Slack-moored semi-submersible wind floater with damping plates in waves: linear diffraction modelling with mean forces and experimentsCitation formats

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Slack-moored semi-submersible wind floater with damping plates in waves: linear diffraction modelling with mean forces and experiments. / Stansby, Peter; Carpintero Moreno, Efrain; Apsley, David; Stallard, Timothy.

In: JOURNAL OF FLUIDS AND STRUCTURES, Vol. 90, 2019, p. 410-431.

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@article{d1cfc3bb6e6c4821818bb232962f43e0,
title = "Slack-moored semi-submersible wind floater with damping plates in waves: linear diffraction modelling with mean forces and experiments",
abstract = "A semi-submersible wind platform with four floats of equal diameter, damping plates and relatively small drafts has been designed to support a 5 MW wind turbine at full scale. Motion and mooring forces from wave basin measurements have been compared with time domain linear diffraction modelling accounting for drag forces, mooring forces and mean forces due to zero-difference frequency components, as is standard, and due to damping associated with radiation and drag forces, not previously considered. The platform response in the form of rms acceleration is quite well predicted although peak values can be underestimated. The mean mooring forces are underestimated and peak values are considerably underestimated. In large waves moorings experience high snatch loads. The measured mean forces were applied in the model for further comparison. The mooring was primarily designed to prevent drift of the floater and improved designs could eliminate or reduce snatch loads. However, it is shown that hub acceleration is quite moderate, with peak values less than 4 m/s2 in even the largest waves. The rms platform acceleration is largely decoupled from the mooring forces, as shown by corresponding spectra. In extreme conditions hydrodynamic mooring forces require nonlinear effects due to steep, sometimes breaking, waves to be accounted for. The wind thrust is included in the model using a coefficient from blade element momentum theory based on relative wind velocity. The peak hydrodynamic force would be significantly larger than the maximum wind thrust although the mean hydrodynamic force is significantly smaller. A practical conclusion is that a semi-sub floater with damping plates giving sufficiently low accelerations for operation in large waves may be of relatively shallow draft, less than the depths of many ports which is convenient for deployment.",
keywords = "wind floater, multi-float with damping plates, slack moored, linear diffraction, mean forces, experimental comparison",
author = "Peter Stansby and {Carpintero Moreno}, Efrain and David Apsley and Timothy Stallard",
year = "2019",
doi = "10.1016/j.jfluidstructs.2019.07.010",
language = "English",
volume = "90",
pages = "410--431",
journal = "JOURNAL OF FLUIDS AND STRUCTURES",
issn = "0889-9746",
publisher = "Elsevier BV",

}

RIS

TY - JOUR

T1 - Slack-moored semi-submersible wind floater with damping plates in waves: linear diffraction modelling with mean forces and experiments

AU - Stansby, Peter

AU - Carpintero Moreno, Efrain

AU - Apsley, David

AU - Stallard, Timothy

PY - 2019

Y1 - 2019

N2 - A semi-submersible wind platform with four floats of equal diameter, damping plates and relatively small drafts has been designed to support a 5 MW wind turbine at full scale. Motion and mooring forces from wave basin measurements have been compared with time domain linear diffraction modelling accounting for drag forces, mooring forces and mean forces due to zero-difference frequency components, as is standard, and due to damping associated with radiation and drag forces, not previously considered. The platform response in the form of rms acceleration is quite well predicted although peak values can be underestimated. The mean mooring forces are underestimated and peak values are considerably underestimated. In large waves moorings experience high snatch loads. The measured mean forces were applied in the model for further comparison. The mooring was primarily designed to prevent drift of the floater and improved designs could eliminate or reduce snatch loads. However, it is shown that hub acceleration is quite moderate, with peak values less than 4 m/s2 in even the largest waves. The rms platform acceleration is largely decoupled from the mooring forces, as shown by corresponding spectra. In extreme conditions hydrodynamic mooring forces require nonlinear effects due to steep, sometimes breaking, waves to be accounted for. The wind thrust is included in the model using a coefficient from blade element momentum theory based on relative wind velocity. The peak hydrodynamic force would be significantly larger than the maximum wind thrust although the mean hydrodynamic force is significantly smaller. A practical conclusion is that a semi-sub floater with damping plates giving sufficiently low accelerations for operation in large waves may be of relatively shallow draft, less than the depths of many ports which is convenient for deployment.

AB - A semi-submersible wind platform with four floats of equal diameter, damping plates and relatively small drafts has been designed to support a 5 MW wind turbine at full scale. Motion and mooring forces from wave basin measurements have been compared with time domain linear diffraction modelling accounting for drag forces, mooring forces and mean forces due to zero-difference frequency components, as is standard, and due to damping associated with radiation and drag forces, not previously considered. The platform response in the form of rms acceleration is quite well predicted although peak values can be underestimated. The mean mooring forces are underestimated and peak values are considerably underestimated. In large waves moorings experience high snatch loads. The measured mean forces were applied in the model for further comparison. The mooring was primarily designed to prevent drift of the floater and improved designs could eliminate or reduce snatch loads. However, it is shown that hub acceleration is quite moderate, with peak values less than 4 m/s2 in even the largest waves. The rms platform acceleration is largely decoupled from the mooring forces, as shown by corresponding spectra. In extreme conditions hydrodynamic mooring forces require nonlinear effects due to steep, sometimes breaking, waves to be accounted for. The wind thrust is included in the model using a coefficient from blade element momentum theory based on relative wind velocity. The peak hydrodynamic force would be significantly larger than the maximum wind thrust although the mean hydrodynamic force is significantly smaller. A practical conclusion is that a semi-sub floater with damping plates giving sufficiently low accelerations for operation in large waves may be of relatively shallow draft, less than the depths of many ports which is convenient for deployment.

KW - wind floater

KW - multi-float with damping plates

KW - slack moored

KW - linear diffraction

KW - mean forces

KW - experimental comparison

U2 - 10.1016/j.jfluidstructs.2019.07.010

DO - 10.1016/j.jfluidstructs.2019.07.010

M3 - Article

VL - 90

SP - 410

EP - 431

JO - JOURNAL OF FLUIDS AND STRUCTURES

JF - JOURNAL OF FLUIDS AND STRUCTURES

SN - 0889-9746

ER -