Abstract The accuracy of gravimetric measurements is essential in various fields, from the safety of the navigation of unmanned autonomous vessels to searching for natural resources to the level of underground water to the accuracy of geodetic data. Usually, we have to deal with measurements contaminated by environmental noise, as well as noise generated by different mechanical devices, city transportation systems, and human beings; some of those sources have a periodical nature. In the presented article, we consider the problem of the influence of noise on registered data. A gravimeter is, in fact, a vibration analyzer, so most of the artificial noise caused by engines, machines, and other technical systems is included in the final recorded data. By testing a statistical hypothesis, we try to convince the reader that in recorded time series, there is other information that is deterministic in nature and may have an important impact on the analysis of gravimetric data.

Abstract This paper focuses on assessing the thermal state of a marine gas turbine plant (MGTP), with particular attention being given to the measurement of turbine rotor component temperatures using a specially developed telemetric measurement system (TMS). The study was conducted within the framework of research aimed at evaluating the effects of reduced relative air temperature, which is supplied by the high-pressure compressor (HPC) through nozzle guide vanes (NGV) and a twisting grid (TG) inside the rotor blades (RB) of a high-pressure turbine (HPT), on the thermal state of the HPT rotor. This temperature reduction is achieved via a pre-swirl technique, in which the cooling air is directed toward rotor rotation. The results obtained demonstrate new opportunities for monitoring the thermal condition of turbine components during the modernisation of MGTPs. This approach contributes to improving the overall efficiency of the system by enabling an increase in the gas flow temperature at the inlet to the HPT’s first stage.

Abstract Maintaining a specified distance from target vessels is a common requirement in maritime management. The tracking control is inherently complex, demanding both accurate target tracking and frequent adjustments to the propeller and rudder, which can lead to increased energy consumption and accelerated mechanical wear. This study introduces a distance-keeping tracking model for manoeuvring marine vessels, along with a balanced objective model predictive control (BOMPC) algorithm. BOMPC was developed based on the Marine Manoeuvring Group (MMG) dynamics model. Beyond prioritising the tracking accuracy, the algorithm incorporates the propeller speed and rudder angle from the dynamics model as optimisation criteria within the MPC framework. This enables the simultaneous control of the tracking vessel’s speed and heading, comprehensively addressing both the tracking accuracy requirements of target tracking and the considerations of energy consumption and mechanical wear. The accuracy and effectiveness of the proposed target tracking model and control algorithm are validated through both simulation and experiments. This research has potential applications in maritime management, marine search and rescue, and related domains.

Abstract Industrial development and surveying projects related to oil and natural gas resources and undersea pipelines require comprehensive geological, geophysical, and oceanographic research to be conducted in offshore and coastal areas. These research activities are typically conducted by research vessels or smaller craft that are specially equipped for specific tasks, which often require considerable labour. However, this research method incurs high operating costs and poses risks to occupational safety and property, particularly due to the harsh weather conditions at sea. In addition, high-precision measurements cannot always be effectively taken using these vessels at the sea surface during such projects. Consequently, research institutions and organisations have made significant advancements in developing autonomous underwater vehicles (AUVs) over the past two decades. The aim of this study was to identify an optimal design form for AUVs to enable them to examine the geomorphological, geological, and geophysical structures of the seafloor while also supporting oceanographic research. To achieve this, computational fluid dynamics analyses were conducted on the DARPA (Defense Advanced Research Projects Agency) Suboff submarine model, and the results were validated using experimental data obtained from the literature [1]. After successfully confirming the accuracy of the simulations, which were executed using the commercial software STAR CCM+ (Simulation of Turbulent Flow in Arbitrary Regions - Computational Continuum Mechanics, C++ based), various AUV designs were created based on commonly used geometric shapes for torpedoes. In addition, biomimicry principles were employed to develop AUV models with minimal viscous resistance and energy consumption during underwater operations. The following models, all with the same displacement, were systematically analysed: a mature goose-beaked whale (Ziphius cavirostris), a mature sperm whale (Physeter macrocephalus), an adapted form of the submarine shark (Carcharodon carcharias, also known as the great white shark), four biomimicry-inspired hybrid models and four torpedo-shaped AUVs. The findings from these analyses are discussed in detail.

