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Beam Equation

Amir Naeiji's picture

How can we derive dynamic beam equation from navier equation in elastodynamic? I tried with the displacement vector field:

u=-z*w(x,t)

v=0

w=w(x.t)

and put it in navier equation, but it does not work.

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Min Yi's picture

As for the formulations you have listed, I know you intend to use Euler beam theory. Though I don't derive the dynamic equation, I want to point out that the formulation 'u=-z*w(x,t) ' should be 'u=-z* dw(x,t)/dx '.

Yours Sincerely Min Yi

Wenbin Yu's picture

It is better to use a variational statement equivalent to the Navier equation. Then you can directly substitute your assumptions of the displacement field into the variational statement. however, you do have to note that to derive beam theories this way, one also need to invoke plane stress assumption. A better way to derive beam equations from 3D elasticity theory is using the variational asymptotic method, which is numerically implemented in a general-purpose beam modeling tool,VABS.

Amir Naeiji's picture

amirnaeiji@yahoo.comyahoomessenger ID: amirnaeiji

But I want to derive Timoshenko beam equation directly from Navier equation and it was not working untill now. I want to know what assumption in addition to displacement field, must be applied?

I had found variational approach, but I am searching for Navier approch.

Thank you all.

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