Damping Effect Research Articles

Mechanical properties of a novel negative Poisson's ratio gradient structure

A novel cellular structure is proposed based on bionic structure with negative Poisson's ratio characteristic, and the cell is periodically expanded in the in-plane direction to create a new honeycomb structure. The influence of gradient changes of the structural parameters on the load-bearing capacity and damping characteristics of the structure is investigated through a combination method of finite element numerical simulations and experiments. The results indicate that the concentric gradient arrangement of cell wall thickness and angle parameters, and the symmetrical gradient arrangement of cell height, wall thickness and angle parameters have the most significant influence on the static bearing capacity of the structure. In contrast, the gradient arrangement under the corner circle diameter has minimal effect on the static bearing capacity of the structure. Under the same conditions, the peak values of the transmissibility of C2 (large angle at constraint end and loading end, and smaller angle in the middle) and C3 structures (angle gradually increases from the loading end to the constraint end) are significantly reduced between the frequency 2 Hz and 1024 Hz. The peak values of the transmissibility of the structures C2 and C3 are respectively decreased by 20% and 25% compared to that of the non-gradient structure. This shows that the vibration damping effect of these two structures is better. The structure with the gradient change and the structure without the gradient change of the new honeycomb structure can both achieve certain vibration reduction and isolation from the middle to high frequency range.

Parameter identification of overhead conductor rail support and its influence on the contact forces

Overhead conductor rail (OCR) serves as a crucial device employed in tunnels to power electric locomotives. The OCR is hung by supports mounted on the tunnel ceiling. Previously, the support was usually considered as a linear spring when modelling the OCR. The linear stiffness and mass adopted to the support model were imprecise, and damping was absent. It may be insufficient to reproduce the pantograph-OCR system (POCR) dynamic behaviour. This paper is devoted to improving the accuracy of POCR dynamic model and makes it more realistic. Field tests are conducted in order to identify the support parameters, including stiffness, damping and mass, for the first time. Then, a novel nonlinear stiffness-damping-mass support model is developed utilising the identified parameters and verified by comparing simulation results with measurement data. Finally, in pursuit of improving current collection quality, the effects of support damping and train speeds on contact forces are investigated. The results show that the support damping can mitigate the OCR’s vibration. The increase of support damping within a specific range, 0–200 Ns/m, has a positive effect on the current collection quality.

The Function of Horn Ridges for Impact Damping.

This study explores the damping effects of ram horn ridges on mechanical impacts resulting from ramming. We measured the amplitudes and frequencies of ridges along the axial (pitch) direction of the ridges of ram horns obtained from eight specimens across six different species. While the horns shared a similar spiral-shaped pattern with surface ridges, our findings show variations among the horns, including ridge spacing and growth trends. Additionally, we employed finite element analysis (FEA) to compare a ridged horn model with a non-ridged counterpart to provide an understanding of the damping characteristics of the surface ridges. Our FEA results reveal that the ridged horn decreased the initial ramming pressure by 20.7%, increased the shear stress by 66.9%, and decreased the axial strain by 27.3%, the radial strain by 16.7%, and the shear strain by 14.3% at a 50 ms impact duration compared to those of the non-ridged horn. The damping ratio was increased by 7.9% because of the ridges. This study elucidates three primary functions of the different species of ram horns' spirals and ridges: (1) to transfer longitudinal waves into shear waves, (2) to filter shear waves, and (3) to stabilize the structure by mitigating excessive strain.

