Tower Eigenfrequencies of NREL 5MW Turbine
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Re: Tower Eigenfrequencies of NREL 5MW Turbine
Dear Hamid,
BModes can be used to derive mode shapes and frequencies of blades or towers. When used together with FAST, it is only the blade and tower mode shapes that are needed. For the NREL 5MW turbine atop the MIT/NREL TLP, we've already created mode shapes for FAST using ADAMS in place of BModes. So, we don't have the BModes input files for this system. You should be able to make them yourself, but there really is no need to. If all your interest is in obtaining the natural frequenices of the TLP, you can use the linearization feature of FAST to derive them. Otherwise, these frequencies are published in Table 6 of the following report: viewtopic.php?f=4&t=921.
Best regards,
BModes can be used to derive mode shapes and frequencies of blades or towers. When used together with FAST, it is only the blade and tower mode shapes that are needed. For the NREL 5MW turbine atop the MIT/NREL TLP, we've already created mode shapes for FAST using ADAMS in place of BModes. So, we don't have the BModes input files for this system. You should be able to make them yourself, but there really is no need to. If all your interest is in obtaining the natural frequenices of the TLP, you can use the linearization feature of FAST to derive them. Otherwise, these frequencies are published in Table 6 of the following report: viewtopic.php?f=4&t=921.
Best regards,
Jason Jonkman, Ph.D.
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

 Posts: 17
 Joined: Wed Apr 17, 2013 2:10 am
 Organization: University
 Location: Iran
Re: Tower Eigenfrequencies of NREL 5MW Turbine
Dear Jason
Thanks for your great answers and solutions!
I ran the linearization of FAST for the frequency;
I got the result; thanks for that; but now I need Eigenanalysis.m for MATLAB but there isn't any file like that in CertTest folder! how can I get to that! is the file in somewhere else that I have to download it?
Regards
Hamid
Thanks for your great answers and solutions!
I ran the linearization of FAST for the frequency;
I got the result; thanks for that; but now I need Eigenanalysis.m for MATLAB but there isn't any file like that in CertTest folder! how can I get to that! is the file in somewhere else that I have to download it?
Regards
Hamid

Hamid Hokmabady
M.Sc Student of Civil Engineering
Tabriz University
Tabriz
Iran
Hamid Hokmabady
M.Sc Student of Civil Engineering
Tabriz University
Tabriz
Iran

 Posts: 12
 Joined: Wed Mar 13, 2013 9:34 pm
 Organization: University of Queensland
 Location: Australia
Re: Tower Eigenfrequencies of NREL 5MW Turbine
Dear Hamid,
I'm fairly sure the Eignanalysis.m file you are looking for has been superceded by the mbc3 package, where I think cce.m gives the information you're looking for. Take a look at this post to see if it helps you viewtopic.php?f=4&t=475.
Regards,
Monika
I'm fairly sure the Eignanalysis.m file you are looking for has been superceded by the mbc3 package, where I think cce.m gives the information you're looking for. Take a look at this post to see if it helps you viewtopic.php?f=4&t=475.
Regards,
Monika

 Posts: 17
 Joined: Wed Apr 17, 2013 2:10 am
 Organization: University
 Location: Iran
Re: Tower Eigenfrequencies of NREL 5MW Turbine
Dear Monika;
Thanks for your post
Yeah, your right; I've read that post but I forgot that, thanks for reminding.
Regards
Hamid
Thanks for your post
Yeah, your right; I've read that post but I forgot that, thanks for reminding.
Regards
Hamid

Hamid Hokmabady
M.Sc Student of Civil Engineering
Tabriz University
Tabriz
Iran
Hamid Hokmabady
M.Sc Student of Civil Engineering
Tabriz University
Tabriz
Iran

 Posts: 17
 Joined: Wed Apr 17, 2013 2:10 am
 Organization: University
 Location: Iran
Re: Tower Eigenfrequencies of NREL 5MW Turbine
Hello everyone;
I got the Natural Frequency (Rad/S and Hz) for 5MW TLP as following, USING CCE function in MATLAB:
AvgNaturalFrequency
1: 4.255
2: 4.513
3: 2.749
4: 1.300
5: 1.354
6: 0.617
7: 0.104
8: 0.104
and by Hz:
AvgNaturalFrequencyHz
1: 0.677
2: 0.718
3: 0.437
4: 0.206
5: 0.215
6: 0.098
7: 0.016
8: 0.016
Using CambellDiagram that Jason had been sent for the first mode I mean Surge it is 0.104 rad/s and 0.016Hz but I thinks it is not right!
what is the form of these outputs? is (number 1:) natural frequency of the first DOF (SURGE) or numbers are upside down I mean number 8 is for the first DOF (SURGE)? I have 8 DOF: 6 for structure and 2 first bending modes!
I need structures natural frequency in each DOFs mostly in Surge and Pitch.
I really confused!
Any suggestions would be so great!
I got the Natural Frequency (Rad/S and Hz) for 5MW TLP as following, USING CCE function in MATLAB:
AvgNaturalFrequency
1: 4.255
2: 4.513
3: 2.749
4: 1.300
5: 1.354
6: 0.617
7: 0.104
8: 0.104
and by Hz:
AvgNaturalFrequencyHz
1: 0.677
2: 0.718
3: 0.437
4: 0.206
5: 0.215
6: 0.098
7: 0.016
8: 0.016
Using CambellDiagram that Jason had been sent for the first mode I mean Surge it is 0.104 rad/s and 0.016Hz but I thinks it is not right!
what is the form of these outputs? is (number 1:) natural frequency of the first DOF (SURGE) or numbers are upside down I mean number 8 is for the first DOF (SURGE)? I have 8 DOF: 6 for structure and 2 first bending modes!
I need structures natural frequency in each DOFs mostly in Surge and Pitch.
I really confused!
Any suggestions would be so great!

Hamid Hokmabady
M.Sc Student of Civil Engineering
Tabriz University
Tabriz
Iran
Hamid Hokmabady
M.Sc Student of Civil Engineering
Tabriz University
Tabriz
Iran

 Posts: 5428
 Joined: Thu Nov 03, 2005 4:38 pm
 Location: Boulder, CO
 Contact:
Re: Tower Eigenfrequencies of NREL 5MW Turbine
Dear Hamid,
I'm not really sure I understand your question, but MATLAB's eigensolver (used within CCE) does not sort the eigensolution in the order of increasing frequency. However, the CampbellDiagram.xls workbook, for aid in interpretation, sorts the eigenvalues and eigenvectors by frequency and highlights the dominant components of each mode.
If you are referring to the NREL 5MW turbine atop the MIT/NREL TLP, the first surge natural frequency is 0.0165 Hz. You can find other natural frequencies for this system documented in Table 6 of Denis Matha's MS thesisturned NREL report: http://www.nrel.gov/docs/fy10osti/45891.pdf.
Best regards,
I'm not really sure I understand your question, but MATLAB's eigensolver (used within CCE) does not sort the eigensolution in the order of increasing frequency. However, the CampbellDiagram.xls workbook, for aid in interpretation, sorts the eigenvalues and eigenvectors by frequency and highlights the dominant components of each mode.
If you are referring to the NREL 5MW turbine atop the MIT/NREL TLP, the first surge natural frequency is 0.0165 Hz. You can find other natural frequencies for this system documented in Table 6 of Denis Matha's MS thesisturned NREL report: http://www.nrel.gov/docs/fy10osti/45891.pdf.
Best regards,
Jason Jonkman, Ph.D.
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

