Extreme mooring tensions due to snap loads on a floating offshore wind turbine system

Hsu, Wei-Ting; Thiagarajan, Krish; Manuel, Lance

doi:10.1016/j.marstruc.2017.05.005

Cited by 69 publications

(24 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Slight improvement of C P is observed for the cases in which the rotors were moving as a result of wave forces 32 . Also the dynamic responses of FOWT due to ocean waves have been investigated both numerically and experimentally 5,40‐47 wherein the role of FOWT motion on the structural integrity of the system is explored.…”

Section: Introductionmentioning

confidence: 99%

Aerodynamic characterization of barge and spar type floating offshore wind turbines at different sea states

2020

View full text Add to dashboard Cite

The wake dynamics behind a compliant floating offshore wind turbine (FOWT) with two alternative supporting platforms of spar buoy and barge platform are studied numerically. The computational model is based on the large eddy simulation and the use of the actuator disk model of the FOWT rotor in which the circular actuator disk is discretized with an unstructured two-dimensional triangular mesh in a structured three-dimensional Cartesian grid of the fluid domain. The wake dynamics and platform motions are calculated for laminar and turbulent inflow conditions. The flow solver is verified through a series of experimental wake measurements done behind a porous disk model and is also cross-validated against previously published results. The dynamics of the floating spar and barge structures are calculated from wavestructure interaction for three distinctive sea states. The time history of power extraction and wind force for the floating offshore wind turbine are recorded and compared against a fixed horizontal axis wind turbine. The motion of the barge platform is found to induce low-frequency modulation of the wake, whereas the spar buoy primarily displays similar wake dynamics to the fixed turbine. It is discussed how a single turbine utilizing the spar concept can be more energy efficient under the wave-induced motion. Moreover, for both laminar and turbulent inflow conditions, due to the large axial oscillation experienced by the barge concept, the turbine wake recovers more rapidly. This suggests that for a tighter spacing of the turbines in a farm, the barge platform concept can be leveraged to obtain higher energycapturing efficiency over a fixed area. K E Y W O R D S barge platform, floating wind turbines, spar buoy platform, turbulent flow, wake recovery 1 | INTRODUCTION Wind-based renewable energies are among the fastest-growing technologies within the energy sector, with the vast majority of the wind power being generated today coming from onshore wind farm locations. Offshore wind turbines have been proposed as an alternative to the conventional onshore systems. Compared with their land-based counterparts, offshore wind turbines possess a clear advantage through their access to stronger and steadier winds and their mitigated impact upon human society. 1 The majority of these offshore wind resources are located in regions

show abstract

Section: Introductionmentioning

confidence: 99%

Aerodynamic characterization of barge and spar type floating offshore wind turbines at different sea states

2020

View full text Add to dashboard Cite

show abstract

“…The occurrence of snap events has been demonstrated experimentally by Hsu et al [20] and Azcona et al [2]. The analytical shock condition proposed by Triantafyllou and Bliek [11] and experimentally verified by Gobat and Grosenbaugh [12] states that cable unloading and loading shocks develop when the condition in Equation 34 is met,…”

Section: Shallow Water Environmentmentioning

confidence: 94%

Numerical modelling of seabed impact effects on chain and small diameter mooring cables

Low

Srikanth

et al. 2018

Applied Ocean Research

View full text Add to dashboard Cite

Catenary mooring lines experience liftoff from and grounding on the seabed when undergoing large dynamic motions. Numerical line mooring models account for this interaction using various seabed models and it is known that the action of liftoff and grounding may lead to large dynamic tension fluctuations. These fluctuations may be spurious due to the inability of discretised mooring models to adequately account for the effect of the seabed on the mooring line. In this work, the root cause and conditions that lead to the production of the large dynamic tension fluctuations is determined. The effect of line discretisation and seabed model on the tension fluctuations is investigated using the widely used spring-mattress approach and a modified seabed reaction force model. An in-house mooring code was developed to perform these investigations. For code validation and benchmarking, and to illustrate the existence of the tension fluctuations problem due to nodal grounding in existing mooring line simulation codes, comparisons are made to a commercial software.

show abstract

“…In the current guidelines, incidents of slack in mooring lines are to be avoided in design calculations [3]. However, in many developing applications such as wave energy converters or floating wind turbines, combinations of device motion, water depth and environmental conditions increase the probability of snap loads occurring [4][5][6][7]. Snap loads have been identified as a potential hazard to the structural integrity of the installation, but the uncertainties in their occurrence, identification and simulation is still high [8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Influence of Bending Stiffness on Snap Loads in Marine Cables: A Study Using a High-Order Discontinuous Galerkin Method

Palm

Eskilsson

2020

JMSE

View full text Add to dashboard Cite

Marine cables are primarily designed to support axial loads. The effect of bending stiffness on the cable response is therefore often neglected in numerical analysis. However, in low-tension applications such as umbilical modelling of ROVs or during slack events, the bending forces may affect the slack regime dynamics of the cable. In this paper, we present the implementation of bending stiffness as a rotation-free, nested local Discontinuous Galerkin (DG) method into an existing Lax–Friedrichs-type solver for cable dynamics based on an hp-adaptive DG method. Numerical verification shows exponential convergence of order P and P+1 for odd and even polynomial orders, respectively. Validation of a swinging cable shows good comparison with experimental data, and the importance of bending stiffness is demonstrated. Snap load events in a deep water tether are compared with field-test data. The bending forces affect the low-tension response for shorter lengths of tether (200–500 m), which results in an increasing snap load magnitude for increasing bending stiffness. It is shown that the nested LDG method works well for computing bending effects in marine cables.

show abstract

Extreme mooring tensions due to snap loads on a floating offshore wind turbine system

Cited by 69 publications

References 22 publications

Aerodynamic characterization of barge and spar type floating offshore wind turbines at different sea states

Aerodynamic characterization of barge and spar type floating offshore wind turbines at different sea states

Numerical modelling of seabed impact effects on chain and small diameter mooring cables

Influence of Bending Stiffness on Snap Loads in Marine Cables: A Study Using a High-Order Discontinuous Galerkin Method

Contact Info

Product

Resources

About