This study focuses on the optimal design of small-scale urban wind turbines capable of operating efficiently across varying wind speeds. It specifically explores the design of an axial flux permanent magnet (AFPM) direct-drive generator, eliminating the need for a gearbox to minimize mechanical losses. The initial design incorporates a distributed double-layer winding model with a 12-pole/15-slot configuration. Through electromagnetic analysis, the generator was optimized to achieve the desired effective power output. Additionally, the integration of meta-model-based optimization techniques enhances the precision and efficiency of the design process, offering significant potential for reducing time and cost in the development of small wind turbines. This research advances the understanding of optimization methodologies for small wind turbine design and contributes to sustainable energy solutions in urban environments.

A study is being conducted to develop an offshore wind farm and fishery coexistence plan to jointly use the marine space within an offshore wind farm as a fishery zone. In this study, the results of the application to the Southwest test phase offshore wind farm are presented as a case study to establish a plan for selecting a fishery coexistence zone in the wind farm and to provide guidelines for the layout design. After reviewing the appropriate fishery coexistence model for each sea area and site condition, the offshore wind farm was divided into a protection zone and a middle zone, and a method was established to select the fishery coexistence zone from the middle zone based on the risk index. For the selected coexistence zones, a layout design procedure was established that separates the main passage routes for power generation facility maintenance vessels and fishing vessels, and divides them into seafloor aquaculture zones, artificial reef resource creation zones, and fixed aquaculture zones, taking into account conditions such as the risk index and sea depth. In the case of the Southwest test phase offshore wind farm, it was considered that 19 % to 32 % of the total area of the offshore wind farm could be arranged as a fishery coexistence zone depending on the level of coexistence.

The recent trend in the fatigue design of tubular steel towers is moving away from conventional standards as each manufacturer develops its own design standards through experimental validation to enhance product competitiveness. Therefore, this study researches the effects of post-welding treatment on improving fatigue resistanfce to develop advanced design standards for fatigue. The research approach involves two main steps. First, an efficient welding post-treatment method for tubular steel towers is investigated, the effect of improving fatigue resistance is verified through experimental work, and an "advanced S-N curve" is defined. Second, the impact of fatigue resistance improvement on the overall design is examined for commercialized tubular steel towers. In a 10 MW offshore wind turbine, the weight of the tubular steel tower is reduced by 8.8% with the "advanced S-N curve," and the dominant ratio of the fatigue limit state is also significantly reduced. Thus, fatigue design with post-treatment such as blasting has a positive effect on enhancing product competitiveness.

The rapid growth of floating offshore wind turbines (FOWTs) has positioned them as a crucial technology for harnessing deep-sea wind resources. However, as turbine sizes grow to 20 MW and beyond, new technical challenges arise, particularly concerning tower resonance. This paper proposes a strategy to avoid tower resonance in such large-scale FOWTs by adopting a two-bladed rotor design. The blade passing frequencies of the two-bladed configuration are shifted away from the tower's natural frequency, thereby avoiding resonance and reducing the associated fatigue loads on the tower. Using the IEA 22 MW reference wind turbine as a case study, simulations demonstrate the effectiveness of the strategy in reducing fatigue loads on the tower by avoiding tower resonance. This strategy has the potential to significantly contribute to the structural stability and economic viability of large-scale floating offshore wind turbine towers and is expected to be a promising alternative for future ultra-large FOWTs as a substitute for the traditional three-bladed design.

The ongoing revision of the international standard IEC 61400-23 aims to enhance the reliability of full-scale wind turbine blade testing. This paper examines the revised content of IEC 61400-23 in terms of technical aspects and reliability enhancements of blade testing, drawing on extensive experience with blade certification tests. Key changes in the revised version include broader definitions of test subjects, such as specific sections or sub-components of the blade, modifications in safety factors for calculating test loads in static and fatigue load tests, and conditions for exemptions from blade testing considering design similarity. However, when analyzing these major changes, it is difficult to conclude that the revision effectively improves the reliability of the tests, which is its primary objective. For instance, the necessity to test entire blades has been eliminated, and the safety factor for fatigue formulation error has been removed. Additionally, it is questionable whether the revision positively affects the ease and efficiency of test implementation, given the significant increase in the scale and capacity of testing equipment required for blade section tests and the need to perform static load tests in multiple directions. It is imperative for relevant experts to thoroughly consider the purpose and direction of this IEC 61400-23 revision.

An experimental study was conducted to evaluate the structural behavior of L-type flange joints. For this, one L-type flange joint test specimen for a 5 MW wind tower was designed and manufactured, and the structural behavior of each structural element of the joint was observed under increasing external tensile load (Z). The results of the analysis showed that the test specimen has a safety factor of 40 % compared to the design requirements of IEC 61400-6. In addition, strain gauge recordings showed that the tower shell and bolt comprising the test specimen had already reached the yield state before the final failure mode of the bolt and nut. Also observed in this study was that the experimental results of this specimen were in better agreement with Petersen's model in terms of overall behavior than any of the prediction models reviewed in this study. It is noted that additional experimental study is necessary to observe failure patterns in the threads of the bolt and nut.