Value Of Damping Ratio Research Articles

Active Metadamping: A phenomenon of damping enhancement in metamaterial via feedback control

Metadamping is defined as the enhancement of dissipation (or the damped response) of an acoustic metamaterial over an equivalent phononic crystal for the same amount of prescribed damping.The emergence of metadamping and decay coefficient in conjunction with active feedback control is the prime novelty of this paper. The wave-number-dependent active metadamping is defined as the difference between the damping ratio of the active-controlled and that of the uncontrolled metamaterial to indicate its improved energy dissipation. The controller design is based on the Linear Quadratic Regulator with output feedback of velocity, and displacement as well as velocity. The damping emergence metric over the entire Brillouin zone is obtained from the dispersion relationship by applying Bloch’s theorem, and a parametric study is performed to get an insight into the metadamping phenomenon. Velocity feedback control (VC) provides the highest value of total damping ratio when compared to the case of displacement- and velocity-based feedback control (DVC) for an identical long wave sound speed; however, at the expense of reduced attenuation bandwidth. The decay coefficient of DVC is higher compared to that of VC up to a threshold of long wave speed of sound. Beyond that threshold, both VC and DVC provide almost equal decay. We identified the possibility of obtaining high damping in a stiff metamaterial via active control, which will be useful for applications in the field of vibrations and acoustics, impact mitigation, shock absorption, and vehicle dynamics.

Electric Delta Trike Stability Characteristic and Maneuverability Analysis: Experiment and Multi-Body Dynamic Simulation

This paper reveals the stability characteristics of an electric-powered delta trike (e-trike), which is developed for goods delivery services. The changeable center of gravity position and weight due to electric component placement and the carried good weight can cause instability of the e-trike. Three main parameters are firstly evaluated on the e-trike: 1) geometry, 2) center of gravity, and 3) stiffness and damping coefficient of the suspensions. Single Lane-Change (SLC) and Double Lane-Change (DLC) tests were then conducted following ISO 14791:2000 and ISO 3888-1:2018 standards, respectively. An e-trike model was created and simulated using SIMPACK, a multi-body dynamic software. The simulation results showed that the developed e-trike model can replicate SLC and DLC tests, indicating the model was valid. A parametric study with the validated model was then conducted with various e-trike weights, center of gravity position, and suspension stiffness and damping ratio values. The results showed additional weight and higher center of gravity position can decrease threshold velocity to avoid rollover. The low suspension stiffness also contributed to lower the threshold velocity. However, the damping coefficient value did not change the threshold velocity significantly. These results can be a guideline in designing a delta trike with better performance in stability and maneuverability.

Flexural vibration of multistep rotating Timoshenko shafts using hybrid modeling and optimization techniques

In this paper, the flexural vibration of uniform and non-uniform rotating shafts based on the Timoshenko beam theory is investigated. Considering shear deformation and gyroscopic effects to build an exact framework of a solution, the fourth-order differential equation of vibration is solved by an analytical method. The overall transfer matrix of the system formed by a series of flexible distributed in addition to lumped elements is achieved. The results obtained by the distributed lumped modeling technique (DLMT) are verified with other techniques. The damped frequencies obtained by the hybrid modeling method for a multistep gas turbine rotor system using the Euler–Bernoulli and Timoshenko beam theories are compared with the results of the transfer matrix method (TMM). It is shown that the presented method provides highly accurate results, while with no compromise, it can be simply and effectively employed for complex systems. It is also shown how the Hooke and Jeeves and the ant colony optimization (ACO) besides the direct enumeration method can be applied to obtain the damped natural frequencies of complicated vibrational systems such as the gas turbine rotors. The comparison between the frequency and damping ratio values obtained by the optimization and direct enumeration methods shows less than 1% error for different cases.

