Search Results (224)

Composite bone replicas are widely used in biomechanical testing as alternatives to cadaveric specimens, with numerical models often complementing or replacing experiments. The reliability of these models depends strongly on accurate material parameters. This study investigates a fourth-generation Sawbones composite L5 vertebra, updating cortical material properties under isotropic and transversely isotropic modelling assumptions. Finite element models were calibrated using free-free experimental modal analysis, revealing differences between manufacturer-provided material properties and the measured specimen behaviour. For both models, matching the specimen mass required reducing the cortical density from 1.64 g/cm³ to 1.423 g/cm³. In the isotropic model, the Young’s modulus was reduced from 16,000 MPa to 6500 MPa. In the transversely isotropic model, longitudinal and transverse Young’s moduli were reduced from 16,000 MPa and 11,000 MPa to 6400 MPa and 5500 MPa, respectively, while the shear moduli decreased from 4370 MPa and 6350 MPa to 3500 MPa and 2540 MPa. In both models, the Poisson’s ratio was increased from 0.26 to 0.30. These updates reduced the average eigenfrequency error to 6.12% (isotropic) and 5.83% (transversely isotropic), with the first five modes errors reduced to 3.10% and 2.80%, respectively, substantially improving numerical representation of L5 vertebral mechanics. The updated vertebral FE model and accompanying workflow enhance the reliability of future FE analyses, improve interpretation of Sawbones vertebra biomechanical results, and support vibration-based biomechanical applications such as implant fixation assessment. Full article

Energy harvesting systems face performance limitations, and existing optimizations are not always sufficient; this study addresses these gaps by enhancing piezoelectric energy systems. To improve the performance of piezoelectric energy harvesting systems, an optimization methodology is developed in this study. Since the mechanical strain distribution directly affects energy conversion efficiency, this issue is addressed through optimization of the thickness geometry of a common cantilever-type harvester elastic substrate element via a state-space gradient projection method combined with design sensitivity analysis. The gradient projection method is implemented in MATLAB R2024b software to determine the optimal elastic substrate design, after which the optimized design is simulated in COMSOL 6.3 Multiphysics for strain analysis in a transient study. The optimized cantilever designs are produced by 3D printing using a photopolymer and experimentally validated using piezo sensors and laser measurements for dynamic analysis. Theoretically compared with traditional uniform beams, the optimized cantilever designs maximize strain along the upper layer of the elastic substrate element, leading to a substantial increase in the energy conversion efficiency. This maximization is validated by experimental measurements showing a significant increase in strain in the elastic substrate (approximately 30% at the first eigenfrequency and 70% at the second). The correlation between the experimentally obtained data and the simulation results validates the optimization results. Deviation between the results did not exceed 3% and indicates that cantilever-type energy harvesters with optimized thickness profiles outperform traditional rectangular beams in energy conversion efficiency. Full article

We present a numerical implementation of the proposed Source–Detector Resonance (SDR) as a conceptual analog of a Double-Slit Interference Experiment with discrete particles. Two periodic streams of particles are emitted from two point sources at random integer multiples of a fundamental period P and corresponding frequency $\omega =2\pi /P$ and fly out towards a detection screen. The screen consists of a deep set of identical oscillators with eigenfrequency ${\omega }_0=2\pi /P_0$. In the SDR scenario, $\omega \approx {\omega }_0$. When the particles reach the screen, they implement a periodic forcing of its oscillators at the stream’s fundamental frequency ${\omega }_0$. As a result, an oscillating pattern develops along the screen. The amplitude of oscillation of each oscillator saturates at a value that is determined by the balance between the periodic particle forcing and the damping of each oscillator. This is clearly proportional to the number of particles that reach a certain oscillator per unit time times the fraction of particles that reach it at its resonant frequency. The latter fraction is equal to the ratio of the Power Spectral Density (PSD) of the time series of the particles that reach the oscillator at its resonance frequency PSD(${\omega }_0$) over the PSD at zero frequency PSD(0). If we further assume that each oscillator absorbs a particle and announces a detection with a probability that is proportional to the square of the ratio PSD(${\omega }_0$)/PSD(0); the pattern of particle detections that develops over a thick layer of oscillators is shown to be the same as that of a Double-Slit Interference Experiment. Our result shows that when macroscopic resonant detectors interact with and detect periodic streams of discrete particles, they may create the illusion of an interference measurement, as if each discrete particle manifests a phase of its own. Full article

