Obayashi Corp announced Nov 13, 2019, that it has established construction technologies for floating wind power plants and wind power plants anchored to the seabed.
Obayashi verified compatibility by installing and removing "Skirt Suction," a basic structure developed by the company, on the sea.
The Skirt Suction is a cylindrical foundation that extends downward from the foundation top plate. It intrudes into the seabed and discharges water from the closed space surrounded by the skirt and the seabed surface with a pump to reduce water pressure and gain a load.
By sealing the inside of the foundation, passive suction (pull-out resistance) to resist a sudden pull-out load and passive resistance of the ground are generated.
The Skirt Suction has about three times higher pull-out resistance, compared with the weight and friction resistance of a normal foundation anchored to the seabed. Also, it eliminates the need for a large machine that drives monopiles and jacket piles into the seabed. As a result, the cost of foundation work and construction period can be reduced by about 20% and 40%, respectively.
The Skirt Suction that was installed and removed this time has a total height of 33m, skirt length of 8m and skirt diameter of 12m. It was set up at a water depth of 13m, and the wave power acting on the foundation and the stress, displacement and inclination angle of the foundation were measured over about two weeks. After that, water was poured into the skirt, and the Skirt Suction was then completely removed.
This is the first time in Japan that the Skirt Suction with a size large enough for the foundation of an offshore wind farm has been installed on the sea where there are actual ocean waves and removed. Obayashi obtained a verification technology evaluation certificate for port-related civil technologies from Coastal Development Institute of Technology (CDIT, general incorporated foundation).
In addition, Obayashi invented "Tension Leg Platform-type Floating Offshore Wind Power Generation Facility," which uses the Skirt Suction for the anchor of a floating wind power plant, and obtained an approval in principle (AIP) from Nippon Kaiji Kyokai (ClassNK, general incorporated foundation).
The Tension Leg Platform Type consists of a tension leg for mooring a floating body to the seabed and an anchor for fixing the tension leg on the seabed. It occupies only a small sea area, enabling to reduce impact on living organisms, the amount of mooring materials and the shaking of a wind turbine on the sea and, thus, improve power generation efficiency.