Structural Damping Characteristics Research Articles

A Review of the Hydrodynamic Damping Characteristics of Blade-like Structures: Focus on the Quantitative Identification Methods and Key Influencing Parameters

Abstractcean energy has progressively gained considerable interest due to its sufficient potential to meet the world’s energy demand, and the blade is the core component in electricity generation from the ocean current. However, the widened hydraulic excitation frequency may satisfy the blade resonance due to the time variation in the velocity and angle of attack of the ocean current, even resulting in blade fatigue and destructively interfering with grid stability. A key parameter that determines the resonance amplitude of the blade is the hydrodynamic damping ratio (HDR). However, HDR is difficult to obtain due to the complex fluid–structure interaction (FSI). Therefore, a literature review was conducted on the hydrodynamic damping characteristics of blade-like structures. The experimental and simulation methods used to identify and obtain the HDR quantitatively were described, placing emphasis on the experimental processes and simulation setups. Moreover, the accuracy and efficiency of different simulation methods were compared, and the modal work approach was recommended. The effects of key typical parameters, including flow velocity, angle of attack, gap, rotational speed, and cavitation, on the HDR were then summarized, and the suggestions on operating conditions were presented from the perspective of increasing the HDR. Subsequently, considering multiple flow parameters, several theoretical derivations and semi-empirical prediction formulas for HDR were introduced, and the accuracy and application were discussed. Based on the shortcomings of the existing research, the direction of future research was finally determined. The current work offers a clear understanding of the HDR of blade-like structures, which could improve the evaluation accuracy of flow-induced vibration in the design stage.

Complex mode superposition method of non-classically damped systems based on hysteretic damping model with frequency-dependent loss factors

For non-classically damped systems, it is easy to construct a damping matrix based on a hysteretic damping model. However, the damped natural frequency is non-physical, and the frequency response function is non-causal. These two drawbacks can be overcome by the hysteretic damping model with frequency-dependent loss factors. In this paper, a complex mode superposition method for non-classically damped systems based on the hysteretic damping model with frequency-dependent loss factors is proposed. Frequency-dependent loss factors of the natural frequencies are considered in the transient vibration response, while frequency-dependent loss factors of the external excitation frequencies are considered in the steady state vibration response. By decoupling complex modes in state space and physical space, non-proportional damping characteristics of hybrid structures can be effectively considered. Therefore, the proposed method can be used to calculate the time-domain dynamic responses of hybrid structures, whose loss factors are sensitive to frequency variation and have strong non-proportional damping characteristics. The time-domain dynamic responses of numerical examples are compared based on different mode superposition methods. Shaking table tests are performed on cantilever plates with different damping characteristics. The numerical and test results validate the proposed method. Moreover, the proposed method has a wide range of applications.

Investigation of long-term modal properties of a supertall building under environmental and operational variations

The information on long-term modal properties of civil structures under environmental and operational variations is generally required in structural health monitoring and vibration control. In operational modal analysis (OMA), damping estimates usually present larger fluctuations and uncertainties than natural frequency and mode shape estimates, which affects the precise determination of the long-term damping characteristics of civil structures. To this end, a combined OMA scheme is adopted in this paper based on the variational mode extraction technique and covariance-driven stochastic subspace identification algorithm to reduce errors in modal identification, especially for damping estimates. Through numerical simulation study of a three-story frame structure, the effectiveness and accuracy of the combined scheme for modal estimations are validated. Moreover, the combined approach is further utilized to evaluate the long-term modal properties of a 600 m high skyscraper under environmental and operational variations from the measured response records of 183 days. Based on the reliable modal estimates by the combined method, the effects of environmental factors (air temperature and relative humidity), wind conditions, and building response amplitudes on the long-term modal properties and their statistical characteristics are investigated in detail. This paper aims to provide an effective tool for analyzing the long-term modal properties of civil structures and further reveal the time evolution of the dynamical characteristics of supertall buildings under environmental and operation variations. • Present a combined scheme based on variational mode extraction technique and covariance-driven stochastic subspace identification algorithm to reduce errors in structural modal estimates. • Suggest an empirical formula for determining minimum length of responses required for accurate modal estimates. • Validate effectiveness and accuracy of the combined scheme via numerical simulation study. • Investigate long-term evolution of dynamical characteristics of a 600 m high skyscraper under environmental and operational variations.

