Structural Damping Identification Research Articles

Support condition identification of wind turbines based on a statistical time-domain damping parameter

Owing to the harsh environment, the support conditions of wind turbines inevitably degrade/change over their lifetime, however, the evolution mechanism is not yet well understood. Although the damping parameters are sensitive to structural support and connection conditions, they are difficult to measure and quantify, which is a challenging inverse problem. This study aims to develop an approach to obtain a statistical time-domain damping parameter (STDP) based on operational vibration signals, and to utilize the parameter to identify support conditions of wind turbines. The proposed approach transforms operational vibration signals to free vibration signals by using the random decrement technique and then performs nonparametric statistical analysis to quantify the statistically significant changes in the damping characteristics of a structure. The effectiveness of the STDP method is verified by two challenging cases of bolted connection damage and soil-structure interaction condition changes. The regression analysis demonstrates the ability of the STDP method for the identification of structural overall damping. In contrast with classic modal analysis methods, the proposed method provides a monotonic relationship between the STDP and support conditions, which is significant for structural condition identification.

Vibration analysis of elevator rope with vibration suppressors (Identification of flexural rigidity, viscous damping and structural damping)

Vibration analysis of elevator rope with vibration suppressors (Identification of flexural rigidity, viscous damping and structural damping)

First‐order virtual synchronization: A new methodology for online identification of structural damping in presence of seismic excitation

AbstractThis paper proposes a new method for online identification of damping properties in seismically excited structures. It is a major extension of the recently developed Virtual Synchronization Method (VSM) with the following benefits: Its formulation is simpler and contains fewer design parameters. It includes a sufficient condition which can be validated online to ensure whether it is successful in identification of the structural damping model. It is assumed that the parameters of the damping model are fully unknown whereas the stiffness and mass of the structure are known. Online measurements of the ground motion acceleration, displacement and velocity vectors are available. Using these data, a virtual copy of the original structure is created. Then, the error between the states of the two systems is calculated. It is employed for designing an appropriate virtual controller which forces the virtual system to synchronize with the original one. Consequently, the states of these two systems are used to propose a nonlinear adaptive law to estimate the unknown parameters of the damping model. Provided numerical examples show that the proposed online identification method is efficiently fast, promising and worthy of further studies.

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.

Identification of viscous and structural damping in the dynamic system

Identification of viscous and structural damping in the dynamic system

Identification of viscous and structural damping in the dynamic system

Damping still remains one of the least well-understood aspects of general vibration analysis. In this paper, a new experimental damping identification method, which can be able to identify both viscous and structural damping in the dynamic system, is proposed. The proposed method is a direct method and gives explicit structural and viscous damping matrices. The proposed method requires prior knowledge of accurate mass and stiffness matrices. So, experimental viscous-structural damping is identified in two steps. In the first step, mass and stiffness matrices are updated and subsequently viscous and structural damping matrices are identified using updated mass and stiffness matrices obtained in Step 1. The identified viscous-structural damping matrices are both symmetric and positive definite. The effectiveness of the proposed structural damping identification method is demonstrated by numerical and experimental examples. First, two numerical study of lumped mass system and fixed-fixed beam are presented which is followed by an experimental example of cantilever beam. The effects of coordinate incompleteness and different level of damping are investigated. The results have shown that the proposed method is able to identify accurately both viscous and structural damping in the dynamic system.

Analysis of an experimental setup for structural damping identification

In the present paper, an experimental setup for structural damping determination arising from energy dissipations within the material is presented. The experimental setup is developed in such a way that all unintended damping sources are eliminated. In this connection, priority is also given to the reproducibility of the experimental data. In addition, a vacuum chamber is developed to reduce the damping arising from the interaction with the surrounding medium. Furthermore, beam-shaped specimens are clamped in a suspended way, using screws with an apex to fix the specimens in their nodes of vibration. Then, the influence of test rig specific parameters on the damping value is analyzed. In this context, an ideal setup of the test rig is identified to measure structural damping values arising from dissipations within the material. Finally, a common model for material damping description is parameterized using the experimental data.

Damping Estimation by 2D dr_APES and its Application to a Real Cable-Stayed Bridge

Introduced herein is a new structural damping identification approach based on a two-dimensional (2D) amplitude and phase estimation (APES) method. The original APES method is suitable for application to an undamped and complex harmonic vibration signal. Hence, it has to be modified for application to real damped vibration signals such as the vibration test signals in engineering structures. This modified approach will be named as dr_APES. It can transform one-dimensional (1D) signals in time domain into their corresponding signals in the 2D domain of frequency and damping factor. By applying this dr_APES approach, the three-dimensional (3D) amplitude spectrum, with peaks corresponding to the vibration modes, can be obtained for any given vibration signals. By accurately locating the coordinates of the peaks, modal frequencies and damping factors can be identified. Owing to the high-resolution of the location of 2D ordinates of the spectral line and the value of spectrum, the accurate location of peaks can be estimated, and therefore, the modal frequencies and damping factor can be accurately determined. This is demonstrated by a numerical case study. Moreover, by applying the proposed approach to a real onsite dynamic test on two cables in a cable-stayed bridge, the inherent damping of the two cables was identified accurately, thereby verifying the ability of proposed damping identification approach in meeting the requirement of weak damping characteristics identification in flexible structures such as naked cables.

Direct structural damping identification method using complex FRFs

Most of the identification methods are based only on the viscous damping model and uses modal data. In this paper, a new FRF-based direct structural damping identification method is proposed. The proposed method is a direct method and identifies structural damping matrix explicitly. As the new method is a FRF-based method, it overcomes the problem of closely spaced modes for damping identification. The accuracy of identified structural damping matrix depends upon the accuracy of finite element model. In this paper, FRF-based model updating method is used to obtain accurate mass and stiffness matrices. Thus, the procedure to obtain accurate structural damping matrix is a two-step procedure. In the first step, mass and stiffness matrices are updated and in the second step, structural damping matrix is identified using updated mass and stiffness matrices, which are obtained in the previous step. The effectiveness of the new method is demonstrated by three numerical examples and one experimental example. The numerical studies of lumped mass system, fixed-fixed beam and L-shaped frame structure are carried out. The effects of coordinate incompleteness, ill-conditioning and robustness of method under presence of noise are investigated. The proposed method is able to predict FRFs accurately for the frequency range covering the modes considered. However, beyond the considered modes, the predicted FRFs do not match the experimental FRFs. It is suggested in this work that ill-conditioning problem should be dealt by considering all the modes in the frequency range of interest. The performance of the proposed method is investigated for cases of light, medium and heavily damped structures. The numerical studies are followed by experimental case study of cantilever beam structure. The effectiveness of the proposed method is evaluated by comparing the predicted and the experimental FRFs. The results have shown that the proposed method is able to predict accurately the experimental FRFs with all levels of damping in the system.

Negative Ten Decibels Method for Damping Identification of Light Damping Structure

Half power method is commonly used in structural damping identification because of its simplicity in algorithm. But when the damping is very small, half power method will lead a big error. In order to get more accurate result of small damping structure, this paper suggests using negative ten decibels method (N-10dB) instead of half power method. N-10dB method takes 10-dB bandwidth into consideration, differs from 3-dB of half-power method. The theory of this method is given firstly and proves that it is very simple in algorithm. Subsequent simulation and experiment show that, compared with half power method, N-10dB method have stronger noise resistance, higer precision and is more stable in repeated measurements. Except that, the N-10dB method is also practical in engineering test.

Structural damping identification method using normal FRFs

All structures exhibit some form of damping, but despite a large literature on the damping, it still remains one of the least well-understood aspects of general vibration analysis. The synthesis of damping in structural systems and machines is extremely important if a model is to be used in predicting vibration levels, transient responses, transmissibility, decay times or other characteristics in design and analysis that are dominated by energy dissipation. In this paper, new structural damping identification method using normal frequency response functions (NFRFs) which are obtained experimentally is proposed and tested with the objective that the damped finite element model is able to predict the measured FRFs accurately. The proposed structural damping identification is a direct method. In the proposed method, normal FRFs are estimated from the complex FRFs, which are obtained experimentally of the structure. The estimated normal FRFs are subsequently used for identification of general structural damping. The effectiveness of the proposed structural damping identification method is demonstrated by two numerical simulated examples and one real experimental data. Firstly, a study is performed using a lumped mass system. The lumped mass system study is followed by case involving numerical simulation of fixed–fixed beam. The effect of coordinate incompleteness and robustness of method under presence of noise is investigated. The performance of the proposed structural damping identification method is investigated for cases of light, medium, heavily and non-proportional damped structures. The numerical studies are followed by a case involving actual measured data for the case of a cantilever beam structure. The results have shown that the proposed damping identification method can be used to derive an accurate general structural damping model of the system. This is illustrated by matching the damped identified FRFs with the experimentally obtained FRFs.

