The mechanical behavior of PVC-coated fabric materials for offshore membrane structures was investigated through off-axial tensile testing and orthotropic elastoplastic numerical simulation. Off-axial tensile tests were conducted at 0 degrees, 45 degrees, and 90 degrees to obtain the material properties, including the strain and displacement distribution, stress-strain relationship, and failure strengths. The orthotropic mechanical behavior was captured by the Karafillis-Boyce yield criterion with a linear transformation to define an isotropic plasticity equivalent stress, enabling the application of equivalent plastic strain-based exponential hardening. Failure strength under off-axial loading was also evaluated using both the maximum principal stress criterion and the Tsai-Hill criterion. The comparisons between the experimental results and numerical simulations in strain distribution and stress-strain relationship show strong agreement, supporting the accuracy of the proposed model. This framework provides a comprehensive understanding of the mechanical properties and behavior of PVC-coated fabrics.
This study presents an approach to ice ridge detection and analysis in Arctic seas using artificial intelligence, addressing challenges posed by complex geometries and unpredictable distributions. A machine learning algorithm based on convolutional neural networks and U-Net architecture was developed and validated for automated detection of ice ridges from aerial imagery, achieving high accuracy and robustness. Additionally, statistical analysis of geometric and spatial properties, as well as fractal analysis of ice ridge distributions, provide insights into structural characteristics and scaling behaviors. These advancements improve risk assessment, operational planning, and predictive modeling, representing progress in Arctic Sea research and offshore engineering.
The selection of an anchor foundation is a crucial determinant in ensuring the stability and performance of floating platforms, particularly when subjected to environmental loads such as wind, waves, and currents. Different types of anchor foundations, including torpedo anchors, multi-directional loaded anchors, and fish anchors offer distinct advantages based on factors like water depth, soil conditions, and load requirements. This study investigates the whole installation and pullout process of various anchor types considering the same or different water depths, impact velocities, and installation tilt angles. Additionally, considering material costs for each anchor type provides a comprehensive evaluation encompassing both pull-out performance and cost efficiency. Based on the results obtained from this research endeavor, recommendations can be made for different anchor foundations tailored to diverse application scenarios. The findings from this research aim to provide guidance in selecting optimal anchoring solutions for floating platforms operating under varied marine environments and loading conditions.
The article describes the results of calculating the characteristics of ice drift in the area of the Sabetta port (Gulf of Ob, Kara Sea), observed during landfast ice break-up in summer, 2022. We determined ice drift with the maximum cross-correlation method using images obtained from a coastal radar station. Analysis of the drift vector was carried out using vector algebra methods. The maximum cross-correlation method was verified, and the main statistical characteristics of ice drift were obtained: the mean ice drift in the Sabetta port area and the standard deviation of the drift were estimated, and the spectral density of the drift was calculated. It was found that the average drift vector is directed to the northwest and has a speed of up to 6 cm/s. The primary variability of the drift is determined by the semidiurnal tidal component. The experience gained in the research shows the potential of using coastal radar station data for monitoring and calculating the regime characteristics of ice cover drift and the ice loads on port hydraulic structures.
This article discusses the formation of three new ice ridges created from the old ice during the drift of the polar station "The North Pole-41" in the Arctic basin. Conditions for formation of ice ridges, sail parameters, and other morphometric characteristics are determined. Comparison of block thicknesses with the average values of level ice thickness at the moment of ice ridge formation provides evidence of the formation of ice ridges from residual and second-year old ice, supporting the likelihood of horizontal ice splitting.
This paper investigates the coupled aero-hydro dynamic response of the OC4 semi-submersible floating offshore wind turbine (FOWT) under wind-wave-current conditions. Simulations employ the in-house computational fluid dynamics solver, FOWT-UALM-SJTU, with waves2Foam. Among them, the rotor loads and mooring tension are calculated by the actuatorline and lumped-mass methods. Free-decay tests in surge, heave, and pitch validate the model against other works. Five cases including wind only, wind-wave, and wind-wave-current at 0.6, 1.2, and 1.8 m/s, respectively, reveal that current markedly amplifies surge motion and mooring tension. Rotor-speed root mean square grows slightly, whereas thrust and power drop. Power Spectral Density analyses show low, medium, and high frequency bands dominated by natural modes, wave, and rotor harmonics, with high-order wave components intensified by current. Liutex-Omega vortex identification indicates reduced wake inclination and faster recovery as current strengthens. Present research highlights the necessity of comprehensively considering wind-wave-current interactions in the design and operation of FOWTs.
In this study, super-resolution reconstruction of near-wall turbulence is conducted using two deep neural networks: a conventional super-resolution convolutional neural network (SRCNN) and a U-Net-based super-resolution architecture (UNetSR). The training data are derived from high-fidelity, wall-resolved large eddy simulations of turbulent channel flow at Re' =1,000, while low-resolution inputs are generated by downsampling with ratios r = 4 and r = 8. We focus specially on the reconstruction performance in different regions of the turbulent boundary layer: the inner layer (y+ =15) and the outer layer (y/S = 0.15). The results demonstrate that both methods significantly outperform bicubic interpolation, with U-NetSR showing superior reconstruction accuracy across all test cases. At higher downsampling ratios (r = 8), SRCNN tends to oversmooth the flow field, whereas U-NetSR preserves small-scale structures and high-frequency features more effectively. Moreover, the reconstruction performance is consistently better in the outer layer than in the inner layer, due to the richer and more complex flow details present near the wall. These findings highlight the potential of deep learning-based models, particularly the U-Net architecture, in enhancing the resolution of turbulent fields while reducing computational cost.
A self-propelled Joubert BB2 submarine operating near the free surface was investigated in three fluid environments: homogeneous, strongly stratified, and linearly stratified. The differences in flow fields under various submergence conditions were analyzed. The results show that density stratification has only a minor effect on propeller rotational speed and thrust, with deviations within 3%. When the submarine operates close to the free surface, the flow-field characteristics are nearly identical among the three fluids. However, with increasing submergence depth, the differences in wake disturbances between the stratified and homogeneous fluids become more pronounced. Specifically, the vertical velocity along the submarine axis downstream decreases by 38.7% and 61.9% in the strongly and linearly stratified cases, respectively. Under such conditions, the influence of density stratification cannot be neglected.
This study presents a stochastic model for simulating landfast ice, a critical component of the Arctic marine system. A probabilistic approach describes the spatial and temporal variability of landfast ice. The model incorporates long-term trends, seasonal cycles, and stochastic fluctuations, and its outputs are validated against empirical data. Results reveal significant regional differences in landfast ice behavior, with western areas showing stronger trends. The proposed method offers a flexible tool for simulating landfast ice dynamics under climate change, addressing key limitations of traditional deterministic models.
The paper examines issues related to the assessment of the shear stability of stamukhi and grounded ice islands using the example of ice and soil conditions in the southwestern part of the Laptev Sea (Khatanga Gulf). An algorithm for assessing the stability of stamukha against shear is proposed; the existing algorithm for assessing the stability of ice islands against shear is taken as a basis. Based on the results of ice research expeditions in this area, 16 stamukhi were identified, seven of which had a sail volume exceeding 10,000 m3. The main morphometric characteristics were determined, and the pressure on the seabed was calculated for each of the seven specified stamukhi. It was shown that the process of forming several stamukhi began with level ice thickness 30 cm and continued until the thickness of level ice was 140 cm. The angle of internal friction and cohesion of the common soils of the area, i.e., silty sand and clay, were determined. The analysis of the shear stability of the seven stamukhi of the Khatanga Gulf was carried out by varying the thickness of the surrounding ice. An upper estimate of the failure-mode parameter for ice conditions in the Laptev Sea has been made. An analysis of the shear stability of a grounded spray ice island for conditions in the southwestern part of the Laptev Sea has been conducted. The results obtained in the paper can be used in conceptual assessments of the possibility of using grounded ice structures in shallow Arctic waters.
The article discusses three different options for optimizing the iceberg towing process. A design for a towing system is proposed to reduce the total drag coefficient of a tabular iceberg by changing its spatial orientation. The influence of the jet from the vessel's propellers acting on the front side of the iceberg on the towing force is considered. Measures are proposed to reduce this impact by changing the direction of the vessel's azimuth thrusters. The results of numerical modeling of jet propagation from the vessel's propellers to the iceberg are presented. For the proposed options of iceberg towing optimization, an increase in the speed of the iceberg during towing is estimated while maintaining the same propulsion power of the vessel compared to the basic case. The paper also discusses issues related to the interaction of the rope with the iceberg. For various forms of icebergs, the recommended limit of the coefficient of friction of the rope material on the iceberg has been determined, at which point, the rope will not slip on the iceberg. The results presented in the article can be used when planning and conducting iceberg towing in various areas of the World Ocean.
Efficient fish swimming depends on coordinated fin motions, with the dorsal fin and caudal fin interaction having an important influence on propulsion. The present study employs a Computational Fluid Dynamics approach to solve the Reynolds-Averaged Navier-Stokes equations using the finite volume method. The motions of the fins are implemented through user-defined functions coupled with the dynamic mesh technique. Unsteady, three-dimensional flow field and fin force analyses reveal the connection between flow field evolution and fin hydrodynamic performance. The results indicate that the vortex intensity of the caudal fin is much greater than that of the dorsal fin, and the influence of the dorsal fin wake on the caudal fin flow field is primarily confined to the side where the dorsal fin is located. The dorsal fin enhances the thrust and efficiency of the caudal fin, while the sensitivity of the fins to phase difference increases as the distance between the fins decreases. Adjusting the dorsal fin angle allows modulation of its contribution to propulsion and maneuverability; a larger dorsal fin angle favors increased thrust, whereas a smaller angle enhances normal maneuvering capability.
