Modelling marine growth for OC4 semi-sub

[Abdulelah96]

Dear all,

I want to study how marine growth affect the dynamics of the OC4 FOWT. I am using the OC4 test case input files as reference. I am first modelling in it on the hull/platform. Here is how I am introducing it in HydroDyn.

1. I am defining MGDpth, MGThck and MGDens. For example:

---------------------- MARINE GROWTH -------------------------------------------
             3   NMGDepths      - Number of marine-growth depths specified (-)
MGDpth     MGThck   MGDens
(m)        (m)         (kg/m^3)
 0.0      0.150      1350
-10.0     0.150      1350
-20.0     0.100      1350

2. I am defining its hydrodynamic coefficients MemberCdMG1 and MemberCdMG2 = 1.0 to 1.2 MemberCaMG1, MemberCaMG2 = 0.8 to 1.0. which i suppose it will use the equation C_m=1+C_a.

3. Finally, I run the simulations in OpenFAST.

Is my approach correct or I am missing something? I am still using potential flow loads PropPot = True for all members. I want to confirm that I am not double counting the loads?

Thank you in advance.

Regards,

Abdulelah

[jjonkman]

Dear @Abdulelah96,

What you propose sounds fine.

Note that because this HydroDyn model is a hybrid model consisting of both potential-flow and strip-theory solutions for all members, only the viscous terms from the strip theory solution apply. So, changing strip-theory added mass coefficients MemberCaMG1 and MemberCaMG2 will not affect the solution.

Best regards,