Advanced seismic resilient performance of steel MRF equipped with viscoelastic friction dampers

This paper demonstrates the enhanced resilience performance of steel structures with viscoelastic friction dampers (VEFDs) based on numerical simulations of building responses. Velocity-dependent dampers, which are widely used to increase seismic resilience, may increase the axial force of the column under strong earthquake conditions because the generated force depends on the interstory velocity. This often leads to plastic hinges being placed on the columns of the structure, which can lead to structural collapse via weak-layer failure. In addition, while viscoelastic dampers are effective in reducing story drift, peak acceleration, and peak velocity, the proposed hybrid VEFD offers the additional benefit of reducing base shear via the friction damper. Simulation results for 10- and 20-story buildings with the novel VEFDs show that the proposed dampers can control drift and plastic deformation in structural members. Nonlinear dynamic analysis of 20 far-fault seismic ground motion records conducted using OpenSees also reveals lower peak absolute floor acceleration and velocity. Overall, the results suggest that the proposed VEFD has excellent potential for use in the performance-based seismic design of structures because it can reduce both structural and nonstructural damage. The results verify the damper's effectiveness in controlling story drift without a significant increase in the base shear. Collapse probability assessment also demonstrates the collapse resistance of moment-resisting frames when used in conjunction with VEFDs.

Depinning of domain walls in a notched ferromagnetic nanostrip: role of inertial and nonlinear damping effects

Abstract In this work, we investigate theoretically the static and kinetic depinning field of a domain wall in a notched magnetic nanostrip under the generalized framework of the Landau–Lifshitz-Gilbert equation, which combines inertial and nonlinear viscous-dry friction damping effects. We assume a head-to-head transverse domain wall configuration and analyzed its motion subject to a time-varying external magnetic field. To deduce the equation ruling the spatio-temporal evoution of the magnetic domain wall, we adopt the Schryer and Walker trial function approach. The results show that static and kinetic depinning fields increase as the dry friction dissipation increases. Moreover, viscous dissipation exhibits a weak dependence on the kinetic depinning field and saturated domain wall velocity, while inertial damping due to the relaxation time of angular momentum significantly impacts the kinetic depinning field, depinning time, and breakdown velocity. Our numerical results are in good qualitative agreement with the recent observations reported in the literature.

On Dynamic Analysis and Prevention of Transmission Squawk in Wet Clutches

Abstract The genesis of clutch noise, encompassing squeaks, chatter, shudders, or judders, predominantly arises from friction-induced vibrations. As time progresses, the degradation of the clutch friction lining manifests due to diverse factors, such as the smearing of surface irregularities, elevated transmission fluid temperatures, fluctuating axial pressure, or aggressive shifting. Consequently, the slope of the friction curves tends to assume a negative gradient, giving rise to adverse damping effects like self-excited oscillations or stick-slip oscillations within the clutch pack. A lesser-discussed phenomenon, known as Squawking, occurs through analogous mechanisms discussed in this article. This article delves into investigating the occurrence of squawking noise observed in automatic transmission multi-disc clutches during low-speed up-shifts. The study discerns friction-induced vibrations as the primary contributor to squawk during the inertia phase of the clutch engagement cycle, a facet previously unidentified. During this phase, high-frequency weakly damped oscillating modes become self-excited due to the negative slope of the coefficient of friction versus slip speed curve. The coefficient of friction functions as negative damping during the inertia phase, where the energy dissipation from damping is insufficient to completely halt the oscillations, allowing them to persist at the natural frequency until clutch lock-up. Experimental data validates the proposed model and hypothesis, with results closely aligning with numerical simulations. The paper concludes by offering practical suggestions to prevent and mitigate squawk in automatic transmission wet clutches, with the aim of enhancing overall performance and reducing undesirable noise.

Transient stability of grid following inverters: The impacts of damping and fault ride‐through

AbstractThe interaction of grid following inverters with a weak grid raises risks of transient instability. The effects of damping and fault‐ride through (FRT) make the transient dynamics more complicated. To investigate the impact of FRT on the transient stability of converters, this paper first employs the switch system theory to construct a mathematical model for the synchronous mechanism of inverters. Secondly, the method of semi‐algebraic system real root classification is comprehensively used to analyse the existence of equilibrium points (EPs) and provide necessary and sufficient conditions for their existence. Finally, based on the theory of differential geometry, a method for computing the stability domain of converters is proposed. Compared with traditional methods, the results obtained from this approach are precise and non‐conservative. The study in this paper indicates that the equivalent damping effect from the proportional control in a phase‐locked loop significantly enlarges the stability region, whereas the active current injection shrinks the stability region. The reactive current droop characteristic also has impacts on the stability region, especially with active current injection. The switchover between the droop mode and constant current mode requires extra precaution in the calculation of the EPs and critical fault clearing time.

