3 \page blsurf_hypo_page MG-CADSurf Parameters hypothesis (former BLSURF
10 \section blsurf_general_parameters General parameters
12 \image html blsurf_parameters.png
14 - <b>Name</b> - allows defining the name of the hypothesis (MG-CADSurf
15 Parameters_n by default).
17 - <b>Physical Mesh</b> - can be set to <em>None</em>, <em>Global size</em>
18 or <em>Local size</em>
20 - if set to <em>Global size</em>, only the <b>User size</b>,
21 <b>Max Size</b> and <b>Min Size</b> fields are taken into account.
23 - if set to <em>Local size</em>, behaves like <em>Custom</em> mode and takes into
24 account the "Gradation" parameter and the custom elements sizes given in the
27 - <b>Geometrical mesh</b> - can be set to <em>None</em>, <em>Global size</em>
29 - if set to <em>Global size</em>, allows user input in <b>Mesh angle</b>,
30 <b>Mesh distance</b> and <b>Gradation</b> fields. These fields control
31 computation of the element size, so called <i>geometrical size</i>, conform
32 to the surface geometry considering local curvatures. If both the <b>User size</b>
33 and the <i>geometrical parameters</i> are defined, the eventual element size
34 corresponds to the least of the two.
36 - <b>User size</b> - defines the size of the generated mesh elements. If "Relative value"
37 is checked, the value is relative to the diagonal of the shape.
39 - <b>Max Size</b> - defines the upper limit of mesh element size. If "Relative value"
40 is checked, the value is relative to the diagonal of the shape.
42 - <b>Min Size</b> - defines the lower limit of mesh element size. If "Relative value"
43 is checked, the value is relative to the diagonal of the shape.
45 - <b>Gradation</b> - maximum ratio between the lengths of two adjacent edges.
47 - <b>Quadratic mesh</b> - if checked, quadratic elements will be generated.
49 - <b>Mesh angle</b> - Limiting angle (in degree) between the plane of a triangle of the mesh and each of the tangent planes at the three vertices.
50 The smaller this angle is, the closer the mesh is to the exact surface, and the denser the resulting mesh is.
52 - <b>Mesh distance</b> - Maximum desired distance between a triangle and its supporting CAD surface.
53 The smaller this distance is, the closer the mesh is to the exact surface (only available in isotropic meshing).
55 - <b>Anisotropic</b> - if checked, this parameter defines the maximum anisotropic ratio of the metric governing the anisotropic meshing process.
56 The default value (0) means that the metric (and thus the generated elements) can be arbitrarily stretched.
58 - <b>Remove tiny edges</b> - if checked, the tiny (nano) edges are removed from the generated mesh.
59 The tiny edge value defines the minimal length under which an edge is considered to be a tiny one.
61 - <b>Remove bad elements</b> - if checked, the bad elements (slivers) are removed from the generated mesh.
62 The bad element value defines the aspect ratio triggering the "bad element” classification.
64 - <b>Mesh optimisation</b> - if checked, the mesh will be optimized in order to get better shaped elements.
66 - <b>Allow Quadrangles</b> - if checked, allows the creation of quadrilateral elements.
68 \ref blsurf_top "Back to top"
70 \section blsurf_advanced_parameters Advanced parameters
72 The notion of <i>diag</i> used in the descriptions means the diagonal of the bounding box of the geometrical object to mesh.
74 \image html blsurf_parameters_advanced.png
76 - <b>PreCAD options</b> -if checked, the PreCAD module will be used. This module has
79 - Complete missing or inadequate CAD descriptions.
81 - Perform topology reconstruction and specific geometry
82 enhancement for mesh generation.
84 \n This module requires a specific licence. The following PreCAD
85 options are the most significant and important ones:
87 - <b>Merge Edges</b> - allows PreCAD to optimize the geometry by merging some
88 edges. This option is checked by default.
90 - <b>Process 3D topology</b> - allows PreCAD to perform the cleanup processing.
91 This option is checked by default.
93 - <b>Discard input topology</b> - computes the CAD topology from scratch,
94 without considering the topological information contained in the original CAD
95 (useful for iges files). This option is unchecked by default.
97 - <b>Verbosity level</b> - defines the percentage of "verbosity" of
98 MeshGems-CADSurf and MeshGems-PreCAD [0-100].
100 - <b>ExportGMF</b> - saves the computed mesh into a GMF file (.mesh or .meshb).
