3 \page blsurf_hypo_page MG-CADSurf Parameters hypothesis
9 \section blsurf_general_parameters General parameters
11 \image html blsurf_parameters.png
13 - <b>Name</b> - allows defining the name of the hypothesis (MG-CADSurf
14 Parameters_n by default).
16 - <b>Physical Size</b> group defines a \a physical sizemap.
18 - \b Type of the physical sizemap can be set to <em>None</em>, <em>Global size</em>
19 or <em>Local size</em>
21 - if set to <em>Global size</em>, only the <b>User size</b>,
22 <b>Max Size</b> and <b>Min Size</b> fields are taken into account.
24 - if set to <em>Local size</em>, behaves like <em>Custom</em> mode and takes into
25 account the "Gradation" parameter and the custom elements sizes given in the
28 - <b>Geometrical Size</b> group defines a \a geometrical sizemap.
30 - \b Type of the geometrical sizemap can be set to <em>None</em>, <em>Global size</em>
32 - if set to <em>Global size</em>, allows user input in <b>Mesh angle</b>,
33 <b>Mesh distance</b> and <b>Gradation</b> fields. These fields control
34 computation of the element size, so called <i>geometrical size</i>, conform
35 to the surface geometry considering local curvatures. If both the <b>User size</b>
36 and the <i>geometrical parameters</i> are defined, the eventual element size
37 corresponds to the least of the two.
39 - <b>User size</b> - defines the size of the generated mesh elements. If "Relative value"
40 is checked, the value is relative to the diagonal of the shape.
42 - <b>Max Size</b> - defines the upper limit of mesh element size. If "Relative value"
43 is checked, the value is relative to the diagonal of the shape.
45 - <b>Min Size</b> - defines the lower limit of mesh element size. If "Relative value"
46 is checked, the value is relative to the diagonal of the shape.
48 - <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.
49 The smaller this angle is, the closer the mesh is to the exact surface, and the denser the resulting mesh is.
51 - <b>Mesh distance</b> - Maximum desired distance between a triangle and its supporting CAD surface.
52 The smaller this distance is, the closer the mesh is to the exact surface (only available in isotropic meshing).
54 - <b>Quadratic mesh</b> - if checked, quadratic elements will be generated.
56 - <b>Gradation</b> - maximum ratio between the lengths of two adjacent edges.
58 - <b>Mesh optimisation</b> - if checked, the mesh will be optimized in order to get better shaped elements.
60 - <b>Allow Quadrangles</b> - if checked, allows the creation of quadrilateral elements.
62 - <b>Anisotropic</b> - if checked, this parameter defines the maximum anisotropic ratio of the metric governing the anisotropic meshing process.
63 The default value (0) means that the metric (and thus the generated elements) can be arbitrarily stretched.
65 - <b>Optimize tiny edges</b> - if checked, the tiny (nano) edges are removed from the generated mesh during local mesh optimization.
66 The tiny edge value defines the minimal length under which an edge is considered to be a tiny one.
68 - <b>Remove tiny edges</b> - if checked, the tiny (nano) edges are removed from the generated mesh.
69 The tiny edge value defines the minimal length under which an edge is considered to be a tiny one.
71 - <b>Remove bad elements</b> - if checked, the bad elements (slivers) are removed from the generated mesh.
72 The bad element value defines the aspect ratio triggering the "bad element” classification.
74 - <b>Correct surface intersections</b> - if checked, the mesher will try to prevent all surface intersections, which is useful for future volume mesh generation. The value defines the time that will be spent in the intersection prevention process. For example, the value 3 means that the time of the intersection removal process won't be more than 3 times the time required to mesh without processing the intersections.
76 - <b>Volume Gradation</b> - maximum ratio between the lengths of two adjacent edges affecting quality of a future volume mesh, specially in thin volume areas. The volume gradation parameter must be greater than 1, and should be greater or equal to the value of the classic
77 surface gradation (at the risk of increasing the time of convergence of the gradation process).
78 The closer it is to 1, the smoother the final volume mesh you will build should be.
82 \ref blsurf_top "Back to top"
84 \section blsurf_advanced_parameters Advanced parameters
86 The notion of <i>diag</i> used in the descriptions means the diagonal of the bounding box of the geometrical object to mesh.
88 \image html blsurf_parameters_advanced.png
90 \b Advanced page tab expose mostly useful advanced options. Initially, default values of the options are displayed and they are not modifiable. If an option is activated using a check-box, its value becomes modifiable.
