Transactions of the St. Petersburg State Marine Technical University

BACKGROUND: The separation of the flow on the bearing surfaces of marine equipment leads to a loss of lift, increased resistance and vibration, reducing efficiency and safety. Passive slit profiles make it possible to delay stall without energy consumption, however, the effect of the slit position along the chord at high Reynolds numbers has not been sufficiently studied.

AIM: To determine the slot position that ensures delayed flow separation, improved lift-to-drag performance, and an increased stall angle, as well as to formulate practical recommendations for designing high-performance hydrofoils for marine engineering applications.

METHODS: This numerical study investigates the effect of slot position along the chord on the aerodynamic characteristics of the NACA 4412 airfoil at a high Reynolds number (Re = 3.1 × 10⁶). Using the Reynolds-averaged Navier–Stokes equations with the k–ω SST turbulence model, five slot configurations located between 0.3 C and 0.5 C were analyzed. The numerical methodology was validated against well-established experimental data.

RESULTS: It was shown that an optimally positioned slot can remarkably improve performance at high angles of attack by suppressing flow separation. The optimal configuration, with the slot located at a distance of 0.4 C from the leading edge of the body, provided the most substantial improvements, including a 7° delay in stall angle and an approximately 43% increase in the maximum lift coefficient.

CONCLUSION: This study confirms that passive flow control using a slot, particularly at the 0.4 C chord position, represents a promising design approach for enhancing aerodynamic efficiency and improving stall characteristics of airfoils used in marine engineering applications.

BACKGROUND: The study is based on the issue of increasing pollution of the World Ocean with oil-containing wastewater. However, existing treatment methods do not always ensure the required safety.

AIM: To conduct a multivariate analysis of the toxic potential of neutralized bilge water for aquatic organisms.

METHODS: The study examined bilge water samples using the bilge water composition analyses, such as particle size distribution of particulates; fluorimetric assay of oil-containing component content by weight using Fluorat-02-5M equipment; optical microscopy using the Goryaev chamber, and acute and chronic toxicity analysis of the environment based on daphnia mortality.

RESULTS: The studies showed that bilge water is highly toxic. There is no toxic effect at dilutions of 1:100 and 1:1000. The study determined a critical threshold concentration of oil products of 15–25 ppm characterized by mass mortality of aquatic organisms and acute toxicity.

CONCLUSION: The applicable bilge water treatment standards do not ensure the required environmental safety and it is required to use additional treatment methods. The study indicates the need to improve existing treatment systems to prevent pollution of the marine environment.

BACKGROUND: MARPOL 73/78 regulations require the prevention of maritime air pollution, including any marine diesel engines. When implementing means to increase the capacity of marine diesel power plants and to comply with international requirements, it is required to develop and implement devices designed to reduce harmful substance concentrations in the exhaust gases of diesel power plants of ships and vessels under various operating conditions.

AIM: To create and improve the exhaust gas aftertreatment system for marine diesel power plants; to examine the operating parameters of the gas ejector at different ejection ratios, and to determine the ratio of the central hole area S2 to the annular hole area S1 of the ejector washer for a given diameter of the mixing chamber D3.

METHODS: The most promising methods for reducing the emission toxicity include the exhaust gas NO aftertreatment system as part of the exhaust system of marine diesel power plants. The proposed gas ejector neutralizes toxic components of exhaust gases.

RESULTS: The dimensions of the ejector are determined, as well as the optimal conditions for neutralization of nitrogen oxides of exhaust gases; an algorithm for calculating the operating parameters of the proposed gas ejector is constructed. Based on the calculation results, the values of the flow velocity of the gas ejector were selected to obtain optimal pressure values in it.

CONCLUSION: The resulting models showed that the ejected gas should be caught at the mixing chamber outlet. The ejector cross-sectional area ratio ensures a sufficient turbulence. The ejector gas static pressure at the mixing chamber inlet is less than the total pressure of the ejected gas, which ensures exhaust gas recirculation and the supply of reducing gas (ammonia) to the mixing chamber. The study determined optimal operating parameters of the ejector. It was concluded that there is a need in additional GE field studies to refine the ratios of flow parameters that ensure the uttermost use of the ejector mixing chamber.

BACKGROUND: Taking into account the expansion of technical possibilities for manufacturing plates and panels from polymer composite materials, it is relevant to mathematically substantiate their rational beam reinforcements under given quality criteria and restrictions. When using such materials in plate structures, it is important to take into account their pronounced orthotropy by applying algorithms of indirect optimization methods for finite-element models of plates.

AIM: construction and application of algorithms for indirect optimization methods to finite-element models of orthotropic plates of variable thickness in order to mathematically substantiate rational beam reinforcements of plates and shells made of polymer composite materials under specified quality criteria and constraints.

METHODS: The algorithm was developed based on an indirect iterative approach to satisfying the simple necessary conditions of Kuhn-Tucker optimality, considering isoperimetric restrictions. The Lagrange multiplier technique and the finite element method were employed.

RESULTS: Obtaining optimal configurations of localized stiffnesses (thickenings) and the influence of elastic parameters of an orthotropic material on them is considered.

CONCLUSION: The indirect method of satisfying optimality conditions of the 1st order is an effective means of controlling the properties of anisotropic plates and identifying optimal schemes of beam reinforcements (fins), while it can be no less cost-effective than the methods of homogenization in topological optimization. Consideration of transverse shifts in thickening finite elements, as well as the mutual influence of bending and longitudinal stiffness, can be carried out by constructing more efficient plate-plate finite elements based on the Reissner–Mindlin theory.

