Floating offshore photovoltaic (FOPV) systems offer a promising solution to land-use constraints and support large-scale solar energy development in marine environments. The dynamic responses of floating platforms, which directly affect both structural safety and energy harvesting efficiency, are largely governed by the mooring system. In practice, however, anchors cannot always be installed at their designed locations due to cost constraints and simplified installation procedures. Such stochastic anchor position deviations may alter the dynamic behavior of FOPV systems, thereby affecting system safety and energy efficiency. The aim of this study is to quantitatively evaluate the effects of multiple anchor position deviations under extreme environmental conditions. Specifically, the anchor positional uncertainties were considered through stochastic sampling, time-domain simulations, and statistical modeling. The results showed that anchor position deviations lead to significant right-skewed distributions in both the maximum mooring line tension and the maximum horizontal platform displacement, which are well described by the Generalized Extreme Value (GEV) distribution. The probability that the mooring safety factor falls below the design threshold of 1.67 exceeds 50%, while the probability that the maximum horizontal displacement exceeds the design value reaches 72%, indicating a substantial increase in structural risk. In contrast, connector tensions exhibit only limited variation under stochastic anchor deviations, suggesting a relatively low risk to inter-module structural integrity. Additionally, the power generation performance of the FOPV system is found to be largely insensitive to anchor position deviations.

Floating multi-module (FMM) systems, like floating offshore photovoltaic and floating city, provide an innovative solution to challenges posed by resource scarcity and population growth. These systems consist of multiple identical floating modules, interconnected by connectors and anchored by a mooring system. Connectors, as critical components, are vulnerable to failure due to factors such as extreme and cyclic loads. Such failures can result in accidents like module overturns, collisions, and mooring line failures, which threaten the safety of engineering structures. Therefore, a numerical model of an FMM/connector/mooring system was established, based on 3-D potential flow and multi-body dynamic theory, to investigate the effects of connector failure on system safety. A model test was conducted to validate the accuracy of the developed numerical model. The numerical results show that the maximum surge, sway, and yaw motions are notably increased by connector failure, particularly in the weather-side modules connected to the failed connector. Furthermore, the modal characteristics of the system are markedly changed after failure, with the amplitude curves for surge, sway, and yaw exhibiting multiple peaks, increasing the resonance risk of engineering structures. Meanwhile, due to the connector failure, the horizontal motion trajectories of the modules are transformed from straight lines into complex patterns, such as ellipses or 'infinity'-shapes. Finally, the maximum tensions in the remaining connectors positioned opposite the failed connector are considerably higher than those observed under intact conditions, increasing the risk of cascade connector failures and consequently endangering the safety of engineering structures.

The increasing demand for offshore platforms presents critical challenges to the mechanical properties and sustainability of the classical mooring systems, motivating the need to explore the possibilities of using Carbon Fiber Reinforced Polymer (CFRP) as the mooring material. A reliable service-life prediction model is essential for maintaining the structural integrity of the CFRP mooring system. This paper focuses on developing a probabilistic model for predicting the service life of CFRP mooring lines by considering accumulated fatigue damage and seawater absorption induced degradation. The basic assumption of this model is that the fatigue life of CFRP unit cell fulfills Weibull distribution, and that the fatigue strength of the unit cell and mooring cable fulfills the serial-parallel model. The uncertainties of the service-life associated with the large variety of sea conditions are further taken into account through hydrodynamic analysis based dynamic loading estimation. Another feature of this model is that it could predict residual service life during the service period by taking the structural health monitoring (SHM) data as input to estimate the accumulated damage. Furthermore, this model is used to evaluate the CFRP mooring design for a full-scale in-service offshore platform. The results show that the predicted service life of the designed CFRP mooring lines exceeds the 30-year design service life under the target environmental conditions.

Accurate prediction of structural dynamic responses under complex multi-hazard coupling is critical for the safety assessment of marine engineering structures. However, current deep learning methods are confronted with two key limitations: the inability to fuse multi-source inputs and the challenge of stable long-sequence extrapolation. To break these barriers, this study introduces RecFusionED—a novel hierarchical deep learning framework that enables flexible, high-precision, and sustained structural response extrapolation. Its innovation lies in two core designs: (1) the FusionED unit, which employs a feature-wise linear modulation mechanism to achieve deep fusion of structural parameters with multi-source time-series excitations; and (2) a recursive extrapolation architecture that integrates segmented recursion with dynamic teacher forcing, overcoming performance degradation in long-horizon forecasting and ensuring stable, physically consistent predictions over extended time windows. Validated on a jacket offshore platform subjected to combined wave and seismic loads, FusionED demonstrates exceptional local accuracy, and RecFusionED successfully performs stable temporal extrapolation of response trajectories beyond the training horizon. This framework provides a transformative tool for the dynamic safety assessment of marine structures under realistic multi-hazard scenarios.

