Operational Modal Analysis of Aluminum Beams

2007 ◽  
Vol 50 (1) ◽  
pp. 74-85 ◽  
Author(s):  
S. Rudroju ◽  
A. Gupta ◽  
S. Yandamuri
Keyword(s):  
Modal Analysis ◽  
Impact Test ◽  
Force Measurement ◽  
Operating Conditions ◽  
Impact Testing ◽  
Operational Modal Analysis ◽  
Normal Functioning ◽  
Large Structures ◽  
Output Only ◽  
Ambient Excitation

Natural frequencies obtained by modal analysis are important to engineers interested in predicting the dynamic behavior of structures. Traditional modal analysis involves impact testing or shaker testing, where response signal and input force are measured to obtain the transfer function. However, for large structures, input excitation force measurement may be difficult, if not impossible. Large structures may be subjected to ambient excitation; operational modal analysis (OMA), also known as output-only modal analysis, has been used for extracting modal parameters of these types of structures. The main advantage of operational modal analysis is that no artificial excitation is needed, and the analysis is based on measurements of only the output data of the system. Operational modal analysis tests are performed under the actual operating conditions of the system without any change of boundary conditions; the tests use the ambient loads as input and thus do not interfere with the normal functioning of the system. In this study, six aluminum beams of different configurations (beams with and without cuts of various lengths) were used for conducting experiments. Results based on impact test, shaker test, and operational modal analysis are presented.

Second-Order Blind Identification for Operational Modal Analysis

2007 ◽  
Author(s):  
F. Poncelet ◽  
G. Kerschen ◽  
J. C. Golinval ◽  
F. Marin
Keyword(s):  
Modal Analysis ◽  
Operational Modal Analysis ◽  
Blind Identification ◽  
Modal Parameter ◽  
Engineering Structures ◽  
Experimental Application ◽  
Large Structures ◽  
Output Only ◽  
Modal Parameter Estimation ◽  
Source Signals

For modal analysis of large structures, it is unpractical and expensive to use artificial excitation (e.g., shakers). However, engineering structures are most often subject to ambient loads (e.g., traffic and wind) that can be exploited for modal parameter estimation. One difficulty is that the actual loading conditions cannot generally be measured, and output-only measurements are available. This paper proposes to explore the utility of blind source separation (BSS) techniques for operational modal analysis. The basic idea of BSS is to recover unobserved source signals from their observed mixtures. The feasibility and practicality of the proposed method are demonstrated using an experimental application.

scholarly journals Operational Modal Analysis and the Performance Assessment of Vehicle Suspension Systems

2012 ◽  
Vol 19 (5) ◽  
pp. 1099-1113 ◽  
Author(s):  
L. Soria ◽  
B. Peeters ◽  
J. Anthonis ◽  
H. Van der Auweraer
Keyword(s):  
Modal Analysis ◽  
Cost Effective ◽  
Operating Conditions ◽  
Operational Modal Analysis ◽  
Vehicle Suspension ◽  
Active System ◽  
Passenger Cars ◽  
Suspension Systems ◽  
Controlled Systems ◽  
Output Only

Comfort, road holding and safety of passenger cars are mainly influenced by an appropriate design of suspension systems. Improvements of the dynamic behaviour can be achieved by implementing semi-active or active suspension systems. In these cases, the correct design of a well-performing suspension control strategy is of fundamental importance to obtain satisfying results. Operational Modal Analysis allows the experimental structural identification in those that are the real operating conditions: Moving from output-only data, leading to modal models linearised around the more interesting working points and, in the case of controlled systems, providing the needed information for the optimal design and verification of the controller performance. All these characters are needed for the experimental assessment of vehicle suspension systems. In the paper two suspension architectures are considered equipping the same car type. The former is a semi-active commercial system, the latter a novel prototypic active system. For the assessment of suspension performance, two different kinds of tests have been considered, proving ground tests on different road profiles and laboratory four poster rig tests. By OMA-processing the signals acquired in the different testing conditions and by comparing the results, it is shown how this tool can be effectively utilised to verify the operation and the performance of those systems, by only carrying out a simple, cost-effective road test.

Comparing Measured Responses of an Offshore Structure with Operational Modal Analysis assisted Classical Model Approach

2020 ◽  
pp. 1-10
Author(s):  
Bruna Nabuco ◽  
Sandro D. Amador ◽  
Evangelos I. Katsanos ◽  
Ulf T. Tygesen ◽  
Erik Damgaard Christensen ◽  
...  
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Modal Analysis ◽  
Element Model ◽  
Operating Conditions ◽  
Operational Modal Analysis ◽  
Mode Shapes ◽  
Wave Forces ◽  
Wave Load ◽  
Offshore Structure

Abstract Aiming to ensure the structural integrity of an offshore structure, wave-induced responses have been measured during normal operating conditions. Operational Modal Analysis is applied to the data obtained from continuously monitoring the structure. Sensors placed only on the topside of an offshore platform are sufficient to provide information to identify the modal properties of the structure, such as natural frequencies, damping ratios, and mode shapes. A finite element model is created and updated in line with the identified dynamic properties for applying a modal expansion technique in the interest of accessing information at any point of the structure. Wave radars are also placed at the platform from which the wave forces are calculated based on basic industrial standard models. In this way, the wave kinematics are estimated according to the linear wave theory associated with Wheeler stretching. Since this study is related to offshore structures composed by slender elements, the wave forces are estimated using Morison formulation. By assigning typical values to the drag and inertia coefficients, wave loads are estimated and applied to the updated finite element model. For the diffraction effect, the wave load has also been evaluated according to MacCamy and Fuchs theory. The responses obtained from this procedure are compared with measured responses. In addition to describing the process, this paper presents a case study to verify the theory using monitoring data from a tripod jacket. Results indicate realistic response estimation that contributes to the knowledge about the state of the structure.

scholarly journals Transmissibilty-Based Operational Modal Analysis for Flight Flutter Testing Using Exogenous Inputs

2012 ◽  
Vol 19 (5) ◽  
pp. 1071-1083 ◽  
Author(s):  
Christof Devriendt ◽  
Tim De Troyer ◽  
Gert De Sitter ◽  
Patrick Guillaume
Keyword(s):  
Modal Analysis ◽  
Frequency Domain ◽  
Experimental Modal Analysis ◽  
Operational Modal Analysis ◽  
Modal Parameters ◽  
Input Output ◽  
Output Only ◽  
Flutter Testing

During the recent years several new tools have been introduced by the Vrije Universiteit Brussel in the field of Operational Modal Analysis (OMA) such as the transmissibility based approach and the the frequency-domain OMAX concept. One advantage of the transmissibility based approach is that the ambient forces may be coloured (non-white), if they are fully correlated. The main advantage of the OMAX concept is the fact that it combines the advantages of Operational and Experimental Modal Analysis: ambient (unknown) forces as well as artificial (known) forces are processed simultaneously resulting in improved modal parameters. In this paper, the transmissibility based output-only approach is combined with the input/output OMAX concept. This results in a new methodology in the field of operational modal analysis allowing the estimation of (scaled) modal parameters in the presence of arbitrary ambient (unknown) forces and artificial (known) forces.

Operational Modal Analysis for Dynamic Characterization of a Ro-Lo Ship

2014 ◽  
Vol 58 (04) ◽  
pp. 216-224 ◽  
Author(s):  
Esben Orlowitz ◽  
Anders Brandt
Keyword(s):  
Modal Analysis ◽  
Natural Frequencies ◽  
Operating Conditions ◽  
Operational Modal Analysis ◽  
Mode Shapes ◽  
Dynamic Characterization ◽  
Sea Trial ◽  
Global Modes ◽  
Bending Modes

The dynamic characteristics of ship structures are becoming more important as the flexibility of modern ships increases, for example, to predict reliable design life. This requires an accurate dynamic model of the structure, which, because of complex vibration environment and complex boundary conditions, can only be validated by measurements. In the present paper the use of operational modal analysis (OMA) for dynamic characterization of a ship structure based on experimental data, from a full-scale measurement of a 210-m long Ro-Lo ship during sea trial, is presented. The measurements contain three different data sets obtained under different operating conditions of the ship: 10 knots cruising speed, 18 knots cruising speed, and at anchor. Natural frequencies, modal damping ratios, and mode shapes have been successfully estimated for the first 10 global modes. Damping ratios for the current ship were found within the range 0.9%–1.9% and natural frequencies were found to range from 0.8 to 4.1 Hz for the first 10 global modes of the ship at design speed (18 knots). The three different operating conditions showed, in addition, a speed dependency of the natural frequencies and damping ratios. The natural frequencies were found to be lower for the 18-knots condition compared with the two other conditions, most significantly for the vertical bending modes. Also, for the vertical bending modes, the damping ratios increased by 28%–288% when the speed increased from 10 to 18 knots. Other modes were not found to have the same strong speed dependency.

