Mechanical APDL Basic Analysis Guide - Ansys

To get usable results combine the results of each load step in POST1. You can do so using load case combinations,
by saving and summing all results data at a given circumferential angle. The following example
illustrates this procedure:
/POST1
SET,1,1,,,,90 ! Read load step 1 with circumferential
! angle of 90°
LCWRITE,1 ! Write load case 1 to load case file
SET,2,1,,,,90 ! Read load case 2, with circumferential
! angle of 90°
LCOPER,ADD,1 ! Use load case operations to add results
! from first load case to second
ESEL,S,ELEM,,1 ! Select element number 1
NSLE,S ! Select all nodes on that element
PRNSOL,S ! Calculate and list component stresses
PRNSOL,S,PRIN ! Calculate and list principal
! stresses S1, S2, S3; stress intensity
! SINT; and equivalent stress SEQV
FINISH
See the SET, LCWRITE, LCOPER, ESEL, NSLE, and PRNSOL command descriptions in the Command Reference
for further information.
7.4.3.3. Summable, Non-Summable, and Constant Data
By default, when you perform load case combinations in POST1, the ANSYS program combines only data
that are valid for linear superposition, such as displacements and component stresses. Other data, such as
plastic strains and element volumes, are not combined, because it is not appropriate or meaningful to
combine such data. To determine which data should be combined and which should not, result items are
grouped into summable, non-summable, and constant data. This grouping applies to the following POST1
database operations:
• Load case combinations (using LCOPER ).
• Reading in a load case with active scale factors (using LCFACT or LCASE).
• Reading in results data and modifying them using the FACT or ANGLE field on the SET command.
Summable data are those that can "participate" in the database operations. All primary data (DOF solutions)
are considered summable. Among the derived data, component stresses, elastic strains, thermal gradients
and fluxes, magnetic flux density, etc. are considered summable (see Table 7.2: Examples of Summable POST1
Results (p. 180)). (For an inclusive list of summable data, see the description of the ETABLE command in the
Command Reference.)
Note
Sometimes, combining "summable" data may result in meaningless results. For example, adding
nodal temperatures from two load cases of a linear, pure-conduction analysis gives meaningful
results, but if convection is involved, the addition of temperatures is not meaningful. Therefore,
exercise your engineering judgement when reviewing combined load cases.
Non-summable data are those that are not valid for linear superposition, such as nonlinear data (plastic
strains, hydrostatic pressures), thermal strains, magnetic forces, Joule heat, etc. (see Table 7.3: Examples of
Non-Summable POST1 Results (p. 180)). These data are simply set to zero when the programs performs a
database operation. You may combine non-summable data using LCSUM,ALL before your LCOPER commands,
but you are cautioned on interpreting these values appropriately."
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Notes
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