Structural Damping Research Articles

Vibration Attenuation in a Beam Structure with a Periodic Free-Layer Damping Treatment

In order to improve the vibration reduction performance of damping treatments, a new damping structure consisting of a uniform base layer and two periodically alternating free layers was examined in this study. Closed-form solutions for both the band structure and the forced response of the periodic bi-layer beam were theoretically derived and verified via numerical solutions using the finite-element method. The results showed that the structure with periodic free-layer damping (PFLD) treatment reduced broadband vibrations, and the levels of reduction were dominated by Bragg scattering in the band gaps and damping in the passbands. The vibration experiment verified the derived theory’s accuracy and showed that the PFLD treatment could increase vibration reduction levels in low-frequency band gaps compared with traditional free-layer damping treatments. The effects of the parameters—cell lengths, sub-cell-length ratios, and thickness ratios—were also discussed, providing further understanding of the vibration reduction performance of the bi-layer beam with the PFLD treatment, and this can be used to help designers optimize the periodic bi-layer beam to achieve better performance.

Structural damping estimation from live monitoring of a tall modular building

AbstractThe damping ratio is a key indicator of an individual structure's susceptibility to dynamic loads, including the level of discomfort experienced by the occupants of a tall building subjected to wind loading. While computational models, laboratory studies and empirical data can provide estimates of structural damping, the most reliable way to evaluate true damping ratio values is through modal identification using data from field tests on full‐scale finished structures. As an innovative form of construction, high‐rise modular buildings have not been the subject of previous vibration monitoring investigations, implying an absence of essential structural dynamics information. This paper assesses the reliability of four modal identification methods for estimating the damping ratio of a structure using ambient acceleration response data recorded from the world's tallest modular structure, the Ten Degrees building in Croydon, South London. The methods considered are two implementations of the Bayesian fast Fourier transform (BFFT), the random decrement technique (RDT), and a hybrid of the RDT which first decomposes the ambient data into sub‐signals using analytical mode decomposition (AMD‐RDT). Each method is applied to response data collected during 10 significant wind loading events to evaluate the inherent modal properties of the structure, with the computed damping ratio values compared between methods and events. By reporting the first measured damping ratios for a tall modular structure, the paper makes an important contribution to knowledge about the vibration properties of an emerging form of construction.

Decay of a Thermoelastic Laminated Beam with Microtemperature Effects, Nonlinear Delay, and Nonlinear Structural Damping

This article deals with a non-classical model, namely a thermoelastic laminated beam along with microtemperature effects, nonlinear delay, and nonlinear structural damping, where the last two terms both affect the equation which depicts the dynamics of slip. With the help of convenient conditions in both weight delay and wave speeds, we demonstrate explicit and general energy decay rates of the solution. To attain our interests, we highlight useful properties regarding convex functions and apply a specific approach known as the multiplier technique, which enables us to prove the stability results. Our results here aim to show the impact of different types of damping by taking into account the interaction between them, which extends recent publications in the literature.

Comparative theoretical and experimental analysis of vibration damping performance in multilayer constrained layer damping structures: Aluminium versus glass fiber reinforced polymer

This study investigates the dynamic behavior of multilayer Constrained Layer Damping (CLD) structures, specifically focusing on constraining layers made of aluminum and Glass Fiber Reinforced Polymer (GRP). Numerical simulations are compared with experimental results using the finite element method (FEM) and the widely used Ross–Kerwin–Ungar (RKU) model to achieve this. Experimental modal analysis is conducted on a vibration shaker to validate the FEA findings. The research reveals valuable insights into the damping performance of aluminum and GRP as constraining layers. Notably, aluminum demonstrates superior damping properties, particularly in the higher frequency range (ultimate loss factor 0.2), while GRP exhibits better-damping characteristics in the lower frequency range (ultimate loss factor 0.13). These results underscore the significance of considering the frequency-dependent behavior of materials when selecting appropriate constraining layers. By shedding light on the dynamic behavior and damping performance of multilayer CLD structures with different constraining layers, this study contributes to the effective mitigation of vibrations in various engineering applications. This endeavor will enhance the understanding and application of constraining layer materials for effective structural vibration control, paving the way for improved engineering solutions.

