Effect of Modes Inside or Outside the Studied Band on Accuracy of Decay Rate Method in Vibration Damping Test

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Banghui Yin ◽  
Minqing Wang
Keyword(s):  
Decay Rate ◽  
Frequency Band ◽  
Vibration Damping ◽  
Response Data ◽  
Modal Damping ◽  
Element Simulation ◽  
Positive Variation ◽  
Energy Leakage ◽  
Rate Method ◽  
Loss Factors

The band-averaged damping is determined by modal damping of the modes inside/outside the frequency band. In this paper, the effect of modes inside/outside a frequency band on the accuracy of the decay rate method (DRM) in vibration damping test was studied. First, to study the effect of modes inside a frequency band on the accuracy of DRM, the relationship between the damping loss factors (DLFs) from DRM and that from statistical energy analysis (SEA) was deduced theoretically. As shown from the analytical results, the DLF from DRM is close to that from SEA when the differences of the modal loss factors of the modes in the band are small; while the DLF from DRM is much less than that from the SEA if the differences of the modal loss factors in the band are large. Second, the influence of energy leakage from modes outside a frequency band on damping test results was studied numerically. The study reveals that when there is no mode in a frequency band, the effect of the mode outside the band on the decay rate (DR) of DRM is only related with the DR of the mode instead of the location of the mode; while when the band contains modes, the DR of DRM is influenced by the DR, amplitude, and location of the modes outside the band and the influence has a positive variation with DR, amplitude, and distance from the mode to the band. Finally, plate's transient impact response data from finite element simulation were used to verify the relevant conclusions.

Pedestrian excitation of bridges

2004 ◽  
Vol 218 (5) ◽  
pp. 477-492 ◽  
Author(s):  
D E Newl
Keyword(s):  
Time Delay ◽  
Centre Of Mass ◽  
Worst Case ◽  
Response Data ◽  
Modal Damping ◽  
Natural Movement ◽  
Simplifying Assumptions ◽  
Negative Damping ◽  
Vertical Vibrations ◽  
Pedestrian Excitation

This paper reviews the evidence on dynamic bridge loading caused by moving pedestrians. The phenomenon of ‘synchronization’ by which people respond naturally to an oscillating bridge when this has a frequency close to their natural walking or running frequency is a feature of this phenomenon. By increasing modal damping, synchronization can be prevented, but how much damping is needed in any particular situation? If some simplifying assumptions about how people walk are made, it is possible to predict analytically the minimum damping required to ensure that synchronization does not lead to high vibration levels. The main assumption is that the movement of a pedestrian's centre of mass has two components. One is its natural movement when the person is walking on a stationary pavement. The other is caused by movement of the pavement (or bridge) and is in proportion to pavement amplitude but with a time delay that is arbitrary. When the time delay is a ‘worst case’, pedestrians act as a source of negative damping. This theory supports the adoption of a non-dimensional number which measures the susceptibility of a bridge to pedestrian excitation. Although currently there are not many good bridge response data, predictions using this non-dimensional number are compared with the data that are available and found to be in satisfactory agreement. Both lateral and vertical vibrations are considered.

The influence of stacking technologies on structural dynamic properties of electric motors iron cores

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Sebastian Mönninghoff ◽  
Markus Jaeger ◽  
Kay Hameyer
Keyword(s):  
Simulation Model ◽  
Dynamic Properties ◽  
Shear Stiffness ◽  
Stator Core ◽  
Structural Dynamic ◽  
Content Type ◽  
Modal Characteristics ◽  
Lower Shear ◽  
Modal Damping ◽  
Element Simulation

Purpose It is essential to understand the structural dynamic behavior of electrical machines to predict their acoustic and vibrational behavior. Stacking technology, which is used to manufacture soft magnetic cores, has a strong influence on the material properties. The purpose of this paper is therefore to research the influence of the stacking technologies welding and bonding with bake varnish on the modal properties of iron cores. Design/methodology/approach A finite element simulation model is developed based on homogenization of the stator core. Eigenfrequencies, modeshapes and modal damping ratios are extracted from measurements and are used to validate the simulation model. Findings Modal characteristics depend on the participation of certain material layers at a certain mode. Higher amount of shear deformation results in higher modal damping. Bonded stacks exhibit lower shear stiffness and higher damping ratios. Originality/value This research paper provides insights to the modal characteristics of iron cores used in electric machine and compares the influence of stacking technologies.

Plate Damage Detection Using Vibration-Based and Static Deformation-Based Approaches

2011 ◽  
Author(s):  
Jing Shi ◽  
X. W. Tangpong
Keyword(s):  
Fractal Dimension ◽  
Damage Detection ◽  
Vibration Response ◽  
Static Deformation ◽  
Detection Methods ◽  
Mode Shapes ◽  
Response Data ◽  
Element Simulation ◽  
Catastrophic Failures ◽  
Aluminum Plates