Abstract The rim-driven propeller (RDP) is an innovative propulsion system that is primarily used in underwater vehicles and the bow thrusters of ships. In this study, the Reynolds-averaged Navier-Stokes (RANS) equations are employed together with the moving reference frame method and steady-state numerical simulations to address challenges related to applicability. The SST turbulence model is also incorporated. Initially, a Ka-Series+19A ducted propeller (DP) is considered, and the numerical results for its hydrodynamic performance are found to show a close correlation with experimental data. Notably, the thrust coefficient of the duct at low advance coefficients is high, indicating that the duct can operate efficiently under heavy load conditions. The study then focuses on the RDP, which uses the same propeller but features a distinct duct design due to its rim-driven configuration. The hydrodynamic open-water characteristics of the RDP are obtained and compared with those of the DP. The results reveal that the RDP has lower efficiency than the DP, primarily due to the gap and the presence of the rotor in the RDP. Furthermore, a detailed analysis of the pressure distribution on the surfaces of the blade and duct is presented, as well as the velocity and pressure contours at various downstream positions for both the DP and RDP. Particular attention is paid to the flow gap between the propeller and duct, along with the associated turbulence intensity.

Abstract This study addresses the issues of abundant cold energy in fuel and the high energy consumption of CO2 liquefaction capture by the shipboard carbon capture system in LNG-fuelled vessels. Two liquefied CO2 schemes are proposed: an LNG cold energy and refrigeration cycle integrated CO2 liquefaction system (Scheme 1) and an LNG cold energy and seawater diversion liquefied CO2 system (Scheme 2). The two systems are simulated in Aspen HYSYS software and, based on the simulation data, multiple thermodynamic parameters of the system, including exergy efficiency, cold energy utilisation rate, and energy consumption, are calculated under different vessel operating conditions, thereby verifying the feasibility of the system. On this basis, the systems are optimised, enhancing their overall performance. Through a comparative analysis of the two schemes, Scheme 1 was selected to conduct an economic analysis of typical vessel routes and calculations were conducted to determine the reduction in energy consumption and the decrease in carbon emissions achieved by utilising LNG cold energy for CO2 liquefaction and capture. The results prove that the system should have good practical applications.

Abstract To address the issue of insufficient wave dissipation capacity in standard floating breakwaters consisting of pontoons, this research proposes a combined floating breakwater with T-block connections. AQWA software is used to conduct numerical simulation studies on the dissipation characteristics of waves, and the reliability of the results is confirmed by integrating them with tests of a physical model. It is found that the transmission coefficient of the combined floating breakwater increases with the wave period. When the incident wave period T<6 s, increasing the relative height of the T-block improves the wave dissipation performance; when T>6 s, the effect is weakened; and at T=8 s, the change in height is basically unaffected. Increasing the relative width of the T-block is more significant in terms of the enhancement of the wave dissipation performance, whereas the height of the incident wave has a smaller effect on the transmission coefficient, and the transmission coefficient tends to increase with the increase of the wave height only in the case where T=8 s. The height of the incident wave has little effect on the transmission coefficient. The transmission coefficient increases with the wave height only when T=8 s; when the wave period is small (e.g. 4 s), the effect of wave elimination is enhanced by increasing the draught depth, and the draught does not have a significant effect on the wave dissipation performance when T>6 s. Compared with a typical floating pontoon breakwater with a single- and double-row arrangement, the combined floating pontoon breakwater has a better effect in terms of dissipating the waves, and its advantage is significant for a period T≤6 s, with a 44% increase in the maximum wave abatement compared to a single-row arrangement. In addition, the free-motion response is analysed to clarify the effects of different factors on the transverse and pendulum motion. This study provides an important reference for the design and application of floating pontoon breakwaters.