Numerical modeling for cantilever sandwich smart structures with partially covered constrained viscoelastic layer

A finite element formulation using zig-zag hypothesis is developed for sandwich smart structures with partially smart constrained layer damping (SCLD) treatment. In order to achieve higher accuracy, both of the viscoelastic and elastic layers of the sandwich structures are based on the Reissner–Mindlin theory. An eight-node quadrilateral element with seven mechanical degrees of freedom (DOFs) is considered for the finite element (FE) analysis. Using Hamilton’s principle, a piezoelectric coupled dynamic FE model is obtained. This FE model is validated by frequency and loss factor analysis of an elastic–viscoelastic–elastic plate. Furthermore, the effects of various parameters on the damping characteristics of the cantilever sandwich smart structures are carried out, e.g. coverage percentage and position of SCLD, thickness of the viscoelastic or piezoelectric layer, curvature of structures, and shear modulus and loss factor of the viscoelastic layer.

Finite element model for analysis of vibration damping characteristics of isotropic surface structures

In this paper, a finite element (FE) model was developed to predict the vibration response of isotropic beams, involving several modes of resonance. The cantilever beam model was employed in the FE model in line with Timoshenko’s bending theory. The FE analysis has been carried out using the modal analysis and harmonic analysis tools of Ansys R19.0. The FE model was subjected to a grid independence study to minimize the computational time without sacrificing accuracy. The resonant frequencies were utilized to compute the damping modulus of the material for both the FE and experimental results. The frequency response functions from the finite element analysis were compared with the experimental results of the cantilever beam subjected to impulse hammer excitation. Aluminium alloy AA6061-T6 was taken up as the homogeneous and isotropic beam material for both the experimental and the FE model. The effect of the magnitude and location of the excitation load, the geometry of the FE model on the vibration response was analyzed in detail. The FE model validation with the experimental results shows that the FE model is effective in predicting the damping response of any isotropic material.

Damping characteristics of single-layer aluminum alloy reticulated spatial structures based on improved modal parameter identification method

An improved identification method is proposed for the modal parameter identification of multi-modal vibration attenuation signals based on the analytical mode decomposition and the particle swarm optimization. Through examples of analog signals, it is proved that the proposed method can identify modal parameters under a strong colored noise environment. Field tests were carried out on four in-service aluminum alloy reticulated structures to obtain the acceleration response of the structures. The improved identification method proposed in this paper is used to identify the modal parameters of each acceleration response curve, based on which the damping characteristics of the aluminum alloy reticulated structures are analyzed. The results show that the damping characteristics of such structures obey a three-stage change rule, with the increase of the acceleration amplitude. In addition, a practical calculation method of the damping ratios of aluminum alloy reticulated structures is proposed on the basis of the experimental results.

Determining structural damping and vibroacoustic characteristics of a non-symmetrical vibrating plate in free boundary conditions using the modified Helmholtz equation least squares method

This paper presents a comprehensive study to determine the structural damping and vibroacoustic responses of an arbitrarily shaped planar structure subject to non-contact acoustic excitations under free boundary conditions using a modified HELS (Helmholtz equation least squares) method. The input data consist of the normal surface velocities measured by a laser vibrometer at a discrete number of points on the source surface, and the acoustic pressures measured by a small array of microphones in the field. The normal surface velocity distribution over the entire surface of the plate is then reconstructed by the HELS method and compared to benchmark data. Similarly, the reconstructed acoustic power level spectra are compared to those measured by the array of microphones. The reconstructed vibroacoustic quantities using the modified HELS method are interrogated, and the method's accuracy evaluated. Specifically, a limited number of normal velocity data points on the surface of the target structure are taken as input to the HELS formulations. The reconstructed velocity distributions on the entire surface of the structure with much higher density even for areas of the target structure with little or no input data were compared to the benchmark results. It is worth noticing that no other vibroacoustic technologies are available that allow for complete reconstruction of the normal surface velocity distributions based on limited input data. The dimensionless damping ratio of the structure is also determined. Results indicate that the dimensionless damping ratio for metals, for instance steel, is frequency dependent rather than a constant. Moreover, the empirical formulation developed in this study enables one to get the dimensionless damping ratios continuously over the frequency range from 0 to 10,000 Hz.