Advanced numerical techniques for predicting frequency response functions

Numerical methods have been widely used to predict Frequency Response Functions (FRF) of structures. The FRF can be used to characterize structural dynamics and support sound and vibration control. Generally, frequency sweep is conducted in the FRF calculations to identify damping and resonant frequencies of structures under excitations. However, as numerical models are getting complex and larger, the demands for computational resources (e.g., CPU time, memory, disk space) are greatly increased. Lately, high performance computing (HPC) at the DoD HPC center has been used with advanced numerical techniques to reduce the overall computational time. Those advanced numerical techniques include Krylov subspace and Galerkin Projection (KGP) and Pade Approximation. Significantly CPU time reduction has been demonstrated for relatively smaller FE models. This paper will further discuss adaptive KGP by automating the frequency sweep process via calculated relative residues, then combine with Finite Element Tearing and Interconnecting (FETI) to solve for FRF of a large FEM model in the order of 60M DOF. A flat plate with viscoelastic layer will serve as an example to demonstrate accuracy and efficiency of AKGP with FETI. The benefits of using HPC with advanced numerical techniques to solve for large FEM models are clearly displayed.

Parametric Study of the Efficiency of Fluid Viscous Damper in Structures with Different Heights

Parametric Study of the Efficiency of Fluid Viscous Damper in Structures with Different Heights

Drill-string stability and stress localization: Influence of complex delay effects and dry friction

With the aim of enhancing the understanding of the complex dynamics of deep drilling, an integrated model with complex time delays and Stribeck friction is presented for studies on the axial-torsional dynamics of a drill string. Various aspects of the drill string are considered, including spatial distribution, structural and external damping, dry friction-induced damping, boundary conditions, and complex bit-rock interactions. The drill-string structure is spatially discretized by using the finite element method. With the resulting discretized complex delay system, stability analysis is conducted following the semi-discretization procedure. Through parametric studies, the effects of drilling parameters, dry friction, boundary conditions, and rock-strength properties on the drilling stability are obtained. Subsequently, an optimally tuned boundary condition with compliance is deployed at the top drive to expand the stable region and mitigate self-excited vibrations in the operational parameter space of drilling. To find the distribution of stress along the drill string, numerical simulations are conducted. The dynamical stress caused by self-excited vibrations is illustrated in the spatial–temporal plane. Strain and stress analysis reveal wave propagation along the drill string, including traveling and standing waves. The dynamic effective stress along the drill string is studied, and the von Mises effective stress is determined by combining the axial stress and torsional stress. On the basis of this information, the locations of the vulnerable points along the drill string are found in terms of structural strength. Finally, the tuned boundary condition at the top is deployed in the numerical simulations to show vibration control effectiveness. The results point to two possible vibration-cancellation approaches that can benefit from a tuned top boundary. The findings of this work can serve as a basis for identifying the locations of vulnerable points and alleviating the levels of axial-torsional vibrations in drilling applications.

Sound insulation properties of embedded co-cured composite damping sandwich panel under arbitrary boundary conditions

The embedded co-cured composite damping structures (ECCDS) are widely used in engineering fields, it is necessary to build a predictive model of the dynamics of the ECCDS panel. In this paper, a method is promoted for the first time that can predict the acoustic-vibration coupling characteristics of the coupled cavity-ECCDS panel-cavity system. This paper innovatively combines the spectral-geometry method (SGM), penalty-function method (PFM), and the energy-generalised variational principle to develop coupling model of the ECCDS panel with two closed cavities. The displacement of the ECCDS panel and the sound pressure in the cavities are expressed as improved Fourier series. The modal parameters of the cavities and the ECCDS panel are obtained by solving the standard matrix eigenvalue problem, and the accuracy of this method is verified by comparing it with the finite element method (FEM) and experiment. On this basis, the sound transmission loss (STL) can be obtained by the sound pressure method. The factors affecting the sound insulation performance of the ECCDS panel are investigated by parametric analysis. The results show that the addition of a damping layer can improve the sound insulation performance of composite panels. This paper provides a reference for the application of ECCDS panels in engineering.

