
#1
Oct2111, 04:01 AM

P: 10

I have a springmass system with 200 masses and 199 springs. All masses are 100 tonnes and stiffness 20 MN. The boundary conditions are fixedfree.
I have constructed a lumped mass matrix and stiffness matrix and calculated the lowest natural frequency. Including the boundary conditions I calculated this to be 0.0124 Hz. However, when I calculate the wave speed, I can calculate the period of the wave starting at one end, reflecting at the free end and returning. This frequency (1/T) is more than double the natural frequency I calculated. The wave speed I calculated was 141.4 m/s assuming the distance between masses is 10 metres. Am I using the wrong approach here for calculating the natural frequency both ways? 



#2
Oct2111, 08:31 AM

P: 1,896

How did you calculate the speed of the wave in this system? And what kind of wave?




#3
Oct2111, 08:37 AM

P: 882

And how are they connected? In a simple chain massspringmassspingmass....massspringmass, or rather in some mesh? 



#4
Oct2111, 08:30 PM

P: 10

Natural frequency of large degree of freedom system
Yes I did mean 20 MN/m.
Solved. 


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