Model hybrid magnetorheological damping prediction in machine tools

Vibration is an unbalance effect generated at the tool-workpiece interface during mechanical machining operations. Vibration is one of the most significant problems encountered when increasing material removal rate. It may contribute to tool wear and reduced surface finishing of the workpiece, which is referred to as ‘chatter’. However, to date, there are no significant experimental and corresponding simulation data for easy control with monitoring of the damping system model available to estimate parameters of machining F1140 Steel and to develop adequate models of magnetorheological damper (MRD) vibration control. This research adopts a novel approach to active dampers for MRD, which is manipulated by a control strategy to increase the dynamic structural damping characteristics of machine tools without changing actual machining operations. The operation of the system is actualized by the adoption of shock absorbers and active command of an MRD, thereby increasing the vibration-free zone with an electromagnetic actuator to reduce or possibly eliminate chatter during machining operations. A novel smart tool holder (STH) for real-time sensor data collection was designed in MATLAB, which for monitoring purposes is located at the tip of the tool during operation. The selection of data includes self-developed vibration, frequency monitoring, system stability evaluation, and the runout time. One of the objectives of the STH is to enable the accurate determination of a numerical control metal cutting system in vibration reduction. It was further designed to increase stability and the cutting force that can be achieved with the actuator and can facilitate the use of different control strategies or filters.

A structural damping identification technique for coatings on blisks based on improved component mode mistuning model

Abstract Since the structural damping characteristics of damping coatings are much higher than that of the blisk substrate, the structural damping differences of coatings in each sector directly affect structural damping of the coated blisk. Therefore, for the coated blisk, it is very important to identify the structural damping differences caused by coating. A novel method for structural damping identification of coatings on the coated blisk is proposed. The component mode mistuning (CMM) model is improved for establishing reduced order model (ROM) of coated blisks. In the model, based on the consideration of blisk substrate, the coatings on each sector are decomposed into the mistuned substructures which are independent of each other. Based on this model, the identification formula for structural damping coefficients of coatings on each sector is deduced. A numerical case is given to illustrate the identification procedure. The vibration test methods for obtaining input parameters of damping identification are demonstrated by an actual case. The damping identifications of numerical case and actual case are carried out. The identification results shown that the identification method had high identification accuracy and can be well applied for the damping identification of the hard coating and viscoelastic coating.

A novel analysis method for damping characteristic of a type of double-beam systems with viscoelastic layer

The double-beam system with a viscoelastic layer is a classical mechanical model for many beam-type composite structures. However, few studies have been able to optimize the structure from the perspective of structural damping characteristics. To fully understand the damping characteristics of the viscoelastic double-beam system, an analysis method based on dynamic stiffness method and Wittrick-Williams algorithm is presented in this paper. Through numerical case studies, five typical parameters of the viscoelastic double-beam system are discussed to investigate their influence on the damping characteristic of the system. Finally, the conclusions are used to parametric analysis for a kind of double-sheathing cable systems. Results show that the damping coefficient of the connection layer have a significant effect on the damping characteristic of the double-sheathing cable system compared with other design parameters. The proposed methods and conclusions obtained in this paper are helpful to design and optimize the structural parameters of engineering structures, thus having certain application and promotional value.

Dynamic Instability Analysis of Multifunctional Composite Structures

A dynamic instability analysis of fiber reinforced composite cantilever beams has been carried out in this study. Both experimental and numerical studies are performed to estimate the flutter speeds. Three different types of composite beams [namely, glass fiber reinforced plastics, aluminum fiber reinforced (glass reinforced aluminum), and multifunctional carbon fiber reinforced composites] have been considered in the analysis. A graphite fiber reinforced polymer matrix composite laminate with dimensions of is used in the experiments. The fibers are oriented along 0 deg: that is, along the direction of major dimension of the laminate. The experiments are conducted on three such beams by clamping one end of the beam to a heavy steel frame and leaving the other end free. The natural frequencies, mode shapes, and structural damping characteristics of each beam are estimated using the modal analysis through the fast Fourier transform analyzer. Variation of the damping and the frequency with wind velocity for each beam is illustrated through the and plots. The modal assurance criterion is also verified. Experiments are further continued to perform a dynamic instability analysis by clamping the beam inside the test chamber of a low-speed suction-type wind tunnel. The beam response at various wind speeds is captured through an accelerometer mounted at the tip. Based on the experiments, the flutter speed of the tested beams is estimated to be around . A numerical analysis framework is developed using the ZAERO code to perform the modal and flutter analyses. Numerical results are compared to the experimental results and are found to be in excellent agreement. Therefore, the numerical framework has been further extended to carry out the flutter analysis of the multifunctional composite beams, such as glass reinforced aluminum and plastic lithium–ion battery embedded composite beams. The multifunctional laminated composite beams are observed to have better dynamic stability as compared to the glass fiber reinforced polymer composite beams.

Integrated layout and topology optimization design of multi-component systems under harmonic base acceleration excitations

The integrated optimization of component layout and structural topology is studied in this paper to improve the dynamic performance of the multi-component structure systems under harmonic base acceleration excitations. Considering linear systems, including multi-point constraints interconnecting the components and structures as an integrity, the dynamic responses and the corresponding design sensitivities are analytically derived based on the mode acceleration method. To obtain precise dynamic response, structural real damping characteristics are measured using vibration experiments, which are relevant to the structural dynamic response, especially when the excitation frequencies fall into the resonant frequency band. Further verifications are done by the comparison of Rayleigh damping, constant damping ratio, and hysteretic damping model with experimental results of structures achieved by resin-based additive manufacturing. In this way, structural real damping characteristics are taken into account in the integrated optimization. Numerical examples and vibration testing results are presented to show the validity of the optimization procedure and its potential application in engineering.

Viscoelastic modelling and dynamic characteristics of CNTs-CFRP-2DWF composite shell structures

Abstract The carbon nanotubes (CNTs) are well known for its application in the areas of advanced composite materials for their improved elastic properties. The large specific interfacial surface area owing to tiny dimensions of CNTs may greatly escalation the interfacial sliding which may promote the dissipation of energy in a dynamic situation that makes them very ideal for damping applications in engineering structures/systems. The present article investigates the viscoelastic modelling and dynamic responses of the CNTs – based carbon fiber reinforced two dimensional woven fabrics (CNTs-CFRP-2DWF) composite spherical shell panels where CNTs are reinforced in the polymer matrix phase. The Mori – Tanaka (MT) micromechanics in conjunction with weak interface (WI) theory has been developed for the mathematical formulations of the viscoelastic modelling of CNTs-based polymer matrix phase. Further, strength of material (SOM) method has been employed to formulate viscoelastic material behavior of the yarn and finally the viscoelastic properties of the representative unit cell (RUC) is established based on the unit cell method (UCM). An eight-node shell element with five degree of freedom per node has been formulated to study the vibration damping characteristics of spherical shell structures made by CNTs-CFRP-2DWF composite materials. The shell finite element formulation is based on the transverse shear effect as per the Mindlin's hypothesis, and stress resultant-type Koiter's shell theory. Frequency and temperature dependent material properties of such CNTs-CFRP-2DWF composite materials have been obtained and analysed. Impulse and frequency responses of such structures have been performed to study the effects of various important parameters such as volume fraction of CNTs, interfacial condition, agglomeration, temperature, geometries of shell panel on the material properties and such dynamic responses. Obtained results demonstrate that quick vibration mitigation may be possible using such CNTs-CFRP-2DWF composite material which is desirable to overcome the drawbacks of conventional CFRP woven fabric composite materials.

