211 lines
7.1 KiB
Python
211 lines
7.1 KiB
Python
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import tempfile
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import numpy as np
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def load_gmsh(file_name, gmsh_args=None):
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"""
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Returns a surface mesh from CAD model in Open Cascade
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Breap (.brep), Step (.stp or .step) and Iges formats
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Or returns a surface mesh from 3D volume mesh using gmsh.
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For a list of possible options to pass to GMSH, check:
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http://gmsh.info/doc/texinfo/gmsh.html
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An easy way to install the GMSH SDK is through the `gmsh-sdk`
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package on PyPi, which downloads and sets up gmsh:
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>>> pip install gmsh-sdk
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Parameters
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--------------
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file_name : str
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Location of the file to be imported
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gmsh_args : (n, 2) list
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List of (parameter, value) pairs to be passed to
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gmsh.option.setNumber
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max_element : float or None
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Maximum length of an element in the volume mesh
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Returns
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------------
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mesh : trimesh.Trimesh
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Surface mesh of input geometry
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"""
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# use STL as an intermediate format
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from ..exchange.stl import load_stl
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# do import here to avoid very occasional segfaults
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import gmsh
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# start with default args for the meshing step
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# Mesh.Algorithm=2 MeshAdapt/Delaunay, there are others but they may include quads
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# With this planes are meshed using Delaunay and cylinders are meshed
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# using MeshAdapt
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args = [("Mesh.Algorithm", 2),
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("Mesh.CharacteristicLengthFromCurvature", 1),
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("Mesh.MinimumCirclePoints", 32)]
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# add passed argument tuples last so we can override defaults
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if gmsh_args is not None:
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args.extend(gmsh_args)
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# formats GMSH can load
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supported = ['.brep', '.stp', '.step', '.igs', '.iges',
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'.bdf', '.msh', '.inp', '.diff', '.mesh']
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# check extensions to make sure it is supported format
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if file_name is not None:
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if not any(file_name.lower().endswith(e)
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for e in supported):
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raise ValueError(
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'Supported formats are: BREP (.brep), STEP (.stp or .step), ' +
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'IGES (.igs or .iges), Nastran (.bdf), Gmsh (.msh), Abaqus (*.inp), ' +
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'Diffpack (*.diff), Inria Medit (*.mesh)')
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else:
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raise ValueError('No import since no file was provided!')
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# if we initialize with sys.argv it could be anything
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gmsh.initialize()
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gmsh.option.setNumber("General.Terminal", 1)
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gmsh.model.add('Surface_Mesh_Generation')
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gmsh.open(file_name)
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# create a temporary file for the results
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out_data = tempfile.NamedTemporaryFile(suffix='.stl', delete=False)
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# windows gets mad if two processes try to open the same file
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out_data.close()
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# we have to mesh the surface as these are analytic BREP formats
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if any(file_name.lower().endswith(e)
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for e in ['.brep', '.stp', '.step', '.igs', '.iges']):
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gmsh.model.geo.synchronize()
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# loop through our numbered args which do things, stuff
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for arg in args:
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gmsh.option.setNumber(*arg)
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# generate the mesh
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gmsh.model.mesh.generate(2)
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# write to the temporary file
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gmsh.write(out_data.name)
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else:
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gmsh.plugin.run("NewView")
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gmsh.plugin.run("Skin")
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gmsh.view.write(1, out_data.name)
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# load the data from the temporary outfile
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with open(out_data.name, 'rb') as f:
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kwargs = load_stl(f)
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return kwargs
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def to_volume(mesh,
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file_name=None,
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max_element=None,
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mesher_id=1):
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"""
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Convert a surface mesh to a 3D volume mesh generated by gmsh.
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An easy way to install the gmsh sdk is through the gmsh-sdk
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package on pypi, which downloads and sets up gmsh:
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pip install gmsh-sdk
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Algorithm details, although check gmsh docs for more information:
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The "Delaunay" algorithm is split into three separate steps.
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First, an initial mesh of the union of all the volumes in the model is performed,
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without inserting points in the volume. The surface mesh is then recovered using H.
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Si's boundary recovery algorithm Tetgen/BR. Then a three-dimensional version of the
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2D Delaunay algorithm described above is applied to insert points in the volume to
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respect the mesh size constraints.
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The Frontal" algorithm uses J. Schoeberl's Netgen algorithm.
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The "HXT" algorithm is a new efficient and parallel reimplementaton
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of the Delaunay algorithm.
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The "MMG3D" algorithm (experimental) allows to generate
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anisotropic tetrahedralizations
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Parameters
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--------------
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mesh : trimesh.Trimesh
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Surface mesh of input geometry
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file_name : str or None
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Location to save output, in .msh (gmsh) or .bdf (Nastran) format
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max_element : float or None
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Maximum length of an element in the volume mesh
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mesher_id : int
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3D unstructured algorithms:
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1: Delaunay, 4: Frontal, 7: MMG3D, 10: HXT
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Returns
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------------
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data : None or bytes
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MSH data, only returned if file_name is None
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"""
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# do import here to avoid very occasional segfaults
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import gmsh
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# checks mesher selection
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if mesher_id not in [1, 4, 7, 10]:
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raise ValueError('unavilable mesher selected!')
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else:
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mesher_id = int(mesher_id)
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# set max element length to a best guess if not specified
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if max_element is None:
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max_element = np.sqrt(np.mean(mesh.area_faces))
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if file_name is not None:
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# check extensions to make sure it is supported format
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if not any(file_name.lower().endswith(e)
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for e in ['.bdf', '.msh', '.inp', '.diff', '.mesh']):
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raise ValueError(
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'Only Nastran (.bdf), Gmsh (.msh), Abaqus (*.inp), ' +
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'Diffpack (*.diff) and Inria Medit (*.mesh) formats ' +
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'are available!')
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# exports to disk for gmsh to read using a temp file
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mesh_file = tempfile.NamedTemporaryFile(suffix='.stl', delete=False)
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mesh_file.close()
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mesh.export(mesh_file.name)
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# starts Gmsh Python API script
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gmsh.initialize()
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gmsh.option.setNumber("General.Terminal", 1)
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gmsh.model.add('Nastran_stl')
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gmsh.merge(mesh_file.name)
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dimtag = gmsh.model.getEntities()[0]
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dim = dimtag[0]
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tag = dimtag[1]
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surf_loop = gmsh.model.geo.addSurfaceLoop([tag])
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gmsh.model.geo.addVolume([surf_loop])
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gmsh.model.geo.synchronize()
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# We can then generate a 3D mesh...
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gmsh.option.setNumber("Mesh.Algorithm3D", mesher_id)
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gmsh.option.setNumber("Mesh.CharacteristicLengthMax", max_element)
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gmsh.model.mesh.generate(3)
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dimtag2 = gmsh.model.getEntities()[1]
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dim2 = dimtag2[0]
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tag2 = dimtag2[1]
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p2 = gmsh.model.addPhysicalGroup(dim2, [tag2])
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gmsh.model.setPhysicalName(dim, p2, 'Nastran_bdf')
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data = None
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# if file name is None, return msh data using a tempfile
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if file_name is None:
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out_data = tempfile.NamedTemporaryFile(suffix='.msh', delete=False)
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# windows gets mad if two processes try to open the same file
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out_data.close()
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gmsh.write(out_data.name)
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with open(out_data.name, 'rb') as f:
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data = f.read()
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else:
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gmsh.write(file_name)
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# close up shop
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gmsh.finalize()
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return data
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