Search Results (1,777)

Piezoelectric cantilever beam harvesters are widely considered for self-powered bridge monitoring, yet their performance is often constrained by resonance detuning under low-frequency ambient vibrations. This issue is particularly pronounced in bridge environments, where the dominant vibration frequencies are typically low and narrowly distributed. While several frequency tuning strategies have been proposed, their relative effectiveness under bridge-relevant conditions has not been systematically evaluated within a unified experimental framework. This study experimentally evaluated four tuning strategies for cantilever piezoelectric energy harvesters, i.e., spring tuning, magnetic tuning, tip mass adjustment, and beam length modification, to identify effective methods for matching the dominant frequency of bridge deck vibrations. A unified test platform using a common harvester configuration was established, and performance was quantified by resonant frequency alignment, maximum output voltage, and −3 dB bandwidth. Among the four methods, root-based spring tuning showed the best overall performance, achieving frequency matching while retaining strong electrical output, with a maximum voltage of 9.01 V and a bandwidth of approximately 1.5 Hz. Magnetic tuning also provided accurate frequency control, but reduced voltage by 15–25%. By contrast, tip mass and beam length tuning produced larger resonance shifts but caused voltage reductions of up to approximately 50%. Full article

With the large-scale construction of coastal high-speed railways, understanding the mechanical behavior of high-speed railway box girders under tsunami waves has become increasingly important. Existing studies on tsunami-induced forces on bridge girders have mainly focused on T-girders and plate-girders in highway bridges. In contrast, research on high-speed railway box girders, which are characterized by a significant height-to-width ratio, large cantilevers, and complex ancillary facilities on the girder top, remains relatively scarce, especially regarding its behavior under tsunami waves and the effects of lateral displacement on its dynamic response. In light of this, this study focuses on the investigation of the mechanical behavior of a single-track high-speed railway box girder under tsunami waves, and fifth-order solitary waves and dam-break waves are comparatively employed to simulate the typical unbroken and broken tsunami waves. The interaction between tsunami waves and the fixed railway box girder is numerically conducted, and the characteristics of the interaction process and the variation in maximum forces with girder clearance are thoroughly investigated. After that, the numerical interaction between tsunami waves and the laterally movable railway box girder is comparatively carried out, and the lateral displacement effects on the girder wave forces are exhaustively investigated. The results indicate that unbroken and broken tsunami waves exhibit distinctly different interaction processes with the box girder. With decreasing girder clearance, for the unbroken wave, the maximum horizontal and vertical forces occur when the girder bottom and the cantilever root descend to the initial water surface, respectively; for the broken wave, the horizontal and vertical forces simultaneously occur when the girder bottom nears the water surface with a small clearance. Lateral displacement can reduce wave forces on the girder, but the reduction is quite limited—remaining below 10% at the reference stiffness of an actual bearing. It validates that using a fixed girder model to estimate wave forces on an actual laterally movable girder is a slightly conservative and reasonable approach. This study provides further insight into wave forces acting on coastal high-speed railway box girders in tsunami-prone areas. Full article

HIV-1 protease (PR) is an essential enzyme in the viral life cycle and a primary target of antiretroviral therapies, particularly protease inhibitors (PIs). Understanding the dynamics of viral evolution and the factors governing the emergence or loss of resistance-associated mutations is critical for improving PI efficacy and managing drug resistance in HIV/AIDS treatment. In this study, we investigated the impact of three natural HIV-1 polymorphisms (T12A, L63Q, and H69N), whose prevalence varies depending on treatment status and viral subtype, on the structural stability and conformational dynamics of PR using molecular dynamics (MD) simulations. Three independent 500 ns MD simulations were performed for the native protease and each mutant system. Although none of the mutations disrupts the overall structural integrity of HIV-1 PR, they induce mutation-specific alterations in flexibility and residue interactions. In particular, T12A and H69N exhibit increased structural deviations, especially in the flap regions, along with enhanced conformational fluctuations. In contrast, the L63Q mutation shows a slight reduction in flap flexibility compared to both the native protease and the other mutants. Consistently, the fraction of time spent in open-flap conformations is higher for T12A and H69N and lower for L63Q relative to the native system. Moreover, mutations in the Fulcrum (T12A) and Cantilever (L63Q and H69N) regions do not disrupt the long-range network of correlated motions observed in the native protease, both inter- and intra-monomer, but instead increase the extent of correlated and anti-correlated motions in other regions of PR. Full article