Space mesh antennas require large-diameter reflectors to achieve aperture surfaces with high gain. To date, many pioneering studies have pursued deployable mechanisms capable of achieving high deployment ratios, primarily focusing on ring and umbrella structures for spaceborne antennas. In this work, a conceptual design of a Deployable Pantograph Rib structure-based parabolic Antenna (De-PaRA) is presented by employing pantograph structures that ensure high stowage efficiency. This approach addresses the shortcomings of conventional space antenna mechanisms. In parallel, this study aims to overcome the structural safety issues that may arise from insufficient axial stiffness of the rib geometry after deployment. To achieve these objectives, superelastic shape memory alloy (SMA) wires were integrated along the antenna ribs to reinforce axial stiffness while maintaining constant inter-rib spacing. Modal analysis demonstrated that SMA wire integration increases the axial stiffness by approximately 2-fold, with eigenfrequency rising from 9.932 to 14.3 Hz. A prototype with a 1.6 m deployed diameter, achieving a volume deployment ratio of 58.8, was quantitatively evaluated through multi-body dynamics simulations and experiments. These results demonstrate reliable deployment operation and mechanical feasibility. Full article

The models of excitation of quasiperiodic ELF/VLF emissions with spectral shape repetition periods from 10 to 300 s are discussed. The primary cause of quasiperiodic (QP) emissions is cyclotron instability of electron radiation belts. Relatively slow processes of cyclotron instability evolution are well described within the framework of the plasma magnetospheric maser (PMM) theory based on the averaged self-consistent system of quasilinear equations for particles and waves. The presence of an eigen-frequency of oscillations of PMM parameters allows explaining many properties of QP 1 emissions, in which not very clear spectral bursts are hiss with resonant modulation mainly near the upper spectral boundary by geomagnetic pulsations of the Pc 3–4 range. The analysis of the general problem of equilibrium of radiation belts shows the possibility of its instability, which is caused by the difference in the pitch-angle dependences of the particle source power and the steady state distribution function. In the nonlinear mode of the specified instability, QP 2 emissions are formed, often with an increase in frequencies in individual spectral bursts. This paper mainly focuses on the study of QP 2 emissions with both a normal and an atypical time structure, as well as with large and fast dynamics of the frequency spectrum. Periodic large-scale atmospheric disturbances with a suitable frequency on the ionosphere can significantly affect the operating modes of the PMM and, as a consequence, the quasiperiodic VLF emissions in the magnetosphere. Infrasonic waves at the altitudes of the E region of the ionosphere can provide excitation of atypical quasiperiodic emissions due to a change in the reflection coefficient of whistler waves from the ionosphere from above. The obtained results are important for interpreting observational data on emissions associated with large-scale processes in the atmosphere. To analyze the magnetosphere response to earthquakes, observation data from the Van Allen Probe spacecraft were used. Also, specific examples of quasiperiodic emissions, probably associated with large-scale atmospheric processes, were obtained during the analysis of observational data. Full article

Perforated cylindrical shaped metal plates are used with high efficiency in the manufacture of deflectors, components of cooling systems, wind tunnels, climatic chambers, filters, and cylindrical implants. This is particularly important for lightweight cylindrical structures, where even minor changes in stiffness can affect structural strength. One of the most important parameters determining the mechanical behavior of such structures is the effective elastic modulus of the perforated element which characterizes its resistance to deformation. The research involves plates made of stainless steel 304 alloy, where perforations were created using the laser-cutting method. The cylindrical shape of the samples with height 50 mm, thickness 1 mm, and diameter 48 mm of each specimen was obtained using metal rolling and welding techniques. To determine the effective elastic modulus, a non-destructive material property evaluation method was applied by solving an inverse problem. In this research, resonance frequencies were determined using a laser vibrometer and a full factorial experimental plan was developed. Physical samples were digitized into 3D models using 3D scanning technology. To evaluate the accuracy of the applied finite element numerical model, its convergence analysis was performed. Numerical results were approximated using the least-squares method, while the effective elastic modulus was calculated by formulating and minimizing the error functional between experimental and numerical eigenfrequencies. The results indicate that increasing the relative perforation area from 0% to 50.24% leads to a decrease in the effective elastic modulus from 184.76 GPa to 50.69 GPa, confirming that increasing the perforation area in a stainless steel 304 cylinder reduces its elastic properties. The observed reduction in resonance frequencies and elastic properties is primarily due to the stiffness decrease caused by the higher perforation volume. 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

