Potential flow oscillation
1 Test description
In this test, the default semisubmersible is forced to oscillate in the three traslational degrees of freedom with the Loads only option, which means that the motion can be prescribed and the loads do not affect the motion.
This test is similar to the OC6 Phase I LC2 case, but here we have tests with the motion in the sway and heave directions as well, and we compare loads and moments to an analytical solution (rather than measurements) and in all degrees of freedom.
2 Model
This test uses the Support structure : semisub template.
The model used for this test is shown in the figure below:
3 Analytical solution
The added mass and the radiation memory effect loads are computed according to the theory descibed in the Potential flow theory document. The integration time for the radiation memory effect load is set to 45 seconds.
Six load cases are run, 2 for each degree of freedom. For each degree of freedom, one load case has a period equal to the eigenperiod of the floater in the corresponding direction and an amplitude such that the maximum speed is 2.4 ms. The other load case has a period equal to a fifth of the eigenperiod and a maximum velocity of 1 ms. The load cases are summarised in the table below:
| Load case name | Direction of motion | Amplitude [m] | Period [s] |
| x1 | x | 40.76 | 106.7 |
| x2 | x | 3.40 | 21.34 |
| y1 | y | 42.90 | 112.3 |
| y2 | y | 3.57 | 22.46 |
| z1 | z | 6.68 | 17.5 |
| z2 | z | 0.557 | 3.5 |
4 Results
A simulation of 200 seconds is run. The test is considered passed if the results from Ashes are equal to the analytical solution plus/minus 3% of the maximum value of the time series.
The report for this test can be found on the following link: