Damping Measurements Research Articles

Comparative analysis of MEMS (Micro-Electro-Mechanical Sensor) and IEPE (Integrated Electronics Piezo-Electric) accelerometers for measurement of wide spectrum damping

Damping is an important material property for dynamically loaded structures, such as aircraft, vehicles, and rotary or reciprocating machinery. Low damping may increase vibration amplitudes which can cause excessive dynamic loading and can detrimentally affect a structures performance. Accurate prediction of the dynamic loads is necessary to avoid catastrophic failure especially during resonant vibrations. In this work, a MEMS (micro-electro-mechanical sensor) accelerometer system is constructed to measure vibration over a wide frequency range (from 0-3000 Hz). Measurements of the damping ratio taken with MEMS accelerometers were compared to similar measurements using IEPE (integrated electronics piezo-electric) accelerometers and the experimental results validated against a thermoelastic model and published studies. The damping measured using IEPE accelerometers was larger due to spurious damping effects attributed to the much larger cables. The low spurious damping of the MEMS accelerometers allows for the accurate determination of the damping of a material over a wide frequency range. The MEMS accelerometer setup used in this work offers a method to accurately measure the damping of dynamically loaded, lightweight structures, where attaching traditional accelerometers can cause significant error in the measured damping or where non-contact measurement may be unsuitable.

A New Axial Compressor Test Facility for the Investigation of Aerodynamic Damping Featuring an Electromagnetic Excitation System

Abstract Aerodynamic damping simulations involving detailed computational fluid dynamics (CFD) models are nowadays an integral part of turbomachinery design processes, thanks to advancements made in simulation tools and in computer hardware over the last decades. However, the test cases available in the open literature suitable for the validation and continued development of simulation tools is rather limited. On this background, a new test facility is introduced that allows acquiring relevant and high-quality aerodynamic damping test data on axial compressor rotor test objects in a controlled manner. The test facility is built as a closed loop and thus enables operation at variable pressure levels ranging from near-vacuum to overpressure and with different operating media. Overall damping test data are acquired at controlled synchronous and nonsynchronous vibration conditions. While vibrations of the blades at controlled nonsynchronous vibration conditions can be introduced in the test facility by means of a proprietary electromagnetic excitation system that is acting below the hub line, vibrations at controlled synchronous conditions can be introduced from a set of magnets integrated into the casing. Great care has been spent to create a clean test case without any intruding parts or openings in the test section. In addition, an axial compressor blisk is presented, which acts as test object to show the capabilities of the test facility as well as to allow for detailed investigations of aerodynamic damping. While the first part of the article discusses the setup and the instrumentation of the test facility to excite and measure blade vibration in a nonintrusive way, flow-field measurements and the validation accompanying steady-state Reynolds-averaged Navier-Stokes (RANS) simulations are shown in the second part. The third part of the article focuses on aerodynamic damping measurements for seven different modes at three different pressure levels in total. It can be shown that aerodynamic damping is by far the largest contributor to the overall damping.

Internal damping measurements of additive manufactured metal beams

Modern additive manufacturing (AM) techniques have created an endless number of new design possibilities. Naturally, it is important to understand how the material properties, including internal damping, differ for AM structures. An experimental procedure has been developed to measure an upper bound for the internal damping of metal beams by minimizing the effects of energy dissipation at the supports and acoustic radiation into the surrounding air. In this talk, measurements for the loss factor of several common metals will be compared to equivalent samples constructed by powder bed fusion at varying angles. The results will also be compared to Zener’s thermoelasticity model, developed for isotropic Euler beams in flexure. Reasons for deviation from theory which arise from the manufacturing technique will be explored.

In-situ material damping measurements using the crosshole seismic method

Crosshole seismic testing is commonly used to determine detailed and reliable wave velocity profiles. Material damping measurements can also be performed in crosshole seismic testing, but these measurements require a window function to maintain similar amplitude shapes over the frequency range of interest for the calculation. In-situ seismic testing, including downhole and seismic cone penetration testing (SCPT), also requires a window function for the material damping calculations. However, the length of the window function has the largest influence on the material damping calculation. Therefore, the half-power bandwidth method is introduced to determine the material damping ratio without the window function in crosshole testing by replicating the unconfined, free-free, resonant column (Fr-Fr) test. To demonstrate the influence in the length of the window function, the first cycle of the signal is used in the material damping calculation. The half- power bandwidth method is verified using synthetic signals and field data. Two sets of crosshole and downhole tests were performed, one at a backfill test pad and the second at a Hornsby Bend research site operated by the University of Texas at Austin. The in-situ material damping ratio calculated from these two sets of crosshole tests using the half-power bandwidth method are compare with the Spectral Ratio Slope (SRS) method applied to the downhole testing at these sites. The material damping calculated from the half-power bandwidth method using the full signal results in a reliable and precise damping value compared to the SRS method applied to the downhole data.

