migflow.fluid

Model for Immersed Granular Flow: Fluid user interface

Contact: jonathan.lambrechts@uclouvain.be Webpage: www.migflow.be

MigFlow computes immersed granular flows using an unresolved FEM-DEM model. The continuous phase (mixture) is computed by solving averaged Navier-Stokes equations on unstructured meshes with the continuous finite element method.

class migflow.fluid.FluidProblem(dim, g, mu, rho, alpha=None, sigma=0, coeff_stab=0.01, volume_drag=0.0, quadratic_drag=0.0, solver=None, solver_options='', drag_in_stab=1, drag_coefficient_factor=1, temporal=True, advection=True, usolid=False, p2p1=False, full_implicit=False, model_b=False, temperature_element=None)

Bases: object

Creates the numerical representation of the fluid.

Builds the fluid structure.

Parameters

• dim (int) – Dimension of the problem

• g (ndarray) – Gravity vector

• mu (list) – List of fluid phases viscosities (this should be a vector whom dimension specify if there is one or two fluid)

• rho (list) – List of fluid phases densities (this should be a vector whom dimension specify if there is one or two fluid)

• alpha (Optional[list]) – List of fluid phases dilatation coefficients (this should be a vector whom dimension specify if there is one or two fluid)

• sigma (float) – Surface tension (only when there are two fluids)

• coeff_stab (float) – Optional argument used as coefficient for extra diffusivity added to stabilise the advection of concentration (only for two fluid problem)

• solver (Optional[str]) – possible solver are “pardiso”, “mumps”, “petsc”, “scipy”

• solver_options (str) – Optional argument to specify solver option (only when petsc is used)

• drag_in_stab (int) – States if the drag force is in the stabilisation term

• drag_coefficient_factor (int) – Factor multiplicating the drag coefficient

• temporal (bool) – Enables d/dt (i.e. False = steady)

• advection (bool) – Enables advective terms (i.e. False = Stokes, True = Navier-Stokes)

• usolid (bool) – if False, div.u_solid is evaluated = (porosity-old_porosity)/dt (depracted always True)

• p2p1 (bool) – if False, use p2p1 without stab, else a stabilised p1p1 formulation is used

• temperature_degree (int, optional) – degree of the temperature discretisation.

Raises

• ValueError – If the dimension differs from 2 or 3

• NameError – If C builder cannot be found

__del__()

Deletes the fluid structure.

adapt_mesh(mesh_file_name=None)

Project the current problem unto a new mesh.

mesh_file_name: Name of the msh file. If None the current gmsh model is loaded without the need of a msh file.

add_constraint(constraint_index, constraint_value)

advance_concentration(dt)

Solves the advection equation for the concentration using the current velocity field.

Parameters

dt (float) – Computation time step

assemble_weak_boundaries()

Assembles the weak boundaries contribution to the system.

Parameters

• localm – local mass matrix

• localv – local vector

boundary_force()

Give access to force exerted by the fluid on the boundaries.

Returns

Forces exerted by the fluid on the boundaries.

Return type

np.ndarray

boundary_force_by_contributions(bnd_name)

Returns the forces exerted respectively by the pressure gradient and the viscous stress tensor at the boundaries.

Parameters

bnd_name – boundary name

Returns

(2*D,) : the first D components are the pressure gradient contribution and the last D components are the viscous stress tensor contribution.

Return type

np.ndarray

bulk_force()

Gives access to the volume force at fluid nodes. :returns: Bulk force :rtype: np.ndarray

compute_cfl()

Computes the CFL number divided by the time step

compute_node_force(dt)

Computes the forces to apply on each grain resulting from the fluid motion.

Parameters

dt (float) – Computation time step

compute_node_torque(dt)

Computes the angular drags to apply on each grain resulting from the fluid motion. Only in 2D :type dt: float :param dt: Computation time step

concentration_dg()

Returns the concentration at discontinuous nodes.

Returns

concentration field

Return type

np.ndarray

concentration_dg_grad()

Returns the gradient of the concentration field at discontinuous nodes.

Returns

concentration gradient

Return type

np.ndarray

coordinates()

Gives access to the coordinate of the mesh nodes.

Returns

mesh nodal coordinates

Return type

np.ndarray

coordinates_fields()

Returns the coordinates of each degree of freedom of the solution.

