Digital Twin (DT) technology is increasingly recognized for its potential to enhance product lifecycle management, operational efficiency, and data-driven decision-making across multiple industrial sectors. Although its adoption is growing in fields, such as aerospace and shipbuilding, its application within the Naval Auxiliary Industry—comprising the systems and suppliers that support core naval platforms—remains limited. This paper presents key insights from the TWIN NAVAUX project, which promotes the integration of digital twin technologies within this sector in the Galicia–North Portugal Euroregion. Based on demonstrator and real-world use cases, the study identifies major technical and organizational challenges, including system integration, data interoperability, and the inherent complexity of modelling ships as systems-of-systems (SoS). The work also outlines the essential building blocks required for successful DT deployment, such as standardized communication protocols, robust data acquisition and storage infrastructures, and advanced modelling and simulation techniques. Overall, the findings provide a structured roadmap to support and guide future digital twin implementations in the naval auxiliary domain.
Understanding the motion and deformation behavior of floating photovoltaic (FPV) is crucial for achieving a reliable structural-mooring system design, optimum energy output, and minimizing maintenance works. This study performs two-dimensional experiment to investigate structural motions and tension on the connection between floaters of modular FPV under regular wave in relatively shallow depth with vertical pin connector and taut mooring system. The 1:10 scale model is developed in accordance with the Froude–Cauchy similitude law and made of composite materials to capture structural stiffness. The bottom profiles are varied to investigate the effect of the bottom change to the incoming waves. The results show that pitch has direct correlation with structural tension, with higher pitch results higher tension. Smaller wave periods result in higher pitch response and tension on connection between floaters. The heave and pitch response at the bow and stern area are limited by the pre-tensioned of taut moorings, but wave over-wash occurs in this area. With the same incoming wave heights and periods, sloping bottom profile affects the wave steepness. The local waves within the empty gaps of the model and wave over-wash at the bow and stern area have affected both local and global responses of the FPV model.
Advancements in technology have resulted in the widespread use of AUVs worldwide to monitor underwater regions for applications, such as environmental sensing, underwater exploration, and underwater inspection. However, providing dependable communication among cooperating AUVs is challenging because of the high delays in acoustic signal propagation (attributed to slow relative speed), limited bandwidth, dynamic topologies, packet contention, and limited energy. The proposed method represents an adaptive energy-efficient routing and congestion-control framework with intelligence (AERCCF) to enhance dependable communication among cooperating vehicles during ocean-monitoring missions. AERCCF has congestion-aware traffic handling with flexible multi-parameter routing strategies and an intelligence-based decision-making system that aids in jointly optimizing communication reliability, energy consumption, and network performance. The routing solution focuses on using a combination of parameters rather than individual considerations of residual energy, link reliability, distance from the sink, and node speed. The congestion-control mechanism attempts to prevent packet congestion and queuing by using queue-aware rerouting. The simulation results show better performance incorporating all parameters with a Packet Delivery Ratio (PDR) of 95.8
This study experimentally investigates the hydrodynamic performance of a pile-supported, partially immersed semicircular breakwater with a concave seaward face. The two-dimensional model was suspended between two rows of circular piles and tested under regular wave conditions. Key geometric parameters included relative immersion depths (d/h = 0.25–0.5) and relative pile gaps (P = 0.5–0.83), while wave conditions covered relative water depths (h/L = 0.12–0.36) and wave steepness (Hi/gT2 = 0.0007–0.0076). Structural efficiency was quantified using transmission (Kt), reflection (Kr), and energy dissipation (Kd) coefficients. Results indicate that increasing immersion depth significantly enhances wave attenuation by reducing Kt and increasing Kr and Kd. In contrast, larger pile gaps moderately increase transmission due to a higher relative pile gap. For d/h = 0.25 and P = 0.83, Kt remained below 0.30, while Kr and Kd exceeded 0.52 and 0.62, respectively, demonstrating strong wave-blocking capability. To support preliminary design applications, empirical predictive equations were developed using Multiple Polynomial Regression (MPR). The models showed strong agreement with the experimental data, with normalized root-mean-square errors ranging from 0.019 to 0.048. A comparative evaluation with previous breakwater configurations confirms that the proposed pile-supported semicircular design provides enhanced wave attenuation, characterized by a significant reduction in the transmission coefficient and a higher capacity for wave energy dissipation under a wide range of wave steepness conditions.
