Potential flow OpenFAST Loads
This benchmark validates the computation of wave loads on a floating structure using potential flow theory. The results from Ashes are compared against OpenFAST to verify the implementation of first-order and second-order wave loads.
1 Test Description
The test computes wave loads on a floater using potential flow theory with the structure held fixed (loads only, no motion). The hydrodynamic coefficients are obtained from WAMIT output files:
- First-order wave loads are computed using the .3 file from WAMIT
- Second-order loads are computed using Newman's approximation from the .12d file in WAMIT
The floater is constrained to remain stationary, allowing for direct comparison of the hydrodynamic loads between Ashes and OpenFAST without the influence of structural dynamics or motion response.
2 Load Cases
Six load cases are evaluated to test different wave conditions and heading angles:
- Regular waves, 0° heading - First-order and second-order loads compared
- Irregular waves, 0° heading - First-order and second-order loads compared
- Regular waves, positive heading - First-order loads only
- Regular waves, negative heading - First-order loads only
- Irregular waves, positive heading - First-order loads only
- Irregular waves, negative heading - First-order loads only
For load cases 3 through 6 (non-zero heading angles), only first-order loads are compared. OpenFAST does not support second-order loads with non-zero wave heading angles, so second-order comparisons are limited to the first two load cases with 0° heading.
The benchmark compares the time series of wave loads computed by Ashes and OpenFAST for all six degrees of freedom (surge, sway, heave, roll, pitch, and yaw).
3 Results
Simulations of 120 seconds are carried out. The test passes if the last fifth of the Ashes time series match OpenFAST results within 10% for all load components and load cases.
The report for this test can be found on the following link: