1 files changed, 64 insertions, 0 deletions
diff --git a/evaluator/inertia.py b/evaluator/inertia.py
new file mode 100644
index 0000000..fea728c
--- /dev/null
+++ b/evaluator/inertia.py
@@ -0,0 +1,64 @@
+def get_centroid(aircraft):
+    """Return the coordinates of the centroid."""
+    stringer_area = aircraft.stringer.area
+    cap_area = aircraft.spar.cap_area
+
+    caps_x = [value for spar in aircraft.spar.x for value in spar]
+    caps_z = [value for spar in aircraft.spar.z for value in spar]
+    stringers_x = aircraft.stringer.x
+    stringers_z = aircraft.stringer.z
+
+    denominator = float(
+        len(caps_x) * cap_area + len(stringers_x) * stringer_area)
+
+    centroid_x = float(
+        sum([x * cap_area
+             for x in caps_x]) + sum([x * stringer_area for x in stringers_x]))
+    centroid_x = centroid_x / denominator
+
+    centroid_z = float(
+        sum([z * cap_area
+             for z in caps_z]) + sum([z * stringer_area for z in stringers_z]))
+    centroid_z = centroid_z / denominator
+
+    return (centroid_x, centroid_z)
+
+
+def get_inertia_terms(self):
+    """Obtain all inertia terms."""
+    stringer_area = self.stringer.area
+    cap_area = self.spar.cap_area
+
+    # Adds upper and lower components' coordinates to list
+    x_stringers = self.stringer.x
+    z_stringers = self.stringer.z
+    x_spars = self.spar.x[:][0] + self.spar.x[:][1]
+    z_spars = self.spar.z[:][0] + self.spar.z[:][1]
+    stringer_count = range(len(x_stringers))
+    spar_count = range(len(self.spar.x))
+
+    # I_x is the sum of the contributions of the spar caps and stringers
+    # TODO: replace list indices with dictionary value
+    I_x = sum(
+        [cap_area * (z_spars[i] - self.centroid[1])**2 for i in spar_count])
+    I_x += sum([
+        stringer_area * (z_stringers[i] - self.centroid[1])**2
+        for i in stringer_count
+    ])
+
+    I_z = sum(
+        [cap_area * (x_spars[i] - self.centroid[0])**2 for i in spar_count])
+    I_z += sum([
+        stringer_area * (x_stringers[i] - self.centroid[0])**2
+        for i in stringer_count
+    ])
+
+    I_xz = sum([
+        cap_area * (x_spars[i] - self.centroid[0]) *
+        (z_spars[i] - self.centroid[1]) for i in spar_count
+    ])
+    I_xz += sum([
+        stringer_area * (x_stringers[i] - self.centroid[0]) *
+        (z_stringers[i] - self.centroid[1]) for i in stringer_count
+    ])
+    return (I_x, I_z, I_xz)