Long-term dynamic behavior of monopile supported offshore wind turbines in sand

Abstract

The complexity of the loads acting on the offshore wind turbines (OWTs) structures and the significance of investigation on structure dynamics are explained. Test results obtained from a scaled wind turbine model are also summarized. The model is supported on monopile, subjected to different types of dynamic loading using an innovative out of balance mass system to apply cyclic/dynamic loads. The test results show the natural frequency of the wind turbine structure increases with the number of cycles, but with a reduced rate of increase with the accumulation of soil strain level. The change is found to be dependent on the shear strain level in the soil next to the pile which matches with the expectations from the element tests of the soil. The test results were plotted in a non-dimensional manner in order to be scaled to predict the prototype consequences using element tests of a soil using resonant column apparatus

An innovative cyclic loading device to study long term performance of offshore wind turbines

“…Three months after the installation the natural frequency dropped from its initial value of 1.28-1.32Hz to 1.13-1.15Hz. Scaled model tests carried out by Bhattacharya et al (2012Bhattacharya et al ( , 2013aBhattacharya et al ( , 2013b, Yu et al (2014), Guo et al (2015), Cox et al (2014) indicated that natural frequency may change owing to dynamic soil structure interaction.…”

Distinct-element analysis of an offshore wind turbine monopile under cyclic lateral load

“…The accumulation of lateral displacement was assumed to follow a power law. Other model tests (such as Bhattacharya et al, 2013;Guo et al, 2015;Yu et al, 2015) also showed an increase in foundation stiffness. When this happens, the natural frequency of the whole system also increases as the Eigen frequency is proportional to the square root of stiffness.…”

Bearing capacity of circular footing on sand: A critical state approach

“…Considerable investigation has been carried out on Toyoura sand, which has been employed for calibrating hypoplastic sand models. Numerous studies have reported on the calibration of Toyoura sand, [39][40][41][51][52][53]. The current investigation utilizes finite element method (FEM) simulations of circular footing on the surface of dense Toyoura sand centrifuge test, as previously conducted by [14], in order to determine suitable model parameters.…”