larger value should be used for shell, beam, and link elements. Use a smaller value if the specified time
for a load step is small and a larger value if the specified time for a load step is large.
With the energy dissipation method, the program calculates the damping factor (based on the input
energy dissipation ratio) during the first substep after the command executes. The program uses the
calculated damping factor by predicting the element potential energy and stabilization energy at the
end of the load step based on the data of the current substep, then setting the energy dissipation ratio
equal to or smaller than the specified value. This prediction could be inaccurat e when the problem is
highly nonlinear. It is a good practice to examine the energies after the solution has completed because
the energy dissipation ratio of the solution could be greater than the ratio initially specified via the
STABILIZE command.
Damping Factor
The numerical damping factor is the value that the program uses to calculate stabilization forces for
all subsequent substeps. The damping factor is highly dependent on the element size, shape, material,
and other factors including the size of the load step and time used in the load step. The damping factor
therefore varies from element to element.
During a run using the energy dissipation method, the program calculates the damping factor and reports
an element volume weighted average value in the .out file. The value reported provides a reference
value for you to specify if you want to apply a damping factor as the stabilization control in a subsequent
run. When you input a damping factor as the stabilization control, the program uses that value for all
applicable elements; therefore, the results can differ from those of a run where you use the energy
dissipation method exclusively.
The value used as a damping factor can usually have a much wider range of variance than the value
used for the energy dissipation ratio (which can only change from 0 to 1 in most analyses). If it becomes
apparent that your analysis is too sensitive to the energy dissipation ratio value, try using the damping
factor.
8.11.1.1.2. Applying a Constant or Reduced Stabilization Force
When stabilization is active, the program can apply the stabilization force in two ways: constant (STA-
BILIZE,CONSTANT) or reduced (STABILIZE,REDUCE). The constant option keeps the damping factor
(calculated or input) unchanged during each substep of a load step. The reduced option reduces the
damping factor linearly to zero at the end of the load step.
Although the constant option works well in most cases, some stabilization forces usually remain at the
end of the load step. Unless the stabilization forces are very small, convergence difficulties may occur
if stabilization is deactivated in the next load step. It may be difficult to converge for the first substep
of the following load step because the stabilization forces suddenly becomes zero. In such a case, use
the reduced option for the previous load step.
ExampleConvergence difficulties when using the constant option can occur in an analysis of
creep phenomena, where the load is usually applied quickly in the first load step, but
no new load is applied at the second load step (which usually has a very long time span).
The stabilization forces could be large at the end of the first load step because the time
is short and pseudo velocity is high at the first load step. In this case, if stabilization is
needed for the first load step, the reduced option is best. The second load step is usually
stable so that stabilization is unnecessary.Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationNonlinear Structural Analysis