About a month ago we published an article on “What Every User Should Know About Tables in ANSYS Mechanical APDL” At the end of that article we had a section on “Other Stuff” and expressed our hope to cover those subjects in the future. The future is now. If you are not very familiar with table arrays, make sure you review the previous article before delving into nesting and 4/5 dimension tables in this article.
By the way, the funky table at the end of the article got a lot of good feedback, so I’ve googled around and found some other interesting tables. The one here at the top is what you get if you google “complicated table”
Nested Tables
As you will remember from memorizing the previous article, a common use for tables is the set them up to give you a value for a given “primary variable” that is determined by the solver at a given point in the solution. Possible primary variables are: TIME, FREQ, X, Y, Z, TEMP, VELOCITY, PRESSURE and SECTOR. But what if you want to use one of those primary variables to look up a value, then use that value to then interpolate a second value?
A good example is that you have a piece of rotating equipment and the value of the heat transfer coefficient (HF) is a function of RPM and the radius of a given element face. But RPM varies over time. What you can do is make the HF table point to and RPM table that is based on the primary variable time:
Table: rpm TIME vs
|0.7889E-30
|----------
0.000 | 0.000
10.00 | 5.000
40.00 | 20.00
60.00 | 30.00
(We’ll cover the wrttbl macro below.)
So at a given substep, the program will take time and figure out what RPM needs to be. Then it will use RPM and the radius (X in CSYS 1) to figure out the convection coefficient for each node.
As you can imagine, you can get pretty sophisticated with this. The key is that the name of the table you use for the calculated value is input into the variables to interpolate on for the second table, using the *DIM command.
Another common use is scaling tables based on some value. Let say you have a pressure table and the total pressure is scaled over time, based on time. You would make a pressure table that is dependent on say X and y. It would have two planes. One with 0 values and one with the max values. Then you would make a scale table that scales from 0 to 1 based on time. It would look like this:
As always with tables, double check things and make sure you have your rows and columns correct. Start simple, and then add more detail. Testing out on a 2×2 or 3×3 tables is a good way to start.
4 and 5 Dimension Arrays and Tables
This section applies to both arrays and tables, so it is a bit beyond the scope of the title, but I hope you will forgive me.
Most users will simply use a one, two, or even three dimension array or table (row, column, plane). However, both arrays and tables support two more dimensions: books and shelves. Because this capability is a later addition to the program, it behaves a little differently. You need to add values for the size of the book (KMAX) and the shelf (MMAX) as well as variable names for each: VAR4 and VAR5
The first difference is in the *DIM command. For normal arrays and tables you use:
It is important to be aware of this because if you look at the manual entry for *DIM it only lists the 3 dimension version of the command, and these variations are covered in the notes.
Once the array or table is defined you have to fill it using APDL commands, this size is not supported in the user interface. The same commands are used, but instead of supplying one, two or three indices values, you supply four or five.
The following is an example of defining a table in terms of location (X,Y,Z), Time, and Temperature. This is the most common usage of a five dimension table:
*dim,ldval,tab5,3,3,3,3,3,X,Y,Z,TIME,TEMP ! table
*taxis,ldval(1,1,1,1,1),1,-2.3,0,3.4 ! X Range
*taxis,ldval(1,1,1,1,1),2,-1.2,0,1.8 ! Y Range
*taxis,ldval(1,1,1,1,1),3,-3.6,0,4.5 ! Z Range
*taxis,ldval(1,1,1,1,1),4,0,5,10 ! Time Range
*taxis,ldval(1,1,1,1,1),5,32,320,500 ! Temp Range
*do,ii,1,3
*do,jj,1,3
*do,kk,1,3
*do,ll,1,3
*do,mm,1,3
!silly made up equation to fill the table with
ldval(ii,jj,kk,ll,mm) = ii*.123+jj/.2+ll*kk+mm*JJ*JJ
*enddo
*enddo
*enddo
*enddo
*enddo
Writing a Table to a File
For simple 2D tables with up to 10 columns, I use a cheesy macro I wrote called wrttbl.mac. It was used above. It is a bit of a brute force method, because it has code blocks for from 0 to 10 columns. A more general approach would build the actual *VWRITE commands with *VWRITES… It should also be expanded to do Planes. Maybe for a future article.
Anyhow, here it is, maybe you will find it useful.
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