Abstract As wave-powered unmanned surface vehicles, wave gliders offer an effective platform for persistent marine acoustic monitoring. However, the deployment of deep-towed acoustic systems from these platforms is impeded by challenges such as hydrodynamic drag, motion instability, and flow-induced noise, particularly in elevated sea states. A novel acoustic towing system featuring a wave-shaped cable, with strategically distributed float-sinker pairs, is presented here. Its performance is optimised through parametric tuning of the wave number, wavelength, and amplitude to mitigate drag and suppress vortex-induced vibrations. To understand the complex dynamics of the system, a comprehensive hydrodynamic model combining Euler-Lagrange dynamics with computational fluid dynamics was developed. This integrated framework facilitated a systematic investigation of the critical cable parameters for effective drag reduction and suppression of vortex-induced vibrations. Simulations revealed that low-frequency disturbances induced larger attitude fluctuations in the towed body than their high-frequency counterparts. Furthermore, the vibration-damping effectiveness of the cable was found to increase with wave number, albeit at the cost of reduced towing speed. An analysis of the acceleration power spectral density revealed that a critical, speed-dependent trade-off among damping performance, system stability, and hydrodynamic drag governs the optimal float-sinker configuration. At low speeds (≤0.5 m/s), a configuration of 12–14 float-sinker pairs per wavelength yields superior overall performance. At higher speeds (≥1.0 m/s), a sparser configuration offers lower drag but risks resonant amplification, whereas a denser layout ensures stability at the expense of higher drag. This validation was substantiated by the alignment between the dominant response frequency of the towed body with wave excitation and the effective suppression of high-frequency vibrations. Collectively, these findings demonstrate that strategically configured towing cables can significantly enhance the operational performance of wave glider-based acoustic monitoring systems by improving hydrodynamic efficiency and mitigating flow-induced vibrations and their associated noise. The findings of this research provide a robust foundation for future studies of adaptive towing strategies and multi-body hydrodynamic interactions in marine environments.

Abstract Welding is one of the most widely used joining processes for the fabrication of steel parts. Consequently, it is commonly used in the shipbuilding industry for the fabrication of structural T-stiffeners. However, this process introduces inherent imperfections, such as angular deformation and residual stresses, which can affect structural stability and shorten the lifespan of the parts. This study conducts a literature review to replicate numerical analyses from reference studies, validating the proposed simulation methodology by comparing numerical and experimental thermo-mechanical results. A finite element model is created using MSC Patran and the welding process is simulated with Simufact Welding. Once the methodology is validated, a case study is conducted in which the shielded metal arc welding (SMAW) process is simulated using a simultaneously coupled thermo-elasto-plastic analysis, based on the finite element method. The study aims to determine the influence of welding sequences and mechanical boundary conditions on angular deformation and longitudinal residual stresses in the T-joints of narrow and thin plates made of S355J2 structural steel. These plates are used as structural stiffeners in the stern and bow sections of patrol boats. The goal is to propose an optimal welding sequence and boundary condition configuration that mitigates angular distortion and longitudinal residual stresses in the structural members. The proposed welding sequence consists of four weld lines running from the middle of the plate to the end, whilst the mechanical boundary condition supports the plate along the longitudinal ends.

Abstract To address the challenges of low positioning efficiency, difficulty, and high risk in the hoisting and positioning of a slender-beam payload (SBP) under rough sea conditions, a human-machine cooperative lifting method (HMCLM) is proposed for the first time. In this approach, the operator collaborates with a multi-tagline anti-sway and positioning system (MTAPS) to achieve the rapid and precise positioning of the SBP. A dynamic model of the MTAPS is developed based on multibody dynamics and classical Newtonian mechanics; it also considers the operator’s safety requirements. Simulation analysis is conducted using MATLAB/Simulink, and the results indicate that the HMCLM achieves approximately a 10% improvement in sway reduction compared to the MTAPS. Furthermore, the experimental results demonstrate that the MTAPS achieves an average sway reduction of 89.7% for the double-pendulum system. The proposed HMCLM enables the rapid and precise offshore positioning of the SBP, offering a novel approach to enhancing the efficiency of offshore hoisting operations.