Damping Values Research Articles

Role of SSW on thermal-gradient induced domain-wall dynamics

We study the thermal gradient (TG) induced domain wall (DW) dynamics in a uniaxial nanowire in the framework of the Stochastic-Landau–Lifshitz–Gilbert equation. TG drives the DW in a certain direction, and DW (linear and rotational) velocities increase with TG linearly, which can be explained by the magnonic angular momentum transfer to the DW. Interestingly, from Gilbert damping dependence of DW dynamics for fixed TG, we find that the DW velocity is significantly smaller even for lower damping, and DW velocity increases with damping (for a certain range of damping) and reaches a maximal value for critical damping which is contrary to our usual desire. This can be attributed to the formation of standing spin wave (SSW) modes (from the superposition of the spin waves and their reflection) together with travelling spin wave (TSW) modes. SSW does not carry any net energy/momentum to the DW, while TSW does. Damping α compels the spin current polarization to align with the local spin, which reduces the magnon propagation length and thus α hinders to generate SSWs, and contrarily the number of TSWs increases, which leads to the increment of DW speed with damping. For a similar reason, we observe that DW velocity increases with nanowire length and becomes saturated to maximal value for a certain length. Therefore, these findings may enhance the fundamental understanding as well as provide a way of utilizing the Joule heat in the spintronics (e.g. racetrack memory) devices.

Frequency and damping of hybrid cable networks with cross-ties and external dampers: Full-scale experiments

This paper presents a full-scale experimental study on dynamics of hybrid cable networks composed of three real cables, a rigid cross-tie and three viscous-shear dampers. For comparison, an improved numerical model of cable networks considering cross-ties, dampers, and cross-tie pretension is also provided. The measured frequencies and mode shapes of the cable networks with different configurations and cross-tie locations are found in good agreement with corresponding theoretical predictions. The characteristics of damping variation with respect to cross-tie location and the layout observed from the experiments are generally consistent with the theoretical analysis, although there is a discrepancy between identified and computed values of damping. The experiments show that the cross-tie when located close to the dampers can lead to a reduction in modal damping of low-frequency modes. The dampers in the cable networks provide relatively large damping to global modes and modes dominated by vibrations of cable segments to which the damper is connected. Furthermore, when the cross-tie is installed far away from the external dampers, the cross-tie extended to the ground can effectively improve the system modal damping, as the length of the cable is reduced equivalently and the relative distance of the damper away from the closest anchor as compared to the cable length is increased.

The ultrahigh damping capacity of Mg-Sn-Y alloy

High temperature heat treatment Mg-0.69Sn-0.69Y alloy showed a high damping capacity (the damping value is 0.201 at ε=1 × 10−3) and a very low critical strain amplitude at room temperature (εcr1=2.97 × 10−5), which can be attributed to the co-effects of purified matrix phase and interfaces of subgrains. The substructure is unstable and the damping capacity decreases with the increasing temperature.

Frequency independent damped outrigger systems for multi‐mode seismic control of super tall buildings with frequency independent negative stiffness enhancement

AbstractDamped outrigger system is effective for improving energy dissipation for tall buildings. However, conventional damped outrigger (CDO) system with viscous damping has two limitations: (i) its maximum damping ratio cannot be improved when outrigger/column stiffness is inadequate; (ii) different modes achieve their maximum damping ratios at different outrigger damping values, and thus the dampers cannot be optimized to simultaneously reduce vibrations of multiple modes of concern to their minimum. In this paper, a purely frequency‐independent negative stiffness damped outrigger (FI‐NSDO) system is proposed by combining frequency‐independent damper (FID) and negative stiffness device (NSD). The damped outrigger with FID can achieve the maximum damping ratio for all modes as compared to frequency‐dependent damper like viscous damper. As the NSD has the features of assisting and enhancing motion and frequency‐independence, the utilization of NSD will considerably improve the maximum damping ratios when outrigger/column stiffness is inadequate and maintain the frequency‐independent feature of the whole system. Therefore, the FI‐NSDO has the capability of simultaneously increasing the damping ratios of all target modes to their maximum values. Analysis in frequency domain and time domain, demonstrate that the proposed FI‐NSDO performs better in controlling the multi‐mode vibration of seismic responses.

Sandwich designs for high levels of noise and vibrations

Lightweight materials with high structural damping and reasonably well flexural performance are demanded in some components of aerial vehicles such as interior part of helicopters where high levels of noise and vibrations exist. One of the best choices for this is through the use of a polymer matrix composite with suitable fiber orientations and a structural foam core. In this study, face sheets from a woven carbon fiber reinforced polymer plies and a foam core with three different thicknesses (10.7 mm, 25.4 mm, and 49.8 mm) have been used to manufacture sandwich structures to yield high dynamic values (damping and flexural rigidity). To measure these values, the sandwich beams with free-free boundary conditions were subjected to free vibration tests using a non-contact response measuring system. The measurements were made for the first, second and third natural frequencies, and compared to numerical modal analysis via the ANSYS package program. The results from experimental and numerical methods are found to be reasonably good in agreement and show that the sandwich structures are able to give high damping values, in general. It seems the specimens with relatively low thickness give relatively high damping values compared to the others, whereas the thicker ones are useful for high frequency domains and flexural rigidity. The behaviors of the beams have been found frequency dependent, due to the viscoelastic behavior of the foam cores at high frequency levels.

Inertia changes evolution of motility-induced phase separation in active matter across particle activity.

The effects of inertia in active matter and motility-induced phase separation (MIPS) have attracted growing interest but still remain poorly studied. We studied MIPS behavior in the Langevin dynamics across a broad range of particle activity and damping rate values with molecular dynamic simulations. Here we show that the MIPS stability region across particle activity values consists of several domains separated by discontinuous or sharp changes in susceptibility of mean kinetic energy. These domain boundaries have fingerprints in the system's kinetic energy fluctuations and characteristics of gas, liquid, and solid subphases, such as the number of particles, densities, or the power of energy release due to activity. The observed domain cascade is most stable at intermediate damping rates but loses its distinctness in the Brownian limit or vanishes along with phase separation at lower damping values.

General Discretization Method for Enhanced Kinesthetic Haptic Stability.

The stability of haptic simulation systems has been studied for a safer interaction with virtual environments. In this work, the passivity, uncoupled stability, and fidelity of such systems are analyzed when a viscoelastic virtual environment is implemented using a general discretization method that can also represent methods such as backward difference, Tustin, and zero-order-hold. Dimensionless parametrization and rational delay are considered for device independent analysis. Aiming at expanding the virtual environment dynamic range, equationsto find optimum damping values for maximize stiffness are derived and it is shown that by tuning the parameters for a customized discretization method, the virtual environment dynamic range will supersede the ranges offered by methods such as backward difference, Tustin and zero-order-hold. It is also shown that minimum time delay is required for stable Tustin implementation and that specific delay ranges must be avoided. The proposed discretization method is numerically and experimentally evaluated.

Mechanism of phase structure modulating damping in Fe73Ga27 alloy

The magnetostriction and damping performance of Fe–Ga alloy are closely related to the phase structure. In this paper, the phase structure of Fe73Ga27 alloy was regulated by homogenization + aging treatment. The results show that the Fe73Ga27 alloy with modified-D03 phase has higher damping performance at lower amplitudes, and the damping peak is nearly 1.3 times that of only solution-treated alloy. The modified-D03 phase with tetragonal structure leads to local tetragonal distortion of the matrix, which enhances the magnetostriction and magneto-mechanical damping. In addition, the presence of the modified-D03 phase also increases the sensitivity of the alloy to stress. The Fe73Ga27 alloy with L12 phase as the main phase has higher damping performance at higher amplitudes. When the amplitude is higher than 3 × 10−4, the damping value is more than 1.6 times that of only solution-treated alloy. The mismatch between the L12 phase and matrix with body-centered cubic structure greatly improves the nonmagnetic damping. The strain mismatch between the L12 phase and the matrix causes interfacial sliding under load to provide interfacial damping. The high-density dislocation due to the thermal mismatch effect enhances dislocation damping.

