Every structure has the tendency to vibrate at a given set of natural frequencies.
Each natural frequency is associated with a shape, called a mode shape, that the model tends to assume when vibrating at that frequency.
The modal participation factor is a measure of how strongly a given mode contributes to the response of the structure when subjected to force/displacement excitation in a specific direction.
How it is done?
In dynamic analysis, two related topics, resonance and modal participation, need to be considered.
Resonance occurs when the input load excitation frequency matches one of the natural frequencies of the structure.
In this case, the load amplifies the mode and large displacements can result.
The participation factor indicates how strongly a given mode contributes to the response.
So, it is possible that the excitation could match a natural frequency (i.e. a resonance condition), but the participation factor of the mode is close to zero, and as such little energy will get into that mode and negligible dynamic response will occur.
The basis of the Modal Participation Factor (MPF) method is that each loading input can be split up into the contribution factors associated with each mode shape for the structure.
In NASTRAN both the modal stresses and modal participation factors can be extracted from a single sol 112 analysis.
The modal superposition is then calculated as follows:
Each natural frequency is associated with a shape, called a mode shape, that the model tends to assume when vibrating at that frequency.
The modal participation factor is a measure of how strongly a given mode contributes to the response of the structure when subjected to force/displacement excitation in a specific direction.
How it is done?
In dynamic analysis, two related topics, resonance and modal participation, need to be considered.
Resonance occurs when the input load excitation frequency matches one of the natural frequencies of the structure.
In this case, the load amplifies the mode and large displacements can result.
The participation factor indicates how strongly a given mode contributes to the response.
So, it is possible that the excitation could match a natural frequency (i.e. a resonance condition), but the participation factor of the mode is close to zero, and as such little energy will get into that mode and negligible dynamic response will occur.
The basis of the Modal Participation Factor (MPF) method is that each loading input can be split up into the contribution factors associated with each mode shape for the structure.
In NASTRAN both the modal stresses and modal participation factors can be extracted from a single sol 112 analysis.
The modal superposition is then calculated as follows:
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