Validation of a thermo-mechanical FE model of Onshore wind turbine foundation

Abstract

The growing demand for renewable energy sources has led to the deployment of wind turbines worldwide. One of the most critical parts of the wind turbine is the foundation which plays an important role in maintaining the structural integrity and reliability of the towers throughout the service life. This research project is a case study that focuses on validating the numerical model against the experimental values from an operational onshore wind turbine foundation present at Riemst, Belgium while considering the effect of hydration heat during the concrete curing process. The main aim of this research is to study and compare the behavior of the steel stresses in the on-site foundation with that of the numerical analysis and to see whether an adequate match can be obtained. The study begins with the development of a three-dimensional symmetrical finite element model that captures its intricate geometrical and material properties. The structure’s behavior is simulated under realistic loading conditions to assess its structural performance and identify potential areas of concern. To validate the accuracy of numerical analysis, experimental data obtained from fiber optic sensors are used. After converting the measured strains into stresses, they are carefully compared with the finite element analysis results to identify any variations and fine-tune the model. The validation of the FE model is performed using a 2D plate model in SCIA engineering. The research investigates the effects of hydration heat along with the structural analysis in FEA on the stresses experienced by the steel elements in the mass structure. This further extends to the effects of bedding and inclined piles combined with the thermo-mechanical analysis where properties such as stiffness are varied in the simulations to study their influence on the structural response. It is imperative to note that utilizing the FE model with solely non-linear structural analysis can lead to a significant overestimation of the expected field results, up to a whopping 87 times. To mitigate this issue, the variant with thermo-mechanical analysis is implemented, reducing this estimation to a maximum factor of 58 compared to the field data. It is crucial to achieve a satisfactory level of the project through iterative modifications. Implementing soil bedding on all sides in the thermo-mechanical model is one such step to effectively reduce steel stress to an acceptable level. The model showed steel stresses that are approximately 26 times higher than the actual experimental values. Along with reducing the steel stresses, the crack widths have decreased considerably from 3.4mm to 2.35mm. Hence, the effective way to perform the numerical simulation is to consider thermal-mechanical coupling along with minimizing assumptions and ensuring sufficient stiffness to the structure for reliable assessments of steel stresses and structural integrity of onshore wind turbine foundations. The findings contribute valuable insights into the foundation’s structural behavior under varying operational conditions, highlighting areas of strength and potential advancement. Moreover, the outcomes from this investigation can assist engineers and designers in making informed decisions during the planning and construction phases of wind turbine foundations, leading to more cost-effective and robust structures. Additionally, the methodologies present here may serve as a framework for future research in this field.