Effect Of Material Damping Research Articles

Vibration filtering effect of a novel three-dimensional isolation bearing on metro vibration isolation

Three-dimensional (3D) isolation bearings are effective means to reduce the adverse effects of metro vibrations on structures. The current research focuses on the relationship between the vertical stiffness and metro vibration isolation performance of bearings, but neglects the vibration filtering effect resulting from the inherent resonance and material damping effect of them. In this study, a novel 3D isolation bearing was proposed, composed of spring bearings (SBs) and laminated nature rubber bearings (LNR) vertically in series (denoted as 3DSL), and not only its vertical stiffness but also vibration filtering effect on metro-induced vibration isolation performance were fully studied. The design principle and vibration isolation mechanism of the 3DSL were described, followed by the design and test of three specimens. After that, a case study was conducted to investigate the influence of the 3DSL's filtering effect on metro vibration isolation. The results indicated that the 3DSL exhibited high vertical loading capacity and low vertical stiffness. Furthermore, it was found that the vibration amplitude was slightly amplified in the low-frequency range (1–50 Hz), while significantly reduced in the high-frequency range (50–200 Hz) due to the vibration filtering effect of the 3DSL. Altogether, these results demonstrated that the excellent metro vibration isolation performance of the 3DSL was attributed to the low vertical stiffness and vibration filtering effect. It is recommended to consider both the reduction of vertical stiffness and vibration filtering effect of 3D isolation bearings when designing isolation systems for metro vibrations.

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.

Evaluation of Polymer Materials for MEMS Microphones

Polymers are attractive materials for the fabrication of micro-electro-mechanical system (MEMS) microphones because of their low Young’s moduli, generally lower processing temperatures than silicon, and simple fabrication; such microphones are sensitive and economical. However, an earlier polymer diaphragm revealed lower sensitivity than expected. In addition, the viscoelastic properties of polymer diaphragm have been considered to degrade the sensing performance due to a high-level mechanical noise. Here, we investigated the possibility of the polymer material as a MEMS microphone in terms of stiffness and damping. Stiffness was analyzed and experimentally verified. The obtained polymer diaphragm damping coefficient was compared with the coefficient of a silicon MEMS microphone to explore whether performance was degraded by material damping. All samples were fabricated using a thin film transfer method. SU-8 was mainly used but Polymethyl methacrylate (PMMA) was also selected for comparing the material damping effect. The measured residual stress of an SU-8 diaphragm was 18 MPa; the measured flexibility was similar to the state-of-art of a silicon-based MEMS microphone, and it was proven that there is room for further improvement through process optimization. The damping effect induced by viscoelasticity was very small, compared with the effect of air damping; indeed, the intrinsic damping effect of the polymer on device performance was negligible. [2021-0213]

Propagation Characteristics of Flexural Wave in One-Dimensional Phononic Crystals Based on Lattice Dynamics Model

In this paper, we establish discrete flexural lattice chain models of Bragg and locally resonant phononic crystals by setting mass defect atoms and local resonant elements on the flexural lattice chain. The bandgap characteristics of flexural wave in phononic crystals are studied by establishing the governing equations of the model. The results from models show that with the change of the mass ratio of defective atoms to normal atoms, the bandgap of the flexural wave produced by Bragg scattering shows a certain rule. When the local resonant bandgap and Bragg scattering bandgap are close to each other, the two bandgaps will be coupled to form a wider flexural wave bandgap. The effect of axial strain on bending wave propagation is only the shift of bandgap position. The effect of material damping on the propagation of a bending wave is only energy dissipation at high frequency. In addition, we use finite element simulation to calculate the bandgap of flexural wave in phononic crystals with mass defects, and the results are consistent with lattice chain model. This shows that lattice chain model can effectively guide the bandgap design of phononic crystals. This comprehensive study may help to elucidate the rule of bandgap generation of flexural wave in one-dimensional phononic crystals.

