Tunging scale factor of symmetrig sigmoid function

Tools/parametric_model/src/models/aerodynamic_models/linear_plate_aero_model.py

@@ -41,21 +41,21 @@ def compute_main_wing_feature(self, v_airspeed, angle_of_attack):
 
         # Compute Drag force coeffiecients:
         F_xz_aero_frame[0, 0] = -(
-            1 - sym_sigmoid(angle_of_attack, self.stall_angle))*v_xz**2
+            1 - sym_sigmoid(angle_of_attack, x_offset=self.stall_angle, scale_fac=25))*v_xz**2
         F_xz_aero_frame[0, 1] = -(
-            1 - sym_sigmoid(angle_of_attack, self.stall_angle))*angle_of_attack*v_xz**2
+            1 - sym_sigmoid(angle_of_attack, x_offset=self.stall_angle, scale_fac=25))*angle_of_attack*v_xz**2
         F_xz_aero_frame[0, 2] = -(
-            1 - sym_sigmoid(angle_of_attack, self.stall_angle))*angle_of_attack**2*v_xz**2
+            1 - sym_sigmoid(angle_of_attack, x_offset=self.stall_angle, scale_fac=25))*angle_of_attack**2*v_xz**2
         F_xz_aero_frame[0, 3] = -(sym_sigmoid(angle_of_attack,
-                                  self.stall_angle))*math.sin(angle_of_attack)*v_xz**2
+                                  x_offset=self.stall_angle, scale_fac=25))*math.sin(angle_of_attack)*v_xz**2
 
         # Compute Lift force coefficients:
         F_xz_aero_frame[2, 4] = -(
-            1 - sym_sigmoid(angle_of_attack, self.stall_angle))*angle_of_attack*v_xz**2
+            1 - sym_sigmoid(angle_of_attack, x_offset=self.stall_angle, scale_fac=25))*angle_of_attack*v_xz**2
         F_xz_aero_frame[2, 5] = -(
-            1 - sym_sigmoid(angle_of_attack, self.stall_angle))*v_xz**2
+            1 - sym_sigmoid(angle_of_attack, x_offset=self.stall_angle, scale_fac=25))*v_xz**2
         F_xz_aero_frame[2, 6] = -2 * \
-            sym_sigmoid(angle_of_attack, self.stall_angle) \
+            sym_sigmoid(angle_of_attack, x_offset=self.stall_angle, scale_fac=25) \
             * math.sin(angle_of_attack)*math.cos(angle_of_attack)*v_xz**2
 
         # Transorm from stability axis frame to body FRD frame

Tools/parametric_model/src/tools/math_tools.py

@@ -4,18 +4,36 @@
 
 import math
 import numpy as np
+import matplotlib.pyplot as plt
+from numpy.core.function_base import linspace
 
 
-def sym_sigmoid(x, x_offset=0, scale_fac=1):
+def sym_sigmoid(x, x_offset=0, scale_fac=25):
     # computes a logistic sigmoid function which is symmetric
     # around zero and crosses the 0.5 mark at +- x_offset
     y = 1 - (math.exp(scale_fac*(x+x_offset))) / \
         ((1+math.exp(scale_fac*(x-x_offset)))*(1+math.exp(scale_fac*(x+x_offset))))
     return y
 
 
+def plot_sym_sigmoid(scale_fac, x_offset=0.35, x_range=90):
+    N = x_range*2+1
+    x = np.linspace(-x_range, x_range, N)
+    x_rad = x*math.pi/180.0
+    y = np.zeros(N)
+    for i in range(N):
+        y[i] = sym_sigmoid(x_rad[i], x_offset, scale_fac)
+    plt.plot(x, y)
+    plt.show()
+
+
 def rmse_between_numpy_arrays(np_array1, np_array2):
     difference_array = np.subtract(np_array1, np_array2)
     squared_array = np.square(difference_array)
     mse = squared_array.mean()
     return math.sqrt(mse)
+
+
+if __name__ == "__main__":
+    # run this script to find suitable values for the scale_factor of the symmetric sigmoid function
+    plot_sym_sigmoid(25, x_range=50)