Nearshore coastal regions have become popular for floating photovoltaics (FPV) installations. During propagation over seabed topography towards nearshore FPV systems, waves undergo intricate transformations by shoaling, reflection and refraction, potentially influencing hydrodynamic responses of these emerging marine renewable energy structures in ways that are not well understood. Therefore, wave flume experiments and multiscale fully coupled time-domain fluid-structure interaction (FSI) simulations are performed to examine the topography effect on the nonlinear responses of nearshore FPV systems at a field site in the East China Sea. Experimental results reveal that near-resonant wave interactions in coastal regions drive significant energy transfer among different wave frequencies, amplifying the nonlinear dynamic responses of FPV systems by channeling energy toward their natural modes. As a result, second-order heave and pitch responses are amplified by up to 117.87 % and 136.38 % compared to the case without topography, which in turn lead to an increase in mooring tension. Moreover, the topography-induced amplification of nonlinear wave harmonics enhances the surge mean drift of FPV. This enhancement exhibits a negative correlation with the relative FPV length with respect to the wavelength. Comparisons between experiments and fully coupled simulations for irregular waves indicate that neglecting topography causes the FPV dynamic response model to produce inaccurate estimations of heave/pitch motions, while FSI simulations forced by high-fidelity local wave fields predicted by the fully nonlinear Boussinesq wave model are capable of capturing the observed topographic effect. These findings provide the theoretical basis for design consideration of the safe, cost-effective deployment of efficient FPV systems in coastal waters.

The fluid-structure interaction of a circular cylinder equipped with a flexible splitter plate represents a complex nonlinear system, yet the coupled dynamics governing flow-induced vibration (FIV) suppression remain elusive. In this study, experiments on an elastically mounted cylinder with a flow-adaptive flexible plate are conducted at subcritical Reynolds numbers (R-e = 1100-7700). For a stationary cylinder, plate response modes (straight, symmetric flapping, biased, and hybrid) are dictated by a dimensionless parameter, U-b, reflecting the balance between fluid inertia and structural stiffness. The symmetric flapping mode is identified as a wake-induced forced vibration dictated by Strouhal shedding rather than self-excitation. When coupled with a freely oscillating cylinder, the response bifurcates into three regimes: galloping for stiff plates, optimal FIV suppression (amplitude reduction > 80%), and vibration-return for overly compliant plates. In the suppression regime, low-velocity operation induces anti-phase symmetric flapping that acts as a hydrodynamic energy sink, whereas elevated velocities trigger a spontaneous symmetry-breaking bifurcation into a biased deflection, unilaterally reattaching the shear layer and eradicating periodic shedding. Optimal vibration suppression is robustly achieved within Ub is an element of [546, 1345], providing guidance for passive FIV control.

Seabed levelling plays as a critical role in coastal bridge and tunnel construction. With the growing demand for coastal bridge and tunnel construction in deeper waters, limitations of conventional rubble dumping methods can pose a threat to operational stability and levelling accuracy. To overcome these challenges, an innovative seabed levelling system is developed here, which integrates rubble dumping with seabed levelling. The integrated system combines granular material transport with precision levelling through a support vessel and flexible pipe configuration, wherein the dynamic responses of the flexible pipe are critical due to its influence on the efficiency and safety of material transport during seabed levelling operations. This study aims to quantify the effect of environmental and operational parameters on the safety of the flexible pipe. The results indicated that robot movement parallel to the pipe-laying direction increases effective tension while reducing slope and curvature, whereas robot movement perpendicular to the pipe-laying direction shows minimal impact. Additionally, the alignment environmental loads affect tension and slope, with optimal performance of relatively low values of effective pipe tension and slope when aligned with pipe direction. Internal flow concentration emerges as another key factor, where concentrations can increase pipe weight and slope steepness proportionally, establishing a concentration below 15 % as the recommended operational limit. These results provide essential engineering guidelines for configuring and operating seabed levelling systems in challenging deep-water environments.

