3 \page blsurf_hypo_page BLSURF Parameters hypothesis
6 BLSURF Parameters hypothesis works only with \b DISTENE \b BLSurf 2d
7 algorithm. This algorithm is a commercial software. To obtain a
8 licence, visit http://www.distene.com/corp/eval-distene.html
12 \section blsurf_general_parameters General parameters
14 \image html blsurf_parameters.png
16 - <b>Name</b> - allows defining the name of the hypothesis (BLSURF
17 Parameters_n by default).
19 - <b>Physical Mesh</b> - can be set to <em>None</em>, <em>Custom</em>
22 - if set to <em>Custom</em>, allows user input in the in <b>User size</b>,
23 <b>Max Physical Size</b> and <b>Min Physical Size</b> fields.
25 - if set to <em>Size Map</em>, behaves like <em>Custom</em> mode and takes into
26 account the custom elements sizes given in the Size Map tab.
28 - <b>User size</b> - defines the size of the generated mesh elements.
30 - <b>Max Physical Size</b> - defines the upper limit of mesh element size.
32 - <b>Min Physical Size</b> - defines the lower limit of mesh element size.
34 - <b>Geometrical mesh</b> - if set to <em>Custom</em>, allows user input in
35 <b>Angle Mesh S</b>, <b>Angle Mesh C</b> and <b>Gradation</b>
36 fields. These fields control computation of the element size, so
37 called <i>geometrical size</i>, conform to the surface geometry
38 considering local curvatures. If both the <b>User size</b> and the
39 <i>geometrical size</i> are defined, the eventual element size
40 corresponds to the least of the two.
42 - <b>Angle Mesh S</b> - maximum angle between the mesh face and the
43 tangent to the geometrical surface at each mesh node, in degrees.
45 - <b>Angle Mesh C</b> - maximum angle between the mesh edge and the
46 tangent to the geometrical curve at each mesh node, in degrees.
48 - <b>Max Geometrical Size</b> - defines the upper limit of the
49 <i>geometrical size</i>.
51 - <b>Min Geometrical Size</b> - defines the lower limit of the
52 <i>geometrical size</i>.
54 - <b>Gradation</b> - maximum ratio between the lengths of two adjacent
57 - <b>Allow Quadrangles</b> - if checked, allows the creation of
58 quadrilateral elements.
60 - <b>Patch independent</b> - if checked, geometrical edges are not
61 respected and all geometrical faces are meshed as one hyper-face.
63 \ref blsurf_top "Back to top"
65 \section blsurf_advanced_parameters Advanced parameters
67 The notion of <i>diag</i> used in the descriptions means the diagonal
68 of the bounding box of the geometrical object to mesh.
70 \image html blsurf_parameters_advanced.png
72 - <b>Verbosity level</b> - defines the percentage of "verbosity" of
75 - <b>Topology</b> - allows creation of a conform mesh on a shell of
76 not sewed faces. The following choices are allowed:
78 - <em>"From CAD"</em> means that mesh conformity is assured by conformity
81 - <em>"Pre-process"</em> and <em>"Pre-process++"</em> allow the BLSURF software to
82 pre-process the geometrical model to eventually produce a conform
85 - <em>"PreCAD"</em> is an auxiliary CAD pre-processing module which has
88 - Complete missing or inadequate CAD descriptions.
90 - Perform topology reconstruction and specific geometry
91 enhancement for mesh generation.
93 \n This module requires a specific licence. The following PreCAD
94 options are the most significant and important ones:
96 - <b>Merge Edges</b> - allows PreCAD to optimize the geometry by merging some
97 edges. This option is 0 by default.
99 - <b>Remove nano edges</b> - allows PreCAD to optimize the geometry by removing
100 the nano edges whenever possible. This option is 0 by default.
102 - <b>Nano edge length</b> - gives the length below which an edge is considered as nano
103 for the topology processing. See also the \b remove_nano_edges option. If unset, PreCAD
104 default value is \f$\mathrm{diag} \times 10^{-5}\f$.
106 - <b>Discard input topology</b> - computes the CAD topology from scratch,
107 without considering the topological information contained in the original CAD
108 (useful for iges files). This option is 0 by default.
110 - <b>ExportGMF</b> - saves the computed mesh into a GMF file (.mesh or .meshb).
112 - <b>Add option</b> - provides the choice of multiple PreCAD and BLSURF
113 advanced options, which appear, if selected, in a table where it is
114 possible to input the value of the option and edit it later.
116 - <b>Clear option</b> - removes the option selected in the table.
118 The following BLSURF options are commonly usable:
120 - \b topo_eps1 (real) - is the tolerance level inside a CAD
121 patch. By default is equal to \f$\mathrm{diag} \times 10^{-4}\f$. This tolerance is used to
122 identify nodes to merge within one geometrical face when \b Topology
123 option is to pre-process.
125 - \b topo_eps2 (real) - is the tolerance level between two CAD
126 patches. By default is equal to \f$\mathrm{diag} \times 10^{-4}\f$. This tolerance is used to
127 identify nodes to merge over different geometrical faces when
128 \b Topology option is to pre-process.
130 - \b LSS (real) - is an abbreviation for "length of sub-segment". It is
131 a maximal allowed length of a mesh edge. Default is \f$0.5\f$.
133 - \b frontal (integer)
135 - 1 - the mesh generator inserts points with an advancing front method.
137 - 0 - it inserts them with an algebraic method (on internal edges). This method is
138 slightly faster but generates less regular meshes.
142 - \anchor blsurf_hinterpol_flag \b hinterpol_flag (integer) - determines the computation of an
143 interpolated value <i>v</i> between two points <i>P1</i> and <i>P2</i> on a
144 curve. Let <i>h1</i> be the value at point <i>P1,</i> <i>h2</i> be the value at point
145 <i>P2,</i> and <i>t</i> be a parameter varying from 0 to 1 when moving from <i>P1
148 - 0 - the interpolation is linear: \f$v = h1 + t (h2 - h1 )\f$
150 - 1 - the interpolation is geometric: \f$v = h1 \times \left( \frac{h1}{h2} \right)^{t}\f$
152 - 2 - the interpolation is sinusoidal: \f$v = \frac{h1+h2}{2} + \frac{h1-h2}{2 \cdot \cos(\pi \cdot t)}\f$
156 - \anchor blsurf_hmean_flag \b hmean_flag (integer) - determines the computation of the average of several
159 - -1 - the minimum is computed.
161 - 0 or 2 - the arithmetic average is computed.
163 - 1 - the geometric average is computed.
167 - \b CheckAdjacentEdges, \b CheckCloseEdges and \b CheckWellDefined
168 (integers) - give the number of calls of equally named subroutines the
169 purpose of which is to improve the mesh of domains having narrow
170 parts. At each iteration,\b CheckCloseEdges decreases the sizes of the
171 edges when two boundary curves are neighboring,\b CheckAdjacentEdges
172 balances the sizes of adjacent edges, and \b CheckWellDefined checks if
173 the parametric domain is well defined. Default values are 0.
175 - \b CoefRectangle (real)- defines the relative thickness of the rectangles
176 used by subroutine \b CheckCloseEdges (see above). Default is 0.25.
178 - \b eps_collapse (real) - if more than 0.0, BLSURF removes
179 curves whose lengths are less than \b eps_collapse. To obtain an
180 approximate value of the length of a curve, it is arbitrarily
181 split into 20 edges. Default is 0.0.
183 - \b eps_ends (real) - is used to detect the curves whose lengths are very
184 small, that sometimes constitutes an error. A message is printed
185 if \f$\left|P2-P1\right| < eps\_ends\f$, where <i>P1</i> and <i>P2</i> are the
186 extremities of a curve. Default is \f$\frac{\mathrm{diag}}{500.0}\f$.
188 - \b prefix (char) - is a prefix of the files generated by
189 BLSURF. Default is "x".
191 - \b refs (integer) - reference of a surface, used when exporting
194 The following PreCAD options are commonly usable.
196 - \b closed_geometry (int) - describes whether the working geometry
197 should be closed or not. When activated, this option helps PreCAD to process
198 the dirtiest geometries. By default this option is 0.
