Session: 05-01-01 New Concept and Marine Environment for OSU

Submission Number: 155380

Hydrodynamics and Scour Simulation on an Artificial Reef Applied in Offshore Wind Farm 

As the demand of renewable energy, offshore wind farms (OWFs) were rapidly developed in last decade. Artificial reef effect and considerable ecological benefit has been confirmed in OWFs, because the underwater structures can provide more shelter and habitat for marine species. While, such aggregation only has effect in a local region around pile foundations. A full use on marine space has been proposed as there is usually a very large gap between single wind turbines. For instance, it can introduce aquaculture cages or nets here to gain additional fishery resource. However, such attempt was usually rejected by local managers because the cages or nets on sea surface or in mid-water may hinder routine maintenance in OWFs. While, additional artificial reef structure can be another choice as it is laid on sea bed nearby. But such way has another problem, it may have influence on scour around pile foundations. Scour protection was widely focused in projects such as OWFs, bridge piers, and oil platforms. The managers are concerned about the scour depth because it can affect pile stability and safety of wind turbines. Regularly dumping sand around the pile foundation was usually adopted but it is thought not a good way as using rock or concrete layer for scour mitigation. Lots of experiments were conducted by water tunnel or CFD method to test the scour performance of structures. The combination of scour protection and benthic ecological function has attracted more attentions. This study targets to propose a concept, that is to deploy additional artificial reefs (ARs) in OWFs for both effects of scour protection and ecological enhancement. A type of AR structure with specific slope angles which can be installed with single monopile foundation is designed, on which extra holes can provide more shelters and even change surrounding flow. Commercial CFD software FLUENT is used to solve flow features by scaled model. Eulerian multiphase and k-epsilon RNG turbulence model is adopted to simulate sediment transport, scour performance, and water hydrodynamic around structures. Cases including monopile and that with additional AR are compared. Scour depth and vertical water flux both have stable growth with flow velocity from 0.5 to 1 m/s. Furthermore, the artificial reef shape is optimized in a supercritical Reynolds number condition to enhance scour protection and flow flux upwelling. Usually, a higher flux upwelling indicates there will be a larger water mixed and more nutrients brought from seabed, which is benefit to surrounding marine species. Results show that this artificial reef design can not only have scour protection effect but also strengthen water mixed effect in mid-depth, the optimized AR angle is suggested as from 35° to 45° for the best performance. This research targets to provide suggestion on future combination of OWFs and artificial reef development, and enhance space utilization with ecological benefit as well as scour protection by a lower cost, moreover, no impact on OWFs maintenance.

Presenting Author: Jialu Wang The University of Tokyo

Presenting Author Biography: Jialu WANG
BS and MS in China University of Petroleum (East China)
Docotoral student in The University of Tokyo
Field of interest: Ocean engineering, simulation, CFD, VIV, marine pipeline, offshore wind power, marine ecosystem