Impact of Graphene Nano-Additives to Lithium Grease on the Dynamic and Tribological Behavior of Rolling Bearings

In recent years, reduced graphene oxide (rGO) received considerable interest as a lubricant nano-additive for enhancing sliding and rolling contacts. This paper investigates the tribological and dynamic behavior of ball bearings lubricated by lithium grease at different weight percentages of rGO. Full bearing tests were conducted for experimental modal analysis, vibration analysis, ultrasonic analysis, and infrared thermography. Modal analysis indicated considerable improvements of the damping ratio values up to 50% for the bearings with rGO nano-additives. These findings were confirmed by the corresponding reductions in vibrations and ultrasound levels. The steady-state temperatures of bearings running with lithium grease reached 64 °C, whereas the temperature of bearings lubricated by grease with 2 wt.% rGO measured only 27 °C. A Timken Load test was conducted on grease samples with and without rGO additives. Grease samples having 2, 3.5, and 5 wt.% rGO showed the highest OK load with an increase of 25%, 50%, and 100% as compared to values of lithium grease. For comparison, all tests were conducted on samples of the same grease blended with graphite and MWCNTs’ nano-additives. The results proved the superiority of graphene in enhancing the load-carrying capacity and damping of grease in rolling bearings.

Linear Predictive Coding for Acute Stress Prediction from Computer Mouse Movements.

Prior work demonstrated the potential of using the Linear Predictive Coding (LPC) filter to approximate muscle stiffness and damping from computer mouse movements to predict acute stress levels of users. Theoretically, muscle stiffness and damping in the arm can be estimated using a mass-spring-damper (MSD) biomechanical model. However, the damping frequency (i.e., stiffness) and damping ratio values derived using LPC were not yet compared with those from a theoretical MSD model. This work demonstrates that the damping frequency and damping ratio from LPC are significantly correlated with those from an MSD model, thus confirming the validity of using LPC to infer muscle stiffness and damping. We also compare the stress level binary classification performance using the values from LPC and MSD with each other and with neural network-based baselines. We found comparable performance across all conditions demonstrating LPC and MSD model-based stress prediction efficacy, especially for longer mouse trajectories.Clinical relevance- This work demonstrates the validity of the LPC filter to approximate muscle stiffness and damping and predict acute stress from computer mouse movements.

Characterization of elastic and shear moduli of adapazari soils by dynamic triaxial tests and soil-structure interaction with site properties

Determination of shear modulus along with damping ratio values in the field when shear strains exceeds those maximum strains obtained from laboratory tests has a crucial importance in the seismic design of structures whose interaction with soil is more pronounced. In this study, shear modulus of undisturbed samples, obtained from Adapazarı city center during drilling works conducted within the scope of the geotechnical investigation following the 1999 Kocaeli earthquake, were determined. Elasticity of undisturbed Adapazarı samples was measured using a cyclic triaxial test rig. The aim is to obtain relationships between the elasticity moduli from the stress–strain relations of specimens in dynamic and static loading setups, and the axial strains following termination of dynamic tests. Minimum and maximum shear moduli were determined for non-plastic soils and for soils with the plasticity index of PI = 40%. The elasticity modulus ratio (EN=20/EN=1) for samples with plasticity index of PI = 40% is higher than those with PI = 20% at the same level of deformation. As the plasticity increases at the same deformation level, both of the Eds/EN=1 and Eds/EN=1 ratios increase. Moreover, seismic performance of a reinforced concrete frame is evaluated for both fixed and soil-structure system. Seismic demand in soil-structure model with the frame and soil profile considered in this study is observed to be higher as compared to fixed-base frames.

Reduction of Bias and Uncertainty in Regional Seismic Site Amplification Factors for Seismic Hazard and Risk Analysis

