The function allows the user to operate on the selected curve. There
are 23 types of operations which are grouped into two categories: curve data
operations (such as Integral, Differential, Add, Sum etc.) and curve object
operations (such as Copy, Delete and Paste, etc.). One or more curves must be
selected before selecting the curve operation function. Click OPERATION to
display the control window as shown in Figure
9.4.6.
Figure 9.4.6 Curve Operation Dialog box
All the curve names in the current graphic window are listed in the
curve list which is on the left of the Operation window. A unique curve number
is assigned to each curve. The curve number is usually the combination of a
letter and two-digit number. The user may select a curve by clicking the name
in the list or select multiple curves by pressing SHIFT or CTRL while clicking
the mouse button.
1.
CURVE OBJECT OPERATION
l COPY
This function allows the user to copy the selected curve(s).
l PASTE
This function is used to paste the curve to the current or other
graphic window. After the copy of curve, click the drop-down menu for the PASTE
button to display the two options in Figure
9.4.7(a): Current and From List. Select Current option to
paste the last copied curve. Select From List option to display the dialog box
illustrated in Figure
9.4.7(b). All the copied curves are recorded in this list
and the one in red is the last copied curve. The user may select one or
multiple items from the list, and click the OK button to paste these copied
curves. The user may also click the DELETE CURVE button to delete only the
record that can be pasted from the list, but not to delete the curve actually.
(a) Paste options (b) Curve recall list
Figure
9.4.7 Paste curve of operations
NOTE: The functions of Copy and Paste are different from the other software such as MS-Word. Use the Clipboard function to paste the curve(s) to the graph window of other software.
l DELETE
This function allows the user to delete the selected curve(s) from the
current graph window.
l EXPORT
This function allows the user to export the selected curve(s) in ETA
format, LS-DYNA format, NASTRAN format, or ETA CSV format, or exporting the maximum
Y value and minimum Y value of the selected curve by CSV format from the
current graph window.
2.
CURVE OPTIONS
The Curve Options include 9 types of operations for the list selected
curve. For example, if the user selects a curve from the curve name list and
clicks “1/X” button, the program will perform the reciprocal operation to the Y
values of the selected curve.
l NEGATIVE
This function allows the user to change the Y-axis value of the selected
curves by multiplying -1.
l SCALE
This function allows the user to superimpose the
scale curve that scales the Y-axis value of the selected curves through
multiplying a given Y scale factor.
l INTEGRAL
This function allows the user to calculate the integral of the selected
curve. The new value of Y coordinate equals to the area under the selected curve
from the origin to the current X value.
l DIFFERENTIAL
This function allows the user to calculate the differential of the
selected curve. The new Y-axis value equals to the slope of the curve’s tangent
on the corresponding X point.
l SQUARE
This function allows the user to calculate the square of the selected
curve. The new Y-coordinate value equals to the original Y-axis value
multiplying by itself.
l SQUARE ROOT
The function allows the user to calculate the root of the Y coordinate
of the selected curve. If the Y value is negative, the program will adopt the
square root of its absolute value and maintain the negative mark.
l RECIPROCAL
This function is used to calculate the reciprocal of Y coordinate for
the selected curve.
l ABSOLUTE
This function is used to calculate the absolute value of Y for the
selected curve.
l RESULTANT
This function allows the user to calculate the square root of the sum
of the square of the Y values for the selected curves. The new value is. For a two-dimensional vector, only two curves
need to be selected. This function will be activated after the user selects
more than one curve.
l LOGARITHM
This function allows the user to calculate the logarithm of the Y
values of the selected curve. The original Y value should
be greater than zero.
l NATURAL LOGARITHM
This function allows the user to calculate the natural (Napierian)
logarithm of the Y values of the selected curve.
l FAST FOURIER TRANSFORM
This function allows the user to convert curve data from time domain to
frequency domain response for signal processing analysis. The FFT is a fast
algorithm for computing the Discrete Fourier Transform (DFT). The DFT is a
basic operation to transform an ordered sequence of data samples from a signal,
usually in a time-domain into the frequency-domain. There are various implementation of FFT when
the samples are not the square of two. The algorithms adopted in eta/Post can
deal with both cases.
l HIC 15
Head Injure Criteria 15 is a special function for eta/VPG. It enables
the user to calculate the maximum HIC15 value when the impact time is less than
15 milliseconds. The control parameters in Figure
9.4.8 are used to convert unit. The default HIC value in
eta/Post is calculated in the following units: second (for time) and m/second^2
(for acceleration).
Figure 9.4.8 Unit Conversion Window
l HIC 36
Head Injure Criteria 36 is also a special function for eta/VPG. It enables
the user to calculate the maximum HIC36 value when the impact time is less than
36 milliseconds. The unit conversion method of HIC36 is same as the above
mentioned HIC15.
3.
FILTERS
There are four different filters provided in OPERATION.
Average Filter |
Butterworth Filter |
Finite Impulse Response (FIR) |
SAE Filter |
l AVERAGE
AVERAGE FILTER allows the user to smooth the curve through averaging the
value of a point with a number of neighboring points defined by the user. The
purpose of this operation is to make the curve smoother.
Select the AVERAGE type from the pull-down list. Click SELECT to display the DATA CONTROL window. The program will prompt the user to enter the number of the points for averaging as shown in Figure 9.4.9. The user may enter any positive number in the input box, which displays the default value of 10.
Figure 9.4.9 DATA CONTROL window of AVERAGE filter
After the user enters an appropriate number, click OK to accept the input
value and exit the DATA CONTROL window. Then click APPLY to display the filter
result.
l FIR FILTER
This function allows the user to smooth the curve according to the
Finite Impulse Response (FIR) filter specifications.
