Structural Modification of a Pipe Under Harmonic Excitation Using an Hybrid Numerical/Experimental Method

2011 ◽  
Author(s):  
Charles Bodel
Keyword(s):  
Modal Analysis ◽  
Nuclear Power ◽  
Natural Frequencies ◽  
Harmonic Excitation ◽  
Experimental Modal Analysis ◽  
Point Of View ◽  
Mode Shapes ◽  
Design Stage ◽  
Centrifugal Pumps ◽  
Structural Dynamic

Vibrations generated by centrifugal pumps are difficult to predict at the design stage, for it is hardly possible to accurately determine the natural frequencies of pipes and to avoid coincidences with the blade pass frequency of the pump and its harmonics. One is often led to modify the existing structure, by adding stiffness, mass or damping. This paper illustrates this point on a pipe connected to a pump in a nuclear power plant operated by EDF (E´lectricite´ de France). In October 2010, abnormal vibrations were measured on a thin pipe at the outlet of a pump in a powerplant in France. The French nuclear regulatory commission asked EDF to perform a diagnosis and to define solutions within a few months. EDF/R&D division has used an original method developed in 2004 based on hybrid data, and called LMME-SDM (for Local Model Mode-shapes Expansion Structural Dynamic Modification). The main objective is to define a structure modification able to remove all natural frequencies close to the harmonic excitation. For the purpose of the study, we need a numerical model, which should be fairly correct from a static point of view, but which is not necessarily updated from a dynamic point of view, and an experimental modal analysis carried out under real conditions on the pipe. During the experimental modal analysis, a test of added mass has been carried out so that the method can be validated by comparing the predicted and the observed frequency. This method has already been used in industrial cases in former studies [3], however the study presented here has reached a higher level in complexity. Even if this method is able to give reasonable results compared to measurements, it is close to its limits.

Effect of Weight on the Experimental Modal Analysis of Slender Cantilever Beams

2009 ◽  
Author(s):  
Lawrence Virgin ◽  
David Holland
Keyword(s):  
Modal Analysis ◽  
Natural Frequencies ◽  
Vertical Direction ◽  
Experimental Modal Analysis ◽  
Mode Shapes ◽  
Lateral Stiffness ◽  
Axial Loads ◽  
Horizontal Orientation ◽  
Beam System ◽  
Tensile Forces

It is relatively well known that axial loads tend to influence lateral stiffness and hence natural frequencies of slender structural components. Tensile forces tend to increase the lateral stiffness and compressive forces tend to reduce lateral stiffness, bringing with it the possibility of buckling. In many practical situations this is a negligible effect. But for very slender structures it can be important, including the effect of self-weight. This paper will focus attention on a form of double cantilever beam system, i.e., two cantilevers sharing a common hub. A differential axial load can be applied to this system via orientation in a gravitational field. We shall neglect the effect of gravity when the beams are in their horizontal orientation from a limited theoretical standpoint. It is of course present in the experiments but the cantilevers are much stiffer in one direction than the other, and the beams are clamped with their stiffer resistance in the vertical direction. The focus of the current paper is on the natural frequencies and mode shapes of a two-beam system from an experimental modal analysis perspective.

scholarly journals Rayleigh Damping Coefficients of Laminated Rubber Bearing

2019 ◽  
Vol 8 (4) ◽  
pp. 12294-12300
Keyword(s):  
Finite Element ◽  
Modal Analysis ◽  
Natural Frequencies ◽  
Experimental Modal Analysis ◽  
Mode Shapes ◽  
Ground Structure ◽  
Damping Coefficients ◽  
Rubber Bearing ◽  
Stability And Instability ◽  
Laminated Rubber Bearing