Damping in stay cable with damper: Practical universal damping curve and full-scale measurement

This paper includes two main parts which are the development of a universal damping curve for cables of cable-stayed bridges with dampers and a full-scale measurement of cable damping. In the first part, the universal damping curve is derived for cables with viscous dampers or High Damping Rubber (HDR) dampers. The proposed damping curve is a single curve which incorporates several cable-damper parameters like cable bending stiffness, boundary conditions at cable ends (hinged, fixed or restraint ends), damper stiffness, damper support stiffness and added negative stiffness. A numerical approach by a finite difference method (FDM) is also developed to verify the proposed universal damping curve. In addition to FDM, the accuracy of the proposed curve was confirmed with damping formulations in literature over ten different damper types. The results showed a good agreement of estimated damping between proposed damping curve and others. Additionally, a significant improvement in estimating cable damping was observed through two available full-scale tests, which compared the results between proposed curve and current curve. The second part in this study presents a full-scale measurement of cable vibration and a real application of the proposed damping curve for the identification of damping in cables of Shinminato Bridge (cable lengths from 100 to 200 m). Both HDR and viscous dampers were used for the cable vibration control of the bridge. The results of damping analysis indicated that the HDR damper effectiveness was higher than 0.7 whereas this effectiveness was smaller than 0.4 for the viscous damper.

Real-space observation of ultraconfined in-plane anisotropic acoustic terahertz plasmon polaritons.

Thin layers of in-plane anisotropic materials can support ultraconfined polaritons, whose wavelengths depend on the propagation direction. Such polaritons hold potential for the exploration of fundamental material properties and the development of novel nanophotonic devices. However, the real-space observation of ultraconfined in-plane anisotropic plasmon polaritons (PPs)-which exist in much broader spectral ranges than phonon polaritons-has been elusive. Here we apply terahertz nanoscopy to image in-plane anisotropic low-energy PPs in monoclinic Ag2Te platelets. The hybridization of the PPs with their mirror image-by placing the platelets above a Au layer-increases the direction-dependent relative polariton propagation length and the directional polariton confinement. This allows for verifying a linear dispersion and elliptical isofrequency contour in momentum space, revealing in-plane anisotropic acoustic terahertz PPs. Our work shows high-symmetry (elliptical) polaritons on low-symmetry (monoclinic) crystals and demonstrates the use of terahertz PPs for local measurements of anisotropic charge carrier masses and damping.

Role of intersublattice exchange interaction in ultrafast longitudinal and transverse magnetization dynamics in permalloy

We report on element-specific measurements of ultrafast demagnetization and magnetization precession damping in permalloy thin films. Magnetization dynamics induced by an optical pump at 1.5 eV is probed simultaneously at the ${M}_{2,3}$ edges of Ni and Fe with high-order harmonics for moderate demagnetization rates (less than 50%). The role of the intersublattice exchange interaction in both longitudinal and transverse dynamics is analyzed with a Landau-Lifshitz-Bloch description of ferromagnetically coupled Fe and Ni sublattices. It is shown that the intersublattice exchange interaction governs the dissipation during demagnetization as well as precession damping of the magnetization vector.

Fiber Optic Network Performance Analysis With Fiber To The Home (FTTH) Architecture

<p>Prototype is a tool used as a learning medium that has the same shape and function as the original tool or unit. The use of simulator tools as a means of learning is one of the learning methods that is very well used to find out the components, functions, and how the tool or unit works. Limitations in the delivery of lecture materials regarding Optical Networks due to the absence of modules and prototypes that help the lecture process this prototype is one of the solutions that can be used in the lecture process. Testing this prototype with measurements of damping and power obtained after configuring and installing a fiber to the home network using an optical power meter. Data analysis used in the quality of service in the system is the value of attenuation and power (power link budget) in units of dB and dBm. The results of the test get a good attenuation according to the established ratio. The practicum module is an implementation after the configuration and measurement of damping so that it can be a guide for conducting fiber optic network practicum in the Telecommunication Engineering study program.</p>

Stay cable vibration mitigation: A review

Stay cables in cable-stayed bridges are subjected to various types of dynamic excitation mechanisms under environmental loads. The excited vibrations can have a large amplitude because of low vibration frequencies and small inherent damping of cables. As cables become longer (the longest cables are around 600 m in cable-stayed bridges with a main span of 1000 m), more modes are vulnerable to wind and rain-wind induced vibrations, posing challenges to vibration mitigation. This paper presents a comprehensive review of recent advances in stay cable vibration mitigation, including theoretical modeling of cable damping system and techniques for enhancing multimode damping. Recent results on cable damping measurements, understanding of cable vibrations, and relevant aerodynamic countermeasures are also recalled. The reflections can provide guidance for cable vibration control design of cable-supported bridges and for the maintenance/upgrade of cable vibration mitigation system of existing bridges.