Viscoelastic modeling and vibration damping characteristics of hybrid CNTs-CFRP composite shell structures

The present article deals with the viscoelastic modeling and dynamic responses of the carbon nanotubes (CNTs)-based carbon fiber-reinforced polymer (CNTs-CFRP) composite spherical shell panels where CNTs are reinforced in the polymer matrix phase. The Mori–Tanaka micromechanics in conjunction with weak interface theory has been developed for the mathematical formulations of the viscoelastic modeling of CNTs-based polymer matrix phase. Further, the strength of material method has been employed to formulate the viscoelastic material behavior of the homogenized hybrid CNTs-CFRP composite materials. An eight-noded shell element with five degrees of freedom per node has been formulated to study the vibration damping characteristics of spherical shell structures made by CNTs-CFRP composite materials. Frequency- and temperature-dependent material properties of such hybrid composite materials have been obtained and analyzed. Impulse and frequency responses of such structures have been performed to study the effects of various important parameters on the material properties and such dynamic responses. Obtained results demonstrate that quick vibration mitigation may be possible using such CNTs-based proposed composite materials.

新型轻质复合材料夹芯结构振动阻尼性能研究进展

As a new generation of advanced super-strong lightweight structural materials, composite grid and lattice sandwich structures have received extensive attention from domestic and foreign scholars. An abundant amount of research on such novel sandwich structures focused on the manufacturing techniques and mechanical properties was carried out. However, it needs to be pointed out that, the research on the vibration and damping characteristics of such sandwich structures has just started, which is a new topic. Here a comprehensive review of the state of the research on vibration damping models was made for fiber reinforced resin matrix composite laminates and sandwich structures. Firstly, the related damping mechanisms were elaborated, and then an overview of micro- and macro-damping models for simple composite laminates, viscoelastic damping and novel sandwich structures was given. Finally, the results and shortcomings of the existing research on the vibration damping characteristics of such structures were summarized and the possible development in the future was predicated.

Dynamic properties of Byblos municipality building with soil-structure interaction using geophysical methods

Byblos city is located on the coast north of Beirut, Lebanon, and is one of the oldest continuously-inhabited cities in the world. It is exposed to a moderate-up-to-high level of seismic activity, given its proximity to several major faults such as the Yammouneh and the Mount Lebanon Thrust, among others. To mitigate the risk encountered by Byblos buildings facing earthquake threat, a preliminary study of the dynamic properties of the structures is proposed in this paper. The recently-constructed Byblos Municipality building was chosen as a prototype for this study, given its important role as a vital structure for centralizing the emergency response, in the event of a disaster.The approach consists of using the horizontal to vertical ratio method, HVNR. By analysing the ambient noise recordings, one can determine the structural frequency, damping, and other stiffness characteristics, and identify the natural soil frequency. In order to investigate the soil structure interaction and specifically possible resonance occurrence during earthquakes, the values obtained are compared and analysed. In addition to classical geotechnical tests to reveal the type and properties of the considered in-situ soil, the multichannel analysis of surface waves, MASW, is used to investigate the stiffness of the subsurface conditions and determine the shear wave velocities of the layers. In parallel, the Finite Element Model of the structure is analysed and the result of the fundamental resonance frequencies is compared to the HVNR data, and to the computed values using conventional formulae recommended by classical building codes. Results and comparisons of experimental and numerical investigations are presented for the structure and analysed for further resonance analysis.

