Usage

Note

Recommended way to run pySailingVLM is by Jupyter Notebook which gives you more flexibility. See section Jupyter Notebook.

Command line

In order to run pySailingVLM from the command line, the input file called variable.py must be provided. Example file is shown below. Modify it for your needs.

import os
import numpy as np
import time

mgirths =  np.array([0.00, 1./8, 1./4, 1./2, 3./4, 7./8, 1.00])
jgirths = np.array([0.00, 1./4, 1./2, 3./4, 1.00])

output_args = {
    'case_name': os.path.basename(__file__),  # get name of the current file
    'case_dir': os.path.abspath(''), # get dir of the current file
    'name': os.path.join("results_example_jib_and_mainsail_vlm", time.strftime("%Y-%m-%d_%Hh%Mm%Ss")),
    'file_name': 'my_fancy_results', # name of xlsx excel file
}

solver_args = {
    'n_spanwise':  15,  # No of control points (above the water) per sail, recommended: 50
    'n_chordwise': 10, # No of control points (above the water) per sail, recommended: 50
    'interpolation_type': "spline",  # either "spline" or "linear"
}

conditions_args = {
    'leeway_deg': 5.,    # [deg]
    'heel_deg': 10.,     # [deg]
    'SOG_yacht': 4.63,   # [m/s] yacht speed - speed over ground (leeway is a separate variable)
    'tws_ref': 4.63,     # [m/s] true wind speed
    'alpha_true_wind_deg': 50.,   # [deg] true wind angle (with reference to course over ground) => Course Wind Angle to the boat track = true wind angle to centerline + Leeway
    'reference_water_level_for_wind_profile': -0.,  # [m] this is an attempt to mimick the deck effect
    # by lowering the sheer_above_waterline
    # while keeping the wind profile as in original geometry
    # this shall be negative (H = sail_ctrl_point - water_level)
    'wind_exp_coeff': 0.1428,  # [-] coefficient to determine the exponential wind profile
    'wind_reference_measurment_height': 10.,  # [m] reference height for exponential wind profile
    'rho': 1.225,  # air density [kg/m3]
    'wind_profile': 'exponential', # allowed: 'exponential' or 'flat' or 'logarithmic'
    'roughness': 0.05, # for logarithmic profile only 
}

rig_args = {
    'main_sail_luff': 12.4,  # [m]
    'jib_luff': 10.0,  # [m]
    'foretriangle_height': 11.50,  # [m]
    'foretriangle_base': 3.90,  # [m]
    'sheer_above_waterline': 1.2,#[m]
    'boom_above_sheer': 1.3, # [m],
    'rake_deg': 92. ,  # rake angle [deg]
    'mast_LOA': 0.15,  # [m]
    'sails_def': 'jib_and_main', # definition of sail set, possible: 'jib' or 'main' or 'jib_and_main'
}
# INFO for camber:
# First digit describing maximum camber as percentage of the chord.
# Second digit describing the distance of maximum camber from the airfoil leading edge in tenths of the chord.
main_sail_args = {
    'girths' : mgirths,
    'chords': np.array([4.00, 3.82, 3.64, 3.20, 2.64, 2.32, 2.00]),
    'centerline_twist_deg': 12 * mgirths + 5,
    'camber': 5*np.array([0.01, 0.01, 0.01, 0.01, 0.01, 0.01, 0.01]),
    'camber_distance_from_luff': np.array([0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5]),
}
 
jib_sail_args = {
    'centerline_twist_deg': 15. * jgirths + 7,
    'girths': jgirths,
    'chords': np.array([3.80, 2.98, 2.15, 1.33, 0.5]),
    'camber': 5*np.array([0.01, 0.01, 0.01, 0.01, 0.01]),
    'camber_distance_from_luff': np.array([0.5, 0.5, 0.5, 0.5, 0.5]), # starting from leading edge   
}        

# REFERENCE CSYS
# The origin of the default CSYS is located @ waterline level and aft face of the mast
# The positive x-coord: towards stern
# The positive y-coord: towards leeward side
# The positive z-coord: above the water
# To shift the default CSYS, adjust the 'reference_level_for_moments' variable.
# Shifted CSYS = original + reference_level_for_moments
# As a results the moments will be calculated around the new origin.

# yaw_reference [m] - distance from the aft of the mast towards stern, at which the yawing moment is calculated.
# sway_reference [m] - distance from the aft of the mast towards leeward side. 0 for symmetric yachts ;)
# heeling_reference [m] - distance from the water level,  at which the heeling moment is calculated.
csys_args = {
    'reference_level_for_moments': np.array([0, 0, 0]),  # [yaw_reference, sway_reference, heeling_reference]
}

# GEOMETRY OF THE KEEL
# to estimate heeling moment from keel, does not influence the optimizer.
# reminder: the z coord shall be negative (under the water)
keel_args={
    'center_of_lateral_resistance_upright': np.array([0, 0, -1.0]),  # [m] the coordinates for a yacht standing in upright position
}  

Run script

By default, the program assumes that the variables.py file is located in the working directory. To run the program do:

pySailingVLM

If the variables.py file is located in a different directory, one have to sepecify its location by providing additional option for pySailingVLM script:

pySailingVLM --dvars path_to_foler_with_variables.py

More information is available inside script help:

pySailingVLM --help

Output

pySailingVLM produces output files: data in xlsx file, matplotlib figures and pressure coefficient colormap in html extention (interactive plot). It is saved in the location specified in varaibles.py.

Note

First usage of pySailingVLM will produce Numba warining. This behaviour is correct. Warining messages will disappear during second run of program.

Example warning:

/home/user/miniconda3/envs/sv_build_test_2/lib/python3.10/site-packages/numba/core/lowering.py:107: NumbaDebugInfoWarning: Could not find source for function: <function __numba_array_expr_0x7fbf333f1780 at 0x7fbf33361b40>. Debug line information may be inaccurate.

Jupyter Notebook

Example notebooks: RC44 yacht and Sail with camber.