Showing papers on "Modal testing published in 2014"
TL;DR: In this paper, the Teager energy operator and wavelet transform are combined to produce a new modal curvature, termed as the TEAGO operator-wavelet transform (TEAGO-WT).
106 citations
TL;DR: In this article, a modal analysis based on a high-resolution technique showed that the acoustic black hole (ABH) effect significantly increases the modal overlap factor (MOF) of the beam, thus reducing the resonant behavior of the structure.
81 citations
TL;DR: In this paper, a modification of a high-speed correlation system for the purposes of mechanical structures modal parameters estimation is described, together with hardware modification, which is a complex tool for execution of an experimental and operational modal analysis.
69 citations
TL;DR: In this article, the effects of local damage on the natural frequencies and the corresponding vibration modes of composite pyramidal truss core sandwich structures are studied, and a FEM model is also constructed to investigate their vibration characteristics numerically.
Abstract: The effects of local damage on the natural frequencies and the corresponding vibration modes of composite pyramidal truss core sandwich structures are studied in the present paper. Hot press molding method is used to fabricate intact and damaged pyramidal truss core sandwich structures, and modal testing is carried out to obtain their natural frequencies. A FEM model is also constructed to investigate their vibration characteristics numerically. It is found that the calculated natural frequencies are in relatively good agreement with the measured results. By using the experimentally validated FEM model, a series of numerical analyses are conducted to further explore the effects of damage extent, damage location, damage form on the vibration characteristics of composite pyramidal truss core sandwich structures as well as the influence of boundary conditions. The conclusion derived from this study is expected to be useful for analyzing practical problems related to structural health monitoring of composite lattice sandwich structures.
63 citations
TL;DR: In this article, a flexible beam with piezoelectric pieces on the surface is investigated experimentally using the independent modal space control method, which is able to control the first three modes of the beam independently.
62 citations
TL;DR: This work investigates the leading order behavior of the ‘posterior uncertainties’ of the modal parameters in a Bayesian identification framework and shows rigorously that, among other results, the posterior c.o.v. of the natural frequency and damping ratio are asymptotically equal.
58 citations
TL;DR: In this paper, an approach for structural response reconstruction based on the modal superposition method in the presence of closely spaced modes is proposed, where the entire mode set of a structure is divided into closely spaced modal responses and the rest of the modes.
53 citations
TL;DR: In this paper, the authors proposed a method to predict changes in modal parameters of a generic structure due to the presence of passive people, i.e., natural frequencies, damping ratios and mode shapes.
50 citations
TL;DR: In this paper, a new analytical mode decomposition method in combination with the conventional random decrement technique is proposed for modal parameter identification under ambient vibration, including closely-spaced modes.
43 citations
TL;DR: In this article, experimental modal analysis was conducted on the specimens previously subjected to fatigue loading to determine the modal parameters (natural frequency, damping ratio and mode shape) and the results showed that the changes of modality parameters provided a proper means for predicting the fatigue behavior of composite structures.
38 citations
TL;DR: In this paper, an active vibration control of a free-edge rectangular sandwich plate is proposed and tested using Positive Position Feedback (PPF) technique and is successfully applied with different combinations of inputs/outputs (Single Input Single Output, MultiSISO, Multi Input Multi Output) in order to control the first four normal modes.
TL;DR: In this paper, a Monte-Carlo simulation is performed on a simply supported beam, and the uncertainty on a set of 5000 modal parameters identified with the stochastic subspace identification method is discussed.
TL;DR: In this paper, the closed form of the sensitivity of modal flexibility for a real undamped system is derived based on the algebraic eigen sensitivity method, which is then adopted to detect the damage locat...
Abstract: The closed form of the sensitivity of modal flexibility for a real undamped system is derived based on the algebraic eigen sensitivity method. The formula is then adopted to detect the damage locat...
TL;DR: In this paper, a parametric section model is formulated to synthetically describe the geometrically nonlinear dynamics of cable-stayed and suspended bridges through a planar elastic multi-body system.
TL;DR: In this paper, a mechatronic approach integrating both passive and active controllers is presented to deal with unwanted noise and vibration produced in an automobile wiper system operation, which is a flexible structure with high order, nonlinear model that is considered as a multi objective control problem.
TL;DR: In this paper, a mass normalized mode shape expansion and subsequent physical parameter identification for shear-type structural systems with input-output measurements is investigated, and the issue of global identifiability of the system is also addressed vis-a-vis instrumentation set-ups.
TL;DR: In this paper, a vibration model for the hexapod table is developed and the relevant explicit equations are derived and the safe functional modes of the table in terms of its upper platform's position have subsequently been determined.
