Dear Jason,
Thank you for your prompt response. As you suggested, the output parameters I had chosen were not appropriate for comparison. Replotting the graph with the correct parameters leads to another query.
The time series for the first and fourth nodes of the third member are identical with the same statistical parameters. Does this imply uniform loading instead of linear loading along the length of the transition piece in the splash zone? If yes, is there a reason for this assumption?
Many thanks once again.
Faryal
Dear Faryal,
Presumably your HydroDyn model is set up without wave kinematics or hydrodynamic loads computed above the still water level (SWL) of Z = 0.0 m. Then, member 3, which extends from 0 to 10 m above SWL, does not have hydrodynamic loads applied to it, so, I would expect the same shear force at 0 and 10 m, as you are seeing.
Best regards,
Dear Jason
I’m using OC4 jacket model to do some dynamic analyses. From your previous reply to Abhinav, the base reaction (-ReactFXss) should be the sum of the forces/reactions at the 4 base reaction joints. According to my calculation results, this is true for the shear forces at the 4 base reaction joints (node 1 of member 112, 111, 110 and 109). But the sum of bending moments at the 4 base reaction joints (node 1 of member 112, 111, 110 and 109) are much smaller than -ReactMXss and -ReactMYss.
As member 112, 111, 110 and 109 are vertical members, this cannot be caused by the differences between the local coordinate system and global local coordinate system. Could you please give me some instructions about calculating the sectional bending moment?
Sincerely
Dear Bowen,
Are you comparing the sum of the local joint reaction moments to the total base reaction moment, or are you also considering the local joint forces and moment arms in the calculation?
Best regards,
Dear Jason
Thank you for the reply! I just compared the sum of the local joint reaction moments to the total base reaction moment. My SubDyn file is shown in the annex (I just compared the sum of “M1N1MKxe”, “M2N1MKxe”, “M3N1MKxe” and “M4N1MKxe” to “-ReactMXss” and the sum of “M1N1MKye”, “M2N1MKye”, “M3N1MKye” and “M4N1MKye” to “-ReactMYss”). It seems that the sum of the local joint reaction moments are much smaller than the total base reaction moment (even not in the same order of magnitude). I just want to verify the correctness of my calculation. According to my understanding, “M1N1MKxe”, “M2N1MKxe”, “M3N1MKxe” and “M4N1MKxe” stand for the joint reaction moments at joint 63, 64 ,61 and 62 in local x direction of element coordinate system. As M1, M2, M3 and M4 are all vertical members, The sum of “M1N1MKxe”, “M2N1MKxe”, “M3N1MKxe” and “M4N1MKxe” should equal to “-ReactMXss”. Am I right?
Sincerely
Bowen
NRELOffshrBsline5MW_OC4Jacket_SubDyn2.rar (4.19 KB)
Dear Bowen,
In addition to the moment at each joint, the axial load at each joint, together with the moment arm will also contribute to the total base reaction moment. There are also corrections for applied loads at the joint. The details are explained in section 6.5.3 of the draft SubDyn User’s Guide and Theory Manuel: wind.nrel.gov/nwtc/docs/SubDyn_Manual.pdf.
I hope that helps.
Dear Jason,
Thank you for the reply. Your answer does make sense. There is another problem in my simulation. When I calculated the dynamic response of OC4 jacket with FAST, I can only get the output reaction forces in 9 members. As the materials are limited in elastic stage, the determination of ultimate limit state of the turbine structure requires the verification of every joints and members (below the yield strength). This could bring difficulties when the jacket is made up of 108 members. Is there any way to output the internal force of more than 9 members at one time?
Sincerely
Bowen
Dear Bowen,
Yes, to output the member-end loads at every joint, set OutAll = TRUE in the SubDyn primary input file.
Best regards,
Dear Jason,
Thank you for the reply. Your answer is of great help to me.
Sincerely
Bowen