Natural Frequencies of a Viscoelastic Supported Axially Functionally Graded Bar With Tip Masses

The frequency parameters of an Axially Functionally Graded (AFG) bar for viscoelastic and point mass boundary conditions are studied in this paper. The structures with functionally graded materials under axial loads can be modelled as AFG bars. Those may be considered as support elements with spring and dashpot in the vibration isolation. Keeping the ratio of force frequency and natural frequency at a certain level is ensured to control the natural frequency therefore dynamic amplification factor with different material combinations. Various boundary conditions are attained by changing the spring and damping coefficients of viscoelastic support elements and the ratio of rod mass to tip mass. Researchers assume that the beam material properties in directions of length and thickness change exponentially, individually, or both in their studies. There are a few studies on the AFG rods in the existing studies. Analysis is carried out via the finite element method for the non-dimensional frequency parameters of the bar in MATLAB. The energy equations of the motion are obtained in the frame of axial bar theory considering the material properties of the bar vary longitudinally according to the power-law distribution. The effects of material distribution, spring, damping and tip mass values on the bar's frequency parameters and structural behaviour have been extensively investigated.

Synergistic enhancement in mechanical and damping properties of Cu–11Al–5Mn-0.7Ti–1Ta alloy through aging treatment

In this work, the aging temperature effects on microstructures, mechanical, and damping properties of Cu–11Al–5Mn-0.7Ti–1Ta were investigated. The outcomes indicated aging can effectively enhance both mechanical and damping properties, and the optimum aging temperature of 400 °C was obtained. The associated microstructural changes caused by the precipitated phase after aging resulted in an increase in tensile strength from 386.1 MPa to 631.5 MPa, an increase of 63.5% compared to the original alloy. Meanwhile, the room temperature damping value increased from 0.026 to 0.0581, which was increased by 123.5%. The damping strengthening mechanisms were discussed mainly from the perspective of the change in motionable interface and dislocation behavior induced by precipitated phase after aging treatment. The results in this paper provide a new reference for simultaneously improving mechanical and damping behaviors of Cu–Al–Mn based alloys.

Modelling and stability analysis of a high-speed train braking system

The stability of a braking system is crucial for the steady and safe operation of trains. To investigate the dynamic behaviors and stability of a train braking system as influenced by key parameters, a numerical model integrating mode-coupling, negative friction–velocity slope (NFVS), and stick–slip theories was established. Additionally, the wheelset connected with the braking system was contained in the model considering that mode-coupling and stick–slip characteristics were affected by system structures. Based on this model, the influence and mechanism of stiffness, damping, and NFVS characteristics on mode-coupling of the braking system were revealed. The results showed that when the tangential and normal contact stiffness values of the pad were close, the system experienced mode-coupling instability and vibrations in these two directions were coupled. When the tangential and normal damping values of the pad were unequal, the energy dissipation in the two directions became different and the system instability was enhanced. Additionally, the system complex eigenvalues always had positive real parts and the dynamic behaviors were more complicated by considering NFVS at relatively low speeds. This is because NFVS characteristics can be equivalent to negative damping values, which cause the difference in tangential and normal damping values and continuously input energy into the braking system, then weakening the system stability.

Tailoring good combinations among strength, ductility and damping capacity in a novel Mg-1.5Gd–1Zn damping alloy via hot extrusion

Magnesium alloys with excellent comprehensive properties need to be developed due to the urgent demand in vibration and noise reduction or elimination fields. Herein, a novel high damping Mg-1.5Gd–1Zn alloy that exhibits strength and ductility similar to or even better than those of previously reported low-alloyed high-performance Mg-Gd-Zn alloys is developed by traditional hot extrusion. The specific results show that the good performance combinations of the as-extruded alloys are 314/211/145 MPa for the tensile yield strength (TYS), 21.0%/31.0%/33.0% for the elongation (EL) and 0.017/0.02/0.023 (at strain amplitude ε = 10−3) for the damping value Q−1 at room temperature. In addition, the damping curves for the tested as-extruded alloys exhibit three or two internal friction (IF) peaks during the elevated temperature damping test. Therefore, the resulting microstructures are systematically characterized in the as-extruded alloys. Meanwhile, the damping capacity and its mechanism are thoroughly analyzed and discussed. The alloy combines strength, ductility and damping capacity well, demonstrating its practicability in the reduction or elimination of noise and vibrations.

