variance ( δ IED ), is proposed to investigate the mechanisms underlying the spatial homogeneity of energy absorption. The framework establishes a functional mapping between design variables and crashworthiness indices via a surrogate model constructed using the response surface method, which facilitates sensitivity analysis and supports subsequent structural parametric investigations. Sensitivity analysis results indicate that the thickness of VRB thick zone ( t 0 ) and the strength of high-strength zone ( σ s 0 ) have the greatest impact on crashworthiness indices, whereas the midpoint of thickness transition zone ( p t ) and the midpoint of strength transition zone ( p s ) show relatively minor effects. Finally, a design criterion for homogenizing the IED distribution is proposed to guide the structural design of tubular components, and has been successfully applied to a VRB-VS rear seat, achieving both excellent crashworthiness and significant mass reduction.

Weight reduction is a critical factor in the design of spacecraft and rockets, driving the adoption of composite structures instead of traditional materials. Sandwich composite panels, commonly used in aerospace applications, offer high stiffness-to-weight ratios but are vulnerable to localized deformation under load. Conventional T and L joints, typically made of Aluminum, exacerbate this issue by causing localized stress concentrations, which can lead to permanent structural failure. Additionally, these joints require large supportive areas, increasing the overall weight of the satellite structure. To address these challenges, this study proposes the use of innovative edge inserts as a replacement for traditional joints. These edge inserts are embedded within sandwich panels, which consist of a honeycomb core sandwiched between two face sheets. A comprehensive sensitivity analysis was conducted to evaluate von Mises stress and elemental strain on the inserts under varying load conditions, identifying potential damage and failure modes. Experimental validation through pull-out tests further compared the theoretical analysis with real-world performance, highlighting the effectiveness of edge inserts in enhancing load transfer while minimizing weight. This study demonstrates the potential of edge inserts to significantly improve the performance and reliability of aerospace sandwich structures.

This study presents an analytical investigation into the influence of the flexoelectric effect on shear-horizontal (SH) wave propagation in a structure comprising a piezo–flexo-electric (PFE) layer bonded to a PFE substrate. The interface between the two media is considered to be corrugated. By applying appropriate boundary and interfacial conditions, a frequency equation is derived, linking the wave number to the phase velocity through parameters such as material properties, corrugation amplitudes, layer thickness, and flexoelectric coefficients. This relationship leads to dispersion characteristics that connect wave number and phase velocity. Using these expressions, dispersion curves are generated in Mathematica 7 to demonstrate the effects of corrugation amplitudes, flexoelectric strength, and geometric parameters of the layer and substrate under both electrically open and short-circuited boundary conditions. These findings offer new insights into the design and analysis of PFE devices with realistic interface conditions.