Basics of Eigenfrequency Analysis in Structural Mechanics
In Part 4 of this course on structural mechanics modeling using COMSOL Multiphysics®, we focus on how to perform an eigenfrequency analysis. We begin with an introduction to this type of analysis in general and the different preset study types available in the software for performing it. Thereafter, we complete a step-by-step model build of this type of application.
Discussion & Demo: Eigenfrequency Analysis
The eigenfrequencies, or natural frequencies, of a system are the discrete frequencies at which a structure is prone to vibrate without an external load. Here, we begin with discussing the concept and physical meaning of eigenfrequencies and eigenmodes. We also discuss damping effects in a model and how eigenfrequency problems can be solved with or without damping. Lastly we outline the multiple study types available for prestressed analysis and the steps each preset study consists of.
Follow along in the software by opening the basic bracket model in the Application Libraries (found under Structural Mechanics Module > Tutorials) as we explore how a preload affects the natural frequency and mode shape of a structure. This is accomplished through first performing an eigenfrequency analysis and then using the results to refine the study setting when performing the prestressed, eigenfrequency analysis. During the demonstration, we add a boundary load to the model and discuss the options for the coordinate system selection setting (also covered in the Part 1 demonstration). We explain the logic behind updating the setting to Boundary System and then making further changes in the Boundary System node settings under the Definitions node, namely changing the Frame setting to Reference configuration.
Further Learning
For more information on eigenfrequency analysis and further practice with conducting this type of study as well as useful features for it, please see the following resources:
- Blog – "Tracking Eigenmodes over Parametric Sweeps" (keep track of and categorize modes in eigenfrequency studies)
- Learning Center – Tracking Eigenmodes In Parameter Sweeps (categorize eigenmodes using the mode overlap integral)
- Tutorial Model – Eigenfrequency Analysis of a Free Cylinder (calculate eigenfrequencies and mode shapes)
- Cyclopedia – Eigenfrequency Analysis (a comprehensive, in-depth introduction to this study type)
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