Frequency Damping Research Articles

Effects of Hot Rolling on the Microstructure, Mechanical, and Damping Properties of High‐Nitrogen Stainless Steel

In this study, the mechanical and damping properties of high‐nitrogen stainless steel, containing 0.65 wt% nitrogen, after being subjected to hot rolling to deformation ratios 19%–85% are investigated. Mechanical properties are assessed using tensile testing and Vickers hardness testing while damping properties are analyzed using a dynamic mechanical analyzer. A significant improvement in tensile strength is observed in samples deformed to an 85% reduction, showing an ultimate tensile strength of 1227 MPa compared to the initial 810 MPa of the annealed sample. Both the frequency and temperature damping capacities increase with the amount of deformation, peaking at 66% reduction, before slightly declining at 85% reduction. In the study, Finkelshtain–Rosin internal friction peaks, characteristic of austenitic steels, are identified in the temperature range of 100–250 °C. Deformation up to a 66% thickness reduction results in deformed grains with a continuous increase in dislocation density, accounting for trends in the mechanical and damping properties. However, the 85% reduction leads to a finer microstructure with a high fraction of low‐angle grain boundaries formed through continuous dynamic recrystallization during hot rolling. This creates immobile dislocation networks, which adversely affect the damping properties.

Vibration Behavior of 3D-Printed Graded Composites: Fabrication and Testing.

Multi-head 3D printers afford the ability to create composite structures with significant differences in properties compared to those created through traditional molding techniques. In addition to the usage of different viscoelastic polymeric materials, the selective spatial placement of the build materials enables the creation of layered and graded geometries to achieve specific mechanical and/or vibrational characteristics. This paper describes how the mechanical properties of the individual materials can be used to predict the damping and natural frequencies of a 3D-printed graded structure. Such structures can find usage in rotating machinery, beams, etc., where vibrational characteristics must be controlled. The simulation and experimental results are presented and two forms of the storage and loss modulus are considered: fixed and variable. For the latter condition, E' and E″ are established as functions of temperature and frequency. Modal vibration testing of the graded samples shows a good match between the simulation and experimental trials, thereby supporting the proposed model as a useful tool for prescribing the structure of a printed part with tailored dynamic properties.

On the Damping and Fatigue Characterization of Additively Manufactured Ti-6Al-4V

With the recent implementation of additively manufactured parts into industrial applications, there is a dire need for nondestructive evaluation methods to qualify if these components are fit for service due to their sensitivity to processing conditions. The Impulse Excitation Technique (IET) is applied to additively manufactured Ti-6Al-4V bending specimens to determine natural frequencies and damping properties in order to predict fatigue performance relative to specimens fabricated with different processing parameters. From the damping and natural frequency results, it was found that the specimens, fabricated with intentional underheating to induce lack of fusion defects, had the lowest damping value in the pristine condition and the highest natural frequency. For the three batches of specimens tested, it was determined that the lack of fusion specimens had the best fully-reversed bending fatigue performance with the highest fatigue limit (297 MPa) and longest fatigue lives as compared to the other two batches, implying a relation of decreased fatigue life with increased material damping in the pristine condition. The theory of the IET related to materials is presented with damping and fatigue results, as well as microstructural analysis and fractography of three specimens batches fabricated with different processing parameters.

The impact of current-loop control parameters on the electromagnetic transient voltage performance of voltage-source converter

Since the large-scale integration of renewable energy sources into the AC grid has led to a relative decline in the voltage support capacity of the grid and the deterioration of the voltage dynamic at the grid connection point, especially under fast-scale conditions, the voltage disturbance has become more obvious. To improve the dynamic characteristics of the electromagnetic transient voltage at the grid connection point, this paper uses a practical dynamic damping method to analyze the impact of the converter current inner loop, feedforward voltage, and other links on the dynamic performance of the electromagnetic transient voltage. First, the current inner loop dynamic in the converter’s synchronous coordinate is converted into an equivalent transfer function in the stationary coordinate, and the transfer function between the transient voltage disturbance at the grid connection point and the inner loop current output is established. On this basis, the Bode diagram and the vector diagram of the transfer function in the weak damping frequency band are used to analyze the dynamic damping of the current inner loop parameters and voltage feedforward filter parameters on the voltage disturbance at the grid connection point. The results indicate that moderately increasing the current inner loop bandwidth or reducing the feedforward filter bandwidth can help enhance the electromagnetic transient voltage stability of the grid connection point, but increasing the current inner loop bandwidth will worsen the low-frequency damping characteristics and reduce the feedforward filter bandwidth will still help increase low-frequency damping.

New implicit time integration schemes for structural dynamics combining high frequency damping and high second order accuracy

The time integration schemes, GA-23 and GA-234, recently proposed by the authors for first order problems, are extended to solve second-order problems in structural dynamics. The resulting methods maintain unconditional stability and user-controlled high-frequency damping. They offer improved accuracy and exhibit less numerical damping in the low-frequency regime, outperforming the well-known generalised-α method. When the high-frequency damping is maximised the new schemes can be cast in the format of backward difference formulae, offering more accurate alternatives to the standard second order formula. The effectiveness of the new time integration schemes is validated through a number of numerical examples, including a linear elastic cantilever beam, a nonlinear spring pendulum, and wave propagation on a string.

Healable, Recyclable, and Ultra-Tough Waterborne Polyurethane Elastomer Achieved through High-Density Hydrogen Bonding Cross-Linking Strategy.

With the increasing popularity of elastomers in industry and daily life, their high performance and functionality have attracted widespread attention. However, it is a great challenge for them to possess both high mechanical properties and excellent healing and recovery capabilities due to the limitations of the preparation methods and the intrinsic microstructure of the elastomers. In this study, a strategy of ice-controlled interfacial stepwise cross-linking was proposed to prepare the waterborne polyurethane-based elastomers with ultrahigh-density hydrogen bonding interaction achieved by enhancing the utilization rate of phenol hydroxyl groups of tannic acid to the maximum extent. The elastomers have incredible mechanical properties, including ultrahigh toughness of 1.03 GJ m-3 (which represents the highest level among polyurethane elastomers prepared through common processing techniques to date), extremely high true fracture stress of ∼1.9 GPa, world-record fracture energy of 520 kJ m-2, and exciting multiple functional characteristics, such as highly efficient self-healing ability of 10 min, high resistance to physical damage and chemical corrosion, broad temperature and frequency damping effects, good shape memory effect, and excellent melt-processing recyclability and solvent recyclability. These robust multifunctional elastomers represent considerable potential in various fields, from defense and military industry and civil transportation to precision manufacturing, etc.

REAL-VALUED DAMPED SINUSOID PARAMETER ESTIMATION USING A THREE-POINT INTERPOLATED DISCRETE FOURIER TRANSFORM ALGORITHM

This paper proposes new real-valued damped sinusoid frequency and damping factor estimators. They exploit a three-point Interpolated discrete Fourier transform (IpDFT) algorithm based on the Rife-Vincent class I (RVCI) windows and complex-valued DFT samples. The accuracies of the proposed estimators are compared with those provided by other state-of-the-art interpolated Fourier algorithms using computer simulations when pure, noisy, and noisy and harmonically distorted damped sinusoids are analyzed.

Research on Load Correlation of Blunt Headed Aircraft

Abstract In order to study the influencing factors of static and dynamic loads on short blunt body balanced wing structures in the external atmospheric environment, and to avoid and prevent structural overload and damage, this paper conducted load tests on short blunt body structures and conducted load correlation analysis. This article establishes a dynamic load testing method for internal excitation and measurement, which is more suitable for dynamic load measurement of small structures compared to traditional wind tunnel testing techniques. On this basis, the influencing factors of dynamic loads were studied. By measuring and changing the Mach number, angle of attack, model frequency, and aerodynamic damping data of the model flight, the influence of the above variables on the static and dynamic loads of the model was obtained. The experimental results indicate that the established measurement technique can accurately and effectively obtain static and dynamic test results of the structure. Pneumatic damping is negatively correlated with dynamic loads, with a correlation coefficient of around -0.8. The Mach number and angle of attack are positively correlated with dynamic loads, with a correlation coefficient of around 0.98. This article establishes a new wind tunnel testing and measurement method, analyzes the influencing factors of dynamic loads, and is of great significance for dynamic load measurement and the design of new aircraft.

Triboelectric nanogenerator based on silane-coupled LTA/PDMS for physiological monitoring and biomechanical energy harvesting

Energy harvesting from ambient sources present in the environment is essential to replace traditional energy sources. These strategies can diversify the energy sources, reduce maintenance, lower costs, and provide near-perpetual operation of the devices. In this work, a triboelectric nanogenerator (TENG) based on silane-coupled Linde type A/polydimethylsiloxane (LTA/PDMS) is developed for harsh environmental conditions. The silane-coupled LTA/PDMS-based TENG can produce a high output power density of 42.6 µW/cm2 at a load resistance of 10 MΩ and operates at an open-circuit voltage of 120 V and a short-circuit current of 15 µA under a damping frequency of 14 Hz. Furthermore, the device shows ultra-robust and stable cyclic repeatability for more than 30 k cycles. The fabricated TENG is used for the physiological monitoring and charging of commercial capacitors to drive low-power electronic devices. Hence, these results suggest that the silane-coupled LTA/PDMS approach can be used to fabricate ultra-robust TENGs for harsh environmental conditions and also provides an effective path toward wearable self-powered microelectronic devices.