Measurement of natural frequency and mechanical damping of thin brass diaphragm by pulsed laser generated vibrations

Damped harmonic oscillator model based fitting of nanosecond pulsed laser induced amplitude variations of clamped vibrating circular plate is used to estimate the mechanical damping and natural frequency of the sample in current work. Laser Pulses of 50 mJ energy, 20 ns duration, and focused at a spot of 4 mm diameter at the center of the circular thin brass sheet of 100 µm thickness is used to generate vibrations in the target. Quadrature Michelson interferometer (QMI) with CW laser focused on the opposite side of the target surface is used to measure the amplitude of vibrations. Variations of fringe frequencies are identified in the frequency domain. Finite element based numerical modal analyses are also performed in ANSYS Workbench for the verification of experimental results for the same geometry and materials. Experimental frequencies of vibrations are found to match nearly 2 percent of FEM modes. Moreover, Elastic parameters are also found using the first two mode frequencies and a reasonable agreement is observed while comparing with the elastic parameter data of brass. Current work in itself is a unique attempt of getting mechanical parameters for the determination of elastic parameters in a single laser pulse impulse excited measurement for thin clamped targets.

Inviscid damping of an elliptical vortex subject to an external strain flow

Inviscid spatial Landau damping is studied experimentally for the case of oscillatory motion of a two-dimensional vortex about its elliptical equilibrium in the presence of an applied strain flow. The experiments are performed using electron plasmas in a Penning–Malmberg trap. They exploit the isomorphism between the two-dimensional Euler equations for an ideal fluid and the drift-Poisson equations for the plasma, where plasma density is the analog of vorticity. Perturbed elliptical vortex states are created using E×B strain flows, which are generated by applying voltages to electrodes surrounding the plasma. Measurements of spatial Landau damping (also called critical-layer damping) are in agreement with previous studies in the absence of an applied strain, where the damping is due to a resonance between the local fluid motion and the vortex oscillations. Interestingly, the damping rate does not change significantly over a wide range of applied strain rates. This can be accurately predicted from the initial vorticity profile, even though the resonant frequency is reduced substantially due to the applied strain. For higher amplitude perturbations, nonlinear trapping oscillations also exhibit behavior similar to the strain-free case. In principle, higher-order effects of the applied strain, such as separatrix crossing of peripheral vorticity and interactions with harmonics of the fundamental resonance, are expected to change the damping rate. However, this occurs only for conditions that are not realized in the experiments described here. Vortex-in-cell simulations are used to investigate the possible roles of these effects.

Magnetic damping in ferromagnetic/heavy-metal systems: The role of interfaces and the relation to proximity-induced magnetism

Damping and spin transport in spintronic multilayered systems continues to be a topic of active research. The enhancement of damping in ferromagnet (FM)/spacer layer (SL)/heavy-metal (HM) thin-film systems was studied for ${\mathrm{Co}}_{25}{\mathrm{Fe}}_{75}/\mathrm{SL}/\mathrm{Pt}$ with a nonmagnetic (NM) SL of either Au or Cu with variable thickness, in order to understand the correlation with proximity-induced magnetism (PIM) in the HM. Structural, PIM and magnetic damping measurements were undertaken on the same samples. Specifically, secondary ion mass spectroscopy, element specific x-ray magnetic reflectivity and x-ray magnetic circular dichroism at the Pt and Au ${L}_{3}$ edges, and ferromagnetic resonance methods were used. With increasing thickness of a Cu or Au SL directly between the FM and the Pt layer, the Pt PIM and the damping both fall rapidly, with a relationship between damping and PIM that depends on the SL material. The PIM observed in the Au layer showed a complex dependence on the layer thickness, suggesting some hybridization with the Pt. The role of the number and location of interfaces on the damping was demonstrated with the addition of a SL within the Pt layer, which showed that the specific details of the NM/HM interface also affects the damping. The insertion of a Cu SL within the Pt showed a measurable increase in the overall enhancement of the damping while the insertion of a Au SL into Pt had almost no effect on the damping. Together these results demonstrate the role of both PIM and of additional interfaces in the enhancement of damping in FM/HM systems, which is not fully accounted for by existing theory.

