Sahil Sura
Ansys Employee

Hi @aitor.amatriain,
Modal analysis is one of the fundamental analyses of linear dynamics. It determines the vibration characteristics of a component and thus no load/forces are involved in the analysis.  However, 'Pre-stressed Modal' analysis is a way to study the effects of the loading on the vibrational characteristics of the component. You can perform a pre-stressed modal by linking the results of structural analysis to the modal, ensuring the model's linearity. 
'Pre-stress environment' can be set to the previously linked analysis in the 'Modal' analysis ensuring the results are transferred to the same. (eg. Static structural analysis system is linked to Modal analysis system.)

This considers the supports, load, etc. added in structural analysis to be considered in the current modal analysis.
The main outcomes of Modal analysis are the modal frequencies and the participation factors. 
If you want to gain more insights into the Modal analysis, refer to the following course and references.
Pre-Stress (ansys.com)
Modal Analysis (ansys.com)
Modal Analysis in Ansys Mechanical | Ansys Courses 
If you want to study the vibrational characteristics of the deformed shape just by adding supports, you can export the deformed geometry as .stl file by right-clicking on the 'Total Deformation' and then performing the 'Modal' analysis of the same.
Hope this helps.

Thanks,
Sahil.
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