Method for Predicting Environmental Vibration Impact of Existing Subway Lines and Its Practical Application

To predict accurately the impact of track vibrations caused by subway trains on adjacent buildings and address the problem of their excessive dynamic response, a method for predicting the environmental vibration impact of existing subway lines is proposed in this paper. A coupled numerical dynamical model of the train/track/tunnel system is established using the multi-scale method. Using field-measured soil vibration data, empirical formulas for soil frequency and material damping coefficient are calibrated. By combining the numerical model and the empirical formulas, buildings’ indoor vibrations and noise level can be assessed. At the same time, a solution to the problem of excessive vibration of buildings along a subway line is also proposed that optimizes the track fastener parameters. Field tests verified the accuracy of the prediction method and the effectiveness of the optimized track parameters. These research results provide a reference for predicting the vibration of buildings along subway lines and using the proposed preventive solutions.

The use of ensembles trees machine learning method in estimating damping of granular materials

Granular Materials (GM) employed within the mechanism of particle dampers attenuate the vibration energy due to their interparticle and particle-wall interactions. Estimating their damping effect using the analytical equivalent single mass approach overlooked the particles' individual losses that are built into the total damping. Alternatively, the numerical techniques (e.g., Discrete Element) are time-inefficient and computationally demanding. Therefore, this study explores the implementation of Machine learning (ML) algorithms to estimate the damping effect of GM. The ML model in this study will rely on a Data-Driven Modeling approach (DDM) incorporating the ensemble tress nonlinear regressor method. The models' training and testing data were obtained from an experimental setup of an acrylic beam internally integrated with Stainless Steel (SS) and glass spheres undergoing low excitation amplitude (RMS <1N). The main aim was to map between seven input features (e.g. filling ratio) and one targeted output: the beam's damped frequency response. Three ensemble trees' algorithms were used to create the DDM; Decision Tree, Random Forest, and XGBoost. The hyperparameter combination based on the Gridsearch CV function increases the prediction accuracy of each model. The developed ML models provided high accuracy (86-93%) in predicting the damping effect of the granular materials spheres.

Coupling Coefficient Estimation in Inductive Power Transfer Systems Through Damped Frequency

Coupling Coefficient Estimation in Inductive Power Transfer Systems Through Damped Frequency

Analytical solution of seismic power-based equation of motion

This research proposes an innovative power-based equation of motion (PBEM) for the single degree of freedom (SDOF) system considering seismic excitation. The external or input frequency function, solution of time, relation between external and kinetic powers, and equation of strain-power (SP) are obtained by solving the power balance equation (PBE). The external frequency function is related to both the particular and total solutions of the PBEM. The particular solution of PBEM is applied on the shake table test of the tunnel-soil-pile interaction (TSPI) model, real-scale test of 2-storied reinforced concrete frame structure, and case study of Bolu tunnel for the verification purpose. The differences in verification (PBEM and previous works) results are found to be 21.6 % for the real-scale test and 19.5 % for the case study. These differences may represent a reasonable agreement with verification. Also, the relationship between the kinetic and external powers is verified with the previous shake table test of steel cantilever column, whereas the difference in results is found to be 5 %. Finally, a design chart is proposed for predicting the input frequency function for various frequency ratios and damping.

A selective frequency damping and Janus adhesive hydrogel as bioelectronic interfaces for clinical trials

Maintaining stillness is essential for accurate bioelectrical signal acquisition, but dynamic noise from breathing remains unavoidable. Isotropic adhesives are often used as bioelectronic interfaces to ensure signal fidelity, but they can leave irreversible residues, compromising device accuracy. We propose a hydrogel with selective frequency damping and asymmetric adhesion as a bioelectronic interface. This hydrogel mitigates dynamic noise from breathing, with a damping effect in the breathing frequency range 60 times greater than at other frequencies. It also exhibits an asymmetric adhesion difference of up to 537 times, preventing residues. By homogenizing ion distribution, extending Debye length, and densifying the electric field, the hydrogel ensures stable signal transmission over 10,000 cycles. Additionally, it can non-invasively diagnose otitis media with higher sensitivity than invasive probes and has been effective in clinical polysomnography monitoring, aiding in the diagnosis of obstructive sleep apnea.

