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Section 5
5-241
f
5
- time step of loading, default = one twelfth of the period
corresponding to the frequency of the harmonic loading. It is
best to use the default; or
f
6
- subdivide a ¼ cycle into this many integer time steps. Default
= 3.
f
5
or f
6
is used only to digitize the forcing function. It is not the
DT used to integrate for the responses. More subdivisions or
smaller step size will make the digitized force curve more closely
match a sine wave. The default is usually adequate.
Please be aware that if a Cosine function or Sine with nonzero
phase angle is entered, the force at the arrival time will be
nonzero; there will be a sudden application of force over a single
integration step (DT) at that time.
Example
UNIT . . .
DEFINE TIME HISTORY
TYPE 1 FORCE
0.0 1.0 1.0 1.2 2.0 1.8 3.0 2.2
4.0 2.6 5.0 2.8
TYPE 2 ACCELERATION
0.0 2.5 0.5 2.7 1.0 3.2 1.5 3.8
2.0 4.2 2.5 4.5 3.0 4.5 3.5 2.8
ARRIVAL TIME
0.0 1.0 1.8 2.2 3.5 4.4
DAMPING 0.075
Notes
The 'READ fn' command is to be provided only if the history of
the time varying load is to be read from an external file. fn is the
file name and may be up to 72 characters long. If the data on the
file consists only of amplitudes, then enter f
8
as the delta time
spacing.