Marine biofouling presents significant challenges in the maritime industry, including increased drag, fuel consumption, and maintenance costs. Traditional inspection and mitigation methods are labour-intensive and time-consuming, highlighting the need for automated approaches of biofouling detection and analysis. This study aims to bridge the existing literature gap by introducing an enhanced attention U-Net architecture specifically optimised for the semantic segmentation of marine biofouling in real-world conditions. Our model incorporates spatial attention gates within the skip connections and squeeze-and-excitation modules within each convolution block of a traditional U-Net framework. It was trained and tested on an annotated dataset of 504 in-water biofouling images collected from multiple ship hull surveys, provided by diving companies, classification societies, and NTUA’s archive. It contains images captured under various environmental conditions, which enables better model generalisation. The proposed architecture achieves a test set macro Dice coefficient of 0.775 and a macro accuracy of 0.795, outperforming a simple U-Net baseline across all segmentation metrics. Promising implications arise for deployment in automated inspection systems, potentially enhancing the efficiency of hull and offshore structure inspections by reducing manual effort and improving detection accuracy.
The underwater vehicle seals are elastomeric materials that act as a line of defense against fluid entering the system under external pressure. All seals fixed on underwater vehicles must withstand the ocean environment. The deep-ocean environment is subjected to high pressure, low temperature, and corrosive fluid. Hence, it is important to know which material is suitable and better for seawater applications. In addition to material selection, seal configuration plays a vital role, as different underwater components require application-specific sealing designs. This paper reviews the suitability of elastomeric sealing materials for seawater applications and presents the standard seal configurations commonly employed in underwater vehicles, including hatches, penetrators, viewports, and vent plugs. Furthermore, this paper summarizes important design recommendations and best practices adopted in ocean engineering to enhance sealing performance, reliability, and operational safety in deep-water applications.
Floating offshore wind turbines (FOWTs) deployed in ultra-deep water require mooring solutions that reduce cost and seabed footprint while maintaining robust limit-state performance. This study proposes an anchor-saving shared taut mooring system for a three-turbine array of 15 MW semi-submersible FOWTs at 1500 m water depth, benchmarked against a shared-anchor configuration and a classic individual taut mooring baseline. Coupled time-domain simulations are conducted for representative operating and extreme parked (survival) conditions to quantify peak line tensions, six-degree-of-freedom motions, and sensitivities to chain-polyester segmentation and shared connection-point position. Relative to the individual baseline, the proposed system reduces the peak chain tension of the most heavily loaded shared line by 34.7
This paper presents a computationally fast implementation of the third-order wave interaction theory of Madsen and Fuhrman (2012) for multidirectional irregular waves. The evaluation stage is reformulated from direct summation of sinusoidal waves in the physical domain to spectral accumulation, followed by two-dimensional inverse fast Fourier transform, reducing the cost of full-grid evaluation from 𝒪(N_gN_terms) per time step to 𝒪(N_terms)+𝒪(N_glog N_g). Numerical verification against direct physical-space evaluation shows machine-precision agreement, with typical errors of order 10^-13 – 10^-12 in tests using a finite-depth, high-steepness, multidirectional crossing-sea case. Representative benchmark cases show speedup of roughly three orders of magnitude. The method provides a practical route for higher-order nonlinear surface-field evaluation in larger multidirectional bound wave calculations and related time series where repeated time step evaluations are required, and more broadly suggests spectral-domain accumulation as a scalable strategy for problems involving large-scale superposition of sinusoidal wave components.
Tsunami waves cause significant damage to coastal infrastructure, communities, and ecosystems, highlighting the need for effective mitigation strategies. Submerged breakwaters have emerged as a widely adopted solution for reducing nearshore tsunami wave energy. However, detailed investigations into the influence of breakwater geometry on wave–structure interaction and flow dynamics remain limited. In this study, an open-source solver olaFlow was used to investigate the transformation of solitary waves over four distinct submerged breakwater geometries: trapezoidal, gentle planar, convex, and concave. Numerical experiments were conducted for relative wave heights (0.15–0.43) and submergence ratios (0.62–0.84), using response surface methodology (RSM) based on central composite design (CCD) to assess the transmission (kt), reflection (kr), and dissipation (kd) coefficients in relation to flow processes. The results identify three distinct regimes of wave transformation. In the low regime, weak crest–crest exchange dominated, characterized by high transmission (kt ≈ 0.93) and low reflection (kr ≈ 0.12). In the intermediate regime, coherent vortices formed and incipient backward breaking increased dissipation (kd ≈ 0.40). In the high regime, backward breaking became prevalent, with overturning jets and strong recirculation dominating the energy balance (kd ≈ 0.48). Reflection was found to be primarily dependent on breakwater geometry, while dissipation was controlled by nonlinear processes such as wave steepening, flow separation, and breaking. These results provide a regime-based framework for predicting solitary wave transformation over submerged breakwaters, which can inform the design and optimization of coastal protection structures.