New theory to explain the effect of lactose fines on the performance of adhesive mixtures for inhalation

A new theory for the dispersibility enhancing effect of excipient fines for adhesive mixtures for inhalation is presented in this paper, while at the same time the shortcomings of current hypotheses are discussed. The proposed mechanism, denoted the ‘viscoelastic damping effect’, states that the presence of fines particles acts to dampen the collisions between carrier particles during mixing. As a consequence, fewer fine particles are ‘irreversibly’ pressed into the carriers, which in turn entails a higher fine particle fraction. The mechanism was demonstrated experimentally at different levels of added lactose fines by studying the influence of processing on fine particle fraction. This approach furthermore enabled quantification of the effect. All fine particles present in the blend (APIs and excipient fines) act together to exert the damping effect. The proposed mechanism is able to explain the main body of published data, including the effect of added excipient fines, the effect of an increased drug load, and the effect of removal of carrier fines. The viscoelastic damping mechanism is general in nature and conveys a broader and more general understanding of the behavior of adhesive mixtures for inhalation.

Analysis and experimental evaluation of an inertial eddy current damper for vibration control

Electromagnetic damping features non-contact operation, easy adjustability, convenient processing, and high energy consumption. Combined with the damping efficiency enhancement effect of the inertial system, it is conducive to further improving its damping effect. This paper proposes an inertial mass damper, named the Inertial Eddy Current Damper (IECD). The proposed IECD has the advantage of adjustability, meaning that the eddy current damping force can be adjusted by regulating the current in the coil. First, the mechanical model of the IECD was proposed through theoretical methods. Secondly, performance tests were conducted to verify the accuracy of the proposed mechanical model. Finally, numerical models of structures employing various applications of the IECD were established to conduct seismic response analysis. The results show that the proposed mechanical model effectively reflects the actual performance of the IECD. When used for energy dissipation and vibration reduction, the IECD demonstrates superior control performance in terms of displacement and velocity compared to the LVD, and the switch control strategy can address the issue of poor acceleration control performance. Combining the IECD with isolation bearings not only further reduces the seismic response of the superstructure but also enhances the safety of the isolation bearings, preventing excessive deformation.

The effect of soil conditions on the dynamic response of shield tunnels under train‐induced vibration loads

In this article, the influence of soil condition on the dynamic response of a tunnel and the surrounding soil was studied by both experimental model tests and numerical simulations. We tested a 1/20‐scale tunnel model with three different soil conditions: upper soft soil and lower hard soil, homogeneous soft soil and homogeneous hard soil. We also applied dynamic loads, sweep loads and train loads on the model tunnel for time domain and frequency domain analysis. The experimental and numerical results revealed that the interface between the soft and hard soil strata has an obvious amplification effect on the vibration wave. With the propagation of the vibration wave to the surface, the damping effect of the soil above the tunnel becomes the main factor affecting the dynamic response of soil. The internal force response of the tunnel structure is for the most part concentrated in the section under the excitation load, which is mainly affected by the soil properties beneath the tunnel.

Dynamic optimisation of virtual synchronous generator to enhance stability of power system

AbstractVirtual synchronous generators (VSGs) are essential for the high penetration of renewable energy sources. VSGs have virtual rotating inertia, a damping effect, and synchronising power such as actual SGs. Such features of VSGs offer a promising structure to improve the stability of power systems. VSGs are required to suppress power and system frequency oscillations. In addition, VSGs must operate within a current limit since they are vulnerable to the overcurrent, unlike actual SGs. The authors propose a novel dynamic and optimal VSG to enhance the frequency stability in power systems while guaranteeing the current limit. The proposed approach determines an optimal tuple of inertia and damping of VSG online and guarantees the current limit with the use of a circuit model. The effectiveness of the proposed method is demonstrated via experiments, comparing it with the conventional methods.

