You set up the coordinate system specification by specifying the global coordinates of three points in the local system: the origin of the local system (point a in Figure 2.1.1–1), a point on the local -axis (point b in Figure 2.1.1–1), and a point in the plane of the local system on (or near) the local -axis (point c in Figure 2.1.1–1).

To change the nodal coordinate system that is in effect, define another nodal coordinate system; to revert to input in the global coordinate system, use a nodal coordinate system definition without any associated data.

*SYSTEM
, , , , , 
, , 

*SYSTEM
0, 0, 0, 5, 5, 5
*NODE
1, 0, 0, 1
2, 0, 0, 2
3, 0, 1, 2
*SYSTEM
2, 3, 4
*NODE
4, 0, 0, 1
5, 1, 4, 0
*SYSTEM
*NODE
6, 1, 0, 1
7, 0, 4, 2

When you define a nodal coordinate system within a part (or part instance) definition, it is in effect only within that part (or part instance) definition. Nodes defined in other parts are not affected.

You specify the local () coordinate values relative to the part coordinate system, which subsequently may be translated and/or rotated according to the positioning data given for the instance (see “Defining an assembly,” Section 2.9.1).

Node definitions can be read into ABAQUS from an alternate file. The syntax of such file names is described in “Input syntax rules,” Section 1.2.1.

*NODE, INPUT=file_name

You can specify that a local rectangular Cartesian, cylindrical, or spherical coordinate system be used for a particular node definition. These coordinate systems are shown in Figure 2.1.1–2.

This coordinate system specification is entirely local to the node definition. As the nodal data are read, the coordinates are transformed to rectangular Cartesian coordinates immediately. If a nodal coordinate system is also in effect (see “Specifying a local coordinate system in which to define nodes”), these are local rectangular Cartesian coordinates as defined by the nodal coordinate system, which are subsequently transformed to global Cartesian coordinates.

*NODE, SYSTEM=R

*NODE, SYSTEM=C

*NODE, SYSTEM=S

*NODE, NSET=DISC, SYSTEM=C
1, 10., 20., 5.

*SYSTEM
2, 0, 2

You can choose to assign nodes to a new node set (or to add nodes to an existing node set) in the order in which they are given. The node numbers will not be rearranged, and duplicates will not be removed.

This unsorted node set will affect node copies, node fills, linear constraint equations, multi-point constraints, and substructure nodes associated with retained degrees of freedom. An unsorted node set can be created only by directly defining an unsorted node set as described here or by copying an unsorted node set. Any additions or modifications to a node set using other means will result in a sorted node set.

*NSET, NSET=name, UNSORTED

There are several ways that nodes can be assigned to node sets as they are created.

*NODE, NSET=name
*NCOPY, NEW SET=name
*NFILL, NSET=name
*NGEN, NSET=name
*NMAP, NSET=name

You can assign nodes that you have defined previously (by specifying their coordinates, by filling in nodes between two bounds, or by generating them incrementally) to a node set by listing the nodes forming the set directly, by generating the node set, or by generating a node set from an element set.

*NSET, NSET=name

*NSET, NSET=A12
1, 3
10, 11,
A11

*NSET, NSET=name, GENERATE

*NSET, NSET=A13, GENERATE
100, 120, 10

*NSET, NSET=name, ELSET=name

*ELEMENT, TYPE=B21
50, 1, 2
100, 3, 4
*ELSET, ELSET=B1
50, 100
*NSET, NSET=A14, ELSET=B1

*NSET, NSET=name

*NSET, NSET=SET-A
1,
*NSET, NSET=SET-B
2,
*NSET, NSET=SET-AB
SET-A, SET-B
*NSET, NSET=SET-A
3,

In a model defined in terms of an assembly of part instances, all node sets must be defined within a part, part instance, or the assembly definition. If a node set is defined within a part (or part instance) definition, you can refer to the node numbers directly. To define an assembly-level node set, you must identify the nodes to be added to the set by prefixing each node number with the part instance name and a “.” (as explained in “Defining an assembly,” Section 2.9.1). An assembly-level node set can have the same name as a part-level node set.

*PART, NAME=PartA
   ...
   *NSET, NSET=set1
    1,3,26,500
*END PART

*ASSEMBLY, NAME=Assembly-1
   *INSTANCE, NAME=PartA-1, PART=PartA
    ...
   *END INSTANCE
   *INSTANCE, NAME=PartA-2, PART=PartA
    ...
   *END INSTANCE
   *NSET, NSET=set1
    PartA-1.1, PartA-1.3, PartA-1.26, PartA-1.500
    PartA-2.1, PartA-2.3, PartA-2.26, PartA-2.500
*END ASSEMBLY

*ASSEMBLY, NAME=Assembly-1
   *INSTANCE, NAME=PartA-1, PART=PartA
    ...
   *END INSTANCE
   *INSTANCE, NAME=PartA-2, PART=PartA
    ...
   *END INSTANCE
   *NSET, NSET=set1
    PartA-1.set1, PartA-2.set1
*END ASSEMBLY

*NSET, NSET=NsetName, INSTANCE=InstanceName

*ASSEMBLY, NAME=Assembly-1
   *INSTANCE, NAME=PartA-1, PART=PartA
    ...
   *END INSTANCE
   *INSTANCE, NAME=PartA-2, PART=PartA
    ...
   *END INSTANCE
   *NSET, NSET=set2
    PartA-1.11, PartA-1.12, PartA-1.13, PartA-1.14,
    PartA-2.21, PartA-2.22, PartA-2.23, PartA-2.24
   *NSET, NSET=set3, INSTANCE=PartA-1
    11, 12, 13, 14
   *NSET, NSET=set3, INSTANCE=PartA-2
    21, 22, 23, 24
*END ASSEMBLY

In ABAQUS/CAE many modeling operations are performed by picking geometry with the mouse. For example, a concentrated load can be applied by picking a point on a geometric part instance. Since the *CLOAD option refers to a node set, this “picked” geometry must be translated into a node set in the input file. Such sets are assigned a name by ABAQUS/CAE and marked as internal. You can view these internal sets using display groups in the Visualization module of ABAQUS/CAE (see Chapter 52, “Using display groups to display subsets of your model,” of the ABAQUS/CAE User's Manual).

*NSET, NSET=NsetName, INTERNAL

To define a straight line between the two end nodes, specify the number of the first end node, ; the number of the last end node, ; and the increment in node numbers between each node along the line, i. Therefore, i must be an integer such that is a whole number (not a fraction). The default is .

*NGEN

*NODE
1, 0., 0., 0.
6, 10., 0., 0.
*NGEN
1, 6, 1

To define a circular arc between the two end nodes, specify the number of the first end node, ; the number of the last end node, ; and the increment in node numbers between each node along the arc, i. Therefore, i must be an integer such that is a whole number (not a fraction). The default is .

In addition, you must specify the coordinates of one extra point, the center of the circle, either by giving the node number of a node that has already been defined or by giving the nodal coordinates directly. If both are supplied, the node number will take precedence over the coordinates.

If the coordinates are defined directly, they can be specified in a local coordinate system as described later.

The coordinates of the end nodes will be adjusted radially if the circle cannot be passed through both points. An arc of a circle of 180° through 360° will require more extensive definition. For this case you must define the plane of the circular disc by giving the normal to the disc; the nodes will then be numbered according to the right-hand rule about this normal.

*NGEN, LINE=C

To define a parabola between the two end nodes, specify the number of the first end node, ; the number of the last end node, ; and the increment in node numbers between each node along the parabola, i. Therefore, i must be an integer such that is a whole number (not a fraction). The default is .

In addition, you must specify the coordinates of one extra point, the midpoint on the arc between the two end points, either by giving the node number of a node that has already been defined or by giving the nodal coordinates directly. If both are supplied, the node number will take precedence over the coordinates.

If the coordinates are defined directly, they can be specified in a local coordinate system as described later.

*NGEN, LINE=P

You can specify the coordinates of the extra point that is required for a circle or a parabola in a local rectangular Cartesian system, a cylindrical system, or a spherical system. These coordinate systems are shown in Figure 2.1.1–2.

If a nodal coordinate system is in effect (see “Specifying a local coordinate system in which to define nodes”), the coordinates and normal direction specified in the node definition are assumed to be in the nodal coordinate system. If a nodal coordinate system is in effect and you specify the extra point for a circle or parabola in a local coordinate system, the input is first transformed according to the local system specified in the node definition and subsequently according to the nodal coordinate system.

*NGEN, SYSTEM=RC

*NGEN, SYSTEM=C

*NGEN, SYSTEM=S

You can create new nodes by translating and/or rotating the nodes in the old node set (see Figure 2.1.1–3). You specify the value of the translation in the X-, Y-, and Z-directions.

In addition, you specify the coordinates of the first point defining the rotation axis (point a in Figure 2.1.1–3), the coordinates of the second point defining the rotation axis (point b in Figure 2.1.1–3), and the angle of rotation (in degrees) about the a–b axis. The rotation can be applied multiple times as described later.

If you specify both translation and rotation, the translation is applied once before the rotation.

*NCOPY, OLD SET=name, CHANGE NUMBER=n, SHIFT

*NCOPY, OLD SET=name, CHANGE NUMBER=n, SHIFT, MULTIPLE=m

You can create new nodes by reflecting the coordinates of the old nodes through a line, a plane, or a point.

*NCOPY, OLD SET=name, CHANGE NUMBER=n, REFLECT=LINE

*NCOPY, OLD SET=name, CHANGE NUMBER=n, REFLECT=MIRROR

*NCOPY, OLD SET=name, CHANGE NUMBER=n, REFLECT=POINT

You can create new nodes by projecting the nodes in the old set from a pole node. Each new node will be located such that the corresponding old node is equidistant between the pole node and the new node. The pole node (see Figure 2.1.1–7) is identified by giving its number or, alternatively, its coordinates.

This method is particularly useful for creating nodes that are associated with infinite elements (“Infinite elements,” Section 22.2.1). In this case the pole node should be located at the center of the far-field solution.

