Total Damping Research Articles

Application of viscoelastic dampers for reducing dynamic response of high-speed railway bridges

AbstractDue to the extensive development of high-speed railway lines which are operating at increasing velocities, the dynamic performance of railway bridges has become an important issue of scientific research. The aim of this study is to investigate the possibility of reducing the vertical acceleration and displacement of pre-stressed reinforced concrete bridges beams by using passive nonlinear viscoelastic dampers to retrofit them. The proposed solution is based on connecting the dampers directly to the abutments and the bottom surface of the bridge deck with an eccentricity between the neutral axis of the bridge and the contact point of the viscoelastic dampers. First, the dampers are modeled through the concept of linearized fractional derivatives to obtain energetic equivalent linear viscoelastic dampers. Optimization of the configuration of these dampers was performed then as function of the orientation angle and the eccentricity. Considering two bridges having different length that were studied in the literature with other systems of damping, it was found that the best orientation angle of dampers is close to 60°. It was found also that, in order to satisfy Eurocode 1 requirements, the total equivalent damping coefficient for the actual damping system is less than half of that required for systems using auxiliary beam to fix dampers, which indicates higher efficiency of the proposed solution.

Hysteresis response of nonlinear flutter of a truss girder: Experimental investigations and theoretical predictions

Nonlinear flutter response with hysteresis loop characteristics is a special aerodynamic instability phenomenon, and is of great importance and of practical interest to long span bridge designs. This paper presents a comprehensive study on nonlinear flutter of a bridge deck that has hysteresis loop characteristics over a range of wind speeds close to the flutter onset speed, using a section model wind tunnel test and theoretical analyses. The evolutions of the hysteresis loop in both the single degree of freedom (SDOF) system in torsion and the 2 degrees of freedom (2DOF) system in the vertical direction and in torsion are studied. The formation mechanism of the hysteresis loop is discussed using the equivalent total damping as a function of vibration amplitude. Two nonlinear mathematical models for the SDOF and the 2DOF systems are proposed to predict the nonlinear flutter responses, in which both the structural and aerodynamic damping are expressed as functions of time-varying displacements. An approach is proposed to identify the aerodynamic parameters based on the displacement time histories using a harmonic balancing technique. Using the identified aerodynamic parameters, a distinct dynamic system with the same section was used to validate the accuracy of the proposed models.

Design principles for coupled piezoelectric and electromagnetic hybrid energy harvesters for autonomous sensor systems

Abstract Despite the many studies reporting mW-level power output from various hybridized energy harvesters, few succeeded in demonstrating real-life applications such as the commercial Internet of Things (IoT) sensor modules. This owes in large part to the limited time-averaged power output, especially under the requirement for the power-consuming circuitry such as rectifiers and AC to DC converters. At the heart of the limited power lies the lack of detailed analyses and optimization strategies to hybridizing two or more distinct energy harvesters. Here, we first develop design guidelines and optimization strategies based on a parametric model for hybridized energy harvesters coupling two or more distinct mechanisms. The model treats electric current-generating energy harvesters as electric dampers in the spring-mass-damper system and seeks to minimize the total damping consisting of electrical and mechanical damping. We then demonstrate the design guidelines to an oval-shaped hybrid energy harvester consisting of piezoelectric and electromagnetic generators, achieving the time-averaged power output of 25.45 mW at 60 Hz and 0.5 G input vibration. Also, the detailed analyses reveal that the two coupled generators operate in a complementary manner, maintaining a reasonable power output even when one generator suddenly degrades or fails. We finally demonstrate powering a commercial IoT sensor module with the hybrid energy harvester, receiving the sensed information to a smartphone via Bluetooth connectivity.

