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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