First of all, I would like to thank you for supporting the user community.
My question relates to the output loads calculated by FAST when using an floating platform.
Are PtfmFxt,Fyt,Fzt,Mxt,Myt,Mzt giving the external forces of moment applied to the platform from sea only or from sea and anchors?
Thanks in advance,
Nass et Wind
The platform loads (PtfmFxt through PtfmMzt or PtfmFxi through PtfmMzi) include all of the loads applied to the platform apart from the loads transmitted from the wind turbine and tower. So, they include mooring loads, wave-excitation loads, added mass, radiation damping, hydrostatics, and viscous drag.
At this time, one cannot output the individual contributions to the force (e.g., a hydrostatic-only force). This is something that is on our to-do list.
Then what about the responses, whether the effect of wind turbine load is there in responses or not. ( you said in previous reply that PtfmFxt includes mooring loads, wave-excitation loads, added mass, radiation damping, hydrostatics, and viscous drag apart from the loads transmitted from the wind turbine and tower) that’s why i asked the doubt. what about the total response .
The total response is captured through the FAST equations of motion. What I was referrering to in my post above is simply the outputs that are available related to this response. What outputs (different from what is currently available) are you seeking?
According to your above post you are saying that wind turbine and tower will not affect the PtfmFxyz. But i run two cases
(i) Make rotor speed 0 and wind speed 0.01 (approx to 0)
(ii) with rotor speed 20 and wind speed 9
Then i see there is a change in PtfmFxyz . How ??
one more i want to know about the PtfmFxyz includes gravity forces also or not . Actually i am matching the hydrodynamics calculation from fast and some other software . but they are not matching.
As I stated above, the platform load outputs from FAST (PtfmFxt through PtfmMzt or PtfmFxi through PtfmMzi) include the combined contribution from mooring loads, wave-excitation loads, added mass, radiation damping, hydrostatics, and viscous drag. Loads from the wind turbine and tower don’t directly contribute to the platform loads, but they do, of course, have an indirect effect. For example, the rotor thrust will cause the floating platform to move; the mooring loads, added mass, radiation damping, hydrostatics, and viscous drag all depend on this motion.
When you ask about gravity forces, are you referring to the body weight of the floating platform or something else? The body weight is not included in the platform load output, but of course, the body weight does contribute to the overall system response, and so, has an indrect effect on the platform load outputs.
I hope that helps.
Dear Jonkman ,
Thanks for the reply … If i have more doubt then i will discuss with you.
Can you tell me that when the platform force does not include all the forces then how will be the platform response will effected.
In other words the platform response depends on the platform forces. then if the platform forces does not include all the forces then how the response changes .?
The platform force outputs are just that – outputs available by FAST. Internal to FAST, the force/motion balance is consistent.