Effect of countermeasures on the galloping instability of a long-span suspension footbridge

The aeroelastic stability of a long-span suspension footbridge with a bluff deck (prototype section) was examined through static and dynamic wind tunnel tests using a 1:10 scale sectional model of the main girder, and the corresponding aerodynamic countermeasures were proposed in order to improve the stability. First, dynamic tests of the prototype sectional model in vertical and torsional motions were carried out at three attack angles (α= 3°, 0°, -3°). The results show that the galloping instability of the sectional model occurs at α = 3° and 0°, an observation that has never been made before. Then, the various aerodynamic countermeasures were examined through the dynamic model tests. It was found that the openings set on the vertical web of the prototype section (web-opening section) mitigate the galloping completely for all three attack angles. Finally, static tests of both the prototype and web-opening sectional models were performed to obtain the aerodynamic coefficients, which were further used to investigate the galloping mechanism by applying the Den Hartog criterion. The total damping of the prototype and web-opening models were obtained with consideration of the structural and aerodynamic damping. The total damping of the prototype model was negative for α = 0° to 7°, with the minimum value being -1.07%, suggesting the occurrence of galloping, while that of the web-opening model was positive for all investigated attack angles of α = -12° to 12°.

System Parameter Optimization for a Frequency-Up-Conversion Piezoelectric Energy Harvester With Backward Mechanical-Electric Coupling Effect

Abstract In this work, a parametric model for a frequency-up-conversion piezoelectric energy harvester (PEH) was developed based on the Galerkin method. The PEH is composed of a piezoelectric bimorph and a stopper, which was subjected to a harmonic excitation. Although backward coupling results in a structure dynamic damping, models with neglected backward coupling were often adopted to estimate the output power of a piezoelectric energy harvester. The purpose of this work is to examine the effect of backward coupling on the dynamic response and the output power generation for a frequency-up-conversion PEH. With the same base excitations, we compared the dynamics and output energies of two cases: (1) neglecting the backward coupling effect (BCE) in the model and (2) including the BCE in the model. To obtain the optimum gap with maximum output power, we studied the relationship between the output power and the gap of the steady-state solutions. From the analytical results, it was found that the BCE can be neglected as long as there is no impact or the output power is small. However, once impacts get involved, the piezoelectric backward effect dominates the total damping due to small mechanical damping which is true for most PEH. The backward coupling will significantly diminish both the vibration and output power. Therefore, if the BCE is neglected in an impact-driven frequency-up-conversion PEH, the simplified model will exaggerate the output power.

Soft contribution to the damping rate of a hard photon in a weakly magnetized hot medium

We consider weakly magnetized hot QED plasma comprising electrons and positrons. There are three distinct dispersive (longitudinal and two transverse) modes of a photon in a thermo-magnetic medium. At lowest order in coupling constant, photon is damped in this medium via Compton scattering and pair creation process. We evaluate the damping rate of hard photon by calculating the imaginary part of the each transverse dispersive modes in a thermo-magnetic QED medium. We note that one of the fermions in the loop of one-loop photon self-energy is considered as soft and the other one is hard. Considering the resummed fermion propagator in a weakly magnetized medium for the soft fermion and the Schwinger propagator for hard fermion, we calculate the soft contribution to the damping rate of hard photon. In weak field approximation the thermal and thermo-magnetic contributions to damping rate get separated out for each transverse dispersive mode. The total damping rate for each dispersive mode in presence of magnetic field is found to be reduced than that of the thermal one. This formalism can easily be extended to QCD plasma.

Investigation of chatter stability of cutting process with a rotating tapered cutter bar considering internal and external damping

The damping of cutting system is an important factor influencing stability in boring and milling process. However, systematical and thorough studies of the influencing mechanism of damping, especially on the chatter stability of rotating cutter bar, are still absent. The damping of a cutting system mainly consists of external damping and internal damping. This study focuses on these damping effects on chatter stability of the cutting system with a rotating tapered cutter bar. The partial differential equation of motion of the cutter bar is derived based on the Hamilton principle combined with the Euler-Bernoulli beam theory. It is assumed that the cutter bar is tapered, and its free ends acts on a two-dimensional regenerative cutting force with time-delay effect. The damping mechanisms of external and internal are described by the viscous damping model and the strain-rate-dependent Kelvin-Voigt model, respectively. The partial differential equation of motion is discretized as an ordinary differential equation using the Galerkin method. The Campbell diagram and the decay rate plots including critical rotating speed and instability threshold of the cutter bar are obtained by free vibration analysis. Also, the chatter stability lobes in the cutting process are plotted and the predicted results of stability in frequency domain are compared with those in time domain. The results indicate that the structural parameters of a cutter bar, including the rotation, the ratio of internal and total damping, damping ratio, and taper and aspect ratios have significant effects on cutter bar dynamics and chatter stability of cutting process. In particular, a new chatter instability is observed for the cutting system in higher rotating speed ranges due to the effects of rotation and internal damping. The onset rotating speed of the new chatter instability equals to the instability threshold of rotor system of cutter bar. Finally, the present model is validated by comparing both stability prediction given by previous study and natural frequencies and decay rates by ANSYS FE code.

