Add an Entry Option
APPEND/OVERWRITE
Ramp This function creates a straight line between the start and end points.
Half Sin This function creates a half sine wave between the start and end points, starting with a phase of zero degrees.
Step 1 This function creates a 'rise then along' step. This means that all points after the start point will be at the same level as the end point.
Step 2 This function creates an 'along then rise' step. This means that the signal will be horizontal from the start point until the point before the end point.
Exp 1 This function produces an exponential curve which tends to infinity in the x direction.
Exp 2 This function produces an exponential curve which tends to infinity in the y direction.
VIEW
Centre This option allows a point to be selected to be the center of the screen. The graph is then redrawn with this point in the center.
Page Left This option moves the display window left by one window width.
Page Right This option moves the display window right by one window width.
Full X This option displays the full signal in the x direction.
Full Y This option displays the full signal in the y direction.
Goto End This option will display the last part of the signal in the first 20% of the time window.
Goto Start This option will display the first part of the signal.
Window X This option allows an x axis window to be set. The program will prompt for the start and end points of the window. This allows sections of particular interest to be zoomed in the x direction.
Option Description
Main Index
Window Y This option allows a y axis window to be set. The program will prompt for the start and end points of the window. This allows sections of particular interest to be 'zoomed' in the y direction.
Zoom In This option zooms in by contracting the time window by 5 times.
Zoom Out This option zooms out by expanding the time window by 5 times.
Local Full This option adjusts the y axis limits to fill the current display with the data shown.
MISCELLANEOUS
Cancel This option will cancel any option which is currently part way through its operation.
Restore This function restores a section of signal to its original form. The program will prompt for the user to set the start and end points, after which the data that existed when the program was started will be restored within the selected section. Note that sections beyond the end of the original signal cannot be restored, and also the signal cannot be restored if the input file is a new file.
K/UP In many operations, a prompt for start and/or end points will be
displayed. These points can be picked by the mouse or cursor, however, it may be easier to actually specify these values by keyboard input. To do this use, the K key. It will then be possible to type in the positions in the Command databox. To switch back to full mouse operation in the middle of the option, type UP at the prompt for the point selection.
P If the P key is pressed at any time, the current option is terminated and the whole screen is redrawn.
W If the W key is pressed at any time with the cursor over a menu option, help is displayed for that option.
V If the V key is pressed at any time with the cursor over a menu option, that menu option is invoked.
Option Description
Waveform Creation. This option initiates the waveform generation option which provides facilities for creating square, triangular, or sine waves with an option to carry out multiple wave summation to create multi-frequency/phase periodic waveforms.
The first stage in the waveform creation process is to define the database information concerning the time history about to be created. SeeLoad Files(p. 162) option described earlier for an explanation of the fields.
Having provided the general information, it is then necessary to define the waveform creation parameters. These data are shown inFigure 4-11.
Figure 4-11 Waveform Generation Setup Screen Wave Generation Form of The Data
Sample Rate
Total Time of the Signal Frequency
Start Phase Angle in Degrees Percentage of Positive Slope Percentage of Top Line Amplitude
Each field is explained in the table below.
Field Description
Waveform Type Three types of waveforms are possible, Sine, Triangular, or Square.
Sample Rate The sample rate is the number of points in the signal per second of signal. It is important to remember that an
inadequate number of samples will distort the output signal.
Shannon's sampling theorem says that at least two samples are required to define uniquely the highest frequency in the signal (i.e., the sample rate must be at least twice the maximum frequency in the signal). However, fatigue is an amplitude dependent process and so it is necessary to consider the number of samples to define amplitudes correctly. In practice, it has been found that 10 times the maximum frequency in the signal will define the amplitudes to within 5% accuracy for Sine Waves. For other waveforms, the relationship is worse due to the sharpness of the peaks. It is advisable to check the signal visually after creation using the graphical display option.
Total Time This defines the total time of the signal (i.e., 500 seconds).
Frequency This defines the frequency of the signal (i.e., 10 Hz or
10 cycles/second). This is related to the Sample Rate described above.
Phase Angle in Degrees A sine wave has an initial phase of 0 degrees and a cosine wave has one of 90 degrees. The phase may take any value between 0 to 360 degrees.
Percentage of Positive Slope
This option is only enabled if a Triangular wave is being created. This defines the percentage of each wave that has positive slope. Fifty percent defines as perfectly symmetric triangular peak. If a sharp drop at the end of the peak or a sharp increase at the beginning of the peak is desired this number can be modified to accomplish this.
