Search Results (322)

As an essential component of dynamic loads, traditional time-domain identification methods exhibit notably insufficient accuracy when dealing with distributed dynamic load identification under unknown initial conditions. This paper explores a novel and effective methodology, utilizing the Bayesian framework and orthogonal polynomials fitting, to reconstruct the distributed dynamic loads of thin plate structures over any arbitrary time period under unknown initial conditions. The forced vibration under the orthogonal basis function loads and the free decay vibration after the removal of basis function loads are used to characterize the forced vibration induced by the identified distributed dynamic load and the decay vibration caused by unknown initial conditions, respectively. By integrating structural dynamic responses within a multi-layer Bayesian framework, the time history and spatial distribution of the load over any arbitrary time period are identified. The innovation of this methodology is that the contribution of the initial conditions to the response is independently characterized by the free decay response caused by the removal of the basis function loads, which effectively resolves the issue of insufficient identification accuracy in existing traditional time-domain methods due to unknown initial conditions. Consequently, the accuracy and reliability of the distributed dynamic load identification is significantly enhanced, which provides a new solution for distributed dynamic load identification under unknown initial conditions. Additionally, simulation cases involving various load conditions and noise levels are discussed under unknown initial conditions over arbitrary time periods. The results demonstrate that the proposed method achieves favorable identification accuracy and robustness under unknown initial conditions. Full article

This paper presents a systematic experimental and computational investigation of the free-vibration characteristics of a Laser Powder Bed Fusion (LPBF) AlSi10Mg thick-walled cylinder, a geometry relevant to electric-machine housings, hydraulic sleeves, and pressure-carrying components exposed to resonance-critical service loads. The specimen has an outer diameter of 94 mm, an inner diameter of 64 mm, a wall thickness of 15 mm, and a height of 90 mm, placing it firmly in the thick-walled regime ($d/D=0.68$). A three-dimensional finite element model comprising 23,864 total elements (23,236 SOLID186 solid elements and 628 surface/contact elements) and 106,015 nodes was constructed in Ansys Mechanical using the AlSi10Mg material database entry (E = 75 GPa, $\rho$ = 2670 kg/m³, $\nu$ = 0.33) and solved with the Block Lanczos eigensolver under free–free boundary conditions. Experimental modal analysis (EMA) was conducted using Brüel & Kjær software with an impact hammer with a 260-node measurement grid covering the outer surface and both end rings; frequency response functions were acquired over 0–22,500 Hz. Fourteen flexible modes were identified in simulation; nine corresponding experimental modes were resolved with frequency deviations ranging from 0.13% to 1.10%. In addition to frequency correlation, this paper introduces a non-conservative damping characterization framework comprising: (i) Rayleigh (proportional) damping coefficient extraction from EMA data and assessment of its frequency-domain validity; (ii) a viscoelastic complex-modulus model relating the real storage modulus $E^{\prime }$ and imaginary loss modulus $E^{″}$ to the modal loss factor $\eta$ and damping ratio $\zeta$; and (iii) a practical design workflow for resonance mitigation of future AM structures including electric machine frames. Experimental damping ratios ($\zeta =0.013$–$0.311\%$) are converted to per-mode $E^{″}$ values and loss factors, revealing that energy dissipation in LPBF AlSi10Mg is strongly mode-shape-dependent and cannot be accurately represented by a single Rayleigh model. Full article

The free vibration behaviour of functionally graded (FG) doubly curved nanoshells is explored by adopting a refined first-order shear deformation theory (FSDT) formulated with only four displacement variables. The presented kinematic model, which decomposes the transverse displacement to bending and shear components, provides an efficient and accurate framework for capturing structural response while requiring substantially lower computational effort than traditional higher-order theories. By utilising a power-law pattern, the nanoshell’s material properties are changing continuously within the thickness. Eringen’s nonlocal elasticity theory is implemented, which considers the size-dependent impact that occurs at the nanoscale. The governing equations of motion are constructed via the application of Hamilton’s principle and solved analytically by Navier’s method for simply supported boundary conditions. The current model’s accuracy and dependability are validated by comparisons with published results for various limiting cases such as spherical, cylindrical, and hyperbolic paraboloidal shells. A thorough parametric study is then carried out to examine the effects of the nonlocal parameter, power-law index, side-to-thickness ratio, curvature ratio, and aspect ratio on natural frequencies. Full article

