Investigating complex fluid-structure interactions, FOWT mooring configurations, and CFD validation benchmarks.
Deep dive into physical tank testing and numerical CFD simulation models.
Installation of offshore structures for harvesting energy or oil and gas industries is still burdensome because of the rough sea state. Unless a calm water condition prevailing, installing any substructure or floating structure at offshore sites is very difficult. Hence, there has been great potential for research to investigate offshore structures' installation for normal and more energetic wave conditions. To understand and develop the methodology for the installation, the hydrodynamic response of the structure and impact received by the offshore crane is vital. In this context, the present study focuses on installing a heavy concrete jacket foundation sub-structure (Equivalent steel jacket) of an offshore wind energy structure. Due to the heavyweight and the temporary buoyancy tanks, the structure's response during installation is different from the tubular steel structures predominantly used for jacket structures. In this work, the structure's response in regular waves at different positions of upending is analyzed. Also, the peak force received by the crane at different sea states is measured for different positions of upending. Finally, the forces to be expected while upending the jacket in waves is quantified, and a suitable weather window is suggested. Furthermore, the critical positions in upending are established.
Extreme waves can be modelled in a numerical wave tank (NWT) as a focusing wave in order to generate events that are crucial for designing any offshore structures. The focused wave generation implemented in the completely nonlinear potential solver HOS-NWT with the time-reversal technique was used in the present work. The OpenFOAM based solvers foamStar and foamStarSWENSE, which use the domain decomposition and the functional decomposition approach, respectively, were used to couple with a HOS-NWT to perform the focusing wave interaction with the structure (in this case, a cylinder). The incident waves from HOS-NWT are blended into a foamStar and foamStarSWENSE subdomain, where the waves will propagate and interact with the structure within their domain.In the SWENSE methodology, the total field in the computational domain is divided into the incident field and a complementary field. foamStar solves for the total flow fields, and foamStarSWENSE solves for the complementary (total minus incident) flow fields. The Volume of Fluid (VoF) method was selected to capture the interface. 2D parametric studies for focused wave generation were carried out with solvers, and 3D wave interactions for different mesh types (coarse, medium, and fine) were investigated to understand the convergence for such transient type problems. For verification, the case’s uncertainty was quantified using the Richardson extrapolation approach, and validation was then done by comparing the results to the experiment. The computational efficiency of the two coupling techniques was also compared, and recommendations for solver improvements are made. Both coupling approaches generate a realistic depiction of focused wave interaction and force over the cylinder at a minimum computational cost.
The coupled (Potential theory and Navier Stokes) solver is applied FOWT motion studies, notably similar to the OC3 Hywind SPAR structure. The intention is to develop a numerical tool that allows the study of the survivability of floating structures in extreme sea states. In this study, the moorings are modelled in two ways. One is by considering the mooring lines as a linear spring with defined spring stiffness, and another is by coupling the solver (foamStar) with a lumped-mass mooring dynamics model (MoorDyn). MoorDyn represents mooring line behaviour subject to axial elasticity, hydrodynamic forces, and vertical contact forces with the seabed. The coupled model has been validated against the experiments carried out as part of the SOFTWIND project. The numerical model results of free surface elevation, floating body motions and mooring tensions are compared with the experiments. For wave cases with mild and moderate amplitudes, mooring in the form of a stiffness matrix is sufficient. However, dynamic mooring simulation (MoorDyn) is required for the extreme sea state conditions.
Experimental and numerical investigation of multi-directional focusing waves inside numerical basins. Researching the influence of spreading angles and directionality on local wave elevations, wave run-up, and peak impact force parameters for offshore structures.
Analyzing wave diffraction, drag and inertia loadings on heavy concrete gravity base foundations (GBF) under regular wave regimes and ocean currents. Validated against full-scale physical ocean tank test cases.
High-fidelity simulations of fully coupled wind-wave load interactions for the modular concrete WindCrete SPAR offshore floating platform. Simulating deepwater environments and wave tank validations under regular sea conditions.
Investigating modular TetraSPAR wind turbine platforms subject to critical mooring tensions and rigid body motion limits. Solving fully resolved multi-physics wave interactions during extreme events.
CFD model verification and validation benchmarks involving extreme focusing waves hitting a fixed box structure. Compiling pressure distributions, wave elevations, and free surface profiles against wave tank experiment datasets.
