Hello!,
SOL103 is normal modes/eigenvalue calculation, please note determining the natural frequencies and mode shapes of the structure with damping neglected is the first step in performing an advanced dynamic analysis, but you do not get any dynamic response because with SOL103 not any excitation exist, OK?.

The natural frequencies of a structure are the frequencies at which the structure naturally tends to vibrate if it is subjected to a disturbance. For example, the strings of a piano are each tuned to vibrate at a specific frequency.

When you run a SOL103 analysis you need to set the number of frequencies you want to extract, but the most important is the first one, this is fundamental frequency, the one with maximum energy. You will get a value of the frequency in Hz and also a mode shape. This value is very important, it tells you if your structure is flexible(when below of 33 Hz) or rigid(when above of 33 Hz).

Also,it let you to assess the dynamic interaction between a component and its supporting structure. For example, if a rotating machine, such as an air conditioner fan, is to be installed on the roof of a building, it is necessary to determine if the operating frequency of the rotating fan is close to one of the natural frequencies of the building. If the natural frequencies of the structure are very close to the operating frequency of the fan (1 Hz is a 1 rev per second, then 10 Hz = 600 rpm), the operation of the fan may lead to structural damage or failure, OK?.

You see, not need to perform any dynamic frequency response (SOL111) or modal transient analysis (SOL112), running a simply SOL103 will tell you if your frequencies are well well above of the operational frequency, so risk of resonance is evaluated.

Best regards,
Blas.

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Blas Molero Hidalgo
Ingeniero Industrial
Director

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