Dear Yinping Yang,
The equations you stated for cm_loc and cm_axial are correct. As I said in my prior post, I do not believe that the tower-top mass input data are specified correctly for the WindPACT 1.5-MW turbine in Test03_tower.bmi of the BModes CertTest. I need to ask Gunjit Bir about this.
You are correct that setting ADAMSPrep equal to 2 or 3 will cause FAST to generate the ADAMS dataset. In order to find the cm_loc and cm_axial, you should select all of the tower-top PARTs and choose NacelleCS_M as the reference marker. Since there is no marker at the tower-top CM, you will have to use the Parrallel Axis Theorem to shift the inertias found about the NacelleCS_M marker to the inertias found about the tower-top CM. I calculate:
------------- ADAMS Output -------------------
Aggregate mass for objects:
.Test13_ADAMS.Nacalle_P
.Test13_ADAMS.TailBoom_P
[lines removed]
.Test13_ADAMS.TipBrake3_P
The aggregate mass relative to .Test13_ADAMS.Nacalle_P.NacelleCS_M is:
Mass : 7.8055827759E+004 kg
Center of Mass :
Location : -1.2221466805, 5.0666880962E-008, 1.5637349496 (meter, meter, meter)
Orientation : 359.9999724196, 90.000347689, 355.2981476095 (deg)
Mass Inertia Tensor :
IXX : 3.5622774377E+006 kg-meter2
IYY : 1.9539222007E+006 kg-meter2
IZZ : 1.821096074E+006 kg-meter2
IXY : -1.212354417E-002 kg-meter2
IZX : -1.1141296293E+004 kg-meter2
IYZ : 0.2919524772 kg-meter2
So, cm_loc = -1.222 meter, cm_axial = 1.564 meter, and tip_mass = 7.806E4 kg. Here are the inertias translated to the tower-top CM:
ixx_tip = ( 3.5622774377E+006 kg-meter2 ) - ( 7.8055827759E+004 kg )*( 1.5637349496 meter )2 = 3.371E6 kg-meter2
iyy_tip = ( 1.9539222007E+006 kg-meter2 ) - ( 7.8055827759E+004 kg )( ( -1.2221466805 meter )2 + ( 1.5637349496 meter )2 ) =1.646E6 kg-meter2
izz_tip = ( 1.821096074E+006 kg-meter2 ) - ( 7.8055827759E+004 kg )( -1.2221466805 meter )2 = 1.705E6 kg-meter2
ixy_tip = 0
izx_tip = ( -1.1141296293E+004 kg-meter2 ) + ( 7.8055827759E+004 kg )( -1.2221466805 meter )( 1.5637349496 meter ) = -1.603E5 kg-meter2
iyx_tip = 0
Best regards,