MultiPhysicsVault/.raw/AbaqusAnalysisUserGuide1/AbaqusAnalysisUserGuide1_016.md

• In the second method you specify only the nodes on the bottom face of the cohesive element and Abaqus will create the remaining nodes, numbering them according to an offset number that you specify.
• In the third method, which is applicable only to pore pressure cohesive elements, you specify the nodes on the bottom and top faces. Abaqus will create the remaining middle-face nodes according to an offset number that you specify.

Defining a cohesive element by specifying all nodes

With this method you specify all nodes that define the cohesive element. See “Two-dimensional cohesive element library,” Section 32.5.9; “Three-dimensional cohesive element library,” Section 32.5.10; and “Axisymmetric cohesive element library,” Section 32.5.11, for the element node numbering definition.

Input File Usage:

Use the following option to specify the element number and the nodes that define the element:

*ELEMENT, TYPE=name

For example, the following lines create COH3D8 element number 11 that has node numbers 1, 2, 3, 4, 1001, 1002, 1003, and 1004:

*ELEMENT, TYPE=COH3D8 11, 1, 2, 3, 4, 1001, 1002, 1003, 1004

Defining a cohesive element by specifying only the bottom face nodes

With this method you specify only the nodes on the bottom face of the cohesive element and a positive offset number. With displacement cohesive elements, the offset number is added to the bottom face node numbers to create the corresponding nodes on the top face. With pore pressure cohesive elements, the offset number first is added to the bottom face node numbers to create the corresponding nodes on the top face, then the offset number is added to the top face node numbers to create the corresponding nodes on the middle face.

Input File Usage:

Use the following option to specify the nodes on the bottom face of the element and a positive offset number for nodes on the remaining face or faces:

*ELEMENT, TYPE=name, OFFSET=offset number

For example, the following lines create COH3D8 element number 11 that has node numbers 1, 2, 3, 4, 1001, 1002, 1003, and 1004:

*ELEMENT, TYPE=COH3D8, OFFSET=1000 11, 1, 2, 3, 4

and the following lines create pore pressure cohesive element COH3D8P element number 11 that has node numbers 1, 2, 3, 4, 1001, 1002, 1003, 1004, 2001, 2002, 2003, and 2004 (nodes 1, 2, 3, and 4 define the bottom face; nodes 1001, 1002, 1003, and 1004 define the top face; and nodes 2001, 2002, 2003, and 2004 define the middle face):

*ELEMENT, TYPE=COH3D8P, OFFSET=1000 11, 1, 2, 3, 4

Defining a pore pressure cohesive element by specifying only the bottom and top face nodes

With this method you specify only the nodes on the bottom and top faces of the pore pressure cohesive element and a positive offset number. The offset number is added to the bottom face node numbers to create the corresponding nodes on the middle face.

Input File Usage:

Use the following option to specify the nodes on the bottom and top faces of the pore pressure cohesive element and a positive offset number for the remaining middle-face nodes:

*ELEMENT, TYPE=name, OFFSET=offset number

For example, the following lines create a pore pressure cohesive element COH3D8P element number 11 that has node numbers 1, 2, 3, 4, 1001, 1002, 1003, 1004, 2001, 2002, 2003, and 2004 (nodes 1, 2, 3, and 4 define the bottom face; nodes 1001, 1002, 1003, and 1004 define the top face; and nodes 2001, 2002, 2003, and 2004 define the middle face):

*ELEMENT, TYPE=COH3D8P, OFFSET=2000

11, 1, 2, 3, 4, 1001, 1002, 1003, 1004

Grouping elements into element sets

Element sets are used as convenient cross-references for defining loads, properties, etc. Element sets are the fundamental references of the model and should be used to assist the input definition. The members of an element set can be individual elements or other element sets. An individual element can belong to several element sets.

Elements can be grouped into element sets when they are created or after they have already been defined. In either case each element set is assigned a name. Element set names can be up to 80 characters long.