Returns

fields coordinates

Return type

np.ndarray

curvature()

Returns the curvature at each element.

Returns

curvature

Return type

np.ndarray

dimension()

Returns the dimension of the problem

Returns

dimension

Return type

int

element_tags()

Gives read-only access to the tags of the elements of the mesh.

Returns

mesh elements ags

Return type

np.ndarray

elements()

Gives read-only access to the elements of the mesh.

Returns

mesh elements

Return type

np.ndarray

enable_stability(enable_pspg=True, enable_supg=True)

Enable stabilty flags in the fluid problem :type enable_pspg: bool :param enable_pspg: Enable PSPG stabilisation. Defaults to True. :type enable_pspg: bool, optional :type enable_supg: bool :param enable_supg: Enable SUPG stabilisation. Defaults to True. :type enable_supg: bool, optional

field_index(ifield)

Gives access to all the index of a field into the solution vector.

Parameters

ifield (int) – field index (0,..,dimension-1) is a velocity, dimension gives the pressure.

Returns

index array.

Return type

np.ndarray

fields_gradient()

Returns an continuous gradient estimation of each field on a P1 mesh.

Returns

Fields_gradient

Return type

np.ndarray

full_implicit_euler(**kwargs)

g()

Returns the gravity field.

Returns

gravity field

Return type

np.ndarray

get_default_export(dtype=<class 'numpy.float64'>)

Returns the default fields to write in your output as a dictionnary {field : (values, discretisation_element)} :param dtype: numpy representation. Defaults to np.float64.

Returns

default fields

Return type

dict

get_mapping(etype)

Get mapping associated to an element.

Parameters

etype (str) – element type (“P1”, “P1DG”, “P2”, “P2DG”)

Returns

mapping associated to the element type.

Return type

np.ndarray

get_p1_element()

Returns the P1 element used -> “triangle_p1” or “tetrahedron_p1”

Returns

“triangle_p1”

Return type

str

get_particle_forces(dt)

get_pressure_element()

Returns the discretisation element of the pressure field :returns: pressure element :rtype: str

get_temperature_element()

Returns the velocity element used.

Returns

“element use”

Return type

str

get_velocity_element()

Returns the discretisation element of the velocity field :returns: velocity element :rtype: str

global_map()

Gives access to the map of all the degrees of freedom.

Returns

global mapping

Return type

np.ndarray

ic_source()

implicit_euler(**kwargs)

implicit_euler_advect_nodes(**kwargs)

interpolate(solution=None, velocity=None, velocity_x=None, velocity_y=None, velocity_z=None, pressure=None)

Imposes the solution (or the field) to the prescribed value. If a callback is given, the solution (or field) is estimated at its local position. The solution (or field) is strongly imposed (not weakly).

Parameters

• solution (Union[ndarray, callable, None]) – imposed solution vector

• velocity (Union[ndarray, callable, None]) – imposed velocity vector.

• velocity_x (Union[ndarray, callable, None]) – imposed horizontal velocity component.

• velocity_y (Union[ndarray, callable, None]) – imposed horizontal velocity component.

• velocity_z (Union[ndarray, callable, None]) – imposed horizontal velocity component.

• pressure (Union[ndarray, callable, None]) – imposed pressure field.

load_msh(filename)

Sets the domain geometry for the fluid computation.

Parameters

filename (str) – Name of the msh file. If None the current gmsh model is loaded without the need to a msh file.

local_boundary_force_by_contribution(bnd_name)

Returns the forces exerted by the pressure gradient and the viscous stress at each edge of the boundary.

Parameters

bnd_name (_type_) – boundary name

Returns

the first D components are the pressure gradient contribution and the last D components are the viscous stress tensor contribution.

Return type

np.ndarray(n_edges, 2*D)

local_size()

Returns the number of degree of freedom by element.

Returns

number of degree of freedom by element

Return type

int

mesh_boundaries()

Returns the mesh boundaries information as a dictionnary : {boundary_number : edges} :returns: Mesh information : {boundary_number : edges} :rtype: dict

mesh_velocity()

Give access to the mesh velocity value at the mesh nodes.

Returns

mesh velocities at the mesh nodes

Return type

np.ndarray

move_particles(position, velocity, omega, contact)

Set location of the grains in the mesh and compute the porosity in each cell.

Parameters

• position (ndarray) – List of particles centre positions

• velocity (ndarray) – List of particles velocity

• omega (ndarray) – List of particles angular velocity

• contact (ndarray) – List of particles contact resultant forces

n_elements()

Returns the number of mesh elements.

Returns

number of elements

Return type

int

n_fields()

Returns the number of fluid fields.

Returns

number of fields

Return type

int

n_fluids()

Returns the number of fluids (only one or two).

Returns

Number of fluids

Return type

int

n_nodes()

Returns the number of mesh nodes.

Returns

number of nodes

Return type

int

node_volume()

Returns the volume associated with each node. :returns: node volume :rtype: np.ndarray

old_porosity()

Returns the old porosity.

Returns

old porosity

Return type

np.ndarray

parent_nodes()

Gives access to the parent nodes of each node.

Returns

The parent nodes mapping

Return type

np.ndarray

particle_element_id()

Returns the id of the mesh cell in which particles are located.

Returns

particle element id

Return type

np.ndarray

particle_position()

Gives access to the particles position. :returns: particles position :rtype: np.ndarray

particle_uvw()

Returns the coordinates of the particles inside their element :returns: parametric coordinates of the particles :rtype: np.ndarray

particle_velocity()

Gives access to the particles velocity. :returns: particles velocity :rtype: np.ndarray

particle_volume()

Gives access to the particles volume. :returns: particles volume :rtype: np.ndarray

particle_volume_intersected()

Return type

ndarray

porosity()

Returns the porosity at independant nodes.

Returns

volume fluid fraction

Return type

np.ndarray

pressure()

Reads the pressure solution.

Returns

pressure

Return type

np.ndarray

pressure_index()

Returns the index of the pressure field into the solution vector.

Returns

pressure index array

Return type

np.ndarray

read_mig(odir, t=None, iteration=None)

Reads output file to reload computation.

Parameters

• odir (str) – Directory in which to read the file

• t (Optional[float]) – Time at which to read the file

• read (iteration; iteration to) –

• iteration (-1 for last) –

read_vtk(dirname, i)

(DEPRECATED) Reads output file to reload computation.

Parameters

filename – Name of the file to read

set_concentration_cg(concentration)

Sets the concentration at nodes. :type concentration: ndarray :param concentration: concentration field

set_coordinates(x)

Sets the coordinates of the mesh nodes

Parameters

x (ndarray) – new nodes positions

set_mean_pressure(mean_pressure)

Enables the nodal mean pressure constraint and imposes its value.

Parameters

mean_pressure (float) – add a constraint to impose sum_i vol_i p_i = mean_pressure*volume

set_mesh(nodes, elements, elementTags, boundaries, advected_solution=None)

Sets the domain geometry for the fluid computation.

Parameters

• nodes (ndarray) – (n_node, 3) numpy float array of the nodes coordinates

• elements (and numpy int array with the corresponding boundary) – (n_elements, dimension+1) numpy int array of the elements

• elementsTags – (n_elements) numpy int array of the elements tags

• boundaries (list) – [(name, (n_elements, dimension))] list of pair of name (string)

• elements –

set_open_boundary(tag, velocity=None, pressure=None, concentration=None, viscous_flag=1)

Sets the weak open boundaries (=normal fluxes) for the fluid problem.

Parameters

• tag (Union[str, List[str]]) – Physical tag (or list of tags), set in the mesh, of the open boundaries

• velocity (Union[float, callable, None]) – The velocity value if imposed (callback or number)

• pressure (Union[float, callable, None]) – The pressure value if imposed (callback or number)

• concentration (Union[float, callable, None]) – Concentration outside the boundary

• viscous_flag (bool) – Flag to compute the viscous term at the boundary

set_particles(delassus, volume, position, velocity, omega, contact)

Set location of the grains in the mesh and compute the porosity in each cell.

Parameters

• delassus (ndarray) – List of particles delassus operators

• volume (ndarray) – List of particles volume

• position (ndarray) – List of particles centre positions

• velocity (ndarray) – List of particles velocity

• omega (ndarray) – List of particles angular velocity

• contact (ndarray) – List of particles contact resultant forces

set_stability_flags(pspg=True, supg=True, lsic=True)

Set the stability flags into the Fluid Problem structure. One can enable/disable : the pspg, supg and lsic stabilisations.

set_strong_boundary(tag, pressure=None, velocity=None, velocity_x=None, velocity_y=None, velocity_z=None, solution=None)

Sets the strong boundaries (=constrains) for the fluid problem.