Identification of limiting damping mechanisms in a high quality factor hybrid resonator of space application gyroscope

• Studied hybrid gyroscope resonator damping mechanisms with imperfection sensitivity. • Realized thin film coated high precision resonator with few millions quality factor. • Limiting damping mechanisms are identified at each stage from design to realization. The performance of Hemispherical Resonator Gyroscopes (HRG) is decided by the mechanical resonator’s Quality factor ( Q factor). The Q factor is a measure of energy dissipation. A Q factor of few millions is needed to realize fine resolution millimeter size of the HRG for future interplanetary satellite missions. The objective is to carry out a detailed study of thermoelastic damping (TED), anchor loss, surface loss, material internal friction and fluid damping. A hybrid resonator is designed with very low TED. One of the major contributions of the present work is the study of the effect of thin film coating and different coating configurations on TED. Extensive simulations have been carried out on the effect of different fabrication deviations on anchor loss. A unique sensitivity study of mode interactions and mass unbalance pattern on frequency split and anchor loss mismatch is also done. Based on this, dimensional and geometric tolerances are derived for precision fabrication and the precision hybrid configuration resonator is realized. Surface loss and material internal friction are estimated. Also, surface characterisation has been done using nanoindentation techniques. Q factor of few millions is obtained in a fabricated precision resonator with thin film coating. Based on the estimation of different damping mechanisms and measurements, the limiting mechanisms are identified at each stage from the design to the realization. The Q factor of an uncoated resonator is limited by the surface loss while that of a coated resonator is limited by the coating induced additional TED, the coating material internal friction and the surface loss.

Blade oscillation mechanism for aerodynamic damping measurements at high reduced frequencies

Accurate prediction of aerodynamic damping is essential for flutter and forced response analysis of turbomachinery components. Reaching a high level of confidence in numerical simulations requires that the models have been validated against the experiments. Even though a number of test cases have been established over the past decades, there is still a lack of suitable detailed test data that can be used for validation purposes in particular when it comes to aero damping at high reduced frequencies which is more relevant in the context of forced response analysis. A new transonic cascade test rig, currently undergoing commissioning at KTH, has been designed with the goal to provide detailed blade surface unsteady pressure data for compressor blades profiles oscillating at high reduced frequencies. The paper provides an overview of the blade actuation system employed in the test rig and presents the result of a series of bench tests characterizing the blade vibration amplitudes achieved with this actuation system.

Analysis and Identification of Nonlinear Acoustic Damping in Miniature Loudspeakers

Nonlinear acoustic damping is a key nonlinearity in miniature loudspeakers when the air velocity is at a high amplitude. Measurement of nonlinear acoustic damping is beneficial for predicting and analyzing the performance of miniature loudspeakers. However, the general measuring methods for acoustic impedance, such as the standing-wave tube method or the impedance tube method, are not applicable in this scenario because the nonlinear acoustic damping in miniature loudspeakers is coupled with other system nonlinearities. In this study, a measurement method based on nonlinear system identification was constructed to address this issue. The nonlinear acoustic damping was first theoretically analyzed and then coupled in an equivalent circuit model (ECM) to describe the full dynamics of miniature loudspeakers. Based on the ECM model, the nonlinear acoustic damping was identified using measured electrical data and compared with theoretical calculations. The satisfactory agreement between the identification and theoretical calculations confirms the validity of the proposed identification method.

Magnetoelastic interactions and magnetic damping in Co2Fe0.4Mn0.6Si and Co2FeGa0.5Ge0.5 Heusler alloys thin films for spintronic applications

Co2Fe0.4Mn0.6Si (CFMS) and Co2FeGa0.5Ge0.5 (CFGG) Heusler alloys are among the most promising thin film materials for spintronic devices due to a high spin polarization, low magnetic damping and giant/tunneling magnetoresistance ratios. Despite numerous investigations of Heusler alloys magnetic properties performed up to now, magnetoelastic effects in these materials remain not fully understood; due to quite rare studies of correlations between magnetoelastic and other magnetic properties, such as magnetic dissipation or magnetic anisotropy. In this research we have investigated epitaxial CFMS and CFGG Heusler alloys thin films of thickness in the range of 15–50 nm. We have determined the magnetoelastic tensor components and magnetic damping parameters as a function of the magnetic layer thickness. Magnetic damping measurements revealed the existence of non-Gilbert dissipation related contributions, including two-magnon scattering and spin pumping phenomena. Magnetoelastic constant B11 values and the effective magnetic damping parameter αeff values were found to be in the range of − 6 to 30 × 106 erg/cm3 and between 1 and 12 × 10–3, respectively. The values of saturation magnetostriction λS for CFMS Heusler alloy thin films were also obtained using the strain modulated ferromagnetic resonance technique. The correlation between αeff and B11, depending on magnetic layer thickness was determined based on the performed investigations of the above mentioned magnetic properties.

