SDOF models

[varistor]

Hi All please ignore my ignorance, but can anyone give me an example of a SDOF model? For example if a simple L Bracket was modelled and had a fixed restraint on the back face.

I am a little confused by the degrees of freedom statement that is displayed when cosmos analyses

Jo

 

[skin85]

Hi,

The number of DOFs a system has is defined as the minimum number of independent co-ordinates required to determine the motion of any part of the system at any instant of time.

The L bracket you described is an MDOF. The classic SDOF set-up is displayed at:

http://www.efunda.com/formulae/vibrations/sdof_intro.cfm

In practice most systems are MDOF, the SDOF business is used to explain the theory behind MDOF calculations, in modal analysis for example.

Regards

 

[varistor]

skin85

Thanks for the rapid reply. What I was condused about is that i have seen threads on this forum talking about simplifying a model in cosmos to a SDOF. I cant see how that can be done.

I have also seen references, that say that if the second mode Fn frequency is a lot higher than the first mode,then the structure can be 'assumed' to be SDOF

 

[skin85]

well each natural frequency has an associated mode shape, I guess if mode 1 occured at 200Hz say, and a second mode at 11000Hz then dependent on your parameters you could assume SDOF.

Im not sure about simplifying to SDOF in cosmos, maybe someone else has the answer. It maybe that other threads have allured to restraining their models to only 1DOF out of a possible 6?

http://en.wikipedia.org/wiki/Image:Degrees_of_freedom_(diatomic_molecule).png

This definition of DOF is associated with physics, as opposed to my initial reply which is concerned with engineering.