This study presents the scale effect induced by Reynolds number ( R_e ) on hydrodynamic performance and flow characteristics of a horizontal-axis tidal turbine (HATT) based on both blade element momentum theory (BEMT) and computational fluid dynamics (CFD) techniques. Three different R_e -based model scales are examined under rotational operating conditions corresponding to cut-in speed, peak power, and experimental highest curve region. The BEMT method evaluates the scale effect from blade spanwise refinement of axial and tangential forces. A systematic increase in the axial induction factor along the blade span reflects axial flow deceleration with rising R_e . However, the tangential induction factor decreases signifying a reduction in wake swirl. The RANS-based CFD solver incorporating the Reynolds Stress Turbulence model enhances the scale effect investigation. Uncertainty quantification has been performed according to the International Towing Tank Conference recommended grid-independent procedures to verify the CFD model. The CFD simulation results have provided detailed scale effect insights into the scalar flow field around HATT, including velocity contours, pressure distribution on the blades, wake field and vortex visualization at various rotational speeds according to the intensity and development of turbulence, axial convection velocity fields, pressure gradients, and flow separation. The scale effect on cavitation inception at the suction side leading edge extends from tip to middle of the blade with increasing R_e . The comparative analysis between the BEMT and CFD methods for non-dimensional performance coefficients reveals that the power and torque coefficients decrease with scaling, but the thrust coefficient has less deviation across all the scales. The scale correction factors conclude that a minimal scale effect persists while operating in the peak-power region compared to other operational speeds and the scale effect diminishes as the R_e increases.
The U.S. Navy (USN) in the late 40s developed Navy Oceanographic Meteorological Automatic Device (NOMAD) platform for offshore autonomous meteorological measurements which has seen widespread usage since then because of its performance characteristics as meteorological and oceanographic data buoys, as energy system platform testing, as rocket data acquisition platform from Pacific to Atlantic. This article revisits the NOMAD hulls for engineering design to achieve simpler and less costly construction while this article focuses on hull construction and aspects and seakeeping are investigated in further work. Two hull forms namely NOMAD and HACIYATMAZ™ are analyzed. The HACIYATMAZ™ hull which is built from flat surfaces achieve similar structural performance to a streamlined NOMAD hull while simplifying the hull construction significantly with similar stability characteristics. Shell element-based finite element approach is employed for computational analysis of the hull and uniform quadrilateral elements are employed for deck topology optimization with buckling constraints.
This review paper provides an overview of autonomous underwater vehicles (AUVs) and their operational context, aiming to create foundational knowledge and motivate research. The importance of motion control in AUV research and technology is highlighted. To improve knowledge in this area, a review of AUV motion control which is utilized in numerous underwater tasks was carried out. Peer-reviewed articles from reputable journals published in the past ten years are included in the evaluation, along with foundational works from the preceding 3 decades. The report evaluates important areas of technical research and offers important forecasts for future developments. In order to handle the challenges of the undersea environment, the study examines various control systems in maritime applications, including traditional, advanced, intelligent, and machine learning-based control. Our contribution comprises highlighting current and ongoing research. While the literature review is brief, it focuses on sources that are directly relevant to the innovative results presented over the last decade. This review article presents key findings from a systematic search of the literature on AUV motion control. To highlight the uniqueness of the proposed work, a comparative summary is tabulated against the existing review paper. Finally, based on the reviewed literature, potential research gaps are identified, and future approaches are proposed for further development in this critical topic.
