14.8. The DIRN Data Record - Directions at which the Drag Coefficients are Defined

If this data record is not present the directions used for the drag coefficients are those defined on the DIRN data records in Data Category 6.


      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. The first number refers to the first value input (columns 21-30) and the second number refers to the last value input.

(3)-(8) These are the values of direction at which the following hull drag coefficients are to be defined. These values are associated with the numbers defined in columns 11-20. The following rules govern input of directions:

(a) Direction numbers must be unique.

(b) There must be no gaps in direction numbers; for example, 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° or 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. Symmetry for hull drag coefficients is defined using the SYMX and SYMY data records in Data Category 10.

(g) The directions defined here for drag coefficients are distinct from those used for the wave directions. They do not have to be the same in number or value as those in Data Category 6.