STA BARMOT is a program for preliminary calculation of the natural periods and RAOs (response amplitude operators) of prismatic (or roughly prismatic) marine barges. The RAOs are produced in a form suitable for direct input to OrcaFlex.
Since the roll response of marine barges is generally non-linear, meaning that the roll RAO changes with increasing wave height, the program permits the user to specify the wave height of interest and adjusts the roll amplitude RAO component accordingly. An additional roll damping term can also be specified to account for bilge keels and other appendages.
Presently the results are for "deep" water, or water deeper than one barge length beneath the keel. However, the results for water depths of one half barge length are generally acceptable for preliminary designs. Heave, surge, roll, sway and yaw responses are generally acceptable in water depths where the under-keel clearance is as shallow as the barge beam.
STA BARMOT is not a diffraction or a strip theory program. It is based on model test and other data. It is extremely easy and quick to use.
The opening screen is shown below:
(Click image for larger version, PDF)
It is seen that the only user input required is the three principal barge dimensions (length, breadth, depth) barge total displacement weight, VCG and the gyradii in roll and pitch (if known). From these data STA BARMOT finds the natural periods in heave, roll and pitch, as well as RAO amplitudes and phase angles for all six degrees of freedom.
The user can specify a wave height and the non-linear roll RAO will be set correspondingly. The user can also specify a particular wave direction and period. STA BARMOT displays a graph of the roll, pitch and heave motions corresponding to the selected wave characteristics.
A set of RAO amplitude and phase graphs are produced for wave attack angles of 0, 45, and 90 degrees (head seas, quartering seas, and beam seas). A corresponding set of tabular RAO amplitude and phases is produced for all six DOF. A typical report can be viewed by clicking on the link below.
STA BARMOT Report Example (PDF)
The RAO tables are formatted for direct input to other software (such as OrcaFlex) where the RAOs may be used in time domain simulations.
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