Lars Beuth, Deltares

Numerical Studies of Offshore Monopile Installation

1. Offshore wind turbine foundations

2. Monopile installation simulations – FLOW NS-VIP

3. Next steps

In coming years hundreds of wind turbines installed in European offshore wind farms.

Cost reduction is crucial to raise profitability of billion € investments.

Currently, about 25 % of wind farm investment is spend on foundations.

Deltares and a large group of offshore companies realized high potential to

optimize foundation design and installation for reducing wind farm costs.

2015 estimate 10 % reduction of foundation costs possible. (faster installation, less noise, lower installation loads)

better understanding of pile installation process numerical studies.

Vibrating 10 times faster

than hammering.

Hammering, same location

Source: VIBRO

Pile drivability When can a pile be vibrated into the seafloor, when is impact

driving necessary?

How do factors such as sand density, vibrator frequency,

hammer load, pile diameter influence installation speed?

Soil response to wind and wave loading How does installation influence

lateral pile-soil stiffness? (for different sand densities, vibrator frequencies, hammer

loads, pile diameters)

Rotation over lifetime limited to 1°

Regulatory

bodies informed

2014 VIBRO consortium

2014 VIBRO project

• 3 monopiles vibrated, 3 monopiles hammered in Cuxhaven sandpit.

• Changes of soil density measured through CPT before and after installation.

• Lateral load tests on monopiles to investigate difference in lateral stiffness between

vibrating and hammering.

Source: VIBRO

2015 FLOW NS-VIP project

Extend Cuxhaven study through numerical analyses of pile installation.

Source: VIBRO

1. Offshore wind turbine foundations

2. Monopile installation simulations – FLOW NS-VIP

3. Next steps

• Large soil deformations

• Dynamic and cyclic loading under high frequencies

• Saturated sand

• Generation and dissipation of excess pore water

pressures

• Liquefaction along vibrated pile

• Sand is complex material with stiffness, strength, dilation

depending on density and stress, a wide range of soil

stresses occurs

• Soil-structure interaction along monopile surface

Requirements numerical analyses

Stresses

Simulation of pile installation with the Material Point Method (MPM)

AL-Kafaji, 2013

• Arbitrary large soil deformations

• Advanced modeling of water-saturated soil

• Modeling of soil-structure interaction

Excess pore pressures

MPM is unique in simulating 3D dynamic and quasi-static problems

involving …

Ceccato, 2014

Initial position of material points

Final position of material points

deformed mesh at true scale

Updated Lagrangian FEM (UL-FEM) MPM

MPM is advancement of the Finite Element Method

Better suited for simulating large deformations

Soil density change

Nguyen, 2014

MPM analyses of CPT for calibration of model parameters

Consideration of 20° slice of axisymmetric problem

F

Pile installation Lateral load test

Extrapolation of results onto larger soil volume

Drained quasi-static small deformation analyses

Soil density in cross-section

Stresses during lateral loading,

installation effects considered

MPM well suited numerical studies cost reductions through improved design

tools, regulations, pile designs, installation procedures

First results of vibratory and hammered installation and lateral loading

1. Offshore wind turbine foundations

2. Monopile installation simulations – FLOW NS-VIP

3. Next steps

…

2016 TKI Wind op Zee R&D proposal

JIP SIMON - Simulation of Installation of Monopiles

MPM for fast and accurate predictions of

offshore pile drivability

soil response to pile loading

Recommendations for optimized and novel pile designs and

installation techniques based on extensive numerical studies

Cost reductions in wind farm

construction

Future opportunities :

• Innovation push (offshore installations, numerical studies)

• Future (large-scale) research collaborations

• Increased competitiveness of involved companies on global market

2016 TKI Wind op Zee R&D proposal

2-year JIP SIMON project