In isolating the ground structure and the above ground structure from seismic loads, a significant device called laminated rubber bearing is usually found in structure. The complexity of the material which is made up from a combination of rubber and steel shim plates in alternate layer, has made it difficult to measure damping value. Damping is a dissipation of energy or energy losses in the vibration of the structure. Measuring the accurate amount of damping is fundamental as damping plays a crucial role in fixing the borderline between stability and instability in structural systems. Therefore, to determine the damping value including dynamic properties in any materials, modal analysis can be used. Hence, the main objective of this research is to determine the Rayleigh’s damping coefficients α and β and to evaluate the performance of the laminated rubber bearing using finite element and experimental modal analysis. Finding shows that, the finite element modal analysis with the addition of Rayleigh’s damping coefficients α and β, shows a good agreement with the experimental modal analysis in term of natural frequencies and mode shapes. Findings show that, the values of natural frequencies reduced when precise Rayleigh’s damping coefficient added in the finite element modal analysis. It can be concluded that both finite element and experimental modal analysis method can be used to estimate the accurate values of damping ratio and to determine the Rayleigh’s damping coefficients α and β as well.

INVESTIGATION OF DYNAMIC PROPERTIES OF ELASTOMERIC BEARING COMPONENTS VIA MODAL ANALYSIS

2015 ◽  
Vol 76 (8) ◽  
Author(s):  
A. I. Yusuf ◽  
M. A. Norliyati ◽  
M. A. Yunus ◽  
M. N. Abdul Rani
Keyword(s):  
Modal Analysis ◽  
Dynamic Behavior ◽  
Natural Frequencies ◽  
Dynamic Properties ◽  
Experimental Modal Analysis ◽  
Mode Shapes ◽  
Seismic Loads ◽  
Ground Structure ◽  
Elastomeric Bearing ◽  
Earthquake Load

Elastomeric bearing is a significant device in structures such as in bridges and buildings. It is used to isolate the ground structure (substructure) and the above ground structure (superstructure) from seismic loads such as earthquake load. Understanding the dynamic behavior of the elastomeric bearing in terms of natural frequencies, mode shapes and damping are increasingly important especially in improving the design and the failure limit of the elastomeric bearing. Modal analysis is one of the methods used to determine the dynamic properties of any materials. Hence, the main objective of this research is to determine the dynamic properties of elastomeric bearing components in terms of natural frequencies, mode shapes, and damping via numerical and experimental modal analysis. This method had been successfully performed in investigating the dynamic behavior of rubber and steel shim plate.

Improved Results in Structural Dynamic Calculations by Linking Finite Element Analysis (FEA) and Experimental Modal Analysis (EMA)

1995 ◽  
Author(s):  
Ulrich Gabbert ◽  
Manfred Zehn ◽  
Friedrich Wahl
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Modal Analysis ◽  
Numerical Models ◽  
Mass Matrix ◽  
Computer Time ◽  
Experimental Modal Analysis ◽  
Mode Shapes ◽  
Element Analysis ◽  
Structural Dynamic

Abstract The paper deals with improvements of accuracy of structural dynamic calculations by using both the advantages of Finite Element Analysis (FEA) and Experimental Modal Analysis (EMA). The basis for such improvements are reasonable mechanical and numerical models and accurate frequency response measurements (eigenfrequencies and mode shapes). The paper deals first with reasons for and estimations of errors in numerical and experimental analysis. It can be shown by theory and experiment that neither FEA nor EMA models are unique, due to inevitable incompleteness of the mode shapes and eigenfrequencies from a vibration test. Verification and updating of FE models by linking FEA with EMA are discussed in the paper and mainly focussed on FE models with a large number of degrees of freedom. Hence an update method has been introduced, which leads to an improved model in a relatively small quantity of computer time. It can be shown, that based on measured eigenfrequencies and calculated eigenvectors, an updating of FE-models for real engineering problems, by changing the mass matrix only, is a very efficient procedure with a surprisingly good quality updated model.

