minor edits

models/drag.py

@@ -1,6 +1,23 @@
 import numpy as np
+from input.user_input import *
 
-c_d = 0.47       # drag coefficient balloon (spherical) [-]
 
-def drag(c_d, rho_air, d_b, v):
-    return 0.125 * np.pi * c_d * rho_air * (d_b * v) ** 2
+def Cd_model(fr, re, a_top):
+    k_cd = 19.8
+    k1 = 1.50 * 10 ** 7
+    k2 = 0.86 * 10 ** (-7)
+    a_top0 = np.pi / 4 * 1.383 * V_design ** (2/3)  # a_top0 for zero-pressure shape
+
+    value = 0.2 * k_cd/fr * (k1/re + k2 * re) * a_top / (a_top0 ** (3/2))
+
+    if value > 1.6:
+        value = 1.6
+
+    return value
+
+
+c_d = 0.8  # 0.47
+
+
+def drag(c_d, rho_air, A_proj, v):
+    return 0.5 * c_d * rho_air * A_proj * v ** 2