Effect of DFIG control parameters on small signal stability in power systems

The doubly-fed induction generator (DFIG) with virtual inertia control and reactive damping control gives a renewable energy generation system inertia and damping characteristics similar to those of a thermal power plant, and the parameters of the control strategy have a direct impact on the small-signal stability of the system. This paper firstly introduces the operating characteristics and control strategies of DFIG-based damping control and virtual inertia control, establishes a small-signal model of the control-based DFIG integrated interconnected system, and investigates the effects of virtual inertia and reactive damping values on the small-signal stability of the system; then, the maximum damping ratio of the interval oscillation mode in small disturbance analysis is taken as the optimization objective, and the control parameters are the optimization variables. An optimization method of inertia and damping parameters is established for improving the small disturbance stability of the system. The results show that the optimization procedure could improve the damping ratio of the interval oscillation mode while ensuring the system frequency. The effects of virtual inertia and reactive damping values on the small signal stability of the system are investigated, and an optimal allocation model and method for virtual inertia used to improve the small disturbance stability of the system is proposed.

Towards minimal empirical uncertainty bounds of damping estimates of an offshore wind turbine in idling conditions

Structural damping is a critical quantity for condition assessment and fatigue lifetime prediction in wind energy. Its estimation from operational vibration data comes with a considerable amount of uncertainty, derived from environmental and operational variability and from the quality of the estimation process itself. In this paper, we aim to determine experimentally the damping values and their least possible uncertainty bounds for the first two modes of an idling offshore wind turbine. For this purpose, we use field measurements from a 3.6 MW offshore wind turbine located at the DanTysk wind farm. We select a subset of cases from the wind turbine on idling conditions for a confined interval of environmental and operational conditions, in an attempt to minimize operational variability in the damping estimates. In addition, we make a study on the adjustment parameters of the automated operational modal analysis method, aiming at obtaining the most consistent damping estimates. As a result of the proposed methodology, it is possible to confine the 90% confidence intervals of the damping ratio estimates of the first two tower modes within 0.8 and 1.1 percentual points in the fore-aft and the side-to-side direction, respectively.

An investigation of dynamic vehicle-bridge interaction effects based on a comprehensive set of trains and bridges

The consideration of interaction effects between vehicle and structure is an important aspect in the dynamic analysis of railway bridges. They usually lead to a reduction of the structural responses compared to computations without consideration of the vehicle-bridge interaction. The interaction effects can either be accounted for by Finite Element analysis including multi-body models of the vehicles or in a simplified way – as adopted by the actual regulations – by artificially increasing the bridge damping. In this way, a simplified dynamic analysis under consideration of the interaction effects is possible using the moving load model.However, several studies have shown that the current approach of the additional damping included in Eurocode 1 is non-conservative in many cases, possibly leading to an underestimation of the structural responses. The approach in Eurocode 1 as well as the more recently proposed approaches were based on a limited number of combinations of trains and bridges. In order to verify these approaches in a more thorough way, the present paper investigates the vehicle-bridge interaction effects based on 25 real high-speed passenger trains (including conventional and articulated trains) and over 100 single-span bridges with spans ranging from 5m to 55m.A typical criterion of analyzing the vehicle-bridge interaction phenomenon is the reduction of the structural acceleration computed using a 2D multi-body representation of the vehicle compared to the simplified moving load approach. Therefore, the reduction of the acceleration due to the interaction is discussed in detail and put in relation to the results of previous research. The results of over 800 000dynamic analyses performed in the present study confirm that the additional damping approach depending on the bridge span as included in Eurocode 1 overestimates the actual vehicle-bridge interaction effects. Furthermore, the results show that recent additional damping approaches depending on bridge and train characteristics lead to more reliable additional damping values. Their application requires public availability of train characteristics and an extension of the approaches for articulated as well as heterogeneous trains.

The influence of adhesive materials on the transverse vibrations of single lap joints: an experimental study

ABSTRACT In the past decades, an increasing trend towards the structural combination of lightweight materials and traditional metals has been observed. For these multi-material interfaces, traditional joining technologies such as bolting and welding have to be re-thought and adhesive bonds can be a valid alternative. The substitution of the joints has an impact on the stiffness, damping, and mass distribution of the entire assembly and should be taken into account while designing for NVH, durability, and performance. The aim of this work is to experimentally compare the effect of bolts and adhesive bonding on the vibrational response of the assembly, in terms of modal frequency, shape, and damping. Plate-to-plate single lap joints are tested under transverse vibration. In particular, we compare one M4 bolted connection and three adhesive connections, respectively, realized with stiff epoxy, flexible foam tape, and toughened acrylic. Results show that, in a low-mid frequency region between 0 and 250 Hz, the substitution of bolts with adhesives has a limited influence on mode shapes but can lead up to a 6-fold increase of the modal damping values and 10% increase of the modal frequencies.

