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Substructure & Mooring Definition for IEA 15MW VolturnUS-S
Dear all,
I am trying to understand how the simulation parameters of IEA 15MW VolturnUS-S Semi-submersible is input into QBlade in comparison to OpenFAST input of the same reference turbine. I have some doubts about how substructure properties are specified in QBlade:
- In the QBlade Sample Project input for this reference turbine (QBlade Sample Projects), I noticed that CdN for mooring line had been defined as 1.11, while the same parameters (i.e. Cd in MoorDyn) were specified as 2.0, in MoorDyn input GitHub for IEA15MW. What could be the reason for this difference, or am I not understanding the coefficients correctly?
- Could the mooring line tangential Drag & Added Mass coefficients (i.e. CdAx & CaAx in MoorDyn) be defined in QBlade?
- I notice that Buoyancy Tuner factor of 1.0093 had been defined in QBlade input. What is the background for this tuning factor?
My doubts pertaining to mooring line definition are summarised in the attached snapshot for easy reference.
Thanks & regards,
Andhi
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Hi Andhi,
please note that the official definitions of the reference turbines are constantly being updated, which may explain why the mooring-line properties of the IEA-15 MW floater differ slightly from those in the official GitHub repository.
Axial Drag Coefficient
You can assign an axial drag coefficient via a HYDROMEMBERCOEFF entry. See the Morison-equation/strip-theory modelling section of the QBlade docs for details:
https://docs.qblade.org/src/user/turbine/substructure.html#morison-equation-strip-theory-modelling
Axial Added Mass
Axial added-mass coefficients are not currently supported.
Buoyancy Tuning Factor
The Buoyancy Tuning Factor multiplies the buoyancy force generated by each member, and the SUB_DISPLACEDVOLUME parameter. It linearly scales the buoyancy force and is used to fine-tune the floater’s neutral point (NP), ensuring NP sits at zero height in its equilibrium position.
Best regards,
David
