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2.2.1.6
2.2.1.6

Current coefficients

In this tab the current coefficients can be specified and visualized. There are two possibilities to specify the current coefficients:

  • Database (by default)
  • User-defined

 

Database (by default)

After pressing the “Import file” button the user can browse to a folder and select a file. By default the Current coeffcients database folder is used, which can be altered in the Tools menu. After selecting a file the coefficients are directly shown in the table and in the graph below.

For Termsim and Dynfloat the OCIMF current coefficients are available. The yaw coefficients of these databases are based on the yaw moments around midship. The current yaw moments will be adjusted for the longitudinal position of CoG (LCG) as given in the Ship data panel:

MzCOG = Mz - LCG * Fy

 

User-defined

The user enters the coefficients in the table (for instance from Excel) or edits the imported database file. The number of directions for which the coefficients are given is unlimited. Because there are no symmetry options the coefficients must be given for all directions, starting at 0 degrees up to 360 degrees. The directions need not be equidistant, but must be in increasing order. The dimensionless coefficients are to be calculated as follows:

Cx  =  Fx / (½ ρ V2 T Lpp)
Cy  =  Fy / (½ ρ V2 T Lpp)
Cz  =  Fz / (½ ρ V2 T Lpp)
Cφ  =  Mx / (½ ρ VT Lpp2)
Cθ  =  My / (½ ρ VT Lpp2)
Cψ =  Mz / (½ ρ VT Lpp2)

The roll and pitch coefficients (Cφ and Cθ) should be based on the roll and pitch moments around the centre of gravity (CoG) of the vessel as will be used in the calculations. The current roll and pitch moments are not adjusted when the position of CoG is changed in the Ship data panel.

The yaw coefficient Cψ should be based on the yaw moment around midship. The current yaw moment will be adjusted for the longitudinal position of CoG (LCG) as given in the Ship data panel:

MzCOG = Mz - LCG * Fy

The remaining input items; Height, Moment ref. position wrt section 10, Xmin wrt section10, Xmax wrt section 10, Ref. length and Ref. height are not used in Termsim and Dynfloat runs. They are only required in Shuttle runs when wind shielding is applied.