Wind energy is one of the most studied topics in the renewable energy ecosystem. In the last decades, the focus was on various aspects of onshore wind turbine modeling and analysis.. Especially not Brazil, wind energy has a huge potential that has been researched in recent studies.
Led by Professor Alexandre Simos, from the Department of Naval and Oceanic Engineering of the Polytechnic School (Poli) from USP and thanks to funding provided by the Office of Global Naval Research (ONR Global), a group of researchers is finding ways to increase the country's wind power generation capacity, making a major effort to reduce structural weight in new offshore floating wind turbine designs (also known, in English, como Floating Offshore Wind Turbines – FOWTs).
FOWTs have many opportunities and obstacles. Among the advantages, the availability of constant winds and an adequate speed for the use of turbines at their optimal efficiency. Among the disadvantages are the high installation costs., the mooring lines and the large length of cables needed for power transmission. In this context, alleviating structural weights on the float is certainly welcome..
“In the past decade, we saw a lot of effort in the field of offshore engineering to design, design and validate this new type of floating system. currently, after many demo projects, the feasibility of the concept is proven and, as a result, we are witnessing the first commercial floating wind farms”, says Professor Simos.
Furthermore, the design of FOWTs is a complicated task that must consider variables such as wave responses., current and wind loads, static stability, dynamics and structural behavior of anchor lines. Therefore, several research projects were carried out by different groups., with the aim of developing numerical codes and laying the foundations for the comparative experimental evaluation of FOWTs.
While floating offshore wind turbines will provide an alternative energy source for the fleet's maritime base, Paul Sundaram, scientific director of ONR Global in São Paulo, notes that “the objective was to understand, through modeling, how to design and manage complex structures in the dynamic ocean environment. This is very important to the US Navy., in order to create and build resilient systems developed offshore".
the role of Brazil
Technology will play an important role in the future expansion of wind energy in Brazil. Such growth is projected to take place soon.. The regulations for the installation of offshore wind farms are already being discussed in the Brazilian Congress, and the sector is preparing for new developments, which in fact has enormous potential, especially on the northeast coast of the country.
"In the last years, Brazil very quickly expanded its wind power generation capacity, today superior to 13 GW, near 8% of the country's total capacity. These numbers make wind energy the second source of electricity in the Brazilian grid. All this production is done on land, in many wind farms across the country, but mainly concentrated in the Northeast, where the wind potential is excellent”, highlights Professor Simos.
Poli also has a research group working on offshore systems for the exploration and production of oil and gas, which is a very important economic activity in Brazil. Therefore, the researchers' initial idea was to benefit from their experience in floating oil and gas systems to adapt and develop new computational tools for the analysis of FOWTs. These tools are used to predict the response of structures in waves and wind and to estimate the stresses in the mooring lines, structural loads and vibrations.
It is also important to mention that, in addition to the main objective of generating clean energy for the electricity grid, other applications for FOWTs are being designed. For example, there are projects underway to use them as auxiliary energy for subsea equipment in the oil and gas fields. This will take the technology to deep water and, therefore, new challenges can be faced.
“We are still developing part of the hydrodynamic models to predict the wave forces in the floats. Non-linear effects involved in float drift that can be important for the design of the moorings, are difficult to accurately predict for this type of structure.. We are testing different alternatives and running tests on our wave tank to verify the performance of the numerical models", says teacher Simos.
As FOWTs are relatively new devices, there is still room for design optimization. For example, new concepts of floating hulls aiming to reduce turbine movements are still being designed and proposed. Furthermore, to make the use of FOWTs in deep water economically viable (Bigger than 1.000 meters), the design of optimized mooring systems, made of light materials, will also be a challenge.
"Such structures will be strategic for maritime transport as a source of renewable energy. FOWTs are usually in deeper water, where wind speeds are higher and winds are more constant. Small increases in wind speed can lead to much higher energy production ”, observa Sundaram.