This study explored the hydrodynamic load distribution characteristics of vortex-induced vibration (VIV) of a mining riser under uniform flow through model testing. A novel inverse identification approach based on discrete strain responses was proposed to determine hydrodynamic loads. The Euler-Bernoulli beam differential equation was modified to incorporate dynamic spatiotemporal tension, and a structural response control equation considering variable and temporal tension and nonlinear effects was established. Using this framework, an inverse solution enables accurate identification of hydrodynamic loads on mining risers. The hydrodynamic load of the overhanging mining riser was realized by inverse solution based on the structural response control equation. Vortex-excited load coefficients were obtained via a least squares method. The results indicate that, compared with conventional oil and gas risers, VIV generates a non-uniform, periodic load in mining risers. VIV amplifies the mean drag, with the mean drag coefficient ranging from 1.60 to 1.80, 1.30 to 1.50 times that of conventional rigid risers in the subcritical Reynolds number regime. Cross-flow (CF) vortex loads exhibit approximate symmetry about the riser midpoint, whereas in-line (IL) loads are distinctly asymmetric, contrasting with the symmetric distribution of vortex loads observed in strongly constrained oil and gas risers. These findings provide critical data reference for validating Computational Fluid Dynamics (CFD) simulations of riser hydrodynamics.

With increasing global energy scarcity, Floating Offshore Photovoltaic (FOPV) systems have attracted considerable interest due to their potential advantages. Owing to their lightweight and large-span design, FOPV structures typically exhibit shallow-draft properties. Traditional dynamic analysis methods primarily rely on average wetted surface assumptions based on linear potential theory, while neglecting instantaneous wetted surface variations. This study develops a nonlinear response calculation method that accounts for instantaneous wetted surface changes in shallow-draft FOPV systems, rigorously validated through multiple approaches. Using this validated method, we systematically investigate nonlinear wave forces and dynamic response characteristics of shallow-draft FOPV systems. Our results show that higher-order wave forces induced by wetted surface variations account for up to 40% of the total wave force in shallow-draft configuration. Furthermore, pronounced nonlinear response characteristics are revealed, including a surge resonance (up to a 19-fold increase compared with linear prediction at 7 s) driven by harmonic components, and a heave amplification (up to 1.8-fold relative to linear prediction) resulting from limited hydrostatic restoring forces. In addition, multi-body FOPV systems exhibit more complex dynamic behaviors than single structures. These findings collectively highlight the critical importance of accounting for instantaneous wetted surface variations in the dynamic analysis of shallow-draft FOPV systems.

The dual barge float-over technique, incorporating a passive heave compensation (PHC) system, presents an efficient solution to the challenges posed by the installation of increasingly larger offshore structures. Despite its potential, the efficiency of the PHC system in reducing motions and its influence on the multi-body dynamic characteristics of the dual barge float-over system remain insufficiently explored. In this study, a comprehensive analysis of the PHC system's performance in dual barge float-over installation of a substation was conducted. A numerical model of the system was established in both the frequency and time domains. The motion properties of the multibody system were analyzed under varying gas volumes and damping coefficients in the frequency domain. The results indicate that while the PHC system reduces substation's motion amplitudes around the primary frequencies, it simultaneously induces secondary resonant motions with larger amplitudes in the low- frequency range. However, the time domain simulation based on the North Sea wave scatter diagram data reveals that the influence of these secondary resonant motions on the overall performance of the PHC system is negligible. The analysis proves that the PHC system significantly enhances the dual barge float-over technique's operability, particularly in beam waves and at high wave heights.

Bolt loosening in offshore wind turbine structures poses a significant threat to operational safety and structural integrity. Traditional vibration-based detection methods often suffer from low sensitivity, poor noise robustness, and limited adaptability in complex marine environments. To address these challenges, this paper proposes a novel bolt-loosening identification approach based on empirical mode decomposition and principal component analysis, enhanced through multi-channel data fusion. The method extracts multi-dimensional time-domain features from vibration signals, applies grid-based statistical mapping, and constructs a unified feature matrix for dimensionality reduction. By projecting features into the principal component space, damage is evaluated using a squared prediction error metric, and the number of loosened bolts is identified through nearest-neighbor classification with Mahalanobis distance. The proposed framework is validated via both numerical simulations and scaled physical model experiments under various bolt-loosening conditions and noise levels. Results show that the method accurately detects and quantifies the number of loosened bolts with strong noise resistance and high engineering applicability, providing a practical and reliable solution for structural health monitoring of offshore wind turbines.

The floating offshore photovoltaic (FOPV) system presents exceptional potential for enhancing power generation while reducing land usage. However, existing FOPV concepts face high structural costs and maintenance challenges. This paper aims to introduce a novel FOPV system featuring low-cost, lightweight modules, and an innovative rope-net connection system made from economical flexible polyester ropes. The floating modules, with low air gaps, are assembled to provide buoyancy for photovoltaic panels and are strategically arranged within this adaptable rope-net connecting system. Employing three-dimensional potential flow theory and multi-body dynamics theory, the dynamic responses of this novel FOPV system were investigated. The results indicated that at a wave period of around 5.75 s, the first-and second-order mode responses of the entire FOPV system could be excited, leading to peak horizontal displacements, mooring line tensions, and connecting line tensions. Additionally, under a 0 degrees wave direction, the maximum mooring line tension occurs on the weather-and lee-side mooring lines and is significantly greater than that under oblique waves. In contrast, the connecting line tension is greater under oblique waves than under 0 degrees, with an additional peak appearing in the short-wave range due to coupling with roll and pitch motions. The findings also revealed that as the array size increases, the first-and second-order modal periods of the entire FOPV system increase, whereas heave, roll, and pitch motions remain relatively insensitive to array size.

This paper aims to investigate the dynamic response and hydrodynamic characteristic of multi-module floating photovoltaics (FPV) array through numerical simulation and experimental verification. A model experiment on two-module FPV array model is conducted to investigate the motion response, connector load and mooring tension under both regular and irregular wave conditions. A fully coupled model of two-module FPV array is developed and analyzed to examine the hydrodynamic behavior based on the time-domain motion equations of multi-body. A comparative analysis of the dynamic characteristic of two-module FPV array is conducted, and the simulation results exhibit basically consistency with the experimental results. A novel six-module 0.75 MW FPV array is proposed, whose connector load and mooring tension are analyzed through fully coupled numerical simulation. Additionally, the dynamic response of FPV array is evaluated through multi-body dynamic analysis under broken-line conditions. The results show that the maximum connector load occurs at wave direction of 120 degrees, while the maximum mooring tension occurs at wave direction of 90 degrees. When the mooring fails, the motion response of the FPV array changes minimally, but the remaining mooring tension increases to twice the mooring tension with intact mooring.

Open berths without natural or artificial sheltering structures are subjected to severe and complex marine environmental conditions, critically challenging the safe operational capabilities of berthed ships. Previous research on dynamic response analysis of berthed ships predominantly focused on sheltered port areas while inadequately analyzing the complexity and severity of open-water marine environments. To address this issue, this paper establishes a coupled "Ship-Mooring-Fender" numerical model, combining the Cummins equation (dynamic analysis), catenary theory, and nonlinear fender reaction models, which is validated through DNV Sima software. This study employed time-frequency domain analysis to investigate the influence of multi-directional wind-wave-current combination loads on the dynamic response of a berthed ship and the limitation effect of mooring pretension. And using this coupled model, the impact of extreme tidal fluctuation on the ship offset phenomena and mooring pretension variation is studied. Results show that the influence of combined wind-wave-current conditions exhibits significant directional dependence. Optimal selection of mooring pretension based on predominant sea conditions can reduce the berthed ship's motion. For open berths with fixed mooring line lengths, tidal fluctuations critically affect pretension levels, potentially inducing line entanglement or mooring failure. These analytical results can provide valuable references for the safety assessment of berthed ships.

Mining risers, as critical components of deep-sea mining systems, are susceptible to excessive bending and displacement due to environmental loads, vessel motion, and mining vehicle operations. Accurate monitoring of their spatial deformation is essential for operational safety and efficiency. This paper proposes a novel method for reconstructing the 3D spatial deformation of mining risers using sparse inclination measurements. In this method, the 3D configuration of the riser is projected onto two orthogonal planes, followed by discretization of the structure through dual-axis inclinometer nodes and modeling of each segment using second-order interpolation functions. By integrating spatial curve length equations and correlating the 2D projections through shared coordinates, the 3D shape of the riser is efficiently reconstructed. A numerical simulation on a kilometer-scale deep-sea riser demonstrates the method's feasibility and effectiveness. Inversion accuracy exceeds 92.9 % with a sensor spacing ratio of 1/9, while correlation coefficients remain above 84.3 % and 83.4 % under varying levels of sensor and shipboard GPS noise, respectively. These results confirm that the proposed approach provides both high accuracy and robust performance for real-time spatial deformation reconstruction of mining risers under dynamic conditions.

