With respect to control design I’m trying to determine the translational velocity of the Tower-top / yaw bearing in the inertia frame. The code is Hywind, so the foundation is floating.

I find it a bit difficult, but so fare I got:

h=90 meters

[m/s]=PtfmTVxi -PtfmTVxt +h*YawBrRVyp*2*pi/360

Is this correct?

BR

Søren Christiansen

PhD student

Aalborg University

Denmark

Dear Søren,

I’m not sure I understand your equation, but you can output the translational velocity of the tower-top / yaw bearing in the inertia frame from FAST as follows:

- In the primary FAST input file, set the nacelle inertia measurement unit (IMU) locations in the downwind, lateral, and vertical directions (NcIMUxn, NcIMUyn, and NcIMUzn, respectively) all to 0.0. This will locate the nacelle IMU at the center of the tower-top / yaw bearing.
- Include the nacelle IMU translational velocity outputs (NcIMUTVxs, NcIMUTVys, NcIMUTVzs) in the output list of the primary FAST input file.

The nacelle IMU translational velocity outputs are calculated relative to the inertia frame and output in a coordinate system that is aligned with the instantaneous shaft coordinate system.

I hope that helps.

Best regards,

Dear Jason,

Thank you very much. This is exacly what I was looking for.

Some how I missed this important signal.

Thank you for taking the time to answer my simple question.

Best regards

Søren

Dear Jason,

Could you please confirm if my the below understanding is correct. I have seen that answers are available at various places in various topics. Just asking for a favor here to validate my understanding.

Measure 1) TwrTpTDxi:

This is the motion of ‘Yaw bearing’(located on tower axis at TwrHt) observed by an observer

sitting at the origin of an ‘inertial frame’ and expressed in the same frame (XiYiZi).

Measure 2) YawBrTDxp:

This is the motion of ‘Yaw bearing’ (located on tower axis at TwrHt i.e origin of XpYpZp coordinate system) observed by an observer sitting at the origin of the ‘Tower base frame (XtYtZt)’ and expressed in “baseplate coordinate system(XpYpZp)”.

Measure 3) YawBrTDxt:

This is the motion of Yaw bearing (located on tower axis at TwrHt) observed by an observer

sitting at the origin of the ‘tower base frame ((XtYtZt))’ and expressed in “Tower base coordinate system(XtYtZt)”.

Measure(1) contains the rigid motion of support platform (in the case of movable support) and measure(2) and (3) are purely elasic deflections of tower expressed in different coordinate systems. Right?

Measure 4) YawBrRDxt YawBrRDyt YawBrRDzt

These are the instantaneous Euler angles between XpYpZp frame and XtYtZt frame. (In the Yaw-pitch-Roll) sequence.

Measure 5) TipDxb1

The displacement of the blade tip observed by an observer sitting at the origin of the “Cone Coordinate system of the respective blade” and expressed in “Cone coordinate system” itself.

Measure 6) TipDxc1

The displacement of the blade tip observed by an observer sitting at the origin of “blade Coordinate system of the respective blade” and expressed in “blade coordinate system” itself.

Measure 7) TipALxb1

The acceleration of the blade tip observed by an observer sitting at the origin of the “Inertial” Coordinate system and expressed in “inertial coordinate system” itself.

Thanks.

Regards,

Kumara

Dear @KumaraRaja.Eedara,

I agree with your description of measures (1) through (3).

Regarding measure (4), I agree with your statement except that the rotations do not follow a yaw-pitch-roll Euler sequence. Instead, small to moderate rotations are assumed in ElastoDyn, where the rotation sequence does not matter. See the Equations (1) and (2) in my 2009 Wind Energy Paper for more information: onlinelibrary.wiley.com/doi/abs/10.1002/we.347.

You’ve swapped the descriptions of measure (5) and (6). “b” refers to the blade coordinate system and “c” refers to the coned coordinate system.

Measure (7) is the absolute acceleration in the inertial frame, but it is expressed in the local blade coordinate system (Lb, oriented with the blade cross section as the blade deflects), not the inertial frame coordinate system.

Best regards,