This paper suggests and compares two algorithms, a moving average filter method and a method developed by the National Renewable Energy Laboratory (NREL), to verify the yaw control algorithm characteristic to reduce yaw error for a wind turbine. A characteristic change for yaw movement in accordance with control parameter change that consists of each control method has been verified. Also, yaw simulations were performed using nacelle wind data measured from two areas with different turbulence intensities and the yaw movement data in each area was compared. These two algorithms and real data were compared by calculating mean absolute error (MSE) and the number of yawing (NY). As a result of the analysis, the MSE values were not significantly different between the two algorithms, but the algorithm proposed by the NREL was found to reduce yaw movement by up to 50 percent more than the moving average filter method.

This paper presents the installation procedure for an offshore wind turbine that has a suction bucket as its foundation. It also deals with the evaluation of dynamic characteristics at each installation stage by measuring the natural frequency of that system. Most previous studies mainly focused on the final natural frequency of the wind turbine after all support structures are installed. Consequently, those studies only checked whether this natural frequency could avoid resonance. However, this study checked the natural frequency of the system at each installation stage, which enabled the verification of governing factors of excitation such as waves, currents, wind and the system itself at each stage. From the field test data, it was found that the boat impact method gave a good excitation force, and this could be used for validating the integrity of offshore support structures such as oil and gas platforms. The test results also showed that the discrepancy in natural frequency between field data and analysis data is only 1.5%. This proves that the numerical analysis model is reliable and the wind turbine system was safely installed. This study will be helpful to design offshore wind turbine support structures and check the reliability of the numerical analysis model of offshore wind turbines.

This paper suggests an effective state index that represents a quantitative value for damage in order to predict the life of a bearing for a wind turbine. Two fault modes, lubrication failure and rolling element failure, are artificially made in the laboratory. Then, several degradation tests including the measurement of vibration, temperature and torque are performed under both a constant loading condition and stepwise variable loading condition. With the analysis of the measured vibration under the constant loading condition, the root mean square (RMS) value and a vibration component of bearing fault frequency are chosen as good indicators for the prediction of life. Finally, a state index is proposed by the weighted combination of vibration, temperature and torque. The proposed state index is monotonic, increasing as time goes by under the stepwise variable loading condition as well as constant loading condition. Because the monotonicity is a good characteristic to predict the life of bearings in the machine parts of a wind turbine, it is expected that the proposed state index will be helpful for the prediction of the life of bearings.

Because South Korea is located on the East Asian-Australian Flyway, it is important phenologically as a stopover site for a variety of migratory birds that travel long distances between breeding and wintering grounds. In addition, uninhabited islands along the coast are used for breeding by various waterbirds, which frequently go on foraging trips to feed offspring. For these reasons, as birds may collide with offshore wind farms while flying, or be disturbed during the construction or operation of wind farms, we discussed in this study the necessity of bird monitoring that should occur before the construction of offshore wind farms to minimize potential impacts on birds and help to locate proper construction sites. Monitoring methods were classified into bird diversity survey, spatial distribution survey and migration survey, and each can be divided into aerial, ship-based and land-based surveys according to survey location and means. In the migration survey, trackers and radar can be used for accurate and detailed data collection. Basically, the point census method and line transect method can both be used for monitoring and bird species, number of individuals, observation location and time should be recorded. The data collected from bird monitoring can be used as the basis for the site selection of wind farms.