Dynamic systems characterized by second-order nonlinear ordinary differential equations appear in many fields of physics and engineering. To solve these kinds of problems, time-consuming step-by-step numerical integration methods and convolution methods based on Volterra series in the time domain have been widely used. In contrast, this work develops an efficient generalized pole-residue method based on the Volterra series performed in the Laplace domain. The proposed method involves two steps: (1) the Volterra kernels are decoupled in terms of Laguerre polynomials, and (2) the partial response related to a single Laguerre polynomial is obtained analytically in terms of the pole-residue method. Compared to the traditional pole-residue method for a linear system, one of the novelties of the pole-residue method in this paper is how to deal with the higher-order poles and their corresponding coefficients. Because the proposed method derives an explicit, continuous response function of time, it is much more efficient than traditional numerical methods. Unlike the traditional Laplace domain method, the proposed method is applicable to arbitrary irregular excitations. Because the natural response, forced response and cross response are naturally obtained in the solution procedure, meaningful mathematical and physical insights are gained. In numerical studies, systems with a known equation of motion and an unknown equation of motion are investigated. For each system, regular excitations and complex irregular excitations with different parameters are studied. Numerical studies validate the good accuracy and high efficiency of the proposed method by comparing it with the fourth-order Runge--Kutta method.

Floating offshore photovoltaic (FOPV) systems are key technologies for harnessing offshore solar resources, playing a crucial role in mitigating global climate change. Anchoring systems, essential components of FOPV systems, ensure operational safety by limiting floating body's displacement. However, factors such as positioning errors, uneven seabed, and inhomogeneous loads make it challenging to install anchors exactly at their designed locations. These deviations can significantly alter the system's dynamic responses, particularly under extreme environmental conditions, posing potential safety risks. This study aims to explore the dynamic response characteristics of FOPV systems with varying anchor position deviations under extreme sea states, offering valuable insights for system design. First, a coupled numerical model is developed to capture interactions between multiple modules and their mooring lines. Then, the effects of anchor offset distance, direction, relative position, and the incident direction of sea loads on modules motion and mooring tension are discussed. The results indicate that anchor deviations along the mooring projection direction significantly affect the maximum horizontal motion, maximum mooring tension, and minimum mooring safety coefficient, while the maximum heave motion remains largely unaffected. Additionally, when the displaced anchor and the direction of environmental loads acting on the FOPV system are on the same side, the system's maximum dynamic responses are significantly higher compared to those due to the displaced anchor on the leeward side.

The connector design plays a pivotal role in ensuring the structural integrity and operational efficiency of offshore floating photovoltaic (FPV) systems. This study aims to systematically investigate the impact of various connection types (rigid, rubber, hinged, and flexible) on the hydrodynamic response of offshore FPV arrays, as well as on the structural responses of their connectors. Firstly, a single-float model was developed, and the hydrodynamic coefficients necessary for the time-domain analysis were meticulously derived using frequency-domain methods. Subsequently, a 3 × 3 FPV array model was constructed, including the connectors with specifications tailored to the stiffness and constraints of the four distinct connection types. Finally, a comparative analysis was conducted on the motion responses of the three representative modules (central, edge, and corner), along with the corresponding connectors’ responses. This study demonstrates that floats interconnected by rigid connectors are most significantly influenced by the surrounding floats. The outer floats, in conjunction with their connectors, constitute an outer-frame integrity phenomenon that plays a critical role in maintaining the array stability. Furthermore, the fatigue cycles experienced by the connectors attached to corner modules exhibited an increased sensitivity to the incident wave angle, highlighting the importance of precise wave direction considerations.

To enhance the design efficiency and quality of floating offshore photovoltaic systems, this study proposes an NSGA-II-based method for economic sizing and configuration optimization. The study begins by considering the rotational effects of the floating platform and provides a detailed analysis of the annual power generation calculation for FOPV systems. This includes solar position calculations, geometric optimization of photovoltaic array arrangements, and the impact of platform rotation on radiation and shading effects. Subsequently, a dualobjective optimization approach is introduced, aiming to maximize annual power generation while minimizing the total area of photovoltaic modules within a multi-constraint framework. Key design parameters, such as the number and type of photovoltaic inverters, module selection, tilt angle, and azimuth angle, are optimized. Geometric, wind load, and electrical constraints are incorporated to ensure the feasibility of the design. The proposed optimization algorithm was validated under various operating conditions, including stationary and rotating floating platforms, in the Qingdao and Zhoushan regions of China. The results demonstrate that the method achieved an approximately 2% improvement in annual unit energy generation, highlighting its effectiveness in enhancing system performance.