Abstract: Assuming a sinusoidal machining force, the forced vibration of machine tools’ hexapod table in different directions is addressed in the present study. A vibration model for the hexapod table is developed and the relevant explicit equations are derived. In the vibration equation of the table, the pods are assumed as spring-damper systems and the equivalent stiffness and damping of the pods are evaluated with experimental results by modal testing on a pod of the hexapod table. The results of the analytical approach have been verified by FEM simulation. The theoretical and FEM results exhibit similar trends of changes and are close to each other. The vibration of the table in different positions has been studied under rough and finish machining forces for both down and up milling. The ranges of resonance frequencies and vibration amplitudes have also been investigated. The safe functional modes of the table in terms of its upper platform’s position have subsequently been determined.
TL;DR: In this article, a two-stage least square method for modal parameter estimation of time-varying structures is presented, consisting of a least square complex frequency-domain stage for the estimation of all discrete time samples and a weighted least square stage for estimating continuous-time represented modal parameters.
TL;DR: In this paper, a Bayesian approach that properly accounts for uncertainty in accordance with probability logic for modal identification using forced vibration data is developed, which is applicable for both separated and closely-spaced modes even with a large number of measured degrees of freedom.
Abstract: Modal identification aims to identify the modal parameters of constructed structures based on vibration data. Forced vibration tests allow one to obtain data with a higher signal-to-noise ratio compared with free or ambient vibration tests. Modal identification techniques for forced vibration data exist, but they do not provide a rigorous quantification of the remaining uncertainties of the modal parameters, which is becoming important in modern structural health monitoring and uncertainty propagation. This paper develops a Bayesian approach that properly accounts for uncertainty in accordance with probability logic for modal identification using forced vibration data. The posterior probability density function of the modal parameters to be identified given the data is derived based on the assumed model and the collected data. An efficient algorithm is developed that allows practical implementation in the case of a single shaker. It is applicable for both separated and closely-spaced modes even with a large number of measured degrees of freedom. The proposed method is verified and investigated using synthetic and field test data. Copyright © 2013 John Wiley & Sons, Ltd.
TL;DR: In this paper, a modal frequency sensitivity analysis using original complex nodal matrix (CMFS) is presented, which can determine each no-coupling resonance mode and investigate frequency sensitivity with respect to network component parameters.
Abstract: Modal impedance sensitivity and modal frequency sensitivity are two important characteristics of resonance modal analysis. Modal sensitivity is to calculate the sensitivity of a resonance mode against the parameters of network components. The eigendecomposition of a real matrix transformed from a complex matrix not only increases the dimension of nodal admittance matrix, but also creates two equal resonance frequencies in different modes. In this letter, a modal frequency sensitivity analysis using original complex nodal matrix (CMFS) is presented. The results obtained by this method are compared with those by realistic modal frequency sensitivity (RMFS) and the simulation verifies that this method possesses higher accuracy and applicability than that of RMFS. CMFS can determine each no-coupling resonance mode and investigate frequency sensitivity with respect to network component parameters. In addition, Newton's method is introduced to the shift of resonance frequency cooperating with the CMFS.
TL;DR: In this article, an improved empirical mode decomposition (EMD) algorithm is proposed to identify the modal parameters of transformer winding with obtained experiment data, which shows better accuracy in the identification of damping ratio.
TL;DR: According to modal analysis, the relationship between modal frequency and modal shapes is achieved and PID control based on internal model control is introduced into control of radial active magnetic bearing (AMB).
Abstract: For a magnetically suspended control moment gyroscope, stiffness and damping of magnetic bearing will influence modal frequency of a rotor. In this paper the relationship between modal frequency and stiffness and damping has been investigated. The mathematic calculation model of axial passive magnetic bearing (PMB) stiffness is developed. And PID control based on internal model control is introduced into control of radial active magnetic bearing (AMB), considering the radial coupling of axial PMB, a mathematic calculation model of stiffness and damping of radial AMB is established. According to modal analysis, the relationship between modal frequency and modal shapes is achieved. Radial vibration frequency is mainly influenced by stiffness of radial AMB; however, when stiffness increases, radial vibration will disappear and a high frequency bending modal will appear. Stiffness of axial PMB mainly affects the axial vibration mode, which will turn into high-order bending modal. Axial PMB causes bigger influence on torsion modal of the rotor.
TL;DR: The elastodynamics of a lower-mobility Parallel Kinematic Machine for pure translational motions is analyzed and the vibrational modes and the natural frequencies of the robot are evaluated as functions of the end effector position inside the workspace.