Sensitivity of translational impedance functions of surface foundation to the parameters of soil and applied load

ABSTRACT The effect of soil and loading parameters on the impedance function of a circular disk on homogeneous half space under translational motion is studied. The soil parameters are Poisson’s ratio (ν) and damping ratio (ξ), whereas the loading parameter is the dimensionless frequency (a 0). The impedance functions (spring coefficients and damping coefficients) are initially calculated using the Cone model, for vertical and horizontal modes of vibration. Then, the effect of material damping is observed using three material damping models, namely, Hysteretic model, Voigt model and Kelvin model. The material damping is incorporated using the correspondence principle. Finally, a parameter importance analysis has been carried out to observe the significance of all the parameters considered. The analysis of results suggests that in most of the cases, the spring and damping coefficients are primarily controlled by dimensionless frequency (a 0 and damping ratio (ξ) of soil, respectively

Horizontal vibration of a rigid strip footing on viscoelastic half‐space

AbstractThis paper presented an analytical method for determining the response of a rigid strip foundation resting on the surface of a viscoelastic half‐space to horizontal dynamic loads, and the associated transient soil displacements resulting from the vibration of the footing. This mixed boundary value problem was solved by means of Jacobi orthogonal polynomials, a more efficient method compared to transforming the dual integral equations resulting from the boundary conditions to Fredholm integral equations. Displacements and stresses of the soil‐footing system were accordingly obtained by applying the inverse Fourier transform. Finally, we used the proposed solution to investigate the effects of material damping and Poisson's ratio of soil on the dynamic response of the strip footing, and the resulting soil displacements.

Effect of material damping on the impedance functions of an embedded circular foundation under vertical and horizontal excitation

Machine foundations are generally affected by the vibratory shocks from different machines. The behavior of these foundations is influenced by the properties of underlying soil and the excitation frequency of the applied dynamic load. The influence of material damping on the dynamic impedance functions of a circular disk embedded in homogeneous elastic half space is analyzed using one-dimensional wave propagation in cones (cone model) and the results are presented in the form of dimensionless plots to observe the more realistic response of machine foundations. Three different types of material damping models viz., Hysteretic, Voigt and Kelvin model are introduced in the above elastic solutions using correspondence principle. The spring and damping coefficients of the embedded foundation are then computed in a wide range of frequency of excitation under vertical and horizontal mode of vibration varying the influencing parameters namely dimensionless frequency (a0), Poisson’s ratio (ν), embedment ratio (e/r0) and damping ratio (ξ). The outcomes from the present analysis suggest that the spring coefficient is nonlinearly affected by the dimensionless frequency and embedment ratio, for both the modes of vibration. The effect of material damping on spring coefficient is only significant for a0> 2, irrespective of the damping model used.

Study of the characteristics of train-induced dynamic SIFs of tunnel lining cracks based on the modal superposition approach

Cracks on a tunnel lining are commonly observed during in-site tunnel inspection. The cracks are generated owing to various reasons and can potentially further propagate as they are subjected to repeated dynamic train loads during the entire tunnel service life. The study investigated train-induced dynamic stress intensity factors (SIFs) of tunnel lining cracks by numerical simulations using the modal superposition approach and examined the effects of a wide range of factors. The methodology of the modal superposition approach was adopted and validated to determine dynamic SIFs. Subsequently, the coupled dynamic FE model was established to calculate train-induced SIFs of tunnel lining cracks and radiation damping owing to the infinite surrounding medium was determined. Finally, a parametric analysis was conducted to investigate the effects of crack location, crack depth, wave velocity of the surrounding medium, and material damping on dynamic SIFs of tunnel lining cracks subjected to metro train loads. The results demonstrate that the modal superposition approach can be employed to accurately and effectively calculate the train-induced dynamic SIFs of tunnel lining cracks when radiation damping is considered. The effects of crack location, crack depth, and wave velocity of the surrounding medium are significant, while the effect of material damping is not considerably evident. The maximum dynamic SIF significantly increases with crack depth, while it decreases with the wave velocity of the surrounding medium and material damping ratio. Cracks with greater depth in the poorer medium are more likely to propagate under dynamic train loads.