Site amplification factors in National Building Codes are typically specified as a function of the average shear wave velocity over the first 30 m (Vs30) or site class (A, B, C, D and E) for defined ranges of Vs30 and/or ranges of depth to bedrock. However, a single set of amplification factors may not be representative of site conditions across the country, introducing a bias in seismic hazard and seismic risk analyses. This is exemplified by significant differences in geological settings between East and West coast locations in North America. Western sites are typically characterized by lower impedance contrasts between recent surface deposits and bedrock in comparison to Eastern sites. In North America, site amplification factors have been derived from a combination of field data on ground motions recorded during West Coast earthquakes and numerical models of site responses that are meant to be representative of a wide variety of soil profiles and ground motions. The bias on amplifications and their impact on seismic hazards is investigated for the Montreal area, which ranks second for seismic risks in Canada in terms of population and hazard (PGA of 0.25 g for a 2475 years return period). Representative soil profiles at several locations in Montreal are analyzed with 1-D site response models for natural and synthetic ground motions scaled between 0.1 to 0.5 g. Since bedrock depths are typically shallow (<30 m) across the island, bedrock shear wave velocities have a significant influence on the impedance contrast and amplifications. Bedrock shear wave velocity is usually very variable due to the differences in rock formations, level of weathering and fracturing. The level of this uncertainty is shown to be greatly decreased when rock quality designation (RQD) data, common information when bore hole data are logged, is available since it is highly correlated with both shear and compression wave velocities. The results are used to derive region-specific site amplification factors as a function of both Vs30 and site fundamental frequency and compared to those of the National Building Code of Canada (2015). The results of the study indicate that there are large uncertainties associated with these parameters due to variability in soil profiles, soil properties and input seismic ground motions. Average and confidence intervals for the mean and for predictions of amplification factors are calculated for each site class to quantify this uncertainty. Amplifications normalized relative to class C are obtained by accounting for the correlation between site class amplifications for given ground motions. Non-linearity in the analysis of equivalent linear 1-D site response is taken into account by introducing the non-linear G/Gmax and damping ratios curves. In this method, it is assumed that the shear strain compatible shear modulus and damping ratio values remains constant throughout the duration of the seismic excitation. This assumption is not fully applicable to a case when loose saturated soil profile undergo heavy shaking (PGA > 0.3 g). In this study, all simulations with input motion PGA >0.3 g have been performed by using the EL method instead of the NL method considering that cohesive soils (clay and silt) at Montreal sites are stiff and cohesionless soils (sand and gravel) are considerably dense. In addition, the field and laboratory data required to perform NL analyses are not currently available and may be investigated in future works.

Effect of Cut-outs on the Free Vibration Response of Basalt/Carbon Hybrid Composites

The current work deals with an experimental investigation about the influence of cut-outs on dynamic characteristics of basalt/carbon hybrid fiber reinforced composite laminates. The composite samples have been fabricated via vacuum assisted resin transfer molding technique and cut-outs in the form of triangular, square and circular shapes with equal areas have been processed on them to systematically analyze the influences of cut-outs. The dynamic characteristics of the samples have been examined by conducting free vibration-damping tests and expressed in terms of natural frequency and damping ratio using the frequency response and time-acceleration response. The results show that the damping characteristics of the composite samples can be remarkably improved with the help of cut-outs which provide improvements approximately between 2.41% and 16.65% in damping ratio values. The maximum and minimum variations in damping ratio have observed for non-hybrid carbon fiber reinforced composite samples with triangular cut-out (T-C6) and hybrid basalt/carbon fiber reinforced composite samples with circular cut-out (C-B6), respectively. On the other hand, the presence of cut-outs have led to decreases in natural frequency values as a result of reduction in stiffness caused by the cut-outs. This point out that employment of cut-outs can be a promising application to meet the natural frequency requirements of engineering systems constructed with hybrid fiber reinforced composite laminates.

OPF Calculation with Small-Signal Trajectory Constraints

In order to avoid the complexity of obtaining the sensitivity in the usual optimal flow with small signal stability, which is easily result from the mere consideration of active power output optimization or the change of element model, a new model is proposed to improve the small-signal stability of the system by constraining the perturbation trajectory curve. Based on the time-domain simulation method, a power flow optimization model with small-signal trajectory constraint is established by extracting the damping ratio of the perturbation trajectory and forming constraints. The optimization calculation results of Western Systems Coordinating Council 3-generator 9-node system and China Electric Power Research Institute 6-generator 22-node system prove that the corresponding minimum damping ratio of the system increases with the increase of the constraint value of approximate damping ratio, which demonstrates the effectiveness of the model.

