WAMIT |
 
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WAMIT |
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This section outlines how the relevant data is obtained from WAMIT and converted into Flexcom. The WAMIT data is generally provided in non-dimensional form (denoted by overscored items in the various equations below).
The following parameters are read from the the header block of the WAMIT file.
•Water Density (ρ)
•Acceleration due to Gravity (g)
•Length Scale (L)
The relevant Hydrodynamic Stiffness data is located immediately after the "Hydrostatic and gravitational restoring coefficients:" tag line, as shown in the following example.
Hydrostatic and gravitational restoring coefficients:
C(3,3),C(3,4),C(3,5): 1823.9 0.0000 -6032.3
C(4,4),C(4,5),C(4,6): 19920. 0.0000 0.0000
C(5,5),C(5,6): 0.13182E+07 0.0000
The WAMIT data is converted to Flexcom using the following relations.
Symmetry is assumed between the off-diagonal terms of hydrostatic stiffness matrices, so Flexcom assumes that Cij = Cji for all i & j values, with the exception of C46 and C56 (i.e. C64 and C65 are always set to zero).
The relevant Added Mass and Radiation Damping data is located immediately after the "ADDED-MASS AND DAMPING COEFFICIENTS" tag line, as shown in the following example.
ADDED-MASS AND DAMPING COEFFICIENTS
I J A(I,J) B(I,J)
1 1 1.855784E+02 1.238282E+02
1 3 -1.372237E+02 -7.201145E+01
1 5 2.581553E+04 1.686343E+04
2 2 1.685065E+03 1.521512E+03
2 4 -5.329087E+03 -4.116092E+03
2 6 -1.659771E+03 -1.476585E+03
3 1 -1.706160E+02 -3.923212E+01
3 3 9.427506E+03 4.065720E+03
3 5 -3.385432E+04 -3.088962E+04
4 2 -5.548521E+03 -5.356068E+03
4 4 1.321490E+05 1.908522E+04
4 6 -2.830587E+04 -2.364873E+04
5 1 2.614973E+04 1.905146E+04
5 3 -3.224300E+04 -3.099698E+04
5 5 6.146746E+06 3.397135E+06
6 2 -1.698846E+03 -1.461858E+03
6 4 -2.379884E+04 -1.789628E+04
6 6 8.810688E+05 6.358418E+05
The WAMIT data is converted to Flexcom using the following relations.
where:
k = 3 for (i,j = 1,2,3)
k = 4 for (i = 1,2,3),(j = 4,5,6) or (i = 4,5,6),(j = 1,2,3)
k = 5 for (i,j = 4,5,6)
The relevant data is located after the "RESPONSE AMPLITUDE OPERATORS" tag line as shown in the following example:
RESPONSE AMPLITUDE OPERATORS
Wave Heading (deg) : 0
I Mod[RAO(I)] Pha[RAO(I)]
1 5.55722E-01 -90
2 1.34657E-03 -85
3 1.51839E+00 -179
4 5.81387E-05 -100
5 2.03162E-02 90
6 1.98620E-01 1
The WAMIT data is converted to Flexcom using the following relations.
Where:
n = 0 for (i = 1,2,3)
n = 1 for (i = 4,5,6)
The Hydrodynamic Data Importer provides you with an option of selecting either the Haskind or Diffraction excitation forces, and the relevant Force RAO data is located immediately after the "HASKIND EXCITING FORCES AND MOMENTS" or "DIFFRACTION EXCITING FORCES AND MOMENTS" tag lines, as shown in the following example.
HASKIND EXCITING FORCES AND MOMENTS
Wave Heading (deg) : 180
I Mod[Xh(I)] Pha[Xh(I)]
1 3.453370E+01 130
2 5.291137E-06 92
3 7.375123E+01 -70
4 2.295947E-05 -24
5 4.068666E+03 127
6 6.939258E-05 -88
The WAMIT data is converted to Flexcom using the following relation.
where:
m = 2 for (i = 1,2,3)
m = 3 for (i = 4,5,6)
WAMIT provides QTF data in two different forms. The full QTF data includes QTF coefficients for all possible combinations of wave frequency and wave direction, whereas the abbreviated version contains only the diagonal terms of the full QTF matrix. Given that Second-Order Wave Drift Loads in Flexcom are based on Newman's (1974) approximation only, the relevant QTF data is located immediately after the "SURGE, SWAY & YAW DRIFT FORCES (Momentum Conservation)" tag line, as shown in the following example.
SURGE, SWAY & YAW DRIFT FORCES (Momentum Conservation)
Wave Heading (deg) : 180 180
I Mod[F(I)] Pha[F(I)]
1 1.01572E+00 180
2 1.01946E-07 180
6 1.11558E-06 180
The WAMIT data is converted to Flexcom using the following relation.
where:
k = 1 for (i = 1,2,3)
k = 2 for (i = 4,5,6)
•The order of translational RAOs is changed from WAMIT format (Surge, Sway, Heave) to Flexcom format (Heave, Surge, Sway).
•The order of rotational RAOs is changed from WAMIT format (Roll, Pitch, Yaw) to Flexcom format (Yaw, Roll, Pitch).The definition of wave heading is transformed such that a zero degree heading, which is incident on the stern in the WAMIT format, is incident on the bow in the Flexcom format.
•Wave period values in seconds (WAMIT format) are changed to wave frequency values in Hertz (Flexcom format).
•A positive phase angle in WAMIT format is converted from leading to lagging to conform to Flexcom format.
Further information may be obtained from the WAMIT program documentation which is available via the WAMIT website.