A Vibration Decoupling System for TES Operation in the COSINUS Dry Dilution Refrigerator

COSINUS will be among the first underground experiments to operate Transition Edge Sensors in a dry dilution refrigerator, measuring temperature changes on the order of μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mu$$\\end{document}K. A pulse tube cryocooler is used to cool down to 3K, trading simplified handling, by not using liquid noble gases, for an increased vibration noise level in the acoustic frequency range. As the signals measured with a TES are in the same frequency region, it is necessary to decouple the detectors from all possible noise sources. In COSINUS, a two-level passive decoupling system was developed and tested using piezo-based accelerometers. At the first level, the refrigerator is mechanically isolated from all external noise sources. For the second level an internal spring-based system was developed and tested on a mockup system. On the first level a reduction of the vibrational background up to a factor 4 below 10 Hz could be measured. On the second level a resonance frequency of 1.2 Hz with damping of higher frequencies was achieved.

Improved State-Space Approach Based on Lumped Mass Matrix for Transient Analysis of Large-Scale Locally Nonlinear Structures

Due to the assumption of acceleration variation in traditional step-by-step integration methods such as Newmark, sufficiently small time steps are required to ensure numerical stability and accuracy in dynamic systems. In contrast, the state-space approach, based on piecewise interpolation of discrete load functions, does not rely on predetermined acceleration assumptions and has demonstrated high efficiency in terms of stability and accuracy. The original state-space method requires the calculation of the inverse of the structural mass in the transition matrix. However, when a lumped mass matrix is used, this computation renders the entire mass matrix singular, resulting in an invalid solution expression. To address this issue, this study proposes an improved state-space approach for the transient analysis of large-scale structural systems with local nonlinearities. In this approach, a nonlinear force corrector is introduced as an external force term applied to the linear elastic system to account for the nonlinear behavior of locally yielding components. Consequently, the original nonlinear dynamic system can be transformed into an equivalent linear elastic transient system. Furthermore, based on the lumped mass matrix, a first-order ordinary differential state-space equation for such an equivalent linear elastic transient system is derived. Simulation results from three transient system examples show that the state-space approach outperforms the Newmark method in terms of accuracy and stability for dynamic systems characterized by high frequency and low damping. The prediction results show that the state-space approach appears to be insignificantly affected by the choice of the consistent or lumped mass matrix. The numerical results show that the root-mean-square errors between the consistent and lumped matrices in the top displacement time histories of a 15-storey plane frame under various seismic intensities are all less than 1%, and in the base reaction time histories responses the discrepancies are only about 0.5%, indicating that the use of lumped mass matrices is quite reliable. When many nodes or degrees of freedom have no assigned mass, the dimensionality of the state-space equation can be significantly reduced using the lumped mass approach. Therefore, the simulation of large-scale systems can be simplified by employing the improved state-space approach with lumped mass matrices, yielding results nearly identical to those obtained using traditional methods. In conclusion, the improved state-space approach has great potential for the simulation of transient behavior in large-scale systems with local nonlinearities.

Numerical prediction of ground-borne vibrations due to continuous vibratory driving of circular closed-ended piles

Various types of pile driving work may induce high-intensity ground-borne vibrations. Predicting vibration intensity before adopting mitigation measures is vital for minimizing the impact of vibration on nearby structures and occupants. Vibratory pile driving is a commonly applied foundation construction method. However, numerical simulation models for ground vibrations during a complete process of vibratory driving have rarely been studied. This study introduces an axisymmetric finite element model that utilizes the arbitrary Lagrangian-Eulerian technique to simulate the continuous vibratory driving of a circular closed-ended pile penetrating from the ground surface to a target depth. The model validity was confirmed by assessing the calculated ground vibrations against the findings documented in earlier research. The results showed that the critical penetration depth of piles, at which the maximum peak particle velocity (PPV) occurs, varied with the radial distance and depth of points of interest, contradicting a common preconception. Moreover, the maximum PPV did not always occur on the ground surface across all radial distances. Parametric analysis revealed that an increase in the soil cohesion strength, pile diameter, or soil-pile friction, or a decrease in the driving frequency or soil damping ratio would increase ground vibrations due to vibratory pile driving.