Recharacterization of embedded flaws assumes failure of the short ligament when the flaws are close to the surface so that the flaw becomes a surface flaw. However, as described in BS7910 Annex E, recharacterization should be used with caution because if the short ligament fails suddenly (e.g., by cleavage), then there may be a reduction of fracture toughness due to dynamic loading. To examine the dynamic effect of cleavage fracture on failure, a vintage pipe X52 steel of relatively high ductile-to-brittle transition temperature was tested using single-edge notch tension and modified middlecrack tension specimens at low temperatures down to -140 degrees C. In the case studied, the results showed that less conservative recharacterization (i.e., allowing shorter ligament for recharacterization) would not increase cleavage possibility, and cleavage fracture should not be a concern at usual design temperatures. The tests suggest that an impact-loading scenario from cleavage fracture of the long ligament is unlikely in normal pipeline applications because the lack of constraint in the short ligament will promote ductile rupture and consequent slow transfer of load to the long ligament. This is consistent with most Engineering Critical Assessment procedures of pipeline embedded flaws in which quasi-static loading is assumed.
This study delves into computational fluid dynamics (CFD) applied to roll decay tests for Floating Production, Storage, and Offloading units. The main objective of this work is to investigate complexities of the corresponding CFD simulations and aspects of the numerical setup optimization to enhance understanding of factors influencing precision, computational efficiency, and reliability in such numerical applications. Moreover, different bilge keel configurations along with the presence of other submerged appendages are studied and assessed in a compendious manner.
The coupling loss factor (CLF) is an essential parameter in the rapid assessment of high-frequency structural vibration and sound. This paper utilizes the wave motion theorem to formulate the CLF between two flat plates connected at any angle under harmonic wave incidence. The derived CLF formulation is rigorously validated through literature comparison and commercial software simulations. Numerical results reveal that the CLF exhibits pronounced dependence on the incident wave characteristics while demonstrating significant correlations with excitation frequency, coupling configuration, material properties, and geometric parameters of the structural system. This research significantly enhances comprehension of structural energy attenuation.
To evaluate the performance of real-time energy management strategies, we utilize the dynamic programming method to find the optimal energy flow allocation among two engines and batteries for a dual-engine hybrid power system (DHPS). First, the mathematical models of the DHPS are established. Then, the optimization problem, aimed at minimizing fuel consumption, is formulated. Next, the flowchart of the energy management strategy based on dynamic programming is introduced. Finally, the superiority of the proposed method is validated by comparing it with two real-time energy management strategies. The results show that up to 12.79% of fuel consumption is saved.
To achieve carbon neutrality by 2050, 50,000 m3 liquefied hydrogen storage tanks are being developed. A key design challenge is fatigue from repeated refilling and seismic events. The fatigue crack propagation behavior at cryogenic temperatures, especially with the martensitic transformation of austenitic stainless steels, is unclear. In this study, low-cycle fatigue tests were performed at different temperatures and materials to investigate the relationship between crack tip opening displacement (CTOD) and crack growth rate. The effect of martensitic transformation on CTOD was quantified by electron backscatter diffraction. These results were used to estimate crack propagation in large tanks.
This paper is to study the influence of soil liquefaction on the seismic response of a monopile foundation for the Technical University of Denmark (DTU) 10-MW reference wind turbine (RWT) on the west coast of Taiwan. Taiwan is located in seismically active regions, and the soil conditions of Taiwan's offshore wind farms are softer than those in Europe. Therefore, there is significant interest in assessing the behavior of a wind turbine subjected to seismic load. Based on the flexible volume method and the practical, two-surface plastic constitutive model for sand (P2PSand), the two foundation models of the DTU 10-MW RWT are employed to carry out a series of seismic design load cases as defined in DNV-RP-0585. The results show that soil liquefaction has significant influence on the dynamic response of the DTU 10-MW RWT with monopile foundation under the local environmental conditions in Taiwan. In particular, vertical displacements and rotations are significantly amplified by soil liquefaction during strong ground motions. It means that without considering the potential effect of soil liquefaction, structural responses, including displacement and rotation angle, may be greatly underestimated.
The open ocean water mass has affected the water quality of the Seto Inland Sea. In this study, the entering path and behavior of the open ocean water mass were analyzed using a three-dimensional flow simulation and Lagrangian particle tracking. The analyses revealed that the entering paths changed significantly, depending on the path of the Kuroshio Current. The entering of open ocean water may affect the water quality and primary production not only in the Kii Channel adjacent to the Pacific Ocean but also in other sea areas, including Harima Nada and Osaka Bay.
To tackle the challenges confronted by traditional deep-draft SEMI, a novel donut-type platform featuring a large moon pool is put forward. The computational fluid dynamics method integrated with wind tunnel and wave basin experiments has been employed for moon pool response analysis and for time-domain coupling analysis of the mooring system and steel catenary risers (SCRs). The results show that the donut-type platform has good global performance benefiting from the moon pool damping effect, and the feasibility for SCR application is demonstrated. With additional advantages such as lower topside elevation, larger storage capacity, higher hull structural strength, and better constructability, the donut-type platform could be a competitive new conceptual hull option for SCR utilization.