Infrared plasmonics: STEM-EELS characterization of Fabry-Pérot resonance damping in gold nanowires

Materials possessing strong midinfrared responses are of current interest because of their potential application to long-wavelength metamaterials, photonic devices, molecular detection, and catalysis. Here, we utilize high-energy resolution (80 ${\mathrm{cm}}^{\ensuremath{-}1}$, 10 meV) electron-energy-loss spectroscopy (EELS) in a monochromated and aberration-corrected scanning transmission electron microscope (STEM) to resolve multipolar surface plasmon resonances (SPRs), sometimes called Fabry-P\'erot (FP) resonances, in gold nanowires with mode energies spanning from $\ensuremath{\sim}1000$ to $8000\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. STEM-EELS provides access to these mid- to near-IR responses in a single acquisition, avoiding the difficulties inherent in obtaining the same data using near-field optical techniques. The experimentally measured FP resonance energies and linewidths, together with analytical modeling and full-wave numerical electrodynamics simulations, provide a comprehensive picture of the radiative and intrinsic contributions to the total damping rates. We find some FP modes with dephasing times $g60\phantom{\rule{0.16em}{0ex}}\mathrm{fs}$, which is almost twice the longest previously reported plasmon dephasing time for individual Au nanoparticles in the infrared. The long dephasing times and the broad tunability of the FP resonance energies throughout the infrared region suggest additional opportunities for harnessing infrared plasmonic energy before dephasing occurs.

Optimization Damping of Viscous Dampers to Prevent Collisions Between Adjacent Structures with Unequal Heights as a Case Study

Currently, construction is very dense especially in city centers, and adjacent structures are generally preferred in areas where available land is scarce. These structures often have different heights and are generally constructed without a structural connection to each other. Since adjacent structures may have different dynamic characteristics, collisions may occur when the structures contact each other under earthquake effects. Therefore, this study investigated the optimum values of viscous dampers placed between adjacent structures of unequal height to prevent collisions under different earthquake effects. In the optimization problem determined, the objective function was selected to minimize the total damping coefficient of viscous dampers added to the stories. A new algorithm utilizing numerical optimization methods to find the values of dampers between the structures was introduced to avoid collisions between adjacent structures of different heights. Structural models were used to examine the effects of variations in the height ratios of the structures, the value of damping from the viscous dampers on each floor, the vibration mode of the structures and the values of relative displacement. The proposed method showed that when viscous dampers were optimally placed between adjacent buildings of different heights, the relative displacements under earthquake impacts could be reduced below a target value, thereby avoiding the risk of collisions.

Estimation of damping induced by taut mooring lines

A moored floating structure may exhibit resonant motion responses to low-frequency excitations. Similar to the resonant responses of many vibration systems, the motion amplitude of a moored floating structure is significantly affected by the damping of the entire system. In such cases, the damping contributed by the mooring lines sometimes accounts for as much as 80% of the total damping. While the damping induced by catenary mooring lines is well-investigated, few studies have been conducted on the damping induced by taut mooring lines, especially one partly embedded in soil. The present study develops a simple but accurate model for estimating the damping contributed by mooring lines. A typical type of taut mooring line was used as the reference and the hydrodynamic drag force and soil resistance were taken into consideration. The proposed model was validated by comparing its predictions with those of a previously developed model and experimental measurements obtained by a physical model. Case studies and sensitivity studies were also conducted using the validated model. The damping induced by the soil resistance was found to be considerably smaller than the hydrodynamic damping. The superposition of the wave frequency motion on the low-frequency motion was also observed to significantly amplify the damping induced by the mooring lines.

