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Software breakthrough helps progress new offshore turbine design

By: Tom Russell 19/08/2022 Sandia National Laboratories

Foundations General Windfarms

Sandia National Laboratories’ (Sandia) offshore wind technical lead Brandon Ennis unveiled a new concept for offshore wind turbines. It includes a towerless turbine with blades pulled taut like a bow.

According to Sandia, the design would allow the generator that creates electricity from spinning blades to be placed closer to the water, instead of on the top of a tower 500 feet above. This is makes the turbine less top-heavy and aims to reduce the size and cost of the floating platform needed to keep it afloat. Sandia filed a patent application for the design in 2020.

However, before setting the idea in motion, the team needed to build software capable of modeling the response of the turbine and floating platform to different wind and sea conditions to determine the optimal design of the whole system. It has been revealed that the Sandia team now have a functional design tool, or “drawing board,” and can start designing and optimising the lighter floating wind turbine system.

“To design our floating wind turbine system, we needed a design tool that can simulate the wind, waves, blade elasticity, platform motion and the controllers,” Ennis said. “There are a few tools that can do some of what we need but without all of the pertinent two-way coupled dynamics for design and optimization of this kind of wind turbine. It was a big undertaking, but it was essential. There can’t be a floating, vertical-axis wind turbine industry without a trusted tool like this.”

Most traditional wind turbines are based around a tall tower with three blades turning a horizontal shaft that cranks a generator behind the blades in the turbine’s nacelle

Some turbines have two or more blades supported by a vertical shaft with a generator below the blades. This design, called a Darrieus vertical-axis wind turbine, has a lower center of gravity and can weigh less than a traditional wind turbine, Ennis said, but one of its main challenges is that it’s difficult to protect the turbine from extreme winds.

For traditional, horizontal-axis wind turbines, the blades can rotate away from intense, damaging winds, but the Darrieus design catches the wind from every direction. The new Sandia design replaces the central vertical tower with taut guy wires, Ennis said. These wires can be shortened or lengthened to adjust for changing wind conditions to maximize energy capture while controlling strain. Sandia claims replacing the shaft with wires reduces the weight of the turbine even more, allowing the floating platform to be even smaller and less expensive.

Kevin Moore, a mechanical engineer in Sandia’s wind power group, and the rest of the team built upon earlier work of Sandia engineer Brian Owens to develop the vertical-axis wind turbine design tool. Coe and Michael Devin, another mechanical engineer in the wind power group, also worked on it. The team worked on integrating physics algorithms while also improving the accuracy and speed of the algorithms.

Moore also led the efforts to validate the design tool using data from a land-based, 34-meter-diameter, vertical-axis wind turbine built by Sandia in the ‘80s.

“While working on the validation effort, it has been amazing to see the design quality and innovation of the legacy designers,” Moore said. “It is a privilege to stand on the shoulders of giants while leveraging modern computational resources.”

One of the reasons why the Sandia team is validating the design tool is so that it can eventually be used to certify vertical-axis wind turbine designs to the pertinent design standards, Ennis said.

“Right now, if a company wants to certify a vertical-axis wind turbine, there’s not a trusted design tool so there’s a lot of uncertainty in that process,” Ennis said. “For us to be able to provide a trusted design tool means that the certification bodies would be more willing to approve vertical-axis wind turbine designs, which is necessary for financing and their ultimate deployment.”

Sandia stated the design tool can be used to model and optimise any vertical-axis wind turbine, whether it has a traditional tower or taut guy wires, Ennis said.

“We’re designing the entire system, the turbine and platform and their control, concurrently to reduce the levelized cost of energy, not just the cost of the turbine itself,” Ennis said. “Normally one company will design the turbine, another company designs the floating platform for that fixed turbine design, and then a third company installs that with other systems to make an offshore wind plant; and you get what you get in the end in terms of cost.”

The team hopes to have an optimized floating, vertical-axis wind turbine system design by the end of the year, Ennis said.

“This is a neat tool in terms of the way that it integrates all of these different capabilities,” Coe said. “We were able to link tools developed for modeling the aerodynamics and structural dynamics of vertical-axis wind turbines — areas that Sandia has always been a leader in — and combine it with hydrodynamics and make it more suited for design optimization.”

Development of the offshore wind turbine design software and future work optimizing the design of the whole system is supported by the Department of Energy’s Advanced Research Project Agency-Energy’s ATLANTIS program. The Sandia team is working with project partners FPS Engineering & Technology and the American Bureau of Shipping on the project.

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Software breakthrough helps progress new offshore turbine design

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