Modal Analysis of Systems Using a Neuro-Fuzzy Approach

2010 ◽  
Author(s):  
Farbod Khoshnoud ◽  
Clarence W. de Silva
Keyword(s):  
Neural Networks ◽  
Modal Analysis ◽  
Mode Shape ◽  
Iterative Process ◽  
Analysis Data ◽  
Modal Testing ◽  
Mode Shapes ◽  
Vibration Sensors ◽  
Fuzzy Neural ◽  
Vibration Modeling

A novel method of modal analysis for vibration modeling of systems is presented in this paper. In the developed method, first, mode shapes of the structure that is being analyzed are approximated. The approximate mode shapes are expressed by fuzzy sets where approximate deflections or displacement magnitudes of the mode shapes are described by fuzzy linguistic terms such as Zero, Medium, and Large. Fuzzy membership functions provide a means of dealing with the imprecisely defined system and it gives access to a large repertoire of tools available in the field of fuzzy reasoning. Second, fuzzy representations of the approximate mode shapes, called Fuzzy Mode Shapes in this paper, are updated using modal analysis data as obtained through experimentation. Finally, artificial neural networks are used as a tool to obtain an accurate version of the mode shape data by learning the target set of the data. An appropriate analogy of the application of Fuzzy Mode Shapes in the first step is the Starting Mode Shape Vectors in numerical eigenvector problem where the starting vector is updated through an iterative process. In this paper iterative updating process of mode shapes is carried out for the application of experimental modal testing. In this approach the differences between the fuzzy mode shapes and the corresponding measured modal testing data are minimized through an iterative process. In validating the developed technique for vibration modeling of one-dimensional and two-dimensional elastic bodies and structures, modeling of elastic beams, a clamped-free-clamped-free plate and a frame are used as illustrative examples. The solutions of the corresponding simulations are compared with the results from finite element computations and analytical model solutions. The good agreement of the results obtained for these models justifies the application of the developed method in experimental vibration modeling of systems. Use of the fuzzy-neural approach as developed in the paper expands the coverage of experimentally measured data, which is normally limited to a small number of measurement sets due to the limited number of available vibration sensors in the analyzed system. Neural networks provide a satisfactory interpolation of two sets of data including a) modal test data, which is accurate but is normally available only for a few measured points, and b) Fuzzy Mode Shapes, which are available for large number of points but are approximate.

Analysis of Instabilities in Railway Vehicles Employing Operational Modal Analysis

2015 ◽  
Author(s):  
Lara Erviti Calvo ◽  
Gorka Agirre Castellanos ◽  
Germán Gimenez
Keyword(s):  
Numerical Model ◽  
Modal Analysis ◽  
Mode Shape ◽  
Operational Modal Analysis ◽  
Mode Shapes ◽  
Correct Identification ◽  
Unstable Condition ◽  
Static Tests ◽  
Railway Vehicles ◽  
Damping Rate

The application of Operational Modal Analysis (OMA) in the railway sector opens a broad field of opportunities. The validation of the numerical model employed in the design phase is usually performed employing data obtained in static tests. The drawback is that some suspension parameters, such as dampers, only have an influence in the dynamic behavior and not in the static behavior. Because of that, the use of the mode shapes identified from track measurements in combination with the static tests leads to a more accurate validation of the numerical model. Apart from that, most passenger comfort and dynamic problems are associated to slightly damped modes. A correct identification of the modal parameters can be used as a continuous design improvement tool to improve the comfort and dynamic characteristics of future designs. Another valuable application of OMA techniques is the identification of the mode shapes corresponding to instabilities, due to the safety impact that they have. In railway vehicles, instabilities are associated to mode shapes that present a damping rate which decreases with the increase of the running speed. Above a certain speed value, the excitation coming from track cannot be damped by the vehicle and it reaches an unstable condition. This unstable condition leads to high acceleration levels experienced by the passengers and high interaction forces between the wheel and the rail that may lead to safety hazards. The speed above which the vehicle is unstable is known as critical speed, and has to be greater than the maximum speed of the vehicle with a reasonable safety margin. The use of OMA techniques allows identifying the mode shape that causes the instability. This paper presents the application of OMA techniques to measurements performed on a passenger vehicle, in which the speed was increased until the vehicle was unstable. The mode shape that caused the instability was identified as well as its corresponding natural frequency and damping rate.

