Name
epatch — Regular mesh generation block
Synopsis
epatch id
parameters
...
attributes...
end
Description
epatch generates regular onedimensional, twodimensional, and threedimensional domains which are meshed automatically. For onedimensional patches, straight or curved lines can be modelled. For twodimensional patches, foursided surfaces described by analytical functions can be modelled, creating Q shelltype elements. For three dimensional patches, cubes described by analytical functions can be modelled, creating HE solidtype elements. In addition to nodes end elements the epatch command also generates lists containing vertex, edge, face, and body nodes and elements, thus facilitating ebc and nbc boundary condition generation. Note, however, that the epatch command is by no means a substitute to any modelling and meshing software.
The element patch definition must be enclosed in the
epatch block, the patch being uniquely identified by
, a positive integer
unique for the model. Any number of element patches can be generated
within the same branch definition, provided that the patch boundary
nodes match, i.e. nodes are not merged automatically if several element
patches are generated in one and the same branch. Thus, it is often
easier to generate one element patch per branch and connect the branches
with the automatic option of the join command.
id
Element patches generate elements as follows (see also the figure below for the definition of i, j, and k): For all elements in the kdirection, for all elements in the jdirection, generate elements in the idirection, incrementing the element number by one.
Note that the default initial element number and the default
initial node number are both set to the highest internal element or node
number plus 1, defined so far for the current branch. Internal element
and node number start with 1. If patches and element and node
definitions with the elements and
nodes commands are defined within the same branch
please consider making use the element start index
start_element_id
or the node start index
start_node_id
options to avoid conflicts with external
element or node numbers defined by the elements or
nodes commands and the epatch
element and node generation, which generates internal node
numbers..
Figure 8. Twodimensional element patch definition: Patch edges. The patch face is f7 or mid_surface.
Parameters
eltype
t

Specifies the element type
of the patch. For 1D patches elements of type B, C, L and R are allowed. For 2D patches elements of type T and Q are allowed. For 3D patches, element types HE and  to some extent  TE are allowed. The element type may only be specified once for one and the same patch.t
geometry
gtype parameters...

Specifies the geometry type of the patch to be generated. The following geometry types and their parameters can be defined:
arch radius
r
phi1angle1
phi2angle2
[open yesno]
Creates a line mesh of beam/rod/cable/line elements along a circular arch that is defined in the branch xy plane, with the origin of the circular segment at (0,0,0) and with the angles
phi1
(start angle) andphi2
(end angle) rotating around the zaxis. The circular arch has a radius ofradius
. Required meshing parameters are the number of elementsne1
in the circumferential direction. Theopen
parameter applies only in case where the segment makes a full circle. By default, the coinciding nodes are merged. Settingopen
toyes
retains the duplicate nodes. cylinder radius
r
phi1a1
phi2a2
length l [thicknesst
] [open yesno]
Specifies a cylindrical shell segment. The generated segment is defined in the branch xy plane, with the origin of the circular segment at (0,0,0), a radius
, and with the anglesr
(start angle) andphi1
(end angle) rotating around the zaxis. The axial direction is in the branch zdirection. Required meshing parameters are the number of elementsphi2
ne1
in the circumferential idirection and the number of elementsne2
in the axial jdirection. Thethickness
parameter is element type dependent. Theopen
parameter applies only in case where the segment makes a full circle. By default, the coinciding nodes are merged. Settingopen
toyes
retains the duplicate nodes. cube p1
x y z
... p8x y z

Creates an isoparametric solid mesh of a cube defined by the 8 corner nodes
p1
top8
. Required meshing parameters are the number of elementsne1
in the idirection, the number of elementsne2
in the jdirection, and the number of elementsne3
in the kdirection. All other parameters are element type dependent. line p1
x y z
p2x y z
[thicknesst
]
Creates a straight line mesh of beam/rod/cable/line elements extending from point
p1
to pointp2
, with an optional area or thickness
. Required meshing parameters are the number of elementst
ne1
in the idirection. All other parameters are element type dependent. plate p1
x y z
... p4x y z
[thicknesst
]
Generates an isoparametric rectangular plate mesh defined by the four corner nodes
p1
top4
. The plate has a optional uniform thickness
. Required meshing parameters are the number of elementst
ne1
in the plate idirectionand the number of elementsne2
in the plate jdirection. All other parameters are element type dependent. Thethickness
parameter is element type dependent. ring radius1
r1
radius2r2
phi1angle1
phi2angle2
[thicknesst
] [open yesno]
Specifies a shell element mesh of a ring. The ring is defined in the branch xy plane, with the origin of the circular segment at (0,0,0) and with the angles
phi1
(start angle) andphi2
(end angle) rotating around the zaxis. The ring segment has an inner radiusradius1
and an outer radiusradius2
. Required meshing parameters are the number of elementsne1
in the circumferential (i) direction and the number of elementsne2
in the radial (j) direction. Thethickness
parameter is element type dependent. Theopen
parameter applies only in case where the segment makes a full circle. By default, the coinciding nodes are merged. Settingopen
toyes
retains the duplicate nodes. tube radius1
r1
radius2r2
phi1angle1
phi2angle2
lengthl
[open yesno]
Specifies a solid mesh of a tube. The tube section is defined in the branch xy plane, with the origin of the circular segment at (0,0,0) and with the angles
phi1
(start angle) andphi2
(end angle) rotating around the zaxis. The tube has an inner radiusradius1
and an outer radiusradius2
. The length of the tube is defined by thelength
. Required meshing parameters are and the number of elementsne1
in the circumferential (i) direction, the number of elementsne2
in the radial (j) direction, and the number of elementsne3
in the global z (k) direction. Theopen
parameter applies only in case where the segment makes a full circle. By default, the coinciding nodes are merged. Settingopen
toyes
retains the duplicate nodes.
local
none
edges
all

Specifies if the generated nodes will be assigned a nodelocal DOF reference coordinate system (see
transformation
option of the nodes command). The nodelocal coordinate system is generated according to the geometry type.
generates local reference coordinate systems for all nodes placed on patch edges.edges
generates local reference coordinate systems for all nodes.all
ne1
n

Specifies the number of elements in regular patch in the logical idirection, see figure above (required for all patches).
ne2
n

Specifies the number of elements in regular patch in the logical jdirection, see figure above (required for 2D and 3D patches).
ne3
n

Specifies the number of elements in regular patch in the logical kdirection, see figure above (required for 3D patches).
 orientation
ux uy uz vx vy vz

Defines a local base by which all epatch nodes are rotated (refer to the section on orientation below for more details).
 start_element_id
id

Element identifier of first element generated. All subsequent elements are generated by incrementing the element identifier by 1, first in the idirection, then in the jdirection, and, finally, in the kdirection. The default value is 1.
 start_node_id
id

Node identifier of first node generated. All subsequent nodes are generated by incrementing the node identifier by 1, first in the idirection, then in the jdirection, and, finally, in the kdirection. The default value is 1.
 translation
tx ty tz

Translated the patch by
in the global xdirection, bytx
in the global xdirection, and byty
in the global zdirection.tz
Changing the orientation
The orientation
directive allows to
change the orientation of any patch. This may be useful in the
case of cylindrical patches which have a default orientation
(the cylindrical axis is aligned with the branchglobal
zdirection).
Synopsis:
orientation
[base u_{1} u_{2} u_{3} v_{1} v_{2} v_{3}
]
[rotate axis xyz angle a
]
[rotate axis u_{1} u_{2} u_{3}
angle a
]
[translate x y z
]
end
The following directives can be used to modify the orientation:
base
u_{1} u_{2} u_{3} v_{1} v_{2} v_{3}

Calculate the base from the vectors
u
andv
as follows:u
defines the patch base e_{1},u
xv
defines the patch base e_{3}, and e_{3} xu
defines the patch base e_{2}. rotate axis xyz angle
a

Rotate the current patch base about the x, y, or z axis by
a
degrees, and according to the righthand rule. Successive rotations can be specified. rotate axis
u_{1} u_{2} u_{3}
anglea

Rotate the current patch base about the axis defined by the vector
u_{1} u_{2} u_{3}
, bya
degrees, and according to the righthand rule. Successive rotations can be specified. translate
tx ty tz

Translate the current patch by
tx
in the xdirection,ty
in the ydirection, andtz
in the zdirection.tx
,ty
, andtz
are float values. The default translation is 0.0 in all three directions.
Attributes
All element attributes are element type dependent and can be consulted in the elements section of the user manual.
Additional Notes
A patch is meshed independently of any other patches, and when defining multiple patches, the coinciding nodes of adjacent patches will not be connected. Coinciding nodes can be connected by means of the join command (using the automatic option).
Examples
Generate a cylindrical panel mesh with a 90 degree opening, starting at phi=0. The panel has a radius of 1., a thickness of 0.002, and a length of 1. All nodes shall have a local cylindrical coordinate system (r, phi, z). The panel is meshed with Q9 shell elements.
epatch 1 geometry cylinder radius 1.0 thickness 0.002 phi1 0.0 phi2 90.0 length 1.0 local all ne1 10 ne2 5 eltype Q9.S.MITC mid 1 end
Figure 12. EPATCH example: Cylindrical panel (Q9 shell mesh) and nodelocal cylindrical coordinate system in directions (r,phi,z).
Generate a cylindrical panel mesh identicall to the one in the
preceding example, i.e with a 90 degree opening, starting at phi=0.
The panel has a radius of 1., a thickness of 0.002, and a length of 1.
All nodes shall have a local cylindrical coordinate system (r, phi,
z). The panel is meshed with Q9 shell elements. The cylinder shall be
rotated by +90 degrees around the yaxis: This is achieved by defining
local base vectors with the orientation
parameter.
epatch 1 geometry cylinder radius 1.0 thickness 0.002 phi1 0.0 phi2 90.0 length 1.0 orientation base 1 0 0 0 0 1 end local all ne1 10 ne2 5 eltype Q9.S.MITC mid 1 end
Generate a cylindrical panel mesh with a 90 degree opening, starting at phi=0. The panel has a radius of 1., a thickness of 0.002, and a length of 1. All nodes shall have a local cylindrical coordinate system (r, phi, z).The panel is meshed with 10 by 5 Q8 shell elements.
epatch 1 geometry cylinder eltype Q8.S.MITC radius 10. thickness 2.0 phi1 45.0 phi2 135.0 length 20. local all ne1 10 ne2 5 mid 1 end