Automated Tanker Mooring
This is an example of the use of the tanker analysis macro system supplied in the tools directory. Here, a turret moored tanker is analyzed.

Most of our examples contain a common set of "beginning" commands as well as a common "ending" command. Click here to get documentation for these commands. They will not be discussed directly. The files which are discussed here are:

Here, we discuss how to perform a mooring motions analysis with the Ultramarine "tools", also known as macros. The command input file we will discuss is turret.cif. This discussion will focus on the values used for the motions analysis of a specific tanker and mooring system.

   $*********************************************      connect, etc.
   TKR_GEN 240  -TURRET  22 0 0                 \
                -DRAFT HEAVY                   \
                -LINE 8 131 CHAIN 6 800
The command shown above defines a mooring system, sets the initial condition, and computes the frequency domain database. The option -TURRET 22 0 0 is specifies turret moor established with the turret at the X=22, Y=0, and Z=0 feet the vessel coordinate system. For the vessels contained in the library the origin of the vessel coordinate system is at the intersection of the bow, centerline, and keel. Positive X is toward the stern, Y is positive starboard, and Z is defined by the right hand rule.

The draft of the tanker is defined by the option -DRAFT heavy. Here a designation of a "heavy" draft means the summer draft is be used,

The option -LINES 8 131 chain 6 800 defines the mooring lines which connect the tanker to the sea floor. Here, number of lines is 8. They are at equal angles with a line at 0 degrees. The water depth of 131 feet defines the water depth at the anchors, and the remainder of the data defines each segment of line. For this example we have modeled the entire catenary with one segment.:w One needs four pieces of data per segment:

  • first is the segment type, here specified as chain,
  • this is followed by the diameter, here specified as 6 inches,
  • the length of the line, here specified as 800 feet, and
  • finally, one can specify a "clump weight" at the end of the segment, here we have left this entry blank, therefore the program uses the default value of zero.

Having completed the tanker generation portion we now continue with the tanker simulation.

   $*********************************************      define env.
   TKR_SIM    \
        -PRETEN 200 \
        -SEA    ISSC 180 3.68*3.28 9.19 \
        -WIND   26.8 180 \
        -CURR   .7*3.28   180  -TIME 400 2

The command above performs a frequency domain and a time domain simulation of a moored tanker. The option -PRETENSION 200 defines the pretension in "big force units" (kips) which are be applied to all mooring lines at the beginning of the simulation. The environment waves are defined with the option -SEA issc 180 3.68*3.28 9.19. Here we have defined an issc wave spectrum with heading 180 degrees to the vessel, a significant wave height of 3.68*3.28 (12) feet, and a mean period of 9.19 seconds. The option -WIND 26.8 180 defines a wind speed of 26.8 knots with a heading of 180 degrees to the vessel. The option -CURR .7*3.28 180 defines a current of .7*3.28 (2.29) feet/second with a heading of 180 degrees to the vessel. The use of the option -TIME 400 2 tells the program to perform a time domain analysis in addition to a frequency domain analysis. Here we have specified 400 seconds to be observed at an interval of 2 seconds.

The environment is applied, and an equilibrium position estimated. Once equilibrium has been found, properties of this position are reported. Reports produced include: Current Environment, Current System Configuration, Forces Acting on Tanker, and Connector Forces. Reports for the frequency domain analysis include: Motion Statistics, and Constraint Force Statistics. Reports for the time domain analysis include: Time Statistics of the location of the origin, Location of the Origin during the observed time, Time Statistics of the connector forces, Connector Force Magnitudes during the observed time.