Experimental validation of empirical design of

a scour protection around monopiles under combined wave and current loading

Department of Civil Engineering – Ghent UniversityMaster Programme in Civil Engineering

PromoterProf. dr. ir. Peter Troch

Support Staffir. Leen Baelus, dr. ir. Leen De Vos

ir. Annelies Bolle (IMDC)

Nicolas LoosveldtKenneth Vannieuwenhuyse

Experimental validation of empirical design of

a scour protection around monopiles under combined wave and current loading

Nicolas Loosveldt Kenneth Vannieuwenhuyse

Experimental validation of empirical design of

a scour protection around monopiles under combined wave and current loading

Nicolas Loosveldt Kenneth Vannieuwenhuyse

Department of Civil Engineering - awww.ugent.be

offshore wind farm

• Thornton Bank (30 km offshore)

• 300 MW

• design of scour protection around monopiles under combined wave and current loading

5Department of Civil Engineering - awww.ugent.be

Problem statement

monopile foundation disturbs flow field

amplification of bed shear stresses

erosion of sea bed near monopile

scour protection to protect sea bed

6Department of Civil Engineering - awww.ugent.be

Previous research …

• PhD research Leen De Vos (2008)

• empirical design formulae for scour protection, based on physical scale model tests

• required stone diameter for a [limited] range of wave conditions, current velocities and water depths

• mainly static design, start-up of dynamic design

• … basis for present research

7Department of Civil Engineering - awww.ugent.be

objectives of master thesis

• new physical model tests

• extension of tested parameter ranges– larger stone sizes– “current opposing waves” cases– smaller and larger water depths– monopile diameter– long duration tests

• overall damage number

• experimental validation ánd new results

8Department of Civil Engineering - awww.ugent.be

scale model tests

• flume dimensions: L x W x H = 30m x 1m x 1.2m• wave generation using wave paddle• tidal currents in 2 directions (Qmax = 300 m³/h)• scale of tests: 1:50 (length scale)• sand box: 4m length, sand d50: 100 mm• scour protection: loose rocks (rip-rap) placed on a filter

9Department of Civil Engineering - awww.ugent.be

instrumentation

10Department of Civil Engineering - awww.ugent.be

methodology

1. initial profile of scour protection prior to wave and current loading

2. test run using wave and current loading3. obtained profile of scour protection after 1000 waves, 3000 waves,…

11Department of Civil Engineering - awww.ugent.be

main results

• “validation” of De Vos formula for damage S3D, but:

• larger scatter:– larger stones– smaller water depth– current opposing waves

• effect of pile diameter

• damage stabilises after 5000 waves measured damage in test

pred

icte

d da

mag

e

De Vos (2008)

VLIZ AWARD (2013)

Experimental validation of empirical design of

a scour protection around monopiles under combined wave and current loading

Nicolas Loosveldt Kenneth Vannieuwenhuyse