The ASTF data record may be used to add TO the existing values within the hydrostatic stiffness matrix.
Note: If the analysis includes stage 2 any additional stiffness already in the database will be re-set to zero and must be re-defined.
See the notes at the end of this section about the effects of this data record when using different programs.
2 5 7 11 16 21 31 41
- --- -- ---- ----- ----- --------- --------- ------
|X| | |ASTF|XXXXX| | | | ...
- --- -- ---- ----- ----- --------- --------- ------
| | | | | | |
| | | | |----------------------
| | | | |
| | | | |_(2)-(7)6 Stiffness Values
| | | | (6E10.0)(Units for freedoms
| | | | 1-3 = force/length,
| | | | 4-6 = force*length/RADIAN)
| | | |
| | | |_(1)Row Number of Stiffness Matrix(I5)
| | |
| | |_Compulsory Data Record Keyword(A4)
| |
| |_Optional User Identifier(A2)
|
|_Compulsory END on Last data record in data category(A3)
(1) This number indicates which row of the stiffness matrix the values input in columns 21-80 relate to.
(2)-(7) These are the values which add TO the row (1) in the hydrostatic stiffness matrix.
Stiffness related forces acting on the structure
The linear stiffness matrix relates to the hydrostatic forces contributing to the equations of static equilibrium of a structure. Specifically, the net linear hydrostatic forces F(s), acting at the center of gravity of a structure, when the structure is at an arbitrary position X, is given by:
F(s) = K ( X(e) - X ) + B(e)
where
K = stiffness matrix
X(e) = equilibrium position
B(e) = buoyancy force at equilibrium
If the ASTF data record is used, the program will use X(e) and B(e) as calculated by the program. However, it should be checked that the above expression, which is used to calculate the LINEAR hydrostatic forces throughout the Aqwa suite, produces the forces on the structure intended by the user.
Effect of the ASTF data record when running Aqwa-Line
Additional hydrostatic stiffness is stored in the database and used in the calculation of the RAOs. However, it is not used in the calculation of the 2nd order drift forces.
Effect of the ASTF data record when running Aqwa-Librium/Fer/Drift/Naut
Note that in the equation above the term X(e) is the Aqwa-Line equilibrium position. If the initial position in a subsequent Librium/Fer/Drift/Naut analysis is not as defined in the Line run then there will be restoring forces which will try to return the structure to the Aqwa-Line equilibrium position.
Effect of multiple ASTF data records
If additional stiffness is required and stage 2 is run it is always necessary to use the ASTF data record.