The global expansion of offshore wind turbine (OWT) installations into seismically active regions has heightened concerns about their performance under earthquake loading. Beyond harsh environmental loads, seismic events can severely disrupt OWT operations, potentially resulting in permanent shutdowns. Incorporating soil-structure interaction (SSI) effects significantly influences their resilience and stability—factors that are critical yet poorly understood. Furthermore, the impacts of near-field and far-field ground motions on the seismic SSI behavior of jacket-supported OWTs remain unexplored, representing a critical knowledge gap. Therefore, this study investigates the influence of pulse-like ground motions on the nonlinear dynamic responses of jacket-supported OWT systems, accounting for SSI effects. A high-fidelity numerical model is developed and validated to ensure accuracy within the modeling framework. Following validation, extensive numerical simulations are conducted using earthquake records with and without velocity pulse characteristics. The results elucidate the interplay among pulse-type classifications, SSI effects, and the seismic response of jacket-supported OWTs, thereby supporting improved seismic design and analysis practices for such structures.
This study investigates the issues of leader-following asymptotic synchronization in multi-agent systems (MASs) using a nonfragile retarded sampled-data control (NFRSDC) approach. First, a fixed directed interconnection topology is adopted to model the communication between leader and follower agents. Next, the NFRSDC scheme incorporates a time-varying delay to better reflect practical conditions. Finally, a straightforward linear transformation is applied to derive the error system. Compared to existing sampled-data control methods, the proposed nonfragile retarded sampled-data control (NFRSDC) offers a more practical solution by incorporating both signal communication delays and unknown parameters. Under these assumptions, a distributed NFRSDC scheme is developed using algebraic graph theory and Lyapunov-Krasovskii (LK) stability theory. The control law is formulated in terms of linear matrix inequalities (LMIs) for each follower node, guaranteeing asymptotic synchronization of the closed-loop error system. Finally, the efficacy of the proposed control strategy is validated through numerical simulation model.
The Korean seahorse, Hippocampus haema, was formerly misidentified as H. coronatus but has since been described as a distinct species, and its ecology remains poorly understood. This study examined the morphological characteristics of H. haema to enhance ecological understanding. A total of 913 seahorses collected from Geoje-Hansan Bay, Republic of Korea were measured for snout length (SnL), head length (HL), coronet height (CH), trunk length (TrL), tail length (TaL), height (Ht), and standard length (SL). Specimens were further categorized by sex and maturity to assess morphological differences. Males had significantly larger size-adjusted dimensions than females, with the exception of trunk length (t-test and Mann–Whitney U test, p < 0.01). Immature seahorses displayed significantly lower SnL/SL but higher HL/SL, CH/SL, and Ht/SL compared to mature individuals (Mann–Whitney U test with Bonferroni correction, p < 0.01). Seasonal variations were evident across all groups: males showed significant differences in HL/SL, CH/SL, TrL/SL, and TaL/SL, while females displayed seasonal variations in all morphometric proportions except for TaL/SL (Kruskal–Wallis test, p < 0.01). Immature seahorses exhibited significant seasonal changes in HL/SL, CH/SL, and TaL/SL (Kruskal–Wallis test, p < 0.01). Morphological variations in H. haema were associated with reproductive activity, feeding behavior, and attachment ability. These findings provide valuable insights into the species’ ecological adaptations and contribute to its conservation and management.
This study proposes a novel hybrid anchor system that combines the frictional resistance of ground nails with the passive resistance of vertical plate anchors to enhance pullout performance in retaining structures. The anchor system was developed for use as a reinforcement material in embankment-type reinforced retaining walls. The anchor system was prefabricated using corrugated pipes filled with cement grout, allowing it to be utilized as a reinforcement material for embankments. A model pullout test in crushed stone was conducted to determine the ultimate pullout capacity, supported by large direct shear tests using a three-dimensional printed corrugated anchor surface and large triaxial compression tests to determine the mechanical parameters of the crushed stone. Direct shear tests under normal stresses ranging from 50 to 250 kPa showed that the interface friction coefficient decreases with increasing normal stress and follows a power-law relationship. Triaxial compression tests conducted at confining pressures of 100, 200, and 300 kPa indicated a friction angle of approximately 45°. Model pullout tests measured an average ultimate pullout capacity of 11.84 kN. Component analysis revealed that passive resistance was the dominant component, contributing 63
Exploring and controlling the fundamental properties of the functional metal-tungstate have been a challenging but fascinating task. Before possible utilization in new applications, the proper control of various important parameters in all materials is crucial in the new era of technology. Over the past decade, rigorous research efforts have been made to provide insight and control of the physical properties of functional metal-tungstate using dilute doping of metallic impurities. Subsequently, we apply defect-induced engineering assisted by Cu substitution on the Co sites of CoWO4 to alter and control its physical properties. Firstly, high-quality undoped and Cu-doped CoWO4 (Co1-xCuxWO4 with x = 0, 0.03, 0.06) has been prepared using a solid-state reaction route. The samples were then characterized using X-ray diffraction, and the pure wolframite-monoclinic polycrystalline nature was confirmed regardless of Cu contents. The lattice volume of the samples decreases with the Cu content, confirming the successful substitution of the Cu ions at the Co site. The sample's elemental analysis and presence of the various ionic states of Co, Cu, W, and O have been investigated using X-ray photoemission spectroscopy. The band gap of CoWO4 was successfully controlled by Cu doping, viz., found in decreasing order on increasing Cu doping concentration. On investigation of detailed electrical transport properties, it is evident that the 6 % doping content of the Cu leads to the CoWO4 material in high conduction state as well as higher polarization, which offers the potential use of this material in numerous electronic applications.