200 - \b debug (int) - If debug = 1 PreCAD will be very verbose and will output
201 some intermediate files in the working directory. By default this
204 - \b eps_nano_relative (real) - the same as \b eps_nano, but relatively to
205 the diagonal of the box bounding the geometry. By default this option is \f$10^{-5}\f$.
207 - \b eps_sewing (real) - tolerance of the assembly. It rarely requires to be tuned.
208 By default this option is \f$\mathrm{diag} \times 5 \cdot 10^{-4}\f$.
210 - \b eps_sewing_relative (real) - the same as \b eps_nano but relatively to
211 the diagonal of the box bounding the geometry. By default this option
212 is \f$5 \cdot 10^{-4}\f$.
214 - \b manifold_geometry (int) - describes whether the working geometry should be manifold or not.
215 When activated, this option helps PreCAD to process the dirtiest
216 geometries. By default this option is 0.
218 - \b create_tag_collision (int) - creates new tags from original ones in case
219 of collision (entity merge or association for example). By default
222 - \b periodic_tolerance (real) - defines the maximum distance error accepted between
223 two sets of periodic entities. By default this option is \f$\mathrm{diag} \times 10^{-5}\f$.
225 - \b periodic_tolerance_relative (real) - the same as \b periodic_tolerance but in a relative unit.
226 By default this option is \f$10^{-5}\f$.
228 - \b periodic_split_tolerance (real) - This periodicity processing related option defines
229 the minimum distance between a CAD point and an imprinted point. It allows to indirectly
230 control the number of created points and small edges. By default this
231 option is \f$\mathrm{diag} \times 10^{-4}\f$.
233 - \b periodic_split_tolerance_relative (real - the same as \b
234 periodic_split_tolerance but in a relative unit. By default this
235 option is \f$10^{-4}\f$.
237 The following advanced options are not documented and you can use them
277 \ref blsurf_top "Back to top"
279 \section blsurf_local_size Local size
281 Local sizes can be defined on faces, edges or vertices:
283 - The faces, edges and vertices can belong to the meshed geometrical
284 object or to its sub-shapes (created using <b>Explode</b> command).
286 - Groups of faces, edges and vertices are also handled.
288 - It is possible to attribute the same size to several geometries using multi-selection.
290 - The sizes are constant values or python functions.
292 - In case of a python function, the following rules must be respected:
294 - The name of the function is f.
296 - If geometry is a face or a group of faces, the function is f(u,v).
298 - If geometry is an edge or a group of edges, the function is f(t).
300 - If geometry is a vertex or a group of vertices, the function is f().
302 - The function must return a double.
304 3 different types of size maps can be defined:
306 -# \ref blsurf_sizemap_computation "Computation of the physical size"
307 -# \ref blsurf_attractor "Advanced maps"
308 -# \ref blsurf_attractor_computation "Computation of attractors"
310 \ref blsurf_top "Back to top"
312 \subsection blsurf_sizemap_computation Computation of the physical size
314 \image html blsurf_parameters_sizemap1.png
316 The physical size is obtained by querying sizemap functions associated
317 to the input CAD object for surfaces, curves and points.
318 Each function can either return a value h (which is then trimmed
319 between the two bounds hphymin and hphymax), or "no answer" (by not
320 assigning a value to h), thus providing great flexibility in the
321 specification of the sizes. The computation depends on whether point P
322 is internal to a surface, internal to a curve, or at the end of
325 - If point P is internal to a surface, the CAD surface size function
326 is queried. If no answer is returned, one interpolates with the values
327 at the vertices of the discretized interface curves.
329 - If point P is internal to a curve, the CAD curve size function is
330 queried first. If no answer is returned, the surface size function is
331 queried for every adjacent surface and the mean value of the returned
332 values is computed. If no answer is returned, sizes h1 and h2 at both
333 ends of the curve are considered (see next item) and the interpolated
336 - If point P is at the extremity of several curves, the CAD point size
337 function is queried first. If no answer is returned, the curve size
338 function is queried for every adjacent curve and the mean value of the
339 returned values is computed. If no answer is returned, the surface
340 size function is queried for every adjacent surface and the mean value
341 of the returned values is computed. If there is still no answer
342 returned, the default value hphydef is kept.
