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Designing a sailboat that can sail at high speeds is no easy feat. The challenges of such a task are plenty, and one of the biggest ones is instability. Add to that the cavitation issue, and you have a recipe for disaster. That's where Syroco comes in with its unique approach to designing high-speed sailboats that tackle these challenges head-on. By using out-of-the-box designs and incorporating Cadence Fidelity Fine Marine for CFD simulations, Syroco has been able to optimize its sailboat design workflow and achieve record-breaking speeds of up to 80 knots. In this blog post, we will examine the challenges of designing high-speed sailing boats and how Syroco has overcome some of them using its sailboat design optimization workflow.
Have you ever wondered how a sailboat stays upright while gliding through the water with the sails generating the required lift? It turns out that the secret lies in the righting moment—a force that is designed to counteract the heeling moment caused by the wind. To achieve this, boat designers use a variety of techniques, such as hull design, weight distribution, and the addition of keels or hydrofoils. The higher the righting moment, the more wind power the sails can capture, allowing the boat to move faster and more efficiently.
Righting moment diagram
But that's not all—there are even more advanced techniques that can be used to reduce weight and elevate the boat above the water's surface using hydrofoils. And, to counteract the impact of the wind, a leeward S foil can be used. So, the next time you see a sailboat cruising along the water, remember that there's a whole lot of physics that goes into keeping it upright and gliding smoothly through the waves.
As mentioned before, instability is a significant challenge that needs to be addressed while designing high-speed boats. Along these lines, designers must consider habitation concerns, such as how to make the boat comfortable and livable for those on board.
And if that's not enough to contend with, there's also the issue of cavitation. This occurs when a hydrofoil travels at high speeds, causing a decrease in pressure along the leading edge. As a result, water vaporizes, forming air bubbles or cavities that can wreak havoc on the boat's efficiency. It's a transient effect that's difficult to model accurately, making it more challenging for designers to address.
Super-cavitating vs. sub-cavitating NACA profiles
Syroco's sailboat design is a revolutionary deviation from the conventional sailboats. Their innovative approach solves the problem of the righting moment by ingeniously aligning forces. The kite produces upward force while the hydrofoil submerges the boat, thus creating a perfect balance of forces. No need for conventional foils. Both the kite and hydrofoil can be adjusted to achieve high speeds without any hassle. Syroco has set a remarkable goal of achieving a top speed of 80 knots or 150 km/h, which is much faster than the current speed record of 65 knots. This design is a significant breakthrough in sailboat engineering and brings enormous potential for speed and efficiency.
Syroco Moonshot Schematic
Sailboat design optimization workflow
Syroco uses advanced signal-processing techniques to study hydrofoils in various flow regimes. By analyzing simulation data, it can determine important parameters like drift, drag, and Z coefficient. However, unlocking the remaining three degrees of freedom has proven elusive. To solve this problem, they developed a lifting line code that accessed all six degrees of freedom and revealed how hydrofoils behave under different conditions. They fine-tuned their simulations by comparing the results with experimental data from a research paper published in the 1990s.
Experimental hydrofoil setup (left), Fine Marine CFD domain for chord length = 1m (right)
In their computational setup, the Syroco team has incorporated the Cadence Fidelity Fine Marine adaptive grid refinement (AGR) tool to minimize computational time by using a coarse mesh initially and refining it only where required. They have also fine-tuned their time step and imposed a velocity speed ramp, gradually making the time step finer when entering the flow's transient and super-critical regions. This has allowed them to save valuable time during simulations.
Multi-surface tensor (AGR)
During the hydrofoil simulations, transient cavitation was observed. This phenomenon occurs when the upper flow moves back at a specific point, with a pressure gradient that causes the fluid to retract towards the foil's leading edge, resulting in bubble collapse and generation. To better understand the hydrofoil's behavior at different velocities, the team imposed a velocity speed ramp and found that the pockets of cavitation developed more or less rapidly depending on the angle of attack (AoA).
At low velocities, there is no cavitation, and the system is stable. However, as cavitation develops, it becomes unstable and unpredictable. Despite challenges with unstable and noisy data, they were able to filter and process the data to make them more reliable.
Cavitation fraction AoA -4° and speed ramp plot (left), cavitation fraction AoA -8°and displacement ramp plot and cavitation number ramp plot (right)
Syroco fine-tuned their marine solver, meshing, and time steps to compare the results of their 2D CFD simulations to those obtained in water tunnels. In the simulation, the purple-colored points represent the CFD results obtained at a constant velocity, and the green curve represents the experimental data. The team initially used a constant velocity approach to adjust their marine parameters before moving on to velocity ramp simulations. This allowed them to sweep through all the velocities and maintain the characteristics precisely.
CFD vs. experimental data comparison plots
Designing a sailboat that can reach high speeds is a complex process that involves overcoming many challenges, such as instability and cavitation. Syroco has devised an innovative sailboat design that balances forces ingeniously, successfully solving the problem of righting moment. With this design, Syroco's sailboat can achieve high speeds and efficiency, setting an impressive goal of reaching a top speed. The use of advanced signal-processing techniques and computational fluid dynamics (CFD) simulations has allowed them to optimize their sailboat design and better understand the behavior of hydrofoils under different conditions. With continued innovation and research, it is exciting to think about what the future holds for sailboat design.
Watch the Design With Cadence video on how Syroco Sustainably Reaches Record-Breaking Speeds with Cadence Fidelity Fine Marine by clicking the button below.