Abstract: In the design optimization of a robot the configuration-dependent modal analysis can be a powerful tool to be exploited when high stiffness and high dynamic performances are concurrently required. In this paper the elastodynamics of a lower-mobility Parallel Kinematic Machine for pure translational motions is analyzed. The vibrational modes and the natural frequencies of the robot are evaluated as functions of the end effector position inside the workspace. A finite element model including kinematic joints is used to perform a series of modal analyses in a grid of points inside the workspace. A polynomial regression gives continuous volume maps of the natural frequencies distributions. The numerical model is validated by comparison with experiments: a modal analysis is conducted on a set of inertance Frequency Response Functions acquired on several points of the machine components as a result of an excitation given by an instrumented hammer. A Natural Frequency Difference analysis validates the model under certain conditions and highlights some critical issues to be focused on in future works.
TL;DR: In this article, a finite element model of the human hand-arm system is presented to derive natural frequencies and mode shapes, which is calibrated by considering modal parameters obtained from experimental vibration analyzed by using operational modal analysis (OMA) and transmissibility.
Abstract: This study presents a finite element (FE) model of the human hand-arm system to derive natural frequencies and mode shapes. The FE model is calibrated by considering modal parameters obtained from experimental vibration analyzed by using operational modal analysis (OMA) and transmissibility. Modal and harmonic analyses of the FE model are performed for two boundary conditions. The first one considers fixed shoulder condition while the second one introduces the trunk in order to permit motion of the shoulder. The results show that the natural frequencies of the second model that permits shoulder motion are comparable with those determined from measurements. Especially, the natural frequency about 12 Hz, which is corresponding to the frequency of maximum weight in ISO-5349-1 (2001), is not present in the model with fixed shoulder condition, while it appears in the second model. The results of the present study suggest that improved finite element models of the human hand-arm system may reveal hand-arm injury mechanism, the understanding of which may assist in deriving appropriate frequency weightings for the assessment of different components of the hand-arm vibration syndrome.
TL;DR: In this article, the authors present an impact excitation system that enables repeatable, high bandwidth, single-hit impacts, and controllable impact force for modal testing of miniature structures.
TL;DR: In this article, a damage detection method based on modal strain energy equivalence index (MSEEI) is presented, which can identify structural damage locations and extent with good accuracy.
Abstract: In order to solve structural multi-damage identification problems, a damage detection method based on modal strain energy equivalence index (MSEEI) is presented. First, an accurate expression of modal strain energy (MSE) before and after damage occurs is given. Then, according to the energy equivalence theory that the change in MSE caused by the damage should be equivalent to the energy dissipation caused by the same damage, an energy equivalence equation is deduced. Finally, four roots of the energy equivalence equation are found and a MSEEI is obtained from the four roots. Simulation results demonstrate that the proposed MSEEI method can identify structural damage locations and extent with good accuracy. Identification precision of the proposed method is clearly better than that of the modal strain energy dissipation ratio index (MSEDRI) method.
TL;DR: In this paper, Hankel matrix joint approximate diagonalization (HJAD) is used to identify the modal parameters of a dam under ambient excitation, such as from an earthquake.
TL;DR: In this paper, a method is presented to detect and quantify structural damages from changes in modal parameters (such as natural frequencies and mode shapes), and an inverse problem is formulated to minimize the objective function, defined in terms of discrepancy between the vibration data identified by modal testing and those computed from analytical model, which then solved to locate and assess the structural damage using continuous ant colony optimization algorithm.
Abstract: A method is presented to detect and quantify structural damages from changes in modal parameters (such as natural frequencies and mode shapes). An inverse problem is formulated to minimize the objective function, defined in terms of discrepancy between the vibration data identified by modal testing and those computed from analytical model, which then solved to locate and assess the structural damage using continuous ant colony optimization algorithm. The damage is formulated as stiffness reduction factor. The study indicates potentiality of the developed code to solve a wide range of inverse identification problems.
TL;DR: In this article, an impact-synchronous modal analysis (ISMA) method was proposed to determine the dynamic characteristics of a machine while in different rotating speeds, with a high number of impacts.
Abstract: A new method, namely Impact-synchronous Modal Analysis (ISMA), utilizing the modal extraction technique commonly used in Experimental Modal Analysis performed in the presence of the ambient forces, is proposed. In ISMA, the extraction is performed while the machine is running, utilized Impact-synchronous Time Averaging prior to performing the Fast Fourier Transform. The number of averages had a very important effect when applying ISMA on structures with dominant periodic responses of cyclic loads and ambient excitation. With a sufficient number of impacts, all the unaccounted forces were diminished, leaving only the response due to the impacts. This study demonstrated the effectiveness of averages taken in the determination of dynamic characteristics of a machine while in different rotating speeds. At low operating speeds that coincided with the lower natural modes, ISMA with a high number of impacts determined the dynamic characteristics of the system successfully. Meanwhile, at operating speeds that wer...
TL;DR: In this paper, a lifting approach was proposed to reduce the number of sideband peaks in the harmonic power spectrum to a single peak in the range from zero to half of the scan frequency.