The wake effect in wind farms (WFs) reduces wind speed and increases turbulence intensity downstream, diminishing the power output of downstream wind turbines (WTs) while elevating failure risks and operational costs. To address this, an active wake optimization model considering fatigue damage is proposed in this paper. In order to achieve real-time quantification of fatigue damage within the objective function, an improved rainflow counting method is introduced, enabling accurate and efficient computation. Based on this methodology, the optimization problem is effectively solved. The results demonstrate that the proposed fatigue damage calculation method, when integrated into active wake optimization, can significantly increase the overall output power of the WF while simultaneously reducing cumulative fatigue damage. This approach provides valuable technical support for the efficient and reliable operation of wind farms. This study presents an active wake optimization framework for wind farms that explicitly accounts for turbine fatigue damage. By integrating an improved rainflow counting method with real-time capability, the approach simultaneously increases wind farm power output and reduces cumulative fatigue damage, enabling more efficient and reliable wind farm operation under realistic conditions.
The geometric shape of a buoy is crucial in enhancing the efficiency of wave energy harvesting. However, comparative studies are often compromised by inconsistent design constraints—particularly the failure to maintain identical natural frequency—which obscures the pure effect of geometry. Therefore, this paper proposes a novel S-shaped buoy characterized by three parameters l, α, β, and ensures all buoys are designed with identical diameters, submerged volumes, and resonant frequencies to perform a fair geometric comparison under the same dynamic conditions. Based on wave conditions of the Paracel Islands, six S-shaped buoys with distinct parameter combinations and identical resonant frequencies were evaluated under regular waves, irregular waves, optimal and suboptimal power take-off (PTO) modes. Results show that SB-b buoy (l = 2.6 m, α = 120°, β = 120°) exhibits the best comprehensive performance. Its power absorption under the optimal PTO mode outperforms that of the ellipsoidal and conical buoys by 4.9
Computationally intensive hydrodynamic simulations are commonly used to evaluate the performance of wave energy converter (WEC) arrays, but their cost limits large-scale design exploration. This study investigates surrogate modelling approaches for predicting total farm-level absorbed power of large WEC arrays using simulation datasets generated by a frequency-domain potential-flow hydrodynamic model under wave climate conditions corresponding to offshore Perth and Sydney. Surrogate models trained directly on planar device coordinates are evaluated alongside models that augment these inputs with geometric features describing spatial relationships between devices. Results for arrays comprising 49 and 100 devices show that augmenting coordinate-based inputs with geometric features consistently improves predictive accuracy and explained variance relative to coordinate-only inputs. Additional experiments demonstrate that these models retain meaningful predictive performance even when trained on substantially reduced training datasets. Overall, the results indicate that explicitly encoding spatial relationships within the input representation provides a more effective basis for surrogate modelling of large wave energy farms. The proposed approach improves predictive accuracy and demonstrates improved data efficiency, enabling more computationally efficient analysis and early stage design exploration of large WEC arrays.
This study aims to explore behavior of MHKF-180s hydrofoils in both unsteady cavitating and non-cavitating flows using Realizable k − ϵ turbulence model and Zwart–Gerber–Belamri cavitation model at different angles of attack for a Reynolds number of 1.3 × 106. First of all, the performance of two different cavitation models and four different turbulence models are compared with experimental results available for NACA4412 and Clark-Y hydrofoils. In addition, the hydrodynamic performance of cavitating MHKF-180s hydrofoil is examined across various Reynolds numbers (ranging from 1.1 × 106 to 2.6 × 106) at different angles of attack. The performance is assessed based on parameters, such as lift coefficient, drag coefficient, lift-to-drag ratio, pressure coefficient, cavity shedding, frequency of oscillating cavity etc. Among all the turbulence models, Realizable k − ϵ model stands out to be more precise and reliable. This model captures the flow separation, vapor shedding and vortex shedding more precisely. Furthermore, the hydrodynamic performance of cavitating MHKF-180s hydrofoil is found to be consistent regardless of the Reynolds number. On comparing the performance of cavitating and non-cavitating MHKF-180s hydrofoils, it is observed that cavitating hydrofoil exhibits lower lift, higher drag, and a decreased lift-to-drag ratio, resulting in reduction of the hydrodynamic performance for cavitating case.