Modeling and experimental study of a honeycomb beam filled with damping particles

Honeycomb sandwich laminates which are the basic structural element of spacecraft have inherently low damping. In this paper, we propose to improve the damping characteristics of such structures by adding damping particles in the cells of the honeycomb. This paper presents modeling of a cantilever beam constructed with honeycomb structure with the hexagonal honeycomb cells, filled with particles. The beam is subjected to external dynamic loads and the interactions of damping particles with the walls of the cells and its overall effect on the frequency response function (FRF) and the damping of the beam are obtained. The discrete-element-method (DEM) is used to model the dynamics of the particles in conjunction with the governing equations of motion of the beam and the cell-walls. The particle-particle and particle-wall impact is modeled using Hertz's non-linear dissipative contact model for normal component and Coulomb's laws of friction for tangential component. Contiguous block of cells near the tip of the cantilever beam were filled with the damping particles and the beam was excited with a random signal near the fixed end. The damping and transfer functions obtained experimentally are compared to those obtained from the mathematical model and they are found to match very well. Further the model was used to study the effect of fill fraction, mass ratio, and the level of excitation signal on transfer function. Depending on the mass ratio and fill fraction, significant reductions in vibration levels are observed.

Vibration damping characteristics of carbon nanotubes-based thin hybrid composite spherical shell structures

ABSTRACTThe present work deals with the evaluation of elastic properties and dynamic analyses of thin hybrid composite shell structures, which consist of conventional carbon fiber as the reinforcing phase and multiwalled carbon nanotubes-based polymer as the matrix phase. The Mori-Tanaka and strength of material method has been implemented to determine the elastic properties of such hybrid composite structures without and with considering agglomerations. An eight-noded shell element, which considers stress resultant-type Koiter's shell theory and transverse shear effect as per Mindlin's hypothesis having five degrees of freedom at each node, has been utilized for discretizing and analysis of such hybrid shell structures. The Rayleigh damping model has been implemented in order to study the effect of carbon nanotubes (CNTs) on damping capacity of such hybrid composite shell structures. Different types of spherical shell panels have been analyzed in order to study the time and frequency responses. Results show that the elastic properties as well as damping properties of such hybrid composite structures improved with the addition of CNTs as compared to conventional carbon fiber reinforced composites laminates; effects of some important parameters on the vibration characteristic of such hybrid composite shell structures have also been presented. The effects of agglomeration parameters on the elastic properties and their influences on the dynamic responses considering different layers and stacking sequences have also been investigated.

Damping properties of bi-dimensional sandwich structures with multi-layered frequency-dependent visco-elastic cores

The aim of this paper is to present a finite element model based on first order shear theory (zig-zag approach) to compute the damping characteristics of sandwich structures with multi-layered frequency-dependent viscoelastic cores. The model is validated versus a layerwise finite element model and used to study damping and rigidity of a laminated glass configuration with a multi-layered visco-elastic core composed of acoustic PVB and PVB. It is shown that the rigidity index of the structure (defined as the adimensionalized inverse of the maximal transverse displacement under a static load) evolves linearly with the viscoelastic layers’ thicknesses and quadratically versus elastic layer’s thickness. The first mode damping and resonant frequency show a non monotonous behaviour. In particular, the existence of an optimal faces thickness for damping is shown while a quadratic behaviour of frequency versus acoustic PVB layer thickness is reported.

Effect of Carbon Nanotube on Damping Characteristic of Epoxy Polysulfide Blend Composite

In a Nano-composite structure, it is anticipated that high damping can be achieved by taking advantage of the interfacial friction between the nanotubes and the polymer. The purpose of this paper is to investigate the structural damping characteristics of polymeric composites containing Carbon nanotubes (CNTs) with various amounts with polysulfide rubber (PSR) . The damping characteristics of the specimens with 0 wt% and 0.6 wt% Carbon nanotube contents were computed experimentally. Through comparing with neat resin specimens (epoxy, epoxy +PSR), the study showed that one can enhance damping by adding CNTs fillers into polymeric resins. Similarly experiment showed that the maximum value of damping ratio was obtained at 0.4 wt% CNTs.