Energy harvesting using a novel autoparametric pendulum absorber-harvester

Autoparametric pendulum absorbers can transmit vibrational energy from the hosting structure to the motion of the pendulum and are effective if properly tuned. The motion of the pendulum can be also used to produce electrical power which can be harvested as renewable energy. This paper focuses on a novel configuration of the pendulum absorber-harvester that allows to improve its vibration suppression and energy harvesting characteristics. The novel configuration of the absorber implies using magnets, and its performance is analyzed both theoretically and experimentally. First, a dynamic model of the absorber-harvester is introduced taking the magnetic forces into account. Then analytical expressions describing the system performance are obtained. To achieve the best performance of the absorber-harvester, optimal values of its parameters are determined. The results show that the performance of the novel absorber-harvester is superior as compared to the conventional device in terms of both vibration suppression and energy harvesting. An optimal value of the electrical damping ratio is also found that provides the maximum power output. Finally, an experimental testing is conducted to validate the obtained theoretical results.

Optimal Method for Determination of Rayleigh Damping Co-efficients for Different Materials using Modal Analysis

Rayleigh damping co-efficients are the essential parameters to determine the damping matrix of a system in dynamic analysis. For the systems with multiple degrees of freedom, it is difficult to arrive for suitable Rayleigh damping co-efficients. This paper represents a simple and effective method for the determination of Rayleigh co-efficients α and β for the system with multiple degrees of freedom. An unrealistic constant damping ratio for all modes is assumed to get rational value of α and β, which leads the determination of progressively varying damping ratio for all modes. By comparing the damping ratio arrived from assumed α and β with assumed unrealistic damping ratio, the suitable and most precise values are determined. This method is implemented for different materials with different boundary conditions by considering different significant modes and the effect of above parameters on α and β values are also discussed.

Sloshing induced damping in vertically vibrating systems

All aircraft are subject to a range of loading throughout ground and flight operations, which ultimately define the sizing and weight of the aircraft structure. Active and passive loads alleviation technologies provide an approach to reduce dynamic loads arising from atmospheric gusts and turbulence, leading to more fuel-efficient aircraft designs. Within the H2020 SLOWD project, fuel sloshing is being considered as a method for alleviating loads in aircraft wings via an increase in effective damping. Recent work has considered the transient response of a vertically vibrating, single degree of freedom system coupled to a rectangular liquid-filled tank. This research revealed identifiable dissipation regions in the free vibration responses characterised by their own distinct equivalent damping ratio values. In this work, free surface displacement has been extracted from high-speed camera footage during the chosen sloshing regimes, which are representative of a decaying parametrically excited fluid. These results are compared against a fluid-structure coupled numerical model based upon smoothed particle hydrodynamics, previously shown to have good agreement with the experimental damping response. Further analysis of the free-surface response of the numerical solution notes a presence of an undesired travelling longitudinal wave. The analysis of this discrepancy between the model and experiment is then used to improve the numerical formulation, showing a requirement for modelling surface tension.

A Methodology to Characterize Modal Damping in Vibrating Systems: Application to the Case of Gas Turbine Combustion Chambers

Abstract The present paper proposes a methodology to characterize the modal damping ratio as a function of frequency in vibrating systems, with a focus on gas turbine combustion chambers. Proposed methodology correlates the modal damping ratio to the system modal eigenfrequencies, accurately considering the damping physical effects on the system dynamics and goes beyond the standard proportional damping hypothesis and similar techniques present in the literature. The methodology has been compared under free-free conditions with standard damping ratio laws that can be found in the literature and which may lead sometimes to an overestimation of the real damping ratio values. Experimental data obtained through dedicated ping tests performed on two components of an industrial gas turbine annular combustion chamber have been used for the methodology validation: comparison between simulated and experimental results seems to be encouraging and the proposed methodology for modal damping ratio characterization turns out to be better, with respect to the standard ones, in reproducing not only the experimentally estimated damping law (as a function of the frequency), but also the typical Force Response Functions (FRFs) of the considered vibrating systems. Finally, since the adopted procedure is numerically efficient and based only on low cost experimental techniques, it can be used for describing modal damping in vibrating systems since the early phases of the design, by increasing the design accuracy and reducing times and costs.

