## Natural frequencies - theoretical vs COSMOS results

Hi all,

I am new to the forum and am despreate for the solution for my current task. I am given a canteliver beam with the dimention:

L =1250mm
W= 75mm
D= 30mm
E=200 Gpa
density = 7800kg/m^3
poison ratio=0.3

and I optained the first five natural frequencies from COSMOSWorks 2007, which are 15.7483, 39.2254, 98.4208, 241.795 and 274.422Hz respectively. Looks logical isnt it? However, these values are different from the hand calculated values and I really need to find out why.

The formula I used for hand calculation:

W^2=(1.875^4)(EI/density*area*length^4)
where I = (1/12)(bt^3)

Help needed, urgent!! Many thanks in advance
 PhysOrg.com science news on PhysOrg.com >> Ants and carnivorous plants conspire for mutualistic feeding>> Forecast for Titan: Wild weather could be ahead>> Researchers stitch defects into the world's thinnest semiconductor
 Recognitions: Science Advisor What was different from your hand calcs? Could you possibly be off by a factor of $$2\pi$$?
 1st frequency for example, hand calculations give 5Hz while generated value shows 15Hz. This is a huge difference, and I need to know why if it is supposed to be different. 2 pie converts rad/s to Hz, not a crucial point in this case.

Recognitions: