Dear Tohid,
From your description, it doesn’t sound like you have a right-handed coordinate system in VABS, or your rotor is spinning backwards from most. Do you mean that y points towards the leading edge and z points towards the suction side?
Best regards,
Dear Jason,
Thanks for your reply. you are right that the y points toward leading edg and Z points towards to suction side.
I would like to know if we want to swap data position from VABS coordinates to BeamDyn coordinates, what will be the sign of each terms in both Mass and Stiffness matrix? because of that I assumed the coordinate system in Beamdyn is : z points along the blade from root to tip, y point towards to trailing edg side and x points towards to suction side. we will have in VABS 1=EA,2=K_shredg,3=K_shrflap,4=GJ,5=EI_flap,6=EI_edg, then swapping position to BeamDyn coordinates system will be K_shrflap-3,K_shredg=-2,EA=1, EI_edg=6,EI_flap=-5, GJ=4. I then should change the Mass matrix according this way. please correct me if I am wrong.
Best Regards,
Tohid.
Dear Tohid,
Here is how I would solve your problem.
Write out the matrix that transforms the coordinate system in VABS to the coordinate system in BeamDyn i.e.:
T = [ [ 0 0 1 0 0 0 ];
[ 0 -1 0 0 0 0 ];
[ 1 0 0 0 0 0 ];
[ 0 0 0 0 0 1 ];
[ 0 0 0 0 -1 0 ];
[ 0 0 0 1 0 0 ] ]
Then, the mass and stiffness matrices necessary for BeamDyn can be derived from the mass and stiffness matrices from VABS as follows:
Mass_BeamDyn = TMass_VABST’
Stiff_BeamDyn = TStiff_VABST’
where T’ is the transpose (inverse) of T. This transformation will swap rows and columns and change signs of the off-diagonal terms as necessary.
Best regards,
Dear jason,
Thanks very much for your understanding. Now it’s work well.
Best Regards,
Tohid
Dear Dr. Jason,
fallowing my question related stiffness and mass matrices, I am using BECAS to compute blade distributed properties. what I understand from BECAS is that this calculate mass and stiffness matrix respect to reference point which is defined in geometry input (0,0) point in each section. I am going to calculate the structure properties respect to pitch axis coordinate. I would like to know how can I translate my computation from reference point to pitch axis?
Best Regards,
Tohid.
Dear Tohid,
Section 1.4.1 of the SectionBuilder documentation from Bauchau provides a good description for how to shift the reference axis for 6x6 stiffness and mass matrices that can be decomposed into uncoupled axial-bending and shear-torsion problems e.g. for isotropic materials: soliton.ae.gatech.edu/people/oba … Manual.pdf. I don’t think that there is a direct way for changing the reference axis for fully populated matrices – in this case you would have to change the reference axis and rerun your sectional analysis tool.
Best regards,