Analysis A10 L3: DLC 1.6 serviceability, geometric clearance and structural checks

Warning

This analysis will perform a number of OpenFAST time domain simulations (~100, depending on the metocean combinations), and therefore can take a considerable amount of computing time (2-3 days on an HPC desktop machine, using 1 core).

Introduction

Aim

To perform a series of checks considering the design load case DLC 1.6:

• Serviceability limit state checks:

  • Mean tilt angle < constraint

  • Max tilt angle < constraint

  • MPM tilt angle < constraint

  • Max nacelle acceleration (x, y, z direction) < constraint

  • MPM nacelle acceleration (x, y, z direction) < constraint

• Geometric clearance checks:

  • Min distance between tower (axis) and blade tip > constraint

• Structural integrity checks:

  • Max tower base shear stress < constraint

  • MPM tower base shear stress < constraint

  • Max tower base bending moment < constraint

  • MPM tower base bending moment < constraint

  • Check for local buckling (DNV RP C202 2021)

Constraints

Level 1 (L1)

N/A

Level 2 (L2)

N/A

Level 3 (L3)

ID	Constraint	Units	Value	Description
1	Max_tilt_mean	deg	5.0^^^	Mean tilt angle less than constraint
2	Max_tilt_max	deg	10.0^^^	Max tilt angle less than constraint
3	Max_tilt_MPM	deg	10.0^^^	Most probable maximum tilt angle less than constraint
4	Max_nac_acc_x_max	g	0.3^^^	Max acceleration at tower top (x direction) less than constraint
5	Max_nac_acc_y_max	g	0.3^^^	Max acceleration at tower top (y direction) less than constraint
6	Max_nac_acc_z_max	g	0.3^^^	Max acceleration at tower top (z direction) less than constraint
7	Max_nac_acc_x_MPM	g	0.3^^^	Most probable max acceleration at tower top (x direction) less than constraint
8	Max_nac_acc_y_MPM	g	0.3^^^	Most probable max acceleration at tower top (y direction) less than constraint
9	Max_nac_acc_z_MPM	g	0.3^^^	Most probable max acceleration at tower top (z direction) less than constraint
10	Min_blade_tip_clrnc_from_twr	m	5.0^	Min blade tip clearance from tower AXIS higher than constraint (tower radius)
11	Max_twr_base_shear_max	kN		Max tower base shear force less than constraint
12	Max_twr_base_shear_MPM	kN		Most probable max tower base shear force less than constraint
13	Max_twr_base_bend_max	kNm		Max tower base bending moment less than constraint
14	Max_twr_base_bend_MPM	kNm		Most probable max tower base bending moment less than constraint
15	DNV_RP_C202_2021_buckling_res_cyl_shells	NA	NA	Check: buckling resistance of tower bottom can / shell

Notes
^	For IEA 15MW Reference Wind Turbine (Updated reference values here)
^^	Value agreed in WIND-14 STIFF-STIFF TOWER DESIGN FOR FLOATING WIND TURBINES (Previous TIC LCPE project)
^^^	DNV-RP-0289, Section 5.5 Serviceability limit state

Note

The suggested min value for the blade tip distance from the tower axis is 5m since this is the max diameter of the tower. Remember that the distance is NOT measured from the surface of the tower, but from the tower axis.

Methodology

Level 1 (L1)

N/A

Level 2 (L2)

N/A

Level 3 (L2)

Type	Check	OpenFAST variable	Method
SLS
	Mean tilt angle	PtfmPitch, PtfmRoll	Link
	Max tilt angle	PtfmPitch, PtfmRoll	Link
	MPM tilt angle	PtfmPitch, PtfmRoll	Link
	Max nac. acc. (x,y,z)	NcIMUTAxs, NcIMUTAys, NcIMUTAzs	Link
	MPM nac. acc. (x,y,z)	NcIMUTAxs, NcIMUTAys, NcIMUTAzs	Link
Geometric
	Min distance blade tip-tower axis	TipClrnc1, TipClrnc2, TipClrnc3	Link
Structural
	Max tower base shear	TwrBsFxt, TwrBsFyt	Link
	MPM tower base sheat	TwrBsFxt, TwrBsFyt	Link
	Max tower base bending moment	TwrBsMxt, TwrBsMyt	Link
	MPM tower base bending moment	TwrBsMxt, TwrBsMyt	Link
	Local buckling	Various	Please refer to Eq 3.11, DNV RP C202

Perform the analysis

Prepare the input file

The SCUBE input data can be found in the folder scube\data.

Constraints

• Open the file CNSTR.xlsx

• Familiarise yourself with the variables, explained in the legend sheet

• Select the sheet constraints_A10_L3

• A pre-prepared list of contraints and values can be found. Adjust the value for each constraint (where available) if necessary

• Save and close the spreadsheet file

Tower

• Open the file INPUT_tower.xlsx

• Familiarise yourself with the variables, explained in the legend sheet

• Specify the geometry of the cans in the geometry sheet

• Specify the aerodynamic drag properties of the tower in the drag sheet (if unsure, leave the default values, they can be applied to a wide range of dimensions)

• Specify the tower material characteristics in the material sheet (the default values are for the steel ASTM A572 Grade 50, see more here)

• Save and close the spreadsheet file

Environment

• Open the file INPUT_environment.xlsx

• Familiarise yourself with the variables, explained in the legend sheet

• Specify the relevant (see note below) metocean conditions in the wind_wave sheet

• Save and close the spreadsheet file

Note

For DLC 1.6, only the following columns of the wind_wave sheet are used:

• V_hub__mps (m/s), hub height wind speed

• V_10__mps (m/s), wind speed at 10m height (above sea level)

• Hs_SSS__m (m), Severe Sea State, Spectral significant wave height conditional on V_10_mps

• Tp_SSS__s (s), Severe Sea State, Peak spectral period conditional on V_10_mps and Hs

Run the analysis

• Open a miniforge/miniconda/conda terminal prompt

• Activate the WEIS environment you set up (see Installation)

conda activate weis-env

• Navigate to the root folder scube

• Launch the analysis with the following command

python main.py A10 L3

Expected conda prompt outcome

If all goes well, you should see something similar to the following.

Level 3 (L3)

See the full output here

Common errors

Permission error

PermissionError: [Errno 13] Permission denied: 'data/INPUT_tower.xlsx'

The file INPUT_tower.xlsx is still open on your pc. In order to be safely read by SCUBE, the file needs to be closed.

A similar error can occur for CNSTR.xlsx