Spin-to-charge conversion via dual-mode ferromagnetic resonance in Ta/NiFe/FeMn/CoFeB multilayer

The precise engineering of microwave absorption frequencies is of paramount importance in the advancement of spintronic-based RF devices. In the pursuit of this objective, magnetic thin films demonstrate unrivaled efficacy in enabling external modulation of their microwave responses in a reconfigurable manner. Here, we demonstrate dual-frequency ferromagnetic resonance modes and corresponding spin-to-charge conversion efficiency in thin film structures comprising Ta/NiFe/FeMn/CoFeB multilayer. A systematic thickness variation of the NiFe layer (i.e., 4–20 nm) has been undertaken to elucidate the impact on both static and dynamic properties across the multilayer structure. The presence of two distinct magnetic layers manifests in the emergence of two-step magnetic hysteresis loops, which are incorporated with unique resonant modes. The separation between the resonant fields shows tunable properties with excitation frequencies, thereby offering a wide range of reconfigurable operating parameters. The effective damping parameter has shown a decrement with increasing thickness of the NiFe layers. The effective spin mixing conductance for the NiFe layer was found to be 7.4 ± 0.6 nm−2. The spin-to-charge conversion within these structures has been demonstrated through measurements of the inverse spin Hall effect. Systematic thickness variation revealed that the prominent voltage drop was observed in the NiFe layer compared to the CoFeB layer. Considering the opposite spin Hall angles of Ta and FeMn layer, the direction of the spin flow and spin-to-charge conversion efficiency are summarized.

Tower loads characteristics of a semi-submersible floating wind turbine: An experimental study

For a Floating Wind Turbine (FWT), the tower emerges as a critical structure that connecting the Rotor-Nacelle Assembly (RNA) and the supporting platform, facilitating the transmission of both aerodynamic and hydrodynamic loads. This paper deduces the distinct responses of the bending moment generated by the motion of a FWT compared with a fixed wind turbine. Due to the complexity of the tower load responses, a comprehensive experimental investigation was conducted on a semi-submersible FWT. Stiffness-matched and geometry-matched tower models were designed and fabricated. These models accurately simulate the tower's flexibility and windward areas, impacting the global dynamic response. The model test precisely replicates the marine environmental conditions, incorporating the interactions between wind, waves, and current. It is particularly worth noting that, a multi-fans large-scale Wind Generation System (WGS) with rectifier networks was improved and fabricated to provide a reliable wind field. Results indicate that the tower load responses under the conditions with wind exhibit distinct nP component characteristics. Notably, 1P and 3P responses dominate most tower load responses, with the 3P response typically increasing with wind speed. The extreme value of My.b (y-axis moment at tower-base) is approximately 10 times larger than that of My.t (y-axis moment at tower-top), signifying a significant magnitude difference and reflecting the response characteristics of the tower loads. And the responses of My.b and Fx.t (x-axis force at tower-top) at the natural frequency of pitch motion are notably suppressed by the aerodynamic damping effect of wind. Furthermore, Fx.b (x-axis force at tower-base) and My.b exhibit obvious responses at the natural frequency of pitch motion. As the wave height increases, the wave-frequency response of the tower base load also strengthens, but the high-frequency response still accounts for a certain proportion of energy in the tower top load.

Embedded periodically ABHs and distributed DVAs for passive low-frequency broadband vibration attenuation in thin-walled structures

The acoustic black hole (ABH) structure exhibits remarkable energy focalization above a given cut-on frequency, offering potential for broadband vibration suppression in structures. However, its energy focusing properties diminish significantly below this cut-on frequency. Therefore, it is crucial to enhance the vibration attenuation capabilities of ABH structures within the low frequency range. This study presents a numerical investigation into the impact of thin-walled structures with embedded ABHs and distributed dynamic vibration absorbers (DVAs) on low frequency broadband vibration reduction. Initially, the focusing characteristics of the ABH thin-walled structure is analyzed, aiding in the attached position of DVAs. Furthermore, the influence of the design parameters and attached position of DVA on the broadband damping effect of the structure is explored. The findings indicate that DVAs designed for low frequencies can achieve significant vibration attenuation across the entire frequency spectrum, including low frequencies, when installed at specific focusing positions. When compared to the position with the maximum vibration response, while the attenuation of the low frequency common amplitude value is slightly reduced, greater vibration attenuation across the entire frequency band is achieved. This research offers valuable insights into optimizing the integration of DVAs with ABHs in thin-walled structures for enhanced broadband vibration attenuation.

