16.3. The DACF Data Record - Deactivate Freedom at the Center of Gravity

Note:

  • The DACF data record has no effect in Aqwa-Fer.

  • If all translational freedoms and any (or none) rotational freedoms are required to be 'deactivated' it is preferable to use the DCON data record (see The DCON Data Record - Define Constraint Position). This may require more information but it is a more robust method of preventing movement of the structure.

      2   5  7   11    16
    - --- -- ---- ----- -----
   |X|   |  |DACF|     |     |
    - --- -- ---- ----- -----
       |  |   |     |     |
       |  |   |     |     |_(2)Freedom Number(I5)
       |  |   |     |
       |  |   |     |_(1)Structure Number(I5)
       |  |   |
       |  |   |_Compulsory Data Record Keyword(A4)
       |  |
       |  |_Optional User Identifier(A2)
       |
       |_Compulsory END on last data record in data category(A3)

(1) The structure number must correspond to one of the structures defined in Data Category 2; in other words, if 1 is input, then this will correspond to the structure defined in Data Category ELM1. If 2 is input, then this will correspond to the structure defined in Data Category ELM2, and so on.

(2) Freedom numbers must be from 1 through 6; in other words, 1, 2 and 3 correspond to X, Y, and Z respectively for the translational freedoms and numbers 4, 5 and 6 correspond to X, Y, and Z respectively for the rotational freedoms.

Note:   Axis Systems Associated with the Deactivated Freedoms - if a freedom is deactivated then no motion of the center of gravity will occur in that freedom, where a freedom is defined as motion about an axis system parallel to the fixed reference axes, not the local structure axes.

Example

If translational and rotational motion in the X,Y and Z directions of the structure (as originally defined in Data Category 2) is surge, sway and heave (translational) and roll, pitch and yaw (rotational) respectively, then the following situations are possible:

(i) If the X translational freedom is deactivated, and if the structure is analyzed in a position where its local axes are parallel to the Fixed Reference Axes then surge motion will be eliminated and there will be no restrictions on the sway motion. However, if the structure is yawed by 90 degrees then the local sway motion will be eliminated and there will be no restrictions on the local surge motion.

(ii) If the X rotational freedom is deactivated and if the structure is analyzed in a position where its local axes are parallel to the Fixed Reference Axis then roll motion will be eliminated and there will be no restrictions on the pitch motion. However, if the structure is yawed by 90 degrees then the local pitch motion will be eliminated and there will be no restrictions on the local roll motion.