The same name can be used for a node set and for an element set.

All elements within an element set will be arranged in ascending order of their element number, and duplicates will be removed.

Once elements are assigned to an element set, additional elements can be added to the same element set; however, elements cannot be removed from an element set.

Assigning elements to an element set as they are created

There are several ways that elements can be assigned to element sets as they are created.

Input File Usage:

Use any one of the following options:

*ELEMENT, ELSET=name

*ELGEN, ELSET=name

*ELCOPY, NEW SET=name

Assigning previously defined elements to an element set

You can assign elements that you have defined previously (by specifying their nodes, by generating them incrementally, or by copying existing elements) to an element set by listing the elements forming the set directly or by generating the element set.

Listing the elements that form the set directly

You can list the elements that form the element set directly. Previously defined element sets, as well as individual elements, can be assigned to element sets.

Input File Usage: *ELSET, ELSET=name

For example, the following lines add elements 3, 13, and 20 to set LEFT:

*ELSET, ELSET=LEFT
20
3, 13 

The following lines add elements 5 and 16 to the existing set LEFT:

*ELSET, ELSET=LEFT
5, 16
** The above data line is equivalent to specifying 5, 16, LEFT 

The following lines add elements 22, 14, and all elements in set LEFT to set B:

*ELSET, ELSET=B
22, 14, LEFT 

Thus, element set B contains the following elements: 3, 5, 13, 14, 16, 20, and 22. Element set LEFT can be assigned to element set B since the definition of LEFT occurs before the definition of B.

Generating the element set

To generate an element set, you must specify a first element, ; a last element, ; and the increment in element numbers between these elements, i. All elements going from to in steps of i will be added to the set. Therefore, i must be an integer such that ( e _ { 2 } - e _ { 1 } ) / i is a whole number (not a fraction). The default is .

Input File Usage: *ELSET, ELSET=name, GENERATE

For example, the following lines add elements 1, 3, 5, …, 19, 21 and elements 39, 49, 59, …, 129, 139 to set UP:

*ELSET, ELSET=UP, GENERATE
1, 21, 2
39, 139, 10 

Limitation on updating element sets that are used to define other element sets

If an element set is constructed from previously defined element sets, subsequent updates to these sets are not taken into account.

Input File Usage: *ELSET, ELSET=name
For example, the following lines add elements 1 and 2, but not 3, to the set SET-AB while adding elements 1 and 3 to set SET-A:
*ELSET, ELSET=SET-A
1,
*ELSET, ELSET=SET-B
2,
*ELSET, ELSET=SET-AB
SET-A, SET-B
*ELSET, ELSET=SET-A
3, 

Defining part and assembly sets

In a model defined in terms of an assembly of part instances, all element sets must be defined within a part, part instance, or the assembly definition. If an element set is defined within a part (or part instance), you can refer to the element numbers directly. To define an assembly-level element set, you must identify the elements to be added to the set by prefixing each element number with the part instance name and a “.” (as explained in “Defining an assembly,” Section 2.10.1). An assembly-level element set can have the same name as a part-level element set.

Example

The following input defines an element set, set1, that belongs to part PartA and will be inherited by every instance of PartA:

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

An element set with the same name is defined at the assembly level as follows:

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

*ELSET, ELSET=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-level element set set1 contains all the elements from element sets set1 belonging to part instances PartA-1 and PartA-2. Therefore, the elements are assigned to two separate element sets: one at the part instance level and one at the assembly level. An assembly-level element set called set1 could be created with entirely different elements than those that belong to the part set; part- and assemblylevel element sets are independent. However, since in this example the same elements are assigned to both the part- and assembly-level element sets set1, the assembly-level set could alternatively be defined by

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

This element set definition is equivalent to the previous example, where the elements are listed individually.