*NCOPY, OLD SET=name, CHANGE NUMBER=n, POLE

For example, Figure 2.1.1–8 shows a simple quarter-cylinder model.

*NFILL, NSET=A
INSIDEA, OUTSIDEA, 4, 100
*NFILL, NSET=B
INSIDEB, OUTSIDEB, 4, 100
*NFILL
A, B, 5, 1000

You can concentrate the nodes toward one bound or the other by specifying b, the ratio of adjacent distances between nodes along each line of nodes generated as the nodes go from the first bounding node set to the second.

Thus, if b is less than one, the nodes are concentrated toward the first bounding node set; if b is greater than one, the nodes are concentrated toward the second bounding set. The value of b must be positive.

The bias intervals along the line from the first bounding node are L, , , , , , … (where L is the length of the first interval). In ABAQUS/Standard the bias value can be applied at every interval along the line or at every second interval along the line as described later.

*NFILL, BIAS=b

*NFILL, BIAS=0.6
INSIDE, OUTSIDE, 5, 100

*NFILL, BIAS=b, TWO STEP

In ABAQUS/Standard you can create quarter-point spacing for fracture mechanics calculations with second-order isoparametric elements (“Fracture mechanics: overview,” Section 11.4.1). This spacing gives a square root singularity in the strain field at the crack tip by placing the first node away from that point at one-quarter of the distance to the second point. The remaining nodes on each line are spaced so that the size of the elements will grow as the square of the distance from the singularity, with the midside nodes exactly at the midsides of the elements. This spacing produces a reasonable mesh gradation for this type of problem; however, better results can be obtained for crude meshes by making the size of the crack element smaller than the quarter-point spacing technique does.

*NFILL, SINGULAR

*NFILL, BIAS=0.8
MID, TOP, 4, 100
*NFILL, SINGULAR=1
TIP, OUTER, 5, 20

For all mappings except the blended quadratic mapping, you can specify a scaling factor to be applied to the local coordinates before they are mapped.

This facility is useful for “stretching” some of the coordinates that are given. For example, in cases where the local system uses some angular coordinates and some distance coordinates (cylindrical, spherical, etc.), it may be preferable to generate the mesh in a system that uses distance measures in the angular directions and then scale onto the angular coordinate system for the mapping.

*NMAP, NSET=name
first data line
second data line
scale factor for first local coord, scale factor for second local coord, 
scale factor for third local coord

In the case of a simple shift and/or rotation, point a in Figure 2.1.1–13 defines the origin of the local rectangular coordinate system defining the map. The local -axis is defined by the line joining points a and b. The local – plane is defined by the plane passing through points a, b, and c.

*NMAP, NSET=name, TYPE=RECTANGULAR

For mapping from cylindrical coordinates, point a in Figure 2.1.1–13 defines the origin of the local cylindrical coordinate system defining the map. The line going through point a and point b defines the -axis of the local cylindrical coordinate system. The local – plane for is defined by the plane passing through points a, b, and c.

*NMAP, NSET=name, TYPE=CYLINDRICAL

For mapping from skewed Cartesian coordinates, point a in Figure 2.1.1–13 defines the origin of the local diamond coordinate system defining the map. The line going through point a and point b defines the -axis of the local coordinate system. The line going through point a and point c defines the -axis of the local coordinate system. The line going through point a and point d defines the -axis of the local coordinate system.

*NMAP, NSET=name, TYPE=DIAMOND

For mapping from spherical coordinates, point a in Figure 2.1.1–13 defines the origin of the local spherical coordinate system defining the map. The line going through point a and point b defines the polar axis of the local spherical coordinate system. The plane passing through point a and perpendicular to the polar axis defines the plane. The plane passing through points a, b, and c defines the local plane.

*NMAP, NSET=name, TYPE=SPHERICAL

For mapping from toroidal coordinates, point a in Figure 2.1.1–13 defines the origin of the local toroidal coordinate system defining the map. The axis of the local toroidal system lies in the plane defined by points a, b, and c. The R-coordinate of the toroidal system is defined by the distance between points a and b. The line between points a and b defines the position. For every value of the -coordinate is defined in a plane perpendicular to the plane defined by the points a, b, and c and perpendicular to the axis of the toroidal system. lies in the plane defined by the points a, b, and c.

*NMAP, NSET=name, TYPE=TOROIDAL

To map by means of blended quadratics in ABAQUS/Standard, you define the new (mapped) coordinates of up to 20 “control nodes”: these are the corner and midedge nodes of the block of nodes being mapped. The mapping in this case is like that of a 20-node brick isoparametric element. Any of the midedge nodes can be omitted, thus allowing linear interpolation along that edge of the block. ABAQUS/Standard does not check whether the nodes in the set lie within the physical space of the block defined by the corner and midedge nodes: these control nodes simply define mapping functions that are then applied to all of the nodes in the set.

The control nodes should define a “well”-shaped block; for example, midedge nodes should be close to the midpoint of the edge. Otherwise, the mapping can be very distorted. For example, the nodes of a crack-tip 20-node element with midside nodes at the quarter points will not map correctly and, therefore, should not be used as the control nodes.

*NMAP, NSET=name, TYPE=BLENDED