Vibrational Generation Research Articles

Boundary stabilization of a vibrating string with variable length

We study small vibrations of a string with a length ℓ(t) varying in time at a speed less than the speed of propagation of vibrations. We establish lower and upper estimates for the energy of the string when a dash-pot with constant damping factor η is placed at the moving boundary. The estimates depend explicitly on ℓ(t),η and a function φ that solves the functional equation φ(t+ℓ(t))−φ(t−ℓ(t))=2.

Influence of train-generated vibrations on embankment

Roads and railway lines are often constructed on different geotechnical structures such as tunnels, cuttings, and/or embankments. Three main parts are necessary to consider to evaluate vibration: the source of vibrations, vibration propagation path, and receiver of the signal. This paper describes a review of the influence of train-generated vibrations on an embankment and a building in the surroundings. The first presented case study documents an interpretation of seismic signal in the frequency domain using wavelet transform. The algorithm, which we apply to the computation of the wavelet transform of the velocity component record, is based on the pyramidal algorithm, and the result of this procedure is used for an interpretation of data. The discrete wavelet transform was applied to the construction of a 3-dimension mapping of the time-frequency decomposition. An example of the numerical model on the FEM method (the MIDAS GTS software) shows the vertical displacement of the embankment body during the movement of a train. The creation of these models is strictly based on the results of experimental seismological measurements. Then, the source of vibration is represented by a typical train/vehicle that runs on the nearest part of the railway/road at the most efficient velocity.

Formulation of Electric Voltage for Vibration Generation Device Using Magnetostriction Material

Formulation of Electric Voltage for Vibration Generation Device Using Magnetostriction Material

Field monitoring of vibration characteristics during advanced ductule installation in sandy cobble stratum

The sandy cobble stratum presents a high risk for underground tunnel construction due to its low cohesive properties and susceptibility to loosening and falling. The use of Advanced ductule for grouting reinforcement inevitably results in vibrations, and understanding how these vibrations propagate is crucial in selecting tunnel engineering support schemes and responding to accident risks. Based on a bored tunnel under construction in Xi’an, field vibration propagation characteristics testing were carried out for advanced ductile installation. The time-history response and frequency distribution characteristics of the vibration velocity within the tunnel face under sandy cobble stratum conditions were studied, and the law of vibration propagation attenuation within the tunnel face range was obtained. The results showed that: 1) During the conduit drilling process, the tunnel face mainly experienced vertical vibrations, with the horizontal velocity amplitude accounting for only 15%–20% of the vertical velocity amplitude. At a distance of 1.0 m from the conduit, the vertical velocity amplitude reaches 10.602 mm/s, and the vibration energy concentrates mainly in the frequency range of 150–250 Hz. At a distance of 1.5 m from the conduit, the bidirectional vibration velocity significantly attenuates; 2) The vibration characteristics within the tunnel face can be classified into three primary areas: “Loose and Falling” area, “Significant Vibration” area, and “Vibration Attenuation” area. Loose, falling and significant vibrations occurred mainly within a range of about 1.25 m around the conduit. 3) As the diameter of the conduit decreases, the amplitude of vertical vibration velocity decreases by about 20%. By reducing the design diameter of the advanced ductule in a reasonable manner, it is possible to effectively mitigate the impact of vibration caused by the sandy cobble stratum during installation. This can yield a positive impact, curtailing the occurrence of the tunnel’s collapse phenomenon and ensuring its stability.

Observation of a Two-Dimensional Hydrophobic Collapse at the Surface of Water Using Heterodyne-Detected Surface Sum-Frequency Generation.

We study the effect of sodium chloride (NaCl) on the properties of the interface of water and the surfactant dodecyl sulfate (DS-) using heterodyne-detected vibrational sum-frequency generation spectroscopy. We find that the signal of the O-H stretch vibrations of oriented water molecules at the interface is highly nonlinearly dependent on the NaCl concentration. This nonlinear dependence is explained by a combination of screening of the electric field of surface-bound DS- ions pointing into the bulk and screening of the Coulomb repulsion between the headgroups of the DS- ions in the surface plane. The latter effect strongly increases the oriented water signal within a limited NaCl concentration range of 10-100 mM, indicating a two-dimensional hydrophobic collapse of the surfactant layer. The occurrence of collapse is supported by model calculations of the surface potential and surface surfactant density.