Verification of an energetic-electron-driven β -induced Alfvén eigenmode in the HL-2A tokamak

An energetic-electron-driven β-induced Alfvén eigenmode (e-BAE) in an HL-2A tokamak experiment (discharge #17461) was studied using a gyrokinetic particle simulation code. Investigations of e-BAEs excited by an initial perturbation, an external antenna, and an energetic-electron pressure gradient were performed, and the measured eigenfrequencies were found to be close to the experimental observations and the theoretical predictions. The damping mechanism is also discussed based on the simulation results. The e-BAE becomes unstable when the driving force of the energetic-electron pressure gradient exceeds the total background damping. Simulations show that the e-BAE propagates along the diamagnetic direction of the energetic electrons and that the most unstable mode number is n∕m = 1∕3; these findings are in good agreement with the experimental observations. The simulation results also show that the mode is radially localized near the rational surface. Both the mode width and growth rate increase as the background plasma density increases. As the density and temperature of the energetic electrons increase, the eigenfrequency increases slightly, and the growth rate increases considerably.

Virtual Loudspeaker Effect of Graphene-Based Hybrid Material To Improve Low-Frequency Acoustic Performance.

Closed-box loudspeaker systems (CBLSSs) are compact and simple air-suspension loudspeaker systems, and their low-frequency responses are determined by two fundamental parameters: resonance frequency and total damping. Recently, electronic devices have come to require more compact designs, so the volumes of loudspeaker should be reduced. However, a small loudspeaker cannot retain sufficient acoustic space, resulting in poor low-frequency acoustic performance. Herein, we investigated acoustic characterization of the CBLSS with different filling materials such as thermally expanded graphene oxide (TEGO), activated carbon, graphene platelets, and melamine foam (MF). Upon the powder-based test, the resonance frequency of the loudspeaker decreased and resulted in a volume increasing effect inside of the loudspeaker. The TEGO shows almost double volume increase rate, compared to other particle-based filling materials. Employing hybrid filling material that consists of TEGO in an MF cage (TEGO@MF), the volume increase rate of the novel loudspeaker was over 24% at 300 cc. Because of the high adsorptive characteristics and thermal properties of TEGO, the acoustic performance in the low-frequency domain was clearly enhanced, despite the reduced mass loading. Furthermore, these properties were observed to be highly effective for enhancing the low-frequency acoustic performance of the larger loudspeaker, achieving a volume increase rate of 49.5% in a 700 cc enclosure.

Fast control of dissipation in a superconducting resonator

We report on fast tunability of an electromagnetic environment coupled to a superconducting coplanar waveguide resonator. Namely, we utilize a recently developed quantum-circuit refrigerator (QCR) to experimentally demonstrate a dynamic tunability in the total damping rate of the resonator up to almost two orders of magnitude. Based on the theory, it corresponds to a change in the internal damping rate by nearly four orders of magnitude. The control of the QCR is fully electrical, with the shortest implemented operation times in the range of 10 ns. This experiment constitutes a fast active reset of a superconducting quantum circuit. In the future, a similar scheme can potentially be used to initialize superconducting quantum bits.

Optimal DDBD procedure for designing steel structures with nonlinear fluid viscous dampers

