DATA SET 8: ELEMENT INCIDENCES

Formats for one-, two-, and three-dimensional problems are slightly different. However, the element incidences can all be automatically generated if the global node numbers of elements appear in regular patterns. This data set is not needed if Logical Unit 11 is used as input (i.e., if KVI > 0 in Data Set 2).

One-Dimensional Problems:

No input data is required. Node numbers are automatically generated, which requires the nodal coordinates in ascending or descending order. All elements are assigned material type 1. In order to change the material type, you have to specify material type corrections in Data Set 9 and set NCM in Data Set 2 accordingly.

Two-Dimensional Problems:

Typically, a total of NEL lines are needed, one for each element. However, only one line is needed if a group of elements appears in a regular pattern. Free-field format input for each line contains the following information:

  1. MI = Global element number.
  2. IE(MI,1) = Global node number of the first node of element MI.
  3. IE(MI,2) = Global node number of the second node of element MI.
  4. IE(MI,3) = Global node number of the third node of element MI.
  5. IE(MI,4) = Global node number of the fourth node of element MI.
  6. IE(MI,5) = Material type to be applied to element MI.
  7. MODL = Number of elements in the direction of the smaller increment in node numbers.
  8. NLAY = Number of elements in the direction of the larger increment in node numbers.

IE(MI,1) to IE(MI,4) are numbered beginning with the lower left corner and progressing around the element in a counterclockwise direction. For a logically rectangular block of elements, it is only necessary to specify the first element, the width MODL and the length NLAY, where MODL and NLAY are measured in elements. Element numbering proceeds most rapidly along the MODL dimension and least rapidly along the NLAY dimension. Figure A.1 provides an example. The object is considered to be logically rectangular because it has width MODL = 3 on two opposite sides and length NLAY = 5 on the other two opposite sides. To generate definitions of elements 1 through 15 automatically, including both the incidence and material type, only one line is necessary. If the material type does not follow the same pattern as the element incidences, you can change the material type by using the material type correction option in Data Set 9 and setting NCM in Data Set 2 accordingly.

MI IE(M,1) IE(M,2) IE(M,3) IE(M,4) IE(M,5) MODL NLAY
1 1 5 6 2 1 3 5

Fig. A.1. Automatic generation of a 3 x 5 logically rectangular mesh.

Note: For triangular elements IE(MI,4) has to be set to 0.

 

Three-Dimensional Problems:

Usually, a total of NEL records are needed. Each record contains the following variable and is FREE-FORMATTED.

  1. MI = Global element number of the first element in a sequence,
  2. NSEQ = NSEQ subsequent elements will be automatically generated,
  3. MIAD = Increment of MI for each of the NSEQ subsequent elements,
  4. IE(MI,1) = Global node number of the first node of element MI.
  5. IE(MI,2) = Global node number of the second node of element MI.
  6. IE(MI,3) = Global node number of the third node of element MI.
  7. IE(MI,4) = Global node number of the fourth node of element MI.
  8. IE(MI,5) = Global node number of the fifth node of element MI.
  9. IE(MI,6) = Global node number of the sixth node of element MI.
  10. IE(MI,7) = Global node number of the seventh node of element MI.
  11. IE(MI,8) = Global node number of the eighth node of element MI.
  12. IEMAD = Increment of IE(MI,1) through IE(MI,8) for each of the NSEQ elements.

All elements are assigned material type 1. To change the material type, you have to specify material type corrections in Data Set 9 and set NCM in Data Set 2 accordingly.

Note: For tetrahedral elements, set IE(MI,5) – IE(MI,8) equal to zeros. For pentahedral elements, set IE(MI,7) and IE(MI,8) equal to zeros. For hexahedral elements, IE(MI,1) - IE(MI,8) are numbered according to the convention shown in the Fig. A.2. The first four nodes start from the front lower left corner and progressing around the bottom element surface in a counterclockwise direction. The other four nodes begin from the front upper left corner and progressing around the top element surface in a counterclockwise direction. Pentahedrons are similarly numbered except that there are three nodes on the top and bottom faces.

Figure A.2. Node numbering convention of three-dimensional elements.

v1.0 - 1/14/1999

Jin-Ping Gwo, email: jgwo@umbc.edu