Parameters

• tag (str) – Physical tag (set in the mesh) of the boundary on which the constraint is added

• pressure (Union[float, callable, None]) – value or callback assigned to the pressure field

• velocity (Union[float, callable, None]) – value or callback assigned to the velocity field

• velocity_x (Union[float, callable, None]) – value or callback assigned to the velocity_x field

• velocity_y (Union[float, callable, None]) – value or callback assigned to the velocity_y field

• velocity_z (Union[float, callable, None]) – value or callback assigned to the velocity_z field

• solution (Union[float, callable, None]) – value or callback assigned to the solution field

set_symmetry_boundary(tag, pressure=None)

Sets the weak symmetry boundaries (=normal fluxes) for the fluid problem.

Parameters

• tag (Union[str, List[str]]) – Physical tag (or list of tags), set in the mesh file, of the symmetry boundaries

• pressure (Union[float, callable, None]) – The pressure value if imposed (callback or number)

set_wall_boundary(tag, pressure=None, velocity=None, viscous_flag=None)

Sets the weak wall boundaries (=normal fluxes) for the fluid problem.

Parameters

• tag (Union[str, List[str]]) – Physical tag (or list of tags), set in the mesh, of the wall boundaries

• pressure (Union[float, callable, None]) – The pressure value if imposed (callback or number)

• velocity (Union[float, callable, None]) – The velocity value if imposed (callback or number)

• viscous_flag (Optional[bool]) – Flag to compute the viscous term at the boundary

set_weak_boundary(tag, pressure=None, velocity=None, concentration=None, viscous_flag=None)

Sets the weak boundaries (=normal fluxes) for the fluid problem.

Parameters

• tag (Union[str, List[str]]) – Physical tag (or list of tags), set in the mesh, of the weak boundaries

• pressure (Union[float, callable, None]) – The pressure value if imposed (callback or number)

• velocity (Union[float, callable, None]) – The velocity value if imposed (callback or number)

• concentration (Union[float, callable, None]) – Concentration outside the boundary

• viscous_flag (Optional[bool]) – Flag to compute the viscous term at the boundary

set_weak_boundary_nodal_values(tag, values)

Set the nodal values to use for the weak boundary instead of using a callback or a prescribed value. Only available for p1p1 formulation.

Parameters

• tag (str) – Physical tag (or list of tags), set in the mesh

• values (ndarray) – nodal values imposed on the boundary

Raises :

ValueError: if the tag is not found

solution()

Gives access to the fluid field value at each degree of freedom as a flat array.

Returns

fluid solution

Return type

np.ndarray

solution_at_coordinates(x)

Returns the solution vector interpolated at the given coordinates.

Parameters

x (ndarray) – coordinates

Returns

solution at given coordinates

Return type

np.ndarray

temperature()

Reads the temperature.

Returns

temperature

Return type

np.ndarray

u_background()

Sets the background velocity field at each node.

Parameters

u – background velocity field

Return type

ndarray

u_solid()

Returns the solid velocity as a p1-continuous field.

Returns

solid velocity

Return type

np.ndarray

u_solid_star(dt)

Returns the solid velocity as a p1-continuous field.

Returns

solid velocity

Return type

np.ndarray

update_node_volume()

Update the nodes volume

velocity()

Reads the velocity solution.

Returns

velocity

Return type

np.ndarray

velocity_index()

Returns the index of the velocities into the solution vector as a bidimensionnal array.

Returns

velocities index array

Return type

np.ndarray

volume_flux(bnd_tag)

Computes the integral of the (outgoing) normal velocity through boundary with tag bnd_tag.

Returns

volume flux

Return type

float

write_mig(output_dir, t, fields=None, mesh_dtype=<class 'numpy.float64'>)

Writes the output files for post-visualization. Metadata are stored into a file called “fluid.migf” while the data are stored into the “fluid” directory. :type output_dir: str :param output_dir: Output directory :type t: float :param t: Computational time :param extra_fields: extra field as a dictionnary {name : values at p1 degree of freedom}

write_vtk(output_dir, it, t)

(DEPRECATED) Writes output file for post-visualization. :param output_dir: Output directory :param it: Computation iteration :param t: Computation time

migflow.fluid.removeprefix(str, prefix)

Return type

str