This paper presents an optimal direct displacement-based design (DDBD) procedure for designing steel moment-resisting frames equipped with nonlinear fluid viscous dampers (FVDs). The design method is based on defining an optimization problem to determine the optimal distribution of FVDs along the height of the structure to achieve a desired added damping ratio by FVDs with the minimization of total damping coefficient of dampers. The optimization problem is solved using the distributed genetic algorithm (DGA) to determine the damping coefficient of each FVD. For numerical illustration, the proposed optimal DDBD procedure has been used to design four moment-resisting steel frames of 4, 8, 12, and 20-storey equipped with linear and nonlinear FVDs. The effectiveness of the proposed method has then been evaluated by performing nonlinear time history analysis on the considered frames under 20 earthquake records. Moreover, the effect of the displacement profile on the efficiency of the proposed design method has been discussed. The results of extensive numerical simulations show that using the proposed method for optimal distribution of the dampers in DDBD procedure has been considerably effective in reducing the total damping coefficient and maximum force of the dampers while satisfying the expected performance criteria. It has also been found that designing nonlinear FVDs based on the proposed optimal DDBD method have resulted in a significant reduction in the maximum damper force compared to linear FVDs.

Impact of two-close-frequency heating on ECR ion source plasma radio emission and stability

Experiments have recently demonstrated that kinetic instabilities occurring in magnetoplasma are huge limiting factors to the flux of highly charged ion beams extracted from ECR ion sources. Recently, it has been shown that the two-frequency-heating (TFH) mode has the proven potential to mitigate these instabilities. Since the fundamental physical mechanism of TFH is still unclear, a deeper experimental investigation is necessary. At ATOMKI-Debrecen, the effect on the kinetic instabilities of an argon plasma in a ‘two-close-frequency heating’ scheme has been explored for the first time by using a frequency gap smaller than 1 GHz (i.e. operating in the so-called two-closed-frequency heating mode). A special multi-diagnostics setup has been designed and implemented. In this paper, we will show the data collected by a two-pin, plasma-chamber immersed antenna connected to an RF detector diode and/or to a spectrum analyzer for the detection of plasma radio-self-emission when varying the pumping frequency in single versus double frequency heating mode. Data have been collected simultaneously to the beam extraction and for different frequency gaps and relative power balances. The turbulent regime of the plasma has been tentatively described in a quantitative way, according to the properties of the plasma self-emitted RF spectrum. The measurements show that plasma self-emitted radiation emerges from the internal ECR region everytime (i.e. below the lower pumping frequency) but the almost total instability damping can be effective for some specific combinations of frequency-gap and power balance, thus eventually improving the plasma confinement.

On the use of entangled wire materials in pre-tensioned rocking columns

This research explores potential application of entangled wire materials as intermediate layers between segments of pre-tensioned segmental bridge columns. An ensemble of free-decay vibration tests was conducted on small-scale columns with various configurations of intermediate layers. Wooden blocks were used for segments and the entire system was tightened together using a pre-tensioned steel tendon. Damping and frequency of the columns were determined and compared. It is demonstrated that entangled wire materials substantially increase total damping of the entire system in rocking. This result is very encouraging for future application of entangled wire materials in testing large-scale pre-tensioned segmental bridge columns. However, shear and axial stiffness of the layers require further improvement to reduce their large shear and axial deformations.

Measuring inherent structural damping of structure-TMD systems

A practical method is proposed to enable the inherent structural damping of structures equipped with tuned mass dampers (TMDs) to be quantified. While the traditional random decrement technique cannot be applied to structure-TMD systems, a modified version is presented which accommodates the energy transfer between the structure and TMD. It is shown that cross-correlation functions can be used to determine the random decrement signatures of the structural and TMD responses. Linear regression is combined with an energy balance approach to estimate the inherent structural damping. The total effective damping of the structure is then estimated by using an existing method to predict the added effective damping provided by the TMD.Numerical simulations reveal that the method predicts the inherent structural damping with acceptable accuracy if the duration of the measured response captures at least two thousand structural oscillation cycles, which corresponds to 3–6 h of data for most tall buildings. The method is most accurate when the inherent structural damping is relatively high, and the TMD mass ratio is relatively low. The method is applied to data collected from an anonymous super-tall building equipped with a TMD. The TMD is found to increase the effective damping of the tower from 1.0% to 3.0% of critical. These damping values are supported by measurements conducted when the TMD was briefly locked from moving, and also by theoretical predictions using the assessed dynamic properties of the structure and TMD.

