Reset derived quantity objects data and t at the beginning of a simulation

src/festim/hydrogen_transport_problem.py

@@ -400,6 +400,11 @@ def initialise_exports(self):
                 export.D = D
                 export.D_expr = D_expr
 
+            # reset the data and time for SurfaceQuantity and VolumeQuantity
+            if isinstance(export, (exports.SurfaceQuantity, exports.VolumeQuantity)):
+                export.t = []
+                export.data = []
+
     def define_D_global(self, species):
         """Defines the global diffusion coefficient for a given species
 

test/test_h_transport_problem.py

@@ -348,6 +348,35 @@ def test_initialise_exports_multiple_exports_same_species():
     assert Ds[0].x.array[0] == Ds[1].x.array[0]
 
 
+def test_export_resets_quantities():
+    """Test that the export.data and export.t are correctly reset every time a simulation is initiated."""
+    my_mat = F.Material(D_0=1, E_D=0)
+    H = F.Species("H")
+    surf = F.SurfaceSubdomain1D(id=1, x=4)
+
+    my_export = F.SurfaceFlux(
+        field=H,
+        surface=surf,
+    )
+
+    my_model = F.HydrogenTransportProblem(
+        mesh=F.Mesh1D([0, 1, 2, 3, 4]),
+        subdomains=[F.VolumeSubdomain1D(id=1, borders=[0, 4], material=my_mat), surf],
+        species=[H],
+        temperature=400,
+        exports=[my_export],
+    )
+
+    my_model.settings = F.Settings(atol=1e-15, rtol=1e-15, transient=False)
+
+    for i in range(3):
+        my_model.initialise()
+        my_model.run()
+
+        assert my_model.exports[0].t == [0.0]
+        assert my_model.exports[0].data == [0.0]
+
+
 def test_define_D_global_multispecies():
     """Test that the D_global object is correctly defined when there are multiple
     species in one subdomain"""