- Mapdl.nummrg(label='', toler='', gtoler='', action='', switch='', **kwargs)¶
Merges coincident or equivalently defined items.
APDL Command: NUMMRG
Items to be merged:
NODE - Nodes
ELEM - Elements
KP - Keypoints (will also merge lines, areas, and volumes)
MAT - Materials
TYPE - Element types
REAL - Real constants
CP - Coupled sets
CE - Constraint equations
ALL - All items
Range of coincidence. For Label = NODE and KP, defaults to 1.0E-4 (based on maximum Cartesian coordinate difference between nodes or keypoints). For Label = MAT, REAL, and CE, defaults to 1.0E-7 (based on difference of the values normalized by the values). Only items within range are merged. (For keypoints attached to lines, further restrictions apply. See the GTOLER field and Merging Solid Model Entities below.)
Global solid model tolerance – used only when merging keypoints attached to lines. If specified, GTOLER will override the internal relative solid model tolerance. See Merging Solid Model Entities below.
Specifies whether to merge or select coincident items.
- SELE - Select coincident items but do not merge. Action = SELE is only valid for Label
(Blank) - Merge the coincident items (default).
Specifies whether the lowest or highest numbered coincident item is retained after the merging operation. This option does not apply to keypoints; i.e., for Label = KP, the lowest numbered keypoint is retained regardless of the Switch setting.
- LOW - Retain the lowest numbered coincident item after the merging operation
HIGH - Retain the highest numbered coincident item after the merging operation.
After issuing the command, the area and volume sizes (ASUM and VSUM) may give slightly different results. In order to obtain the same results as before, use /FACET, /NORMAL, and ASUM / VSUM.
The merge operation is useful for tying separate, but coincident, parts of a model together. If not all items are to be checked for merging, use the select commands (NSEL, ESEL, etc.) to select items. Only selected items are included in the merge operation for nodes, keypoints, and elements.
By default, the merge operation retains the lowest numbered coincident item. Higher numbered coincident items are deleted. Set Switch to HIGH to retain the highest numbered coincident item after the merging operation. Applicable related items are also checked for deleted item numbers and if found, are replaced with the retained item number. For example, if nodes are merged, element connectivities (except superelements), mesh item range associativity, coupled degrees of freedom, constraint equations, master degrees of freedom, gap conditions, degree of freedom constraints, nodal force loads, nodal surface loads, and nodal body force loads are checked. Merging material numbers [NUMMRG,ALL or NUMMRG,MAT] does not update the material number referenced:
By temperature-dependent film coefficients as part of convection load or a temperature-dependent emissivity as part of a surface-to-surface radiation load [SF, SFE, SFL, SFA]
By real constants for multi-material elements (such as SOLID65)
If a unique load is defined among merged nodes, the value is kept and applied to the retained node. If loads are not unique (not recommended), only the value on the lowest node (or highest if Switch = HIGH) will be kept, except for “force” loads for which the values will be summed if they are not defined using tabular boundary conditions.
Note:: The unused nodes (not recommended) in elements, couplings, constraint equations, etc. may become active after the merge operation.
The Action field provides the option of visualizing the coincident items before the merging operation.
Caution:: When merging entities in a model that has already been meshed, the order in which you issue multiple NUMMRG commands is significant. If you want to merge two adjacent meshed regions that have coincident nodes and keypoints, always merge nodes [NUMMRG,NODE] before merging keypoints [NUMMRG,KP]. Merging keypoints before nodes can result in some of the nodes becoming “orphaned”; that is, the nodes lose their association with the solid model. Orphaned nodes can cause certain operations (such as boundary condition transfers, surface load transfers, and so on) to fail. However, using NUMMRG should be avoided if at all possible, as the procedure outlined above may even cause meshing failure, especially after multiple merging and meshing operations.
After a NUMMRG,NODE, is issued, some nodes may be attached to more than one solid entity. As a result, subsequent attempts to transfer solid model loads to the elements may not be successful. Issue NUMMRG,KP to correct this problem. Do NOT issue VCLEAR before issuing NUMMRG,KP.
For NUMMRG,ELEM, elements must be identical in all aspects, including the direction of the element coordinate system.
For certain solid and shell elements (181, 185, 190, etc) ANSYS will interpret coincident faces as internal and eliminate them. To prevent this from occurring, shrink the entities by a very small factor to delineate coincident items (/SHRINK, 0.0001) and no internal nodes, lines, areas or elements will be eliminated.
When working with solid models, you may have better success with the gluing operations (AGLUE, LGLUE, VGLUE). Please read the following information when attempting to merge solid model entities.
Gluing Operations vs. Merging Operations
Adjacent, touching regions can be joined by gluing them (AGLUE, LGLUE, VGLUE) or by merging coincident keypoints (NUMMRG,KP, which also causes merging of identical lines, areas, and volumes). In many situations, either approach will work just fine. Some factors, however, may lead to a preference for one method over the other.
Gluing is possible regardless of the initial alignment or offset of the input entities. Keypoint merging is possible only if each keypoint on one side of the face to be joined is matched by a coincident keypoint on the other side. This is commonly the case after a symmetry reflection (ARSYM or VSYMM) or a copy (AGEN or VGEN), especially for a model built entirely in ANSYS rather than imported from a CAD system. When the geometry is extremely precise, and the configuration is correct for keypoint merging, NUMMRG is more efficient and robust than AGLUE or VGLUE.