Interview: ETNZ and Cadence have a yacht to talk about!
Emirates Team New Zealand (ETNZ) and Cadence International will be building a close technical partnership over the next four years, continuing their cooperation after this year’s very successful America’s Cup, where ETNZ won the ‘Auld Mug’ and became world champion. Once again Cadence will bring in the best of their next generation CFD software to help ETNZ in their quest to defend their title in 2021.
The following interview with Nick Hutchins, CFD Specialist at ETNZ and Benoit Mallol, Product Manager for the marine applications at Cadence Design Systems, reveals some of the main challenges and requirements of ETNZ.
BM: What is your role in the ETNZ team?
NH: I have the responsibility to run our VPP (Velocity Prediction Program) tool to represent the performances of the boat in all conditions of wind, and for the different possible drafts, angles and speeds. I am also the CFD (Computational Fluid Dynamics) specialist, taking care of all the numerical simulations.
BM: What were the main constraints in using CFD simulation for the America’s Cup?
NH: At ETNZ, we do a lot of CFD runs especially during the design phase, where we cannot afford to spend time in the towing tank. The turnaround time is simply much smaller with CFD. In short, we have performed several thousand CFD simulations to find optimized shapes, which also include the feedback from the sailors. We have HPC (High Performance Computing) clusters for this purpose, but we also work with different sub-contractors to investigate a wider range of possibilities than we can do ourselves. They are also using Cadence's software, which definitely makes the collaboration easier.
BM: What technical challenges did you have to face to find the best shapes?
NH: Once the process is fully mastered in terms of accuracy and CPU time, the CFD chain must be fully automatic. We have used the scripting capabilities but also the Wizard options that FINE™/Marine allows; that was a great asset. Without these tools, we could not have investigated such a number of designs.
We have used the scripting capabilities but also the Wizard options that FINE™/Marine allows; that was a great asset. Without these tools, we could not have investigated such a number of designs.
BM: Given the range of speeds these amazing catamarans can now reach, designers have to deal with very high Froude numbers, cavitation or ventilation to name a few. I guess your job is more difficult with these physical phenomena.
NH: Indeed, it is nice to go faster and faster but we have to be sure that the foils will not break during the race! Also, cavitation or ventilation could increase the drag force, or just reduce the lift force necessary to make the boat fly. We have to make sure these phenomena are under control.
BM: Finally, were the comparisons between FINE™/Marine and the measured data convincing during the different races?
NH: Absolutely! It is difficult to compare with real sailing conditions, but in the end the trends were all confirmed quite accurately. Only CFD, and in particular FINE™/Marine, could provide such reliability.
BM: What is your vision for future CFD challenges in the next America’s cup?
NH: The new major change in design for the next America’s cup is that we are going back to monohull, bringing completely different challenges in terms of hydrodynamics. I think we need to better understand the interaction between the flow and the structure deformation of the boat and its appendages. Simulations with coupled fluid and structure information should allow us to perform such investigations. Also, we did not perform enough simulations in waves for the last campaign. Even if the America’s cup boats usually sail in calm seas from beautiful bays in the near shore, we have to be prepared for everything. Bad weather conditions create short and small waves that we would like to better study.
I think we need to better understand the interaction between the flow and the structure deformation of the boat and its appendages. Simulations with coupled fluid and structure information should allow us to perform such investigations.
BM: Can you take advantage of the new features that we recently presented at our User Meeting?
NH: I really liked your new optimization modules: the morphing and the new optimization algorithms, combined with the robust design capabilities, opens up large possibilities in terms of efficient designs which are less sensitive to operating uncertainties or manufacturing tolerances. Last but not least, combining the best of your structured and unstructured mesh generators will be a big plus in terms of accuracy! We will definitely try them out.