OC4 Task 30 Phase II Load case 2.1

[Bertrand.Canetti]

Dear all,

For the load case 2.1, deterministic waves, I have respected the following conditions:

- AeroDyn and InflowWind = 0
- ServoDyn = 0
- HydroDyn = 1 with H = 6 m, T = 10 s
- Support DOF (platform + tower enabled)

And yet, I do obtain a weird slow frequency in my surge response.



I did not find where this additional frequency could come from. I have tried disabling the tower DOF, it is the same.

Thank you for your help,

Bertrand

[Jason.Jonkman]

Dear Bertrand,

What you are seeing is the surge natural period of the OC4-DeepCwind semisubmersible (which is around 120 s).

Best regards,

[Bertrand.Canetti]

Dear Jason,

Thank you for your answer.

Ok, but could you explain why this frequency is not visible in the surge OC4 results for load case 2.1 in the Code Comparison paper, page 8, figure 6?



Best regards,
Bertrand

[Jason.Jonkman]

Dear Bertrand,

The response you are showing from OC4 is taken after all start-up transients die out. The surge oscillation at its natural frequency results from the nonequilibrium condition and will decay away over time.

Best regards,