Dear @Marwa.Mohamed ,
Thank you for sharing the calculation method for ocean currents in the IEC standard, but I have a question about Eq. (5). How is the surface velocity Uw(0) determined as shown in Eq. (5)? Uw(0)=0.01*V1-hour(z=10m)?
Best regards,
Dear @Russell.Xu,
Iām not sure I understand your question. The equation for U_w(0) is stated in Eq. (5), based on the 1-hour mean wind-speed at 10 m elevation.
Best regards,
Dear @Jason.Jonkman
Thank you for your response. Maybe I didnāt express my question clearly. I would like to inquire if U_w(0) is equal to 0.01 multiplied by the 1-hour mean wind-speed at 10 m elevation V1-hour(z=10m) according to Eq. (5). As shown in Eq. (5), Uw(0)=0,01*V1-hour(z=10m). Therefore, I am somewhat confused about this.
Best regards,
Dear @Russell.Xu,
Yes, that is what is stated in the IEC 61400-3-1 standard for the wind-generated near-surface current, which are used to compute the 1- and 50-year return values of U_w(0).
Best regards,
Dear @Jason.Jonkman
Thank you for your prompt response. I have fully understood about it.
Best regards,
Dear @Jason.Jonkman ,
I am trying to study the current, wave and wind effects on OC3 Hywind model. I have a few queries related to modelling current in OpenFAST. I have come across few related topics in the forum, but still could not understand few things. Please do help me with the following aspects:
a) In OpenFAST documentation, there is the explaination for current models. Could you please elaborate a bit more on difference between those models and when to use those models? Like in my case, I have wind and tide generated current velocity values; which model would be best for generating this in OpenFAST?
b) I am just changing the current velocity and heading in Hydrodyn. I would like to know whether any other commands should be changed?
Thanks and regards,
Dear @Arya.Thomas,
Here are my responses:
a) The sub-surface and near-surface current models supported by the SeaState/HydroDyn modules of OpenFAST come from the IEC 61400-3-1 and -3-2 design standards for fixed and floating offshore wind turbines, where the sub-surface current (power-law) profile is meant for tides and storm surges and the near-surface (linear to 20-m depth) profile is meant for wind-generated current.
b) You shouldnāt need to change anything else in the OC3-Hywind spar model to enable current, given that current-induced loads are introduced through the viscous drag term of the strip-theory solution, which is enabled for the OC3-Hywind spar model provided by NREL.
Best regards,
Thanks Jason for the insights.
Can we change the near-surface reference depth to our own site specific value ? Also, from which all output commands could we get the current loadings?
Regards,
Dear @Arya.Thomas,
Indeed, the reference depth for the near-surface current is user-specified via CurrNSRef, where IEC specifies CurrNSRef = 20 m.
HydroDyn doesnāt have an output that isolates the current load, but you should be able to see the effect of current in the viscous-drag load at each node (MĪ±NĪ²FDxi, etc.) or in the total integrated hydrodynamic loads (HydroFxi, etc.).
Best regards,