Share this page on:

Conference programme 

Back to the programme printer.gif Print

Poster session

Lead Session Chair:
Stephan Barth, Managing Director, ForWind - Center for Wind Energy Research, Germany
Yong Jun Cho University of Seoul, Korea, Republic of
Co-authors:
Yong Jun Cho (1) F P Kee Sok Yang (3) Byung Kyu Kim (3)
(1) University of Seoul, Seoul, Korea, Republic of (2) Korea Coastal Engineering Cooperation, Seoul, (3) Koea Port Engineering Cooperation, Seoul, Korea, Republic of

Printer friendly version: printer.gif Print

Poster
Download poster(0.67 MB)

Presenter's biography

Biographies are supplied directly by presenters at OFFSHORE 2015 and are published here unedited

Dr. Cho has been working in the coastal engineering for 25 years. Now he works for University of Seoul. He earned his PhD degree from North Carolina State University, Raleigh, USA in1990.

Abstract

Development of counter measures against scouring at the toe of offshore wind turbine foundations

Introduction

In Europe, most offshore wind turbines installed in shallow waters are suffering from scouring problems.

After review, we concluded that the strength of horseshoe vortex is proportional to strength of the standing waves formed in the water near the offshore wind power converter.

Based on this rationale, we proposed a hybrid monopile, which is a monopile with an additional light turbine mounted at its toe that can dissipate the incoming wave energy with the rotation that occurs when the turbine is exposed to waves and currents.

The weakening of the standing waves in this manner would lead to less sediment transport.

Approach

we developed a more reasonable scour protection method to make offshore wind turbines more affordable.

First, we noted that the strength of the horseshoe vortex is proportional to the strength of the standing wave formed near an offshore wind turbine.

Based on these facts, we proposed a hybrid mono-pile that has a turbine mounted to the lower portion of a monopile. If the turbine mounted on a hybrid mono-pile is exposed to a wave or current, the turbine easily rotates in order to dissipate the wave energy.

A weakened standing wave with less reflection can lead to less sediment transport.

Main body of abstract

Based on the rationale used in this study, a hybrid monopile with light turbines mounted at the toe is proposed in order to mitigate the standing waves in front of the pile by diverting the incoming wave energy into mechanical energy with light turbines rotating with respect to the vertical axis of the pile when it is exposed to waves or current.

Numerical simulation was performed to verify the effectiveness of the hybrid monopile scour control. The numerical model was composed of mass balance and the Navier-Stokes Eq. which is the most robust hydrodynamic model and its numerical integration was carried out based on the volume of fluid (VOF) method.

In order to verify the scouring control effects of the hybrid monopile proposed in this study, we first numerically simulated the wave propagation via a simple monopile. Then, we moved on to the cases of a quattropod, tripod, three leaves, and hybrid monopiles.





Conclusion

For the cases of a quattropod, tripod, and three leaves monopiles, it turns out that the scouring is slightly mitigated, but the extent of the mitigation falls far short of our expectations to develop a robust scouring protection method for offshore wind turbine.

For the case of a hybrid monopile, the scouring reduction effects of a hybrid monopile are verified by taking into consideration the fact that a significant portion of the initially deployed silts are still in touch with the bed.



Learning objectives
The traditional scouring prevention methods using multiple layers of rocks are very vulnerable to wave attacks.

For the case of a hybrid monopile, the scouring reduction effects of a hybrid monopile are verified by taking into consideration the fact that a significant portion of the initially deployed silts are still in touch with the bed.