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