94 - <b>Enforce CAD edge sizes</b> - Relaxes the given sizemap constraint around CAD edges to allow a better
95 element quality and a better geometric approximation. It is only useful in combination with the
98 - <b>Priority of geometry over Jacobian</b> - This parameter determines whether or not the geometry accuracy
99 is more important than the negative Jacobian correction. When this parameter is set to 0,
100 MeshGems-CADSurf is allowed to lose the CAD-mesh associativity in order to correct the last negative Jacobians.
102 - <b>Maximal number of points per patch</b> - This parameter controls the maximum amount of points MeshGems-CADSurf
103 is allowed to generate on a single CAD patch. For an automatic gestion of the memory, you can set this parameter to ”0”.
105 - <b>Rectify Jacobian</b> - The quadratic elements generation is a processing of the MeshGems-CADSurf
106 meshing process which inserts the extra nodes on the CAD. This parameter determines whether
107 MeshGems-CADSurf will try to correct or not all the elements of the surface mesh with negative
108 Jacobians by moving the internal nodes of the mesh.
110 - <b>Respect geometry</b> - This patch independent option can be deactivated to allow MeshGems-CADSurf
111 to lower the geometry accuracy in its patch independent process.
113 - <b>Tiny edges avoid surface intersections</b> - This option defines the priority between the tiny feature
114 suppression and the surface intersection prevention. By default, MeshGems-CADSurf gives the priority
115 to the surface intersection prevention rather than to tiny edge or bad surface element removal. These
116 mesh features are then removed only if it does not lead to surface intersections. This behaviour can be
117 deactivated by setting this parameter to 0, giving priority to the tiny edge or bad surface element
121 - <b>CAD preprocessor</b> options. The CAD preprocessor (formerly known as PreCAD) has two main goals:
123 - Complete missing or inadequate CAD descriptions.
125 - Perform topology reconstruction and specific geometry
126 enhancement for mesh generation.
128 \n All options are unchecked by default. No cleanup is made by default so that the mesh matches the shape. If the user has a bad shape (e.g. imported shape), he can activate some options to improve the mesh.
130 - <b>Closed geometry</b> - describes whether the working geometry should be closed or not.
131 When activated, this option helps PreCAD to process the dirtiest geometries.
133 - \b Debug - If debug = yes PreCAD will be very verbose and will output some intermediate files in the working directory.
135 - <b>Discard input topology</b> - compute the CAD topology from scratch,
136 without considering the topological information contained in the original CAD
137 (useful for iges files). This option is unchecked by default.
139 - <b>Merge Edges</b> - optimize the geometry by merging some
142 - <b>Periodic tolerance</b> - This parameter defines the maximum size difference between two periodic edges and also the maximum distance error between two periodic entities.
144 - <b>Remove duplicate CAD faces</b> - optimize the geometry by merging the
145 duplicate CAD faces. This option is unchecked by default.
147 - <b>Required entities</b> - The required entities control the correction operations. Accepted values for this parameter are:
148 - respect : MeshGems-CADSurf is not allowed to alter any required entity, even for correction purposes,
149 - ignore : MeshGems-CADSurf will ignore the required entities in its processing,
150 - clear : MeshGems-CADSurf will clear any required status for the entities. There will not be any entity marked as required in the generated mesh.
152 - <b>Sewing tolerance</b> - tolerance of the assembly. It rarely requires to be tuned.
154 - \b Tags - controls the optimisation process. Possible values are:
155 - "respect" - PreCAD is not allowed to cross the CAD attributes boundaries for optimisation purpose.
156 - "ignore" - PreCAD is allowed to cross the CAD attributes boundaries for optimisation.
157 - "clear" - PreCAD will erase each tgas of each entities, and will thus be allowed to cross the CAD attributes boundaries in its optimisation purpose.
160 - <b>Add option</b> - adds a new line in <b>Other options</b> section where you can type an option name and value. The following advanced MG-CADSurf options can be used:
162 - \b create_tag_on_collision (bool) - If this option is activated, MeshGems-CADSurf will create new tags to
163 describe tag collisions (when it locally changes the topology, depending on the patch independent
164 options). When this option is not activated, only one tag is preserved while the other one is dropped.