Comparison of FEA and SEA methods for predicting railway-induced vibration propagation through over-station developments

The design process for Over-Station Developments (OSDs) includes consideration of the potential impacts of railway-induced vibrations to ensure that structure-borne noise and occupant comfort standards are maintained during railway operations. Should an OSD be identified as sensitive to railway operational structure-borne noise or vibration impacts, the inclusion of adequate track vibration isolation measures becomes essential for mitigation. This paper presents a comparative study of two methodologies for predicting vibration propagation through structures and consequent structure-borne noise levels—Finite Element Analysis (FEA) and Statistical Energy Analysis (SEA). Specifically, this study provides an indication of the range of predicted results and emphasizes the computational efficiency and scalability of these methods when determining track isolation requirements for structures.

Prediction of low frequency vibration propagation from operating rail tunnels

Predicting the propagation of vibrations from rail tunnels is important for quantifying and mitigating the environmental impacts of operating railways. In the general case, vibrations propagating from rail tunnels are attenuated by material damping and geometric effects. Often these effects are aggregated in empirical or numerical models which offer little insight into the physical behaviors that are involved and may be limited in terms of their applicability according to frequency range and tunnel-receiver geometry. This paper examines the aspects of low frequency vibration propagation from rail tunnels that are of relevance to predicting tactile vibration impacts and the influence of operating railway vibrations on sensitive imaging equipment. Fundamental geometric considerations and numerical models are used to determine the influence of pseudo-static effects, source-receiver geometry, layered ground and material damping effects, and the relationship between average and maximum vibration levels that are dependent upon source-receiver distance.

A study on the ground loss and foundation coupling loss for railway vibration prediction in greater Perth area of Western Australia

Railway noise and vibration have emerged as significant concerns affecting the well-being of residents living in proximity to railway tracks and the structural integrity of nearby infrastructure. As such, accurate and reliable predictions of railway vibration levels are necessary in order to properly assess the risks and develop effective mitigations. The propagation of railway vibration from the source to the receiving point involves a complex process, wherein ground loss and foundation coupling loss play crucial roles. Therefore, comprehensive capture of these factors is necessary for improving the accuracy of railway vibration prediction. This paper presents a study focused on the measurements of ground damping loss and foundation coupling loss in great Perth area of Western Australia. The measurements have been undertaken in generally sandy soil conditions. The foundation coupling loss was primarily measured at single-storey residential dwellings. The collected field data were subsequently analyzed to identify the characteristics of ground loss and foundation coupling loss. The study revealed that ground loss and foundation coupling loss exhibited variability dependent on the specific location, ground conditions, and structural characteristics of the dwellings. These measured results can serve as input for modeling efforts, thereby enabling more accurate prediction of railway vibration levels. Furthermore, the study provides valuable insights into the characterization of vibration propagation in sandy soils.

Development of methodological approaches to assess the functional state of the inner ear labyrinth

Modeling the propagation of sound vibrations from the foot plate of the stirrup in the oval window to the perceiving formations of the organ of Corti is a difficult experimental problem. In the search for the causes of hearing loss, tone threshold audiometry has traditionally been considered as the basis of diagnosis. The presence of an air-bone gap on an audiogram was associated with a dysfunction of the middle ear; however, in many cases, an air-bone gap is detected when the pathology is localized in the structures of the inner ear. The review shows that pathological conditions that impair intracochlear sound conduction are successfully detected using computed tomography of the temporal bones. The classification of pathological conditions of the labyrinth, giving the bone-air gap on the tone threshold audiogram, was performed.