Damage detection is important for sensing and analyzing the degradation of structures, and can effectively avoid potential catastrophic failures. Among the numerous studies in literature, most emphasis was given to the damage detection based on vibration response signals for simple beam structures. In this paper, the feasibility of roughness method for plates was investigated using both vibration-based data and static deformation data. Two detection methods, namely, roughness method and fractal dimension method, were used to analyze the data. Both types of data were obtained for aluminum plates using finite element simulation. It was found that both methods were able to detect the damage and locate its position precisely with the two types of signals. The effectiveness of damage detection using static deformation data was further demonstrated by experimenting with a cracked cantilever beam. A computer vision camera efficiently and automatically collected the static deformation data, and this approach showed great potential compared with the expensive and time-consuming collection process for vibration response data such as mode shapes.

scholarly journals Probability distribution of decay rate: a statistical time-domain damping parameter for structural damage identification

2018 ◽  
Vol 18 (1) ◽  
pp. 66-86 ◽  
Author(s):  
Ali M Ay ◽  
Suiyang Khoo ◽  
Ying Wang
Keyword(s):  
Statistical Analysis ◽  
Probability Distribution ◽  
Free Vibration ◽  
Decay Rate ◽  
Structural Damage ◽  
Damage Identification ◽  
Scale Model ◽  
Data Set ◽  
Comparison Results ◽  
Rate Method

This article proposes a novel vibration-based damage identification method, named the probability distribution of decay rate. By introducing a statistical framework, the probability distribution of decay rate method estimates the damage-induced changes in overall damping behaviour of a free-vibration dynamic system. Utilising free-vibration impulse response data, a one-dimensional data set of local maxima–minima points is constructed. A statistical analysis of this data set is then performed to derive damage-sensitive parameters. It is demonstrated that through the use of a statistical analysis framework, a number of enhancements are attained in terms of both robustness and leniency in estimating the significantly nonlinear property of overall damping. An impact hammer test is conducted in the laboratory to verify the efficacy of the proposed probability distribution of decay rate method. The test was performed on a scale-model steel Warren-truss bridge structure, subjected to bolt-connection failures. The comparison results between the probability distribution of decay rate method and the standard experimental modal analysis method confirm that the former is effective for damage identification of complex structures, particularly with real experimental data and steel-frame structure assemblies.

Energy Based Comparison of Test and Analysis Response in the Frequency Domain

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
Daniel C. Kammer ◽  
Sonny Nimityongskul
Keyword(s):  
Frequency Band ◽  
Stochastic Systems ◽  
Model Updating ◽  
Element Model ◽  
Response Curves ◽  
Test Analysis ◽  
Response Data ◽  
Power Spectral ◽  
Modal Density ◽  
Mean Square Response

Accepted modal based techniques for comparing finite element model and test data for test/analysis correlation and subsequent model updating are impossible to use in the high modal density midfrequency regime. A new approach is presented for comparing test and analysis representations using frequency-based response data instead of modal parameters. The new method uses frequency band averaging of the output power spectral densities with the central frequency of the band running over the complete frequency range of interest. The result of this computation can be interpreted in several different ways but the immediate physical connection is that it produces the mean-square response, or energy, of the system to random input limited to the averaging frequency band. The averaging process is consistent with the averaging done in statistical energy analysis for stochastic systems. The averaged response curves can be compared on a pointwise basis, or they can be compared within a running frequency band.

scholarly journals Damping Measurements Using Operational Data

1996 ◽  
Vol 118 (3) ◽  
pp. 190-193 ◽  
Author(s):  
G. H. James ◽  
T. G. Carne ◽  
P. S. Veers
Keyword(s):  
Wind Turbine ◽  
Strain Gauge ◽  
Test Bed ◽  
Data Set ◽  
Response Data ◽  
Modal Damping ◽  
Gauge Data ◽  
Prediction And Control ◽  
And Control ◽  
Operational Data

We have measured modal damping using strain-gauge data from an operating wind turbine. This new technique for measuring modal damping is easier and less expensive than previously used methods. Auto-correlation and cross-correlation functions of the strain-gauge data have been shown to consist of decaying sinusoids which correspond to the modal frequencies and damping ratios of the wind turbine. We have verified the method by extracting damping values from an analytically generated data set. Actual operating response data from the DOE/Sandia 34-m Test Bed has been used to calculate modal damping ratios as a function of rotor rotation rate. This capability will allow more accurate fatigue life prediction and control.

The Effect of Visco-Elastic Core Thickness on Modal Loss Factors of a Thick Three-Layer Cylinder

2007 ◽  
Author(s):  
Hamid R. Hamidzadeh
Keyword(s):  
Elastic Moduli ◽  
Natural Frequencies ◽  
Middle Layer ◽  
Constrained Layer Damping ◽  
Governing Equations ◽  
Modal Damping ◽  
Core Thickness ◽  
Elastic Cylinders ◽  
Thick Layers ◽  
Loss Factors

Free vibration of damped three-layer sandwich cylinders with thick layers is considered. In particular, the effect of the different thicknesses for the middle layer on the overall natural frequencies and modal damping factors are studied. The constrained layer damping is accomplished by sandwiching a linear visco-elastic material between two isotropic elastic cylinders with the same properties. The governing equations are derived using the theory of elasto-dynamic, by employing complex elastic moduli for the sandwiched layer. Dimensionless natural frequencies and modal loss-factors for the first three thickness modes associated with wave numbers of n = 0, 1, 2, 3, and 4 are tabulated for a range of thicknesses for the middle visco-elastic layer while keeping the thicknesses of inner and outer layers unchanged.

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