Modal Analysis and Modal Testing

2008 ◽  
pp. 565-574 ◽  
Author(s):  
David J. Ewins
Keyword(s):  
Modal Analysis ◽  
Modal Testing

Towards a Technique for Nonlinear Modal Analysis

2012 ◽  
Author(s):  
Simon A. Neild ◽  
Andrea Cammarano ◽  
David J. Wagg
Keyword(s):  
Normal Form ◽  
Modal Analysis ◽  
Equations Of Motion ◽  
Transformation Process ◽  
Second Order ◽  
Identity Transformation ◽  
Modal Testing ◽  
System Response ◽  
Weakly Nonlinear ◽  
Nonlinear Modal Analysis

In this paper we discuss a theoretical technique for decomposing multi-degree-of-freedom weakly nonlinear systems into a simpler form — an approach which has parallels with the well know method for linear modal analysis. The key outcome is that the system resonances, both linear and nonlinear are revealed by the transformation process. For each resonance, parameters can be obtained which characterise the backbone curves, and higher harmonic components of the response. The underlying mathematical technique is based on a near identity normal form transformation. This is an established technique for analysing weakly nonlinear vibrating systems, but in this approach we use a variation of the method for systems of equations written in second-order form. This is a much more natural approach for structural dynamics where the governing equations of motion are written in this form as standard practice. In fact the first step in the method is to carry out a linear modal transformation using linear modes as would typically done for a linear system. The near identity transform is then applied as a second step in the process and one which identifies the nonlinear resonances in the system being considered. For an example system with cubic nonlinearities, we show how the resulting transformed equations can be used to obtain a time independent representation of the system response. We will discuss how the analysis can be carried out with applied forcing, and how the approximations about response frequencies, made during the near-identity transformation, affect the accuracy of the technique. In fact we show that the second-order normal form approach can actually improve the predictions of sub- and super-harmonic responses. Finally we comment on how this theoretical technique could be used as part of a modal testing approach in future work.

Experimental Identification Approach of Dynamic Parameters of Precise Horizontal Machining Centre Based on Component-System

2011 ◽  
Vol 467-469 ◽  
pp. 1686-1690
Author(s):  
Zhi Feng Liu ◽  
Zhong Hua Chu ◽  
Qiang Cheng ◽  
Guang Bo Liu ◽  
Dong Sheng Xuan
Keyword(s):  
Finite Element ◽  
Modal Analysis ◽  
Natural Frequencies ◽  
Modal Testing ◽  
Element Calculation ◽  
Element Simulation ◽  
Modes Of Vibration ◽  
Identification Approach ◽  
Comparison Of The Results ◽  
Machine Structure

This paper integrates experiment modal analysis and the analytical modal analysis to study on the vibration phenomena occurring occasionally at the different components of a precise horizontal machining centre. The paper is focused on extracting the mode shape of the major components of the machine in order to ensure resonance phenomena as a cause of vibration. At first the main natural frequencies with the corresponding modes of vibration of the machine structure are obtained by the experiment modal analysis. Then the dynamic behavior of the machine components is simulated using a finite element simulation model. The comparison of the results based on finite element calculation with their experimental counterparts shows the reasonableness. The model is evaluated and corrected with experimental results by modal testing of the machine components.

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.

Operational Modal Analysis of Lateral Rotordynamic Modes of Rotating Machinery

2014 ◽  
Author(s):  
Eoin Peter Carden ◽  
Stefano Morosi
Keyword(s):  
Modal Analysis ◽  
Rotating Machinery ◽  
Operational Modal Analysis ◽  
Modal Testing ◽  
Normal Operation ◽  
Stability Margins ◽  
Normal Production ◽  
Testing Techniques ◽  
Excitation Force ◽  
Operational Range

The lateral rotordynamic response of turbomachinery is typically speed dependent due to hydrodynamic lubricated bearings, seals, gyroscopic and centrifugal effects, etc. Rotordynamic tools are used to predict the behavior of the machine during operation, however validating these results is challenging. Traditional experimental modal testing techniques rely on controlled and measured excitation together with measured responses. However, during operation this is unpractical, as the actual excitation force is rarely known. Operational modal analysis (OMA) can identify the modal parameters of a system over its entire operational range from measurement of response due to some (unknown) excitation. OMA has proven successful on non-rotating structures, but has seldom been applied to rotating machinery. Three case studies are presented demonstrating the use of OMA in identifying lateral rotors modes based on measurements from existing radial proximity probes during normal production undertaken as part of commissioning campaigns. Challenges encountered in using and interpreting OMA results are discussed. The results show that proximity probe data acquired during normal operation may be used as input to OMA for the assessment of stability margins of rotating machinery, to produce experimentally derived Campbell diagrams and to identify backwards as well as forwards whirling modes.

PREDICTION OF RESONANCE CHARACTERISTICS OF THE FOREARM BONES USING FINITE ELEMENT ANALYSIS

2006 ◽  
Vol 10 (04) ◽  
pp. 205-215 ◽  
Author(s):  
Kyu-Jung Kim ◽  
Il-Kyu Hwang
Keyword(s):  
Finite Element ◽  
Modal Analysis ◽  
Bone Health ◽  
Structural Integrity ◽  
Dental Treatment ◽  
Modal Testing ◽  
Long Bone ◽  
Element Analysis ◽  
Forearm Bones

Modal analysis is often used as a diagnostic tool for osteoporosis, fracture healing, and dental treatment monitoring by measuring the resonance characteristics of an anatomical structure. The objective of this study was to conduct parametric finite element modal analysis of the forearm bones using geometric models reconstructed from the Visible Human Project datasets in order to gain insights into the structural integrity of the forearm complex and their implications on bone health. The reported fundamental resonant frequency of the ulna was matched to calibrate the material properties of each anatomical component of the ulna, and subsequently sensitivities of each material parameter were assessed. Resonance characteristics of the radius for four vibration modes were then estimated using the calibrated material data from the calibration simulation. The ulna had the fundamental mode in mediolateral bending at 400 Hz, while the radius in anterior–posterior bending at 411 Hz. The axial and torsional modes always had higher fundamental resonant frequencies over 1700 Hz for both bones. It was suggested that the parametric finite element modal analysis in conjunction with in vivo modal testing may be applicable for determining the physical properties of a long bone for quantitative assessment of bone health.

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.

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.

The Modal Analysis and Optimum Structure Design of Automobile Air Cleaner

2012 ◽  
Vol 516-517 ◽  
pp. 1117-1120
Author(s):  
Fang Zhang ◽  
Hong Zhou
Keyword(s):  
Modal Analysis ◽  
Element Model ◽  
Structure Design ◽  
Modal Testing ◽  
Optimum Structure ◽  
Reference Standard ◽  
Dynamic Design ◽  
Fea Model ◽  
Air Cleaner ◽  
Different Order

In this paper, a finite element model of an automotive air cleaner is established. Through the free modal analysis of this FEA model, combined with Modal Testing which modified the FEA model, different order modal frequency and modal characteristics are acquired, which supply the reference standard for dynamic design. According to the analysis, the local unreasonable structure will be optimized.

Modal Hammering Test and Sensitivity Analysis for BIW Vehicle

2014 ◽  
Vol 599-601 ◽  
pp. 985-991
Author(s):  
Cheng Wu Liu
Keyword(s):  
Sensitivity Analysis ◽  
Modal Analysis ◽  
Structural Parameters ◽  
Low Frequency ◽  
Modal Testing ◽  
Testing System ◽  
Modal Parameter ◽  
Modal Assurance Criterion ◽  
Body In White ◽  
Modal Parameter Estimation

Aiming at the defects of classical modal parameter estimation approach, the impulse hammer modal test during body-in-white (BIW) stage was done through polyMAX method method. Based on modal analysis theory, an experimental model of BIW was established. The compositions of the experimental modal testing system, the design of testing scheme as well as its validation were described in detail in this paper. The collected data were identified via the polyMAX modal analysis method. The dynamic characteristics of BIW were confirmed by Modal Assurance Criterion. Influence of low frequency distribution characteristics on complete vehicle NVH was also analyzed. On the basis of above investigation, sensitivity analysis of the structure of BIW was conducted and sensitive structural parameters were determined. The test results show that the modal testing system can meet the requirement of precision with reliable results of parameter identification and sensitivity analysis, which can serve as a basis for the improvement of BIW structural design.

Experimental Study of the Static Modal Analysis on Milling Machine Tool

2014 ◽  
Vol 903 ◽  
pp. 123-128 ◽  
Author(s):  
Norlida Jamil ◽  
Ahmad Razlan Yusoff ◽  
Muhammad Hatifi Mansor
Keyword(s):  
Machine Tool ◽  
Modal Analysis ◽  
Mechanical Test ◽  
Modal Testing ◽  
Machining Process ◽  
The Finite Element Method ◽  
Excited Vibration ◽  
Good Consistency ◽  
Tool Vibrations ◽  
Design Software

Machine tool vibrations have great impact on machining process. Modal testing is a form of vibration testing which is able to determine the Frequency Response Function (FRF) of the mechanical test structures. In this paper, the main focus is to identify a procedure to obtain natural frequency values for machine tool components in order to establish better conditions in the cutting process on the machine tool. For this purpose, a 3D model of the machine tools structure is made using design software and exported to analysis software. Later on, the Finite Element Method (FEM) modal analysis was used to obtain the natural frequencies. The model is evaluated and corrected through an experimental modal test. In the experiment, the machine tool vibration is excited by impact hammer and the response of excited vibration is recorded. In the end, the result of both FEM and experimental shows a good consistency in comparison.

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