Percentage of Top Line This option is only enabled if a Square wave is being created.
This defines the amount of the top of the square wave that makes up the entire signal.
Form of the Data Amplitude/Mean or Minimum/Maximum values are allowable to define the form of the wave. With Min/Max the two input lines to the side of the Form of the Data will change to Minimum Data Value and Maximum Data Value.
Having created the first waveform, an option to add further frequencies to the wave by choosing the Summation option is presented. The comments on sample rates above must be taken into account also in the Summation option. Sample rates must be the same when summing waveforms. The screen shown inFigure 4-12is displayed after the first wave creation.
If Summation is selected, the screen shown inFigure 4-12is presented in order to add to the previous wave. When done, select the Finish option.
Figure 4-12 Waveform Summation Screen
Amplitude The amplitude of the signal is the height of the peak above the mean level. The magnitude of the signal must be in the units defined on the previous setup page. The phase of the signal is defined in degrees and the convention is as used to describe sine/cosine waves.
The amplitude of the signal is the height of the peak above the mean level. The magnitude of the signal must be in the units defined on the previous setup page. The phase of the signal is defined in degrees and the convention is as used to describe sine/cosine waves.
Mean of Data The mean is the DC offset of the signal from zero.
Minimum of Data This is the minimum Y-value of the signal in the units defined on the previous setup page.
Maximum of Data This is the maximum Y-value of the signal in the units defined on the previous setup page.
Field Description
ptime Results
Cancel
OK Help
Sine wave: mywave created
Amplitude Min/max Form of The Data
Next Frequency Next Start Phase Angle
Next Amplitude Next Mean of Data Next Minimum of Data Next Maximum of Data 1 Sample Rate TotalTime Frequency Amplitude Mean Phase
100 1 1 1 0 0
◆
◆◆
Next Action ◆ Finish ◆◆ Summation
Main Index
Duplicate File. To use this option, first indicate which loading file is to be duplicated. Type the name if it is known, or use the List function to select a file by highlighting the file to be
duplicated. PSDF matrix files cannot be duplicated.
Once the correct file is selected, the duplicate screen appears as shown inFigure 4-13. The fields in this screen are intuitive and are described more fully in theLoad Files(p. 162) option. A new, unique name must be supplied and at least the first description field must be filled. Press the OK button to accept the name and descriptions. The name and descriptions of the time history being duplicated also appear at the top of the screen.
Figure 4-13 The Duplicate File Screen
Block Program. Time histories can be easily created by specifying a number of constant amplitude block with possible varying means values between them. After selecting this option and specifying a file name, description and other descriptive data for the time history, the following form appears. You may specify the constant amplitude blocks either by inputting their amplitudes or the maximum and minimum values.
Figure 4-14 Block Form Creation Type
The next form that appears allows for specification of the amplitude/mean or
maximum/minimum values. The amplitude/mean form is shown here. You may enter as many blocks as you wish. When a block is defined press the OK button. The Block Number will
ptime
Cancel
OK Help
Current history
Description 1 Description 2 New Name Description 1 Description 2
mydata
Example time history
ptime
Help Block loading method ◆ Amplitude ◆◆ Max/Min
Cancel OK
increment one. You may view the blocks already defined by pressing the List button. Press the Cancel button when all blocks have been defined or leave the Block Number databox blank when pressing OK.
Figure 4-15 Block Program Creation Form ptime
Block Program Definition
Cancel
OK Help
Block Number (blank to end)
Cycle Amplitude 0
Cycle Mean 0
Number of Cycles 0
List 1
Main Index
White Noise. If white noise is chosen, aside from the standard input, the user must supply a random number seed from which a pseudo-random number will be generated (the resultant wave sequence will, in fact, repeat after a very large number of cycles). It has been proven that the best seed is an odd number. Different seeds produce different pseudo-random sequences.
