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Cylindrical spouted-bed: Improve documentation of the example and fix…
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… typos (#1373)

Description
This PR improves the documentation for the cylindrical spouted bed example. The example works very well, but the timing reported in the documentation were completly off (like so off it makes no sense. For example it was reported that the example would take 8 days to run, it took 5 hours on my computer while I was doing other stuff and other simulations at the same time). I have simplified the wording of the example and improved the discussion. The animations and etc. I have not touched, they are already great as they are. The example works fine as is though.

Co-authored-by: Laura Prieto Saavedra <[email protected]>
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blaisb and lpsaavedra authored Nov 21, 2024
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50 changes: 20 additions & 30 deletions ...olved-cfd-dem/gas-solid-spouted-cylinder-bed/gas-solid-spouted-cylinder-bed.rst
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Expand Up @@ -13,7 +13,7 @@ Features
- Simulates a solid-gas cylinder-shaped spouted bed

---------------------------
Files Used in This Example
Files Used in this Example
---------------------------

Both files mentioned below are located in the example's folder (``examples/unresolved-cfd-dem/gas-solid-spouted-cylinder-bed``).
Expand All @@ -25,13 +25,13 @@ Both files mentioned below are located in the example's folder (``examples/unres
Description of the Case
-----------------------

This example simulates the spouting of spherical particles in air in a cylinder. As noted in the example of `Gas-Solid Spouted Bed <../gas-solid-spouted-bed/gas-solid-spouted-bed.html>`_, we use ``lethe-particles`` to fill the bed with particles, and ``lethe-fluid-particles`` as the CFD-DEM solver.
This example simulates the spouting of spherical particles in a cylinder. As noted in the example of `Gas-Solid Spouted Bed <../gas-solid-spouted-bed/gas-solid-spouted-bed.html>`_, we use ``lethe-particles`` to fill the bed with particles, and ``lethe-fluid-particles`` as the unresolved CFD-DEM solver.

-------------------
DEM Parameter File
-------------------

Here, we will focus only on the parts that have been modified compared to `Gas-Solid Spouted Bed <../gas-solid-spouted-bed/gas-solid-spouted-bed.html>`_. It is also strongly recommended to visit `DEM parameters <../../../parameters/dem/dem.html>`_ for a detailed description on the concepts and physical meanings of the DEM parameters.
Here, we will focus only on the parts that have been modified compared to the `Gas-Solid Spouted Bed <../gas-solid-spouted-bed/gas-solid-spouted-bed.html>`_ example. It is also strongly recommended to visit the `DEM parameters <../../../parameters/dem/dem.html>`_ for a detailed description on the concepts and physical meanings of the DEM parameters.

Mesh
~~~~~
Expand All @@ -44,15 +44,15 @@ In this example, we are simulating a cylinder shaped spouted bed. We introduce t
:name: geometry
:height: 15cm

The geometry of the bed was created using `Pointiwise <../../../tools/pointwise/pointowise.html>`_, and the overview of created mesh is:
The geometry of the bed was created using `Pointwise <../../../tools/pointwise/pointwise.html>`_. An overview of the mesh is:

.. image:: images/mesh.png
:alt: The geometry and boundary conditions
:align: center
:name: mesh_ver
:height: 10cm

In unresolved CFD-DEM, the averaging volume used to calculate the void fraction needs to be large enough to contain several particles (>10). Since the averaging volume used in the quadrature-centred method is generally related to the cell volume, this introduces a limitation on the cell size. In general, the averaging volume, which in this case is controlled by the cell size, should be approximately three time larger than the diameter of the particles in order to get stable calculation.
In unresolved CFD-DEM, the averaging volume used to calculate the void fraction needs to be large enough to contain several particles (>10). Since the averaging volume used in the quadrature-centred method is generally related to the cell volume, this introduces a limitation on the cell size. In general, the averaging volume, which in this case is controlled by the cell size, should be approximately three times larger than the diameter of the particles in order to get stable calculation.

.. code-block:: text
Expand All @@ -67,7 +67,7 @@ where the file name includes the path to the mesh file. Here, we activate ``expa
Lagrangian Physical Properties
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The physical properties section is almost the same as the previous spouted bed example. Here, parameters for the gravity, the diameter, density, and the number of particles are modified. In this simulation, we use 100,000 particles with a 5 mm diameter.
In this simulation, we use 100,000 particles with a 5 mm diameter. The rest of the particle properties are relatively standard.

.. code-block:: text
Expand All @@ -78,13 +78,13 @@ The physical properties section is almost the same as the previous spouted bed e
set diameter = 0.005
set number = 100000
set density particles = 100
set young modulus particles = 10000000
set young modulus particles = 1e7
set poisson ratio particles = 0.25
set restitution coefficient particles = 0.97
set friction coefficient particles = 0.4
set rolling friction particles = 0.3
end
set young modulus wall = 10000000
set young modulus wall = 1e7
set poisson ratio wall = 0.25
set restitution coefficient wall = 0.33
set friction coefficient wall = 0.2
Expand All @@ -94,7 +94,7 @@ The physical properties section is almost the same as the previous spouted bed e
Insertion Info
~~~~~~~~~~~~~~~~~~~

The ``insertion info`` subsection manages the insertion of particles. The insertion box parameter is set so that it can fit in the cylinder.
The ``insertion info`` subsection manages the insertion of particles. The insertion box parameter is set so that it can fit within the cylinder.

.. code-block:: text
Expand All @@ -111,7 +111,7 @@ The ``insertion info`` subsection manages the insertion of particles. The insert
Floating Walls
~~~~~~~~~~~~~~~~~~~

When we pack the cylinder with particles, we need to keep them inside and prevent them from falling through the small inlet channel. To do so, we place a floating wall at the bottom of the cylinder, which is :math:`z = 0` plain, as in:
We place a floating wall at the bottom of the cylinder, which is at :math:`z = 0`, to ensure that the particles remain within the cylinder during the loading step.

.. code-block:: text
Expand All @@ -136,29 +136,29 @@ When we pack the cylinder with particles, we need to keep them inside and preven
---------------------------
Running the DEM Simulation
---------------------------
Launching the simulation is as simple as specifying the executable name and the parameter file. Assuming that the ``lethe-particles`` executable is within your path, the simulation can be launched in parallel as follows:
Assuming that the ``lethe-particles`` executable is within your path, the simulation can be launched in parallel as follows:

.. code-block:: text
:class: copy-button
mpirun -np 8 lethe-particles packing-particles.prm
.. note::
Running the packing should take approximately 10 hours on 8 cores using Intel(R) Core(TM) i7-9700K.
Running the packing should take approximately 10 minutes on 8 cores.

After the particles have been packed inside the square bed, we can move on to the fluid-particles simulation.
After the particles have been packed inside the bed, we can move on to the fluid-particles simulation.


-----------------------
CFD-DEM Parameter File
-----------------------

The CFD-DEM simulation is carried out using the packed bed previously generated. Here we will focus on the modified section as well. We recommend visiting `Unresolved CFD-DEM Parameters Guide <../../../parameters/unresolved-cfd-dem/unresolved-cfd-dem.html>`_ for a detailed description.
The CFD-DEM simulation is carried out using the packed bed previously generated. Here we will focus on the modified section as well. We recommend visiting the `Unresolved CFD-DEM Parameters Guide <../../../parameters/unresolved-cfd-dem/unresolved-cfd-dem.html>`_ for a detailed description.

Simulation Control
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The simulation is run for 5 seconds with a time step of 0.001 seconds. The time scheme and setting for output is shown as follows.
The simulation is run for 5 seconds with a time step of 0.001 seconds. The time scheme and setting for output is shown as follows:

.. code-block:: text
Expand Down Expand Up @@ -189,8 +189,7 @@ We set the inlet velocity to 2.5 m/s, and the background velocity to 0.5 m/s on
subsection boundary conditions
set time dependent = false
set number = 5
subsection bc 0 #outlet
set id = 3
set type = outlet
Expand Down Expand Up @@ -239,7 +238,7 @@ We set the inlet velocity to 2.5 m/s, and the background velocity to 0.5 m/s on
CFD-DEM
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here, we enable grad-div stabilization , and take the time derivative of the void fraction into account.
Here, we enable grad-div stabilization, and take the time derivative of the void fraction into account.

.. code-block:: text
Expand Down Expand Up @@ -267,20 +266,13 @@ Running the CFD-DEM Simulation

The simulation is run using the ``lethe-fluid-particles`` application. Assuming that the ``lethe-fluid-particles`` executable is within your path, the simulation can be launched as per the following command:

.. code-block:: text
:class: copy-button
lethe-fluid-particles gas-solid-spouted-cylinder-bed.prm
or in parallel (where 8 represents the number of processors)

.. code-block:: text
:class: copy-button
mpirun -np 8 lethe-particles gas-solid-spouted-cylinder-bed.prm
.. note::
Running the packing should take approximately 8 days on 8 cores using Intel(R) Core(TM) i7-9700K.
Running the packing should take approximately 5 days on 8 cores.

---------
Results
Expand All @@ -291,9 +283,7 @@ We briefly discuss the results that can be obtained from this example here.
Total Pressure Drop
~~~~~~~~~~~~~~~~~~~

Here, we show the simulated pressure drop.

This graph illustrates the variation of pressure drop from 1 second to 5 seconds. We can see the pressure oscillation which is caused by the bubbly state.
The following plot illustrates the variation of pressure drop from 1 second to 5 seconds. We can see the pressure oscillation which is caused by the bubbly state of the spouted bed.

.. image:: images/pressure_drop.png
:alt: Pressure drop as a function of time
Expand All @@ -302,7 +292,7 @@ This graph illustrates the variation of pressure drop from 1 second to 5 seconds

Visualization
~~~~~~~~~~~~~
The results are shown in an animation below. As seen, the bubbly flow can be observed on the right side. the color of the particles represents their IDs, allowing for the visualization of the mixing. On the left side, we show the fluid velocity field.
In the following animation, the bubbly flow can be observed on the right side. the color of the particles represents their IDs, allowing for the visualization of the mixing. On the left side, we show the fluid velocity field.

.. raw:: html

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25 changes: 14 additions & 11 deletions ...ples/unresolved-cfd-dem/gas-solid-spouted-cylinder-bed/gas-solid-spouted-cylinder-bed.prm
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Expand Up @@ -11,12 +11,12 @@ set dimension = 3
#---------------------------------------------------

subsection simulation control
set method = bdf2
set number mesh adapt = 0
set output frequency = 50
set time end = 5
set time step = 0.001
set output path = output/
set method = bdf2
set number mesh adapt = 0
set output frequency = 50
set time end = 5
set time step = 0.001
set output path = output/
end

#---------------------------------------------------
Expand All @@ -39,6 +39,10 @@ subsection FEM
set pressure order = 1
end

#---------------------------------------------------
# Timer
#---------------------------------------------------

subsection timer
set type = iteration
end
Expand Down Expand Up @@ -118,7 +122,6 @@ end
# Boundary Conditions
#---------------------------------------------------


subsection boundary conditions
set time dependent = false
set number = 5
Expand All @@ -144,16 +147,16 @@ subsection boundary conditions
end

subsection bc 2 #wall
set id = 6
set id = 6
set type = slip
end

subsection bc 3 #channel_wall
set id = 5
set id = 5
set type = slip
end
subsection bc 4 #bed_wall_bottom

subsection bc 4 #bed_wall_bottom
set id = 4
set type = function
subsection u
Expand Down

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