 Posts: 15
 Joined: Mon Apr 02, 2012 4:08 am
 Organization: RWTH Aachen University
 Location: Germany
Re: Tower Eigenfrequencies of NREL 5MW Turbine
Dear all,
I am working with BMODES and I have a question about the input for the 5MW Turbine:
Hier
http://wind.nrel.gov/public/jjonkman/BM ... nopile.bmi
in the towertop mass properties I reda the following:
3.500003109E+005 tip_mass bladetip or towertop mass (kg)
0.4137754432 cm_loc tipmass c.m. offset from the tower axis measured along xtower axis (m)
1.9669893542 cm_axial tipmass c.m. offset tower tip measures axially along the z axis (m)
4.370E7 ixx_tip blade lag mass moment of inertia about the tipsection x reference axis (kgm^2)
2.353E7 iyy_tip blade flap mass moment of inertia about the tipsection y reference axis (kgm^2)
2.542E7 izz_tip torsion mass moment of inertia about the tipsection z reference axis (kgm^2)
0. ixy_tip cross product of inertia about x and y reference axes(kgm^2)
1.169E6 izx_tip cross product of inertia about z and x reference axes(kgm^2)
0. iyz_tip cross product of inertia about y and z reference axes(kgm^2)
But then in the article:
"Modal Dynamics of Large Wind Turbines with Different Support Structures" from G. Bir and J. Jonkman I read the following values
which referring to the BMODES tower axes systems must be transformed from the the cm coordinate system to the tipsection reference axis . Is that right?
In this case, the input data of the CS_Monopile.bmi are not correct, I guess.
Any idea?
Thanks
I am working with BMODES and I have a question about the input for the 5MW Turbine:
Hier
http://wind.nrel.gov/public/jjonkman/BM ... nopile.bmi
in the towertop mass properties I reda the following:
3.500003109E+005 tip_mass bladetip or towertop mass (kg)
0.4137754432 cm_loc tipmass c.m. offset from the tower axis measured along xtower axis (m)
1.9669893542 cm_axial tipmass c.m. offset tower tip measures axially along the z axis (m)
4.370E7 ixx_tip blade lag mass moment of inertia about the tipsection x reference axis (kgm^2)
2.353E7 iyy_tip blade flap mass moment of inertia about the tipsection y reference axis (kgm^2)
2.542E7 izz_tip torsion mass moment of inertia about the tipsection z reference axis (kgm^2)
0. ixy_tip cross product of inertia about x and y reference axes(kgm^2)
1.169E6 izx_tip cross product of inertia about z and x reference axes(kgm^2)
0. iyz_tip cross product of inertia about y and z reference axes(kgm^2)
But then in the article:
"Modal Dynamics of Large Wind Turbines with Different Support Structures" from G. Bir and J. Jonkman I read the following values
which referring to the BMODES tower axes systems must be transformed from the the cm coordinate system to the tipsection reference axis . Is that right?
In this case, the input data of the CS_Monopile.bmi are not correct, I guess.
Any idea?
Thanks
Francesca Taddei, PhD
Technische Universität München  Faculty of Civil, Geo and Environmental Engineering
Chair of Structural Mechanics
Arcisstr. 21 · 80333 München
Tel: +49.89.289.28326
Fax: +49.89.289.28665
www.bm.bgu.tum.de
Technische Universität München  Faculty of Civil, Geo and Environmental Engineering
Chair of Structural Mechanics
Arcisstr. 21 · 80333 München
Tel: +49.89.289.28326
Fax: +49.89.289.28665
www.bm.bgu.tum.de

 Posts: 5428
 Joined: Thu Nov 03, 2005 4:38 pm
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Re: Tower Eigenfrequencies of NREL 5MW Turbine
Dear Francesca,
The BModes inputs for towertop inertia (ixx_tip, etc.) are specified about the center of mass (CM) of the tower top. The BModes input file you linked to and Table 1 from the paper you referenced are consistent.
Best regards,
The BModes inputs for towertop inertia (ixx_tip, etc.) are specified about the center of mass (CM) of the tower top. The BModes input file you linked to and Table 1 from the paper you referenced are consistent.
Best regards,
Jason Jonkman, Ph.D.
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

 Posts: 28
 Joined: Thu Apr 02, 2015 11:09 am
 Organization: Texas A&M University
 Location: United States
Re: Tower Eigenfrequencies of NREL 5MW Turbine
Dear Dr. Jason.
Could you let me know how you obtained those towerhead mass moment of inertia in above table 1? I thought that those was calculated by using FAST linearization, but I could not make the same moment of inertia Ixx as values in above table 1 when I used linearization.
Sincerely,
Daniel Kim.
Could you let me know how you obtained those towerhead mass moment of inertia in above table 1? I thought that those was calculated by using FAST linearization, but I could not make the same moment of inertia Ixx as values in above table 1 when I used linearization.
Sincerely,
Daniel Kim.

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Re: Tower Eigenfrequencies of NREL 5MW Turbine
Dear Daniel,
We obtained the data presented in Table 1 using the aggregate mass tool of MSC.ADAMS  see my post dated Jun 07, 2013 in the following forum topic for more information: viewtopic.php?f=3&t=842&p=3426.
You could also obtain these properties using the FAST v7 linearization if you set up your model to eliminate the platform and tower and locate the platform reference point at the yaw bearing.
Best regards,
We obtained the data presented in Table 1 using the aggregate mass tool of MSC.ADAMS  see my post dated Jun 07, 2013 in the following forum topic for more information: viewtopic.php?f=3&t=842&p=3426.
You could also obtain these properties using the FAST v7 linearization if you set up your model to eliminate the platform and tower and locate the platform reference point at the yaw bearing.
Best regards,
Jason Jonkman, Ph.D.
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

 Posts: 28
 Joined: Thu Apr 02, 2015 11:09 am
 Organization: Texas A&M University
 Location: United States
Re: Tower Eigenfrequencies of NREL 5MW Turbine
Dear Dr. Jason.
When I used the FAST linearization, I obtained following results regarding tower top mass properties. The first column is given in NREL, and the second column is values calculated by me using FAST linearization (v7.00)
Title 1st column 2nd column
Topmass 3.50000E+05 3.50000E+05
cm_loc 4.13775E01 4.13774E01 (From Tower center line)
cm_axi 1.96699E+00 1.96699E+00 (From Tower Top)
ixx_tip 4.37000E+07 3.86484E+07 (w.r.t. CM of RNA)
iyy_tip 2.35300E+07 2.35557E+07
izz_tip 2.54200E+07 2.54085E+07
In order to calculate this, I used very small tower and platform mass and located platform reference point* at 89.56699 from MWL (z coordinate CM of RNA). Also, I used default angle of azimuth value and initial azimuth. (0.0 AzimB1Up & 0.0 Azimuth ) . When FAST linearization is used, smaller Ixx_tip is obtained than when Adams is used. I don't know why this difference is generated. I am not sure whether Ixx = 3.86484 is correct or I make some mistakes in linearization input files. Could you check this? I used NRELOffshrBsline5MW_OC3Hywind.zip in http://wind.nrel.gov/public/jjonkman/NR ... Bsline5MW/ I changed some values like followings for linearization.
In NRELOffshrBsline5MW_Floating_OC3Hywind.fst
2 AnalMode
0 PCMode
0.0 RotSpeed
In NRELOffshrBsline5MW_Linear.dat
False CalcStdy
2 MdlOrder
In NRELOffshrBsline5MW_Platform_OC3Hywind.dat
0.0 TwrDraft
0.0 PtfmCM
8.9566990E+01 PtfmRef
0.0 PtfmMass
0.0 PtfmRIner
0.0 PtfmPIner
0.0 PtfmYIner
0 PtfmLdMod
In NRELOffshrBsline5MW_Tower_OC3Hywind.dat
Very small mass density 0.0000001kg/m
* If PtfmRef is less than TwrDraft, an error is occured, but I modified the source code so that the error is ignored.
Sincerely,
Daniel Kim.
When I used the FAST linearization, I obtained following results regarding tower top mass properties. The first column is given in NREL, and the second column is values calculated by me using FAST linearization (v7.00)
Title 1st column 2nd column
Topmass 3.50000E+05 3.50000E+05
cm_loc 4.13775E01 4.13774E01 (From Tower center line)
cm_axi 1.96699E+00 1.96699E+00 (From Tower Top)
ixx_tip 4.37000E+07 3.86484E+07 (w.r.t. CM of RNA)
iyy_tip 2.35300E+07 2.35557E+07
izz_tip 2.54200E+07 2.54085E+07
In order to calculate this, I used very small tower and platform mass and located platform reference point* at 89.56699 from MWL (z coordinate CM of RNA). Also, I used default angle of azimuth value and initial azimuth. (0.0 AzimB1Up & 0.0 Azimuth ) . When FAST linearization is used, smaller Ixx_tip is obtained than when Adams is used. I don't know why this difference is generated. I am not sure whether Ixx = 3.86484 is correct or I make some mistakes in linearization input files. Could you check this? I used NRELOffshrBsline5MW_OC3Hywind.zip in http://wind.nrel.gov/public/jjonkman/NR ... Bsline5MW/ I changed some values like followings for linearization.
In NRELOffshrBsline5MW_Floating_OC3Hywind.fst
2 AnalMode
0 PCMode
0.0 RotSpeed
In NRELOffshrBsline5MW_Linear.dat
False CalcStdy
2 MdlOrder
In NRELOffshrBsline5MW_Platform_OC3Hywind.dat
0.0 TwrDraft
0.0 PtfmCM
8.9566990E+01 PtfmRef
0.0 PtfmMass
0.0 PtfmRIner
0.0 PtfmPIner
0.0 PtfmYIner
0 PtfmLdMod
In NRELOffshrBsline5MW_Tower_OC3Hywind.dat
Very small mass density 0.0000001kg/m
* If PtfmRef is less than TwrDraft, an error is occured, but I modified the source code so that the error is ignored.
Sincerely,
Daniel Kim.
Last edited by Daniel.Kim on Wed Mar 15, 2017 9:08 pm, edited 2 times in total.