Wall-proximity effects on vortex-induced vibrations of a circular cylinder

Vortex-induced vibrations (VIV) of an elastically supported circular cylinder (of diameter D) undergoing a wall interference are investigated for a mass-damping ratio 0.31, Reynolds numbers 1.77 × 103–1.24 × 104, and wall-cylinder gap height ratios e* = e/D = 0.1–1.6. Measurements of vibration responses and vortex shedding frequencies are done using a laser vibrometer and a hotwire anemometer, respectively, while particle image velocimetry techniques are employed to capture flow fields. This investigation aims to assimilate the effect of e* on vibration response, frequency response, VIV range, quality factor of VIV, added mass, added damping, lift force, and flow structure. A smaller e* is observed to increase the added mass, reduce the maximum vibration amplitude, and shorten the VIV range while enhancing the quality factor of VIV. The increase in added mass and the decrease in the maximum vibration amplitude in the VIV range are dramatic when e* is decreased from 0.6. Decreasing e* significantly impacts the flow structures and vortex shedding modes, resulting in intensified asymmetry in pressure distributions. The interference between the wall and the cylinder is further reflected by increasing time-mean lift forces and decreasing fluctuating lift forces with decreasing e* < 0.6.

Application of nonlinear stiffness mechanism on energy harvesting from vortex-induced vibrations

This study investigates the potential of vortex-induced vibration (VIV) as a renewable energy source, achieved when fluid flow interacts with a bluff body, inducing self-sustained oscillations through vortex shedding in the wake. While VIV research has traditionally focused on understanding its mechanisms and mitigating detrimental effects, interest in VIV energy harvesting has surged as a means to convert marine hydrokinetic (MHK) energy into usable electrical power. The nonlinear effects of two linear oblique springs on VIV energy harvesting are explored using the wake oscillator model, encompassing bistable and Duffing hardening stiffness. The study examines the response and energy harvesting performance while considering the impact of undeformed spring length, structural damping, and initial conditions on VIV energy conversion. Findings show that nonlinear stiffness application in the VIV system can broaden the synchronization bandwidth or reduce the VIV initiation flow speed. Bistable stiffness may broaden the synchronization velocity range, while Duffing hardening stiffness efficiently reduces the VIV initiation speed with small energy harvesting loss. Combining both stiffness types with appropriate control strategies presents a promising approach for achieving a broad synchronization VIV bandwidth and low initiation flow speed. Key parameters, such as the nondimensional parameter defining spring system obliquity and the ratio between undeformed spring length and cylinder diameter, significantly influence VIV response and energy harvesting. Moreover, optimal structural damping is vital to maximize energy harvesting efficiency, and understanding and controlling initial conditions are crucial for optimizing VIV synchronization bandwidth and energy harvesting efficiency for both bistable and Duffing hardening stiffness. This study provides valuable insights into VIV system dynamics and energy conversion potential with nonlinear springs, offering promising avenues for enhancing energy harvesting efficiency and inspiring further applications of nonlinear effects in VIV energy converters.

Flow-induced vibration of an elliptic cylinder with a splitter-plate attachment at low-Reynolds number: Self-limited oscillations

Flow-induced vibrations (FIV) of a rigid, elastically-mounted elliptical cylinder-plate assembly which is free to move in the cross-flow (transverse) direction is studied using numerical simulations. These simulations were conducted for a laminar flow at a Reynolds number of Re=100 over a reduced velocity range of Ur= 2–30, with a low mass ratio (m∗=10) and zero structural damping, for various values of the aspect ratio AR of the elliptical cylinder; namely, AR= 0.5, 0.67, 0.75, 1, 1.5 and 2. It is shown that the characteristics of the FIV response of an elliptical cylinder-plate assembly that occurs over a limited velocity range (viz., self-limited FIV) such as the vibration amplitude, the reduced-velocity range with vibrations, the nature of the branching behaviour (e.g., synchronization and non-synchronization branches in the amplitude response), and the vortex-shedding (wake) modes are strongly dependent on the aspect ratio. The self-limited FIV response of the assembly is enhanced for AR increasing from 0.75 to 1.5. However, it is found that for AR=2, the reduced-velocity range over which the FIV response occurs is significantly shortened owing to the absence of a non-synchronization branch in the amplitude response for this case. There is a critical value (AR)cri of the aspect ratio below which oscillations in an elliptical cylinder-plate assembly cannot be induced. This critical value occurs in the range 0.67<(AR)cri<0.75 for an assembly in a laminar flow at Re=100 for a fixed splitter-plate length LSP/D=0.5 (D is the equivalent diameter of the ellipsoidal cylinder). A careful analysis shows that there is close relationship between the presence of structural oscillations in the assembly and the location of flow separation points on the windward surface of the elliptical cylinder.

