Add content to mesh page

Author: ggiraldof

tutorial/meshing.rst

@@ -1,9 +1,109 @@
 Meshing
 =======
 
-To Do:
+The CFD numerical method used for the incompressible setup requires
+the discretization of the fluid domain, a process also known as meshing.
+In the Simscale platform, a mesh is an individual object that needs a model
+to specify its properties, such as sizing. The mesh also has to be computed 
+before the simulation can be run.
 
-* How to create a mesh
-* How to setup mesh sizing, automatic
-* How to compute the mesh and check the progress
-* How to assing the mesh to the simulation
+Mesh Model
+----------
+
+Similar to a simulation, we first need to specify the mesh parameters
+with a model object. It can be done as follows:
+
+
+.. code-block:: python
+
+    import simscale_sdk as sim
+
+    mesh_model = sim.SimmetrixMeshingFluid(
+        sizing=sim.AutomaticMeshSizingSimmetrix(
+            fineness=5,
+            curvature=sim.AutomaticCurvature(),
+        ),
+        automatic_layer_settings=sim.AutomaticLayerOn(
+            number_of_layers=3,
+            total_relative_thickness=0.4,
+            growth_rate=1.5
+        ),
+        pysics_based_meshing=True,
+        hex_core=True,
+    )
+
+
+Here we make use of the automatic sizing with fineness level 5. Also, physics-based
+meshing allows to take into account boundary conditions for layer creation. boundary
+layer settings are entered manually with 3 layers on walls. Finally, the hex_core
+is entered to improve the orthogonality of the mesh.
+
+Mesh Operation
+--------------
+
+Now that we have a proper mesh model, we can create the mesh operation, which links
+the project, the geometry and the model:
+
+
+.. code-block:: python
+
+    import simscale_sdk as sim
+
+    mesh_operation_api = sim.MeshOperationsApi(api_client)
+
+    mesh_operation = mesh_operation_api.create_mesh_operation(
+        project_id,
+        sim.MeshOperation(
+            name="Pipe junction mesh",
+            geometry_id=geometry_id,
+            model=mesh_model,
+        )
+    )
+
+
+The mesh operation object is used to launch the computation and track its progress:
+
+
+.. code-block:: python
+
+    mesh_operation_api.start_mesh_operation(
+        project_id,
+        mesh_operation.mesh_operation_id,
+        simulation_id=simulation_id,
+    )
+
+    while mesh_operation.status not in ("FINISHED", "CANCELED", "FAILED"):
+
+        mesh_operation = mesh_operation_api.get_mesh_operation(
+            project_id,
+            mesh_operation.mesh_operation_id,
+        )
+
+        time.sleep(30)
+
+    print(f"Mesh with id={mesh_operation.mesh_id} was completed with status {mesh_operation.status}")
+
+
+You should recognize this pattern from the geometry import process. Of course, it is
+possible to improve the loop, as was done there, to include a time limit or use 
+parallel async computation of multiple meshes.
+
+Link Mesh to simulation
+-----------------------
+
+Finally, when the mesh is succesfully computed, we can link it to our simulation spec
+so the platform knows that it should use it as part of the simulation computation:
+
+
+.. code-block:: python
+
+    # Might not be needed if the simulation_spec object is updated
+    simulation_spec = simulations_api.get_simulation(project_id, simulation_id)
+
+    simulation_spec.mesh_id = mesh_operation.mesh_id
+
+    simulations_api.update_simulation(project_id, simulation_id, simulation_spec)
+
+
+Now our simulation is ready for computation, with its physics model and a mesh
+completely defined.