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Message 1 of 5

09-23-2015
05:15 AM

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Modal analysis of cantilever beam - by hand and by Robot

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Hello all,

It might be trivial, but I can't figure out the differences obtained when calculating the problem by hand and by Robot.

The problem is very simple. For the given cantivever beam with uniform loading, one should calculate the modal properties.

The results calculated by hand and by Robot are **equal** with respect to the **stiffness** and the **mass**, but the **period**, **frequency** and **pulsation** are **different**.

Please check the screen-shots.

09-23-2015
05:15 AM

Modal analysis of cantilever beam - by hand and by Robot

Hello all,

It might be trivial, but I can't figure out the differences obtained when calculating the problem by hand and by Robot.

The problem is very simple. For the given cantivever beam with uniform loading, one should calculate the modal properties.

The results calculated by hand and by Robot are **equal** with respect to the **stiffness** and the **mass**, but the **period**, **frequency** and **pulsation** are **different**.

Please check the screen-shots.

4 REPLIES 4

Message 2 of 5

09-25-2015
01:29 AM

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09-25-2015
01:29 AM

Message 3 of 5

09-25-2015
03:00 AM

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Thank you Rafal for going through my question.

It seems that acording to Roark the calculation is corect.

I will check one more time my calculation, but I am pretty sure that the hand calculation was Ok.

09-25-2015
03:00 AM

Thank you Rafal for going through my question.

It seems that acording to Roark the calculation is corect.

I will check one more time my calculation, but I am pretty sure that the hand calculation was Ok.

Message 4 of 5

09-30-2015
09:57 AM

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When you calculate k = 1/delta I think you missed to convert force to mass ... : F = k delta -> mg = k delta -> k = mg/delta and then the results follows no? (because if F=1 then m is not equal to 1) no?

09-30-2015
09:57 AM

Message 5 of 5

09-30-2015
03:53 PM

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Well I don't think so. The stiffness was obtained following the concept of deflections resulting from unit forces.

The force to mass conversion was done later when calculating the mass.

What I think causes the differences is that we can not use the concept of single degree of freedom system when dealing with systems with continuous mass distribution as in our case with the uniform load.

Any other comments would be helpful.

09-30-2015
03:53 PM

Well I don't think so. The stiffness was obtained following the concept of deflections resulting from unit forces.

The force to mass conversion was done later when calculating the mass.

What I think causes the differences is that we can not use the concept of single degree of freedom system when dealing with systems with continuous mass distribution as in our case with the uniform load.

Any other comments would be helpful.

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