Modal Analysis of a Container Filled with Water

2014 ◽  
Vol 592-594 ◽  
pp. 2122-2126
Author(s):  
M.L. Chandravanshi ◽  
Alok Kumar Mukhopadhyay
Keyword(s):  
Modal Analysis ◽  
Natural Frequencies ◽  
Fem Analysis ◽  
Structural Vibration ◽  
Mode Shapes ◽  
Design Stage ◽  
Modal Parameters ◽  
Element Analysis ◽  
Empty Container ◽  
Ansys Workbench

Modal analysis plays an important role at design stage which helps in diagnosing problems related to structural vibration. This paper delineates about the experimental work to investigate the modal parameters, such as mode shapes and natural frequencies of a metallic container. The modal parameters have been experimentally determined for the empty container, the container filled with one liter of water and the container filled with two liters of water. Theoretical analysis is also carried out through finite element analysis using ANSYS workbench 14 for finding out modal parameters of the empty container only. The boundary conditions of the container in the experimental and FEM analysis have been kept same. The values of modal parameters obtained by the two methods then compared for their proximity

scholarly journals Experimental Modal Analysis of Business Jet Fuselage Tail Section Sub-Assemblies

2020 ◽  
Author(s):  
Ian A. Donaldson ◽  
Chris K. Mechefske
Keyword(s):  
Modal Analysis ◽  
Computational Models ◽  
Natural Frequencies ◽  
Model Updating ◽  
Experimental Modal Analysis ◽  
Experimental Results ◽  
Modal Testing ◽  
Experimental Methodology ◽  
Mode Shapes ◽  
Business Jet

Abstract Experimental modal testing is a technique through which the dynamic response of a system can be found. Parameters such as the natural frequencies and mode shapes of a system can be extracted through experimentation, and these results can be used to confirm computational models and guide structural improvements. This paper provides an overview of experimental modal analysis performed on two aircraft fuselage half scale subassemblies, with the use of shaker excitation. The experimental methodology including the construction of each structure, data acquisition parameters, and validity checks, is presented in detail. Linearity and repeatability checks were used to validate the testing methodology and increase the level of confidence in the experimental results. The experimental natural frequencies were correlated with the computational results, and recommendations were made. The experimental results presented in this work provide a basis for computational model updating work to be considered in future work.

Experimental and Numerical Investigation of Residual Stress Stiffening Influence on Dynamic Response of Welded Structures

2019 ◽  
Author(s):  
AmirHossein MajidiRad ◽  
Yimesker S. Yihun
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Modal Analysis ◽  
Natural Frequencies ◽  
Model Updating ◽  
Experimental Modal Analysis ◽  
Experimental Results ◽  
Welding Residual Stress ◽  
Dynamic Responses ◽  
Mode Shapes

Abstract This paper presents the study of welding residual stress-stiffening effect on the dynamic responses and vibrational parameters of welded aluminum parts through an experimental modal analysis and Center Hole Drilling (CHD) residual stress measurement methods. Having a great corrosion resistance, AA5056 was utilized in this research that has been used in aircraft and ship structures; making the welding assesment of crucial. Natural frequencies and damping factors of several specimens are compared before and after the welding along with verification of experimental modal analysis integrity using Euler-Bernoulli relations. Finite element modeling of welding, cutting and modal/stress analysis of samples are also done to compare the experimental results. The results obtained from the precise modal analysis of all samples show that welding made the structure harder leading to 2% increase in natural frequencies and changing damping factors of different mode shapes. Cutting also reduced the level of residual stresses up to 34%. A good agreement is shown between the modal analysis and the experimental results. The technique used in the experiment and finite element simulation along with modeling assumptions are beneficial to other applications where model updating is required or a prediction of residual stress stiffening influence on modal responses is important.