To address severe strata pressure induced by large end-area hanging spans and poor caving of thick, hard roofs in western coal mines, this study takes the 1302 working face of Zhujiamao Coal Mine as a case study. A multiscale mechanical model is developed to describe the progressive evolution of a stratified hard roof from a continuous beam to a cantilever beam and finally to an arched triangular hanging roof. Limit criteria for the maximum hanging length under bending and shear failure are derived, indicating that bending governs end-area roof instability. The theoretical results show good agreement with field observations and numerical simulations, providing guidance for liquid nitrogen fracturing target selection. Coupled FLAC3D-3DEC simulations reveal the staged deformation of overlying strata and clarify the spatial correspondence between the “O-X” fracture pattern and the arched triangular hanging roof. Based on these findings, a collaborative weakening strategy integrating directional drilling, hydraulic pre-cracking, and deep liquid nitrogen fracturing is proposed. Field observations and comparative tests confirm that this method effectively forms a three-dimensional fracture network, reduces roof stiffness and strength, shortens the caving interval, lowers peak shield resistance, and promotes stable caving of the end-area hanging roof. Full article

Traditional topology optimization methods often face challenges such as slow convergence, high sensitivity to initial structures, and limited exploration of the design space when dealing with multi-physics coupling problems. To address these challenges, this study proposes an efficient design framework integrating reinforcement learning and topology optimization. The framework first employs a Deep Q-Network (DQN) agent to dynamically adjust penalty factors, accelerating the convergence process, and uses its pre-optimization results as the initial conditions for the Bidirectional Evolutionary Structural Optimization (BESO) method, thereby enhancing optimization efficiency and structural performance. By introducing an anisotropic material model, the design space is expanded, further unlocking the potential for structural lightweighting. On this basis, a dual-objective optimization strategy for mechanical compliance and thermal compliance is adopted, enabling the final structure to adapt to various physical working conditions. Finally, the optimal design is extended from two-dimensional to three-dimensional, facilitating subsequent manufacturing and verification. Numerical examples demonstrate that compared with traditional methods, the proposed pre-optimization method achieves a 22.463% reduction in structural compliance and improves thermal management performance. The framework demonstrates robust convergence across different boundary conditions (MBB and cantilever beams) and expands the design space through anisotropic microstructures, offering a practical solution for multi-physics lightweight design. Full article

Sometimes only a portion of the surface of a concrete element is loaded, which causes stress concentration in that region. To safely transfer concentric loads to concrete components such as column bases, short cantilevers, superstructure piers, post-tensioned elements, and support anchors, it is imperative to investigate the local compressive characteristics of concrete. To learn more about this subject, further research is required, as there are currently insufficient studies in this field. Therefore, the local compressive behavior of concrete under concentric stresses is the main focus of this work. Concrete is represented as block samples with dimensions of 200 × 200 × 250 mm. A stiff steel plate is used to apply concentric loading on the surface of the samples. The primary parameters are the bearing plate dimensions, shape (square, rectangle, and circular with varying areas), and rectangularity. Additionally, the bearing plate’s movement is examined. The stress-slip curves, ultimate bearing strengths, failures, and related slippages of the tested samples are discussed. The findings revealed that the upper surface of the concrete samples exhibited localized deterioration beneath the bearing plate. Additionally, the ultimate bearing strength of the sample loaded with the 6 × 6 cm square plate was 163% greater than that of the sample loaded with the 10 × 10 cm square plate. Furthermore, the sample loaded with the circular plate with a diameter of 4 cm had an ultimate bearing strength that was 181% greater than the sample loaded with the circular plate with a diameter of 11 cm. It is clear that the samples loaded with a circular plate of varying diameters had an ultimate bearing strength that was 8.5–11% higher than the samples loaded with a square plate of varying lengths. Full article

This paper extends the continuous movable parameterisation framework to allow for the consideration of gust load alleviation in the movable layout optimisation process. A finite impulse response filter was introduced to model the feed-forward controller and allow for the dynamic response of the movables. The extended framework was demonstrated using an ultra-high-aspect-ratio cantilever wing aircraft model. The optimisation reduced the root bending moment by 46% when both the wing movables and horizontal tailplane were used, and by 14% when only the wing movables were available. The optimisation positioned the movables to satisfy the handling qualities constraint, while having the largest effect on the root bending moment. Finally, the results show that the framework can be efficiently used to explore the movable layout design space. Full article