Recurrence rate spectrograms for impact localization in wood

Characteristics like cellular grain structure, inhomogeneous density, aging, and altering environmental conditions (moisture, temperature) give wood highly anisotropic viscoelastic properties and non-linear vibrational wave propagation properties. Nonlinearity limits the use of linear methods, such as modal analysis and parameter identification via transfer functions. Acoustic localization of natural damage to wood, like crack growth, is of general interest in structural health monitoring of timber structures. Time-difference of arrival or energy attenuation is commonly used for localization, which are prone to boundary reflections or require the frequency response function. Recent advancements in machine learning-based classification of non-linear signals can achieve a much higher accuracy when recurrence rate-based spectrograms are used compared relative to conventional short-time Fourier transforms, especially in the presence of noise. Hence, in this work, multi-sensor measurements of impulse induced vibration in wood beams are classified by their distance to the excitation, based on their time series, avoiding a priori knowledge of a transfer function for the localization. The machine learning model is trained across various widths and thicknesses of samples, giving a localization estimate independent of beam dimensions. This research will contribute to early detection of damage in the field of vibration-based structural health monitoring of wood.

Exploring pulse mitigation in heterogeneous granular metamaterials

Recognizing the need for effective control of vibration and sound propagation in various industries, this study investigates the potential of designing heterogeneous granular networks for vibroacoustic transmission mitigation. It introduces new models of granular systems: decorated, stepped, and tapered 2-level branching structures. The research assesses changes in particle size (5–10 mm radii) and material properties (density and Young's Modulus) to create finely-tuned composites that significantly modulate pulse waves. The discrete element method predicts wave propagation in these granular metamaterials, comparing monodispersed chains, conventional chain networks, and the proposed heterogeneous structures. Their pulse diffusion capacity is evaluated, showing how collective responses can be adjusted by altering physical parameters like particle size and composition. Preliminary findings underscore the utility of these configurations in advancing the development of elastic and acoustic metamaterials, demonstrating a peak amplitude reduction more than five times greater than an equivalent monomer system. With versatility across a wide frequency range, these metamaterials could pioneer a new direction in impact mitigation.

Investigating vibration-based methods of measuring impact noise insulation to improve reproducibility at low frequencies

Standard impact noise insulation testing is based on measuring the average sound level in a reverberant field in order to estimate the incident and/or radiated sound power. While this method is straightforward, the variation under reproducibility conditions is significant, and a significant portion of the uncertainty is due to the complications of measuring the sound field in the receiving space. This variation is largest at low frequencies, where the effects of spatial variation and modes in the receiving room are well documented. Measuring the vibration on the surfaces of an assembly, or measuring the vibration propagation through an assembly, may provide another measure of the impact insulation of the assembly that is not affected by the sources of uncertainty associated with measuring the sound field in a room. This paper reports on the results of preliminary investigations on floor assemblies in situ while excited by impact sources and the comparison with conventional receiving room sound pressure measurements.

Field Measurement and Energy Analysis of Ground-Borne Vibration around High-Speed Railway Viaduct

In order to investigate the vibration characteristics and propagation mechanism of ground vibrations induced by high-speed train passing through the viaduct, a field experiment is carried out, and the measured data is deeply analyzed. Besides the independent time domain and frequency domain analysis, the continuous wavelet transform (CWT) is performed on the vibration signal to analyze the energy distribution characteristics of ground vibrations from the view of time-frequency synchronous analysis. The experimental results show that the ground vibrations have obvious nonstationary characteristics; the first dominant frequency of ground vibration is concentrated between 40–55 Hz, which is affected by the excitation frequency of the train wheel axle and the peak frequency of wheel-rail interaction force. The ground vibrations attenuate gradually as the distance from the railway track increases, in which the high-frequency components above 50 Hz attenuate faster, low-frequency components below 8 Hz continuously decay in the near field, and medium-frequency components within 8−50 Hz decay slower with a longer transmission distance. Compared with traditional methods, time-frequency synchronous analysis of ground vibration signals is more accurate and intuitive, and the CWT can be used as a promising method in the analysis of ground-borne vibration from high-speed railway.