Rainflow Matrix. The Rainflow Matrix option allows you to create a matrix file in the form of a histogram. You may select an existing time history file and rainflow cycle count it or you may read in the data from an ASCII file.
ptime
White Noise Input Form
Cancel
OK Help
Sample Rate
Total Time of Signal
Mean
Random Number Seed Standard Deviation
100
100
0
1
0
ptime
Rainflow Parameters
Cancel
OK Help
Input Filename
Rainflow Matrix
List
Input Type ◆ TimeHistory ◆◆ ASCII
Matrix Size ◆ 32 ◆◆ 64 ◆◆ 128
Input the existing time history file or the ASCII file in the Input File name databox. Give it a new name or keep the same name in the Rainflow Matrix databox. A .cyhextension will be added to the name. For matrices created from Time Histories, you may select the matrix size (bin size).
The default is 128 which is most accurate.
The ASCII file is defined by keyword/value pairs to specify the matrix size, axes limits and data type. The data then follows and can be specified either by bin location + number of cycles or as a range mean pair + number of cycles.
Lines beginning with the # character are comment lines and are ignored.
The first line in the file must be #V6.0 Mandatory keywords are:
BINS=<value> where <value> is 32, 64 or 128
RANGE_MIN=<value> where value is minimum range of matrix.
MEAN_MIN=<value> where value is minimum mean value of matrix.
The size of the matrix axes can be specified either by
RANGE_SIZE=<value> where <value> is the range bin size MEAN_SIZE=<value> where <value> is the mean bin size
or
RANGE_MAX=<value> where <value> is the range maximum.
MEAN_MAX=<value> where <value> is the mean maximum.
The data is then entered, starting with one of the following lines:
BIN_DATA or RANGE_MEAN_DATA
For BIN_DATA, the data is specified as follows, one entry per line.
<range bin> <mean bin> <number of cycles>
For RANGE_MEAN_DATA,
<range value> <mean value> <number of cycles>
An example of BIN_DATA follows:
#V6.0
# Example using BIN_DATA BINS=32
MEAN_MIN=-1.1 MEAN_MAX=1.1 RANGE_MIN=0 RANGE_MAX=2.1 BIN_DATA:
31 15 5 16 9 10 16 23 10 8 2 20 8 32 20
Main Index
An example of RANGE_MEAN_DATA follows:
#V6.0
# Example using RANGE_MEAN_DATA BINS=32
PSDF Matrix.This is a simple utility to allow you to create a file that contains the relationship between PSDFs and CSDFs and the corresponding FE load cases from a frequency response (FRF) analysis. This is a necessary step when dealing with multiple load inputs from FRF analysis.
After entering a name and giving a description and the number of loads, a spreadsheet is presented. The names of the loading PSDFs should be entered in the diagonal terms and the names of the loading CSDFs should be entered in the off-diagonal terms. Click on a cell and start typing the name of the PSDF/CSDF as it has been defined in the database. You do not need to include the .psdextension. The program will automatically pick this up. The loading PSDFs and CSDFs MUST have already been defined and exist in the PTIME database.
Make sure you enter the load PSDFs in the same order that the loading will be defined from the FE run, i.e. load case 1 corresponds to PSDF in row/column 11, load case 2 corresponds to PSDF in row/column 22, etc. If there are no cross terms (loads are completely independent of one another), then enter either 0 or NONE in the off-diagonal terms.
You may make as many changes as you wish while you are in this spreadsheet. Once you are satisfied, use the F1 key or OK from the File pulldown to accept the matrix. Once the matrix is defined it CANNOT be changed. You will have to delete it and re-enter it; or you can edit the
filename.pmxfile with an editor. Alternatively you can create the matrix file entirely in an external editor and then load it into PTIME. SeeASCII Convert + Load(p. 164).
PSDF matrix file format is shown below:
Filename:xxxxxx.pmx Number of load cases=n
nrows byncolumns Example 1: 5load.pmx
(5 load case matrix created manually using a text editor, no cross correlation)
5
test101.psd NONE NONE NONE NONE NONE test102.psd NONE NONE NONE NONE NONE test103.psd NONE NONE NONE NONE NONE test104.psd NONE NONE NONE NONE NONE test105.psd
Example 2:3load.pmx
(3 load case matrix created with PTIME, some cross correlation terms)
3
test105.psd test12.csd test13.csd test12.csd test105.psd NONE test13.csd NONE test105.psd
Create PSDF from Time History. The Auto Spectral Density program, MASD, is spawned from this option. It allows the conversion of a time domain signal into a frequency domain signal or power spectral density function (PSDF). It performs a frequency analysis on a single
parameter input file, a .dacfile for example. MASD produces an output file that indicates the frequency content of the input file. This module is described inAuto Spectral Density (MASD) (p. 210)