OC6 Phase I


1 Test description

In this section we compare the results produced by Ashes to those from the OC6 project, described in Robertson et al. (2020b). In the OC6 project, several participants with different aeroelastic software produce results with the DeepCwind floater and compare them to experimental results.

The DeepCwind floater is a semisubmersible, described in Robertson et al. (2022a). The OC6 Phase I project looked at experimental results where different tests were carried out on a scaled down version of the DeepCwind floater. Two configurations are tested: constrained (where the model cannot move freely) and moored. 

2 Model

This test uses the Spport structure : Semisubmersible template.
The CSV for this test depends on the load case and can be downloaded i the corresponding subsections (see below) 

The DeepCwind model is shown in the figure below:



3 Benchmarks

The data from this project as well as a detailed definition of the load cases and sensors can be found on this link: https://a2e.energy.gov/data/oc6/oc6.phase1a

A brief description of the load cases simulated in Ashes is given below:
  • LC1: constrained configuration. The model is towed in calm water, at 6 different speeds, namely 0.5 m/s, 1 m/s, 1.5 m/s, 2 m/s, 2.5 m/s and 3 m/s. These speeds correspond to load cases LC11 to LC16.
  • LC3: constrained configuration. LC31 and LC32 corespond to regular waves and LC33 corresponds to irregular waves. The floater is not moving.

4 Results

The results produced by Ashes are compared to all the participants of the project and the experimental results.

4.1 LC1

For this load case, we proceeded as follows: we applied the force that was necessary to move the model at the required speed. We then compared the force in Ashes to the force obtained by the other participants. Only a visual check is performed on the force comparison, and the test is considered passed if the speed is not within 5% of the target value.

The reports containing the results can be dowloaded from the following links:
https://www.simis.io/downloads/open/benchmarks/current/OC6_Phase_I_LC1.pdf
https://www.simis.io/downloads/open/benchmarks/current/OC6_Phase_I_LC1_speed.pdf


Note: this load case was meant to be used to tune the drag coefficient of the models. We have just taken the drag coefficients from Robertson et al. (2014f). It is expected that the results from Ashes would produce an even better match if the coefficients were tuned.

4.2 LC3

At the time of writing, potential flow loading is only available for irregular waves. Thus, to model the hydrodynamic loading using potential flow theory for the regular wave cases, an irregular wave spectrum of one component was created.

As for the previous load case, when comparing to other participants, only a visual check is performed. The reports containing the results can be downloaded from the following links:
https://www.simis.io/downloads/open/benchmarks/current/OC6_Phase_I_LC3.pdf


Note: only hydrodynamic forces and moments were provided by participants. In Ashes, this was achieved by removing gravity and buoyancy loads.