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Re: Tower Eigenfrequencies of NREL 5MW Turbine
Dear Daniel,
I'm not sure. I'm quite confident that ixx_tip = 4.370E7 kg*m^2 is correct for the NREL 5MW turbine.
Perhaps there is a problem because you overwrote the error that PfmRef < TwrDraft? Do you get the correct result if you set PtfmRef = 0.0, linearize to obtain the mass matrix, then transform the inertias from the tower base to the rotor CM?
Best regards,
I'm not sure. I'm quite confident that ixx_tip = 4.370E7 kg*m^2 is correct for the NREL 5MW turbine.
Perhaps there is a problem because you overwrote the error that PfmRef < TwrDraft? Do you get the correct result if you set PtfmRef = 0.0, linearize to obtain the mass matrix, then transform the inertias from the tower base to the rotor CM?
Best regards,
Jason Jonkman, Ph.D.
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

 Posts: 28
 Joined: Thu Apr 02, 2015 11:09 am
 Organization: Texas A&M University
 Location: United States
Re: Tower Eigenfrequencies of NREL 5MW Turbine
Dear Dr. Jason.
Even though I calculated Ixx w.r.t the tower base (0.0 TwrDraft, 0.0 PtfmCM , 0.0 PtfmRef) without modifying source code and transformed Ixx w.r.t CM of RNA, the result was the same as 3.8648381E+07.
Ixx w.r.t. tower base: 2.8464364E+09
Ixx w.r.t CM of RNA: 2.8464364E+09  35,000*89.566990^2 = 3.8648381E+07
I used the NRELOffshrBsline5MW_OC3Hywind.zip in http://wind.nrel.gov/public/jjonkman/NR ... Bsline5MW/ , and I didn't change other variances except for values that I listed above. I have to make the consistent input files regarding towertop between BModes and FAST in other case, so I am first checking the existing NREL 5MW wind turbine, but the results are not matched to the given values, which is calculated by ADAMS. How can I confirm it? Have you obtained inertia results of NREL 5MW towertop by using FAST linearization and compared them to the results obtained from ADAMS?
Sincerely,
HyoungChul Kim.
Even though I calculated Ixx w.r.t the tower base (0.0 TwrDraft, 0.0 PtfmCM , 0.0 PtfmRef) without modifying source code and transformed Ixx w.r.t CM of RNA, the result was the same as 3.8648381E+07.
Ixx w.r.t. tower base: 2.8464364E+09
Ixx w.r.t CM of RNA: 2.8464364E+09  35,000*89.566990^2 = 3.8648381E+07
I used the NRELOffshrBsline5MW_OC3Hywind.zip in http://wind.nrel.gov/public/jjonkman/NR ... Bsline5MW/ , and I didn't change other variances except for values that I listed above. I have to make the consistent input files regarding towertop between BModes and FAST in other case, so I am first checking the existing NREL 5MW wind turbine, but the results are not matched to the given values, which is calculated by ADAMS. How can I confirm it? Have you obtained inertia results of NREL 5MW towertop by using FAST linearization and compared them to the results obtained from ADAMS?
Sincerely,
HyoungChul Kim.

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 Location: Boulder, CO
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Re: Tower Eigenfrequencies of NREL 5MW Turbine
Dear HyoungChul,
Good question. I was able to reproduce your results using a linearization analysis with FAST v7. While I have the old ADAMS models, unfortunately, I no longer have a working MSC.ADAMS license to check the aggregate mass results we've used in the past. There must be something set differently between these models, but I don't recall seeing these differences before. I'm now just as confused as you.
Best regards,
Good question. I was able to reproduce your results using a linearization analysis with FAST v7. While I have the old ADAMS models, unfortunately, I no longer have a working MSC.ADAMS license to check the aggregate mass results we've used in the past. There must be something set differently between these models, but I don't recall seeing these differences before. I'm now just as confused as you.
Best regards,
Jason Jonkman, Ph.D.
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

 Posts: 35
 Joined: Tue Jan 10, 2017 5:37 am
 Organization: Hochschule Aalen
 Location: Germany  Baden Wuerttemberg
Re: Tower Eigenfrequencies of NREL 5MW Turbine
Dear Jason,
I have a question about the izx_tip (cross product of inertia about z and x reference axes) value of the BModes v1.03.01 Input File.
When I calculate the first 10 modes of the NREL 5MW Tower, there is no influence of the value on the BModes results. The modes and the frequencies are exactly the same. I tested ixz_tip with a value of 0, 1.169E6 and 1.169E7.
So, when is it necessary to enter the izx_tip value?
Attached the results of BModes in the command window.
Thank you for your answer.
Best regards,
René
I have a question about the izx_tip (cross product of inertia about z and x reference axes) value of the BModes v1.03.01 Input File.
When I calculate the first 10 modes of the NREL 5MW Tower, there is no influence of the value on the BModes results. The modes and the frequencies are exactly the same. I tested ixz_tip with a value of 0, 1.169E6 and 1.169E7.
So, when is it necessary to enter the izx_tip value?
Attached the results of BModes in the command window.
Code: Select all
with ixz_tip = 0:
eigenvalue(450) = 0.390794D+11 mode 1 frequency = 0.329475
eigenvalue(449) = 0.398465D+11 mode 2 frequency = 0.332693
eigenvalue(448) = 0.126954D+13 mode 3 frequency = 1.877897
eigenvalue(447) = 0.187182D+13 mode 4 frequency = 2.280244
eigenvalue(446) = 0.774666D+13 mode 5 frequency = 4.638803
eigenvalue(445) = 0.921857D+13 mode 6 frequency = 5.060349
eigenvalue(444) = 0.459755D+14 mode 7 frequency = 11.300868
eigenvalue(443) = 0.471883D+14 mode 8 frequency = 11.448961
eigenvalue(442) = 0.169404D+15 mode 9 frequency = 21.692580
eigenvalue(441) = 0.170534D+15 mode 10 frequency = 21.764779
with ixz_tip = 1.169E6:
eigenvalue(450) = 0.390794D+11 mode 1 frequency = 0.329475
eigenvalue(449) = 0.398465D+11 mode 2 frequency = 0.332693
eigenvalue(448) = 0.126954D+13 mode 3 frequency = 1.877897
eigenvalue(447) = 0.187182D+13 mode 4 frequency = 2.280244
eigenvalue(446) = 0.774666D+13 mode 5 frequency = 4.638803
eigenvalue(445) = 0.921857D+13 mode 6 frequency = 5.060349
eigenvalue(444) = 0.459755D+14 mode 7 frequency = 11.300868
eigenvalue(443) = 0.471883D+14 mode 8 frequency = 11.448961
eigenvalue(442) = 0.169404D+15 mode 9 frequency = 21.692580
eigenvalue(441) = 0.170534D+15 mode 10 frequency = 21.764779
Thank you for your answer.
Best regards,
René
Last edited by Rene.Mebus on Mon May 15, 2017 8:54 am, edited 1 time in total.
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