165 By default this option is 1.
167 - \b tiny_edge_respect_geometry (bool) - This option defines the behaviour of the tiny edge removal algorithm
168 regarding volume collapse. By default, all tiny edges will be removed, regardless of any potential
169 volume collapse. When this option is activated, it will prevent volume from being collapsed during the tiny edge removal process.
170 By default this option is 0.
172 - \b manifold_geometry (int) - describes whether the working geometry should be manifold or not.
173 When activated, this option helps PreCAD to process the dirtiest
174 geometries. By default this option is 0.
178 - <b>Verbosity level</b> - defines the percentage of "verbosity" of
179 MeshGems-CADSurf [0-10].
181 - <b>ExportGMF</b> - saves the computed mesh into a GMF file (.mesh or .meshb).
185 \ref blsurf_top "Back to top"
187 \section blsurf_local_size Local size
189 Local sizes can be defined on faces, edges or vertices:
191 - The faces, edges and vertices can belong to the meshed geometrical
192 object or to its sub-shapes (created using <b>Explode</b> command).
194 - Groups of faces, edges and vertices are also handled.
196 - It is possible to attribute the same size to several geometries using multi-selection.
198 - The sizes are constant values or python functions.
200 - In case of a python function, the following rules must be respected:
202 - The name of the function is f.
204 - If geometry is a face or a group of faces, the function is f(u,v).
206 - If geometry is an edge or a group of edges, the function is f(t).
208 - If geometry is a vertex or a group of vertices, the function is f().
210 - The function must return a double.
212 3 different types of size maps can be defined:
214 -# \ref blsurf_sizemap_computation "Computation of the physical size"
215 -# \ref blsurf_attractor "Advanced maps"
216 -# \ref blsurf_attractor_computation "Computation of attractors"
218 \ref blsurf_top "Back to top"
220 \subsection blsurf_sizemap_computation Computation of the physical size
222 \image html blsurf_parameters_sizemap1.png
224 The physical size is obtained by querying sizemap functions associated
225 to the input CAD object for surfaces, curves and points.
226 Each function can either return a value h (which is then trimmed
227 between the two bounds hphymin and hphymax), or "no answer" (by not
228 assigning a value to h), thus providing great flexibility in the
229 specification of the sizes. The computation depends on whether point P
230 is internal to a surface, internal to a curve, or at the end of
233 - If point P is internal to a surface, the CAD surface size function
234 is queried. If no answer is returned, one interpolates with the values
235 at the vertices of the discretized interface curves.
237 - If point P is internal to a curve, the CAD curve size function is
238 queried first. If no answer is returned, the surface size function is
239 queried for every adjacent surface and the mean value of the returned
240 values is computed. If no answer is returned, sizes h1 and h2 at both
241 ends of the curve are considered (see next item) and the interpolated
244 - If point P is at the extremity of several curves, the CAD point size
245 function is queried first. If no answer is returned, the curve size
246 function is queried for every adjacent curve and the mean value of the
247 returned values is computed. If no answer is returned, the surface
248 size function is queried for every adjacent surface and the mean value
249 of the returned values is computed. If there is still no answer
250 returned, the default value hphydef is kept.
252 In order to compute the mean of several values, the arithmetic mean is
253 used by default, but this can be modified by the parameter
254 \ref blsurf_hmean_flag "hmean flag". In the same way, in order to
255 interpolate two values, a linear interpolation is used by default, but
256 this can be modified by \ref blsurf_hinterpol_flag "hinterpol flag".
258 \ref blsurf_local_size "Back to \"Local size\""\n
259 \ref blsurf_top "Back to top"
261 \subsection blsurf_attractor Advanced maps
263 \image html blsurf_parameters_sizemap2.png
265 More specific size maps can be defined on faces.
267 - <i> Attractors </i> allow to define the size of the mesh elements
268 on a face so that the mesh is the finest on the attractor shape and
269 becomes coarser when getting far from this shape.
271 - The selected attractor can be a Vertex, an Edge, a Wire or a
272 Compound mixing several entities of those types.
274 - The attractor doesn't have to be a sub-shape of the shape to mesh.
276 - The size will grow exponentially (see the formula below) but is
277 bounded by gradation, \n so if you want the formula to be strictly
278 respected, you should set the <i>gradation</i>
279 to its maximum (2.5) in the <i>arguments</i> tab.
281 - Furthermore you can choose to <i> keep the size constant </i>
282 until a certain distance from a shape. This option can be combined or
283 not with an <i>attractor</i> size map described above.