Experimental investigations on the vortex-shedding from a highly tapered circular cylinder in smooth flow

This paper presents the results of a wind tunnel test campaign conducted to investigate the aeroelastic and aerodynamic behaviour of a tapered circular cylinder in smooth flow conditions. The model under investigation is a single-mode aeroelastic one, whose taper ratio (in terms of diameter) is 8 %. Its global dynamic response was measured through the use of an internally-mounted piezo-electric accelerometer. The sensitivity of the vortex-induced response to different levels of structural damping was explored. The harmonic content of the wake was also measured through a hot-wire anemometer positioned downstream of the wind tunnel model at different heights: this allowed the detection of the portion of the model whose local resonance was accountable for the highest vortex-induced structural response. To further expand the findings of the wake measurements, four ‘rings’ of surface-mounted pressure sensors were installed on the wind tunnel model. The Reynolds number that was covered during the experiments ranged between 9.3×103 and 3.2×104.The experimental investigations revealed that the tapering has a beneficial effect with respect to vortex-induced oscillations, reducing their magnitudes when compared against the ones of a parallel-sided circular cylinder. On the other hand, the lock-in region was found to be wider, exhibiting three distinct peak regions for the lowest level of structural damping. The combined results from the accelerometer, the hot-wire anemometer and the pressure measurements, and the application of tailored time–frequency analyses based on the continuous wavelet transform, revealed that the maximum dynamic response is linked to the local resonance between the fundamental frequency and the bottom portion of the structure. Furthermore, the magnitudes of the local mean aerodynamic drag coefficient and the local standard deviation of the (vortex-induced) lift coefficient were found to be considerably lower than those of a parallel-sided circular cylinder.

Применение динамических гасителей колебаний для повышения устойчивости башенных сооружений связи к ветровым воздействиям

Purpose: To investigate the application of dynamic vibration dampers in communication tower structures to protect them from the effects of wind loads. Methods: To analyze the design features of existing tower structures. To consider the effect of various factors including wind loads on the choice of tower structure design. To analyze the climatic parameters of the construction area and to determine the type of tower structure as the subject for conducting this research. To determine the quality criteria of vibration damping, on the basis of which the selection of design dynamic vibration dampener (DVD) construction is carried out, and to calculate its weight. To conduct the calculation study of the selected type of building with regard to wind loads and evaluate the effectiveness of the proposed solution of the dynamic vibration dampener to increase the stability of communication tower structures in areas with wind gusts over 25 m/s. Results: The results of the research of dynamic vibration dampener design aimed at improvement of operating conditions of telecommunication facilities in the areas with increased wind load are presented. Practical significance: It is shown that the use of dynamic vibration dampers in tower constructions of cellular communication makes it possible to reduce the vibration amplitude and the maximum horizontal displacements occurring in the tower structure under wind load.