Low Gilbert damping in Bi/In-doped YIG thin films with giant Faraday effect

Abstract Magnetic films with low Gilbert damping are crucial for magnonic devices, which provide a promising platform for realizing ultralow-energy devices. In this study, low Gilbert damping and coercive field were observed in Bi/In-doped yttrium iron garnet (BiIn:YIG) thin films. The BiIn:YIG (444) films were deposited onto different substrates using pulsed laser deposition. Low coercivity (<1 Oe) with saturation magnetization of 125.09 emu/cc was achieved along the in-plane direction of BiIn:YIG film. The values of Gilbert damping and inhomogeneous broadening of ferromagnetic resonance in BiIn:YIG films were obtained to be as low as 4.05 × 10−4 and 5.62 Oe, respectively. In addition to low damping, the giant Faraday rotation angles (up to 2.9 × 104 deg/cm) were also observed in the BiIn:YIG film. By modifying the magnetic structure and coupling effect between Bi3+ and Fe3+ of Bi:YIG, doped In3+ plays a key role on variation of the magnetic properties. The low damping and giant Faraday effect made the BiIn:YIG film an appealing candidate for magnonic and magneto-optical devices.

Experimental, theoretical and optimization studies on multimode vibration reduction of floating raft system based on NES cells

Most of the studies on multimode vibration reduction of floating raft systems remain at the stage of theoretical analysis, while relevant experimental studies are rare. In this paper, an experimental setup for a scaled-down floating raft system is constructed. The vertical track nonlinear energy sink (TNES) cells are experimentally applied for the first time to suppress the multimode vibration of the floating raft system. To ensure the damping effect is not affected by additional mass, the TNES cells are always installed on the floating raft system. The TNES is able to achieve vibration suppression by allowing unrestricted movement of its vibrator. Two damping systems with different TNESs placement are proposed. Experimental modal analysis is performed on the floating raft structure to determine its response characteristics. Based on the results, different magnitudes of excitation force are applied to each order mode to effectively suppress the multimode vibration of the system. Meanwhile, the nonlinear system coupled with TNES cells is analyzed using the harmonic balance method (HBM) to obtain the approximate analytical solution. The system responses obtained from the analytical solution are compared with the experimental data results. The particle swarm optimization (PSO) algorithm is used to obtain the optimal parameters of the TNESs for vibration suppression. The results show that the multimodal vibration of the floating raft structure is effectively suppressed by the TNES cells in both experimental and theoretical analyses. The vibration suppression effect for all modes is significantly improved by the PSO algorithm. In conclusion, the research content of this paper provides a practical and feasible vibration suppression solution for the design of floating raft systems.

A State-of-the-Science Review of the Effect of Damp- and Mold-Affected Housing on Mental Health.

While it is well-established that exposure to dampness or mold in homes negatively affects physical health, the association with mental health remains less well evidenced. As plausible psychosocial and biological pathways exist between dampness and mold exposure and poor mental health, a review of evidence is required. This State-of-the-Science review sought to assess what is known about the mental health effects of dampness or mold exposure and identify gaps in the literature and priorities for further research. A comprehensive search of electronic databases (MEDLINE, Embase, PsycInfo, Global Health, Web of Science, and Scopus) was conducted to identify relevant studies published from 2003 to 2023. Eligible studies included observational study designs such as cohort and cross-sectional studies. Target studies for review assessed the effect of dampness and/or mold on mental health outcomes. Of the 1,169 records retrieved, 19 studies met the inclusion criteria. The available evidence described positive associations between residential dampness/mold exposure and poor mental health. In adults, associations were observed for outcomes such as depression, stress, and anxiety, while for children, associations were observed for emotional symptoms and emotional dysregulation. Identified studies generally reported associations between exposure to dampness/mold in the home and poorer mental and emotional health. Given the methodological limitations present in the current evidence base, it is recommended that more research be conducted. https://doi.org/10.1289/EHP14341.

