Merge pull request #299 from isteinbrecher/fix-bug-in-arc-length

Fix bug in create arc function

Author: isteinbrecher

src/meshpy/mesh_creation_functions/beam_basic_geometry.py

@@ -179,8 +179,6 @@ def create_beam_mesh_arc_segment_via_axis(
     axis_point,
     start_point,
     angle,
-    *,
-    start_node=None,
     **kwargs,
 ):
     """Generate a circular segment of beam elements.
@@ -241,14 +239,13 @@ def create_beam_mesh_arc_segment_via_axis(
     center = start_point - distance
 
     # Get the rotation at the start
-    if start_node is None:
-        tangent = _np.cross(axis, distance)
-        tangent /= _np.linalg.norm(tangent)
-        start_rotation = _Rotation.from_rotation_matrix(
-            _np.transpose(_np.array([tangent, -distance / radius, axis]))
-        )
-    else:
-        start_rotation = _get_single_node(start_node).rotation
+    # No need to check the start node here, as eventual rotation offsets in
+    # tangential direction will be covered by the create beam functionality.
+    tangent = _np.cross(axis, distance)
+    tangent /= _np.linalg.norm(tangent)
+    start_rotation = _Rotation.from_rotation_matrix(
+        _np.transpose(_np.array([tangent, -distance / radius, axis]))
+    )
 
     def get_beam_geometry(alpha, beta):
         """Return a function for the position and rotation along the beam
@@ -273,7 +270,6 @@ def beam_function(xi):
         function_generator=get_beam_geometry,
         interval=[0.0, angle],
         interval_length=angle * radius,
-        start_node=start_node,
         **kwargs,
     )
 

src/meshpy/mesh_creation_functions/beam_generic.py

@@ -194,7 +194,7 @@ def check_given_node(node):
         if node not in mesh.nodes:
             raise ValueError("The given node is not in the current mesh")
 
-    def get_relative_twist(rotation_node, rotation_function):
+    def get_relative_twist(rotation_node, rotation_function, name):
         """Check if the rotation at a node and the one returned by the function
         match.
 
@@ -210,7 +210,7 @@ def get_relative_twist(rotation_node, rotation_function):
         elif not _mpy.allow_beam_rotation:
             # The settings do not allow for a rotation of the beam
             raise ValueError(
-                "Given nodal rotation does not match with given rotation function!"
+                f"Given rotation of the {name} node does not match with given rotation function!"
             )
         else:
             # Evaluate the relative rotation
@@ -221,7 +221,7 @@ def get_relative_twist(rotation_node, rotation_function):
                 return rotation_function.inv() * rotation_node
             else:
                 raise ValueError(
-                    "The tangent of the start node does not match with the given function!"
+                    f"The tangent of the {name} node does not match with the given function!"
                 )
 
     # Position and rotation at the start and end of the interval
@@ -235,14 +235,16 @@ def get_relative_twist(rotation_node, rotation_function):
         nodes = [start_node]
         check_given_node(start_node)
         _, start_rotation = function_over_whole_interval(-1.0)
-        relative_twist_start = get_relative_twist(start_node.rotation, start_rotation)
+        relative_twist_start = get_relative_twist(
+            start_node.rotation, start_rotation, "start"
+        )
 
     # If an end node is given, check what behavior is wanted.
     if end_node is not None:
         end_node = _get_single_node(end_node)
         check_given_node(end_node)
         _, end_rotation = function_over_whole_interval(1.0)
-        relative_twist_end = get_relative_twist(end_node.rotation, end_rotation)
+        relative_twist_end = get_relative_twist(end_node.rotation, end_rotation, "end")
 
     # Check if a relative twist has to be applied
     if relative_twist_start is not None and relative_twist_end is not None:

tests/reference-files/test_mesh_creation_functions_arc_segment_start_end_node.dat

