The hydrostatic stiffness in the hydrodynamic database can be modified to a user specified value creating additional stiffness automatically. This is achieved by specifying the required GMX and GMY (about the global X/Y axis) in Data Category 7 as follows:
2 5 7 11 16 21 31 41 51
- --- -- ---- ----- ----- ----------- --------- ---------
|X| | |GMXX| | | | | |
- --- -- ---- ----- ----- ----------- --------- ---------
|X| | |GMYY| | | | | |
- --- -- ---- ----- ----- ----------- --------- ---------
| | | |
| | | |_ (1) Required Value
| | |
| | |_ Data Record Name(A4)
| |
| |_Optional User Identifier (A2)
|
|_Compulsory END on last data record in Data Category (A3)
(1) Aqwa firstly calculates the hydrostatic stiffness matrix based only on the cut water plane and displaced volume properties. It then adjusts the second moments of area IXX, IYY and recalculates its associated properties, PHI (principal axis), GMX/GMY, BMX/BMY etc. to give the required GM values. The associated additional hydrostatic stiffness is calculated automatically and stored in the hydrodynamic database.
Note:
This data record is ignored if there is any internal tank associated with this structure.
If the GM value input is less than that based on the geometry alone, the resulting additional stiffness will be negative. This would be the case if ballast tanks were being modeled, making the structure less stable, statically.