102 - <b>Add option</b> - provides the choice of multiple PreCAD and MG-CADSurf
103 advanced options, which appear, if selected, in a table where it is
104 possible to input the value of the option and edit it later.
106 - <b>Clear option</b> - removes the option selected in the table.
108 The following MG-CADSurf options are commonly usable:
110 - \b frontal (integer)
112 - 1 - the mesh generator inserts points with an advancing front method.
114 - 0 - it inserts them with an algebraic method (on internal edges). This method is
115 slightly faster but generates less regular meshes.
119 - \anchor blsurf_hinterpol_flag \b hinterpol_flag (integer) - determines the computation of an
120 interpolated value <i>v</i> between two points <i>P1</i> and <i>P2</i> on a
121 curve. Let <i>h1</i> be the value at point <i>P1,</i> <i>h2</i> be the value at point
122 <i>P2,</i> and <i>t</i> be a parameter varying from 0 to 1 when moving from <i>P1
125 - 0 - the interpolation is linear: \f$v = h1 + t (h2 - h1 )\f$
127 - 1 - the interpolation is geometric: \f$v = h1 \times \left( \frac{h1}{h2} \right)^{t}\f$
129 - 2 - the interpolation is sinusoidal: \f$v = \frac{h1+h2}{2} + \frac{h1-h2}{2 \cdot \cos(\pi \cdot t)}\f$
133 - \anchor blsurf_hmean_flag \b hmean_flag (integer) - determines the computation of the average of several
136 - -1 - the minimum is computed.
138 - 0 or 2 - the arithmetic average is computed.
140 - 1 - the geometric average is computed.
144 The following PreCAD options are commonly usable.
146 - \b closed_geometry (boolean) - describes whether the working geometry
147 should be closed or not. When activated, this option helps PreCAD to process
148 the dirtiest geometries. By default this option is 0.
150 - \b create_tag_collision (boolean) - creates new tags from original ones in case
151 of collision (entity merge or association for example). By default
154 - \b debug (bool) - If debug = 1 PreCAD will be very verbose and will output
155 some intermediate files in the working directory. By default this
158 - \b manifold_geometry (int) - describes whether the working geometry should be manifold or not.
159 When activated, this option helps PreCAD to process the dirtiest
160 geometries. By default this option is 0.
162 - \b periodic_tolerance (real) - defines the maximum distance error accepted between
163 two sets of periodic entities. By default this option is \f$\mathrm{diag} \times 10^{-5}\f$.
165 - \b remove_tiny_edges (boolean) -optimize the geometry by removing the nano edges whenever possible.
166 By default this option is 0.
168 - \b required_entities (char) -controls the correction operations. Possible values are:
170 - "respect" - PreCAD is not allowed to correct or optimize a required edge.
172 - "ignore" - PreCAD is allowed to correct a required edge.
174 - "clear" - PreCAD will erase "required" status of each required entities, and will thus
175 be allowed to correct a required edge.
177 \n By default this option is "respect".
179 - \b sewing_tolerance (real) - tolerance of the assembly. It rarely requires to be tuned.
180 By default this option is \f$\mathrm{diag} \times 5 \cdot 10^{-4}\f$.
182 - \b tags (char) -controls the optimisation process. Possible values are:
184 - "respect" - PreCAD is not allowed to cross the CAD attributes boundaries for optimisation purpose.
186 - "ignore" - PreCAD is allowed to cross the CAD attributes boundaries for optimisation.
188 - "clear" - PreCAD will erase each tgas of each entities, and will thus
189 be allowed to cross the CAD attributes boundaries in its optimisation purpose.
191 \n By default this option is "respect".
193 - \b tiny_edge_length (real) - the length below which en edge is considered as nano for the topology processing.
194 By default this option is \f$10^{-5}\f$.
196 \ref blsurf_top "Back to top"
198 \section blsurf_local_size Local size
200 Local sizes can be defined on faces, edges or vertices:
202 - The faces, edges and vertices can belong to the meshed geometrical
203 object or to its sub-shapes (created using <b>Explode</b> command).
205 - Groups of faces, edges and vertices are also handled.
207 - It is possible to attribute the same size to several geometries using multi-selection.
209 - The sizes are constant values or python functions.
211 - In case of a python function, the following rules must be respected:
213 - The name of the function is f.
215 - If geometry is a face or a group of faces, the function is f(u,v).
217 - If geometry is an edge or a group of edges, the function is f(t).
219 - If geometry is a vertex or a group of vertices, the function is f().
221 - The function must return a double.
223 3 different types of size maps can be defined:
225 -# \ref blsurf_sizemap_computation "Computation of the physical size"
226 -# \ref blsurf_attractor "Advanced maps"
227 -# \ref blsurf_attractor_computation "Computation of attractors"
229 \ref blsurf_top "Back to top"
231 \subsection blsurf_sizemap_computation Computation of the physical size
233 \image html blsurf_parameters_sizemap1.png
235 The physical size is obtained by querying sizemap functions associated
236 to the input CAD object for surfaces, curves and points.
237 Each function can either return a value h (which is then trimmed
238 between the two bounds hphymin and hphymax), or "no answer" (by not
239 assigning a value to h), thus providing great flexibility in the
240 specification of the sizes. The computation depends on whether point P
241 is internal to a surface, internal to a curve, or at the end of
244 - If point P is internal to a surface, the CAD surface size function
245 is queried. If no answer is returned, one interpolates with the values
246 at the vertices of the discretized interface curves.
248 - If point P is internal to a curve, the CAD curve size function is
249 queried first. If no answer is returned, the surface size function is
250 queried for every adjacent surface and the mean value of the returned
251 values is computed. If no answer is returned, sizes h1 and h2 at both
252 ends of the curve are considered (see next item) and the interpolated
255 - If point P is at the extremity of several curves, the CAD point size
256 function is queried first. If no answer is returned, the curve size
257 function is queried for every adjacent curve and the mean value of the
258 returned values is computed. If no answer is returned, the surface
259 size function is queried for every adjacent surface and the mean value
260 of the returned values is computed. If there is still no answer
261 returned, the default value hphydef is kept.
263 In order to compute the mean of several values, the arithmetic mean is
264 used by default, but this can be modified by the parameter
265 \ref blsurf_hmean_flag "hmean flag". In the same way, in order to
266 interpolate two values, a linear interpolation is used by default, but
267 this can be modified by \ref blsurf_hinterpol_flag "hinterpol flag".
269 \ref blsurf_local_size "Back to \"Local size\""\n
270 \ref blsurf_top "Back to top"
272 \subsection blsurf_attractor Advanced maps
274 \image html blsurf_parameters_sizemap2.png
276 More specific size maps can be defined on faces.
278 - <i> Attractors </i> allow to define the size of the mesh elements
279 on a face so that the mesh is the finest on the attractor shape and
280 becomes coarser when getting far from this shape.
282 - The selected attractor can be a Vertex, an Edge, a Wire or a
283 Compound mixing several entities of those types.
285 - The attractor doesn't have to be a sub-shape of the shape to mesh.
287 - The size will grow exponentially (see the formula below) but is
288 bounded by gradation, \n so if you want the formula to be strictly
289 respected, you should set the <i>gradation</i>
290 to its maximum (2.5) in the <i>arguments</i> tab.
292 - Furthermore you can choose to <i> keep the size constant </i>
293 until a certain distance from a shape. This option can be combined or
294 not with an <i>attractor</i> size map described above.
296 - If the two options are combined the size will remain constant
297 until the distance specified in "constant over" and grow then as
298 prescribed by the attractor function.
300 - Else the growing is only controled by the standard arguments of
301 MG-CADSurf (gradation ...).
303 \image html blsurf_const_size_near_shape2.png "Example of size map with constant size option, the size is kept constant on the left side of the surface until a certain distance"
305 \note The validation of the hypothesis might take a few seconds if
306 attractors are defined or the "constant size" option is used because a
307 map of distances has to be built on the whole surface for each face
308 where such a hypothesis has been defined.
310 \sa Sample TUI Script of the \ref tui_blsurf "creation of a MG-CADSurf hypothesis", including size map.
312 \ref blsurf_local_size "Back to \"Local size\""\n
313 \ref blsurf_top "Back to top"
315 \subsection blsurf_attractor_computation Computation of attractors
317 The size grows exponentially following the equation :
318 \f$h(d) = \mathrm{User Size} + (\mathrm{h\_start} - \mathrm{User Size}) \times e ^ { - \left( \frac{d}{R} \right) ^ {2} }\f$
322 - h_start is the desired size on the given attractor shape
324 - d is the distance of the current point from the attractor
325 shape. The distance is the geodesic distance (i.e. calculated by following the surface to be meshed)
327 - R is called the distance of influence and allows controlling the growth rate of the mesh
329 \image html blsurf_attractors2.png "Example of mesh created using attractors, the attractors here are the side edges and the size grows from the side of the surface towards the apex"
331 \ref blsurf_local_size "Back to \"Local size\""\n
332 \ref blsurf_top "Back to top"
334 \section blsurf_enforced_elements Enforced vertices
336 \image html blsurf_parameters_enforced_vertices.png
338 It is possible to define some enforced vertices to MG-CADSurf algorithm.
339 An enforced vertex is defined on a Face or a Compound by
341 - selecting an existing Vertex or Compound,
343 - or creating a new vertex given its coordinates.
345 The enforced vertex is the projection of a point defined by its
346 (x,y,z) coordinates on the selected face.
348 - It is possible to define several enforced vertices on a face or a group of faces.
350 - If the projected point is on the boundary or outside of the face, it will be ignored.
352 - If a group name is specified : If the group exists, the enforced nodes will be added in the existing group, if the group does not exist it will be created.
354 All the internal vertices of the faces can be considered as enforced vertices if the corresponding checkbox is checked.
355 A group can optionnaly be defined on those enforced vertices.
357 \sa Sample TUI Script of the \ref tui_blsurf "creation of a MG-CADSurf hypothesis", including enforced vertices.
359 \ref blsurf_top "Back to top"
362 \section blsurf_periodicity Periodicity
364 \subsection periodicity_introduction Introduction
366 Periodicity is used to have the same discretization on two faces (in 3D) or two edges (in 2D).
367 This is useful for instance for a Representative Volume Element so that the translated meshes share the same nodes on the common faces.
369 In GUI, periodicity association uses PreCAD (optional MG-CADSurf add-on). Be sure to have a PreCAD license to be able to use it. Otherwise, use \ref periodicity_tui_basic_api_usage "the basic API in TUI" or the \ref periodicity_tui_advanced_api_usage "the advanced API in TUI".
371 \image html blsurf_periodicity_translation.png "Two periodic faces (translation)"
373 \image html blsurf_periodicity_reflexion.png "Two periodic faces (reflexion)"
375 \image html blsurf_periodicity_2D.png "Associations of edges in 2D (both red edges are associated with each other)"
377 \subsection periodicity_gui_usage GUI usage
379 \image html blsurf_parameters_periodicity.png
381 The periodicity association can be defined:
383 - on 2 groups of faces (in 3D)
384 - on 2 groups of edges (in 2D)
386 If the transformation is a translation, PreCAD makes the periodicity association with only this information.
388 Otherwise, for instance a rotation, the user has to define 3 non-colinear vertices and their image by the transformation.
390 \subsection periodicity_tui_precad_usage TUI PreCAD usage
392 The two methods to define periodicity with PreCAD are:
393 - BLSURFPluginBuilder.BLSURF_Algorithm.AddPreCadFacesPeriodicity
394 - BLSURFPluginBuilder.BLSURF_Algorithm.AddPreCadEdgesPeriodicity
396 List of source and target vertices to define a transformation are optional.
398 \sa Sample TUI Script of the definition of MG-CADSurf periodicity \ref tui_blsurf_periodicity_preCAD "using preCAD".
400 \subsection periodicity_tui_basic_api_usage TUI Basic API usage
402 In the CADSurf basic API, only available in TUI, the periodicity must be defined face by face, edge by edge and vertex by vertex.
405 - BLSURFPluginBuilder.BLSURF_Algorithm.AddFacePeriodicity
406 - BLSURFPluginBuilder.BLSURF_Algorithm.AddEdgePeriodicity
407 - BLSURFPluginBuilder.BLSURF_Algorithm.AddEdgePeriodicityWithoutFaces
408 - BLSURFPluginBuilder.BLSURF_Algorithm.AddVertexPeriodicity
410 Sample TUI Script of the definition of MG-CADSurf periodicity \ref tui_blsurf_periodicity_basic "using basic API (without preCAD)".
412 \subsection periodicity_tui_advanced_api_usage TUI Advanced API usage
414 To ease the periodicity description, the basic API methods can be called through two advanced methods, given two geom groups and a python geom transformation:
416 - BLSURFPluginBuilder.BLSURF_Algorithm.AddAdvancedFacesPeriodicity (in 3D)
417 - BLSURFPluginBuilder.BLSURF_Algorithm.AddAdvancedEdgesPeriodicity (in 2D)
419 Sample TUI Script of the definition of MG-CADSurf periodicity \ref tui_blsurf_periodicity_advanced "using advanced API (without preCAD)".
421 \ref blsurf_top "Back to top"