Analyzing the effect of hydrodynamic damping on the wake behavior in circular blade cascades: numerical study on a global mode

Abstract In this study, a numerical investigation has been performed to extract and compare the hydrodynamic damping of a non-rotating system of eight planar hydrofoils, arranged in a radial configuration, with the related wake behaviour downstream the structure. A modal acoustic analysis has been performed on the structure in order to extract the global modes corresponding to Nodal Diameter 0. Using the deformation related to the global mode, the hydrodynamic damping has been extracted for different velocities, ranging from 2 to 14 m/s, by analyzing the work done on the structure from the fluid, following the so-called “flutter” method developed by ANSYS®. The related wake behaviour has been analyzed for each specific velocity and hydrodynamic damping conditions. This numerical study has been performed in ANSYS Mechanical® and CFX®. The results for the present geometry suggest that the primary factor governing vortex shedding frequency is the motion of the body itself, in the present case locked to the excitation frequency of the global structural mode (ND0). The study identifies a lock-in region around 10 m/s, consistent with empirical formulas. After the region of lock-in, the fluctuations of velocity and pressure values tend to converge, indicating a stabilization of the wake dynamics. The observed hydrodynamic damping trend exhibits a linear pattern preceding the lock-in region, succeeded by a steep rise thereafter. This pattern aligns with established literature, affirming its consistency with prior research findings. Overall, this numerical approach offers valuable insights into wake behavior and hydrodynamic damping value serving as a promising tool for preliminary estimation and analysis of oscillating systems in water flowing environments. Its low computational complexity and rapid completion time make it a viable alternative to more complex FSI simulations, facilitating comprehensive exploration of multiple flow scenarios within a reasonable time frame of weeks.

Effects of wave damping and finite perpendicular scale on three-dimensional Alfvén wave parametric decay in low-beta plasmas

Effects of wave damping and finite perpendicular scale on three-dimensional Alfvén wave parametric decay in low-beta plasmas

Conceptual study of an innovative friction damper for the seismic retrofit of precast RC structures with poor connections

Precast RC structures have been widely used in industrial and commercial buildings since the 60 s in the most developed areas. However, during those decades of economic growth, most buildings were constructed without seismic design criteria, accounting for gravity loads only. For this reason, this structural typology often faces a significant seismic risk in earthquake-prone areas due to the lack of effective connection between structural elements. As a result, the seismic retrofit of precast RC structures is essential to prolong their service life and mitigate seismic losses. The present work shows the conceptualisation study of an innovative seismic protection device called Bidirectional Rotational Friction Damper (BRFD) for precast RC structures that behave simultaneously as a beam-to-column joint and damper. This device unifies the concepts of rotational friction dampers and a movable plate system, producing a damping effect along two main directions. Furthermore, the device's ability to dissipate energy through friction enables it to remain undamaged during multiple seismic events while maintaining its damping capacity. After defining a simplified analytical model, to evaluate the influence of the BRFD on a structure's behaviour during a seismic event, a case study was conducted on a single-story, single-bay precast reinforced concrete structure made of plane parallel frames, i.e. that lacks secondary frames. Quasi-static and nonlinear time history analyses were performed to evaluate the BRFD efficacy in reducing seismic forces and displacements, and an importance analysis was carried out using a multi-criteria decision-making (MCDM) approach to identify the optimal configuration of the BRFD for the case study. The main results highlight that introducing the BRFD positively influences the dynamic performance of the structure, producing a significant reduction of interstorey drift and total base shear and preventing structural and non-structural damage.