If you’re using APDL for finite element analysis, then you’re bound to come across the *Get command. This command is integral to the entire finite element modeling and analysis process. Learning how to use it will greatly improve your proficiency in using APDL commands.
First, let’s take a look at how ANSYS Help explains the usage of the *Get command:
*GET, Par, Entity, ENTNUM, Item1, IT1NUM, Item2, IT2NUM
Par: the variable name defined to store the extracted data;
Entity: the keyword that specifies the object to extract information from, including NODE, ELEM, KP, LINE, AREA, VOLU, PDS, etc.;
ENTNUM: the numerical identifier of the current object, such as the node number for a node or the element number for an element;
Item1: the information to extract, which can be quite diverse;
IT1NUM: used in conjunction with Item1.
With so many parameters to input, how can we determine the specific input? Next, I’ll show you how to use Help to search for the keywords of *Get.
Before searching, we first need to understand which category the data we want to extract belongs to. Is it preprocessing data? Solving data? Postprocessing data? Once we know which category the data falls under, we can follow Help to find the relevant keywords.
We’ll use the most common operation, extracting the displacement in the X direction of a certain node after the analysis, to illustrate this process.
There’s no doubt that extracting the X-direction displacement belongs to postprocessing, which means the data we need to extract falls under the category of postprocessing. Therefore, when we look at Help, we can skip to the postprocessing section. Here’s an example:
Through the above process, we can find the input format for using the command to extract node displacement data. Pay attention to the specific items corresponding to each parameter in the last image.
For example, if we need to extract the X-direction displacement data of node 22 and assign it to the variable nodeA, the format is as follows:
The above process is the general procedure for using *Get. Beginners may find it cumbersome, but it’s a gradually familiarizing process. When we can remember common *Get command operations, we can easily extract data, greatly improving our work efficiency.
Here are some common *Get commands:
!Extract the maximum number of items
!Extract the minimum number of items
!Extract the total number of items
The items referred to here can include keypoints (kp), lines (line), areas (area), volumes (volume), nodes (node), and elements (elem). In the specific usage process, we simply replace kp with the corresponding keyword.
!Obtain the number of sub-steps in a certain load step (especially suitable for nonlinear analysis with automatic time steps)
!Extract node displacement
!Extract node stress
Since stress has many types, IT1num can be divided into many types as well, such as:
*GET, Par, NODE,S,X(Y/Z/XY/YZ/XZ) ! indicating the extraction of stress components
*GET, Par, NODE,S,1(2/3) ! indicating the extraction of the three principal stresses
*GET, Par, NODE,S,INT(EQV) !indicating the extracting equivalent stress.
!Extracting support reactions:
*GET, Par, Fsum, 0, item, FX/FY/FZ/MX/MY/MZ
!Extracting the frequencies of each mode (buckling) analysis step:
*GET, Par, Mode, N, Freq