Vortex-induced vibration (VIV) is one of the main causes of fatigue failure in subsea pipelines and has recently attracted significant attention from researchers. Previous studies have mainly focused on idealized straight pipes, with limited consideration of gravity-induced slight curvature in free-spanning fluid-conveying pipes. In reality, the deformation configuration of a free-spanning fluid-conveying pipe is not fixed but varies with parameters such as internal flow velocity and tension, which in turn affect its dynamic behavior. A theoretical model, taking into account the axial stretching effect and the gravity-induced initial slight curvature, is developed to predict the VIV responses of free-spanning fluid-conveying pipes. The governing equations are derived based on Hamilton’s principle. The interaction between the external flow and the pipe structure is simulated using the van der Pol equation. By combining the Galerkin method and the Runge–Kutta method, the vibration responses of the pipe are obtained. The accuracy of the proposed model is validated by comparing the predicted VIV response curves and bifurcation diagrams with those reported in previous studies. The initial static deformation of the structure under different tensions and internal velocities is obtained through numerical calculations. It is found that the gravity-induced slight curvature leads to a reduction in the VIV response mode. The static deformation of the pipe decreases with increasing axial tension, while it increases with increasing internal flow velocity. Under the same external flow velocity, the gravity-induced initial deformation reduces the dominant vibration frequency and causes the vibration response to transition from quasi-periodic to periodic motion. Full article

Laminated carbon fiber reinforced polymer (CFRP) beams are widely used in lightweight structures, yet their vibration response depends strongly on laminate architecture, boundary conditions, thickness, and material anisotropy. Previous studies often examined these effects separately or relied on a single analytical or numerical approach. This study presents a multi fidelity framework integrating classical laminate theory (CLT), the Vinson–Sierakowski (VS) equivalent modulus method, and three-dimensional finite element analysis for modal prediction and parametric design of symmetric CFRP laminated beams. Three stacking sequences, [0/0/0/0], [0/45/45/0], and [0/90/90/0], were evaluated under clamped-free (CF) and clamped-clamped (CC) conditions. ANSYS models using quadratic HEX20 solid elements served as the numerical reference. Across 36 validation frequencies, the mean absolute percentage errors were 3.05% for CLT and 2.28% for VS, giving VS a 25.1% lower average error. The [0/0/0/0] laminate produced the highest frequencies. The first numerical frequency increased from 36.37 to 230.20 Hz when the boundary condition changed from clamped-free to clamped-clamped. Increasing thickness from 2 to 8 mm raised the first frequency from 18.20 to 72.62 Hz, while increasing $E_1/E_2$ from 10 to 30 raised it from 30.80 to 53.85 Hz. The framework supports rapid screening, laminate level interpretation, and detailed numerical verification for vibration-oriented composite beam design. Full article

This study investigates the forced transverse vibration of a thin rotating annular disc subjected to time-varying point forces that are fixed in space and act perpendicular to the disc surface. Earlier analytical treatments of this problem have almost always been restricted to a single support condition, most often the clamped–free disc of a hard-disk drive. The boundary conditions of the disc have not been treated as a design variable of the forced response. The contribution of this work is to remove that restriction: the same generalised Galerkin formulation is applied to clamped–clamped, clamped–free and free–clamped rotating annular discs, and the sensitivity of the forced response to the excitation parameters is compared across all three. The governing differential equation, which includes gyroscopic coupling and the membrane stresses induced by rotation, is nondimensionalised and solved by the Galerkin method with polynomial radial trial functions. The modal equations are then integrated in state-space form with light modal damping. The physical transverse response at a fixed observation point is characterised by power spectral density diagrams assembled into waterfall plots, and the corresponding steady-state harmonic responses are obtained in closed form from the frequency-domain resolvent of the same state-space model. The formulation is verified against an independent radial finite-element model for all three boundary conditions and against published rotating clamped–free natural frequencies. The central finding concerns how the excitation parameters act on the response. The excitation frequency, the radial position of a force, and the angular separation and phase of a pair of forces act as largely independent levers. The quantitative sensitivity to each lever, however, is set by the boundary conditions, as is the force placement that minimises a chosen travelling-wave family. The radial position that minimises the excitation of a chosen radial family is governed by the interior node of that mode, which lies at $r\approx 52$, 68 and 44 mm for the clamped–clamped, clamped–free and free–clamped discs, respectively, and does not in general coincide with a free edge. Angular separation, by contrast, suppresses a nodal-diameter family in a manner that is essentially boundary-condition independent. The parameter dependences are shown to be steady-state properties: the driven spectral line of the finite-duration records reproduces the resolvent solution to within $0.09$ dB. Full article