Effect of Bass Bar Tension on Modal Parameters of a Violin's Top Plate

2015 ◽  
Vol 39 (1) ◽  
pp. 145-149 ◽  
Author(s):  
Ewa B. Skrodzka ◽  
Bogumił B.J. Linde ◽  
Antoni Krupa
Keyword(s):  
Modal Analysis ◽  
Experimental Modal Analysis ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Normal Value ◽  
Modal Damping

Abstract Experimental modal analysis of a violin with three different tensions of a bass bar has been performed. The bass bar tension is the only intentionally introduced modification of the instrument. The aim of the study was to find differences and similarities between top plate modal parameters determined by a bass bar perfectly fitting the shape of the top plate, the bass bar with a tension usually applied by luthiers (normal), and the tension higher than the normal value. In the modal analysis four signature modes are taken into account. Bass bar tension does not change the sequence of mode shapes. Changes in modal damping are insignificant. An increase in bass bar tension causes an increase in modal frequencies A0 and B(1+) and does not change the frequencies of modes CBR and B(1-).

scholarly journals Spatially Resolved Experimental Modal Analysis on High-Speed Composite Rotors Using a Non-Contact, Non-Rotating Sensor

Sensors ◽  
2021 ◽  
Vol 21 (14) ◽  
pp. 4705
Author(s):  
Julian Lich ◽  
Tino Wollmann ◽  
Angelos Filippatos ◽  
Maik Gude ◽  
Juergen Czarske ◽  
...  
Keyword(s):  
High Speed ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Fiber Reinforced ◽  
Structural Dynamic ◽  
Spatially Resolved ◽  
Glass Fiber Reinforced ◽  
Vibration Responses ◽  
And Performance

Due to their lightweight properties, fiber-reinforced composites are well suited for large and fast rotating structures, such as fan blades in turbomachines. To investigate rotor safety and performance, in situ measurements of the structural dynamic behaviour must be performed during rotating conditions. An approach to measuring spatially resolved vibration responses of a rotating structure with a non-contact, non-rotating sensor is investigated here. The resulting spectra can be assigned to specific locations on the structure and have similar properties to the spectra measured with co-rotating sensors, such as strain gauges. The sampling frequency is increased by performing consecutive measurements with a constant excitation function and varying time delays. The method allows for a paradigm shift to unambiguous identification of natural frequencies and mode shapes with arbitrary rotor shapes and excitation functions without the need for co-rotating sensors. Deflection measurements on a glass fiber-reinforced polymer disk were performed with a diffraction grating-based sensor system at 40 measurement points with an uncertainty below 15 μrad and a commercial triangulation sensor at 200 measurement points at surface speeds up to 300 m/s. A rotation-induced increase of two natural frequencies was measured, and their mode shapes were derived at the corresponding rotational speeds. A strain gauge was used for validation.

The Use of Modan 3D in Experimental Modal Analysis

2013 ◽  
Vol 486 ◽  
pp. 36-41 ◽  
Author(s):  
Róbert Huňady ◽  
František Trebuňa ◽  
Martin Hagara ◽  
Martin Schrötter
Keyword(s):  
Modal Analysis ◽  
Vibration Analysis ◽  
High Speed ◽  
Mechanical Vibration ◽  
Steel Sample ◽  
Experimental Modal Analysis ◽  
Image Correlation ◽  
Optical Methods ◽  
Mode Shapes ◽  
Vibration Modes

Experimental modal analysis is a relatively young part of dynamics, which deals with the vibration modes identification of machines or their parts. Its development has started since the beginning of the eighties, when the computers hardware equipment has improved and the fast Fourier transform (FFT) could be used for the results determination. Nowadays it provides an uncountable set of vibration analysis possibilities starting with conventional contact transducers of acceleration and ending with modern noncontact optical methods. In this contribution we mention the use of high-speed digital image correlation by experimental determination of mode shapes and modal frequencies. The aim of our work is to create a program application called Modan 3D enabling the performing of experimental modal analysis and operational modal analysis. In this paper the experimental modal analysis of a thin steel sample performed with Q-450 Dantec Dynamics is described. In Modan 3D the experiment data were processed and the vibration modes were determined. The reached results were verified by PULSE modulus specialized for mechanical vibration analysis.

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