Potential flow wave excitation loads
1 Test description
In this test, the first order wave excitation loads computed according to Potential flow theory with Ashes are compared to results produced by OpenFast. The model and environmental conditions correspond to those presented in Robertson et al. (2021b).
2 Model
This test uses the Support structure - semisubmersible template.
Two load cases are run, with two different models.The models corresponding to load case 1.1 and 2.1 are shown in the left and right figures below, respectively.
The models correspond to one column of the OC5-DeepCwind semisubmerible, with and without heave plate.
Two load cases are run, corresponding to the two different models with two different irregular wave conditions:
- LC1.1: model without heave plate, Jonswap spectrum with Hs = 7 m and Tp = 12 s (configuration C and wave condition J1 in Robertson et al. (2021b))
- LC2.1: model with heave plate, Jonswap spectrum with Hs = 5 m and Tp = 12 s (configuration D and wave condition J2 in Robertson et al. (2021b))
In both cases, the model is constrained. The incident wave excitation loads are computed using frequency domain wave excitation coefficients provided for the OC7 project and then transformed to time domain, as described in the Potential flow theory document.
More details about the model and the testing conditions can be found in Robertson et al. (2021b).
3 Benchmarked solution
Wave elevation time series and corresponding wave loads produced using OpenFast were kindly provided by Lu Wang and Yingqian Liao from NREL.
These loads are reproduced with Ashes. To obtain the same wave elevation, the method detailed in the Wave spectrum input file document was used, with a cutoff frequency of 0.5 Hz. This resulted in a spectrum with around 5500 wave components.
4 Results
A simulation of 100 seconds is run for each load case. The test is considered passed if the results from Ashes are within 10% of those from OpenFast.
The report for this test can be found on the following link: