...
...
Software
...
performs
...
computation
...
with
...
16
...
digits
...
of
...
accuracy,
...
some
...
of
...
which
...
may
...
be
...
lost
...
when
...
analysis
...
involves
...
systems
...
of
...
significantly
...
different
...
stiffness,
...
where
...
lower-order
...
values
...
are
...
truncated
...
to
...
suit
...
operations
...
with
...
higher-order
...
values.
...
When
...
lost
...
accuracy
...
occurs,
...
a
...
warning
...
message
...
reports
...
the
...
location
...
of
...
the
...
occurrence
...
such
...
that
...
users
...
may
...
edit
...
the
...
model
...
if
...
necessary.
...
Some
...
situations
...
where
...
numerical
...
instability
...
may
...
occur
...
include:
...
- When the rigid-diaphragm assumption is applied to a slab with flexible interconnecting objects.
- When multiple releases are assigned to a joint, causing joint DOF to become orphaned (without stiffness). In this instance, numerical instability warnings indicate a modeling problem which should be corrected.
Depending on the number of digits lost, actions which result include the following:
- Less than 6 does not generate a response because the values and solution are sufficiently accurate.
- Between 6 and 11 lost digits of accuracy may or may not create numerical problems, therefore a warning message is reported which reads: The results of the analysis may still be acceptable but the user should carefully check the results, especially the global sums of loads.
- Over 11 digits lost causes analysis to terminate because results may not be sufficiently accurate. The location of the numerical problem is indicated, and a warning message is presented which prompts the user to check and revise the model.