Sensitivity analysis of frequency response functions with imaginary parts decoupling based on multicomplex-step perturbation

Imaginary perturbation is used in the complex step differentiation method to compute first-order derivatives, widely known as an effective approach for sensitivity analysis in structural dynamics. However, coupling of imaginary parts occurs in the damped frequency response functions when employing this method. To mitigate this coupling, a novel approach for sensitivity analysis based on multicomplex-step perturbation is proposed in this paper, for sensitivity analysis of Frequency Response Functions in structural dynamics. The structural parameters are perturbed in multicomplex domain, the dimensions of structural matrices are expanded using the Cauchy Riemann matrix representation, the equation of motion for sensitivity analysis in frequency domain is transformed to matrix operation in field of real numbers, imaginary term will not exist in the equation of motion for sensitivity analysis, the imaginary part of the frequency response function and the imaginary part of the perturbation are decoupled, the structural frequency response functions and the corresponding sensitivities are obtained from the dimension-expanded equation of motion. A truss structure and a solar wing are adopted to verify the accuracy of the proposed method. Results show that the sensitivity of FRFs can be effectively calculated using the proposed method. Compare to the finite difference method, the proposed method is not depended on the step-size selection procedure. The multi-order and mixed-order sensitivity matrices, especially Hessian matrix can also be obtained using the proposed method.

Mechanism of eccentricity influence on 3-DOF aerodynamic stability: New insights into instability evolution, energy harvesting, and vibration control

The inconsistency of mass center and elastic center, i.e., eccentricity, widely exists in various engineering structures and components, including iced conductors, wind turbine blades, airfoils, and cable-supported bridges, and can also be extended to the application of energy harvesting and vibration control. Although the eccentricity influence on aerodynamic stability has already been recognized as important, the underlying mechanism remains rather unclear. This study established a comprehensive framework of explicit eigenvalue solutions, offering in-depth insights into the aerodynamic stability mechanism in a vertical-horizontal-torsional 3-degree-of-freedom linear system under all possible frequency scenarios. These solutions elucidated the coupling mechanism of eccentricity, aerodynamic damping, aerodynamic stiffness, and structural frequencies. Remarkably straightforward criteria to predict the promoting/suppressing effect of eccentricity were proposed, consisting of eccentric angle and aerodynamic forces, which not only align with the traditional principles but also offer a broader application range in terms of structure types and wind speeds. Validations of the proposed solutions were performed for all frequency cases via numerical studies. For instability tendency evaluation, numerical studies on a thin plate showed that eccentricity has a significant impact due to the strong aerodynamic effect and large ratio of width/gyration radius, highlighting the importance of considering small eccentricity errors during experiments. Examination for energy harvesting revealed that a small eccentricity can dramatically enhance power generation efficiency, and the explicit solutions successfully explained the rules governing performance changes against frequency ratio, mass center position, rotation center position, etc. The analysis of a bundled conductor showed that the double pendulum can control galloping because it diminishes the eccentricity effect by shifting the eccentric angle. The proposed explicit solution framework provides a systematic view and new insights into the aerodynamic instability mechanism influenced by eccentricity, serving as a reference for the design and studies of various engineering structures, energy harvesting, and vibration control.

Assessment of the Compound Damping of a System with Parallelly Coupled Anti-Seismic Devices

(1) Background: Romanian earthquakes caused severe damage over time to a significant number of constructions, and that is why efforts are being made to make structural systems safer. (2) Methods: For structural systems with protection against seismic actions or vibrational actions that have linear viscous dissipation devices, the requirement to assess the equivalent modal damping rate for the entire functional assembly related to the other dynamic parameters arises. (3) Results: This article presents the analytical development of formulas for the compound damping and circular frequency when anti-seismic devices have different dynamic characteristics and their application in order to solve some real engineering cases of bridges and viaducts in Romania with distinct viscoelastic supports. In support of this idea, some experimental tests on a beam system resting on two different anti-seismic elastic supports highlighted the fact that the compound damping of the system can be calculated with the relations established in this paper, provided that the displacements in the horizontal direction of excitation are in the linear domain. Also, we determined the seismic response considering the Vrancea 1977 accelerogram for critical damping ratios of 5% and 18.5%, and then we obtained the variation in the factor of transmissibility depending on the frequency, in order to highlight the optimized value of the equivalent amortization/damping. (4) Conclusions: In the specific context of Romanian seismicity, seismic isolation through the use of isolators with different characteristics represents an optimal technical solution, and it is also optimal from an economic point of view, with an appropriate level of dynamic isolation obtained.