This paper presents a theoretical study on the electromechanical coupling response of piezoelectric–flexoelectric–semiconductor (PFS) nanocantilevers by adopting flexoelectric elasticity and semiconductor theory. A unified mechanical–electrical model is established to incorporate a strain gradient, the piezoelectric effect, semiconducting characteristics, and flexoelectricity at micro-/nanoscales. Analytical solutions for deflection, electric potential, and electron concentration are obtained under three types of electrical boundary conditions. Numerical results show that flexoelectricity significantly enhances the effective bending stiffness of the beam under open-circuit conditions with or without surface electrodes, especially in thinner structures. With a fixed external electric potential condition, the applied potential can effectively modulate the deflection by adjusting the polarization field. The induced electric potential, under the open-circuit condition with surface electrodes, exhibits a peak value at a critical thickness and flexoelectric coefficient due to the synergistic effect of the strain gradient and flexoelectricity. The electron screening effect induced by the high doping concentration is found to suppress the induced potential considerably. The present work provides a fundamental understanding of PFS coupling and provides guidance for the design of high-sensitivity micro–nano-electromechanical systems/devices. Full article

In response to the pressing need for miniaturized MEMS microphones in wearable technology and mobile devices, and to surmount the technical limitations inherent in conventional piezoelectric microphones, which typically depend on enlarging chip dimensions or decreasing stiffness to attain low resonance frequencies, this study introduces a novel piezoelectric MEMS microphone (PMM) design predicated on a flexibility-enhanced rotating structure. The proposed design utilizes an aluminum scandium nitride (Al_0.8Sc_0.2N) piezoelectric thin film with 20% scandium doping and incorporates four equivalent sensing units formed by four curved cutting lines centrally located on the chip. This configuration employs a nested arrangement of four cantilever beams to substantially increase vibration compliance, thereby effectively lowering the natural frequency without altering the chip’s external size. Three-dimensional finite element simulations reveal that, relative to traditional triangular cantilever beam architectures, the flexibility-enhanced rotating structure reduces the natural frequency from 15.6 kHz to 13.49 kHz while enhancing sensitivity from −44.6 dB to −40 dB. The device was fabricated via a comprehensive microfabrication process and subsequently characterized within a standardized acoustic testing environment. Experimental results indicate that the microphone attains a sensitivity of −43.84 dB at 1 kHz and exhibits a first resonance frequency of 13.5 kHz, closely aligning with simulation predictions. Furthermore, the signal-to-noise ratio (SNR) reaches 58.3 dB across the full range of human-audible frequencies. By leveraging the flexibility-enhanced rotating structure, this work achieves an optimal compromise between elevated sensitivity and reduced resonance frequency within a compact form factor, thereby offering a viable technical solution for the advancement of high-performance miniature acoustic sensors. Full article

Large-span structures may experience progressive collapse involving complex member collisions, for which efficient and accurate simulation remains a challenging problem in engineering practice. Conventional finite element methods are computationally inefficient in such scenarios due to repeated reconstruction of contact constraints and global stiffness matrices, while existing member discrete element method (MDEM) approaches lack a unified contact algorithm capable of handling both “point–line” and “line–line” contact modes. To address these limitations, this study extends the MDEM framework for structural collision analyses by establishing unified “point–line” and “line–line” contact models. A “virtual contact point pair” concept was introduced to define critical contact constraints, and corresponding contact force formulations were derived. A Fortran-based computational program was developed. Numerical validation through typical examples showed that the maximum relative error was 4.2% for the elastic ring problem and 3.1% for the double cantilever beam, while the rebound angle deviation in the flexible ring impact case was less than 2°. The proposed method avoids global stiffness matrix reconstruction and achieves a 95–98% accuracy compared to reference solutions under recommended parameters, providing an efficient approach for simulating member collisions in large-span structural collapse and supporting engineering analyses and design. Full article

This study addresses several key limitations identified in previous research on additively manufactured PLA composites. Unlike most earlier studies that focused primarily on the characterization of as-printed materials, the present work systematically investigates both mechanical and surface behavior before, during, and after artificial aging. In addition, six different printing configurations and reinforcement types (PVC and fiberglass mesh) were analyzed under controlled conditions, enabling a more reliable assessment of their combined influence on composite performance. Printed specimens were artificially aged for 45 and 90 days. The aging protocol combined cyclic changes in moisture, temperature, UV, and IR agents, trying to mimic real exploitation conditions as realistically as possible. The chemical and surface changes during aging were tracked using FTIR spectroscopy, colorimetry, contact angle, and surface free energy measurements. Mechanical performance at 0, 45, and 90 days was evaluated through tensile, three-point bending, and Charpy impact tests, as well as full-scale cantilever loading tests of real printed drone arms. Results show that artificial aging causes measurable chemical and surface modifications, as indicated by changes in the FTIR degradation index and surface wettability. However, these changes do not result in severe mechanical degradation within the investigated aging period. Reinforcement in the form of incorporated PVC and fiberglass mesh significantly affected failure behavior. Specimens printed with higher infill density and thicker infill lines generally exhibit improved mechanical properties. Specimens stiffness and impact resistance were also altered. Results demonstrate that reinforced PLA structures are suitable for lightweight drone applications. Full article

