Search Results (90)

Filled joints significantly influence the dynamic response of rock masses, exhibiting coupled nonlinear compression-hardening and viscous deformation. However, the combined effects of these mechanisms on wave propagation remain unclear. This study develops a theoretical model based on a nonlinear viscoelastic formulation, in which a compression-hardening spring (governed by the Bandis–Barton model, with its initial compressive stiffness and maximum allowable closure) is connected in series with a viscous dashpot. Using the displacement discontinuity method and the method of characteristics, we analyze the transmission of compressive stress waves across a filled joint. The results show that the transmission coefficient increases with incident wave amplitude but decreases with frequency, whereas reflection exhibits the opposite trends. The initial compressive stiffness has a minimal impact on transmission but induces a nonlinear decrease in reflection. Increasing the maximum allowable closure slightly reduces transmission but sharply increases reflection, whereas higher viscous stiffness enhances transmission and slightly suppresses reflection. Energy attenuation grows rapidly with amplitude before stabilizing. The initial compressive stiffness is most influential at low amplitudes, the maximum allowable closure is most significant at moderate amplitudes, and viscous effects remain consistent across all amplitudes. Increases in frequency lead to a nonlinear decrease in attenuation, with the initial compressive stiffness and maximum allowable closure dominating at high frequencies, and viscous effects prevailing at low frequencies. This work systematically reveals the coupled roles of nonlinear compression-hardening and viscosity in wave propagation across filled joints, providing theoretical support for dynamic hazard mitigation and geophysical exploration. Full article

This work presents an experimental and theoretical study of a pitching point-absorber wave energy converter (WEC) equipped with a nonlinear stiffness mechanism (NSM) based on a pre-compressed spring. The mechanism is designed to reduce the equivalent restoring stiffness and enhance the device response without external control. A 1:13 scale prototype of the Lafkenewen WEC, deployed off Lebu (Chile), was tested in regular waves within a wave tank for two configurations: with and without the NSM. The rotational response amplitude operator (RAO) was obtained from experiments and compared against a linear hydrodynamic model formulated via Newtonian mechanics and frequency domain radiation/excitation coefficients. Dry friction at the hinge was represented as an equivalent viscous damping term identified iteratively. Unlike narrow-resonance WECs, both configurations exhibited a broadband response without a sharp resonance peak in the $0.7$–$1.2$ Hz range, due to significant radiation damping and hinge friction. The NSM produced a moderate amplification of the rotational RAO (up to ∼32%) while preserving the broadband character. Theoretical predictions agreed with the measurements when dry friction was included. These results demonstrate that passive stiffness reduction via an NSM enhances wave–structure energy transfer even in systems dominated by effective damping and provides a consistent basis for future nonlinear time domain modeling and control-oriented studies. Full article

Prefabricated H-section steel composite wall columns (PHSWCs) are crucial for advancing modular steel construction, yet their elastic buckling performance lacks a universally accurate predictive model due to the complex interplay between section interaction and semi-rigid bolted connections. To address this, a comprehensive theoretical framework for elastic buckling analysis is developed in this study. The model integrates Euler–Bernoulli beam theory for the H-sections, a three-dimensional spring system to represent the stiffness of bolted connections, and the Green strain tensor to account for geometric nonlinearity. Validation against ABAQUS (2020) and ANSYS (2021 R1) shows high accuracy (average errors: 1.0% and 1.2%, respectively). Furthermore, a unified formula for the normalized slenderness ratio is derived via stepwise regression, which elegantly degenerates to the classical Euler solution under limiting conditions. The main conclusion is that this framework enables rapid and precise buckling analysis, reducing parametric study time by 95% compared to detailed finite element modeling. It establishes a bolt density coefficient threshold of η = 0.5 that separates composite from independent section behavior, with an optimal design range of η = 0.2 to 0.25, thereby offering a robust theoretical basis for PHSWC design. Full article

This paper analyzes the physics of the TMD-Inerter for harmonic vibrations. The basic TMD-Inerter layout is assumed, where the inerter is installed between the TMD mass and the structural mass. For harmonic vibrations, the inerter force can be formulated as a function of terminal displacements. This formulation demonstrates that the inerter force is, in fact, a negative stiffness force with frequency-dependent negative stiffness coefficient. Based on this finding, the optimal stiffness tuning of the TMD-Inerter is derived. As this stiffness tuning can only be realized by a controlled actuator, the tuning of the spring of the TMD-Inerter is presented. As this spring is a passive element, its optimum tuning must be made at a selected frequency of vibration. It is shown that the average of the TMD natural frequency and structural eigenfrequency leads to a close to optimal spring tuning. This approach needs to be combined with increased damping of the TMD-Inerter to minimize the structural displacement response. Despite the close to optimal tunings of stiffness and damping, the resulting primary structure displacement response is approximately 41.6% greater than that due to the classical TMD. The reason for this lies in the fact that the passive spring of the TMD-Inerter cannot compensate for the frequency-dependent negative stiffness of the inerter within the entire frequency range. Full article

To enhance the stability and consistency of topdressing depth during maize fertilization, an inter-row deep fertilizer application unit was designed. Through analysis of the coherence between subsurface pressure and topdressing depth stability obtained from stability performance tests, structural optimizations were implemented on the deep application unit. This resulted in an integrated vibration damping device incorporating a magnetorheological damper (MR damper fertilizer application unit). The MR damper fertilizer application unit was validated through simulation testing. Using an orthogonal experimental design approach, soil bin tests were conducted to identify the preferred parameter ensemble for this unit. Subsequent field trials under these optimized parameters enabled comparative performance evaluation of both fertilizer application units under actual operating conditions. The simulation results indicated that the MR damper fertilizer application unit achieved reductions in the standard deviation of the gauge wheel’s force on the ground by 39.6%, 41.0%, and 44.6% at three distinct operational speeds, respectively. The soil bin tests identified the optimal operational parameters as follows: MR damper current of 0.6 A, vibration damping system spring stiffness of 8 N/mm, and a working speed of 7.2 km/h. Field testing results indicated that, when utilizing the optimal parameters, the MR damper fertilizer application unit achieved a 6.9% improvement in the rate of qualified topdressing depth and a 3.8% reduction in the depth variation coefficient compared to the conventional deep fertilizer application unit. Compared to traditional fertilizer applicators, this study effectively addresses issues of poor fertilization depth uniformity and low qualification rates caused by severe gauge wheel bouncing due to uneven terrain during field operations. Full article

An improved Mass–Spring Model (iMSM) is developed by adding central springs to the conventional Mass–Spring Models (MSMs) of tubular structures. This improvement is necessary to model fibers that have enough stiffness so that they do not collapse under transverse loading. Such is the case with many pulp fibers used in papermaking. Four different types of pulp fibers (Aspen CTMP, Aspen BCTMP, Birch BCTMP, and Spruce BKP) were simulated in the study. A geometric model and iMSM of a single fiber were developed, in which the topological structure of iMSM is explained in detail. The mass of mass points and the elastic coefficient of different springs in iMSM were calculated using axial tensile and torsional responses. A dynamic simulation of transverse bending of the fiber over a rigid cylinder and subjected to a transverse pressure was used to determine the effective elastic modulus for four different single fibers and compared to experimental values with an average relative error of 8.49%. The dynamic simulations were completed in 1.04–2.64 min for the four different paper fibers representing sufficient speeds to meet the needs of most real application scenarios. The acceptable accuracy and the fast simulation speed with the developed iMSM fiber model demonstrate the feasibility of the methodology in analyzing paper structures as well as similar fiber-based materials. Full article

This paper presents an enhanced pseudo-rigid body model (PRBM) integrated with the LuGre friction law to analyze the dynamic behavior of flexure-hinge-based piezoelectric stick–slip actuators (PSSAs). The PRBM captures flexure compliance through Lagrangian dynamics, while Newtonian mechanics describe the piezoelectric stack and slider motion. Non-linear contact effects, including stick–slip transitions, are modeled using the LuGre formulation. A mass–spring–damper model (MSDM) is also implemented as a baseline for comparison. The models are solved in MATLAB Simulink version R2021a and validated against experimental data from a published prototype. The enhanced PRBM achieves strong agreement with experiments, with a root mean square error of 20.19%, compared to 51.65% for the MSDM. By reformulating the equations into closed-form expressions, it removes symbolic evaluations required in the standard PRBM, resulting in one to two orders of magnitude faster simulation time while preserving accuracy. Stable transient simulations are achieved at fine time steps ($\Delta t={10}^{-8}$ s). A systematic parametric study highlights preload force, flexure stiffness, friction coefficients, and tangential stiffness as dominant factors in extending the linear frequency–velocity regime. Overall, the PRBM–LuGre framework bridges the gap between computationally intensive finite element analysis and oversimplified lumped models, providing an accurate and efficient tool for design-oriented optimization of compliant piezoelectric actuators. Full article

The torsional, lateral, and axial vibrations that occur during drilling operations have negative effects on the drilling equipment. These negative effects can cause huge economic impacts, as the failure of drilling tools results in wasted materials, non-productive time, and substantial expenses for equipment repairs. Many researchers have tried to reduce these vibrations and have tested several models in their studies. In most of these models, the drill string used in oil wells behaves like a rotating torsion pendulum (mass spring), represented by different discs. The top drive (with the rotary table) and the BHA (with the drill pipes) have been considered together as a linear spring with constant torsional stiffness and torsional damping coefficients. In this article, three models with different degrees of freedom are considered, with the aim of analyzing the effect of variations in the stiffness and damping coefficients on the severity of torsional vibrations. A comparative study has been conducted between the three models for dynamic responses to parametric variation effects. To ensure the relevance of the considered models, the field data of torsional vibrations while drilling were used to support the modeling assumption and the designed simulation scenarios. The main novelty of this work is its rigorous comparative analysis of how the stiffness and damping coefficients influence the severity of torsional vibrations based on field measurements, which has a direct application in operational energy efficiency and equipment reliability. The results demonstrated that the variation of the damping coefficient does not significantly affect the severity of the torsional vibrations. However, it is highly recommended to consider all existing frictions in the tool string to obtain a reliable torsional vibration model that can reproduce the physical phenomenon of stick–slip. Furthermore, this study contributes to the improvement of operational energy efficiency and equipment reliability in fossil energy extraction processes. Full article

Good seat comfort can bring a pleasant experience to commercial vehicle drivers. Therefore, it is necessary to study the vibration characteristics of commercial vehicle seats. This study focuses on commercial vehicle seats with air spring suspension. The friction damping expression of the suspension system was derived. Comprehensive simulation and experimental investigations were conducted on the vertical vibration transmission characteristics of the seat. A multi-objective optimization framework was established by integrating the NSGA-II algorithm with a BP neural network. Specifically, a nonlinear mathematical model was developed using the GA-BP neural network algorithm, with four design parameters as optimization variables: air spring stiffness (K₁), damper damping coefficient (C₁), cushion equivalent stiffness (K₂), and cushion equivalent damping coefficient (C₂). The optimization objective was defined as minimizing the maximum seat transmissibility (T_R) at the resonance frequency (f). Through the NSGA-II, Pareto optimal solutions were systematically explored, and an optimal parameter combination was identified to enhance the dynamic comfort of the commercial vehicle seat. Full article

In this paper, a formula for the spring constant $K_x$ for the horizontal movement of rigid rectangular foundations resting on elastic subsoil and spring coefficient ${\beta }_x$ in this formula was derived, which demonstrates that ${\beta }_x$ depends on Poisson’s ratio ν. It was also shown that ${\beta }_x$, which has already been presented in the literature, was determined for a constant value ν = 0.3. It was shown that the values of ${\beta }_x$ and $K_x$, obtained from the formulas derived in this paper and the calculations based on the formulas and nomogram for the ${\beta }_x$ given in the literature, may differ by 8–11%. For the adopted parameters, among others ν = 0.5, and for the side ratio α = 10, the value of spring constant is in the first case $K_x=1$45.9 MN/m and in the second case $K_x$ = 158.3 MN/m (differ by 8%), while for ν = 0.1, is, respectively, $K_x$ = 517.8 N/m and $K_x$ = 464.3 MN/m (differ by 11%). Numerical FEM 3D analysis verified analytical solutions for the concrete foundation footing and the soil layer beneath it. This paper also provides useful nomograms that can be used to easily read the values $K_x$ and ${\beta }_x$. The use of the proposed formulas in this paper, refined formulas for determining $K_x$and ${\beta }_x$ in engineering calculations, can improve the accuracy of the analyses related to the influence of soil stiffness in horizontal movement. Full article

The end conditions of columns constitute an important design parameter as they change their stiffness. The degree of restraint of the column modifies its fundamental frequency and mode of vibration. The rotational stiffness at its ends may transform from zero (hinged) to infinite (clamped). For intermediate values, the rotational movement is partially restricted, and it is classified as semi-rigid. In this work, the seismic response for a linearly variable section column and with gradual change in the rotational fixity is studied. A parametric solution is developed using the Rayleigh method, derived for cases of non-prismatic columns, and considering the axially distributed force along the column height. The obtained generalized stiffness and mass are used to perform approximate seismic evaluation at low effort and examine the influence of the changes to the structure. The analysis indicated that with a spring coefficient of 5 EI/l, the displacement drops by 50%, meaning that this range can produce significant influence on the structural response. The relationship between the top load and the column self-weight equal to 0.3 defines the limit for the hinged–hinged boundary condition to exist. As research recommendations, analysis of columns with variable cross-sections and different shapes, different distributed loadings, applying the rotational spring for both ends and over the shape functions, and analysis of buildings by an equivalent system are suggested. Experimental activity is indicated as a possibility for future investigations. Full article

This paper presents an investigation into the influence of varying potential well depths on the performance of a dual−coupled beam energy harvester (DEH). Firstly, three varying potential well depths were established with different polynomial coefficients of nonlinear restoring force and analyzed in simulation. Numerical results revealed that whether the initial potential well depth is shallow or not, the optimal power output can be attained when the stiffness of the coupling spring is a half of the monostable−to−bistable coupling spring stiffness, which was also validated by an experiment. Specifically, at a deeper initial potential well depth of 0.64 mJ, the system demonstrated superior energy conversion capabilities. Compared to traditional BEH and LEH, the output RMS voltage of Beam 1 and total RMS power of the DEH increased by 103.06% and 49.6%, respectively. The RMS power increased by 16.4% at a potential well depth of 0.9 mJ. In addition, regardless of the potential well depth, the DEH can always achieve the optimal operating bandwidth when the coupling spring stiffness is near the monostable−to−bistable transition region. Full article

This study presents a spectro-geometric vibration model for analyzing free as well as forced vibration properties for FGM cylindrical double-walled shells with internal structures. The boundary conditions and coupling effects are modeled using an artificial virtual spring approach, which allows for the simulation of arbitrary boundary and coupling conditions by varying the elastic spring stiffness coefficients. The spectral geometry method is employed to represent the displacement variables of the FGM substructure, overcoming the discontinuity phenomenon commonly observed when traditional Fourier series are used. The dynamic equations of the FGM cylindrical double-walled shell with an internal structure are derived using the first-order shear deformation assumption and the Rayleigh–Ritz method, and the corresponding vibration solutions are computed. The model’s reliability and prediction accuracy are confirmed through convergence checks and numerical comparisons. Additionally, parametric studies are conducted to examine the influence of material constants, position parameters, and geometric parameters on the shell’s inherent characteristics and steady-state response. Full article

In practice, the structural analysis and design of pedestrian systems subjected to human-induced vibrations is often based on simplified biodynamic models that can be used in place of even more complex computational strategies to describe Human-Structure Interaction (HSI) phenomena. Among various walking features, the vertical reaction force that a pedestrian transfers to the supporting structure during motion is a key input for design, but results from the combination of multiple influencing parameters and dynamic interactions. Robust and practical strategies to support a realistic HSI description and analysis have hence been the object of several studies. Following earlier research efforts, this paper focuses on the optimised calibration of the input parameters for the consolidated Spring-Mass-Damper (SMD) biodynamic model, which reduces a single pedestrian to an equivalent SDOF (with body mass m, spring stiffness k, and viscous damping coefficient c) and is often used for vibration serviceability purposes. In the present study, this calibration process is carried out with smartphone-based acquisitions and experimental records from the Centre of Mass (CoM) of each pedestrian to possibly replace more complex laboratory configurations and devices. To verify the potential and accuracy of such a smartphone-based approach, different pedestrians/volunteers and substructures (i.e., a rigid concrete slab or a timber floor prototype) are taken into account, and a total of 145 original gaits are post-processed for SMD modelling purposes. The analysis of the experimental results shows a rather close match with previous findings in terms of key pedestrian parameters. This outcome poses the basis for a more generalised application of the smartphone-based strategy to a multitude of similar applications and configurations of practical interest. The validity of calibration output and its possible sensitivity are further assessed in terms of expected effects on substructures, with a critical discussion of the most important results. Full article

Tapered piles are a new type of pile foundation known for their simple construction and high bearing capacity, commonly used in railway, highway, or building foundation treatment. This study proposes a unified dynamic Winkler model for vertical and lateral vibration response of tapered piles in the frequency domain using the impedance function transfer matrix method. The computational expressions are obtained for the different springs and damping of tapered piles with different dimensions using the elastodynamic theoretical of rigid embedded foundations, and the dynamic interaction mechanisms of vertical and lateral vibrations between tapered piles and soil are analyzed. The rationality of the simplified model is validated by comparison with existing literature and finite element simulation results. Finally, an example is provided to discuss the influences of the dimensional parameters of the pile and soil properties on vertical, lateral, and rocking dynamic impedance. The analytical findings demonstrate that the lateral and rocking dynamic impedances of tapered piles undergo a substantially greater enhancement relative to their vertical counterpart as the taper angle is progressively enlarged, assuming the pile volume remains constant. The dynamic impedance of tapered piles under vertical and lateral vibration in upper hard and lower weak soil layers, or upper weak and lower hard soil layers, are both greater than those in a homogeneous foundation. Specifically, the vertical dynamic stiffness of tapered piles in double-layered soils is approximately twice that of homogeneous soil. The rocking dynamic stiffness of the pile is significantly influenced by the soil properties around the pile foundation, whereas the soil properties have little impact on the rocking damping coefficient. Overall, the vertical dynamic characteristics are less influenced by the geometric features of the upper part of the tapered pile, while the lateral dynamic characteristics are significantly affected by these features. The lateral dynamic impedance of the tapered pile increases with the diameter of the upper part of the pile. Furthermore, the vertical, lateral, and rocking dynamic impedance of the pile can be effectively improved by enhancing the soil properties around its upper section. These results can provide theoretical references for the engineering practice. Full article