pipemesh 0.2.2

A package for making pipe network meshes.

pipemesh

These tools use the GMSH-SDK (or GMSH API), available here.

The documentation for pipemesh can be found here.

Installation

python3 -m pip install --user pipemesh

Once completed, navigate to site-packages/pipemesh. Place the files libgmsh.so, libgmsh.so.4.3 and libgmsh.so.4.3.0, which can be downloaded from the GMSH website (link above).

pipes.py

Using the pieces above and the Network class, pipes and pipe networks can be easily built. A Network is started with:

from pipemesh import pipes
network = pipes.Network(1, 0.3, [1,0,0], 0.1)

Then added to using one of the following commands:

network.add_cylinder(1, 0.1, out_number=1)
network.add_t_junction([-1,-1,0], 0.05)
network.add_curve([0,1,0], 0.5, 0.05)
network.add_mitered([0, 1, 0], 0.05, out_number=2)

Where out_number specifies which outlet of the pipe the piece will be added to. For more information on each function, the documentation is currently only within the files.

Examples:

• Chicane with mitered bends:

network = pipes.Network(1, 0.3, [1,0,0], 0.1)
network.add_cylinder(1, 0.1)
network.add_mitered([0,1,0], 0.1)
network.add_cylinder(1, 0.1)
network.add_mitered([1,0,0], 0.1)
network.add_cylinder(1, 0.1)

• Pipe with two junctions:

network.add_t_junction([-1,1,0], 0.05)
network.add_t_junction([-1,-1,0], 0.05)
network.add_cylinder(1, 0.1, out_number=2)
network.add_curve([-1,0,0], 0.5, 0.05, out_number=3)
network.add_cylinder(1.5, 0.1, out_number=3)

Once the network is complete, you can fuse the objects together and create physical surfaces and volumes, and set the local mesh sizes. Information can be obtained and written to file. This is all done with one call.

network.generate(filename="example", binary=False, write_info=False, mesh_format="msh2", write_xml=False run_gui=False)

Which will write the file "example.msh", as a msh2 binary file.

Network has get_phys_ids methods, which can be used with AutoMPML.

Requirements for pipes.py:

• libgmsh.so, libgmsh.so.4.3, libgmsh.so.4.3.0 from the GMSH SDK.
• NumPy, SciPy

AutoMPML

The file auto_mpml.py contains the class AutoMPML. This edits a basic pipe flow simulation .mpml file used with IC-FERST by inputting the user values in the right places. This isn't actually automatic, but can save time by not editing mpml files with Diamond. Options that can be changed are relevant to conducting a pipe flow investigation with IC-FERST.

Example:

from pipemesh import pipes
from pipemesh.icferst import auto_mpml

# Generate a network
network = pipes.Network(0.1, 0.3, [0, 0, -1], 0.1)
network.add_t_junction([1, 0, 1], 0.1)
network.generate(filename="pipe", binary=True, write_info=True, write_xml=True, run_gui=False)

# Get physical ids of inlets and outlets
entry_phys_ids = network.get_inlet_outlet_phys_ids()
# Get physical ids of cylinder surfaces
cyl_phys_ids = network.get_cyl_phys_ids()
# Select the inlet and the first outlet as inlets
inlets = entry_phys_ids[:2]
# Select the remainding inlet/outlets as outlets
outlets = entry_phys_ids[2:]

# Get velocity vectors for velocity magnitude 0.02
vel = 0.02
inlet_velocities = network.get_velocities_vel_mag(inlets, vel, 1000, 1e-3)

# Create options object
options = auto_mpml.AutoMPML()
# Change various options (the defaults are fairly sensible)
options.set_all(sim_name="junction_flow_test_case",
                msh_file="src/pipe",
                dump_ids=entry_phys_ids,
                density=1000,
                inlet_phys_ids=inlets, inlet_velocities=inlet_velocities,
                outlet_phys_ids=outlets,
                cyl_phys_ids=cyl_phys_ids,
                max_no_nodes=10000,
                min_mesh_size=0.2,
                finish_time=1.0,
                t_adapt_delay=0.5
                )
# Write mpml file - extension not needed.
options.write_mpml("generated_mpml")

As the options can be set in python, this means that multiple simulations can be set up, with for example, varying reynolds numbers or varying input surfaces. For full information on what settings can be changed, visit the documentation.

pieces.py

Contains classes (and some useful functions for said classes) which represent cylindrical GMSH objects. The classes store information of the object, such as the centre and direction of its faces, as well as functions to update the information when transformations are applied to them. This makes the information a little easier to access than using just the GMSH API. To use these individually start your file with:

from pipemesh import pieces
model = gmsh.model
mesh = model.mesh
gmsh.initialize()
gmsh.option.setNumber("Mesh.CharacteristicLengthMax", 0.1)  # max mesh length
model.add("Example")  # optional, add a model name.

The available pieces to put in are:

• Cylinder

piece = pieces.Cylinder(1, 0.5, [1,0,0], 0.1)
# Length, radius, direction, mesh size

• Cylinder with changing radius

piece = pieces.ChangeRadius(2, 1.8, 0.3, 0.2, [1 ,0, 0], 0.1)
# length, change length, start radius, end radius, direction, mesh size

• Smooth bends

piece = pieces.Curve(0.5, [1,0,-1], [0,1,0], 1, 0.2)
# radius of cylinder, in direction, out direction, bend radius, mesh size

• Mitered bends

piece = pieces.Mitered(0.5, [0, 1, 0], [1, 0, 0], 0.2)
# radius of cylinder, in direction, out direction, mesh size

• T Junctions

piece = pieces.TJunction(0.5, [1, 0, 0], [1, 1, -1], 0.1)
# radius, direction, t direction, mesh size

The mesh can be created and saved using:

mesh.generate(3)
gmsh.option.setNumber("Mesh.Binary", 1)  # 1 for binary, 0 for ASCII
gmsh.write(filename.msh)  # .msh2 for legacy format

To view the mesh in the GMSH GUI, call

gmsh.fltk.run()

To finish, and end use of gmsh, call

gmsh.finalize()

As of yet, just using the pieces on their own is limited, as they do not have translate, or rotate functions, but if desired, the user can look into the GMSH-SDK and develop some, or use pipes (below) to generate pipe meshes.