Seismic vibrations attenuation via damped layered periodic foundations

In recent years, a new type of seismic isolation system which exploits the filtering effect of bandgaps, named Periodic Foundation, has been proposed to isolate the upper structure from ground motion. To date, several works have been conducted to validate the feasibility and efficiency of this new isolation system. However, these works focused on the filtering effect related to the foundation periodicity, while energy dissipation due to materials absorption was ignored. To fill this gap, in this paper we investigate the effect of material damping on the performance of layered periodic foundations. Both the dispersion (related to the periodicity of the periodic foundation) and dissipation (related to the material damping of the periodic foundation) attenuation mechanisms, as well as their interaction, are investigated. First, the complex dispersion relation of a damped layered periodic foundation is formulated to assess the influence of material damping on the dispersive properties of the infinite periodic system. Second, the Riccati-transfer matrix method is used to calculate the dynamic transfer function of the damped layered periodic foundation, from which the energy dispersion and dissipation properties of the system are studied. Third, seismic responses of six-story shear-type buildings equipped with a solid foundation (fixed base), a traditional base isolation (i.e., equivalent of a layered periodic foundation with one unit-cell) and a layered periodic foundation with three unit-cells, are studied and compared. In more detail, the pseudo-excitation method is used to deal with non-classical damped systems under seismic accelerations for different soil conditions. Results show that, thanks to the filtering effect of the layered periodic foundation, the seismic responses of the upper structure are significantly mitigated within the expected frequency attenuation zone. Furthermore, including material damping leads to a further reduction of the upper structure seismic response, within the pass bands. Overall, the seismic performance of the upper structure under ground motions in different site conditions is improved by employing a damped layered periodic foundation with more than one unit cell.

Numerical investigation on transverse vibration responses of non-uniform composite plates

In this study, the numerical investigation on the traverse vibration responses of the non-uniform composite plates is performed using a finite element method. The First-order shear deformation theory (FSDT) is used to formulate the governing differential equations of motion of various non-uniform composite plates. The material damping effects are included in the formulation by including material properties as a complex elastic modulus in terms of storage modulus and loss modulus. The dynamic response of various non-uniform configurations under harmonic forced excitation is studied and the design guidelines are provided to identify the suitable non-uniform composite configurations.

Audio-Material Reconstruction for Virtualized Reality Using a Probabilistic Damping Model.

Modal sound synthesis has been used to create realistic sounds from rigid-body objects, but requires accurate real-world material parameters. These material parameters can be estimated from recorded sounds of an impacted object, but external factors can interfere with accurate parameter estimation. We present a novel technique for estimating the damping parameters of materials from recorded impact sounds that probabilistically models these external factors. We represent the combined effects of material damping, support damping, and sampling inaccuracies with a probabilistic generative model, then use maximum likelihood estimation to fit a damping model to recorded data. This technique greatly reduces the human effort needed and does not require the precise object geometry or the exact hit location. We validate the effectiveness of this technique with a comprehensive analysis of a synthetic dataset and a perceptual study on object identification. We also present a study establishing human performance on the same parameter estimation task for comparison.

Damping capacity in pseudo-elastic and ferro-elastic shape memory alloy-reinforced hybrid composite beam

Reinforcing a composite beam with shape memory alloy wires may have several benefits such as reduction of buckling risks or elimination of unwanted oscillations. In this paper, the vibration damping of a typical shape memory alloy-reinforced composite or hybrid beam is explored. To formulate the thermo-mechanical behavior of embedded shape memory alloy wires, three-dimensional Panico–Brinson model is employed and tailored to one-dimensional model. This material model can simulate pseudo-elastic and ferro-elastic forms of martensite transformations which occurs in cyclic loadings. Besides, unlike the former studies which rely on classical beam theories, the first-order shear deformation beam theory is used to obtain more accurate estimations of shape memory alloy-wire hysteresis loops and their decaying characteristics. In order to explore the effects of a transient concentrated load applied in the middle of a beam, the governing equations are developed and discretized by differential quadrature–integral quadrature combined method. Incremental time marching solution of the problem is accomplished using the Newmark technique. Results are assessed by comparing with available literature. Considering different types of boundary conditions, the influence of pseudo-elastic and ferro-elastic hysteresis loops on the material damping effects, shape memory alloy volume fraction, and resonance phenomenon is studied in detail.