344 In order to compute the mean of several values, the arithmetic mean is
345 used by default, but this can be modified by the parameter
346 \ref blsurf_hmean_flag "hmean flag". In the same way, in order to
347 interpolate two values, a linear interpolation is used by default, but
348 this can be modified by \ref blsurf_hinterpol_flag "hinterpol flag".
350 \ref blsurf_local_size "Back to \"Local size\""\n
351 \ref blsurf_top "Back to top"
353 \subsection blsurf_attractor Advanced maps
355 \image html blsurf_parameters_sizemap2.png
357 More specific size maps can be defined on faces.
359 - <i> Attractors </i> allow to define the size of the mesh elements
360 on a face so that the mesh is the finest on the attractor shape and
361 becomes coarser when getting far from this shape.
363 - The selected attractor can be a Vertex, an Edge, a Wire or a
364 Compound mixing several entities of those types.
366 - The attractor doesn't have to be a sub-shape of the shape to mesh.
368 - The size will grow exponentially (see the formula below) but is
369 bounded by gradation, \n so if you want the formula to be strictly
370 respected, you should set the <i>gradation</i>
371 to its maximum (2.5) in the <i>arguments</i> tab.
373 - Furthermore you can choose to <i> keep the size constant </i>
374 until a certain distance from a shape. This option can be combined or
375 not with an <i>attractor</i> size map described above.
377 - If the two options are combined the size will remain constant
378 until the distance specified in "constant over" and grow then as
379 prescribed by the attractor function.
381 - Else the growing is only controled by the standard arguments of
382 BLSURF (gradation ...).
384 \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"
386 \note The validation of the hypothesis might take a few seconds if
387 attractors are defined or the "constant size" option is used because a
388 map of distances has to be built on the whole surface for each face
389 where such a hypothesis has been defined.
391 \sa Sample TUI Script of the \ref tui_blsurf "creation of a BLSurf hypothesis", including size map.
393 \ref blsurf_local_size "Back to \"Local size\""\n
394 \ref blsurf_top "Back to top"
396 \subsection blsurf_attractor_computation Computation of attractors
398 The size grows exponentially following the equation :
399 \f$h(d) = \mathrm{User Size} + (\mathrm{h\_start} - \mathrm{User Size}) \times e ^ { - \left( \frac{d}{R} \right) ^ {2} }\f$
403 - h_start is the desired size on the given attractor shape
405 - d is the distance of the current point from the attractor
406 shape. The distance is the geodesic distance (i.e. calculated by following the surface to be meshed)
408 - R is called the distance of influence and allows controlling the growth rate of the mesh
410 \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"
412 \ref blsurf_local_size "Back to \"Local size\""\n
413 \ref blsurf_top "Back to top"
415 \section blsurf_enforced_elements Enforced vertices
417 \image html blsurf_parameters_enforced_vertices.png
419 It is possible to define some enforced vertices to BLSurf algorithm.
420 An enforced vertex is defined on a Face or a Compound by
422 - selecting an existing Vertex or Compound,
424 - or creating a new vertex given its coordinates.
426 The enforced vertex is the projection of a point defined by its
427 (x,y,z) coordinates on the selected face.
429 - It is possible to define several enforced vertices on a face or a group of faces.
431 - If the projected point is on the boundary or outside of the face, it will be ignored.
433 - If a group name is specified, the enforced nodes will be added in the group. If the group does not exist it will be created.
435 \sa Sample TUI Script of the \ref tui_blsurf "creation of a BLSurf hypothesis", including enforced vertices.
437 \ref blsurf_top "Back to top"
439 \section blsurf_limitations Limitations
441 Currently BLSURF plugin has the following limitations.
443 - BLSURF algorithm cannot be used as a local algorithm (on
444 sub-meshes) or as a provider of a low-level
445 mesh for some 3D algorithms, because the BLSURF mesher (and
446 consequently plugin) does not provide the information on node
447 parameters on edges (U) and faces (U,V). For example the
448 following combinations of algorithms are impossible:
450 - global MEFISTO or Quadrangle(mapping) + local BLSURF;
452 - BLSURF + Projection 2D from faces meshed by BLSURF;
454 - local BLSURF + Extrusion 3D;
456 \ref blsurf_top "Back to top"