Aseismic performances of constrained damping lining structures made of rubber-sand-concrete

Flexible damping technology considering aseismic materials and aseismic structures seems be a good solution for engineering structures. In this study, a constrained damping structure for underground tunnel lining, using a rubber-sand-concrete (RSC) as the aseismic material, is proposed. The aseismic performances of constrained damping structure were investigated by a series of hammer impact tests. The damping layer thickness and shape effects on the aseismic performance such as effective duration and acceleration amplitude of time-domain analysis, composite loss factor and damping ratio of the transfer function analysis, and total vibration level of octave spectrum analysis were discussed. The hammer impact tests revealed that the relationship between the aseismic performance and damping layer thickness was not linear, and that the hollow damping layer had a better aseismic performance than the flat damping layer one. The aseismic performances of constrained damping structure under different seismicity magnitudes and geological conditions were investigated. The effects of the peak ground acceleration (PGA) and tunnel overburden depth on the aseismic performances such as the maximum principal stress and equivalent plastic strain (PEEQ) were discussed. The numerical results show the constrained damping structure proposed in this paper has a good aseismic performance, with PGA in the range (0.2–1.2)g and tunnel overburden depth in the range of 0–300 m.

Behavior factor estimation for seismic design of unreinforced masonry buildings

The use of new geo-sourced construction materials in seismic areas requires the assessment of the structure ductility in order to properly design the building. This research aims to propose a procedure for behavior factor estimation in case of using a new construction material. In particular, in this paper, the proposed methodology is applied to an unreinforced masonry building in an average-risk seismic zone. Before application for seismic design, the reliability of the selected equivalent frame modeling approach is validated by comparison of dynamic features obtained from both numerical and operational modal analysis. An existing stone masonry building is selected as case study to validate the modeling approach. A measurement campaign provides the structural response to ambient vibrations and structural damping. After validating the model in elastic conditions, the building ductility capacity is estimated using a numerical pushover analysis, for different load combinations and distributions, according to the European design code, under the assumption of perfect plasticity. The proposed procedure provides a behavior factor obtained specifically for the analyzed building, using a relationship between ductility demand and behavior factor deduced from dynamic analysis. The average ductility demand is estimated numerically, for a set of synthetic acceleration signals compatible with the Eurocode elastic response spectrum and a given behavior factor. Finally, it is suggested to verify the near collapse limit state of the building structure not only in terms of target to capacity displacement ratio but also in terms of load ratio, since it can be more restrictive in some instances.

Stability of delaminated composite beams subjected to retarded periodic follower force

This work deals with the stability problem of elastic composite cantilever beams subjected to a delayed, periodically changing follower force. The equation of motion of the periodic system with time delay is deduced based on some previous works. Composite beams with and without delamination are considered, and the finite element method is applied to carry out the spatial discretization of the structures. Besides, for the delaminated case further two cases are involved. The first case is when the delamination is in the midplane of the beam, while the second case involves an asymmetrically placed delamination, respectively. The Floquet theory is applied to derive the transition matrix of the periodic system. An important aspect is that the time delay and the principal period of the dynamic force are equal to each other. The discretization over the time domain is performed by using the Chebyshev polynomials of the first kind. Basically, there are five parameters governing the dynamic problem including among others the time delay and the static and dynamic forces. The stability behavior is shown for the intact and delaminated beams on the parameter planes for large number of cases by using the unit circle criteria. The presence and absence of structural damping is also analyzed in each case. The results indicate that some planes are sensitive to the mesh resolution, others are not. Moreover, on some planes significant differences may take place between the intact and delaminated beams from the standpoint of stable zones.

Structural stiffness and equivalent viscous damping in a supercritical carbon dioxide lubricated hybrid journal bearing under hydrostatic status

PurposeThe purpose of this paper is to propose a type of hybrid bearing lubricated with supercritical carbon dioxide (S-CO2) and to investigate the stiffness and damping characteristics of the bearing under hydrostatic status.Design/methodology/approachEstablished a test rig for radial bearings lubricated with S-CO2 and used it to measure the dynamic coefficients by recording the relative and absolute displacements of bearing. Test bearing is mounted on a nonrotating, stiff shaft. Using static loading experiments to obtain structural stiffness. The dynamic coefficient regularities of the test bearing under hydrostatic status were revealed through dynamic loading experiments.FindingsExperiment results indicate that test bearing displayed increased stiffness when subjected to high excitation frequencies and low excitation forces, as well as elevated damping when exposed to low excitation frequencies and low excitation forces. Additionally, an increase in either environmental pressure or hydrostatic recess pressure can elevate the dynamic coefficient. The effect of temperature on the dynamic coefficient is more pronounced around the critical temperature of S-CO2.Originality/valueDesigned a type of hybrid bearing for use in the Brayton cycle that is lubricated with S-CO2 and uses hydrostatic lubrication during start-stop and hydrodynamic lubrication during high-speed operation. The hybrid bearing reduces the wear and friction power consumption of gas bearing. However, few experimental analyses have been conducted by researchers in this field.

