The Taiwan Strait is located on the southeast coast of China. Due to the “funnelling” , offshore wind energy resources are quite abundant and have a very high value of offshore wind power development. However, tropical cyclones in this area are frequent, with an average of 4 tropical cyclones affecting the Taiwan Strait each year. The impact of tropical cyclones on offshore wind power has both advantages and disadvantages. It can bring a lot of wind resources and greatly increase the amount of electricity generated in summer. Unfavorable aspects is that it can cause damage to wind turbines and pose great threat to the safe operation of the offshore wind farm.
In order to study the impact of tropical cyclones on offshore wind farms and wind turbine safety design, based on the measured wind data with two 90-meter-high gradient wind towers at sea, using three tropical cyclones observed during 2013-2015 (“1312 Trami” , “1410 Matmo”, “1307 Soulik”), studied the turbulence characteristics, gust characteristics, wind shear characteristics of the strong winds in the tropical cyclone vortex center, the south and north of the vortex center. The frequency of wind speed of each safety level under the influence of tropical cyclone is analyzed, which provides a basis for the safe operation and economic benefits of offshore wind farms.
The research shows that:
- when the tropical cyclone center passes, the turbulence intensity has a sudden increase process, and the abrupt time is synchronized with the wind direction transition. Before and after the tropical cyclone approaches, with the higher wind speed, the turbulence intensity is maintained at a small value of about 0.1. When the cyclone center passes, the wind speed rapidly decreases with the wind direction, and the turbulence intensity increases rapidly at 90 meters about 0.58.This phenomenon occurs on both the north and south sides of the tropical cyclone track, but the turbulence intensity is not as sharp as the center of the track, generally between 0.15-0.2, the northern part of the track is more obvious than the southern part.
- The variation of turbulence intensity with wind speed conforms to IEC 61400-1 2005 WTGS standard turbulence intensity curve, but less than Class C under 5-25m/s wind speed condition.
- The gust coefficient (the ratio of instantaneous wind speed in 3 seconds to average wind speed in 10 minutes) during the influence of tropical cyclones is generally between 1.2 and 1.3. With the increase of wind speed and height, the gust coefficient decreases, but not significant.
- The variation of wind speed with height during the influence of tropical cyclone, i.e. the wind shear, is smaller than 0.05.
- Research shows that about 60% of tropical cyclones (wind speed ＜25m/s) in the Taiwan Strait are available. 20-30% of them (25m/s≤ wind speed ＜ 34m/s) reach early warning wind speed, and 10% of them (≥ 34m/s) are defensive wind speed.