Fix: hole destruction not being recognized caused by subtractive modelling (#192); Fix: Geometries with overlapping regions generate a warning about potentially incorrect results when plastic properties are calculated. Tests: Tests added to verify warnings raised with plastic properties calcs with overlapping regions and to verify hole destruction

Author: connorferster

sectionproperties/analysis/section.py

@@ -2,6 +2,7 @@
 
 import copy
 from dataclasses import dataclass, asdict
+import warnings
 
 import matplotlib.pyplot as plt
 import matplotlib.tri as tri
@@ -826,6 +827,20 @@ def calculate_plastic_properties(self, verbose=False, debug=False):
             err = "Calculate geometric properties before performing a plastic analysis."
             raise RuntimeError(err)
 
+        # check if any geometry are overlapped
+        if isinstance(self.geometry, section_geometry.CompoundGeometry):
+            polygons = [sec_geom.geom for sec_geom in self.geometry.geoms]
+            overlapped_regions = section_geometry.check_geometry_overlaps(polygons)
+            if overlapped_regions:
+                warnings.warn(
+                    "\nThe section geometry contains overlapping regions and the area of these overlapped regions "
+                    "will be 'double counted' in the plastic analysis which may result in incorrect values.\n"
+                    "If you do not intend for this double counting to occur, use a subtractive modelling approach "
+                    "to remove the overlapping region.\n"
+                    "Please see https://sectionproperties.readthedocs.io/en/latest/rst/advanced_geom.html for more "
+                    "information."
+                )
+
         def calc_plastic():
             plastic_section = PlasticSection(self.geometry)
             plastic_section.calculate_plastic_properties(self, verbose)
@@ -2002,6 +2017,7 @@ def calculate_plastic_properties(self, section, verbose):
         :param bool verbose: If set to True, the number of iterations required for each plastic
             axis is printed to the terminal.
         """
+
         # 1) Calculate plastic properties for centroidal axis
         # calculate distances to the extreme fibres
         fibres = self.calculate_extreme_fibres(

sectionproperties/pre/geometry.py

@@ -1677,7 +1677,11 @@ def compile_geometry(self):
                     )
 
         elif isinstance(unionized_poly, Polygon):
-            inadvertent_holes += Geometry(unionized_poly).holes
+            if Geometry(unionized_poly).holes:
+                inadvertent_holes += Geometry(unionized_poly).holes
+            else:  # Holes have been destroyed through operations
+                inadvertent_holes = []
+                self.holes = []
 
         extra_holes = []
         if set(inadvertent_holes) - set(self.holes):
@@ -1872,3 +1876,14 @@ def round_polygon_vertices(poly: Polygon, tol: int) -> Polygon:
     if not rounded_exterior.any():
         return Polygon()
     return Polygon(rounded_exterior, rounded_interiors)
+
+
+def check_geometry_overlaps(lop: List[Polygon]) -> bool:
+    """
+    Returns True if any of the Polygon in the list of Polygons, 'lop',
+    are overlapping with any other Polygons in 'lop'. Returns False
+    if all Polygon are disjoint.
+    """
+    union_area = unary_union(lop).area
+    sum_polygons = sum([poly.area for poly in lop])
+    return union_area != sum_polygons

sectionproperties/tests/test_sections.py

@@ -21,21 +21,29 @@
 
 big_sq = rectangular_section(d=300, b=250)
 small_sq = rectangular_section(d=100, b=75)
-small_hole = rectangular_section(d=40, b=30)
+small_hole = rectangular_section(d=40, b=30).align_center(small_sq)
 i_sec = i_section(d=200, b=100, t_f=20, t_w=10, r=12, n_r=12)
-
-small_sq = small_sq - small_hole.align_center(small_sq)
+small_sq_w_hole = small_sq - small_hole
 composite = (
     big_sq
-    + small_sq.align_to(big_sq, on="top", inner=True).align_to(big_sq, on="top")
+    + small_sq_w_hole.align_to(big_sq, on="top", inner=True).align_to(big_sq, on="top")
     + i_sec.align_to(big_sq, on="bottom", inner=True).align_to(big_sq, on="right")
 )
-composite.compile_geometry()
 composite.create_mesh([200])
 comp_sec = Section(composite)
 comp_sec.calculate_geometric_properties()
 comp_sec.calculate_plastic_properties()
 
+# Subtractive modelling
+nested_geom = (small_sq - small_hole) + small_hole
+nested_geom.create_mesh([50])
+nested_sec = Section(nested_geom)
+
+# Overlapped modelling
+overlay_geom = small_sq + small_hole
+overlay_geom.create_mesh([50])
+overlay_sec = Section(overlay_geom)
+
 
 def test_material_persistence():
     # Test ensures that the material attribute gets transformed
@@ -61,6 +69,7 @@ def test_for_incidental_holes():
     # a I Section up against a rectangle.
     # There should be two holes created after .compile_geometry()
     assert len(composite.holes) == 2
+    assert len(nested_geom.holes) == 0
 
 
 def test_geometry_from_points():
@@ -138,10 +147,13 @@ def test_compound_geometry_from_points():
     assert (new_geom.geom - wkt_test_geom) == Polygon()
 
 
-def test_nested_compound_geometry_from_points():
+def test_multinested_compound_geometry_from_points():
     """
-    Tests a nested compound geometry can be built .from_points, that the control_points
-    and hole nodes persist in the right locations, and that ...
+    Testing a multi-nested section. This section contains three nested materials in concentric
+    square rings with a hole going through the center of the whole section. This test confirms
+    that the section can be successfully built using .from_points, that the control_points
+    and hole nodes persist in the right locations, and that the plastic section calculation
+    raises a warning because the nested regions overlap.
     """
     points = [
         [-50.0, 50.0],
@@ -196,6 +208,15 @@ def test_nested_compound_geometry_from_points():
     ]
     assert nested_compound.holes == [(0, 0), (0, 0), (0, 0)]
 
+    # Section contains overlapping geometries which will result in potentially incorrect
+    # plastic properties calculation (depends on user intent and geometry).
+    # Test to ensure a warning is raised about this to notify the user.
+    nested_compound.create_mesh([25, 30, 35])
+    nested_compound_sec = Section(nested_compound)
+    nested_compound_sec.calculate_geometric_properties()
+    with pytest.warns(UserWarning):
+        nested_compound_sec.calculate_plastic_properties()
+
 
 def test_geometry_from_dxf():
     section_holes_dxf = (
@@ -251,10 +272,25 @@ def test_plastic_centroid():
     section.calculate_geometric_properties()
     section.calculate_plastic_properties()
 
+    # Checking sections that were defined above
+    #
+    nested_sec.calculate_geometric_properties()
+    nested_sec.calculate_plastic_properties()
+    overlay_sec.calculate_geometric_properties()
+
+    with pytest.warns(UserWarning):
+        overlay_sec.calculate_plastic_properties()
+
+    # section
     x_pc, y_pc = section.get_pc()
     assert x_pc == pytest.approx(82.5)
     assert y_pc == pytest.approx(250.360654576)
 
+    # nested_sec
+    x_pc, y_pc = nested_sec.get_pc()
+    assert x_pc == pytest.approx(37.5)
+    assert y_pc == pytest.approx(50)
+
 
 def test_geometry_from_3dm_file_simple():
     section = pathlib.Path.cwd() / "sectionproperties" / "tests" / "3in x 2in.3dm"