Alternate method for defining assembly-level element sets

Sometimes it is not convenient to define an assembly-level element set by referring to part-level element sets. In such cases a set definition containing many elements can get quite lengthy. Therefore, an alternate method is provided.

Input File Usage: *ELSET, ELSET=ElsetName, INSTANCE=InstanceName

The following example shows two equivalent ways to define an assembly-level element set; once by prefixing each element number with a part instance name (as shown above) and once using the more compact INSTANCE notation:

*ASSEMBLY, NAME=Assembly-1
*INSTANCE, NAME=PartA-1, PART=PartA
...
*END INSTANCE
*INSTANCE, NAME=PartA-2, PART=PartA
...
*END INSTANCE
*ELSET, ELSET=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
*ELSET, ELSET=set3, INSTANCE=PartA-1
11, 12, 13, 14
*ELSET, ELSET=set3, INSTANCE=PartA-2
21, 22, 23, 24
*END ASSEMBLY

When the *ELSET option is used more than once with the same name, as it is with set3, the elements in the second use of *ELSET are appended to the set created by the first use of *ELSET.

Internal element sets created by Abaqus/CAE

In Abaqus/CAE many modeling operations are performed by picking geometry with the mouse. For example, a surface can be created by picking a face on a geometric part instance. Since the *SURFACE option refers to an element set, this “picked” geometry must be translated into an element 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 78, “Using display groups to display subsets of your model,” of the Abaqus/CAE User’s Guide).

Input File Usage: *ELSET, ELSET=ElsetName, INTERNAL

Transferring of element sets

If the results of an Abaqus/Explicit analysis are imported into an Abaqus/Standard analysis (or vice versa) or results from an Abaqus/Standard analysis are imported into another Abaqus/Standard analysis (see “Transferring results between Abaqus analyses: overview,” Section 9.2.1), all element set definitions in the original analysis are imported by default. Alternatively, you can import only selected element set definitions; see “Importing element set and node set definitions” in “Transferring results between Abaqus analyses: overview,” Section 9.2.1, for details.

If a three-dimensional model is generated from a symmetric model (see “Symmetric model generation,” Section 10.4.1), all element sets in the original model will be used (and expanded) in the generated model.

Creating elements from existing elements by generating them incrementally

You can generate elements incrementally from existing elements. The newly created elements are always the same element type as that of the master element.

Abaqus first generates a row of elements by copying the node pattern of a given element with prescribed increments in the node and element numbers. This row can then be repeated to form a layer, which can also be repeated to form a block.

To generate a row of elements, you must specify the following information:

• The master element number. The master element must exist at the time that the generation is specified, although it can be an element that has just been defined in this same element generation.

• The number of elements to be defined in the first row generated, including the master element.
• The increment in node numbers of corresponding nodes from element to element in the row. The default is 1. All element node numbers (except special-purpose nodes, discussed later) will increase by the same value.
• The increment in element numbers in the row. The default is 1.

To copy this newly created master row to create a layer of elements, you must specify the following additional information:

• The number of rows to be defined, including the master row.
• The increment in node numbers of corresponding nodes from row to row.
• The increment in element numbers of corresponding elements from row to row.

To copy this newly created master layer to create a block of elements, you must specify the following additional information:

• The number of layers to be defined, including the master layer.
• The increment in node numbers of corresponding nodes from layer to layer.
• The increment in element numbers of corresponding elements from layer to layer.

Input File Usage: *ELGEN

For example, the elements forming the quarter cylinder shown in Figure 2.2.1–1 can be generated by the following lines:

*ELGEN

1, 3, 1, 1, 5, 10, 10, 6, 100, 100

Incrementing special-purpose nodes

By default, the following nodes are not incremented:

• rigid body reference nodes for IRS-type and drag chain elements; and
• nodes used to define the direction of the first cross-section axis for beams or frames in space.

You can specify that all nodes should be incremented. You define the increment between node numbers as described above. Usually the incrementation of all nodes is needed only for nodes used to define the direction of the first cross-section axis for beams in space.

Input File Usage: *ELGEN, ALL NODES

Creating elements by copying existing elements

You can create new elements by copying existing elements. You must identify the existing element set to copy and specify an integer constant that will be added to the node numbers of the existing elements to define the node numbers of the new elements. Likewise, you must specify an integer constant that will be added to the element numbers of existing elements to define element numbers for the elements being created.

radar

Element	Value
1	501
2	511
3	521
4	421
5	531
6	431
7	441
8	541
9	341
10	341
11	331
12	231
13	231
14	241
15	141
16	141
17	131
18	131
19	221
20	221
21	21
22	21
23	22
24	22
25	21
26	21
27	201
28	101
29	111
30	111
31	31
32	31
33	31
34	31
35	31
36	31
37	31
38	31
39	31
40	301
41	41
42	42
43	42
44	42
45	42
46	42
47	42
48	42
49	42
50	501
51	511
52	521
53	531
54	541
a. Element n (2 elements)

a. Element numbers
(Only visible elements shown).

radar

Node	Value
1	101
2	11
3	12
4	13
5	14
6	24
7	33
8	43
9	44
10	53
11	111
12	21
13	22
14	14
15	23
16	32
17	31
18	31
19	131
20	201
21	211
22	121
23	22
24	33
25	42
26	41
27	41
28	141
29	151
30	301
31	311
32	321
33	32
34	33
35	43
36	42
37	41
38	141
39	141
40	151
41	141
42	141
43	43
44	44
45	52
46	51
47	51
48	52
49	53
50	601
51	51
52	52
53	53
54	54
55	551
56	651
57	641
58	541
59	531
60	631
61	621
62	521
63	531
64	541
65	641
66	631
67	531
68	521
69	511
70	501
71	411
72	311
73	211
74	111
75	121
76	221
77	321
78	331
79	341
80	351
81	361
82	371
83	381
84	391
85	401
86	411
87	421
88	431
89	441
90	451
91	461
92	471
93	481
94	491
95	501
96	511
97	521
98	531
99	541
100	551

b. Node numbers
(Only visible nodes shown).

Figure 2.2.1–1 Element generation example.

You can assign the newly created elements to an element set. If you do not specify an element set name for the newly created elements, they are not assigned to an element set.

Input File Usage:

*ELCOPY, OLD SET=name, NEW SET=new_name, SHIFT NODES=number, ELEMENT SHIFT=number

For example, the following data lines will generate new elements in set B that are copies of all elements in set A at the time this option is processed, with 1000 added to each element number and to each node number in the definitions of the new elements. The members of set A at the time the line is processed are those elements defined to be in set A by all element generation and element set definition lines that appear in the input file prior to this *ELCOPY option.

*ELCOPY, OLD SET=A, NEW SET=B, ELEMENT SHIFT=1000, SHIFT NODES=1000

Special considerations for continuum elements

When copying existing elements, you can choose to modify the node numbering sequence for the elements being created to avoid creating continuum elements that violate the Abaqus convention for counterclockwise element numbering. This modification is normally required when the nodes have been generated by copying existing nodes (“Creating nodes by copying existing nodes” in “Node definition,” Section 2.1.1).

Input File Usage:

*ELCOPY, REFLECT

For example, assume element 1 is in element set A and is defined by nodes 1, 2, 3, 4. The following data line will generate element number 11, also in set A, with nodes 11, 14, 13, and 12:

*ELCOPY, OLD SET=A, NEW SET=A, ELEMENT SHIFT=10, SHIFT NODES=10, REFLECT

If the REFLECT parameter is not used, the new element will be defined by the node sequence 11, 12, 13, 14 and will violate the counterclockwise element numbering convention used with continuum elements (see Figure 2.2.1–2).

text_image

13 14 12 11 4 3 1 2 y x

Figure 2.2.1–2 Example of modification of node numbering sequence.