Accurate prediction of design load cases for large wind turbines is crucial in the practical design process to minimize weight and ensure structural safety. This study examines the characteristics and potential discrepancies of different numerical analysis methods under rapidly varying wind environments, such as the extreme coherent gust (ECG) load case. Both the traditional Blade Element Momentum (BEM) theory and an advanced numerical method based on Computational Fluid Dynamics (CFD), coupled with Multi-Body Dynamics (MBD) load analysis, are employed to analyze the ECG condition. In the CFD-based approach, a full-configuration wind turbine model, including the rotor, hub, nacelle, and tower, was analyzed to achieve high-fidelity predictions while incorporating wind conditions that vary over time. Computational analyses using these different methods were performed and compared for a 5 MW wind turbine model. A wind-profile generation code for the ECG condition was developed and implemented in accordance with the GL Guideline. The results show that the different approaches generally agree well in normal wind conditions; however, somewhat different results were observed in the ECG condition.

This paper investigates wind loads acting on a nacelle with wind tunnel testing to address potential safety issues during wind turbine installation. When installing a nacelle using a crane mounted on a wind turbine tower, the proximity of the tower to the heavy nacelle can lead to a potential collision with the tower due to wind loads. Nine potential configurations during the nacelle installation process were tested. The drag and torque acting on the nacelle were experimentally measured for wind directions ranging from 0 to 180 degrees. The largest drag and torque were observed when the nacelle was positioned directly above the tower. Drag was maximum at 90 degrees to the wind direction, and torque was maximum at 60 degrees to the wind direction. When the nacelle was positioned behind the tower, the wind effect was minimal. The most dangerous situation was determined to be the moment when the nacelle was positioned directly over the tower, where the torque had the largest effect.

In offshore wind development projects, support structures account for a significant portion of capital expenditure and represent a comparatively large area for cost reduction. Therefore, it is crucial to understand the cost distribution of support structures for site selection, as well as identify how costs vary depending on support structure types and turbine capacities. This study establishes a cost model composed of cost estimation equations to derive the cost distribution of support structures, with the aim of making the economic information maps required for the implementation of the offshore wind site allocation system. Based on statistical data of capital expenditures from domestic and international projects, cost models were developed for three types of fixed support structures - monopiles, jacket piles, and suction buckets - applied to 10 MW and 15 MW turbines, and the resulting cost trends were examined. The analysis, primarily based on European cases, indicated that unit costs decrease by approximately 30% when applying 15 MW turbines compared to 10 MW turbines. Among the structures, jacket piles had the highest costs, followed by suction buckets and monopiles, a trend that was reflected in the cost models.

The direct-drive type of generator shows different vibration phenomena than the geared type of drive train, with the main resonance force being the pole/slot frequency in the former and the gear mesh frequency in the latter. Most of the simulation model is made up of elastic surroundings and an elastic FEM structure, which uses many nodes and element and therefore takes a lot of time to analyze. This can be reduced using the Craig-Bampton method, which involves determining a few of the structure's natural frequencies. The direct drive generator analysis model is a test facility that runs a simulation from the minimum rpm to the maximum rpm to verify the resonance frequency and operating speed. The vibration analysis results show that there is a resonance spot near the rated rpm area, which poses a risk to generator operation. Additional steady-state analysis should be carried out near the resonance speed. The steady-state analysis show that the vibration values are within the limits as defined in the VDI guidelines, and that this generator test facility would be safe during rated rpm operation.

Time-domain dynamic analysis is commonly used to assess stresses in floating offshore wind turbine (FOWT) substructures, but it is computationally expensive. To reduce computational cost, response-superposition stress reconstruction is being widely studied. In this study, an in-house code implementing this approach (POSCO Pseudo-Dynamic Method, POS-PDM) is benchmarked against dynamic and quasi-static analyses for a semi-submersible FOWT substructure in ultimate (ULS) and fatigue (FLS) limit states. For ULS, POS-PDM reproduces stress histories with correlation coefficients exceeding 0.97 and peak stress errors within 3%. For FLS, quasi-static analysis and POS-PDM both underestimated fatigue damage relative to dynamic analysis, and POS-PDM showed the largest underestimation. Overall, POS-PDM is suitable for ULS assessment and preliminary fatigue screening, whereas final fatigue design and its extension to other floater types requires dynamic analysis and further validation.

