Mechanical APDL Basic Analysis Guide

See the SET,LCWRITE,LCOPER,ESEL,NSLE, and PRNSOL command descriptions in the Command
Reference for further information.

7.3.3.3. Summable, Non-Summable, and Constant Data

By default, when you perform load case combinations in POST1, the 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. 191)). (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 mean-

ingful. 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. 192)). 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."

Constant data are those that cannot be meaningfully combined, such as element volumes and element
centroidal coordinates (see Table 7.4: Examples of Constant POST1 Results (p. 192)). These data are held
constant (unchanged) when the program performs a database operation.

Table 7.2: Examples of Summable POST1 Results

"Vector" Data

Item Component Item Component Item Component

U X, Y, Z ROT X, Y, Z V X, Y, Z

X, Y, Z, XY, YZ,

XZ

X, Y, Z, XY, YZ, EPEL

XZ

A X, Y, Z S

TG X, Y, Z TF X, Y, Z PG X, Y, Z

EF X, Y, Z D X, Y, Z H X, Y, Z

B X, Y, Z F X, Y, Z M X, Y, Z

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Additional POST1 Postprocessing