Electromagnetic linear actuators are widely used in applications requiring fast, repeatable, and controlled mechanical excitation. This work proposes and experimentally validates a current-controlled actuation methodology for generating controlled and repeatable mechanical excitation for the automated acoustical inspection of hard cheeses. The proposed system is based on a push-type solenoid actuator driven by a closed-loop converter that generates a predefined current profile to obtain a controlled impact force on wheel cheeses. The system development was approached based on actuator simulations using the finite element method (FEM). This allows us to analyze the electromagnetic force generation process to identify the current waveform that produces an effective impact while ensuring vibration-free plunger return and avoiding bouncing at the end of its stroke. For acoustic measurements, a synchronized four-microphone acquisition system based on A2B was integrated. A preliminary experimental campaign to validate the concept and the development approach was conducted on a wheel of aged Pecorino cheese. The acquired acoustic responses showed highly repeatable impacts, with intra-class spectral variations below 1 dB under identical experimental conditions. Furthermore, the increase in damage artificially introduced on the tested cheese wheel caused measurable shifts in resonance frequencies, variations in spectral amplitudes, and the appearance of defect-related resonances. The results demonstrate the feasibility of the proposed approach for objective, repeatable, and non-destructive acoustic inspection of hard cheeses, providing a basis for future automated quality assessment systems. Full article

Distributed optical vibration sensing (DOVS) provides dense spatiotemporal measurements for pavement and traffic monitoring, but nonstationary background noise, spatially confined responses, and data-quality anomalies complicate vehicle-event detection. This study presents a deterministic, training-free, and interpretable detector for single-lane highway DOVS matrices. The algorithm forms a detrended absolute-amplitude representation and combines percentile-based temporal candidate detection, robust background estimates based on the median and median absolute deviation (MAD), a candidate spatial-width fraction derived from channel-specific thresholds, track-direction evidence, and explicit decision rules. Evaluation on 3085 manually labeled matrices acquired from 2023 to 2026 yielded 87.23% accuracy, 87.42% precision, 87.31% recall, and an F1-score of 87.36%. In a secondary analysis, excluding 98 quality-flagged matrices increased precision to 91.28% and F1-score to 89.20%; the exclusion removed 67 of 196 false positives and no false negatives. Relative to the diagnostic-refinement configuration, the final rule set increased F1-score by 2.173 percentage points, with a matrix-level bootstrap 95% confidence interval of 1.437–2.963 percentage points. The exact McNemar test for paired correctness differences gave p = 6.60 × 10⁻⁹. A sensitivity configuration changed only four classifications and produced no meaningful gain. These results quantify performance at the tested site; narrow responses, upward-like tracks, data-quality anomalies, single-annotator labels, and post hoc rule selection limit broader inference. Full article

This work presents the design evolution, fabrication, and characterisation of an additively manufactured ring-type thermal airflow sensor for in-pipe flow monitoring, developed employing exclusively Fused Deposition Modelling (FDM) additive manufacturing technology and a commercially available Carbon Nanotube (CNT)-enriched Biopolymer Polylactic Acid (PLA) composite filament. The design evolution proceeds through three progressive stages. In the first stage, a flat heater element is characterised through Constant-Current (CC) Joule heating experiments in order to derive the corresponding Temperature Coefficient of Resistance (TCR) and Thermal Resistance from the obtained experimental data. Consequently, a Finite Element Method (FEM) model implemented in COMSOL Multiphysics^® and calibrated with the extracted material parameters validates the experimental temperature–power relationship and predicts the convective cooling behaviour at various airflow velocities. In the second stage, the geometry is optimised by introducing a conductive trace with a reduced-cross-section central region; as a result, an equivalent thermal localisation is achieved at approximately 26% lower supplied power with respect to the initial heating element, enabled by the design freedom inherent in the FDM process. We should note that the specific sensing geometry can also be directly embedded into any 3D-printed structural component (e.g., a bracket or housing), enabling simultaneous local thermal heating and/or thermal monitoring together with structural functionality within a single printed part. In the third and final stage—the target device—a fully monolithic ring-type airflow sensor is directly integrated into a 3D-printed pipe segment during the printing process. Under constant-current excitation at 40 mA, the device exhibits a monotonically decreasing resistance with increasing airflow (ΔR ≈ 117 Ω over 0–4 m/s) due to convective cooling, while in a single flow-interruption cycle, approximately 79% of the flow-induced resistance change was recovered upon flow removal, with a residual offset of approximately 3% of the heated baseline. A coupled electrothermal FEM model of the device further supports the experimental response by comparing the simulated temperature rise with the values inferred from resistance measurements, while also clarifying the role of the effective internal convective cooling conditions imposed by the pipe geometry. Key features of the proposed device are low raw-consumables cost, fast on-site manufacturing employing a commercially available desktop 3D printer, monolithic construction free of wire-bonded interconnections, and simplicity, indicating its potential for flow monitoring and condition-based maintenance systems aboard vessels as well as in a wide range of industrial sectors. We should note that the present characterisation was performed under laboratory conditions employing a single prototype per design stage; the effects of humidity, salt exposure, vibration, temperature cycling, and material-batch variability remain to be assessed prior to shipboard deployment. Full article

Rolling-element bearings remain a leading cause of unplanned downtime in industrial machinery, while vibration-based condition monitoring has matured, the post-2018 literature has converged on machine-learning classifiers whose interpretability layer remains restricted to expert analysts. This paper presents an operator-centred visualization framework supported by two time-frequency methods: the Zhao–Atlas–Marks Distribution (ZAMD), a Cohen’s-class representation with a cross-term-suppressing cone kernel, and Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN), evaluated through its Hilbert spectral analysis output. Both methods produce two-dimensional time-frequency artefacts with a similar visual structure—impact-related energy bursts that recur at the characteristic fault frequencies—and are presented in side-by-side form for each fault class. A four-stage framework wraps either method with the characteristic fault frequencies (supplied as a comparison reference) and colour-coded, healthy baseline-referenced scaling. The framework is demonstrated on a laboratory bearing rig (KOYO 6302, 600 RPM) across inner-race, outer-race, and ball-spin fault classes. A preliminary readability assessment of annotated ZAMD-generated artefacts, with twelve non-specialist participants from a brewing and packaging industrial context, recorded 89.8% aggregate classification accuracy (194 of 216 trials) at a mean response time of 15.4 s. Because no label-free or alternative-format control conditions were included, this result characterises the annotated artefact as a whole and does not isolate the contribution of the time-frequency representation from that of the annotation layer; it is established for the ZAMD engine only. The two methods are compared as visualization engines—qualitatively, through the structure of their side-by-side time-frequency artefacts, and quantitatively, through computational cost—whereas the non-specialist readability assessment characterises the ZAMD-based framework specifically. CEEMDAN is positioned as a candidate alternative engine whose time-frequency output is shown to be structurally similar but whose operator readability has not been tested with human participants and is identified as future work. Full article

Functionally graded multi-material architected structures fabricated by fused deposition modeling (FDM) were investigated to evaluate their multifunctional mechanical and dynamic performance. Sixteen honeycomb configurations incorporating poly(lactic acid) (PLA), thermoplastic polyurethane (TPU), and wood-filled PLA (WWF-PLA) were designed by systematically varying material distribution, cellular geometry, and structural density as integrated architected configurations. Compression, flexural, dynamic mechanical, free-vibration, density reduction, and water absorption tests were conducted, and the experimental responses were objectively evaluated using the CRITIC–WASPAS multi-criteria decision-making framework. Among the investigated configurations, A16 exhibited the highest overall performance, achieving 41.8 MPa compressive strength, 56.4 MPa flexural strength, 1425 MPa storage modulus, 0.162 loss factor (tan δ), 3.7% damping ratio, and 39% density reduction. Compared with the baseline configuration (A1), A16 demonstrated improvements of 14.5%, 17.0%, 20.8%, 44.6%, 76.2%, and 77.3% in the respective performance metrics. The proposed framework provides an objective approach for ranking integrated architected designs for lightweight multifunctional engineering applications. Full article