This study investigates the residual stresses developed during the curing process of polymer fiber-reinforced composites and their influence on fracture behavior, particularly the initiation and propagation of interlaminar cracks. The main objective is to quantify how different curing histories, including incomplete cure, alter the spatial distribution of residual stresses and, in turn, affect the mode-I fracture response of carbon-fiber/epoxy laminates. A transient thermal–structural finite element framework incorporating an autocatalytic cure kinetics model was used to simulate the curing process and predict residual stress development in a unidirectional carbon-fiber/epoxy laminate with an edge crack, considering thermal, chemical, and geometric effects. The cure model was calibrated using isothermal differential scanning calorimetry data to determine the degree of cure under different thermal conditions. The key novelty of this work is the integration of a validated cure-kinetics-based curing simulation with fracture analysis, enabling direct correlation of thermal history and degree of cure with spatially varying residual stresses at the crack front and their effect on fracture toughness. Numerical load–displacement predictions were compared with double cantilever beam experimental results and showed good agreement for the curing profiles examined. The results demonstrate that residual stresses generated by different cure cycles, including hold conditions and incomplete curing, significantly influence fracture toughness. In particular, the incomplete-cure profile produced an approximately 40% reduction in toughness compared with profiles that achieved complete cure, highlighting the importance of cure history in determining final structural performance. Full article

Biological systems regulate motion and suppress unwanted vibrations through learning, adaptation, and predictive control under uncertainty. Inspired by these principles, Bayesian system identification has emerged as a powerful framework for modeling and estimation, particularly in the presence of uncertainty in structural systems. Flexible structures in aerospace and robotics require advanced control to mitigate vibrations under model uncertainty. This paper proposes a data-driven strategy leveraging a Gaussian Process (GP) integrated within a Nonlinear Model Predictive Control (NMPC) framework. The core innovation lies in using a Gaussian Process Nonlinear AutoRegressive model with eXogenous input (GP-NARX) as a probabilistic predictor to capture structural dynamics while quantifying uncertainty. The operational mechanism involves a tight coupling where the GP provides multi-step-ahead forecasts that the NMPC optimizer uses to minimize a cost function subject to constraints. Validated through simulations on Duffing oscillators, linear oscillators, and cantilever beams, the GP-NMPC achieved an 88.2% reduction in displacement amplitude compared to uncontrolled systems. Quantitative analysis shows high predictive accuracy, with a Root Mean Square Error (RMSE) of 0.0031 and a Standardized Mean-Squared Error (SMSE) below 0.05. Furthermore, Mean Standardized Log Loss (MSLL) evaluations confirm the reliability of the predictive uncertainty within the control loop. These results demonstrate strong performance in both regulation and tracking tasks, justifying this Bayesian-predictive coupling as a powerful approach for high-performance structural vibration control and a potential foundation for bio-inspired mechanical design. Full article

This study investigates the mechanisms of nonlinear modal interactions in a circularly curved cantilever beam, utilizing the geometrically exact Timoshenko beam formulation. The governing equations take into account shear deformation, rotary inertia, and the geometric nonlinearities associated with significant deflections. A Chebyshev pseudospectral scheme is employed to achieve highly accurate linear eigenvalues, which are subsequently used in a nonlinear modal projection to develop a reduced-order model. Explicit expressions for the quadratic and cubic modal coupling coefficients are derived. The Harmonic Balance Method is then applied to explore internal resonance phenomena, frequency modulation behavior, and the transfer of energy between non-commensurate lateral and normal vibration modes. Full article

Heat is a crucial factor in all biological processes; therefore, measuring heat change can be a powerful tool for monitoring bioprocesses and metabolism, analyzing biomolecular interactions, and studying cells. The insights gained from thermal measurements can also aid healthcare applications, such as drug susceptibility testing and disease diagnosis. Calorimetry, the science of measuring heat, has seen many advances. However, the pressing need for miniaturization, combined with breakthroughs in micro- and nanofabrication, has led to the development of chip calorimeters and accelerated their innovation. In this comprehensive review, we discuss significant advances in chip calorimetry, including figures of merit, various applications, and key challenges. The review offers an overview of the current state of the art, highlighting prospects and opportunities. Full article