2 5 7 11 16 21 31 41
- --- -- ---- ----- ----- --------- --------- ------
|X| | |DIRN| | | | | ...
- --- -- ---- ----- ----- --------- --------- ------
| | | | | | | |
| | | | | |----------------------
| | | | | |
| | | | | |_(3)-(8)Up to 6 Values of Direction(6F10.0)(DEGREES)
| | | | |
| | | | |
| | | | |_(2)Terminal Direction Number(I5)
| | | |
| | | |_(1)Initial Direction Number(I5)
| | |
| | |
| | |_Compulsory Data Record Keyword(A4)
| |
| |_Optional User Identifier(A2)
|
|_Compulsory END on last data record in data category (A3)
(1)-(2) These are the direction numbers associated with the values in columns 21-80. These numbers must be used in subsequent data categories when referring to the direction values where they are used to cross check the data input. The first number refers to the first value input (columns 21-30) and the second number refers to the last value input. If the first number is zero or blank the program will generate directions automatically - see below.
(3)-(8) These are the values of direction at which the hydrodynamic parameters (Data Categories 7 and 8) are to be calculated. They are also the default directions at which the hull drag coefficients (Data Category 10) are to be input. These values are associated with the numbers defined in columns 11-20 (see parameters (3)-(8) in The FREQ/PERD/HRTZ Data Record - Frequencies/Periods at which the Hydrodynamic Parameters are Computed).
Rules Governing Input of Directions
| (a) Direction numbers must be unique. |
| (b) There must be no 'gaps' in direction numbers, e.g. if five directions are input then these must be numbered 1 through 5. |
| (c) Directions must be distinct and unique. |
| (d) If no symmetry is defined, direction values must be input for the directions from -180° to +180°. |
| If SYMX is specified, direction values must be input for the directions from -180° to 0° or from 0° to +180°. |
| If SYMY is specified, direction values must be input for the directions from -90° to +90°. |
| If both SYMX and SYMY are specified, direction values must be input for one 90° quadrant. |
| (e) When all data records in this data category have been input, ascending numbers must correspond to ascending direction values. |
| (f) Although more than one direction data record can be used, the total number of directions cannot exceed 41. 41 directions can be input when there is no symmetry, 21 directions can be input when there is one plane of symmetry, and 11 directions when there are two symmetry planes. |
| (g) The interval between two adjacent wave directions is recommended to be less than or equal to 90° for any non-forward speed case. |
Examples
These two data records define 9 directions, numbered from 1 to 9, with values from -180° to 0°.
- --- -- ---- ----- ----- --------- --------- --------- --------- ---------- ----------
| | | |DIRN| 1| 5| -180.0| -157.5| -135.0| -112.5| -90.0| |
| | | |DIRN| 6| 9| -67.5| -45.0| -22.5| 0.0| | |
- --- -- ---- ----- ----- --------- --------- --------- --------- ---------- ----------
Direction Generation
Automatic generation of directions is specified by setting the 1st direction number to 0 (or blank). Aqwa will then generate directions numbered from the previous direction to the final direction number on the data record. The generated directions will be equally spaced between the first and last directions on the data record.
This data record will generate 21 directions numbered from 1 to 21, equally spaced between 0.0° and 180°.
- --- -- ---- ----- ----- --------- ---------
| | | |DIRN| 0| 21| 0.0| 180.0|
- --- -- ---- ----- ----- --------- ---------
These data records will generate 5 directions numbered from 1 to 5, equally spaced between 0 and 40°, followed bya single direction at 45°, followed by 5 more directions numbered from 7 to 11, equally spaced between 50 and 90°.
- --- -- ---- ----- ----- --------- ---------
| | | |DIRN| 0| 5| 0.0| 40.0|
| | | |DIRN| 6| 6| 45.0| |
| | | |DIRN| 0| 11| 50.0| 90.0|
- --- -- ---- ----- ----- --------- ---------