The presented research is focused on a proposal to improve a tank container structure by introducing sandwich components in the bottom to reduce its load while transported by rail. This solution will help to reduce loads by means of the energy-absorbing material included in the sandwich components. The proposed improvement is substantiated with mathematical modeling of the dynamic load of the tank container. It is found that the use of sandwich components in its structure can reduce the dynamic load by 12 to 18%, depending on the characteristics of the energy-absorbing material. This study also includes computer modeling of the dynamic load on the tank container, which makes it possible to identify the acceleration distribution fields acting on the tank container, and to determine their numerical values. The mathematical model of the dynamic load of the tank container is verified. Fisher’s exact test was used. The coefficient of determination was 0.81. The calculation was performed within the confidence interval from −0.95 to +0.95. It is found that the hypothesis of the adequacy for the model is not rejected. The study also includes a modal analysis of the tank container. The results of the modal analysis revealed that the safe operation of the tank container during transportation is ensured, as the first eigenfrequency is 13.8 Hz. The achieved results can be used for developing modern tank container designs. Full article

We observed vibrational eigenmodes for a variety of millimeter-scale objects, including glass and sapphire lenses, by placing them on a piezoelectric ‘shaker’ driven by a broadband noise or frequency sweep signal, and using an optomechanical microphone to pick up their vibrational signatures emitted into the surrounding air. High-quality vibrational modes were detected over the ~0–8 MHz range for a typical object–microphone spacing of 1–10 mm. The observed eigenfrequencies are shown to be in excellent agreement with numerical predictions. Non-contact detection of resonant vibrational eigenmodes in the MHz ultrasound range could find application in the quality control of numerous industrial parts, such as ball bearings and lenses. Full article

The concept of the typical section has been widely used in aeroelasticity to analyse the dynamic behaviour of wings by reducing three-dimensional models to two-dimensional models. This work proposes a formal definition of the typical section based on flutter and divergence speeds, identifying the span-wise location that best represents the aeroelastic behaviour of a given wing. The typical section of a set of cantilever wings with varying aspect ratios, taper ratios, and sweep angles is analysed by means of numerical models. The results show that the typical sections for flutter and divergence differ in location, a difference that increases with the aspect ratio and the sweep angle. The influence of the wing geometry and the ratio between the plunge and pitch eigenfrequencies in the location of the typical sections is also analysed. Full article

In the simulation of 3C-SiC strain gauges in dynamic environment—particularly those involving vibrations and wave propagation—the accurate representation of energy dissipation is essential for reliable predictive modeling. This paper discusses the implementation of both isotropic and anisotropic damping models within COMSOL Multiphysics. In particular, it focuses on the use of an anisotropic loss factor, represented either as a scalar (η_S) for isotropic cases or as a symmetric 6 × 6 loss factor matrix (${\mathsf{\eta }}_{\mathrm{D}}$) for anisotropic dissipation. This formulation enables the directional dependence of damping behavior to be captured, which is particularly important in composite materials, layered media, and metamaterials where energy dissipation mechanisms vary with orientation. The paper also explores the numerical implications of using anisotropic damping, such as its influence on eigenfrequency solutions, frequency response functions, and transient dynamic simulations. Furthermore, it highlights how the inclusion of directional damping can improve the correlation between simulated and experimental results in scenarios where standard isotropic models fail to capture key physical behaviors. Full article

The paper addresses the phenomena of negative effective mass and negative effective density emerging in systems driven by entropic elastic forces. The elasticity of polymers is, at least partially, of entropic origin, and it represents the tendency of a polymer to evolve into a more probable state, rather than into one of lower potential energy. Entropy forces are temperature-dependent; thus, the temperature dependence of the effective mass and effective density arises. The effect of the negative effective mass is a resonance effect, emerging in core–shell mechanical systems, which takes place when the frequency of the harmonic external force acting on a core–shell system connected by an ideal spring approaches from above to the eigen-frequency of the system. We address the situation when the ideal spring connecting the core to the shell is made from a polymer material, and its elasticity is of an entropic origin. The effective mass is calculated, and it is temperature-dependent. The chain of core–shell units connected with a polymer spring is studied. The effective density of the spring is temperature-dependent. Optical and acoustical branches of vibrations are elucidated. The negative mass and density become attainable under the variation of the temperature of the system. In the situation when only one of the springs demonstrates temperature dependence, entropic behavior is investigated. Exemplifications of the effect are addressed. Full article