scholarly journals Dynamic Modal Analysis of Vertical Machining Centre Components

2009 ◽  
Vol 2009 ◽  
pp. 1-10 ◽  
Author(s):  
Anayet U. Patwari ◽  
Waleed F. Faris ◽  
A. K. M. Nurul Amin ◽  
S. K. Loh
Keyword(s):  
Modal Analysis ◽  
Mode Shape ◽  
Modal Testing ◽  
Machine Component ◽  
Vibration Modes ◽  
Structural Dynamic ◽  
Element Simulation ◽  
Analysis Technique ◽  
Design Software

The paper presents a systematic procedure and details of the use of experimental and analytical modal analysis technique for structural dynamic evaluation processes of a vertical machining centre. The main results deal with assessment of the mode shape of the different components of the vertical machining centre. The simplified experimental modal analysis of different components of milling machine was carried out. This model of the different machine tool's structure is made by design software and analyzed by finite element simulation using ABAQUS software to extract the different theoretical mode shape of the components. The model is evaluated and corrected with experimental results by modal testing of the machine components in which the natural frequencies and the shape of vibration modes are analyzed. The analysis resulted in determination of the direction of the maximal compliance of a particular machine component.

Experimental Modal Analysis of a Half-Scale Model Twin-Engine Aircraft Rear Fuselage Engine Mount Support Frame

2017 ◽  
Author(s):  
Diego A. Chamberlain ◽  
Chris K. Mechefske
Keyword(s):  
Modal Analysis ◽  
Natural Frequencies ◽  
Testing Procedure ◽  
Modal Testing ◽  
Scale Model ◽  
Mode Shapes ◽  
Component Testing ◽  
Fitting Procedures ◽  
Engine Mount ◽  
Set Up

Experimental modal testing using an impact hammer is a commonly used method for obtaining the modal parameters of any structure for which the vibrational behavior is of interest. Natural frequencies and associated mode shapes of the structure can be extracted directly from measured FRFs (Frequency Response Functions) through various curve fitting procedures. This paper provides an overview of the modal testing conducted on an aerospace component. Testing set-up, experimental equipment and the methodology employed are all described in detail. Further validation of the testing procedure was done by ensuring that the experimental results satisfy the requirements of repeatability, reciprocity and linearity. The relevant ISO standard has been referenced and important concepts to modal analysis are expanded upon. Recorded natural frequencies, coherence and a description of the observed mode shapes are presented along with notable trends.

The Comparative Modal Analysis of Simulation and Experiment on the Electronic Button-Sewing Machine Shell

2013 ◽  
Vol 668 ◽  
pp. 612-615
Author(s):  
Li Zhang ◽  
Guang Yuan Nie ◽  
Hong Wu ◽  
Jie Chen
Keyword(s):  
Comparative Analysis ◽  
Modal Analysis ◽  
Natural Frequency ◽  
Mode Shape ◽  
Damping Ratio ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Ansys Software ◽  
Sewing Machine ◽  
Simulation And Experiment

In this paper, the simulation with ANSYS software and the experimental modal analysis by impacting are carried out on the electronic button-sewing machine shell. The modal parameters, such as the natural frequency, the damping ratio and the mode shape, are obtained. Comparative analysis of their results shows that the mode shapes of the machine shell are mainly the outward-expanding and inward-contracting vibrations, which provides a useful reference for vibration and noise reduction of the electronic button-sewing machine.

Finite Element Model Verification for the Use of Piezoelectric Sensor in Structural Modal Analysis

2006 ◽  
Vol 22 (2) ◽  
pp. 107-114 ◽  
Author(s):  
B.-T. Wang ◽  
P.-H. Chen ◽  
R.-L. Chen
Keyword(s):  
Finite Element ◽  
Modal Analysis ◽  
Piezoelectric Materials ◽  
Piezoelectric Sensor ◽  
Model Verification ◽  
Modal Testing ◽  
Mode Shapes ◽  
Response Analysis ◽  
Pvdf Film ◽  
Element Analysis

AbstractThis paper presents the theoretical modal analysis for the use of PVDF sensor in structural modal testing via finite element analysis (FEA). A series of rectangular PVDF films are adhered on the surface of cantilever beam as sensors, while the point impact force is applied as the actuator for experimental modal analysis (EMA). Natural frequencies and mode shapes determined from both FEA and EMA are validated. In FEA, the beam structure is modeled by 3D solid elements, and the PVDF films are modeled by 3D coupled field piezoelectric elements. Both modal analysis and harmonic response analysis are performed to obtain the structural modal parameters and frequency response functions, respectively. Results show that both FEA and EMA results agree well. In particular, the PVDF sensor mode shapes, proportional to the slope difference between the two edges of PVDF film, are numerically and experimentally validated by FEA and EMA, respectively. Therefore, the simulation of PVDF films for vibration analysis in FEA can be verified and easily extended to other complex structures that may contain piezoelectric materials.

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.

scholarly journals Exact Damage Identification of Plate-Like Structure using Mode Shapes

2020 ◽  
Vol 9 (4) ◽  
pp. 1264-1272
Keyword(s):  
Modal Analysis ◽  
Mode Shape ◽  
Natural Frequencies ◽  
Damage Identification ◽  
Mode Shapes ◽  
Absolute Difference ◽  
Virtual Instrumentation ◽  
Crack Orientation ◽  
Labview Software ◽  
Alternative Approaches

In this paper, Mode Shape Based Damaged Detection Technique (MSBDT) has been applied for plate-like structures to recognize the damage location and quantify the damage length. Two alternative approaches are exclusively used to extract damage indexes through mode shapes of undamaged plate (i.e. reference data) and damaged plate. The absolute difference of mode shapes used in first approach and mode shape curvatures used in second approach of undamaged and damaged plates. Healthy Aluminium plate was tested in the laboratory for accurate material properties and considered three different damage cases by changing the crack orientation and location for successfully implementation of above approaches. In order to make certain the sensitivity of the proposed approaches, natural frequencies and corresponding mode shapes for first six modes in transverse direction of a plate are obtained by Finite Element Modal Analysis (FEMA) in ANSYS 18.1 and validated by Experimental Modal Analysis (EMA) in virtual instrumentation environment using LabView software.

Characterization of the Modal Characteristics of Structures Operating in Dense Liquid Turbopumps

2017 ◽  
Author(s):  
Joseph Chiu ◽  
Andrew M. Brown
Keyword(s):  
Natural Frequency ◽  
Mode Shape ◽  
Numerical Solutions ◽  
Forced Response ◽  
Modal Testing ◽  
Liquid Oxygen ◽  
Mode Shapes ◽  
Annular Disk ◽  
Modal Characteristics ◽  
Modal Test

It is well-known that the natural frequencies of structures immersed in heavy liquids will decrease due to the fluid “added-mass” effect. This reduction has not been precisely determined, though, with indications that it is in the 20–40% range for water. In contrast, the mode shapes of these structures have always been assumed to be invariant in liquids. Recent modal testing at NASA/Marshall Space Flight Center of turbomachinery inducer blades in liquid oxygen, which has a density slightly greater than water, indicates that the mode shapes change appreciably, though. This paper presents a study that examines and quantifies the change in mode shapes as well as more accurately defines the natural frequency reduction. A literature survey was initially conducted and test-verified analytical solutions for the natural frequency reductions were found for simple geometries, including a rectangular plate and an annular disk. The ANSYS© fluid/structure coupling methodology was then applied to obtain numerical solutions, which compared favorably with the published results. This initial study indicated that mode shape changes only occur for non-symmetric boundary conditions. Techniques learned from this analysis were then applied to the more complex inducer model. ANSYS numerical results for both natural frequency and mode shape compared well with modal test in air and water. A number of parametric studies were also performed to examine the effect of fluid density on the structural modes, reflecting the differing propellants used in rocket engine turbomachinery. Some important findings were that the numerical order of mode shapes changes with density initially, and then with higher densities the mode shapes themselves warp as well. Valuable results from this study include observations on the causes and types of mode shape alteration and an improved prediction for natural frequency reduction in the range of 30–41% for preliminary design. Increased understanding and accurate prediction of these modal characteristics is critical for assessing resonant response, correlating finite element models to modal test, and performing forced response in turbomachinery.

scholarly journals Laboratory investigation of a bridge scour monitoring method using decentralized modal analysis

2021 ◽  
pp. 147592172098512
Author(s):  
Muhammad Arslan Khan ◽  
Daniel P McCrum ◽  
Luke J Prendergast ◽  
Eugene J OBrien ◽  
Paul C Fitzgerald ◽  
...  
Keyword(s):  
Modal Analysis ◽  
Mode Shape ◽  
Experimental Tests ◽  
Linear Increase ◽  
Mode Shapes ◽  
Bridge Scour ◽  
Scaled Model ◽  
Global Mode ◽  
Monitoring Method ◽  
Output Only

Scour is a significant issue for bridges worldwide that influences the global stiffness of bridge structures and hence alters the dynamic behaviour of these systems. For the first time, this article presents a new approach to detect bridge scour at shallow pad foundations, using a decentralized modal analysis approach through re-deployable accelerometers to extract modal information. A numerical model of a bridge with four simply supported spans on piers is created to test the approach. Scour is modelled as a reduction in foundation stiffness under a given pier. A passing half-car vehicle model is simulated to excite the bridge in phases of measurement to obtain segments of the mode shape using output-only modal analysis. Two points of the bridge are used to obtain modal amplitudes in each phase, which are combined to estimate the global mode shape. A damage indicator is postulated based on fitting curves to the mode shapes, using maximum likelihood, which can locate scour damage. The root mean square difference between the healthy and scoured mode shape curves exhibits an almost linear increase with increasing foundation stiffness loss under scour. Experimental tests have been carried out on a scaled model bridge to validate the approach presented in this article.

Modal Analysis of the Milling Machine Structure through FEM and Experimental Test

2011 ◽  
Vol 383-390 ◽  
pp. 6717-6721 ◽  
Author(s):  
S. Pedrammehr ◽  
Hamid Farrokhi ◽  
A. Khani Sheykh Rajab ◽  
S. Pakzad ◽  
M. Mahboubkhah ◽  
...  
Keyword(s):  
Machine Tool ◽  
Modal Analysis ◽  
Natural Frequencies ◽  
Modal Testing ◽  
Machining Process ◽  
Mode Shapes ◽  
Milling Machine ◽  
Machine Tool Structure ◽  
Tool Vibrations ◽  
Machine Structure

Machine tool vibrations have great impact on machining process. In this paper the dynamic behavior and modal parameters of milling machine is presented. For this purpose, the CAD model of the milling machine structure is provided in CATIA and then Natural frequencies and mode shapes of the machine tool structure are carried out through FEM modal analysis under ANSYS Workbench. The model is evaluated and corrected with experimental results by modal testing on FP4M milling machine. Finally, the natural frequencies and mode shapes obtained by both experimental and FEM modal analysis are compared. The results of two methods are in widely agreement.

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