Elevated concentrations cause upright alpha-synuclein conformation at lipid interfaces

The amyloid aggregation of α-synuclein (αS), related to Parkinson’s disease, can be catalyzed by lipid membranes. Despite the importance of lipid surfaces, the 3D-structure and orientation of lipid-bound αS is still not known in detail. Here, we report interface-specific vibrational sum-frequency generation (VSFG) experiments that reveal how monomeric αS binds to an anionic lipid interface over a large range of αS-lipid ratios. To interpret the experimental data, we present a frame-selection method ("ViscaSelect”) in which out-of-equilibrium molecular dynamics simulations are used to generate structural hypotheses that are compared to experimental amide-I spectra via excitonic spectral calculations. At low and physiological αS concentrations, we derive flat-lying helical structures as previously reported. However, at elevated and potentially disease-related concentrations, a transition to interface-protruding αS structures occurs. Such an upright conformation promotes lateral interactions between αS monomers and may explain how lipid membranes catalyze the formation of αS amyloids at elevated protein concentrations.

Magnetoelastic Losses in the Linear Response Region for Three- and Four-Axis Idealized Magnets

In the presented studies, a description of the losses related to relaxation processes in idealized three- and four-axis ferromagnets, as well as ferrites, is considered for the case of a linear response (small perturbations) on the basis of a macroscopic approach. The description takes into account reversible 90° displacements of domain walls (DW) of concentrations (с), ways of DW pinning by linear defects, and processes of DW displacements and rotations of the spontaneous magnetization vector I⃗s, caused by a longitudinal elastic stress wave σ. As a result, the anisotropy of amplitude-independent losses emerges due to displacement processes. Frequency dependence of losses is obtained with consideration of the magnetic symmetry of the crystal, its magnetostructural parameters, and the concentration of magnetic phases ci. The paper also describes the internal frictionn Q-1, the absorption coefficient a, the velocity of propagation of elastic vibrations v and the Δ (1/E)-effect, thus allowing to reveal the texture in the distribution of DWs by their types.
 It is shown that if the relaxation times of rotation processes τ = β / 2K1 and displacement processes τc = βс / mω20 are the same, then the maxima of the dependence of internal friction on frequency Qc-1(ω) and QB-1(ω) superimpose on each other.
 The revealed features of magneto-elastic energy dissipation are of interest for laboratory studies and have promising applications in practice for determining the orientation of crystals, describing the texture, and calculating the differential ΔЕ-effect in magnets. The features of the ΔЕ-effect for the considered cases are also revealed.

Structural Anomality of the Adsorbed Water on Al-Doped Silica Revealed by Heterodyne-Detected Vibrational Sum-Frequency Generation Spectroscopy

Structural Anomality of the Adsorbed Water on Al-Doped Silica Revealed by Heterodyne-Detected Vibrational Sum-Frequency Generation Spectroscopy

Fully First-Principles Surface Spectroscopy with Machine Learning.

Our current understanding of the structure and dynamics of aqueous interfaces at the molecular level has grown substantially due to the continuous development of surface-specific spectroscopies, such as vibrational sum-frequency generation (VSFG). As in other vibrational spectroscopies, we must turn to atomistic simulations to extract all of the information encoded in the VSFG spectra. The high computational cost associated with existing methods means that they have limitations in representing systems with complex electronic structure or in achieving statistical convergence. In this work, we combine high-dimensional neural network interatomic potentials and symmetry-adapted Gaussian process regression to overcome these constraints. We show that it is possible to model VSFG signals with fully ab initio accuracy using machine learning and illustrate the versatility of our approach on the water/air interface. Our strategy allows us to identify the main sources of theoretical inaccuracy and establish a clear pathway toward the modeling of surface-sensitive spectroscopy of complex interfaces.

Analysis of Vibration and Noise in a Permanent Magnet Synchronous Motor Based on Temperature-Dependent Characteristics of Permanent Magnet

