Research Projects

Offshore wind energy is one of the fastest growing renewable energies. With advancements of technology, offshore wind energy industry is leading towards high capacity (more than 15 MW capacity of each turbine) offshore wind turbine (OWT). For high-capacity turbine, very large diameter monopile is required which may not suitable due to fabrication and installation challenges complexities. Therefore, it is urgently needed to develop a foundation for such high capacity OWTs. To the end, novel reinforced foundations are proposed here which can be used for next generation higher capacity (15-20MW) Xtra Large (XL) OWTs. Moreover, the proposed reinforced foundations are resilient against earthquake, liquefaction and scour. In one of the reinforced models, a circular plate (with upside ribs) is attached with monopile at seabed level. Main purpose of the plate is to increase contact (frictional) surface area over seabed. The ribs can protect the circular plate from bending and over stressing caused by extreme environmental loading conditions (including earthquake). Load coming on monopile (from wind, sea wave, self-weight and earthquake load) is distributed over larger surface area on the sea bed through the plate which reduces the stress and increases the lateral load carrying capacity of the foundation. In another reinforced model, monopile and suction caisson are merged together. Its size/dimension is less than that of conventional monopile and caisson. Actually, when a turbine size increases, monopile becomes less cost-effective and more challenging to install. On the other hand, suction caisson foundation is not suitable for deep water OWTs; and it can be susceptible to uplift or overturning. To overcome these issues, both the foundations are merged together which not only overcomes their limitations but also gives additional benefits such as suitable for XL OWTs (15-20MW) and seismic resilience. For the reinforced foundation, diameter and length of monopile will be 40-80% of the conventional monopile. And, caisson lid diameter will vary from 3D (D-diameter of the monopile) up to 70% of the conventional caisson lid diameter; and its skirt length (caisson depth) will vary 30-70% of the conventional caisson. Based on experimental results (and numerical simulations), optimum dimensions will be identified, and the same will be used for further study. As limited study is available on behaviour of OWT monopile subjected to earthquake, and its seismic behaviours is not well understood. Therefore, first of all, a series of physical model tests (including shake table tests) and numerical simulations will be performed on scaled model of OWT monopile (15-20MW) in order to understand the exact behaviour of monopile subjected to earthquake loadings. Later, a number of lab experiments will be conducted to examine the effectiveness of the reinforced foundations by comparing their performances with conventional monopile. Shake table tests will be performed to determine effects of earthquake loadings, liquefaction and scour. Various transducers will be used to measure different parameters during the tests. For example, laser displacement transducers, strain gauges, pore water pressure transducers, accelerometers and load cells will be used to measure displacements of monopiles, strains on monopile, pore water pressures in soils, acceleration time histories, and forces on monopile respectively. Numerical simulation will also be carried out to make clear the mechanisms. The proposal contains multidisciplinary aspects: (i) Geotechnical Engineering and (ii) Ocean Engineering (hydrodynamic performance) of OWT foundations. Hydrodynamic performance of OWT foundations will be evaluated by conducting flume tests (flume length=50m) and numerical studies, which will be done by the Co-PI of Department of Water Resources and Ocean Engineering; and Geotechnical Engineering aspects of the study will be conducted by PI of the Department of Civil Engineering.