Experimental Modal Analysis
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This 4-day course is designed for test engineers involved in acquisition and reduction of vibration data for the development of a modal model. Practical aspects of modal analysis theory, digital signals processing, excitation techniques and modal parameter estimation are addressed.
What You Will Learn:
- Basic fundamental background of experimental modal analysis
- Digital signal processing techniques necessary for performing a modal test
- How to successfully conduct an impact test for acquisition of frequency response functions
- How to specify shaker excitation techniques for modal testing
- Techniques for the reduction of measured data to form a modal model
- Approaches for validation of the derived model
- Techniques for the quality assessment of acquired data
From this course you will obtain the knowledge and ability to perform experimental modal tests and reduce data to develop a modal model of the system.
- Overview. Troubling shooting noise and vibration problems.
- Modal Testing Considerations. Overview of modal test setup and conduct of test. Practical considerations for the setup of a test.
- Experimental Modal Theory. Single degree of freedom equations. Time and Laplace domain formulations. Definition of poles and residues. Development of the system transfer function and the point to point frequency response function.
- Experimental Modal Theory. Multiple degree of freedom systems. Time and Laplace domain formulations. Modal Space. Modal vector orthogonality and vector independence. Superposition of sdof systems.
- Digital Signal Processing for experimental modal analysis.Identification of sampling and quantization problems. Discussion on aliasing, leakage and the need for windows. The use of rectangular, hanning, and flattop windows; measurement distortion due to the use of windows. Frequency response estimators. Description of auto power spectrum, cross power spectrum, frequency response function and coherence.
- Excitation Techniques – impact excitation. The selection of hammer tips. The need for pre-trigger delay. Double impact problems. The proper selection and use of force/exponential windows for impact testing. Examples of impact setup with proper and improper setups.
- Excitation Techniques – shaker excitation. The use of random and deterministic excitations for experimental modal testing. Identification of specialized excitation techniques such as pseudo-random, burst random, sine chirp and digital stepped sine for the efficient excitation of structures without the need for window functions.
- Transducers and calibration
- Modal Parameter Estimation. Concepts in parameter estimation. Single degree of freedom methods vs. multiple degree of freedom methods. The use of the time and the frequency domain representations of data. Identification of local, global and polyreference curvefitting methods. Commonly implemented commercial curvefitting techniques.
- Validation of extracted modal parameters.
- Practical discussion on real world testing – problems and pitfalls.
- Case Studies. Acquisition of data for a simple structure followed by the data reduction through the use of commercially available software.
Dr. Peter Avitabile is a Professor of Mechanical Engineering at the University of Massachusetts Lowell and Co-Director of the Structural Dynamics and Acoustic Systems Laboratory. Pete has 4 decades of experience in design and analysis using FEM and experimental techniques. His main area of research is structural dynamics specializing in the areas of modeling, testing and correlation of analytical and experimental models along with advanced applications for developing structural dynamic models. Pete has contributed over 200 technical papers in the area as well as his 17 year “Modal Space” article series in the Experimental Techniques magazine published by the Society for Experimental Mechanics.
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