Interior permanent magnet synchronous motors (IPMSMs) are widely utilized due to their high power density. However, noise and vibration issues are often encountered in these motors. While researchers have extensively investigated individual aspects such as noise, vibration, and heat generation in PMSMs, there has been a lack of comprehensive studies examining the interrelationships among these factors. In this paper, a novel approach is proposed for predicting vibration by considering the radial force in the air gap as the exciting force, while also accounting for the changes in the permanent magnet (PM) characteristics caused by heat generation during motor operation. The method involves decomposing and identifying vibration components associated with each vibration mode and predicting noise based on the sound radiation efficiency of each mode. By constructing a vibration map based on current and temperature at a specific frequency, the components most affected by current variations and PM characteristics can be identified. This allows for the proposal of design improvements aimed at reducing vibration. Furthermore, by comparing the vibration map with the noise map, it is confirmed that vibration serves as a source of noise and influences its generation. However, it is found that vibration and noise are not strictly proportional. Overall, a comprehensive analysis of the correlations between vibration, noise, and other factors in IPMSMs is presented in this study. The proposed method and findings contribute to the understanding of the complex dynamics involved and provide valuable insights for the design of quieter and more efficient motor systems.

Study of the inhibitory effect of a soft cushion on the propagation of pressure pulsation in pumped storage power stations

AbstractHigh‐frequency pressure pulsations are hydraulic phenomena that are frequently observed in pumped storage power stations. These pulsations can propagate through the steel pipes, concrete lining, and the surrounding rock system, which in turn may have detrimental effects on the environment, such as noise pollution, and relocation of the local residents. This paper proposes a vibration‐damping concept that involves wrapping a local soft cushion layer outside the buried steel pipe; this layer could partially eliminate the pressure fluctuations in the headrace tunnel, thereby reducing the ground vibrations caused by the pressure pulsations. In this study, the finite element method was used to model the propagation of vibrations in the surrounding rock and fluid‐filled pipes, including static simulation of the structure, and dynamic simulation of the surrounding rock. The simulation results suggest that adding an appropriate local soft bedding layer can effectively reduce the ground vibrations by more than 60% and the possible surface noise within the standard vertical vibration norms. The inhibitory effect of the soft cushion on the propagation of vibrations is determined by the wrapping angle, thickness, and material of the bedding layer. This effect increases with increasing wrapping angle and thickness of the bedding layer, and decreases with increasing elastic modulus of the material. After the addition of the bedding layer between the steel pipe and concrete lining, the pressure in the inner pipe is primarily borne by the steel lining rather than the coupling of the steel lining, concrete lining, and the surrounding rock. Hence, the thickness of the part of the steel liner in contact with the soft bedding layer should be increased. In addition, the thickness variations in the steel pipe joints should be smooth to avoid stress concentration.

The modified CUF-EFG method for the dynamic analysis of GPLs-CNTs-reinforced FG multilayer thick cylindrical shells under shock loadings: A modified meshless implementation

The main scope of this paper is to develop the Carrera unified formulation in cylindrical coordinates for two-dimensional meshless modelling of graphene platelet and carbon nanotube reinforced functionally graded multilayer thick cylindrical shells with the same accuracy of three-dimensional modelling. The cylindrical shell is composed of several homogeneous layers with uniform distribution of both GPL and CNT contents in each layer. The effective macroscopic mechanical properties of each GPLs and CNTs reinforced layer are estimated using the modified Halpin-Tsai (H-T) micromechanical model and rule of mixture. The volume fraction of nanofillers gradually changes layer to layer by nonlinear continuous function which leads to functionally graded (FG) distribution of nanofillers. Five grading patterns of layer distribution along the thickness direction of cylindrical shell are considered to investigate the effect of layer arrangement on dynamic behavior of cylindrical shells. The FG multilayer hybrid nanocomposite cylindrical shell is assumed to be under mechanical shock loading. The numerical method for dynamic analysis of multilayer cylindrical shell is based on element free Galerkin (EFG) method with radial basis shape functions in the framework of displacement-based Carrera unified formulation (CUF). The present EFG-CUF method is compared with analytical method for isotropic homogeneous shells and results available in the literature for FG multilayer cylindrical shells. Considering the results related to various expansion orders, proved accuracy and efficiency of proposed method for dynamic analysis of thin to thick FG multilayer cylindrical shells at high expansion orders ‘n > 2’. After verifying the analytical method, the effects of several key factors such as layer distribution patterns, volume fraction index, number of layers, nanofiller weight fraction, aspect ratios of cylinder, and damping ratio on static, free vibration, time history and wave propagation of cylinder are studied in detail.