General HydroStatics
Ship Stability Software
Command of the Week
(New or interesting aspects of GHS that you may not know about)

(Requires GHS version 16.00A or later with SeaKeeping Module)

SEAKEEPING is a fully-integrated GHS command, which means it can be used in run files just like any other command. This gives the user complete flexibility when using SEAKEEPING to run calculations. For example, it is often desirable to run SEAKEEPING at multiple wave headings. This can be accomplished using a relatively simple macro such as the following:

 vari (real) h,hmin,hint,hmax,s 
 macro headings   set h={h} plus {hint}   \\ ***** SEAKEEPING at HEADING of {h} DEGREES ***** \   sea /head:{h} /speed:{s}   if {h}={hmax} then exit   exit headings  /
 set h={hmin} minus {hint}  .headings
In the above example, the user must only set the minimum, interval, and maximum wave heading variables and GHS does the rest of the work. The result is a single report file containing response statistics and RAOs for each wave heading.

This is all well and good, but SEAKEEPING makes a lot of data, and multiple wave headings means multiple RAO plots. Wouldn't it be nice to have all of those RAOs on a single plot? Absolutely, and GHS can do all of the post-processing as well. A couple parsing macros and a custom plot yields:

One might even be interested in running multiple wave spectra, or multiple vessel speeds for each wave heading, and comparing the results. This approach may be extended and customized to address complex test matrices. Because SEAKEEPING is a command, the power to perform custom analyses is in the hands of the user.

An example of the multiple heading run file may be found here. The run file used to parse and plot the multiple RAOs may be found here.

[NOTE: Since this COW was published in January of 2018, there have been significant improvements to the SEAKEEPING command, including the ability to run a range of headings from a single command call, comma-delimited data file output, and the addition of the SK.LIB macro library. While the above run files are good examples of macro loops and report file parsing, an updated run file is provided here.]
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