285 - If the two options are combined the size will remain constant
286 until the distance specified in "constant over" and grow then as
287 prescribed by the attractor function.
289 - Else the growing is only controled by the standard arguments of
290 MG-CADSurf (gradation ...).
292 \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"
294 \note The validation of the hypothesis might take a few seconds if
295 attractors are defined or the "constant size" option is used because a
296 map of distances has to be built on the whole surface for each face
297 where such a hypothesis has been defined.
299 \sa Sample TUI Script of the \ref tui_blsurf "creation of a MG-CADSurf hypothesis", including size map.
301 \ref blsurf_local_size "Back to \"Local size\""\n
302 \ref blsurf_top "Back to top"
304 \subsection blsurf_attractor_computation Computation of attractors
306 The size grows exponentially following the equation :
307 \f$h(d) = \mathrm{User Size} + (\mathrm{h\_start} - \mathrm{User Size}) \times e ^ { - \left( \frac{d}{R} \right) ^ {2} }\f$
311 - h_start is the desired size on the given attractor shape
313 - d is the distance of the current point from the attractor
314 shape. The distance is the geodesic distance (i.e. calculated by following the surface to be meshed)
316 - R is called the distance of influence and allows controlling the growth rate of the mesh
318 \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"
320 \ref blsurf_local_size "Back to \"Local size\""\n
321 \ref blsurf_top "Back to top"
323 \section blsurf_enforced_elements Enforced vertices
325 \image html blsurf_parameters_enforced_vertices.png
327 It is possible to define some enforced vertices to MG-CADSurf algorithm.
328 An enforced vertex is defined on a Face or a Compound by
330 - selecting an existing Vertex or Compound,
332 - or creating a new vertex given its coordinates.
334 The enforced vertex is the projection of a point defined by its
335 (x,y,z) coordinates on the selected face.
337 - It is possible to define several enforced vertices on a face or a group of faces.
339 - If the projected point is on the boundary or outside of the face, it will be ignored.
341 - 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.
343 All the internal vertices of the faces can be considered as enforced vertices if the corresponding checkbox is checked.
344 A group can optionnaly be defined on those enforced vertices.
346 \sa Sample TUI Script of the \ref tui_blsurf "creation of a MG-CADSurf hypothesis", including enforced vertices.
348 \ref blsurf_top "Back to top"
351 \section blsurf_periodicity Periodicity
353 \subsection periodicity_introduction Introduction
355 Periodicity is used to have the same discretization on two faces (in 3D) or two edges (in 2D).
356 This is useful for instance for a Representative Volume Element so that the translated meshes share the same nodes on the common faces.
358 Periodicity association uses PreCAD (MG-CADSurf preprocessor). You don't need an extra PreCAD license. It is included in MG-CADSurf since MeshGems V2.2.
360 \image html blsurf_periodicity_translation.png "Two periodic faces (translation)"
362 \image html blsurf_periodicity_reflexion.png "Two periodic faces (reflexion)"
364 \image html blsurf_periodicity_2D.png "Associations of edges in 2D (both red edges are associated with each other)"
366 \subsection periodicity_gui_usage GUI usage
368 \image html blsurf_parameters_periodicity.png
370 The periodicity association can be defined:
372 - on 2 groups of faces (in 3D)
373 - on 2 groups of edges (in 2D)
375 If the transformation is a translation, PreCAD makes the periodicity association with only this information.
377 Otherwise, for instance a rotation, the user has to define 3 non-colinear vertices and their image by the transformation.
379 \subsection periodicity_tui_precad_usage TUI PreCAD usage
381 The two methods to define periodicity with PreCAD are
382 (the former name of <em>MG-CADSurf</em> is \a BLSURF and names
383 of the corresponding classes and modules still include \a "BLSURF"):
384 - BLSURFPluginBuilder.BLSURF_Algorithm.AddPreCadFacesPeriodicity
385 - BLSURFPluginBuilder.BLSURF_Algorithm.AddPreCadEdgesPeriodicity
387 List of source and target vertices to define a transformation are optional.
389 \sa Sample TUI Script of the definition of MG-CADSurf periodicity \ref tui_blsurf_periodicity_preCAD "using preCAD".
391 \ref blsurf_top "Back to top"
393 For more information on MeshGems-CADSurf, you can read its documentation at $MESHGEMS_ROOT_DIR/Docs/mg-cadsurf_user_manual.pdf
