Hello,

In the elastoDyn_blade.dat, the flapwise and edgewise stiffness flexural stiffness properties are presented in units of [Nm^2]. If I wanted to compute the stiffness of both [N/m]. Would it be correct to use cantilever beam theory. For example, the deflection of a beam is (L=1):

y(x) = (P(x) / EI) * (-x^3 + 3x - 2)

where x is the distance along the cantilever from the tip of the blade.

The stiffness k(x) is:

k(x)_flapwise = P(x) / y(x) = 6EI_flapwise / (-x^3 + 3x - 2)

k(x)_edgewise = P(x) / y(x) = 6EI_edgewise / (-x^3 + 3x - 2)

Thank you.

Dear @Oisin.Conway,

I’m not sure I understand what you are seeking in terms of a stiffness in N/m, which is useful for a discrete spring, but not for a distributed load of a cantilevered beam. Also, the deflection of a cantilevered beam will depend on the applied load.

Best regards,

Hello @Jason.Jonkman , thank you for the response. The finite element software I am using takes the input of flapwise and edgewise stiffness in N/m rather than flexural stiffness [Nm^2].

May I ask, what approach you would take in order to find the stiffness in N/m?

Dear @Oisin.Conway,

Can you clarify what beam formulation your FE software is using? I can see the axial and shear stiffness in a Timoshenko beam formulation would be expressed in N/m, but the bending stiffness in such a formulation would then be expressed in N*m. See, e.g., the documentation of the Timoshenko beam formulation used by the SubDyn module of OpenFAST for more information: 4.2.5.6. SubDyn Theory — OpenFAST v3.5.3 documentation.

Best regards,

Hello @Jason.Jonkman ,

It actually appears to be a labelling error which mislead me.

Thank you again for your assistance.