Towards the Fully-coupled Numerical Modelling of Floating Wind Turbines

AbstractThe aim of this study is to model the interactions between fluids and solids using fully nonlinear models. Non- linearity is important in the context of floating wind turbines, for example, to model breaking waves impacting on the structure and the effect of the solid's elasticity. The fluid- and solid-dynamics equations are solved using two unstructured finite-element models, which are coupled at every time step. Importantly, the coupling ensures that the action-reaction principle is satisfied at a discrete level, independently of the order of representation of the discrete fields. To the authors’ knowledge, the present algorithm is novel in that it can simultaneously handle: (i) non- matching fluid and solid meshes, (ii) different polynomial orders of the basis functions on each mesh, and (iii) different fluid and solid time steps. First, results are shown for the flow past a fixed actuator-disk immersed in a uniform flow and representing a wind turbine. The present numerical results for the velocity deficit induced by the disk are shown to be in good agreement with the semi-analytical solution, for three values of thrust coefficients. The presence of a non-zero fluid viscosity in the numerical simulation affects wake recovery and fluid entrainment around the disk. Second, the dynamic response of a cylindrical pile is computed when placed at an interface between air and water. The results qualitatively demonstrate that the present models are applicable to the modelling of multiple fluids interacting with a floating solid. This work provides a first-step towards the fully coupled simulation of offshore wind turbines supported by a floating spar

Physical Model Tests on Spar Buoy for Offshore Floating Wind Energy Conversion

ABSTRACT: The present paper describes the experiences gained from the design methodology and operation of a 3D physical modelexperiment aimed to investigate the dynamic behaviour of a spar buoy floating offshore wind turbine. The physical model consists in a Froude-scaled NREL 5MW reference wind turbine (RWT) supported on the OC3-Hywind floating platform. Experimental tests have been performed at Danish Hydraulic Institute (DHI) offshore wave basin within the European Union-Hydralab+ Initiative, in April 2019. The floating wind turbine model has been subjected to a combination of regular and irregular wave attacks and different wind loads. Measurements of displacements, rotations, accelerations, forces response of the floating model and at the mooring lines have been carried out. First, free decay tests have been analysed to obtain the natural frequency and the modal damping ratios of each degree of freedom governing the offshore. Then, the results concerning regular waves, with orthogonal incidence to the structure, are presented. The results show that most of longitudinal dynamic response occurs at the wave frequency and most of lateral dynamic response occurs at rigid-body frequencies.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654110, HYDRALAB+

Genome Characterization of the Oleaginous Fungus Mortierella alpina

Mortierella alpina is an oleaginous fungus which can produce lipids accounting for up to 50% of its dry weight in the form of triacylglycerols. It is used commercially for the production of arachidonic acid. Using a combination of high throughput sequencing and lipid profiling, we have assembled the M. alpina genome, mapped its lipogenesis pathway and determined its major lipid species. The 38.38 Mb M. alpina genome shows a high degree of gene duplications. Approximately 50% of its 12,796 gene models, and 60% of genes in the predicted lipogenesis pathway, belong to multigene families. Notably, M. alpina has 18 lipase genes, of which 11 contain the class 2 lipase domain and may share a similar function. M. alpina's fatty acid synthase is a single polypeptide containing all of the catalytic domains required for fatty acid synthesis from acetyl-CoA and malonyl-CoA, whereas in many fungi this enzyme is comprised of two polypeptides. Major lipids were profiled to confirm the products predicted in the lipogenesis pathway. M. alpina produces a complex mixture of glycerolipids, glycerophospholipids and sphingolipids. In contrast, only two major sterol lipids, desmosterol and 24(28)-methylene-cholesterol, were detected. Phylogenetic analysis based on genes involved in lipid metabolism suggests that oleaginous fungi may have acquired their lipogenic capacity during evolution after the divergence of Ascomycota, Basidiomycota, Chytridiomycota and Mucoromycota. Our study provides the first draft genome and comprehensive lipid profile for M. alpina, and lays the foundation for possible genetic engineering of M. alpina to produce higher levels and diverse contents of dietary lipids