The relationship between significant wave height ($H_{1/3}$) and period ($T_{1/3}$) was obtained using wave data from the East and Yellow coasts of the Korean Peninsula to facilitate the calculations of the wave parameters. In addition, the JONSWAP spectral parameters were estimated and analyzed for all wave height ranges. The relational expression between the two wave variables ($H_{1/3}$~$T_{1/3}$) obtained from this study showed a significant difference from the previously proposed relational expressions, most of which tended to follow the lower limit of the data. Meanwhile, the suggested peak enhancement factor (PEF,$\mathsf{\gamma }$) is 1–7; however, for this study, a peak control factor (PCF,${\mathsf{\gamma }}_c$) with a range of 0–10 was introduced. As a result of the analysis, the PCF was determined to be 1.13–1.42, which is approximately 40% smaller than the previously proposed $\mathsf{\gamma } = 3.3$. The probability density distribution of the appropriate PCF was then calculated, and the gamma and log-normal distributions for the East and Yellow coasts of the Korean Peninsula were found, respectively. This study covered waves of all range heights, and the analysis results can be used as important data to explain the characteristics of the sea area.

The tailings that remain after the collection and screening of Mn nodules are directly discharged into the ocean and are anticipated to influence the ocean environment and marine organisms. The primary factors determining the influence (diffusion) range are the ocean currents and the settling velocity of the tailings; the latter is directly correlated with the time that the tailings remain in the water column. Flocculation is affected by the actual tailing discharge conditions. The settling velocity of the tailings is expected to increase as a result of flocculation; therefore, data on the size distribution of flocs are needed to compute the settling velocity of the tailings. In this study, a method for estimating the floc size distribution of the tailings is proposed, and the general flocculation process is analyzed using the apparent settling velocity, which is readily estimated by simple settling experiments conducted with standard tailings at different concentrations. The apparent falling time-curve followed a power function, and the flocculated grain size was 3–4 times larger than that before flocculation. In addition, flocculation and falling were significantly inhibited by the time required for flocculation. The method suggested in this study was validated by using a numerical particle-tracking model based on the autoencoder concept, which estimates the apparent settling velocity using the flocculated grain size distribution. The computed time-velocity curve agreed well with the apparent time curve obtained in the experiment, with an error of approximately 5–10% except in the initial time range (0–30 s), despite the qualitative nature of the assumptions.

Many mathematical models have been proposed to estimate vertical tidal current profiles. However, as previous studies have shown that tidal current energy sites have different characteristics in their vertical tidal current profiles, it is necessary to estimate the profiles from field-measured data for practical purposes. In this study, we measured layered tidal currents over two months using an acoustic Doppler current profiler (ADCP) to analyze the characteristics of vertical tidal current profiles at the Jangjuk Strait, a candidate site for tidal current energy. As a result, the power law parameter $\alpha$ and bed roughness $\beta$ were estimated as 4.51–12.41 and 0.38–0.42, respectively. Additionally, the maximum roughness length representing seabed roughness in the logarithmic profile was estimated as 0.221 m, and the estimated friction velocity was 0.038–0.194 m/s. Furthermore, a high correlation was observed between the depth-averaged tidal current velocity and friction velocities at all sites during flood and ebb tide conditions. A high correlation was also found between the bed roughness, roughness length, and power law exponent at relatively deeper sites. Tidal current energy sites display distinct characteristics compared to other sea areas. Therefore, it is essential to account for field conditions when conducting numerical modeling and design.

Ko, D.-H. and Lee, U.-J., 2023. Reliability analysis of offshore wind structures considering the Korean met-ocean conditions. In: Lee, J.L.; Lee, H.; Min, B.I.; Chang, J.-I.; Cho, G.T.; Yoon, J.-S., and Lee, J. (eds.), Multidisciplinary Approaches to Coastal and Marine Management. Journal of Coastal Research, Special Issue No. 116, pp. 603-607. Charlotte (North Carolina), ISSN 0749-0208. IEC and DNV documents, which are developed for the design of offshore wind turbines, have been developed based on the experiences of the offshore wind industry. Moreover, IEC and DNV documents adopt the reliability design method, a partial safety factor based on the limit state design. However, since these documents were developed under European met-ocean conditions, it is necessary to develop a reliability design method suitable for the Korean met-ocean conditions to satisfy the safety level required by overseas documents. Thus, this paper conducted the reliability analysis of offshore wind structures considering the Korean met-ocean conditions. The Monte Carlo Simulation method was used as a reliability analysis technique. Moreover, design variables such as waves and winds of the Korean west sea were calculated by numerical simulation, and design parameters were estimated using extreme analysis. In addition, partial safety factors were suggested to satisfy the target reliability required by IEC. As a result, in the case of the Korean west sea, where typhoons are dominant, the reliability index was calculated lower than in Europe due to the higher variation of design variables such as wind. These results showed that a more careful approach should be taken to installing offshore wind turbines in areas affected by typhoons. Furthermore, it is judged that it is necessary to calibrate the partial safety factors considering the met-ocean conditions of the specific sites.

In this study, a smoothing method was applied to improve the accuracy of peak wave period estimation using water surface elevation data collected from two oceanographic and meteorological observation towers situated on the western coast of the Korean Peninsula. The effectiveness of the smoothing method was validated by assessing the surface elevation variance and total wave energy. Subsequently, we examined the impact of the smoothing application. The results of our analysis revealed a reduction of approximately 27% in comparison to the confidence interval of the initially estimated spectrum upon applying the smoothing method. Furthermore, a slight variation of approximately 1–2 s was observed between the peak wave period calculated from the estimated spectrum and that obtained through the smoothing process. Utilizing statistical methods to determine the optimal smoothing parameter count, we observed an increasing trend as the range of significant wave heights decreased.