fix(): Validate domain_type and check for deleted surfaces in half-body simulations

flow360/component/simulation/meshing_param/volume_params.py

@@ -374,6 +374,57 @@ def _validate_only_in_beta_mesher(cls, value):
             "`domain_type` is only supported when using both GAI surface mesher and beta volume mesher."
         )
 
+    @pd.field_validator("domain_type", mode="after")
+    @classmethod
+    def _validate_domain_type_bbox(cls, value):
+        """
+        Ensure that when domain_type is used, the model actually spans across Y=0.
+        """
+        validation_info = get_validation_info()
+        if validation_info is None:
+            return value
+
+        if (
+            value not in ("half_body_positive_y", "half_body_negative_y")
+            or validation_info.global_bounding_box is None
+        ):
+            return value
+
+        y_min = validation_info.global_bounding_box[0][1]
+        y_max = validation_info.global_bounding_box[1][1]
+
+        largest_dimension = -float("inf")
+        for dim in range(3):
+            dimension = (
+                validation_info.global_bounding_box[1][dim]
+                - validation_info.global_bounding_box[0][dim]
+            )
+            largest_dimension = max(largest_dimension, dimension)
+
+        tolerance = largest_dimension * validation_info.planar_face_tolerance
+
+        # Check if model crosses Y=0
+        crossing = y_min < -tolerance and y_max > tolerance
+        if crossing:
+            return value
+
+        # If not crossing, check if it matches the requested domain
+        if value == "half_body_positive_y":
+            # Should be on positive side (y > 0)
+            if y_min >= -tolerance:
+                return value
+
+        if value == "half_body_negative_y":
+            # Should be on negative side (y < 0)
+            if y_max <= tolerance:
+                return value
+
+        raise ValueError(
+            f"The model does not cross the symmetry plane (Y=0) with tolerance {tolerance:.2g}. "
+            f"Model Y range: [{y_min:.2g}, {y_max:.2g}]. "
+            "Please check if `domain_type` is set correctly."
+        )
+
 
 class AutomatedFarfield(_FarfieldBase):
     """

flow360/component/simulation/primitives.py

@@ -554,14 +554,15 @@ def _overlaps(self, ghost_surface_center_y: Optional[float], length_tolerance: f
         return True
 
     def _will_be_deleted_by_mesher(
-        # pylint: disable=too-many-arguments, too-many-return-statements
+        # pylint: disable=too-many-arguments, too-many-return-statements, too-many-branches
         self,
         at_least_one_body_transformed: bool,
         farfield_method: Optional[Literal["auto", "quasi-3d", "quasi-3d-periodic", "user-defined"]],
         global_bounding_box: Optional[BoundingBoxType],
         planar_face_tolerance: Optional[float],
         half_model_symmetry_plane_center_y: Optional[float],
         quasi_3d_symmetry_planes_center_y: Optional[tuple[float]],
+        farfield_domain_type: Optional[str] = None,
     ) -> bool:
         """
         Check against the automated farfield method and
@@ -576,12 +577,24 @@ def _will_be_deleted_by_mesher(
             # VolumeMesh or Geometry/SurfaceMesh with legacy schema.
             return False
 
+        length_tolerance = global_bounding_box.largest_dimension * planar_face_tolerance
+
+        if farfield_domain_type in ("half_body_positive_y", "half_body_negative_y"):
+            if self.private_attributes is not None:
+                # pylint: disable=no-member
+                y_min = self.private_attributes.bounding_box.ymin
+                y_max = self.private_attributes.bounding_box.ymax
+
+                if farfield_domain_type == "half_body_positive_y" and y_max < -length_tolerance:
+                    return True
+
+                if farfield_domain_type == "half_body_negative_y" and y_min > length_tolerance:
+                    return True
+
         if farfield_method == "user-defined":
             # Not applicable to user defined farfield
             return False
 
-        length_tolerance = global_bounding_box.largest_dimension * planar_face_tolerance
-
         if farfield_method == "auto":
             if half_model_symmetry_plane_center_y is None:
                 # Legacy schema.

flow360/component/simulation/user_defined_dynamics/user_defined_dynamics.py

@@ -136,6 +136,7 @@ def ensure_output_surface_existence(cls, value):
             planar_face_tolerance=validation_info.planar_face_tolerance,
             half_model_symmetry_plane_center_y=validation_info.half_model_symmetry_plane_center_y,
             quasi_3d_symmetry_planes_center_y=validation_info.quasi_3d_symmetry_planes_center_y,
+            farfield_domain_type=validation_info.farfield_domain_type,
         ):
             raise ValueError(
                 f"Boundary `{value.name}` will likely be deleted after mesh generation. Therefore it cannot be used."