An over-damped multimodal adaptive nonlinear static analysis for seismic assessment of infilled RC buildings

In the world, many existing buildings with RC framed structure are extremely vulnerable, as they were designed to sustain gravity loads only, or to resist seismic actions lower than those expected today. Since a complete renewal of the existing building heritage is not possible, the seismic assessment of existing structures has gained importance in recent years to identify the structural deficiencies and design the most appropriate retrofit interventions. This paper proposes a multimodal adaptive nonlinear static method of analysis named overDamped Displacement Adaptive Procedure (D-DAP). This method has been developed from the combination of the approaches adopted by Pinho et al. and Lenza et al. In addition, the D-DAP explicitly considers the increase of the energy dissipation due the cumulated damage in the structure by updating the value of equivalent viscous damping ratio according to a new damping law properly calibrated for RC frames with and without infill panels.

The Flexural Fatigue Behavior of Honeycomb Sandwich Composites Following Low Velocity Impacts

This study experimentally investigated the flexural fatigue behaviors of honeycomb sandwich composites subjected to low velocity impact damage by considering the type and thickness of the face sheet material, the cell size and the core height parameters. Carbon-fiber reinforced composite and the aluminum alloy was used as the face sheet material. First, the static strength of undamaged and damaged specimens was determined by three-point bending loads. Secondly, the fatigue behaviors of the damaged and undamaged specimens were determined. Low velocity impact damage decreased the flexural strength and fatigue lives but increased the damping ratio for all specimens. Maximum damping ratio values were observed on specimens with a aluminum face sheet.

Mechanical performance of rubberized cement paste with calcium sulfoaluminate cement addition

Due to an increasing amount of waste tires produced yearly, environmental concerns arise as waste tires in landfills pose both a fire hazard, and a habitat for rodents and mosquitos. As a result, the reuse of waste tires in the form of waste rubber in concrete has been attempted. Previous research work has shown that the inclusion of waste rubber in concrete results in a drastic decrease in compressive strength. The limitations regarding the use of rubberized concrete are related to the interfacial transition zone between rubber and paste. Due to mismatch in free surface energy between rubber and cement paste, an interfacial gap is often reported to be present. This investigation aims to determine the effect of expansive cement, specifically calcium sulfoaluminate cement (CSA), has on the performance on rubberized cement samples, and its effect on the interfacial transition zone. A comprehensive experimental plan was carried out including pullout and compressive tests, scanning electron microscopy (SEM) imaging of fractured surface, and non-destructive tests through resonant frequency and dynamic mechanical analysis (DMA); furthermore, a temperature sweep via DMA was done to determine damping factor as a function of temperature. Results from compressive strength indicate a marked increase in the performance of rubberized samples with expansive cement. Pullout results, dynamic modulus and damping ratio values, shrinkage measurements, and scanning electron microscopy (SEM) imaging validate the hypothesis that a decreased interfacial gap at the rubber-paste interface obtained from using expansive cement results in increased mechanical performance.

Identification of upper branch for vortex-induced vibration of a circular cylinder at [formula omitted

In this study flow around a circular cylinder undergoing transverse-only vortex-induced vibrations is investigated using a two-dimensional in-house CFD code. The Navier–Stokes equations, the continuity and pressure Poisson equations written for an incompressible constant property Newtonian fluid coupled with the structural equation are solved using the finite difference method. Systematic computations are carried out for different damping ratio values between ζ=0% and 5%. Reduced velocity is varied in U∗=2.5−7.5, while Reynolds number and mass ratio are fixed at Re=300 and m∗=10, respectively. Up until now, researchers have reported an upper branch only at high Reynolds numbers and low m∗ζ values. However, in this study we have observed a three-branch behavior (initial, upper and lower branches) at Re=300 for ζ≤1%. The upper branch is bounded by two gradual phase changes: at the boundary adjacent to the initial branch, the time-averaged phase difference of vortex force, and at the boundary to the lower branch, the time-averaged phase difference of transverse fluid force relative to the cylinder displacement changes between 0° and 180°. Unbounded variations and phase slips are observed in the time-dependent phase differences, which explains the gradual changes in their time-mean values. In some ranges of the upper branch the second harmonic frequency component plays an important role in the spectra of transverse fluid force, which is closely related to the observed asymmetrical vortex structure. Increasing the structural damping above ζ=1%, only initial and lower branches are found. The comparison of peak oscillation amplitude against an empirical relationship provided in the literature shows very good agreement for ζ≥1%. A Griffin plot is also used for the comparison of peak response data where the currently obtained results and those in the literature collapse onto almost a single curve.

