What is Dynamic Analysis?

[manigreat]

Hello everyone,
1)Can any one tell me exactly the definition of Dynamic Anslysis?

2) I have modelled a bearing pedestal. I have choosed Shell63 as my element. I have applied a mass of 1000 kg on top of the pedestal. When i found the frequencies of the pedestal,the values are in decimal i.e., 1).35Hz 2) .55Hz etc. When ever i am doing a modal analysis i am getting frequencies in fraction( very low values) when i am choosing shell63 or solid 72. When the mass is low, the values are some what higher. Can any explain the reason for this?

 

[EdR]

Dynamic analysis is necessary when things move....more precisely when the behavior is described by the equation
m x''+c x' + k x = F

For question 2.....Think of a SDOF system where

omega = sqrt (K/M)....

As M gets smaller omega (and the frequency) get bigger...

Ed.R.

 

[corus]

Frequency depends on stiffness and inversely on mass. A low mass will give you a higher frequency. Make sure you check your units if you think the values of frequency you are getting are too small. Preferably use SI units of Kg, Newtons and metres to get the correct units of Hz.

 

[mecheng187]

Manigreat,

I am guessing that you might not have constrained the model. When performing a modal analysis you and you don't constrain the model, the first few (six, depending on the which constraints were omitted) modes calculated will have effectively zero values for frequency. Imagine the model moves off in one direction and never comes back, resulting in a zero frequency. You may need to constrain your model or tell the program to expect the unconstrained modes. The higher modes may show correct values depending on how many you asked for. See more theory and information regarding vibration analysis at

http://feaservices.com