flow360/component/simulation/validation/validation_utils.py

@@ -84,6 +84,7 @@ def check_deleted_surface_in_entity_list(value):
             planar_face_tolerance=validation_info.planar_face_tolerance,
             half_model_symmetry_plane_center_y=validation_info.half_model_symmetry_plane_center_y,
             quasi_3d_symmetry_planes_center_y=validation_info.quasi_3d_symmetry_planes_center_y,
+            farfield_domain_type=validation_info.farfield_domain_type,
         ):
             raise ValueError(
                 f"Boundary `{surface.name}` will likely be deleted after mesh generation. "
@@ -115,6 +116,7 @@ def check_deleted_surface_pair(value):
             planar_face_tolerance=validation_info.planar_face_tolerance,
             half_model_symmetry_plane_center_y=validation_info.half_model_symmetry_plane_center_y,
             quasi_3d_symmetry_planes_center_y=validation_info.quasi_3d_symmetry_planes_center_y,
+            farfield_domain_type=validation_info.farfield_domain_type,
         ):
             raise ValueError(
                 f"Boundary `{surface.name}` will likely be deleted after mesh generation. "
@@ -173,6 +175,12 @@ def check_symmetric_boundary_existence(stored_entities):
         if item.private_attribute_entity_type_name != "GhostCircularPlane":
             continue
 
+        if validation_info.farfield_domain_type in (
+            "half_body_positive_y",
+            "half_body_negative_y",
+        ):
+            continue
+
         if not item.exists(validation_info):
             # pylint: disable=protected-access
             y_min, y_max, tolerance, largest_dimension = item._get_existence_dependency(

tests/simulation/params/test_automated_farfield.py

@@ -8,6 +8,8 @@
 from flow360.component.project_utils import set_up_params_for_uploading
 from flow360.component.resource_base import local_metadata_builder
 from flow360.component.simulation import services
+from flow360.component.simulation.entity_info import SurfaceMeshEntityInfo
+from flow360.component.simulation.framework.param_utils import AssetCache
 from flow360.component.simulation.meshing_param.face_params import SurfaceRefinement
 from flow360.component.simulation.meshing_param.params import (
     MeshingDefaults,
@@ -481,3 +483,81 @@ def _test_and_show_errors(geometry):
     assert errors_1 is None
     assert errors_2 is None
     assert errors_3 is None
+
+
+def test_domain_type_bounding_box_check():
+    # Case 1: Model does not cross Y=0 (Positive Half)
+    # y range [1, 10]
+    # Request half_body_positive_y -> Should pass (aligned)
+
+    dummy_boundary = Surface(name="dummy")
+
+    asset_cache_positive = AssetCache(
+        project_length_unit="m",
+        use_inhouse_mesher=True,
+        use_geometry_AI=True,
+        project_entity_info=SurfaceMeshEntityInfo(
+            global_bounding_box=[[0, 1, 0], [10, 10, 10]],
+            ghost_entities=[],
+            boundaries=[dummy_boundary],
+        ),
+    )
+
+    farfield_pos = UserDefinedFarfield(domain_type="half_body_positive_y")
+
+    with SI_unit_system:
+        params = SimulationParams(
+            meshing=MeshingParams(
+                defaults=MeshingDefaults(
+                    planar_face_tolerance=0.01,
+                    geometry_accuracy=1e-5,
+                    boundary_layer_first_layer_thickness=1e-3,
+                ),
+                volume_zones=[farfield_pos],
+            ),
+            models=[Wall(entities=[dummy_boundary])],  # Assign BC to avoid missing BC error
+            private_attribute_asset_cache=asset_cache_positive,
+        )
+
+    params_dict = params.model_dump(mode="json", exclude_none=True)
+    _, errors, _ = services.validate_model(
+        params_as_dict=params_dict,
+        validated_by=services.ValidationCalledBy.LOCAL,
+        root_item_type="SurfaceMesh",
+        validation_level="All",
+    )
+
+    domain_errors = [
+        e for e in (errors or []) if "The model does not cross the symmetry plane" in e["msg"]
+    ]
+    assert len(domain_errors) == 0
+
+    # Case 2: Misaligned
+    # Request half_body_negative_y on Positive Model -> Should Fail
+    farfield_neg = UserDefinedFarfield(domain_type="half_body_negative_y")
+
+    with SI_unit_system:
+        params = SimulationParams(
+            meshing=MeshingParams(
+                defaults=MeshingDefaults(
+                    planar_face_tolerance=0.01,
+                    geometry_accuracy=1e-5,
+                    boundary_layer_first_layer_thickness=1e-3,
+                ),
+                volume_zones=[farfield_neg],
+            ),
+            models=[Wall(entities=[dummy_boundary])],
+            private_attribute_asset_cache=asset_cache_positive,
+        )
+
+    params_dict = params.model_dump(mode="json", exclude_none=True)
+    _, errors, _ = services.validate_model(
+        params_as_dict=params_dict,
+        validated_by=services.ValidationCalledBy.LOCAL,
+        root_item_type="SurfaceMesh",
+        validation_level="All",
+    )
+
+    assert errors is not None
+    domain_errors = [e for e in errors if "The model does not cross the symmetry plane" in e["msg"]]
+    assert len(domain_errors) == 1

tests/simulation/params/test_validators_params.py

@@ -2279,3 +2279,93 @@ def test_ghost_surface_pair_requires_quasi_3d_periodic_farfield():
     # Case 4: Farfield method IS "quasi-3d-periodic" → should pass
     with SI_unit_system, ValidationContext(CASE, quasi_3d_periodic_farfield_context):
         Periodic(surface_pairs=(periodic_1, periodic_2), spec=Translational())
+
+
+def test_deleted_surfaces_domain_type():
+    # Mock Asset Cache
+    surface_pos = Surface(
+        name="pos_surf",
+        private_attributes=SurfacePrivateAttributes(bounding_box=[[0, 1, 0], [1, 2, 1]]),
+    )
+    surface_neg = Surface(
+        name="neg_surf",
+        private_attributes=SurfacePrivateAttributes(bounding_box=[[0, -2, 0], [1, -1, 1]]),
+    )
+    surface_cross = Surface(
+        name="cross_surf",
+        private_attributes=SurfacePrivateAttributes(
+            bounding_box=[[0, -0.000001, 0], [1, 0.000001, 1]]
+        ),
+    )
+
+    asset_cache = AssetCache(
+        project_length_unit="m",
+        use_inhouse_mesher=True,
+        use_geometry_AI=True,
+        project_entity_info=SurfaceMeshEntityInfo(
+            global_bounding_box=[[0, -2, 0], [1, 2, 1]],  # Crosses Y=0
+            boundaries=[surface_pos, surface_neg, surface_cross],
+        ),
+    )
+
+    # Test half_body_positive_y -> keeps positive, deletes negative
+    farfield = UserDefinedFarfield(domain_type="half_body_positive_y")
+
+    with SI_unit_system:
+        params = SimulationParams(
+            meshing=MeshingParams(
+                defaults=MeshingDefaults(
+                    planar_face_tolerance=1e-4,
+                    geometry_accuracy=1e-5,
+                    boundary_layer_first_layer_thickness=1e-3,
+                ),
+                volume_zones=[farfield],
+            ),
+            models=[
+                Wall(entities=[surface_pos]),  # OK
+                Wall(entities=[surface_neg]),  # Error
+                Wall(entities=[surface_cross]),  # OK (touches 0)
+            ],
+            private_attribute_asset_cache=asset_cache,
+        )
+
+    _, errors, _ = validate_model(
+        params_as_dict=params.model_dump(mode="json"),
+        validated_by=ValidationCalledBy.LOCAL,
+        root_item_type="SurfaceMesh",
+        validation_level="All",
+    )
+
+    assert len(errors) == 1
+    assert "Boundary `neg_surf` will likely be deleted" in errors[0]["msg"]
+
+    # Test half_body_negative_y -> keeps negative, deletes positive
+    farfield_neg = UserDefinedFarfield(domain_type="half_body_negative_y")
+
+    with SI_unit_system:
+        params = SimulationParams(
+            meshing=MeshingParams(
+                defaults=MeshingDefaults(
+                    planar_face_tolerance=1e-4,
+                    geometry_accuracy=1e-5,
+                    boundary_layer_first_layer_thickness=1e-3,
+                ),
+                volume_zones=[farfield_neg],
+            ),
+            models=[
+                Wall(entities=[surface_pos]),  # Error
+                Wall(entities=[surface_neg]),  # OK
+                Wall(entities=[surface_cross]),  # OK
+            ],
+            private_attribute_asset_cache=asset_cache,
+        )
+
+    _, errors, _ = validate_model(
+        params_as_dict=params.model_dump(mode="json"),
+        validated_by=ValidationCalledBy.LOCAL,
+        root_item_type="SurfaceMesh",
+        validation_level="All",
+    )
+
+    assert len(errors) == 1
+    assert "Boundary `pos_surf` will likely be deleted" in errors[0]["msg"]