Dear all,

starting from the RAFT studies example, I was setting up an LCOE optimization problem, using RAFT for the simulation of a single FOWT response. The used analysis and modeling options are reported below.

Analysis options:

general:

folder_output: outputs/15_RAFT_Rect

fname_output: refturb_outputdesign_variables:

floating:

joints:

flag: True

z_coordinate:

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

lower_bound: -40.0

upper_bound: -15.0

r_coordinate:

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

lower_bound: 40. #35.8125

upper_bound: 70. #64.6875

members:

flag: True

groups:

- names: [column1,column2,column3]

diameter:

lower_bound: 9.5 #9.375

upper_bound: 20.0 #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_user:

name: financese.lcoedriver:

optimization:

flag: True # Flag to enable optimization

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

tol: 1.e-2 # Optimality tolerance

max_iter: 100 # Maximum number of iterations (SLSQP)recorder:

flag: True # Flag to activate OpenMDAO recorder

file_name: log_opt.sql # Name of OpenMDAO recorder

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

Modeling options:

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

# gamma_f: 1.35 # Safety factor for fatigue loads

# gamma_m: 1.3 # Safety factor for material properties

# gamma_n: 1.0 # Safety factor for …

# gamma_b: 1.1 # Safety factor for …

# gamma_fatigue: 1.755 # Safety factor for fatigue loads

# buckling_length: 30 # Buckling parameter

# soil_springs: True

# gravity_foundation: False

# frame3dd:

# shear: True

# geom: True

# tol: 1e-9

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: 0

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

The optimization ends successfully, but I have found a very large final value of the BOS cost per kW from the output file (~14500 $/kW). This results in a very large LCOE value (around 300 $/MWh) as well and in a low sensitivity of the LCOE on the platform sizing, which is the final objective of the optimization. I was wondering where to look for possible error in the settings and if there is a way to set different values of the cost parameters (maybe in the Orbit module).

Thanks in advance.

Best regards,