Off the shores of South Korea, South Dakota School of Mines & Technology professor Sangchul Bang is making history. Designing suction pile foundations for a 2,500-megawatt (MW) wind farm, his nearly $200,000 contract with Korea Electric Power Corporation Research Institute (KEPRI) will result in foundations for 500 windmills ranging from 3 MW to 7 MW each – the largest ever constructed.
The world’s current record holder stands at 5.5 MW, a prototype with the potential to power 1,100 households each year. Wind energy currently supplies 3 percent of the world’s electricity and is projected to more than double by 2018, with the World Wind Energy Association predicting a fourfold increase in wind power capacity by 2020.
Prior to the design of offshore wind farms, towers such as these are installed to monitor the meteorological data at the planned site, accruing measurements of atmospheric air pressures, wind velocities and directions, tidal wave conditions and ocean current velocities and directions at various elevations. The data is then used to locate wind turbine orientations and elevations.
Housed underneath the towers, embedded in the seafloor, suction pile foundations are large-diameter and hollow, a structure Bang likens to an upside-down cup. Installed with a pump, they suck water out from the top and support the windmill above against external loads such as self-weight, wind, ocean currents, earthquakes, collisions and the like.
“The largest suction pile that I have designed and installed has a diameter of 40 feet and a height of 56 feet, weighing about 4 million pounds. I have used suction piles for the foundations of caisson-type breakwater, mooring of floating breakwaters, temporary mooring of immersed underwater tunnels having four driving lanes and now the meteorological towers. Basically, suction piles are a foundation structure that allows very weak ocean floor soils to provide the necessary support of extremely heavy superstructure loads,” Bang explained.
The current project presents a unique challenge as each type of windmill – 3 MW, 5 MW, 5.5 MW and 7 MW – will have a different configuration with varying lengths and number of blades as well as variant soil conditions, such as clay layers or sand, from one site to another. Thus, the foundation of each windmill must be designed individually.
With plans for the first windmill to be installed and operational by late 2015, Bang is currently training an engineer from KEPRI at the SD Mines campus on how to design, analyze and install suction piles in offshore environments. Another engineer plans to arrive in 2015, and Bang will be closely involved as the offshore wind farm progresses.