Seismic response and liquefaction characteristics of wide and shallow multi-bucket jacket foundation under scour conditions

Scour has a significant effect on the seismic response of offshore structures. Compared to monopiles, MBJFs are shallow foundations and scouring has a more detrimental effect on their earthquake performance. However, the combined impacts of scour and earthquake on the structural response and liquefaction characteristics of the MBJFs have not been completely investigated. Based on the secondary development of the ABAQUS program, this paper proposes a method for calculating the seismic response and liquefaction of MBJF under local scour conditions. The seismic response and liquefaction characteristics of MBJF-supported OWTs in silty soil are evaluated under different scour depths, scour ranges, earthquake motions, soil conditions, and structural damping. In comparison to the unscoured condition, the results show that the maximum horizontal displacement, lateral acceleration, and bending moment of MBJF-supported OWTs increase by 30%, 97%, and 58%, respectively. Liquefaction is generated mostly in the soil outside the bucket rather than inside. An increase in soil density can improve the lateral acceleration of the structure and reduce the proportion of liquefaction in the soil. The maximum reduction in liquefaction can be 70.2% for an increase of 23% in soil densities. Disregarding structural damping will overestimate the structural response and the proportion of soil liquefaction. The findings may shed light on the seismic response and liquefaction characteristics of MBJF-supported OWTs located in complex offshore scour environments.

Approximate controllability for a stochastic elastic system with structural damping and infinite delay

Abstract In this article, we study the existence of mild solutions and the approximate controllability for a class of stochastic elastic systems with structural damping and infinite delay in Hilbert spaces. The estimation of the control function is discussed, where the expression of the control function is constructed by the defined resolvent operator. Under this estimate, the existence of mild solutions for this system is obtained by the Schauder fixed point theorem and the stochastic analysis theory, and sufficient conditions for the approximate controllability are formulated and proved by using the so-called resolvent operator type condition. Finally, an example is given to illustrate the applicability of our conclusion.

Seismic resilient design and negative stiffness-assisted nonlinear isolation system for adjacent non-coaxial buildings linked by corridors

Adjacent non-coaxial buildings have been widely built owing to complementary functions, while the non-coaxial layout could cause a great torsion effect and seismic-induced damage. This study proposes a negative stiffness-assisted hybrid isolation system and a corresponding earthquake-resilient design methodology to upgrade the multi-performances of the adjacent non-coaxial buildings and linking corridors. The hybrid isolation system includes synthetic employment of various isolators and negative-stiffness amplification systems comprised of nonlinear viscous dampers for adjacent structures, as well as tailored friction bearing for linking corridors. The mechanical property and model of the adjacent non-coaxial buildings are established, based on which a typical case is introduced. Next, the conception of the earthquake-resilient design method and procedure is elaborated, following which the functionality of each component in the hybrid system is investigated. The advantages of the developed hybrid isolation system and design methodology are illustrated by a systematic parametric analysis and time history analysis for the typical case. The results show that the torsional effect can be a dominant problem in non-coaxial adjacent buildings, which can be solved by the flexibly tailored negative stiffness effect produced by the negative stiffness-assisted isolation system. The collaboration within the proposed hybrid isolation system can produce improved isolating and enhanced nonlinear energy dissipation effects on adjacent buildings, simultaneously limiting the isolation displacement without weakening the isolating effect. The optimized friction sliding bearings effectively reduce the relative torsion concentrated on the linking corridors with a maintained function. The hybrid isolation system and earthquake-resilient design can be adopted as a high-efficiency solution to the non-coaxial linked historic buildings with insufficient seismic resistance.