How do you validate and update your modal parameters from experimental data?

1 Modal parameter estimation

The first step is to estimate the modal parameters from the experimental data, such as frequency response functions (FRFs) or time domain signals. Modal parameters include natural frequencies, damping ratios, and mode shapes of the structure. There are various techniques for modal parameter estimation, such as curve fitting, frequency domain decomposition, or subspace identification. The choice of technique depends on the type and quality of the data, the complexity of the structure, and the accuracy and robustness required.

2 Modal parameter validation

The second step is to validate the estimated modal parameters, by checking their consistency, reliability, and physical meaning. You can use different criteria and indicators for modal parameter validation, such as modal assurance criterion (MAC), modal complexity factor (MCF), or modal scaling factor (MSF). You can also compare the estimated parameters with the theoretical or analytical ones, or with the results from other experiments or techniques.

3 Modal parameter updating

The third step is to update the modal parameters, by adjusting the numerical model to match the experimental data. Modal parameter updating is a process of minimizing the discrepancy between the measured and predicted FRFs, by modifying the model parameters, such as stiffness, mass, or damping. You can use different methods for modal parameter updating, such as sensitivity-based methods, optimization methods, or Bayesian methods. The goal of modal parameter updating is to improve the accuracy and confidence of the numerical model, and to identify and correct any sources of error or uncertainty.

4 Modal analysis software

To perform the modal analysis and vibration testing, you will need a suitable software that can handle the data acquisition, processing, and visualization. There are many software options available for modal analysis, such as MATLAB, ME'scope, LMS Test.Lab, or Polytec. The software should have the features and functions that suit your needs and preferences, such as user interface, data format, analysis technique, output format, or integration with other tools.

5 Modal analysis best practices

To ensure the quality and validity of your modal analysis and vibration testing, it's important to plan and design the experiment carefully, considering the objectives, scope, and constraints of your project. You should also choose the appropriate excitation and measurement methods, equipment, and settings for the characteristics and behavior of your structure. Additionally, you should perform a proper data quality check, filtering, and calibration to eliminate any noise, distortion, or error in your data. Furthermore, you should select the optimal modal parameter estimation, validation, and updating techniques based on the data type, structure complexity, and accuracy requirements. Lastly, you should interpret and report your results clearly and comprehensively while highlighting the main findings, limitations, and implications of your analysis.