This study presents the design and hybrid modeling of a spar-type floating offshore wind turbine (FOWT) platform optimised for deployment at a shallower water depth of 40 m. A parametric optimization was conducted to develop a new spar platform for a 300-kW wind turbine. The final design was evaluated using a potential-flow-based numerical model to assess hydrodynamic stability—including natural periods—and mooring safety constraints. A 1:40 Froude-scaled physical model was then constructed and tested in a wave flume (40 m × 1 m × 1.4 m) under regular, irregular, and wind–wave combined conditions. Due to geometric limitations of the flume, a modified mooring layout with shortened leeward chains was used and validated numerically to ensure accurate representation of the original configuration. Experimental results showed minimal heave motion and pitch angles below 12°, satisfying the design criterion. Surge and pitch were more sensitive to long-period waves, consistent with numerical predictions. Under wind–wave coupling, the numerical model, simplified with a constant thrust load, overestimated pitch motion—indicating a need for more advanced aero-hydro coupling. The deviation between numerical and experimental results remained within 15
This study examines the impact of seabed undulations, shaped as semi-circular and triangular patches, on the hydrodynamic performance of an oscillating water column (OWC) wave energy converter. The undulations are placed at a finite distance from the OWC to create gap resonance under the influence of incident wave-currents. The seabed patch is assumed to be impermeable for most test conditions, and permeability is added to mimic natural sandbars in front of the OWC. The multi-domain boundary element method (MDBEM) is used to solve the boundary value problem, with results validated against experimental and numerical data. The study investigates the influence of current velocity (via Froude number), number of undulations, lip-wall spacing, chamber spacing, lip-wall draft and inclination, wave angle, wavelength, and undulation geometry on key hydrodynamic parameters. These include OWC efficiency, radiation susceptance, conductance, and wall forces. Effects are analyzed across different relative water depths and clear spacing. The influence of semi-circular and triangular undulations, porosity, and undulation count is studied using surface plots. Comparative analysis shows that semi-circular and trapezoidal seabed patches improve OWC efficiency more than a plane seabed. Wave-currents further enhance energy capture, making these configurations more effective for wave energy conversion.
Polymetallic nodules are commonly found on deep-sea floors. To enhance the accuracy of resource assessment for these nodules, a new evaluation method that utilises image enhancement techniques to estimate their abundance based on key parameters, such as quantity, coverage rate and size, was proposed. The deep-sea mining environment presents challenges, as the image of polymetallic nodules often exhibits low-contrast and blue–green colour, making identification difficult. To address this, a method that combines the Sea-thru algorithm with YOLOv8 was proposed. This approach estimates scene depth based on varying light attenuation rates in water, improving the recognition accuracy of polymetallic nodules in deep-sea imagery. Additionally, to enhance the estimation accuracy of nodule mineral coverage affected by sediment occlusion, employed a binary morphological dilation method. By modelling polymetallic nodules as regular circles and assessing their height above the seabed, a quantitative expression for the actual grain size of buried nodules was provided, further enhancing the accuracy of mineral resource assessments. This method provides a solid foundation for decision-making in mining vehicle operations and route planning, thereby enhancing mining efficiency.
A comprehensive evaluation of free-running Computational Fluid Dynamics (CFD) and System-Based (SB) approaches is presented for simulating transient maneuvers of the Office of Naval Research Tumblehome (ONRT) surface combatant, with a current focus on operations in calm water. The transient maneuvers considered include crashback, crash-ahead, turning from rest [Acceleration Turning (AT)], turning at rest, and complete in-behind four-quadrant propulsion operation. Simulations are conducted across multiple vessel speeds using two CFD solvers (CFDShip-Iowa V4.5 and ReFRESCO), and one SB method (aNySim-XMF). The research is performed in support of NATO AVT-399, which aims to assess the predictive capabilities of current tools relative to the STANAG maneuvering performance criteria. According to the CFD and SB predictions for cruising speed, the ONRT will satisfy STANAG criteria regarding stopping and turning from rest abilities. Notable differences between CFD and SB predictions arise in turning at rest scenarios due to complex propeller inflow effects and the omission of propeller side-force modeling in the SB approach. AT simulations exhibit significant differences in transient maneuvering metrics, such as Time to reach 90° ( T_90^* ) and Advance (AD), compared to previous CFD and experimental results for conventional turning circle maneuvers, attributable to reduced initial forward speed. Ongoing and future efforts include the development of scale-effect correlation curves, additional crashback and transient Propeller Open-Water (POW), and targeted experiments in the Iowa Institute of Hydraulic Research (IIHR) wave basin. These efforts aim to enhance the predictive fidelity of both CFD and SB approaches in support of mission-specific naval performance requirements.