Defect detection in pipe structures using stochastic resonance of Duffing oscillator and ultrasonic guided waves

Ultrasonic guided wave based non-destructive testing is an effective method to inspect defects in long-distance pipe structures. This paper proposes a novel defect detection approach for the pipes using stochastic resonance of Duffing oscillator and ultrasonic guided waves. Stochastic resonance can improve the signal-to-noise ratio (SNR) in the output signal, because it can enhance the periodic component while attenuate the noise components. A detection system is first developed based on Duffing oscillator. The echo signal between the incident signal and end echo is used as the input to the Duffing oscillator, and the normalized power spectrum of the output signal is calculated to obtain the SNR of the output signal. The SNR curve is shown versus the change of the damping ratio value. When stochastic resonance occurs, the SNR is at the peak, corresponding to the optimal value of damping ratio. With the optimal damping ratio value, the power spectrum of the output signal from the Duffing oscillator is used to detect the characteristic frequency. If there is a distinct characteristic frequency with the same excitation frequency as the guided wave excitation signal, it can be concluded that there is a defect in the pipe. Both numerical simulations and experimental studies are conducted to investigate the accuracy and effectiveness of the proposed approach in defect detection in pipes. The detection results demonstrate that the proposed approach can significantly enhance the sensitivity of using weak guided wave signals for minor defect detection in pipe structures.

High strain damping for sands from load-controlled cyclic tests: Correlation between stored strain energy and pore water pressure

Undrained stress-controlled cyclic triaxial and direct simple shear test data on five different clean sands was analyzed in terms of dissipated and stored strain energy. A new method was developed to calculate damping ratio from undrained stress-controlled tests and its plausibility was examined with the help of pore water pressure data. Results from different methods in the literature to calculate damping ratio were also evaluated. The data analysis shows that the damping ratio results calculated with the new method were in some agreement with the damping ratio values for sands summarized by Seed & Idriss (1970) [1] for shear strains up to 0.4%. For shear strains larger than 0.4%, the new method provides more accurate estimates of damping ratio that are also conceptually more reasonable than those obtained with linear equivalent approximations. For strains in excess of 1%, damping ratio trends with strain obtained with the new method are clearly superior, although reliable experimental data is limited. In general, equivalent linear calculation of damping ratio can lead to an overestimation of damping for shear strains smaller than 1% and an underestimation of damping for the shear strains larger than 1%.

Estimation of damping in riveted short cantilever beams

In layered and riveted structures, vibration damping happens because of a micro slip that occurs because of a relative motion at the common interfaces of the respective jointed layers. Other parameters that influence the damping mechanism in layered and riveted beams are the amplitude of initial excitation, overall length of the beam, rivet diameter, overall beam thickness, and many layers. In this investigation, using the analytical models such as the Euler–Bernoulli beam theory and Timoshenko beam theory and half-power bandwidth method, the free transverse vibration analysis of layered and riveted short cantilever beams is carried out for observing the damping mechanism by estimating the damping ratio, and the obtained results from the Euler–Bernoulli beam theory and Timoshenko beam theory analytical models are validated by the half-power bandwidth method. Although the Euler–Bernoulli beam model overestimates the damping ratio value by a very less fraction, both the models can be used to evaluate damping for short riveted cantilever beams along with the half-power bandwidth method.