Experimental Identification of Overall Structural Damping of System

The dynamic behaviour of large and complex structures largely depends on damping resistance in the structure. A portion of the structural energy is lost to deformations in material, friction between the contact surfaces, and relative motion within the structure. Often, in an analysis of numerical models, before the dynamic analysis of transient events (transient analysis), the damping resistance is adopted on the basis of recommendations, which implies an error of transient response (introduced by frequencies, logarithmic decrements and maximal amplitudes). Decreasing amortized vibratory movement is dependent on the extent of the structural damping. This paper presents the importance of structural damping in structural analysis and shows the experimental and theoretical procedure for identifying G values of the structural damping coefficient. A model for determining the G coefficient is shown in the example of a real tower crane structure. The experimentally obtained values were then used in the transient numerical FEM analysis, as the basis for adopting the conclusions about the dynamic behaviour of this class of structures (transportation machines). The effect of the external perturbation force of trapezoidal impulse form (lifting and quickly lowering of load) is introduced and the dynamic task, as an example of the use of the G coefficient G, is solved. The experimentally determined damping (theoretically isolated for tall truss structures) can be used in similar transient analyses.

Structural Damping Identification for Mistuned Bladed Disks and Blisks

To accurately predict the dynamics of most structures, a representation of damping must be used. This paper focuses on structural damping and the identification of structural damping for complex systems with cyclic symmetry such as bladed disks and integrated (one-piece) bladed disks (blisks) with mistuning. The damping identification methodology is demonstrated together with two measurement filters for a complex structure, namely an integrated bladed disk with stiffness mistuning.

Structural damping identification based on an iterative regularization method

A time domain structural damping identification method is presented in this paper. The damping of a structure is assumed to be time-invariant Rayleigh damping, time-variant Rayleigh damping and modal damping, respectively, and an iterative regularization method is proposed to identify these three types of damping in turn. A sensitivity approach is adopted in the formulation of the ill-posed inverse problem. A new constraint is imposed on the identified iterative increment as well as on the unknown structural parameters to ensure their physical meaning in the identification process is not lost. The proposed method is verified in numerical studies with a space frame structure and laboratory measurements of accelerations with accurate results.

Identification of structural damping in time domain

A structural damping identification procedure is proposed based on the sensitivity of acceleration response of the analytical model with model updating technique making use of the measured acceleration response. The viscous damping model obtained from the inverse modal transformation is adopted. The time-varying sensitivity matrix is computed by the Newmark method. Numerical study with a three-dimensional five-bay frame structure subjected to support excitation and a one-storey plane frame structure is performed to demonstrate the efficiency and validity of the proposed method. The effect of different sampling rates is studied. The damping ratios can be identified accurately from two “measured” acceleration responses with a high level of measurement white noise as well as model errors in the analytical model. The same procedure is later shown to be able to monitor the damping ratios of a time-varying system using moving windows of data in the identification with satisfactory results.

Damage detection by means of structural damping identification

Vibration measurements in structures under ambient or controlled excitation open a way to damage assessment by correlating changes in the dynamic system parameters–natural frequencies, modal shapes or damping–with damage. Most methods proposed in the literature are based on the measurement of natural frequencies or modal shapes, associating damage to local reduction of the structural stiffness while completely ignoring damping, both in the identification procedure as well as in the correlation of changes in the spectral properties of the structure with damage. In numerous applications these methods, however, present some practical limitations on account of the low sensitivity of natural frequencies or modal shapes to damage. The main objective of this paper is to present a novel scheme to detect structural damage by means of the instantaneous damping coefficient identification using a wavelet transform. Laboratory tests as well as numerical simulations showed that in many commonly used structural systems damage causes important changes in damping. Thus, parameters that characterize structural damping can be used as damage-sensitive system properties. It is further shown that the wavelet transform can be conveniently employed in a procedure for instantaneous frequencies and damping identification from free vibration structural response.

What is the best method for structural damping identification? Part 1: A survey of methods

Identification of damping matrices from measured frequency response functions is a difficult and error-prone procedure. In practice, the assumption of proportional damping is frequently made without physical justification. Several researchers have suggested identification algorithms for the full damping matrix. A critical review is presented of algorithms which work in the frequency domain. Some novel approaches are included: one new algorithm is based on matrix perturbation theory, while others are hybrid combinations of earlier methods. The sensitivity of the algorithms to measurement noise and other commonly encountered difficulties in realistic measurements is addressed. Representative results from a simulation study comparing all the methods will be presented, leading to recommendations for the choice of identification algorithms in practice.

What is the best method for structural damping identification? Part 2: Comparison of performance

Damping identification in structural vibration from measured frequency response functions is a difficult task. Several methods have been proposed in the literature to identify the damping matrix. Some employ modal parameters such as natural frequencies, damping factors, and mode shapes, while others work directly from the frequency response function matrix. In practice, in the presence of noise and incompleteness of data, it is hard to guess how well any of these methods will perform. This paper reports a systematic simulation study to test the relative benefits/disadvantages of a wide range of approaches, existing and novel. Representative model systems have been chosen to test performance under various conditions of measurement noise, system complexity, damping type, modal overlap factor, and modal truncation. A very wide range of results is summarized by computing various norms of performance for all the methods studied. Recommendations are made for the best methods to extract reliable damping information from practical measurements.