Register to reply 
Natural frequency of large degree of freedom system 
Share this thread: 
#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: 1,969

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. 


Register to reply 
Related Discussions  
Modelling damped two degree of freedom vibration system  Differential Equations  0  
Degree of Freedom of system  Introductory Physics Homework  9  
Mechanical system with two degree of freedom  Introductory Physics Homework  0  
2 degree of freedom system  Mechanical Engineering  0  
Multi Degree of Freedom System  Advanced Physics Homework  0 