Common Time Domain Commands

Hydrostatics, Stability, and Ballasting

Seakeeping

Jacket/Deck Installation

Mooring

Using Our Tools

The purpose here is to document commands which are used most often for time domain analysis when performing a mooring analysis.

The the command

   $
   $*********************************************     Time Domain
   $
   TDOM   -NEWMARK

performs a time domain simulation, and the option -NEWMARK tells the program to use the Newmark Method. For more on TDOM, click here.

Post processing of the resulting data is done in the Process Post-Processing menu. For more details, click here.

   $
   $*********************************************     Time Domain Post
   $
   PRCPOST
     CF_MAGNITUDE -EVENT 0 9000 1
       REPORT
     END
     TOT_CFORCE -EVENT 0 9000 1
       REPORT
       VLIST
       STATISTIC 1 3
       PLOT 1 3 -NO
     END
     TRAJECTORY-EVENT 0 9000 1
       VLIST
       STATISTIC 1 2 6 7 8
       REPORT LOCATION
     END
     POINTS -EVENT 0 9000 1
       REPORT
     END
   END
   &DCPTIME Time For Time Post Processing

The first command enters the proper menu. Here, as within the frequency response menu, the commands can be separated into sets. The four sets of commands accomplish four tasks:

looking at the connector force magnitude, with CF_MAGNITUDE,
looking at the sum of all connector forces on the barge, with TOT_CFORCE ,
looking at the trajectory of the barge, done with TRAJECTORY, and
looking at the motions of the points of interest, done with POINTS

The option -EVENT is used to produce information at 1 second intervals. If this is omitted, then all information computed will be available for inspection. The 0 and 9000 here are the lower and upper limits on the information. (e.g. to produce information from 10 to 20 seconds in increments of .5 second, one would use -EVENT 10 20 .5). If an upper bound is specified which is greater than the maximum of the sample, the maximum will be used. After each of the major commands is issued, the program automatically places you in the Disposition menu. (For more on Disposition, click here.) In all cases, we ask for the standard reports with REPORT. The REPORT command after TRAJECTORY has additional information. Here, there are three reports to choose from: LOCATION, VELOCITY and ACCELERATION. By specifying only LOCATION, we do not get the other two. For the TOT_CFORCE and the TRAJECTORY, however, we ask for additional information.

The command, STATISTIC produces a statistics report which includes the mean, RMS, variance, averages for the 1/3, 1/100 and 1/1000 highest peak, etc. By default, this report is written to the command channel and the log file. If you add the option -HARD it will be written to the output file. Now, computation of statistics assumes that there is an independent and a dependent variable. The numbers following the command define these variables. The first number is the "number" of the independent variable, and those that follow are the "numbers" of the dependent variables. The command VLIST results in a list of the variables available and their corresponding numbers. In the above, the first number in both cases is 1. This says that the independent variable is the event number (time).

The PLOT command produces a plot with variable number 1 plotted along the X axis and variable number 3 along the Y axis. Here, this results in a plot of the total connector force in the Y direction vs. time.

The last occurrence of the command END exits us from the Process Post-Processing menu.

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