Anisotropic Damping and Stiffness of laminated steel parts using adhesive bonding – an empirical influence study

Layered part manufacturing enables part topology to be optimized internally by structuring individual layers separately, which is especially promising for large machine parts. However, the resulting part properties as a function of the selected manufacturing parameters are largely unexplored. Therefore, this paper investigates the impacts of the slicing direction, the sheet thickness as well as the adhesive on anisotropic damping and stiffness values of adhesively bonded steel parts. A cantilever beam of symmetric cross-section is chosen as an easy-to-manufacture geometry. Three redundant specimens were prepared for each of six parameter variations investigated within this study, resulting in a total of 18 investigated beams. The results indicate highly anisotropic stiffness and damping as a function of the layer build-up direction and it was found that the modal damping rises with increasing amount of adhesive. These findings must be taken into account for future applications of layered lightweight machine parts and their simulative predictability should be studied.

Analysis of tuned mass damper effect on vibration control over tall building in seismic prone areas – A state-of-art review

Vibrations are one of the main environmental elements that influence buildings and mechanical structures, potentially shortening their lifespan. Taller, lighter, more flexible structures are required by current trends in the construction sector, yet they have relatively low damping values. This raises the likelihood of failure and causes issues with serviceability. If the frequency of excitation coincides with one of the inherent frequencies of the system, many building structures and bridges will collapse due to vibration. Today, a variety of techniques are available to reduce a structure's vibrations. One of these is the idea of using a tuned mass damper, which has become popular recently. In this paper a study has been investigated which is on the behaviour of tall building when it is equipped with Tuned Mass Damper. It is observed that buildings with Tuned Mass Damper are more resistant to seismic vibrations compared to the buildings without Tuned Mass Dampers.

Performance-Based Design of an Irregular RC Structure with and without Supplemental Damping

Many countries are undertaking changes in earthquake design codes, the main reason for it is that the existing building codes do not specify the performance criteria of individual structural elements under various levels of shaking. Even though some buildings performed well in life safety aspects, many of those failed in safeguarding the building from high extent of structural damage under severe shaking. Retrofitting had also proved to be uneconomical for the buildings to perform better under severe shaking. In the current earthquake codes, the displacements and forces are within the elastic limit i.e., the assumed behaviour is linear. But the response of a structure to the major earthquakes is not elastic. There is a high chance of yielding and the development of plastic hinges in the members. Therefore, it is required to perform the non-linear analysis for assessing the inelastic behaviour of the structure. In the present study non-linear static analysis was adopted to assess the seismic performance of an irregular building in plan with re-entrant corners using the capacity spectrum method. If either the drift limit of the structure or the response of the hinges is exceeding the desired level of performance, the structure is fed with supplemental damping to ensure the required performance. It was observed that the formation of hinges crossed life safety level and entered the collapse prevention state. As the response exceeded the desired level of performance a methodology to calculate the required supplemental damping for the structure is proposed. Depending on the level of safety of the structure, an appropriate supplemental damping value can be obtained from the proposed performance plots.

Elevated damping properties of lead-free solders under electric current stressing

Effects of electric current stressing on damping properties of pure Sn, Sn0.7Cu, Sn3.5Ag, and Sn0.3Ag0.7Cu were investigated by dynamic mechanical analysis. The results show that the critical strain of the four solders decreased, the strain-amplitude-related damping value and the damping properties increased with increasing current. Meanwhile, the internal friction peak shifted to high temperature with the increase in frequency under the same current. Under the same current and frequency, the damping properties and the internal friction peak offset of pure Sn were largest, and those of Sn0.3Ag0.7Cu were smallest. The elevated damping properties of solders under current stressing can be explained by the Granato-Lücke (G-L) model. The above findings should be inspiring on material optimization and selection as well as reliability evaluation in the service condition of current stressing not only in electric packaging but also in other areas.