Mechanical APDL Basic Analysis Guide - Ansys

RESP requires two previously defined variables: one containing frequency values for the response spectrum
(field LFTAB) and the other containing the displacement time-history (field LDTAB). The frequency values
in LFTAB represent not only the abscissa of the response spectrum curve, but also the frequencies of the
one-degree-of-freedom oscillators used to generate the response spectrum. You can create the LFTAB
variable using either the FILLDATA command or the DATA command.
The displacement time-history values in LDTAB usually result from a transient dynamic analysis of a single-
DOF system. You can create the LDTAB variable using the DATA command (if the displacement time-history
is on a file) or the NSOL command (Main Menu> TimeHist Postpro> Define Variables). A numerical timeintegration
scheme is used to calculate the response spectrum.
8.8.3. Data Smoothing
If you are working with noisy results data such as from an explicit dynamic analysis, you may want to "smooth"
the response. This may allow for better understanding / visualization of the response by smoothing out
local fluctuations while preserving the global characteristics of the response. The time-history "smooth" operation
allows fitting a 'n'th order polynomial to the actual response.
This operation can be used only on static or transient results i.e., complex data cannot be fitted.
8.8.3.1. Interactive
This capability is available in the variable viewer's calculator through a function smooth (x1,x2,n) where x2
is the dependent time history variable (such as TIME), and x1 is the independent time history variable (such
as response at a point), and 'n' is the order of fit. This function is available only by typing in the expression
portion of the calculator.
For example to evaluate a second order fit for the UY response at the midpoint of a structure: (smooth
variable x1 with respect to variable x2 of order “n”):
Smoothed_response = SMOOTH ({UY_AT_MIDPOINT},{TIME},2)
8.8.3.2. Batch
If you're working with noisy results data, you may want to "smooth" that data to a smoother representative
curve.
Four arrays are required for smoothing data. The first two contain the noisy data from the independent and
the dependent variables, respectively; the second two will contain the smoothed data (after smoothing takes
place) from the independent and dependent variables, respectively. You must always create the first two
vectors (*DIM) and fill these vectors with the noisy data (VGET) before smoothing the data. If you are
working in interactive mode, ANSYS automatically creates the third and fourth vector, but if you are working
in batch mode, you must also create these vectors (*DIM) before smoothing the data (ANSYS will fill these
with the smoothed data).
Once these arrays have been created, you can smooth the data using the SMOOTH command (Main Menu>
TimeHist Postpro> Smooth Data). You can choose to smooth all or some of the data points using the
DATAP field, and you can choose how high the fitting order for the smoothed curve is to be using the
FITPT field. DATAP defaults to all points, and FITPT defaults to one-half of the data points. To plot the
results, you can choose to plot unsmoothed, smoothed, or both sets of data.
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8.8.3. Data Smoothing
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