Transactions of the St. Petersburg State Marine Technical University

Background: Tip vortex cavitation is a common hydrodynamic phenomenon that significantly impairs the performance of marine propellers and leads to several negative effects, including increased underwater radiated noise, accelerated blade surface erosion, as well as reduced thrust and hydrodynamic efficiency. Therefore, developing methods to suppress tip vortex cavitation is of great practical importance.

Aim: This study aims to investigate the effect of roughness location on tip vortex cavitation and the hydrodynamic characteristics of the four-bladed, fixed-pitch INSEAN E779A propeller using computational fluid dynamics.

Methods: Different roughening scenarios were tested, including applying roughness to the pressure side, the suction side, and both sides of the blade. The flow around the four-bladed fixed-pitch propeller INSEAN E779A was numerically modelled and simulated at an advance ratio J = 0.77 and cavitation number σ = 2.082. The RANS method was used for turbulence modelling, and the well-known SST k-ω turbulence model was used to close the RANS equations. The numerical results were validated against available experimental data, and good agreement was observed.

Results: The results consistently demonstrated that the location of roughness application is crucial for effective cavitation mitigation. Applying uniform roughness exclusively to the suction side emerged as the most effective strategy, reducing the blade surface area exposed to vapor by 21.3%. Conversely, applying roughness solely to the pressure side increased cavitation extent, while roughening both sides reduced cavitation but incurred the largest propulsive efficiency penalty of 7.34%.

Conclusion: Strategic application of surface roughness, specifically on the suction side, offers a favorable balance between cavitation suppression and hydrodynamic efficiency loss. This approach represents a practically feasible passive method for mitigating tip vortex cavitation in ship propellers.

Background: The analysis of the stress-strain state of ship hull structures and welds containing defects in the form of cracks is a critically important task for ensuring the strength and durability of marine vessels. Of particular interest are slightly curved cracks, the shape of which is closest to the actual defects that occur in structures. An accurate assessment of their effect on stress concentration in the vicinity of the crack tip is necessary for predicting the development of fracture.

Aim: This work aimed to develop a mathematical model and evaluate the effect of the weak curvature of a semi-infinite crack on the local stress-strain state and stress intensity factor at the crack tip for ship hull structures and welds.

Methods: The perturbation method is used, based on the expansion of the solution into an asymptotic series with respect to a small parameter characterizing the curvature of the crack. To construct corrections to the solution, the apparatus of weight functions is used, which makes it possible to obtain an integral representation for the stress intensity factors.

Results: Explicit asymptotic formulas for stress intensity factors have been obtained, which show that the effect of crack curvature on the local stress-strain state is integral and is determined by the entire history of curvature changes along the crack.

Conclusions: The developed algorithm makes it possible to estimate the stress-strain state in the vicinity of the tip of a weakly curved crack with the required accuracy. The results obtained can be used to refine the strength and durability criteria for ship structures in the presence of defects of complex shape.

Background: The development of marine electronic systems requires the introduction of miniature, reliable, and durable microelectronic components. A promising solution is the use of multilayer and two-dimensional materials in this environment, for example, graphene and transition metal dichalcogenides. When using these materials, the formation of stable electrical contacts must be ensured, which traditionally requires the use of complex and expensive technological processes.

Aim: This work aims to study the physico-chemical foundations and experimental capabilities of direct-write printing technology for forming electrical contacts on multilayer materials used in marine electronic systems.

Methods: Direct-write printing technology with silver-containing ink was used. Printing was performed on substrates with graphene and similar coatings. The conditions for wetting and annealing were examined, and the electrical properties of the contacts were investigated. Theoretical modeling of contact processes based on existing models and software was also carried out.

Results: Direct-write printing enables the creation of ohmic contacts with linear current-voltage characteristics, bypassing the stages of standard contact formation processes. The possibility of creating stable contacts at annealing temperatures of up to 150 °C was established. According to the results of theoretical modeling, it was revealed: 1) a reduction in resistance, and 2) excellent compatibility of silver-containing ink with graphene structures.

Conclusion: Direct-write printing is a technologically simple and cost-effective method for forming electrical contacts on multilayer materials, making it promising for the development of sensor, switching, and measurement modules in marine electronics. The obtained results confirm the feasibility of implementing maskless additive fabrication techniques in shipbuilding engineering practice and in the educational programs of technical universities.

Background: Numerous studies have demonstrated the significant influence of second-order nonlinear forces on the resulting motion amplitudes. Most calculations were performed for individual ships, but no studies have been conducted on the influence of individual ship parameters on the values of nonlinear forces and the resulting motion amplitudes. Therefore, studying the effect of changes in ship length on second-order nonlinear motion amplitudes is a pressing issue.

Aim: This study aimed to investigate the influence of changes in the length of ships of a systematic series on nonlinear motion amplitudes.

Methods: The method of integral equations was used to calculate nonlinear forces and the amplitudes of nonlinear motions caused by them.

Results: Analysis of the obtained results showed that reducing ship size leads to increased amplitudes of nonlinear transverse motion types and an expansion of the zone of nonlinearity influence. Under irregular wave conditions, reducing ship size leads to an increased influence of nonlinear factors at sea state 7.8.

Conclusion: The paper presents the results of calculations of nonlinear motion amplitudes and wave drift forces for a systematic series of ships under regular and irregular wave conditions, taking into account second-order nonlinear forces. A study was conducted on the influence of the main dimensions of the ship on nonlinear motion amplitudes.