BACKGROUND: Various time-dependent external forces have a substantial effect on the changes of an underwater vehicle moving in a water environment. Improving the accuracy of calculations of the kinematic characteristics of its oscillatory motion requires taking into account higher-order nonlinear hydrodynamic forces, the influence of which has been confirmed by experimental data and operational practice. Existing calculation methods have substantial limitations associated with the simplified treatment of the second-order potential and the difficulties in describing nonlinear boundary conditions. The relevance of this study is due to the absence of calculation methods for estimating the oscillation parameters of an underwater vehicle, which poses a considerable problem in the design and operation of such vehicles.

AIM: To develop a method for calculating second-order nonlinear forces for several underwater vehicles and the corresponding motion amplitudes under bichromatic wave excitation.

METHODS: The two-dimensional nonlinear problem of calculating motion characteristics was solved using the small-parameter method and integral equation techniques. The calculations were performed using a program written in FORTRAN 90 programming language.

RESULTS: This paper presents the results of a study of second-order nonlinear forces associated with difference- and sum-frequency components arising during the oscillatory motion of an underwater vehicle.

CONCLUSION: The components of second-order nonlinear forces and moments associated with both the sum and the difference of frequencies increase many times over as the object submergence depth decreases.

BACKGROUND: The study is based on the urgent issue of ship hull biofouling in contemporary shipping, which leads to a notable reduction of the equipment and structure service life. This issue is especially relevant in tropical waters with temperature conditions optimal for the development of marine biocenoses.

AIM: To develop and assess the performance of modified antifouling coatings based on HS-5226 enamel with added FMT corrosion inhibitor to protect ship structures from biofouling and corrosion in tropical marine climate.

METHODS: Marine exposure in the coastal zone of the South China Sea (Khanh Hoa, Vietnam); laboratory copper diffusion tests, and biotesting to assess the environmental safety.

RESULTS: The paper presents a study of new protective coatings for marine structures in tropical climate. The authors developed a protection system based on modified antifouling enamel HS-5226 with the FMT biocidal component, effectively inhibiting biofouling on ship hulls. The coating's biocidal stability was observed throughout the testing period in the marine environment. Key performance indicators have been verified by experiment. There was no mass attachment of barnacles and bryozoans to the modified pieces during the first 60 days of exposure. The protective coating maintains its integrity when the piece is immersed in seawater. Tests in the South China Sea showed an 80% reduction in biofouling and high corrosion resistance of the coatings.

CONCLUSION: A notably reduced biofouling rate was achieved on pieces with a modified coating. Optimal release rate of active substances is observed. We note the temporary wastewater toxicity neutralizing within two months. The study shows that the developed compositions may be used to protect ship structures; its data may be used to develop new generations of protective coatings.

BACKGROUND: The development of the theory and applications of Fourier spectral analysis of signals has led to the development of numerous methods, including the most popular Fast Fourier Transform. Almost all existing analytical methods require an access time of at least one period for the lowest frequency signals in the analyzed spectrum. However, in practice, it is often required to solve problems where the access time should be less than the period of the lowest frequency signal in the analyzed spectrum or less than the period of any harmonic signal in the analyzed Fourier spectrum. Solving this problem by digital processing is an urgent task.

AIM: To consider and study the Discrete Fourier Transform spectral analysis of signals when the access time to the analyzed signal is less than the period of any polyharmonic signal in the analyzed spectrum.

METHODS: The Discrete Fourier Transform analysis of signals was used.

RESULTS: Tests of the analyzed algorithms showed that the error of amplitude and phase shift of the spectral components of a 16-bit analog-to-digital converter does not exceed 1.5%.

CONCLUSION: The analyzed method allowed to achieve the access time to the highest frequency signal (the fifth harmonic) of a tenth of the period.

BACKGROUND: Piezoceramic transducers are the main working parts of hydro- and electroacoustic systems. The manufacturing of such transducers includes multiple operations; whereas the shaping of piezoelectric ceramics and the application of metal electrodes to its surface (metallization) largely determine the operational parameters of the transducers.

AIM: To analyze the possible use of electrophysical fields (ultrasonic and ultra-high-frequency (UHF) electromagnetic fields) to intensify the piezoelectric ceramics shaping and metallization processes.

METHODS: The authors use contemporary structural analysis of piezoelectric ceramics, such as electron microscopy, atomic force microscopy, X-ray structural analysis, local X-ray spectral analysis, and mathematical and computer modeling of piezoelectric ceramics shaping and metallization processes.

RESULTS: Original engineering flow charts for ultrasonic shaping and ultra-high-frequency metallization of industrial piezoelectric ceramics have been developed. The article describes the nature of electrophysical effect on shaping and metallization and physical models of these processes. In addition, it presents process conditions of ultrasonic shaping and UHF metallization of piezoelectric ceramics and shows their advantages over industrial processes. The penetration depth of silver into piezoelectric ceramics during UHF metallization is marginally greater than industrial metallization, which demonstrates high performance of the new technology.

CONCLUSION: Electrophysical fields generated by industrial ultrasonic and ultra-high-frequency process equipment allow to successfully increase the performance of piezoceramic transducers.