Parametric models for 3D topographic amplification of ground motions considering subsurface soils

Amplification of seismic waves due to surface topography and subsurface soils has often been observed to cause intensive damage in past earthquakes. Due to its complexity, topographic amplification has not yet been considered in most seismic design codes. In this study, we simulate ground-motion amplification based on 3D Spectral Element Method, using Hong Kong Island as a local testbed site. The analyses revealed that topographic amplification of ground motions is frequency-dependent. If the site is made of homogenous rock, the amplification factor is best correlated with the curvature smoothed over a characteristic length equal to half of the wavelength in rock. Amplification of high frequency wave is correlated with small-scale features, and amplification of long-period waves is correlated with large-scale features in horizontal dimension. The maximum topography amplification generally ranges from 1.6 to 2.0 on the protruded areas. When a low-velocity subsurface soil layer is considered, the topographic amplification pattern is significantly influenced by the thickness of the soil layer, as wavelength in soil is relatively short. The characteristic length reduces as soil thickness increases, and the amplification pattern becomes closely correlated to smaller-scale topographic features as well as slope angles. Results also show that the effect of material damping can be decoupled from the topographic effects and modeled using a theoretical attenuation factor. The study proposed parametric models to predict 3D topographic amplification using simple proxies considering subsurface soils, material damping and input wave frequencies, which gives accurate results with a standard deviation of residuals within 0.1–0.15.

Guided wave excitation and propagation in damped composite plates

Guided wave attenuation in composites due to material damping is strong, anisotropic, and cannot be neglected. Material damping is a critical parameter in selection of a particular wave mode for long-range structural health monitoring in composites. In this article, a semi-analytical finite element approach is presented to model guided wave excitation and propagation in damped composite plates. The theoretical framework is formulated using finite element method to describe the material behavior in the thickness direction while assuming analytical expressions in the wave propagation direction along the plate. In the proposed method, the Kelvin–Voigt damping model using a complex frequency-dependent stiffness matrix is utilized to account for anisotropic damping effects of composites. Thus, the existing semi-analytical finite element approach is being extended to include material damping effect. Theoretical predictions are experimentally validated using scanning laser Doppler vibrometer measurements of guided wave propagation generated by a circular piezoelectric wafer active sensor transducer in a unidirectional carbon fiber reinforced polymer composite plate. The proposed method achieves good agreement with the experimental results.

Analysis of different techniques to improve sound transmission loss in cylindrical shells

In this study, sound transmission through double- and triple-walled shells is investigated. The structure-acoustic equations based on Donnell's shell theory are presented and transmission losses calculated by this approach are compared with the transmission losses obtained according to Love's theory. An experimental set-up is also constructed to compare natural frequencies obtained from Donnell and Love's theories with experimental results in the high frequency region. Both comparisons show that Donnell's theory predicts the sound transmission characteristics and vibrational behavior better than Love's theory in the high frequency region. The transmission losses of the double- and triple-walled construction are then presented for various radii and thicknesses. Then the effects of air gap size as an important design parameter are studied. Sound transmission characteristics through a circular cylindrical shell are also computed along with consideration of the effects of material damping. Modest absorption is shown to greatly reduce the sound transmission at ring frequency and coincidence frequency. Also the effects of five common gases that are used for filling the gap are investigated.

