Dear all,

I am studying an optimization problem for a floating wind turbine. I have used the example at link , using RAFT for the computation of the FOWT response.

I have tried to run two different optimization considering the column draft and radial distance from central column as design variables. The two optimization runs differ in the range of variation of the design variables: the first one has a smaller variation range than the second one. The final configurations have different masses (with a difference of about 12%), the estimated AEP remains unchanged between the two final designs, however, the LCOE values reported among the “financese” variables are the same for both cases. I am not sure if the LCOE estimation performed in financese is insensitive to platform mass calculation? I report the analysis options and modeling options below.

general:

folder_output: outputs/15_RAFT_Rect

fname_output: refturb_outputdesign_variables:

## control:

## servo:

## pitch_control:

## omega:

## flag: True

## min: 0.1

## max: 0.5

floating:

joints:

flag: True

z_coordinate:

- names: [main_keel, col1_keel, col2_keel, col3_keel]

lower_bound: -40.0

upper_bound: -10.0

r_coordinate:

- names: [col1_keel, col1_freeboard, col2_keel, col2_freeboard, col3_keel, col3_freeboard]

lower_bound: 38.8125

upper_bound: 64.6875

# members:

# flag: True

# groups:

# - names: [column1,column2,column3]

# diameter:

# lower_bound: 9.375

# upper_bound: 15.625

# constant: True

# thickness:

# lower_bound: 0.05

# upper_bound: 0.25

# constant: True

# - names: [Y_pontoon_lower1, Y_pontoon_lower2, Y_pontoon_lower3]

# diameter:

# lower_bound: 7.5

# upper_bound: 12.5constraints:

control:

rotor_overspeed:

flag: False

min: 0.0

max: 0.25

Max_PtfmPitch:

flag: True

max: 5.5

Std_PtfmPitch:

flag: True

max: 2.

Max_Offset:

flag: True

max: 30.

floating:

stress:

flag: True

global_buckling:

flag: True

shell_buckling:

flag: Truemerit_figure: platform_mass # Merit figure of the optimization problem. The options are ‘AEP’ - ‘LCOE’ - ‘Cp’ - ‘blade_mass’ - ‘blade_tip_deflection’

driver:

optimization:

flag: True # Flag to enable optimization

solver: LN_COBYLA # Optimization solver. Other options are ‘SLSQP’ - ‘CONMIN’

tol: 1.e-2 # Optimality tolerance

max_iter: 50 # Maximum number of iterations (SLSQP)## design_of_experiments:

## flag: True # Flag to enable design of experiments

## run_parallel: False # Flag to run using parallel processing

## generator: LatinHypercube # Type of input generator. (Uniform)

## num_samples: 12 # number of samples for (Uniform only)

recorder:

flag: True # Flag to activate OpenMDAO recorder

file_name: log_opt.sql # Name of OpenMDAO recorder

includes: [‘raft’,‘floating’,‘platform’]

General:

verbosity: False # When set to True, the code prints to screen many infos

openfast_configuration:

use_exe: True

allow_fails: True

fail_value: 9999WISDEM:

RotorSE:

flag: True

spar_cap_ss: Spar_Cap_SS

spar_cap_ps: Spar_Cap_PS

te_ss: TE_reinforcement_SS

te_ps: TE_reinforcement_PS

TowerSE:

flag: True

DriveSE:

flag: True

FloatingSE:

flag: True

# BOS:

# flag: TrueLevel3: # Options for WEIS fidelity level 3 = nonlinear time domain

flag: False

simulation:

DT: 0.01

CompElast: 1

CompInflow: 1

CompAero: 2

CompServo: 1

CompHydro: 1

CompSub: 0

CompMooring: 3

CompIce: 0

OutFileFmt: 3

linearization:

Linearize: False

ElastoDyn:

FlapDOF1: True

FlapDOF2: True

EdgeDOF: True

TeetDOF: False

DrTrDOF: False

GenDOF: True

YawDOF: False

TwFADOF1 : True

TwFADOF2 : True

TwSSDOF1 : True

TwSSDOF2 : True

PtfmSgDOF: True

PtfmSwDOF: True

PtfmHvDOF: True

PtfmRDOF : True

PtfmPDOF : True

PtfmYDOF : True

HydroDyn:

WvLowCOff: 0.15708

WvHiCOff: 3.2

WaveSeed1: 123456789

AddBQuad1: [9.23e5, 0.0, 0.0, 0.0, -8.92e6, 0.0]

AddBQuad2: [0.0, 9.23e5, 0.0, 8.92e6, 0.0, 0.0]

AddBQuad3: [0.0, 0.0, 2.3e6, 0.0, 0.0, 0.0]

AddBQuad4: [0.0, 8.92e6, 0.0, 1.68e10, 0.0, 0.0]

AddBQuad5: [-8.92e6, 0.0, 0.0, 0.0, 1.68e10, 0.0]

AddBQuad6: [0.0, 0.0, 0.0, 0.0, 0.0, 4.8e10]

PotMod: 1

# WaveMod: 0Level1:

flag: True

potential_model_override: 0

trim_ballast: 2

heave_tol: 1

save_designs: TrueROSCO:

flag: True

SD_Mode: 0

PS_Mode: 1

ps_percent: 0.85

F_LPFType: 2

F_NotchType: 2

Fl_Mode: 2

tuning_yaml: …/…/examples/01_aeroelasticse/OpenFAST_models/IEA-15-240-RWT/IEA-15-240-RWT-UMaineSemi/IEA15MW-UMaineSemi.yaml

zeta_pc: [1]

omega_pc: [0.2]

U_pc: [12]

zeta_vs: 0.85 # Torque controller desired damping ratio [-]

omega_vs: 0.12

twr_freq: 3.2

ptfm_freq: 0.2

Kp_float: -10DLC_driver:

metocean_conditions:

wind_speed: [4., 6., 8., 10., 12., 14., 16., 18., 20., 22., 24.]

wave_height_NSS: [0.83, 0.88, 0.94, 1.03, 1.16, 1.34, 1.57, 1.86, 2.22, 2.62, 3.07]

wave_period_NSS: [6.9, 6.96, 7.02, 7.12, 7.25, 7.43, 7.66, 7.94, 8.27, 8.63, 9.01]

wave_height_SSS: [6.3, 8, 8, 8.1, 8.5, 8.5, 9.8, 9.8, 9.8, 9.8, 9.9]

wave_period_SSS: [11.5, 12.7, 12.7, 12.8, 13.1, 13.1, 14.1, 14.1, 14.1, 14.1, 14.1]

wave_height1: 6.98

wave_period1: 11.7

wave_height50: 10.68

wave_period50: 14.2

DLCs:

- DLC: “1.1”

n_seeds: 1

# - DLC: “1.3”

# n_seeds: 6

- DLC: “1.4”

- DLC: “1.5”

- DLC: “1.6”

n_seeds: 1

- DLC: “6.1”

n_seeds: 1

# - DLC: “6.3”

# n_seeds: 6

I also noticed that in the generated output file the units reproted for the variable financese.plant_aep are USD/kW/h. Is this correct?

Moreover, I am not sure about the meaning of the “constant” keyword in the design variable in the member diameter and thickness. Does it constrain the diameter or thickness to be constant along member axis? Setting this parameter to false, the run terminated with the following error.

Thanks in advance for your support.

Best regards,