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HYDRODAMPING

Hello,

I have a question about “HYDRODAMPING” which we set to make a spar.
Do we need to set the value of “HYDRODAMPING” even if we use the “explicit buoyancy” option ?
I couldn’t understand about “HYDRODAMPING” by QBlade documentation. Could you tell me about it ?

Koma

Hi Koma,

check this overview for the different approaches to model hydrodynamics.

Damping can be modeled distributed via Morison elements, lumped via 6×6 SUB_HYDRODAMPING and SUB_HYDROQUADDAMPING matrices or through a lumped potential flow hydrodynamic database.

The buoyancy can be modeled in several different ways as well.

BR,

David

Thank you for telling me. I’ll try the method which you told me.

Best Regards,
Koma

Hello,

I’m sorry, I have one more question about “HYDRODAMPING”.
I tried to model damping through a lumped potential flow hydrodynamics database, and I tried to check if the settings are proper. I used two files to check the settings.
The first file is an original spar file which we can download on QBlade HP. I didn’t change any settings.
The second file is a spar file which I changed settings from original file to model damping through a lumped potential flow hydrodynamics database.
I ran the simulation by using the above two files, and I mainly compared them by displacement.
However, the simulation results are very different.

Then, I’d like to ask you if there are additional points that should be changed to calculate properly.
Regarding the second file, specifically, I changed as follows.

・change the value of Isbouy in SUBMEMBERS from 0 to 1.
・delete SUB_HYDROSTIFFNESS SUB_ HYDRODAMPING and SUB_HYDROQUADDAMPING matricies
・delete SUB _HYDROCONSTFORCE

Additionally, the version of Sparbuoy file which I use is 1.1.

Best Regards,
Koma

Hi Koma,

the NREL 5MW Sparbuoy model from QBlade’s download page uses the following approaches:

  • Rigid Cylindrical Substructure Elements with Morison Drag
  • Linear Potential Flow Radiation and Excitation Forces (USE_EXCITATION & USE_RADIATION)
  • Linear Hydrodynamic Stiffness Matrix for Buoyancy evaluation (SUB_HYDROSTIFFNESS)
  • Lumped Hydrodynamic Added Mass Matrix (SUB_HYDROADDEDMASS)
  • Linear Hydrodynamic Drag Matrix for tuning the model

If you plan to modify this model, it is important to ensure that if a modeling feature, like “lumped SUB_HYDROADDEDMASS,” is removed, it should be replaced with a different approach, such as the Morison method for added mass. This replacement will help achieve a similar system response. In other words: the different hydrodynamic contributions need to be set up consistently to produce consistent results across the different modeling approaches.

BR,

David

 

 

I apologize for the late reply. Thank you for answering my question. Thanks to your advice, I have solved it.

Best regards,
Koma