Simulating the wind and the weather

Calculating the service life of wind turbines

Wind power has the greatest potential of all methods of renewable energy generation. Why? Because the costs of wind power technology are comparatively low, and its suitability for day-to-day operation is well-established. Wind turbines have increased rapidly in size over recent years, as the larger a wind turbine, the more profitable it is. Today, turbines with powers of up to 6 MW are being built, and in the future, developers will continue to try to improve wind turbines without compromising their reliability and availability. The ultimate aim: to build wind turbines with a service life of 20 years. The Steinbeis Transfer Center for New Technologies in Traffic Engineering, based in Ulm, southern Germany, has developed special tools to help developers simulate the service life of wind turbines.

The technical challenge in building a wind turbine is that extremely heavy components (the rotor and nacelle) must be mounted on top of a relatively elastic beam (the tower). This vibratory system is subject to a high dynamic load by the wind, and in the case of offshore turbines, also by waves. Data such as the forces and moments in the rotor hub, measured under different wind conditions, is used as the basis for calculating the service life of a wind turbine. Infrequent events such as emergency shutdowns also have to be included in the simulation. In total, this results in several hundred scenarios. The damage in each of these scenarios, weighted according to its frequency, must be added together to give a realistic model of the events a wind turbine experiences over its service life.

The advanced state of wind power in Germany means that German standards in this area enjoy an excellent reputation worldwide, and German design principles have also been adopted around the world. Enter winLIFE. It’s a simulation program developed by the Steinbeis Transfer Centers for New Technologies in Traffic Engineering and Traffic Engineering Simulation Software. In use for over 20 years, the program now uses these standards to generate S-N curves. win-LIFE was originally developed for the automobile construction industry. But as the problems and processes in wind turbine development are very similar, winLIFE has been used successfully in this area for several years. Due to high demand, it is now being advanced specifically for wind turbines. One area of focus is making the program more efficient to use, especially with regard to automatic calculation in combination with the finite element analysis (FEA) to efficiently enable calculus of variations – a much-needed feature.

Due to the complexity of their operating conditions, wind turbines need to be simulated as complete systems, both for basic studies and for estimating reliability and service life. To do this, all environmental conditions must be included in the simulation. So wind, including all turbulence, is defined as a vector field as a function of time – and for offshore turbines, wave height is also defined as a function of time. The entire dynamics of the wind turbine are modeled in an multi-body system/FEA simulation, allowing all dynamic phenomena to be included. The software program S4WT (SAMCEF for Wind Turbines), developed by the SAMCEF Group, is an multi-body system/FEA simulation system that does all of the above. It can also be used to calculate the stress tensors for all relevant points. So to calculate the service life of wind turbines after running an multibody system/FEA simulation, the Steinbeis team of experts integrated winLIFE into S4WT. Many rules and standards covering the measurement of components in wind turbines are already incorporated into win- LIFE. Now, with the integration of winLIFE in S4WT, industry professionals can simulate almost all components of a turbine and estimate their service life.

All around the world, huge amounts of money are being invested in wind turbines. Simulations during turbine development play an extremely important role in ensuring that these turbines really can stay operational for 20 years – with as few breakdowns as possible.

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