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AutoFEM Analysis Frequency Analysis Steps |  |
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AutoFEM Analysis Frequency Analysis Steps | |
Frequency analysis is performed in several stages. The sequence of the user's steps for putting together a study and running a structure's frequency calculation is in many parts similar to the algorithm described for the Static Analysis. Therefore, we will point out in this chapter only certain details specific to stability calculations:
1. Creating "Study". When creating a study, specify the study type - "Frequency analysis" in the command's properties window.
2. Applying boundary conditions. In a frequency analysis study, the boundary conditions are solely defined by restraints. Defining restraints is a necessary prerequisite for performing a correct frequency calculation. The combined restraints on a body's motion must satisfy the following condition:
To be subjected to frequency analysis, a model must be restrained so as to exclude its free motion in the space as a solid body. Failing to meet this condition will cause incorrect results of Finite Element modelling or abortion of computations. |
3. Solving. Before running calculations, the user should specify the number of natural frequencies and, if necessary, elaborate on the solution algorithm.
4. Analysis of frequency calculation results. The results of a frequency analysis are:
Natural vibration frequency (Hz) – corresponds to the expected resonant frequency of the structure. In theory, the number of natural frequencies is unlimited for any body. The results reflect only the frequencies for selected modes of natural vibration.
Natural vibration mode with respect to a given frequency. Let us illustrate the physical meaning of the "vibration mode" term. A vibration mode shows what will be the relative deformations (displacements) in a structure in the case of resonance at the respective natural frequency. Please take a special notice on that the vibration modes displayed in the Postprocessor window after completing calculations are relative amplitudes of vibration. By analysing those modes, one can make conclusions about the pattern of resonant displacements, but not about their factual amplitude. By knowing the expected vibration mode at a certain natural frequency, you can introduce an additional restraint or support at the part of the structure corresponding to the maximum vibration in this mode, which would effectively manage the part's natural properties.
By default, the vibration modes are displayed in the Postprocessor window without colour-coding; the latter can be enabled in the visualization properties.
Consider also the convenience of animation for analysing the pattern of the structure's motion at a certain frequency. Remember to enable the "Animation" option in the properties of the calculation results window (accessible by 
in the Postprocessor window) in order to have an animation, and specify the desired animation parameters.
See also: Frequency Analysis, Frequency Analysis Steps, Settings of Frequency Solver