MASSAGE creates, annihilates, and moves nodes and swaps
connections in a 2D or 3D mesh in order to improve element aspect
ratios and establish user-desired edge lengths.
Specifically, MASSAGE performs up to four iterations of a loop
which calls AGD3D (a routine for automated merging of nodes), RECON (a
routine for automated reconnection of edges), and SGD (a routine for
element aspect ratio improvement using smoothing). MASSAGE then
calls CEL_CHAIN which performs Rivara edge refinement and then
another call to RECON. In the case of 2-D surface grids, this is then
followed by a call to CER_CHAIN which is another edge refinement
routine and then a final call to RECON if necessary.
AGD3D will attempt to merge edges that are shorter than merge_length.
CEL_CHAIN will attempt to bisect edges that are longer than bisection_length .
For 2D surfaces, CER_CHAIN will attempt to bisect edges that deviate from an
averaged surface normal (“have a roughness of”) greater than
tolroughness.
RECON will attempt to create ‘nice’ elements by using face swapping. The LaGriT command MODE/RECON
can alter the meaning of ‘nice’. The default is to reconnect to restore the delaunay criterion.
Calling MODE / RECON/GEOM prior to the MASSAGE call will create ‘plumper’ elements. SGD will attempt to improve element aspect ratios by moving nodes.
Note: Since CEL_CHAIN is called only once at the end of MASSAGE,
it may be necessary to call MASSAGE twice for optimal results.
This is because annihilation of nodes is done with an intent to
improve element aspect ratios, but cannot be effective if there are
too few nodes initially.
Note: The user may wish to call RMPOINT/COMPRESS after
MASSAGE operations that merge a significant number of nodes.
massage/bisection_length/merge_length/toldamage/[[tolroughness]]/ & [ifirst,ilast,istride]/ [nosmooth] / [norecon] & [strictmergelength]/[ignoremats]/ & [lite]/[checkaxy]/[semiexclusive]/[exclusive]
bisection_length edge length that will trigger bisection. can either be a scalar value or a
node attribute.
merge_length is the edge length value that will trigger merging.
toldamage is a parameter which controls how much the mesh interface and external boundaries will be deformed. Roughly, it measures the depths of ‘dents’ that are invariably introduced when nodes are moved, annihilated, and faces are swapped.
tolroughness (for 2D surface grids only) measure of grid roughness (deviation from average surface
normal) that triggers refinement.
The following are guidelines for using these primary parameters:
When setting the bisection parameter bisection_length as a scalar value, if the edge length is greater than scalar value, the edge will be refined.
If a node attribute is used, the edge length is compared to the minimum value of the two nodes, if edge length is greater, the edge will be refined. Thus, one should put a minimum floor value (probably equal to
twice the desired minimum edge lenth) for the field. Otherwise the
code will refine indefinitely. For an example of an appropriate field see MASSAGE2.
The value of bisection_length should not be smaller than merge_length, or the action of
merging nodes together will be largely pointless because the newer,
longer edges created by merging will simply be bisected again.
It is recommended that bisection_length be at least three times as large as merge_length.
If the damage parameter toldamage is set to an extremely small number, there will be few if any node movements, but annihilations, or face swaps will be allowed. Conversely, if this parameter is set too large, boundaries may be significantly deformed. Setting toldamage equal to approximately .01 times the diameter of the mesh frequently gives acceptable results.
Merges of edges of length <= merge_length are meant to coarsen the mesh, but are not meant to deform surfaces and material interfaces on this scale. The amount of material/surface deformation set with toldamage is meant to be considerably less than merge_length. On the other hand, the maximum roughness tolerated in the graph
tolroughness should be considerably more than toldamage, or roughness refinement will be triggered by actions such as flipping or merging.
The following are guidelines for setting these parameters:
bisection_length >= 3 times merge_length >> toldamage
tolroughness >= 10 times toldamage (for 2D surface grids)
For example, for a grid with diameter of order 3, these values are suggested:
bisection_length, merge_length, toldamage, tolroughness = .3, .1, .01, .1
If bisection_length or merge_length is omitted, the omitted parameter will be set so that bisection_length = 3 times merge_length.
If bisection_length and merge_length are omitted, both values will be taken to infinity.
If toldamage is omitted, no node annihilation will take place.
If tolroughness is omitted, no refinement on roughness will occur and thus the format is compatible
with old commands where refinement on roughness did not occur.
nosmooth will turn off the smooth step by skipping the call to SGD.
norecon will turn off all recon steps.
lite will specify only one iteration of the merging/reconnection/smoothing loop is executed,
and a reconnection after edge refinement is omitted. This is
suitable for applications, such as Gradient Weighted Moving Finite
Elements, where MASSAGE is called repeatedly.
ignoremats causes MASSAGE to process the multimaterial mesh in a single
material mode; it ignores multi-material interfaces.
strictmergelength forces strict interpretation of merge_length so that there is no merging along the edges of flat elements. This is important if ignoremats is specified to avoid losing the interfaces.
checkaxy for 2D meshes, ensures the output mesh will have positive xy-projected triangle areas, provided that the input mesh had them in the first place.
exclusive applies to point sets, edge refinement operations will only be performed on edges whose
endpoints are both in the PSET that MASSAGE is working on. (As usual, new nodes created by refinement are added to the PSET so that MASSAGE can refine edges recursively.) The default
behavior is inclusive, where only ONE edge endpoint has to belong
to the PSET for the edge to be eligible for refinement.
semiexclusive represents an intermediate case between inclusive and exclusive. Refinment is triggered only by edges with both endpoints in the PSET, but some edges with less than two endpoints in the PSET might be refined as part of a ‘Rivara chain’ triggered by the refinement of an edge with both endpoints in the PSET.
massage/[0.3/0.1/0.01]
Mesh edges longer than 0.3 will be bisected; mesh edges shorter than 0.1 might be collapsed if that causes damage (normal surface motion) to material interfaces or external boundaries less than 0.01 ; smoothing of nodes causing damage less than 0.01 is allowed ; face swapping causing damage less than 0.01 is allowed.
massage/[H_SCALE/0.1/0.01]/
Same as above, except that the bisection_length is a node field called H_SCALE in this case.
massage/[[0.3/0.1/0.01/0.1]
Same as above but for 2-D surface meshes, roughness greater than 0.1 will trigger refinement.
massage/0.3/0.1/0.01/pset,get,[pset1]
Mesh edges (containing at least one endpoint in pset1) longer than 0.3 will be bisected; mesh edges shorter than 0.1 might be collapsed if that causes damage (normal surface motion) to material interfaces or external boundaries less than 0.01 and if the annihilated node is in pset1; smoothing of nodes in pset1 causing damage less than 0.01 is allowed; face swapping causing damage less than 0.01 is allowed (unfortunately, LaGriT at this time does not restrict swapping to pset1).
massage/0.3/0.1/0.01/pset,get,pset1,nosmooth
As above, but without smoothing.
massage/1.e+20/0.1/0.1/1,0,0/nosmooth
Because of the virtually infinite value of [bisection_length],no edges will be bisected. Since merge_length=toldamage=0.1, merging of edges of length less than 0.1 will be considered, and will not be rejected because of excessive damage. Hence we expect that all edges of length less than 0.1 will be merged away (except in those cases where merging would invert tetrahedra or change material topology). Because nosmooth is specified, no smoothing will take place. Face swapping causing damage less than [toldamage] is allowed
massage[/1.e+20/1.e-9/1.e-9/1,0,0]/nosmooth/strictmergelength /ignoremats
This set of arguments will remove degenerate elements from a mesh by merging nodes that have the same coordinate values ( within 1.e-9).