High-Resolution Lamb Wave Inspection in Viscoelastic Composite Laminates

Lamb wave inspection is a promising structural health monitoring method for carbon fiber reinforced plastic laminates. The optimal design of the excitation waveform based on Lamb wave pulse compression is an effective way to improve the inspection resolution in elastic plates. However, due to the viscoelastic property of the composite materials, the material damping effect will influence the amplitude response of the output signals; thus, the current design strategy is no longer applicable. The purpose of this paper is to develop an excitation waveform design strategy based on pulse compression to meet the demands of high-resolution Lamb wave inspection in composite materials. Different parameters that affect the design of excitation such as material damping effect, amplitude response, relative frequency bandwidth, and the selection of excitation waveform are considered synthetically. In addition, an excitation waveform design strategy based on the corrected amplitude response is also established to eliminate the effect of material damping and thus achieve better detection resolution. Finally, an experiment was carried out on a quasi-isotropic composite plate. The experimental results validate the robustness of the amplitude response correction method and the effectiveness of the excitation waveform design strategy.

Transient dynamic analysis of pile foundation responses due to ocean waves using the scaled boundary finite element method

In this study, a semi-analytical numerical method, the scaled boundary finite element method, is employed to investigate the time-dependent behaviour of pile foundations when subjected to ocean wave loads. Individual piles present steady-state vibrations at the same frequency as external waves considering the material damping effect. In the case with a group of two piles, the structural behaviour of pile foundations is a multivariable function of the wave properties and the spatial arrangement of piles, and each pile responses differently to various parameter combinations. The leading pile, which interacts with incoming waves earlier, normally experiences greater displacement amplitude than the subsequent pile. Both piles show relatively greater displacement in cases with large wave numbers. When the two piles are closely spaced or when the wave number is small, their responses tend to have phase difference and move towards different directions. This study is expected to shed light on the transient behaviour of pile foundations, when wave load is a dominant factor.

Effects of semiconduction on electromechanical energy conversion in piezoelectrics

We study the effect of semiconduction on mechanical-to-electrical energy conversion through a theoretical analysis on the thickness-extensional vibration of a piezoelectric semiconductor plate driven mechanically. An analytical solution is obtained. A ZnO plate is used as a numerical example. Results show that both the electrical output power and the energy conversion efficiency are sensitive to semiconduction at a moderate carrier density of 1015 m−3, and that the effect of the dissipation due to semiconduction can be comparable to the effect of material damping when the material quality factor is in the usual range of 102–103.

Nonlinear Material Loss Factors of Single-Layer Latticed Domes Subjected to Earthquake Ground Motions

AbstractThe quantification of damping in a structure is of significant interest in structural dynamics. At present, there is still no clear consensus on how damping issues are resolved. Although the Rayleigh damping model, which combines mass-proportional and stiffness-proportional parts, leads to reasonable engineering demand parameters of a structure within its elastic range, it does not include nonlinear response history analysis. On the other hand, a great deal of material tests demonstrate that most metallic materials under cyclic loading exhibit a stress-strain relationship that is not elastic even at stresses well below the yield point, however, the material damping effect is seldom taken into account in dynamic analysis. The present study proposes an approach that explicitly considers the additional material damping effect based on Goodman’s theory on energy dissipation of materials. The approach is applied to the nonlinear dynamic analyses of single-layer latticed domes subjected to earthquake gr...

Efficient application of encapsulated bubbles and foam elements to mitigate offshore piling noise

The very high noise levels of offshore piling noise during the installation of offshore wind converters are dangerous to marine life like harbor porpoises and fishes. Encapsulated bubbles and foam elements are successfully used to reduce the very high noise levels. There are different physical effects such as impedance mismatch, resonance and scattering effects and material damping effects that are responsible to the measured noise reduction between about 10 dB (SEL) and 23 dB (SEL). The radiation of underwater noise from the pile surface, the propagation and the reflections of the radiated waves are investigated together with the influence of encapsulated bubbles and foam elements in the near field of the pile. Only a very small part of the impact energy is radiated directly from the pile into the surrounding water. Most of the hammer energy is driven into the ground. A small part from this is radiated indirectly from the ground into the water. The efficiency of encapsulated bubbles and foam elements in underwater noise mitigation is investigated by theoretical studies, laboratory measurements, and by offshore measurements with different elements and combinations.