@@ -0,0 +1,22 @@
+// -----------------------------------------------------------------------------
+// This input file was created with MeshPy.
+// Copyright (c) 2018-2025
+//     Ivo Steinbrecher
+//     Institute for Mathematics and Computer-Based Simulation
+//     Universitaet der Bundeswehr Muenchen
+//     https://www.unibw.de/imcs-en
+// -----------------------------------------------------------------------------
+-----------------------------------------------------------------------MATERIALS
+MAT 1 MAT_BeamReissnerElastHyper YOUNG -1.0 POISSONRATIO 0.0 DENS 0.0 CROSSAREA 3.141592653589793 SHEARCORR 1 MOMINPOL 1.5707963267948966 MOMIN2 0.7853981633974483 MOMIN3 0.7853981633974483
+---------------------------------------------------------------------NODE COORDS
+NODE 1 COORD 0 0 0
+NODE 2 COORD 1.68294196962 0.919395388264 0
+NODE 3 COORD 0.331792265387 0.0277135368741 0
+NODE 4 COORD 0.654389393592 0.110086107371 0
+NODE 5 COORD 0.958851077208 0.244834876219 0
+NODE 6 COORD 1.23673960614 0.428225478446 0
+NODE 7 COORD 1.48035370639 0.655175511834 0
+--------------------------------------------------------------STRUCTURE ELEMENTS
+1 BEAM3R HERM2LINE3 1 4 3 MAT 1 TRIADS 0 0 0 0 0 0.333333333333 0 0 0.166666666667
+2 BEAM3R HERM2LINE3 4 6 5 MAT 1 TRIADS 0 0 0.333333333333 0 0 0.666666666667 0 0 0.5
+3 BEAM3R HERM2LINE3 6 2 7 MAT 1 TRIADS 0 0 0.666666666667 0 0 1 0 0 0.833333333333

tests/test_mesh_creation_functions.py

@@ -155,6 +155,81 @@ def test_mesh_creation_functions_arc_segment_via_axis(
     assert_results_equal(get_corresponding_reference_file_path(), input_file)
 
 
+def test_mesh_creation_functions_arc_segment_start_end_node(
+    assert_results_equal, get_corresponding_reference_file_path
+):
+    """Check that if start end nodes with non-matching positions or tangents
+    are provided we get an error."""
+
+    angle = 1.0
+    radius = 2.0
+    start_node_pos = [0, 0, 0]
+    start_node_rot = Rotation()
+    end_node_pos = radius * np.array([np.sin(angle), 1.0 - np.cos(angle), 0])
+    end_node_rot = Rotation([0, 0, 1], angle)
+
+    def create_beam(*, start_node=None, end_node=None):
+        """This is the base function we use to generate the beam in this test
+        case."""
+        input_file = InputFile()
+        mat = MaterialReissner()
+        if start_node is not None:
+            input_file.add(start_node)
+        if end_node is not None:
+            input_file.add(end_node)
+        create_beam_mesh_arc_segment_via_axis(
+            input_file,
+            Beam3rHerm2Line3,
+            mat,
+            [0, 0, 1],
+            [0, radius, 0],
+            [0, 0, 0],
+            angle,
+            n_el=3,
+            start_node=start_node,
+            end_node=end_node,
+        )
+        return input_file
+
+    # This should work as expected, as all the values match.
+    start_node = NodeCosserat(start_node_pos, start_node_rot)
+    end_node = NodeCosserat(end_node_pos, end_node_rot)
+    input_file = create_beam(start_node=start_node, end_node=end_node)
+    assert_results_equal(get_corresponding_reference_file_path(), input_file)
+
+    # Create with start node where the position does not match.
+    with pytest.raises(
+        ValueError,
+        match="start_node position does not match with function!",
+    ):
+        start_node = NodeCosserat([0, 1, 0], start_node_rot)
+        create_beam(start_node=start_node)
+
+    # Create with start node where the rotation does not match.
+    with pytest.raises(
+        ValueError,
+        match="The tangent of the start node does not match with the given function!",
+    ):
+        start_node = NodeCosserat(start_node_pos, Rotation([1, 2, 3], np.pi / 3))
+        create_beam(start_node=start_node)
+
+    # Create with end node where the position does not match.
+    with pytest.raises(
+        ValueError,
+        match="end_node position does not match with function!",
+    ):
+        end_node = NodeCosserat([0, 0, 0], end_node_rot)
+        create_beam(end_node=end_node)
+
+    # Create with end node where the rotation does not match.
+    with pytest.raises(
+        ValueError,
+        match="The tangent of the end node does not match with the given function!",
+    ):
+        end_node = NodeCosserat(end_node_pos, Rotation([1, 2, 3], np.pi / 3))
+        create_beam(end_node=end_node)
+
+
 def test_mesh_creation_functions_arc_segment_via_rotation(
     assert_results_equal, get_corresponding_reference_file_path
 ):