Numerical modelling of a mussel line system by means of lumped-mass approach

This paper describes a numerical model to simulate the behavior of a mussel longline system, subjected to environmental loads such as waves and current. The mussel line system consists of an anchor, a mooring chain, a long backbone line, mussel collector lines and buoys. The lumped-mass open-source code MoorDyn is modified for the current application. Waves are modelled as a directional spectrum, and the current as a homogeneous velocity field with an exponential vertical distribution. A Coulomb model is implemented to model the horizontal friction between nodes and the seabed. Cylindrical buoys with three translational degrees-of-freedom are modelled by extending the simplified hydrodynamic model in use for line's internal nodes with additional properties like cylinder height, diameter and mass. Clump weights are modelled in a similar way. For validation purposes, the results of the present software are compared with the commercially available lumped-mass based mooring dynamic software, OrcaFlex

Deliverable 1.1.1.1 BEL-Float project | Dataset containing the results of numerical simulations (motions, forces) of the operational performance analysis - Part 1/9

This dataset contains the results of OpenFAST simulations performed on the DeepCwind OC4 semi-submersible combined with the 5MW NREL turbine for various wind and wave conditions. The basis of the OpenFAST input files are taken from OpenFAST r-test GitHub repository (5MW_OC4Semi_WSt_WavesWN) and adapted to simulate various wind and wave conditions. The turbulent wind field as the input to the InflowWind module is generated using TurbSim. The simulations are performed on a modified version of OpenFAST v3.5.3 to which adaptation to the code is made to extract additional Morison drag output up to 16 cylindrical members. This adapted code is uploaded on GitHub as a branch from a forked OpenFAST repository. In total there are 1152 simulation results consists of 768 irregular waves and 384 regular waves cases. The complete dataset is divided into 9 sub-datasets to which this is part number 1. A report describing this dataset will be made available on BEL-Float project website by November 2024: https://www.owi-lab.be/bel-float

Floating wind turbine platform in waves : computationally-efficient algorithm for numerical simulation

This study has developed a numerical tool capable of performing mooring design optimization analysis for floating wind turbine (FWT) platforms. The numerical model is capable of: i) correctly model the physical behavior of a moored FWT platform and ii) run at a low computational cost (i.e., faster than real-time) allowing for the evaluations of many different mooring configurations. The numerical model is based on the Cummins-Ogilvie equation of motion. These hybrid frequency-time-domain approach, allows to perform fast time-domain simulation of floating bodies including external forces such as mooring lines or viscous effects. Firstly, the platform's excitation force and hydrodynamic coefficients are obtained in the frequency domain utilizing a Boundary Element Method (BEM) solver. Secondly, the results from the BEM solver are converted to the time-domain via convolution integral of the impulse response functions to calculate the radiation force and inverse discrete Fourier transform to compute the excitation force. Thirdly, viscous effect are considered via the Morison Equation using empirical coefficients. Finally, the mooring lines are modelled according to the lumped-mass approach, omitting the coupling between internal nodes allowing the system to be transformed into numerous ordinary differential equations that are solved individually. The established numerical tool can be further coupled with a single and/or multi-objective optimization methods (e.g., genetic algorithm, particle swarm optimization, etc.) to perform a mooring design loop for an FWT platform achieving the optimal configuration in terms of platform motions, mooring line tensions and cost

Waves-current effect investigation on monopile excitation force employing approximate forward speed approach

Monopile foundations have become one of the most viable options for fixed offshore wind turbines. In the recent years, the monopile diameter has been increased to accommodate bigger wind turbines. Consequently, the wave diffraction force component can also significantly influence the structural performance of the monopile. This paper numerically investigates the excitation force on a monopile that is exposed to wave and current loads. The simulations were performed with a BEM solver called Capytaine that has been adapted to include the Approximate Forward Speed (AFS) approach. The AFS accounts for forward-speed (or current) effect by giving correction terms on the zero-speed excitation and radiation forces, where the zero-speed components are obtained from Capytaine. In this paper, the code is validated for a large cylinder case (i.e. the diameter is equal to the water depth) in a wave-current condition for which semi-analytical results exist in literature

Validation of a computationally efficient time-domain numerical tool against DeepCwind experimental data

This paper presents the algorithm of a computationally efficient and reliable time-domain numerical tool capable of modelling floating wind turbine (FWT) platforms subjected to waves loads. Validation is performed against the experimental data of the DeepCwind semi-submersible. The platform's responses are modelled according to the Cummins’ equation of motion using frequency-domain hydrodynamic coefficients. Convolution integral of the impulse response functions for radiation forces is modelled using the recursive approach. The Morison equation is implemented to account for the drift force and viscous damping induced by the large heave plate. Mooring lines are modelled according to the lumped mass approach using an adapted version of the open source code MoorDyn. Modifications are done to model the hydrodynamic forces in the mooring lines subjected to waves and currents. A comparison is performed against DualSPHysics externally coupled with the MoorDyn+. This work is a foundation to further develop an FWT design optimization tool