BeamDyn input file parameters are determined

[EVElove444]

How to obtain the matrix of mass and stiffness in the file 'NRELOffshrBsline5MW_BeamDyn_Blade', the layup design is re-done, and the mass and stiffness parameters need to be re-calculated.
best regards

[jjonkman]

Dear @EVElove444,

Well, that depends on what your data source is. If your deriving the 6x6 cross-sectional mass and stiffness matrices from the cross sectional geometry and composite material properties, you can use a sectional-analysis tools such as VABS, PreComp, NuMAD/BPE, BECAS, ANBA, and/or SONATA.

Best regards,

[EVElove444]

May I ask how to deduce the 6x6 cross-section mass and stiffness matrix after obtaining the section characteristics according to PreComp or BPE?
Best regards,

[EVElove444]

I am very sorry to bother you. I have obtained the flapping inertia, EdgIner, flapping stiffness and EdgStff by using the section analysis tool. How can I obtain the 6x6 matrix of the mass and stiffness of each section?
Best regards,

[jjonkman]

Dear @EVElove444,

PreComp and BPE directly calculate and output the cross-section mass and stiffness matrices. That said, while BPE can calculate the 6x6 matrices, PreComp is limited to calculating 4x4 matrices as PreComp does not consider the shear-related terms.

The form of the mass and stiffness matrices used by BeamDyn expressed in terms of simple beam properties (without sectional offsets and composite couplings) is documented here: https://openfast.readthedocs.io/en/main/source/user/beamdyn/input_files.html#distributed-properties.

Best regards,

[EVElove444]

Dear @jjonkman

I have used BPE to calculate the 6X6 mass and stiffness matrix of the blade, but there is no calculation of DAMPINGCOEFFICIENT. Do you have a tool that can calculate the damping coefficient and extract the 6x6 matrix from the BPE file?

[jjonkman]

Dear @EVElove444,

BPE does not calculate damping.

Damping in BeamDyn is specified via a stiffness-proportional constant (mu). Typically you would have a desired damping ratio of a given blade mode and you could derive mu from that.

Best regards,

[EVElove444]

Dear@jjonkman
Typically you would have a desired damping ratio of a given blade mode and you could derive mu from that.It is common to question what the predetermined damping coefficients should be. Is it correct to assign a value of 0.01 to all of them?
Best regards,

[jjonkman]

Dear @EVElove444,

I would use mu = zeta/(pi*n_f), where zeta is the damping ratio and n_f is the natural frequency of the blade mode in Hz (at least for flapwise and edgewise bending and torsion). In the absence of more information, I would use zeta in the range of 0.005 to 0.02, with the lower end being more conservative.

Best regards,

[EVElove444]

Hello, is it correct that Xcm and Ycm (are the local coordinates of the sectional center of mass,) are not 0 in the section features calculated by BPE? Is it different from the coordinate system in Openfast?
Best regards,

[jjonkman]

Dear @EVElove444,

The sectional center of mass offsets in BeamDyn should be the offsets relative to the BeamDyn reference axis. You should use the same reference axis in BPE when calculating the sectional 6x6 mass and stiffness matrices.

Best regards,

[EVElove444]

Dear @EVElove444,
Hello, how is the reference system of the stiffness and mass matrices defined in BeamDyn?
Best regards,

[jjonkman]

Dear @EVElove444,

The reference axis in BeamDyn follows the axis defined via the key points and their initial twist in the BeamDyn primary input file. See the online BeamDyn documentation on readthedocs for more information: https://openfast.readthedocs.io/en/main/source/user/beamdyn/input_files.html#geometry-parameter.

Best regards,