Merge branch 'main' into bearing_seal_locals_fix

ross/disk_element.py

@@ -388,6 +388,23 @@ def from_geometry(
         """Create a disk element from geometry properties.
 
         This class method will create a disk element from geometry data.
+        Properties are calculated as per :cite:`friswell2010dynamics`, appendix 1
+        for a hollow cylinder:
+
+        Mass:
+
+        :math:`m = \\rho \\pi w (d_o^2 - d_i^2) / 4`
+
+        Polar moment of inertia:
+
+        :math:`I_p = m (d_o^2 + d_i^2) / 8`
+
+        Diametral moment of inertia:
+
+        :math:`I_d = \\frac{1}{2} I_p + \\frac{1}{12} m w^2`
+
+        Where :math:`\\rho` is the material density, :math:`w` is the disk width,
+        :math:`d_o` is the outer diameter and :math:`d_i` is the inner diameter.
 
         Parameters
         ----------
@@ -427,14 +444,9 @@ def from_geometry(
         >>> disk.Ip
         0.32956362089137037
         """
-        m = 0.25 * material.rho * np.pi * width * (o_d**2 - i_d**2)
-        # fmt: off
-        Id = (
-            0.015625 * material.rho * np.pi * width * (o_d ** 4 - i_d ** 4)
-            + m * (width ** 2) / 12
-        )
-        # fmt: on
-        Ip = 0.03125 * material.rho * np.pi * width * (o_d**4 - i_d**4)
+        m = material.rho * np.pi * width * (o_d**2 - i_d**2) / 4
+        Ip = m * (o_d**2 + i_d**2) / 8
+        Id = 1 / 2 * Ip + 1 / 12 * m * width**2
 
         tag = tag