def plot_isherwood(frontal_area, lateral_area, superstructure_area, Loa, breadth, S, s_L, masts, plot_surge=True,
plot_sway=True, plot_yaw=True, subplots=False):
"""Plot the wind coefficients calculated by Isherwood's formulas.
Args:
frontal_area (float) -- frontal area of the vessel in m^2
lateral_area (float) -- lateral area of the vessel in m^2
superstructure_area (float) -- lateral area of the superstructure in m^2
Loa (float) -- length over all in m
breadth (float) -- breadth in m
S (float) -- length of the lateral projection
s_L (float) -- centroid of the wind area in the lateral direction, ahead of Lpp/2, in m
masts (int) -- number of distinct groups of masts
plot_surge (bool) -- plot C_X (default: True)
plot_sway (bool) -- plot C_Y (default: True)
plot_yaw (bool) -- plot C_N (default: True)
subplots (bool) -- plot subplots if True, everything together if False (default: False)
Returns:
N/A
"""
# These values in degrees.
start = 0.0
stop = 180.0
step = 0.1
angles_deg = np.arange(start, stop, step)
angles_rad = np.arange(radians(start), radians(stop), radians(step))
# Find the coefficients.
C_Xs, C_Ys, C_Ns = [], [], []
for angle in angles_rad:
C_X, C_Y, C_N = wc.isherwood(frontal_area, lateral_area, superstructure_area, Loa, breadth, S, s_L, masts, angle)
C_Xs.append(C_X)
C_Ys.append(C_Y)
C_Ns.append(C_N)
# Start plotting.
number_of_plots = int(plot_surge + plot_sway + plot_yaw)
if subplots == True and plot_surge == True:
plt.subplot(number_of_plots, 1, int(plot_surge))
plt.title("Isherwood coefficient in surge")
if plot_surge == True:
plt.plot(angles_deg, C_Xs, 'b', label = "C_X")
plt.legend()
if subplots == True and plot_sway == True:
plt.subplot(number_of_plots, 1, int(plot_surge + plot_sway))
plt.title("Isherwood coefficient in sway")
if plot_sway == True:
plt.plot(angles_deg, C_Ys, 'r', label = "C_Y")
plt.legend()
if subplots == True and plot_yaw == True:
plt.subplot(number_of_plots, 1, number_of_plots)
plt.title("Isherwood coefficient in yaw")
if plot_yaw == True:
plt.plot(angles_deg, C_Ns, 'k', label = "C_N")
plt.legend()
if subplots == False:
plt.title("Isherwood wind coefficients")
plt.ylim([-1.0, 1.0])
plt.show()
def wind_forces_and_moment(wind_speed, wind_direction, frontal_area, lateral_area, Loa, s_L, coeffs=
CoefficientType.blendermann, vessel_type=None, superstructure_area=None, breadth=None,
S=None, masts=None, temperature=20.0, vessel_heading=0.0, vessel_speed_surge=0.0,
vessel_speed_sway=0.0):
"""Return the wind force (surge and sway) and moment (yaw) acting
on the vessel.
Args:
wind_speed (float) -- wind speed in m/s
wind_direction (float) -- wind direction in radians
frontal_area (float) -- frontal area of the vessel in m^2
lateral_area (float) -- lateral area of the vessel in m^2
Loa (float) -- vessel length over all in m
s_L (float) -- centroid of the wind area in the lateral direction, ahead of Lpp/2, in m
coeffs (CoefficientType) -- how to determine the wind coefficients
vessel_type (string) -- vessel type to use with Blendermann (default: None)
superstructure_area (float) -- lateral superstructure area in m^2 for use with Isherwood (default: None)
breadth (float) -- vessel breadth in m (default: None)
S (float) -- length of the lateral proj. in m for use with Isherwood (default: None)
masts (int) -- number of masts or king posts for use with Isherwood (default: None)
temperature (float) -- temperature in degrees C (default: 20)
vessel_heading (float) -- vessel heading in radians (default: 0.0)
vessel_speed_surge (float) -- vessel speed in surge in m/s (default: 0.0)
vessel_speed_sway (float) -- vessel speed in sway in m/s (default: 0.0)
Returns:
wind_forces_and_moment (np.matrix) -- the wind forces and moment in kN/kNm
"""
rho_w = calculate_rho_w(temperature)
# Relative velocities
wind_speed_surge = wind_speed * np.cos(wind_direction - vessel_heading)
wind_speed_sway = wind_speed * np.sin(wind_direction - vessel_heading)
relative_velocity_surge = vessel_speed_surge - wind_speed_surge
relative_velocity_sway = vessel_speed_sway - wind_speed_sway
relative_wind_speed = np.sqrt(relative_velocity_surge**2 + relative_velocity_sway**2)
# The wind is coming from the angle of attack
angle_of_attack = np.arctan2(relative_velocity_sway, relative_velocity_surge) + pi
# Calculate coefficients depending on coefficient calculation method
if coeffs is CoefficientType.blendermann:
if vessel_type == None:
print("Please enter the correct parameters for Blendermann.\n")
C_X, C_Y, C_N = 0, 0, 0
else:
C_X, C_Y, C_N = wc.blendermann(vessel_type, frontal_area, lateral_area, Loa, s_L, angle_of_attack)
elif coeffs is CoefficientType.isherwood:
if superstructure_area == None or breadth == None or S == None or masts == None:
print("Please enter the correct parameters for Isherwood.\n")
C_X, C_Y, C_N = 0, 0, 0
else:
C_X, C_Y, C_N = wc.isherwood(frontal_area, lateral_area, superstructure_area, Loa, breadth, S, s_L, masts,
angle_of_attack)
q = 0.5 * rho_w * relative_wind_speed**2
wind_force_surge = 10**-3 * q * C_X * frontal_area
wind_force_sway = 10**-3 * q * C_Y * lateral_area
wind_moment_yaw = 10**-3 * q * C_N * lateral_area * Loa
wind_forces_and_moment = np.matrix([[wind_force_surge],
[wind_force_sway],
[wind_moment_yaw]])
return wind_forces_and_moment