Select the FIR type from the pull-down list. Click SELECT to display
the DATA CONTROL window. The program will prompt the user to enter the
corresponding parameters in the control window. The user may enter any
appropriate parameters in the DATA CONTROL windows, which displays the default
values as shown in Figure
9.4.10.
Figure 9.4.10 DATA CONTROL of FIR filter FIR
PASSBAND FREQUENCY
The maximum Passband frequency is determined through the equation:
Passbanduser = (Total Number of Points on Graph/Time Duration). The default
value is 10% of the maximum Passband frequency.
STOPBAND FREQUENCY
Stopband frequency is defined as:
Stopband = Passbanduser + (Passbanmax - Passbanduser). The default value
depends on the Passbanduser.
MAXIMUM PASSBAND RIPPLE (MAX PASSBRIPP)
Passband Ripple value is between 0.0 and 1.0 dB.
MINIMUM STOPBAND ATTENUATION
(MIN.ATT.1.0+ DB)
Stopband attenuation must be greater than 1.0 dB. The Stopband
frequency and maximum Passband Ripple should not be too close to either the lowest
or highest limits. Attenuation factors commonly range between 10 and 50. It is
recommended that the user choose a Passhand frequency that is approximately 5
to 20% of the number. Too small a number will lead to a computational error and
too large a number will cause the program to stall. After entering the
parameter, click OK to accept it and exit DATA CONTROL window.
Then click APPLY to display the filter result.
l SAE FILTER
This function allows the user to smooth curves according to the Society
of Automotive (SAE) filter specification.
Select the SAE type from the pull-down list. Click SELECT to display
the DATA CONTROL window. The program will prompt the user to enter the Cutoff
value as shown in Figure
9.4.11. The user may enter any appropriate value in the DATA
CONTROL window, which displays the default values of 10.
Figure 9.4.11 DATA CONTROL window of SAE filter SAE
After entering the parameter, click OK to accept it and exit DATA
CONTROL window.
Then click APPLY to display the filter result.
l BUTTERWORTH
FILTER
This function allows the user to smooth the curves according to the
Butterworth filter specifications.
Select the BUTTERWORTH from the pull-down list. Click SELECT to display the DATA CONTROL window. The program will prompt the user to enter the corresponding parameters in the control window. The user may enter any appropriate parameters in the DATA CONTROL window, which displays the default values as shown in Figure 9.4.12.
Figure 9.4.12 DATA CONTROL window of Butterworth filter Butterworth
4.
COMPUTATION
This function allows the user to create a new curve through the
algebraic operation of several selected curves including Add, Subtract,
Multiply, Divide, etc. This operation usually requires to selecting the order
of the curve.
l ADD
This function adds the Y values from two or more curves.
l SUBTRACT
This function subtracts the Y values of the second curve from the first
one.
l MULTIPLY
This function multiplies the Y values of the selected curves.
l DIVIDE
This function divides the Y values of the first curve by the second
curve.
l
BRACKET
This function enables the user to define the left and right brackets to
group a series of operations.
l CROSS PLOT
This function enables the user to make a cross plot of two selected
curves. The new X-axis value is obtained from the Y-axis value of the second
selected curve, and the new Y-axis value from the Y-axis value of the first
curve. For example, if the user wants to plot a load defection curve, they
should click the load curve as the first curve, and the deflect curve as the
second curve. The program will plot the load as the Y coordinate and deflection
as X coordinate in the new curve. It is
recommended to plot the cross plot curve to a new graph window to obtain a
proper scaling.
l SUM
This function enables the user to make a sum operation for two or more
curves.
l AVERAGE
This function enables the user to make an average operation for two or
more curves.
5.
RESULTING CURVE
The RESULTING CURVE window displays the curve operation expression in
real time during the definition and operation process. When the user clicks the
curve name in the curve name window, the program displays the curve number in
the Resulting Curve window. When the user clicks an operation, the program will
add the operation symbol at an appropriate location related to the curve
number. For example, if the user clicks
the first curve name from the curve name window and then clicks “+” (Add) from
the computation group and then the second curve name, the program will display
C1 + C2 in the Resulting Curve window.
If the user than clicks the from the Curve Option group, the program will
display C1+C2:Rt(). This means the program is adding the first curve to the
square root of the second curve.
There are two colors for the expression in RESULTING CURVE window. One
is black and another is red. If the color of the expression is black, it means
that the defined operation is valid and the user can press APPLY to perform the
operation. If the color of the expression is red, it indicates that the
expression is not correct.
The user may use the UNDO button to erase the last operation. The user
may also click the text box in RESULTING CURVE and use the keyboard entry to
edit the expression. However, the latter method is not very convenient, and is
not recommended for the new user.
6.
APPLY
This function executes the defined operations in the Resulting Curve
window.
7.
UNDO
This function allows the user to cancel the last operation. The user
may click UNDO many times to correct the operation.
8.
CLEAR
This function allows the user to erase all the defined operations at any
time while defining the operation.
NOTE: During the operation of
curves, some curve operations require the sample frequency and intervals at the
same time, e.g. binary arithmetic operation. Some other operations require the number
of samples e.g. Differential, Integral etc. During these operations, if the
parameters are not provided, the program will display an error prompt message.
There are four filters as discussed earlier in this chapter. All the filters
have the optimized default parameter settings for convenience. There are two categories
of these filters, non-recursive and recursive. Butterworth filter is a lowpass
recursive filter while the FIR and average filters are non-recursive filters.
The computation is less for FIR filters than that for Butterworth. However,
Butterworth filter gives more power and less signal loss.
9.
NEW GRAPH
This function allows the user to create the new graph window to plot
the new curve(s). By default, the new
curve is plotted in the current graph window when the user clicks APPLY.