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

Ÿ   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.

Ÿ   STOPBAND FREQUENCY

Stopband frequency is defined as:  Stopband = Passbanduser + (Passbanmax - Passbanduser). The default value depends on the Passbanduser.

Ÿ   MAXIMUM PASSBAND RIPPLE (MAX PASSBRIPP)

Passband Ripple value is between 0.0 and 1.0 dB.

Ÿ  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.