BACKGROUND: Studying the combustion process in marine gas piston engines is an important task, as it allows determining the optimal design and operating characteristics of the engine to ensure its efficiency, which helps reduce fuel consumption, improve natural gas combustion efficiency, and lower the concentration of pollutants in exhaust gases.

AIM: This study presents a numerical investigation of the combustion process of a methane-air mixture and examines the patterns of changes in the kinetics of chemical reactions and the characteristics of laminar flame in a high-speed marine engine.

METHODS: A numerical study of the combustion processes of a methane-air mixture was performed using the detailed kinetic mechanism GRI-Mech 3.0 and the conservation equations for mass, energy, and state, as well as the Arrhenius equation. The fuel-air ratio in the study varied from 0.7 to 1.3; the temperature of the methane-air mixture varied from 400 to 800 K; and the pressure in the combustion chamber varied from 1 to 10 MPa.

RESULTS: A methodology for numerically studying the fuel combustion process in a marine gas piston engine has been developed. Patterns of changes in chemical reaction kinetics, adiabatic flame temperature, laminar flame propagation velocity, and flame sensitivity with changes in the fuel-to-fuel ratio and thermodynamic characteristics of the engine's combustion chamber have been obtained.

CONCLUSIONS: It was established that the propagation velocity and adiabatic temperature of a methane-air flame depend on the excess air ratio, pressure, and temperature in the combustion chamber and reach maximum values at the stoichiometric composition of the mixture. An integrated analysis of reaction pathways showed that the excess air ratio affects the reaction pathway rather than the chemical mechanism at the flame front. Based on the sensitivity analysis of reactions occurring at the flame front, an abbreviated kinetic mechanism for methane combustion in a piston engine was proposed.

BACKGROUND: With the tightening of International Maritime Organization requirements aimed at reducing the carbon footprint and achieving net-zero emissions by 2050, liquefied natural gas (LNG) is considered the primary transition fuel for the maritime power sector. However, the environmental advantages of LNG-powered systems are offset by the methane slip effect, which peaks at low and variable load conditions.

AIM: This study aimed to develop and validate load distribution algorithms for a hybrid propulsion system consisting of a gas-fired piston engine (powered by liquefied natural gas) and a lithium-ion battery.

METHODS: The methodology was based on a comprehensive approach combining mathematical modeling, theoretical optimization, adaptive control theory, and numerical simulation. Mathematical modeling involves constructing a state-space representation that integrates submodels of the gas engine, the lithium-ion battery, and the load profile. Theoretical optimization relies on the Equivalent Consumption Minimization Strategy (ECMS) as the core algorithmic framework. Adaptive control is implemented through a dual-loop hierarchical regulator featuring an adaptive equivalence factor. Forecasting techniques are incorporated by introducing a correction method for the equivalence factor based on spectral load prediction, utilizing a moving horizon prediction window and autoregression. Finally, numerical modeling and verification are carried out in the MATLAB/Simulink environment, where the developed algorithms are validated through comparative analysis against alternative strategies, namely the non-hybrid configuration and the conventional peak-shaving approach.

RESULTS: The simulations performed confirm the high efficiency of the proposed approach. Firstly, significant fuel savings are achieved: integral LNG consumption is reduced by 7.2% compared to a non-hybrid configuration and by 2.1% relative to the traditional peak-shaving strategy. Even more significant is the environmental benefit: methane emissions are cut by 14.6% compared to the peak-shaving strategy. This is achieved by maintaining the gas engine within the 60%–80% load range of its nominal value, corresponding to the minimum emission zone. Furthermore, the system’s dynamic performance is improved: the frequency of gas engine starts is reduced by 83%, substantially extending its overhaul life. Accurate energy balance maintenance is also ensured: the battery state of charge returns to its initial level by the end of the cycle (69.8% against a 70% target), guaranteeing repeatable operating modes from voyage to voyage.

CONCLUSION: The proposed adaptive ECMS algorithm with spectral correction enables not only fuel savings but also a significant reduction in the greenhouse effect by suppressing methane slip. The developed methodology is recommended for implementation in the control systems of next-generation marine power complexes.

The transition of underwater shipbuilding to fuel cell power systems requires solving the key problem of the low density of gaseous hydrogen and the associated explosion and fire hazards in confined compartments. Known hydrogen storage methods (compressed gas, cryogenic liquid, metal hydrides, liquid organic hydrogen carriers (LOHC), adsorption, chemical donors) have been developed primarily for land or surface applications and do not account for the strict constraints of underwater vehicles in terms of volume, mass, stealth, and safety during long-term autonomous navigation. This work, for the first time, systematically evaluates these methods specifically against the criteria of underwater technology, revealing not isolated advantages but the fundamental impossibility of meeting all requirements with any single method. As a result of a comparative analysis of six approaches, it was found that the highest volumetric density (108–150 kg H₂/m³) and long-term storage safety are provided by chemically bound forms—ammonia, LOHC, and metal hydrides; however, metal hydrides have low gravimetric efficiency and slow gas release, while ammonia requires high-temperature cracking. Compressed and cryogenic hydrogen, in contrast, allow rapid fuel delivery but are associated with continuous leakage or the risk of catastrophic failure. Based on the obtained data, a hybrid scheme is proposed that is absent from known analogues: the main hydrogen reserve is stored as ammonia or LOHC (high density and safety), while peak loads during maneuvering are compensated by rechargeable batteries that are recharged during the mission by the electrochemical generator. From reading the full text of the article, the reader learns for the first time a quantitative justification for precisely such a hybrid architecture for manned underwater vehicles, including recommendations for selecting buffer systems and directions for further development of low-temperature dehydrogenation catalysts.