Dynamic Behavior of Rolling Tires Under Different Operating Conditions

2012 ◽  
Author(s):  
S. Vercammen ◽  
C. González Díaz ◽  
P. Kindt ◽  
C. Thiry ◽  
J. Middelberg ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Modal Analysis ◽  
Dynamic Behavior ◽  
Operating Conditions ◽  
Operational Modal Analysis ◽  
Modal Parameters ◽  
Road Noise ◽  
Vibration Measurements ◽  
Noise And Vibration ◽  
Propagation Behavior

Although tire/road noise and tire vibration phenomena have been studied for decades, there are still some missing links in the process of accurately predicting and controlling the overall tire/road noise and vibration. An important missing link is represented by the effect of rolling on the dynamic behavior of a tire. Consequently, inside the European seventh framework program, an industry-academia partnership project, named TIRE-DYN, has been founded between KU Leuven, Goodyear and LMS International. By means of experimental and numerical analyses, the effects of rolling on the tire dynamic behavior are quantified. This paper presents the results of vibration measurements on a rotating tire with an embedded accelerometer. Modal parameters of the rolling tire are estimated from an operational modal analysis. In addition, the dispersion curves, which give detailed insight in the wave propagation behavior of a structure, are analyzed for the rolling tire. The goal of these analyses is to deepen the understanding on the influence of rolling on the tire dynamic behavior.

scholarly journals Virtual Structural Monitoring of Wind Turbines Using Operational Modal Analysis Techniques

2013 ◽  
Vol 569-570 ◽  
pp. 523-530 ◽  
Author(s):  
Emilio di Lorenzo ◽  
Simone Manzato ◽  
Bart Peeters ◽  
Herman van der Auweraer
Keyword(s):  
Modal Analysis ◽  
Wind Turbines ◽  
Numerical Models ◽  
Structural Condition ◽  
Operational Modal Analysis ◽  
Critical Aspect ◽  
Operational Conditions ◽  
Open Issue ◽  
Output Only ◽  
Large Wind

Operational Modal Analysis (OMA), also known as output-only modal analysis, allows identifying modal parameters only by using the response measurements of the structures in operational conditions when the input forces cannot be measured. These information can then be used to improve numerical models in order to monitor the operating and structural conditions of the system. This is a critical aspect both for condition monitoring and maintenance of large wind turbines, particularly in the off-shore sector where operation and maintenance represent a high percentage of total costs. Although OMA is widely applied, the wind turbine case still remains an open issue. Numerical aeroelastic models could be used, once they have been validated, to introduce virtual damages to the structures in order to analyze the generated data. Results from such models can then be used as baseline to monitor the operating and structural condition of the machine.

A frequency domain blind identification method for operational modal analysis using a limited number of sensors

2020 ◽  
Vol 26 (17-18) ◽  
pp. 1383-1398
Author(s):  
Xinhui Li ◽  
Jerome Antoni ◽  
Michael J Brennan ◽  
Tiejun Yang ◽  
Zhigang Liu
Keyword(s):  
Modal Analysis ◽  
Frequency Domain ◽  
Blind Source Separation ◽  
Source Separation ◽  
Operating Conditions ◽  
Operational Modal Analysis ◽  
Modal Identification ◽  
Frequency Range ◽  
Vibration Data ◽  
Spatial Aliasing

Operational modal analysis is an experimental modal analysis approach, which uses vibration data collected when the structure is under operating conditions. Amongst the methods for operational modal analysis, blind source separation–based methods have been shown to be efficient and powerful. The existing blind source separation modal identification methods, however, require the number of sensors to be at least equal to the number of modes in the frequency range of interest to avoid spatial aliasing. In this article, a frequency domain algorithm that overcomes this problem is proposed, which is based on the joint diagonalization of a set of weighted covariance matrices. In the proposed approach, the frequency range of interest is partitioned into several frequency ranges in which the number of active modes in each band is less than the number of sensors. Numerical simulations and an experimental example demonstrate the efficacy of the method.

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