Analysis of the internal damping on temperature of magnesium alloy evaluated for different states of material

The application of magnesium alloys in automotive is witness the developments and successful application of these alloys in automotive components and they have a potential application for car body, cylinder blocks and engine block. The article is focused on chemical analysis, evaluation of microstructures and measurement of internal damping depending on the temperature of the experimental material. The commercially available magnesium alloy AZ61 was chosen as the experimental material. Changes of internal damping depending on temperature were measured for the material in the initial state, in the state after the respective heat treatment and in the state after plastic deformation. Measurements of the temperature dependence of the internal damping took place from room temperature to 400 °C and the measured values of internal damping were then graphically evaluated and compared.

Simulation assessment of the half-power bandwidth method in testing shock absorbers

AbstractThe work deals with usability of the half-power bandwidth method in the diagnostic testing of automotive shock absorbers. In all the simulation tests, the front and rear suspension system of a present-day medium-classmotor car was considered. At the first stage, calculations were made in the frequency domain for a linear “quarter-car” model with two degrees of freedom; then, simulations were carried out in the time domain with using a similar but strongly nonlinear model. In the latter case, actual characteristics (corresponding to those obtained from test rig measurements) of shock absorber damping, suspension and tire elasticity, sliding friction in the suspension, and “wheel hop” were considered. The calculations were carried out every time for twelve levels of viscous damping in the suspension system, which made 48 calculation series in total. The factors of gain in the vertical force between the tester’s vibration plate and the vehicle tire (relative to the input force applied) and the dimensionless coefficients of viscous damping in the suspension system, determined by the half-power bandwidth method, were thoroughly analyzed. The calculation results were presented in graphical form. Attention was also paid to the distortions caused by the force of inertia of the tester’s vibration plate.

Effect of rapeseed oil on the rheological, mechanical and thermal properties of plastic lubricants

A strong difference in the physico-chemical properties of the plastic lubricants studied was found in this study through pressure drop, thermal analysis, vibration damping, texture hardness and rheological measurements. Oxidation aging of the lubricant sample containing rapeseed oil additive was proposed. Its higher thermal sensitivity was simultaneously confirmed by frequency dependent complex shear modulus of elasticity measurements as well as by rheological testing. Rapeseed oil modified lubricant showed a higher decrease in both storage and moduli losses due to a temperature increase from 16 to 26 ° C compared to the rapeseed oil free sample. Simultaneously, the flow curves were shifted to the higher shear stresses (for plastic lubricant without rapeseed oil additive) typical for rheopectic fluids. For the rapeseed oil modified lubricant, the flow curves were shifted to the lower shear stresses, indicating its thixotropic fluid behaviour. The synthetic lubricant without rapeseed oil additive exhibited higher dissipative rheological behaviour as reflected by decreasing first resonance frequency peak position compared to the rapeseed oil modified lubricant as obtained from vibration damping measurements. It was found that the synthetic lubricant exhibited better vibration damping properties and mechanical energy dissipation into heat due to its higher viscous friction than the rapeseed oil modified lubricant under experimental conditions.

Experimental Characterization of Nonlinear Damping in the F-16 Wing Structure

Earlier work did not find any static stiffness nonlinearities in the F-16 wing structure, but suggested that dynamic nonlinearities may be present. Computational studies have demonstrated that small amounts of nonlinear structural damping are sufficient to change a diverging flutter oscillation into a limited amplitude oscillation. Experimental damping measurements of a fixture-mounted F-16 wing were made to determine whether damping nonlinearities are significant and to quantify the nature of any structural damping present in the built-up wing structure. Three fundamental component configurations of the wing were examined: wing box only, wing (i.e., wing box with leading- and trailing-edge control surfaces), and wing with wingtip launcher. A ground vibration test approach was used with a stepped-sine excitation technique over a range of excitation forces. Damping and frequency were extracted from measured frequency response functions of the stepped-sine test data using a modified single degree-of-freedom modal analysis technique. Nonlinear damping with respect to bending mode displacement was observed for all test configurations. The overall magnitude of the damping increased when control surfaces were installed on the wing box. The presence of a wingtip launcher decreased the damping at higher displacements.