This study presents a measurement-based fatigue assessment procedure for an operating wind turbine tower using one month of monitoring data. Strain gauges and a two-axis inclinometer were installed, and the acquired signals were validated through synchronization and outlier removal. After validation, additional preprocessing, including filtering, was performed. Rainflow Counting was applied to obtain strain-range cycles, which were converted to stresses and evaluated using the FAT 80 S-N curve and Miner's rule. The one-month cumulative damage was 0.00233 from strain gauges and 0.00286 from inclinometer data. Comparison with a Gamma distribution showed a narrow-band strain-range pattern dominated by normal operation, indicating that high-amplitude, low-frequency events were not captured. The procedure provides a validated framework for processing measurement data and supports future long-term monitoring-based remaining useful life assessment of wind turbine support structures.

In this work, a study was conducted on a wing sail applied as an auxiliary propulsion system for ships. The basic theory of a wing sail applies the airfoil theory of aircraft. The design concept of wing sails applies the Bernoulli equation and the Coanda effect of fluid dynamics. Domestic and international wing sail research trends were investigated prior to this study. In this study, the design of the aerodynamic shape of a wing sail for an efficient propulsion system was conducted. The composite materials are mostly used in large-scale structures to reduce weight. Therefore, the basic concepts for performing the large-scale structural design of a wing sail using composite materials were investigated.

Underwater noise from operating an offshore wind turbine is mainly attributed to mechanical vibrations from the nacelle, yet systematic long-term studies on its frequency characteristics remain limited. This study investigates the correlation between underwater noise and turbine vibration using a simplified acoustic monitoring system. The relationship between tower vibration and radiated underwater sound was verified with simultaneous measurements. For long-term monitoring, buoy-based and seabed-mounted acoustic systems were installed near an operating offshore wind turbine, enabling continuous observations for about one year. The results showed no significant variation in underwater noise related to seasonal or tidal changes. A tonal component generated by mechanical vibrations was dominant for the underwater noise. Based on the magnitude of the tonal component and the long-term average of background noise, conservative estimation of sound propagation distance for the wind turbine noise was performed. These findings are expected to serve as a basic reference for future research on underwater noise propagation from offshore wind turbines.

This paper presents the results of the electromagnetic analysis for the optimal and stable operation design of a 15 MW super-large offshore wind power transformer. Unlike previous studies focused on lower capacity models (e.g., 5-10 MW), this research addresses the unique challenges of the 15MW class, such as higher current/voltage levels and the stringent requirement for a compact, high-durability design for nacelle installation in harsh offshore environments. Using Ansys Maxwell, we conducted Steady-state and Transient analyses on a SolidWorks-modeled transformer. We analyzed the sensitivity of leakage inductance by varying the core-winding gap (47-63 mm), determining that the 61 mm gap yields a significantly improved coupling coefficient. Furthermore, by optimizing the winding specifications (1st turn: 10, 2nd turn: 1668), the total loss was minimized to 79.346 kW, achieving 99.18 % of the design loss target. The derived key design factors, including electric field distribution and electromagnetic force, establish essential optimization parameters for developing a reliable, lightweight, and compact prototype, contributing directly to domestic independence in the super-large wind power component market.

In accordance with the government's carbon net-zero policy and the expansion of renewable energy, domestic offshore wind power plants are spreading rapidly. By 2030, the development of offshore wind power plant with a scale of several tens of GW will be promoted. Therefore, large-scale offshore wind power plants are positioned as major power sources among those of the national power system. Accordingly, securing the stability, continuity, and resilience of wind power plants are becoming essential requirements for stable power supply. In particular, offshore wind power plants are installed in special environmental conditions such as the sea. Due to high lightning frequency marine weather conditions and high structural characteristics of wind power plants, they are very vulnerable to lightning risk. The blades, nacelles, controllers, and communication facilities of offshore wind turbines are always exposed to the risk of failure due to direct lightning strikes or close discharge. This paper analyzes domestic and international standards and technology trends, and investigates the necessity of real-time lightning prediction based on the Thunderstorm Warning System, which predicts the occurrence of lightning in advance and enables active response.