Force RAOs |
 
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Force RAOs |
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Flexcom supports two different schemes for laying out the data in the RAO file, namely the MCS layout and the Line layout. This former is the standard layout traditionally used by Flexcom. The Line layout is a more recent addition to the software, and it represents a more general layout that, for example, simplifies copying and pasting RAO data from spreadsheet programs.
RAO data comprises two types of lines, a data line and a comment line. The letter C (uppercase essential) in Column 1 identifies a comment line. Comment lines are completely ignored by Flexcom, and are intended to allow you to include comments in an RAO file for other users or to assist in later scrutiny. Comment lines can be included at any point in the RAO file.
Any line that is not a comment line is a data line. The actual data values expected on a data line are, of course, a function of position within the file. Numerical inputs on a data line are in free format, and can be specified as floating point numbers with or without exponent. Use an uppercase E when specifying an exponent. Either commas or blanks may separate a number of values on a particular data line; do not use TABs.
The MCS layout begins with a single line defining the incident wave heading at which the RAOs are being defined. This is followed by a block of three lines specifying the incident wave frequency and the relevant RAO amplitudes and phases for this heading and wave frequency, as shown below. Note that entries shown below in italics should be replaced with their actual numeric values in the RAO file.
HEADING=Wave Heading
Wave Frequency
Heave RAO, Surge RAO, Sway RAO, Yaw RAO, Roll RAO, Pitch RAO
Heave Phase, Surge Phase, Sway Phase, Yaw Phase, Roll Phase, Pitch Phase
The block of three lines specifying the incident wave frequency, RAOs and phases are repeated as often as necessary until the RAOs are defined over the required range of wave frequencies. To define RAOs at more incident wave headings, you simply repeat the HEADING= line for the new wave heading, and the RAO data for this wave heading is specified as before. If RAOs are being defined for more than one incident wave heading, then they must also be defined for more than one frequency at each wave heading, and the number of frequencies at which the RAOs are defined is the same for each heading. If the RAOs are independent of the incident wave heading, then the HEADING= line should be omitted.
The Line layout is very similar to the standard MCS layout, with the exception that the RAO and phase data for a particular heading and frequency appear on a single line, the format of which is shown below. Note that, for clarity, the data shown below is split over a number of lines, but is in reality specified on a single line of the RAO file.
Wave Heading, Wave Frequency, Heave RAO, Heave Phase, Surge RAO, Surge Phase, Sway RAO, Sway Phase,
Yaw RAO, Yaw Phase, Roll RAO, Roll Phase, Pitch RAO, Pitch Phase
This line is repeated for every wave frequency and every wave heading for which RAOs are being defined. As with the MCS layout, if RAOs are being defined at more than one incident wave heading, then they must also be defined at more than one frequency at each wave heading, and the number of frequencies at which the RAOs are defined is the same for each heading. So, for example, if RAOs were to be defined at three wave headings and ten frequencies per heading, then 30 lines of data would be required to specify the RAOs using the Line layout. If the same wave heading is specified on all lines, then Flexcom assumes that the RAOs are independent of wave heading. Note also that the order in which the lines of RAO data appear is not important. Flexcom automatically sorts the RAO data by heading and frequency.
•*FORCE RAO is used to specify force RAOs for a floating body.
If you would like to see an example of how this keyword is used in practice, refer to E02 - CALM Buoy - Complex.