Jan 13, 2020
Wind energy is one of the most studied topics in the renewable energy ecosystem. In recent decades, the focus has been on various aspects of land wind turbine modeling and analysis. Especially in 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 Ocean Engineering at USP Polytechnic School (Poli) and thanks to funding provided by the Global Naval Research Office (ONR Global), a group of researchers is finding ways to increase generation capacity of the country’s wind power, making a major effort to reduce structural weight in new offshore floating wind turbine projects (also known as Floating Offshore Wind Turbines – FOWTs).
FOWTs have many opportunities and obstacles. Among the advantages, the availability of constant winds and a suitable speed for the use of turbines at their optimum efficiency. Disadvantages include the high installation costs, mooring lines and long cable length required for power transmission. In this context, relieving structural weights in the float is certainly welcome.
“Over the past decade, we have seen a lot of effort in the offshore engineering field to design and validate this new type of floating system. Today, after many demonstration projects, the viability of the concept is proven and as a result we are witnessing the first commercial floating wind farms, ”says Professor Simos.
In addition, 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, aiming to develop numerical codes and to establish the basis for the experimental comparative evaluation of FOWTs.
While floating offshore wind turbines will provide an alternative source of energy for the fleet’s marine base, Paul Sundaram, chief scientific officer at ONR Global in Sao Paulo, notes that “the goal was to understand, through modeling, how to design and manage complex structures in the fleet. Dynamic ocean environment. This is very important for the United States Navy in order to build resilient systems developed offshore. ”
Technology will play an important role in the future expansion of wind energy in Brazil. Such growth is projected to occur soon. The regulation for the installation of offshore wind farms is already being discussed in the Brazilian Congress, and the sector is preparing for new developments, which in fact have enormous potential, especially in the northeast coast of the country.
“In recent years, Brazil has rapidly expanded its wind power generation capacity, now exceeding 13 GW, about 8% of the country’s total capacity. These figures make wind power the second source of electricity in the Brazilian grid. All this production is done on land, in many wind farms throughout the country, but mainly concentrated in the Northeast, where the wind potential is excellent, ”says Professor Simos.
Poli also has a research group that works on offshore systems for oil and gas exploration and production, which is a very important economic activity in Brazil. Thus, the researchers’ initial idea was to benefit from the experience in floating oil and gas systems to adapt and develop new computational tools for FOWT analysis. These tools are used to predict the response of structures in waves and wind and to estimate mooring line tensions, structural loads and vibrations.
It is also important to mention that in addition to the main purpose of generating clean power for the 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 may be faced.
“We are still developing some of the hydrodynamic models to predict wave forces on floats. Nonlinear effects involved in float drift that may be important for lash design are difficult to accurately predict for this type of structure. We are testing different alternatives and conducting tests on our wave tank to verify the performance of numerical models, ”says Professor Simos.
Because FOWTs are relatively new devices, there is still room for design optimization. For example, new floating hull concepts aimed at reducing turbine motion are still being designed and proposed. In addition, to make the use of deepwater FOWTs (greater than 1,000 meters) economical, designing optimized mooring systems made of lightweight materials will also be a challenge.
“Such structures will be strategic for maritime transport as a renewable energy source. 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 output, ”notes Sundaram.