This study presents an analytical and experimental approach to enhance cantilever-based piezoelectric energy harvesters by optimizing thickness distribution. Using a gradient projection algorithm within a state-space framework, the unimorph beam’s geometry is tailored while constraining the first natural frequency. The objective is to amplify axial strain within the piezoelectric layers, thereby increasing electric polarization and maximizing the conversion efficiency of mechanical vibrations into electrical energy. The steady-state response under harmonic base excitation at resonance was modeled to evaluate the harvester’s dynamic behavior against uniform-thickness counterparts. Results show that the optimized beam achieves significantly higher output voltage and energy harvesting efficiency. Simulations reveal effective strain concentration in regions of high piezoelectric sensitivity, enhancing power generation under resonant conditions. Two independent experimental setups were employed for empirical validation: a non-contact laser vibrometry system (Polytec 3D) and a first resonant base excitation setup. Eigenfrequencies matched within 5% using a Polytec multipath interferometry system, and constant excitation tests showed approximately 30% higher in optimal shapes electrical potential value generation. The outcome of this study highlights the efficacy of geometric tailoring—specifically, non-linear thickness shaping—as a key strategy in achieving enhanced energy output from piezoelectric harvesters operating at their fundamental frequency. This work establishes a practical route for optimizing unimorph structures in real-world applications requiring efficient energy capture from low-frequency ambient vibrations. Full article

This work presents the theoretical design and finite element modeling of high-sensitivity microcantilevers for biosensing applications, integrating piezoelectric actuation with novel ultrananocrystalline diamond (UNCD) structures. Microcantilevers were designed based on projections to grow a multilayer metal/AlN/metal/UNCD stack on silicon substrates, optimized to detect adsorption of biomolecules on the surface of exposed UNCD microcantilevers at the picogram scale. A central design criterion was to match the microcantilever’s eigenfrequency with the resonant frequency of the AlN-based piezoelectric actuator, enabling efficient dynamic excitation. The beam length was tuned to ensure a ≥2 kHz resonant frequency shift upon adsorption of 1 pg of mass distributed on the exposed surface of a UNCD-based microcantilever. Subsequently, a Gaussian distribution mass function with a variance of 5 µm was implemented to evaluate the resonant frequency shift upon mass addition at a certain point on the microcantilever where a variation from 600 Hz to 100 Hz was observed when the mass distribution center was located at the tip of the microcantilever and the piezoelectric borderline, respectively. Both frequency and time domain analyses were performed to predict the resonance behavior, oscillation amplitude, and quality factor. To ensure the reliability of the simulations, the model was first validated using experimental results reported in the literature for an AlN/nanocrystalline diamond (NCD) microcantilever. The results confirmed that the AlN/UNCD architecture exhibits higher resonant frequencies and enhanced sensitivity compared to equivalent AlN/Si structures. The findings demonstrate that using a UNCD-based microcantilever not only improves biocompatibility but also significantly enhances the mechanical performance of the biosensor, offering a robust foundation for the development of next-generation MEMS-based biochemical detection platforms. The research reported here introduces a novel design methodology that integrates piezoelectric actuation with UNCD microcantilevers through eigenfrequency matching, enabling efficient picogram-scale mass detection. Unlike previous approaches, it combines actuator and cantilever optimization within a unified finite element framework, validated against experimental data published in the literature for similar piezo-actuated sensors using materials with inferior biocompatibility compared with the novel UNCD. The dual-domain simulation strategy offers accurate prediction of key performance metrics, establishing a robust and scalable path for next-generation MEMS biosensors. Full article

Bearings are critical yet vulnerable components in mechanical equipment, with potential failures that can significantly impact system performance. As stochastic resonance methods effectively convert noise energy into fault characteristic energy within bearing vibration signals, they remain a research focus in bearing fault diagnosis. This study proposes a coupled neuron model based on biological stochastic resonance effects for processing bearing vibration signals. To enhance parameter optimization, we develop an improved deep reinforcement learning algorithm that incorporates a prioritized experience replay buffer into the network architecture. Using the SNR as the evaluation metric, the algorithm performs data screening on the replay buffer parameters before training the deep network for predicting coupled neuron model performance. In terms of experimental content, the study performed data processing on simulated signals and vibration signals of gearbox bearing faults collected in the laboratory environment. By comparing the coupled neuron model optimized with a reinforcement learning algorithm, particle swarm algorithm, and quantum particle swarm algorithm, the experimental results show that the coupled neuron model optimized with a deep reinforcement learning algorithm has the optimal signal-to-noise ratio of the output signal and recognition rate of the bearing faults, which are −13.0407 dB and 100%, respectively. The method shows significant performance advantages in realizing the energy enhancement of the bearing fault eigenfrequency and provides a more efficient and accurate solution for bearing fault diagnosis, which has important engineering application value. Full article