The long-term durability of concrete structures is significantly affected by moisture. Excessive moisture may cause drying shrinkage, crack formation, and accelerated corrosion of embedded reinforcement; therefore, reliable and non-destructive moisture assessment is essential for structural durability evaluation. In this study, a controlled acoustic measurement method and a machine learning-based classification framework are presented for the non-destructive identification of moisture levels in concrete specimens. A magnet-assisted free-fall steel ball mechanism was used to generate standardized impacts instead of conventional manual hammer excitation. To reduce environmental vibration noise and capture internal material responses, acoustic signals were recorded using a piezoelectric contact microphone. Experiments were conducted on concrete specimens prepared at nine moisture levels under both large-sample (BIG) and small-sample (SMALL) conditions. Power Spectral Density (PSD) and Mel-Frequency Cepstral Coefficients (MFCC) were extracted from the recorded impact signals and used as input features. Individual machine learning classifiers were compared with a hybrid stacking ensemble model to evaluate discriminative performance and probabilistic reliability. The results showed that MFCC features provided higher classification performance than PSD features under both dataset conditions. For the BIG specimens, the MFCC-based model achieved an accuracy of 0.9872, whereas the PSD-based model achieved 0.9811. For the SMALL specimens, MFCC reached an accuracy of 0.9822, while PSD achieved 0.9750. The AUC-ROC values of the proposed model ranged from 0.9980 to 0.9996 in the multi-class classification of nine moisture levels. These findings demonstrate that controlled impact acoustics combined with MFCC-based representation and stacking-based ensemble learning provides a rapid, low-cost, and reliable NDT approach for concrete moisture classification. Full article

This paper investigates the dynamic characteristics of rotating functionally graded material (FGM) micro-beams based on Euler–Bernoulli beam theory, Euler–Bernoulli beam theory incorporating shear deformation, and Timoshenko theory. The deformation field of the micro-beam is described within a floating coordinate system using the meshless point interpolation method (PIM/RPIM). The couple stress tensor and curvature tensor, which capture the size effect, are incorporated into the potential energy formulation. Employing Lagrange’s equations of the second kind, a higher-order rigid-flexible coupled dynamic model for rotating FGM micro-beams is established under various beam theories. Simulation results obtained from the Euler–Bernoulli theory with shear correction and the Timoshenko model are compared with those from the classical beam model and previous literature. The influences of material gradient index, material characteristic length parameter, and rotational speed profiles on the transient dynamic response and steady-state free vibration of rotating micro-beams are systematically examined. The results show that increasing the material gradient index reduces the structural stiffness, resulting in lower natural frequencies and larger vibration amplitudes, whereas increasing the characteristic length parameter enhances the size effect and improves system stiffness. Full article

Studies of third-order shear-deformation theory (TSDT) and an advanced shear coefficient for thick-walled functionally graded material (FGM) spherical shells subjected to thermal vibrations triggered by sinusoidal temperature are presented. The nonlinear TSDT and linear and nonlinear shear coefficient can be converted into fully homogeneous equation algorithms under the sinusoidal form of free vibrations to obtain the fundamental natural frequency by using Newton’s numerical method. Then, the generalized differential quadrature (GDQ) method can be used to prepare dynamic discrete equations of motion triggered by sinusoidal temperature field in thick FGM spherical shells for materials SUS304 and Si₃N₄. The Young’s modulus expressed as a power-law function of thick FGM spherical shells is considered and subjected to applied thermal load. The response results of thermal stress and center displacement are compared for the cases of linear and nonlinear advanced shear coefficient, and simply and fully homogeneous equation algorithms, respectively. The practical insights for temperature effect considered in the calculation of stress and displacement are very clear and practical for FGM structures with geometries of spherical shells. The power-law function property of FGMs can be used under high temperature for four-sided simply supported constraints. Full article

This study examines the geometrically nonlinear free vibration behaviour of a clamped–clamped Euler–Bernoulli beam weakened by an open transverse crack. The crack is modelled through an equivalent rotational flexibility formulation grounded in fracture mechanics, while geometric nonlinearity is incorporated by accounting for mid-plane stretching associated with large vibration amplitudes. A reduced-order formulation is established using a Galerkin approach with eigenfunctions that explicitly depend on the presence of the crack, leading to a nonlinear eigenvalue problem in which the response is amplitude-dependent. The primary aim is to clarify how crack severity and vibration amplitude jointly influence the distribution of nonlinear bending stresses along the beam. Unlike much of the existing literature, which predominantly emphasises frequency–amplitude interactions, this work adopts a stress-oriented framework and offers a detailed characterisation of the spatial variation in the normalised stress field. The results indicate that bending stresses increase markedly as vibration amplitude grows, with the most pronounced effects occurring near the clamped ends where curvature is highest. Furthermore, deeper cracks significantly intensify stress concentrations due to the associated local reduction in stiffness. Overall, the findings provide enhanced physical understanding of the nonlinear dynamic behaviour of cracked beam structures and establish a useful foundation for evaluating structural integrity under conditions of large-amplitude vibration. Full article