Effects of Repeated Pulmonary Exposure to Carbon Nanotubes on Lung function

The development of nanotechnology has increased the risk of exposure to types of particles other than combustion-derived ones in the environment, namely, industrial nanomaterials. However, their health impacts have not been fully elucidated yet. This study examined the effects of pulmonary exposure to two types of carbon nanotube (single-walled carbon nanotubes: SWCNT, and multi-walled carbon nanotube: MWCNT) on lung physiology in mice. ICR mice were divided into three experimental groups to repeatedly administer vehicle, SWCNT (50 μg/animal), or MWCNT through intratracheal route; thereafter lung function was examined. The values of total respiratory system resistance (R: P<0.05), elastance (E), Newtonian resistance (Rn), tissue damping (G: P<0.05), and tissue elastance (H) were higher and the value of compliance (C) was lower in the SWCNT group than in the vehicle group. On the other hand, MWCNT tended to augment the values. Taken together, CNT themselves inhaled, can impair airway function.

Ship Roll Damping Coefficient Prediction Using CFD

For a ship undergoing roll motion at a resonance frequency, the roll restoring moment and virtual moment of inertia counteract each other and only the damping moment resists the roll exciting moments. Hence, accurate computation of the roll damping moment improves the roll motion prediction. There are several methods to calculate the damping moment; however, most of them fail to consider the viscous effects, such as the potential theory-based method. The experimental measurements take into account the viscous effect; however, they are expensive. The Computational Fluid Dynamics (CFD) method is an alternative to accurately consider the viscous effect. In this study, a CFD approach based on harmonic exciting roll motion technique is adopted to compute the roll motion characteristics and damping coefficients at different conditions. The impact of appendages, Froude number, and degrees of freedom on roll motion characteristics and damping coefficients are investigated for the model scale and full scale to study the scale effects. The results at the model scale are compared against experimental measurements and good correlation was found. 1. Introduction Controlling the roll motion of a ship in a seaway is essential for the safety and habitability. The roll motion of a ship is nonlinear, and the nonlinearity increases at the resonance as the ship experiences larger roll motion. Accurately computing the roll damping at the resonance frequency is important because the moment of inertia and restoring moment counteract each other and the damping moment opposes the roll motion. The total roll damping consists of friction damping, body eddy shedding damping, surface wave damping, lift force damping, and appendages damping. The wave and lift force damping can be calculated by potential flow theory based methods, whereas others are influenced by viscosity. In general, most roll damping calculation methods are based on empirical models, and Ikeda's method (Ikeda et al. 1978) is most common one. Although this method works quite well for conventional ships, the predicted results are sometimes conservative or underestimated for unconventional ships (Gu et al. 2013). Large roll damping is strongly nonlinear and is influenced by fluid viscosity and flow characteristics such as flow separation and vortex shedding. Empirical or semi-empirical methods cannot account the flow characteristics of such a complex flow. Roll damping calculation for conventional ships by Ikeda's simplified method can fit experimental data quite well at small roll angles. However, when the roll angle is large, it is out of the acceptable range of Ikeda's method, and the accuracy of the computed damping coefficient is low (Kawahara et al. 2012).

Co25Fe75Thin Films with Ultralow Total Damping of Ferromagnetic Resonance

We measure the dynamic properties of $\text{Co}_{25}\text{Fe}_{75}$ thin films grown by dc magnetron sputtering. Using ferromagnetic resonance spectroscopy, we demonstrate an ultralow total damping parameter in the out-of-plane configuration of < 0.0013, whereas for the in-plane configuration we find a minimum total damping of < 0.0020. In both cases, we observe low inhomogeneous linewidth broadening in macroscopic films. We observe a minimum full-width half-maximum linewidth of 1 mT at 10 GHz resonance frequency for a 12 nm thick film. We characterize the morphology and structure of these films as a function of seed layer combinations and find large variation of the qualitative behavior of the in-plane linewidth vs. resonance frequency. Finally, we use wavevector-dependent Brillouin light scattering spectroscopy to characterize the spin-wave dispersion at wave vectors up to 23 $\mu \text{m}^{-1}$.