[FXC-5958] Implements target_surface_node_count for GAI Surf360 and new mesher ref

flow360/component/simulation/meshing_param/meshing_specs.py

@@ -194,6 +194,14 @@ class MeshingDefaults(Flow360BaseModel):
         context=SURFACE_MESH,
     )
 
+    target_surface_node_count: Optional[pd.PositiveInt] = ContextField(
+        None,
+        description="Target number of surface mesh nodes. When specified, the surface mesher "
+        "will rescale the meshing parameters to achieve approximately this number of nodes. "
+        "This option is only supported when using geometry AI and can not be overridden per face.",
+        context=SURFACE_MESH,
+    )
+
     curvature_resolution_angle: AngleType.Positive = ContextField(
         12 * u.deg,
         description=(
@@ -312,6 +320,7 @@ def invalid_geometry_accuracy(cls, value, param_info: ParamsValidationInfo):
     @contextual_field_validator(
         "surface_max_aspect_ratio",
         "surface_max_adaptation_iterations",
+        "target_surface_node_count",
         "resolve_face_boundaries",
         "preserve_thin_geometry",
         "sealing_size",

flow360/component/simulation/translator/surface_meshing_translator.py

@@ -788,6 +788,7 @@ def _get_gai_setting_whitelist(input_params: SimulationParams) -> dict:
         "preserve_thin_geometry": None,
         "surface_max_aspect_ratio": None,
         "surface_max_adaptation_iterations": None,
+        "target_surface_node_count": None,
         "sealing_size": None,
         "remove_hidden_geometry": None,
         "min_passage_size": None,

tests/simulation/translator/test_surface_meshing_translator.py

@@ -1734,3 +1734,115 @@ def test_gai_no_stationary_enclosed_entities():
     for zone in volume_zones:
         if zone["type"] in ("RotationVolume", "RotationCylinder"):
             assert "stationary_enclosed_entities" not in zone
+
+
+def test_gai_target_surface_node_count_set():
+    """target_surface_node_count passes through the GAI whitelist when set."""
+    param_dict = {
+        "private_attribute_asset_cache": {
+            "use_inhouse_mesher": True,
+            "use_geometry_AI": True,
+            "project_entity_info": {"type_name": "GeometryEntityInfo"},
+        },
+    }
+
+    with SI_unit_system:
+        params = SimulationParams(
+            meshing=MeshingParams(
+                defaults=MeshingDefaults(
+                    surface_max_edge_length=0.1,
+                    geometry_accuracy=0.01,
+                    target_surface_node_count=50000,
+                ),
+                volume_zones=[AutomatedFarfield()],
+            ),
+            private_attribute_asset_cache=AssetCache.model_validate(
+                param_dict["private_attribute_asset_cache"]
+            ),
+        )
+
+    translated = get_surface_meshing_json(params, 1 * u.m)
+    assert "meshing" in translated
+    assert "defaults" in translated["meshing"]
+    assert "target_surface_node_count" in translated["meshing"]["defaults"]
+    assert translated["meshing"]["defaults"]["target_surface_node_count"] == 50000
+
+
+def test_gai_target_surface_node_count_absent():
+    """target_surface_node_count is absent from GAI JSON when not set."""
+    param_dict = {
+        "private_attribute_asset_cache": {
+            "use_inhouse_mesher": True,
+            "use_geometry_AI": True,
+            "project_entity_info": {"type_name": "GeometryEntityInfo"},
+        },
+    }
+
+    with SI_unit_system:
+        params = SimulationParams(
+            meshing=MeshingParams(
+                defaults=MeshingDefaults(
+                    surface_max_edge_length=0.1,
+                    geometry_accuracy=0.01,
+                ),
+                volume_zones=[AutomatedFarfield()],
+            ),
+            private_attribute_asset_cache=AssetCache.model_validate(
+                param_dict["private_attribute_asset_cache"]
+            ),
+        )
+
+    translated = get_surface_meshing_json(params, 1 * u.m)
+    assert "meshing" in translated
+    assert "defaults" in translated["meshing"]
+    assert "target_surface_node_count" not in translated["meshing"]["defaults"]
+
+
+def test_legacy_target_surface_node_count_rejected(get_om6wing_geometry):
+    """target_surface_node_count is rejected for legacy (non-GAI) flows."""
+    my_geometry = TempGeometry("om6wing.csm")
+    with SI_unit_system:
+        params = SimulationParams(
+            private_attribute_asset_cache=AssetCache(
+                project_entity_info=my_geometry._get_entity_info()
+            ),
+            meshing=MeshingParams(
+                defaults=MeshingDefaults(
+                    surface_edge_growth_rate=1.2,
+                    curvature_resolution_angle=12 * u.deg,
+                    surface_max_edge_length=1 * u.m,
+                    target_surface_node_count=5000,
+                    edge_split_layers=0,
+                ),
+            ),
+        )
+
+    params, err, warnings = validate_params_with_context(params, "Geometry", "SurfaceMesh")
+    assert (
+        err is not None
+    ), "Expected validation error for target_surface_node_count in non-GAI flow"
+    assert "target_surface_node_count" in str(err)
+
+
+def test_legacy_target_surface_node_count_absent(get_om6wing_geometry):
+    """target_surface_node_count is absent from legacy translated JSON when not set."""
+    my_geometry = TempGeometry("om6wing.csm")
+    with SI_unit_system:
+        params = SimulationParams(
+            private_attribute_asset_cache=AssetCache(
+                project_entity_info=my_geometry._get_entity_info()
+            ),
+            meshing=MeshingParams(
+                defaults=MeshingDefaults(
+                    surface_edge_growth_rate=1.2,
+                    curvature_resolution_angle=12 * u.deg,
+                    surface_max_edge_length=1 * u.m,
+                    edge_split_layers=0,
+                ),
+            ),
+        )
+
+    params, err, warnings = validate_params_with_context(params, "Geometry", "SurfaceMesh")
+    assert err is None, f"Validation error: {err}"
+    translated = get_surface_meshing_json(params, mesh_unit=get_om6wing_geometry.mesh_unit)
+    assert "target_surface_node_count" not in translated