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Nan or Inf Vel … Error
Hi David, I want to do a simulation just with wave condition and without wind, so I set the uniform wind velocity 0, but the error of ‘Nan or Inf Vel at blade at section ………’ occurs, and if I change the wind velocity to 0.1 or some value else, there is no error. I don’t know how why. Thanks.
Best regards,
Yueguotian
Hi Yueguotion,
I know that there was a bug that caused such behavior when using zero inflow velocity with the unsteady BEM. However, this was already fixed a while ago and should not appear in the latest release. May I ask which version of QBlade-CE you were using when experiencing this issue?
If you want to fully exclude aerodynamic forces from a time domain simulation you can simply uncheck the option “Include Aerodynamic Forces & Moments” in the Simulation Definition Dialog. If you dont uncheck this option you will include aerodynamics – and even when the inflow velocity is zero the rotor will experience some aerodynamic loading that is resulting from the relative velocities caused by the floater motion.
BR,
David
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Thank you, David. I use version 2.0.4.8. I will check the latest version and take your advise. If I still use the old version to simulate the turbine response with wave and without wind, I just need to turn off the “Include Aerodynamic Forces & Moments” option, no matter the wind velocity I set, is it right? Also I want to confirm that whether the blade is rigid in the video in your website(the attached fig), there seems no deformation of the blade.
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Hi,
I just saw that the issue was fixed with 2.0.4.9, so you should be fine, or you can also simply deactivate aero forces as you suggested. The turbine model in the video that you mention is elastic, but its operating in 14m/s wind, so the blades are pitched to regulate power and the rotor thrust is fairly low – so blade deflections are low as well. When you closely look however, some small deflections should be visible!
BR,
David
Quote from David on 21. November 2022, 12:30Hi,
I just saw that the issue was fixed with 2.0.4.9, so you should be fine, or you can also simply deactivate aero forces as you suggested. The turbine model in the video that you mention is elastic, but its operating in 14m/s wind, so the blades are pitched to regulate power and the rotor thrust is fairly low – so blade deflections are low as well. When you closely look however, some small deflections should be visible!
BR,
David
I see that, thanks, David, but if I want to simulate the floating turbine, e.g. OC4, with rigid blade for making comparisons to that with flexible blade, how can I set the parameters or which files should I change? and I also want to ask the free decay test simulation(the validation case of OC3 spar model), is it right just set the floater initial condition? Suppose I make the surge decay test simulation, I just set the x translation 22 ? I am not sure about the turbine initial condition setting. Many thanks!
Best regards,
Yueguotian
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Hi,
to simulate with an almost “rigid” blade you could simply increase the blade stiffness in the structural blade file. A quick way to do this would be the following:
- Edit the turbine definition and click on “View/Edit Struct”, then scroll down until you have found the structural blade data table
- Instead of changing the siffness directly in the structural data table simply change the STIFFTUNER value, this value is multiplied with all stiffness related values in the data table. (setting STIFFTUNER to 100 would increase the overall blade stiffness by a factor of 100)
- Save the turbine under a new name as the “stiff” version
BR,
David
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Quote from David on 21. November 2022, 16:36Hi,
to simulate with an almost “rigid” blade you could simply increase the blade stiffness in the structural blade file. A quick way to do this would be the following:
- Edit the turbine definition and click on “View/Edit Struct”, then scroll down until you have found the structural blade data table
- Instead of changing the siffness directly in the structural data table simply change the STIFFTUNER value, this value is multiplied with all stiffness related values in the data table. (setting STIFFTUNER to 100 would increase the overall blade stiffness by a factor of 100)
- Save the turbine under a new name as the “stiff” version
BR,
David
Hi David, that should be the best way, your advice is much appreciated. As for the free decay test simulation, is it right just set the floater initial condition? Thank you.
BR,
Yueguotian
Hi,
for the free decay simulations you should set the initial floater displacement / rotation as you propose. The floater is “frozen” during the ramp-up part of the simulation, during which the mooring lines are relaxed, and then “released” after the ramp-up time has passed.
BR,
David
That’ clear, thank you, David.
BR,
Yueguotian
