Mechanical APDL Basic Analysis Guide - Ansys

Chapter 7:The General Postprocessor (POST1)
Note
You can define a load case at any arbitrary time by using the SET command (to specify the time
argument) and then using LCWRITE to create that load case file. The values will be a linear interpolation
of the results already available before and after your specified time.
A load case combination is an operation between load cases, typically between the load case currently in
the database and a load case on a separate results file (or on the load case file, explained later). The outcome
of the operation overwrites the results portion of the database, which permits you to display and list the
load case combination.
A typical load case combination involves the following steps:
1. Define load cases using the LCDEF command (Main Menu> General Postproc> Load Case> Create
Load Case).
2. Read one of the load cases into the database using the LCASE command (Main Menu> General
Postproc> Load Case> Read Load Case).
3. Perform the desired operation using the LCOPER command (Main Menu> General Postproc> Load
Case> operation).
As an example, suppose the results file contains results for several load steps, and you want to compare
load steps 5 and 7 and store the maximum in memory. The commands to do this would look like this:
LCDEF,1,5 ! Load case 1 points to load step 5
LCDEF,2,7 ! Load case 2 points to load step 7
LCASE,1 ! Reads load case 1 into memory
LCOPER,MAX,2 ! Compares database with load case 2 and stores the
! maximum in memory
The database now contains the maximum of the two load cases, and you can perform any desired postprocessing
function.
Note
Load case operations (LCOPER) are performed only on the raw solution results in the solution
coordinate system.
The solution results are:
• Element component stresses, strains, and nodal forces in the element coordinate systems
• Nodal degree-of-freedom values, applied forces, and reaction forces in the nodal coordinate systems
To have a load case operation act on the principal/equivalent stresses instead of the component stresses,
issue the SUMTYPE,PRIN command.
It is important that you know how load case operations are performed. Many load case operations, such as
mode combinations, involve squaring, which renders the solution results unsuitable for transformation to
the results coordinate system, typically the Global Cartesian, and unsuitable for performing nodal or element
averages. A typical postprocessing function such as printing or displaying average nodal stresses (PRNSOL,
PLNSOL), for example, involves both a coordinate system transformation to the results coordinate system
and a nodal average. Furthermore, unless SUMTYPE,PRIN has been requested, principal/equivalent stresses
are not meaningful when computed from squared component values.
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