Using Aggregate Mass in ADAMS to Check NREL CS_Monopile.bmi

Wind & Water Structural Analysis
#1

Dear Jason,

I first used Aggregate Mass in ADAMS to calculate SNL 13.2MW mass moment of inertia and I used the outputs into .bmi file. The results of N.F are quite off from what I got from ADAMS (with only Twr DoFs on).

I then downloaded wind.nrel.gov/public/jjonkman/BModes/
and wind.nrel.gov/public/jjonkman/NR … Bsline5MW/
offshore part to run the Aggregate Mass in ADAMS.

I specified a rigid NRELOffshrBsline5MW_Monopile_RF with all DoFs turning off since I only want to see the mass moment of inertia.
I used FAST 2012Feb edition I believe and thus I delete the line added in the new FAST this year.
I generated ADAMS model and get the mass inertia properties as following:

The aggregate mass in the global reference frame is:
Mass : 3.500003109E+005 kg
Center of Mass :
Location : -0.4106407744, -2.3123880885E-009, 109.5667156223 (meter, meter, meter)
Orientation : 89.9989498566, 5.3861985327, 270.0010456486 (deg)
Mass Inertia Tensor :
IXX : 4.2454591844E+009 kg-meter2
IYY : 4.2253361673E+009 kg-meter2
IZZ : 2.5520945258E+007 kg-meter2
IXY : 0.2290994561 kg-meter2
IZX : -1.4007405804E+007 kg-meter2
IYZ : 2.8746322068 kg-meter2

which I updated your .bmi, the results are quite off again.

Please help me to check I am doing the right thing.

Thanks,

Regards.
Check NREL.zip (108 KB)
BModesJJ.zip (421 KB)

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#2

Dear Lingling,

Here are the data I get (calculated by ADAMS) regarding the mass & inertia of the rigid rotor-nacelle assembly (RNA) for the NREL 5-MW turbine:

Mass : 3.500003109E+005 kg
Center of Mass :
Location : -0.4137754432, -8.3126516178E-009, 1.9669893542 (meter, meter, meter)
Orientation : 359.9999911963, 90.0000955298, 354.6136364306 (deg)
Mass Inertia Tensor :
IXX : 4.5050443961E+007 kg-meter2
IYY : 2.4940615741E+007 kg-meter2
IZZ : 2.5477667652E+007 kg-meter2
IXY : 0.2010825213 kg-meter2
IZX : 1.4540376371E+006 kg-meter2
IYZ : 2.8803379356 kg-meter2

The center-of-mass (CM) location, orientation, and inertias above are all relative to FAST’s nacelle coordinate system, which originates at the yaw bearing (i.e., tower top) with “X” pointing downwind, “Y” pointing to the left when looking downwind, and “Z” pointing vertically upwards.

Some of the values you report are close to these; others (especially the Z-coordinate of the CM and the IXX and IYY inertias) are quite a bit different because you’ve output yours relative to the global reference frame.

However, what BModes needs as input is the inertias of the RNA specified relative ot the CM of the RNA. Here are the inertias I report above translated to the CM of the RNA:

Ixx = 4.370E7 kgm^2
Iyy = 2.353E7 kgm^2
Izz = 2.542E7 kgm^2
Izx = 1.169E6 kgm^2

See my Nov 23, 2009 post in the forum topic found here for more information: http://forums.nrel.gov/t/tower-fore-aft-modes-shapes/193/1.

I hope that helps!

Best regards,

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Structural loads at pitch and yaw actuator
#3

Dear Jason,

That is great!

Thanks,

Regards

#4

Dear Jason,

Did you use my uploaded .adm file in ADAMS to get these number? I tried it again and I had these number:

The aggregate mass relative to .NRELOffshrBsline5MW_Monopile_RF_ADAMS.Nacelle_P.NacelleCS_M is:
Mass : 3.500003109E+005 kg
Center of Mass :
Location : -0.4106407744, -2.3123880885E-009, 1.9667156223 (meter, meter, meter)
Orientation : 89.9989498566, 5.3861985327, 270.0010456486 (deg)
Mass Inertia Tensor :
IXX : 4.5106432675E+007 kg-meter2
IYY : 2.4983415493E+007 kg-meter2
IZZ : 2.5520945258E+007 kg-meter2
IXY : 0.2290994561 kg-meter2
IZX : 1.4573394965E+006 kg-meter2
IYZ : 2.9617168196 kg-meter2

And there is an error info showing that “ERROR: The inertia tensor is ill formed. Both the CM/IM orientation and IP will be incorrect.”

Does this mean I have some problem with my model or I did a wrong thing with ADAMS? How can we interpret the orientation of outputs?

Really appreciate,

Regards.

Tower Eigenfrequencies of NREL 5MW Turbine
#5

Dear Lingling,

No, I didn’t use your version of the *.adm file. I posted values from an analysis I had run a while ago. However, the results I posted in my Jun 07 post are nearly identical to your results from Jun 08; I suspect that there are only very small differences between our models.

I recall getting that same error about the inertia tensor being ill formed, but don’t remember what caused it. I suggest you ask MSC Technical Support if you are concerned. The results look reasonable to me.

The “Orientation” specifies the 3-1-3 rotational sequence needed to orient the principle axes relative to the inertia frame coordinate system.

I hope that helps.

Best regards,

#6

Dear Jason,

According to the BModes User Manual (authored by Gunjit S. Bir and dated Sept 2007), for example, ixx_tip is “the side-to-side moment of inertia of the tip mass about the tip section x_T reference axis” (Table 2, pp.12) . My interpretation therefore is that the RNA inertia parameters are specified relative to the tower top central point.

However, I came across your June 7th, 2013 post which contradicts the above:

Could you confirm that this is true, in particular for the BModes version which allows a hub_conn=2 boundary condition (downloadable from drive.google.com/drive/folders/ … zksGRnrqxJ)?

Thank you,
Jing

#7

Dear Jing.Li,

I confirm that ixx_tip is the side-to-side inertia about the x axis passing through the center of mass of the rotor-nacelle assembly.

Best regards,

#8

Hi Jason,

Thank you very much for your response!

Best regards,
Jing