Flexible and rigid response in modal transient analysis
Flexible and rigid response in modal transient analysis
(OP)
Hi members,
I have an issue in understating how modal transient analysis works free free structures. If I apply a time varying force with frequencies well above zero( say 40hz), and ask Nastran an FE solver to consider only flexible modes in analysis, the result is a mean zero response of accelerations and forces. Does this mean I am losing data from rigid rotations and translations caused by mean force (0hz) force component.
Also, rigid modes do not strain, but in reality any constantly accelerating body deforms means it strains. If I include rigid modes in my solution will I get the strains consequently internal reactions caused by these rigid motions, I find it difficult to comprehend why modes which do not strain will give any reaction force. Can sincerest shed light on this?
I have an issue in understating how modal transient analysis works free free structures. If I apply a time varying force with frequencies well above zero( say 40hz), and ask Nastran an FE solver to consider only flexible modes in analysis, the result is a mean zero response of accelerations and forces. Does this mean I am losing data from rigid rotations and translations caused by mean force (0hz) force component.
Also, rigid modes do not strain, but in reality any constantly accelerating body deforms means it strains. If I include rigid modes in my solution will I get the strains consequently internal reactions caused by these rigid motions, I find it difficult to comprehend why modes which do not strain will give any reaction force. Can sincerest shed light on this?





RE: Flexible and rigid response in modal transient analysis
Consider a structure in free fall. No strain. Uniform acceleration. Until you get this right the rest will be inexplicable.
Cheers
Greg Locock
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RE: Flexible and rigid response in modal transient analysis