Seakeeping Observations of SA Agulhas II Using Cadence Fidelity FINE/Marine

Introduction

Breakthrough advancements in marine CFD technology have replaced the age-old technique of towing tank testing. When designing a ship prototype, the sea motions are taken into consideration to determine the dimensions of the ship. The use of a towing tank test for this purpose is facing downhill because it is both expensive and time-consuming when testing multiple models before concluding on the best design. Today, the shift left approach is slowly being realized and employed in the marine industry to reduce the time to market, and hence, there is widespread use of CFD tools for the early prediction of faults in the ship's design cycle.

Below is an example showcasing the use of Cadence Fidelity FINE/Marine for studying the seakeeping of SA Agulhas II: 

Figure 1.  Image of SAA II vessel during relief voyage in Antarctica.

About SA Agulhas II

SA Agulhas II, a successor of SA. Agulhas, South Africa’s icebreaking supply vessel and research ship built by STX Finland in 2012 and owned by the South African Department of Environmental Affairs (DEA). Between February and March 2022, the wreck of Shackleton’s ship Endurance, which had sunk after being hit by an iceberg in 1915, was located by SA Agulhas II with a submersible vehicle. Currently, the sound and vibration group (SVRG) at Stellenbosch University is studying the seakeeping of the SA Agulhas II, and they are using the Cadence CFD tool for this task.

Benefits of Using Cadence Fidelity FINE/Marine

Cadence Fidelity FINE/Marine offers a seamless workflow from geometry preparation to post-processing. Using the Cadence CFD tool, the SVRG team produced a high-quality grid composed of unstructured, fully hexahedral mesh with anisotropic cell refinement while having high control over cell distribution. An accurate resolution of the boundary layer was possible using the inflation technique in HEXPRESS, maintaining the first cell size, essential for turbulence modeling, and ensuring a smooth transition to the Euler mesh.

Figure 2. Surface Mesh of SAA II

Through an automated process, the C-Wizard drastically reduces engineering time for a complete CFD simulation setup. The time spent on setting numerical parameters is saved because the user receives a complete definition of the required simulations, including numerical aspects.

Results

For the design draft conditions, figures 2(a) and 2(b) depict the traveling shot of SAA II at 12kms and the wetted surface area of 1671m2, respectively, displaying a bow spray.

Figure 3. (a)SAA II traveling at 12km speed (left), (b)The calculated wetted surface areas of 1671 m2 (right).

In unsteady simulations for seakeeping, the accuracy and grid density were increased, and a wavelength of 126 m was noted, resulting in a wave period and encounter period of 9s and 6.3 s, respectively, and a wave height of about 1.6m. Although these are regular waves, an out-of-phase response was observed and will be investigated by the SVRG team in more detail in their upcoming work, where appendages and irregular sea spectra will be implemented, along with the rough sea conditions in the SAA II operation.

Conclusion

Cadence Fidelity FINE/Marine tool can be a lifesaver for both academic as well as commercial studies on different ship designs. The C-Wizard tool can ease the entire workflow from geometry clean-up to post-processing, ensuring limited human intervention and faster time to result. In the case of strong waves of high amplitude, grid deformation algorithms are often challenged. For this, FINE/Marine has been tested on many configurations, and essential modules have been implemented to tackle the possible shortcomings.

For more information on the seakeeping case study of SAA II, check out our partner Numeca Ingenieurburo’s website: https://www.numeca.de/en/case-studies-full-scale-cfd-simulation/

To learn more about FINE/Marine and the C-Wizard tool, watch this webinar: