Transactions of the St. Petersburg State Marine Technical University

BACKGROUND: UUnder certain circumstances, the performance of marine robotic systems may be affected by dynamic marine conditions, requiring data inputs immediately before a robot operation. As electrical data input is not always possible, contactless data input by inductive technology is relevant. When entering data directly through the robot body, it is required to build a mathematical computer model to determine the inductive coupling feasibility and performance based on the effect of the metal wall.

AIM: To build a signal transmission model with a metal wall between magnetic antennas and determine the effect of aluminum and steel walls on the operation of inductive coupling using the developed model.

METHODS: The model was built based using the spectral method of locating the signal at the output of an electrical circuit. By multiplying the spectral signal density by the transfer characteristics of the magnetic antenna and the metal wall in the frequency domain followed by the inverse Fourier transform, we find the signal received by the magnetic antenna in the time domain.

RESULTS: The metal wall is a layer of medium with high electrical conductivity leading to quick signal attenuation in the layer of material. With increasing electrical conductivity and magnetic permeability, the specific attenuation in the material increases. In addition, increased wall thickness leads to an increased total attenuation with its specific value remaining unchanged. Further, the wall limits the frequency bandwidth and distorts the signal spectrum.

CONCLUSION: The developed computer model reliably reproduces the amplitude and phase distortions of the received signal and may be used to simulate the operation of inductive coupling. This computer model allows to evaluate the possibility of input and select the best system parameters to ensure signal transmission.

BACKGROUND: A pressing issue of contemporary designs of small-sized marine diesel engines is finding ways to produce the highest quality mixture and improving components to increase their efficiency, durability, sustainability, and competitiveness.

AIM: This paper studies a valve of a factory-made small-sized marine diesel engine and a modified valve with additional spiral guides (blades, screens) to analyze the influence of the loads occurring in the engine cylinder as a result of the crankshaft rotation (CSR) as illustrated by a small-sized marine diesel engine Ch8.5/11. The structural material was homogeneous.

METHODS: The finite element method implemented in the Ansys software was used to perform an unsteady-state thermomechanical analysis of valves of various designs made from a homogeneous material as illustrated by a valve of a small-sized marine diesel engine Ch8.5/11, where the previously studied temperature fields were converted to the pressure acting on the valve, with its follow-up analysis, study, and comparison.

RESULTS: During the study, the total deformations and operating stresses were calculated and visualized using the finite element method, the actual safety factor was calculated, and the valve’s spiral guide values were analyzed. For the unsteady-state analysis, we selected the highest stresses exerted on the valves during the operation of a small-sized marine engine.

CONCLUSION: The findings show that the total deformation is actually unchanged when the valve design is modified; whereas the operating stress has increased significantly and was the highest in the six-blade valve. The obtained values and software visualization show that the actual safety factor of valves with blades is significantly reduced.

BACKGROUND: The paper proposes new beam finite elements with variable cross-section for modeling non-prismatic sections of sailing ship and yacht rigging when calculating the overall strength and stability of the mast(s)–standing rigging system.

AIM: This work aimed to determine and present explicit expressions for the components of the stiffness and stability matrices of finite elements with and without transverse shear during bending in two principal planes of inertia, tension/compression, and torsion.

METHODS: The matrix components are determined by the variational finite element method and are given for the general case, when the moments of inertia and the cross-sectional area of a certain type are approximated by the element length using a quadratic polynomial, and for special cases of bending a beam with a solid circular and annular cross-section, where its varies linearly along the element length.

RESULTS: The paper presents the solutions of test problems and a comparison with other known finite elements. The efficiency of the proposed elements for calculating a non-prismatic unrigged mast of a sailing yacht is shown in comparison with similar prismatic elements.

CONCLUSION: The developed non-prismatic finite element B4 is included in the FESTA (Finite Element Stability Analysis) program library and can be used to model beam elements of structures with various cross-sections. The element can be used both for modeling and calculating solid and tubular elements of sailboat masts and for modeling non-prismatic frame connections of a set of hulls for ships and vessels.

BACKGROUND. The active development of autonomous small craft navigation poses a new navigation problem. High maneuverability of the boats determines their wide bandwidth exceeding the upper wave spectrum limit. Therefore, it is quite difficult to separate the useful control signal and the disturbance signal using conventional frequency filtering methods. This leads to two key negative effects, including a lower movement accuracy of the boat along a given trajectory and a reduced service life of the actuators of the propulsion and steering system due to constant compensation for wave disturbances. Thus, an algorithm is required that can estimate the real-time basic apparent wave frequency, which is necessary for effective separation of the control signal and wave interference.

AIM: To develop a method allowing to assess the basic apparent frequency of waves acting on an unmanned high-speed boat.

METHODS: Nonlinear identification by extended Kalman filter.

RESULTS: The authors propose a mathematical model to synthesize an extended Kalman filter allowing to estimate the peak wave frequency based on the measured yaw rate of an unmanned high-speed boat.

CONCLUSION: The synthesized extended Kalman filter effectively tracks the peak apparent frequency of the waves acting on the boat hull.

BACKGROUND: In the contemporary shipbuilding industry, the issue of corrosion protection of ship hulls is becoming especially relevant. Existing protection methods do not completely prevent corrosion, leading to significant economic losses and reduced performance of ships. Nanofillers for paints and coatings is a promising solution of this issue. These technologies allow to develop coatings with the properties exceeding standards. Nanofillers can increase adhesion strength, improve hydrophobic properties, etc. The paper presents a comprehensive study of the influence of nanofillers on the protective properties of paints and coatings and offers recommendations for their sustainable use in shipbuilding.

The study is relevant as today, the published papers on the effect of nanofillers on corrosion resistance are scarce.

AIM: This work aimed to determine the influence of different types of fillers on the protective properties and corrosion resistance of paints and coatings.

METHODS: The study utilized used chalk and talc nanoscale fillers and polarization curve techniques to determine the coating's corrosion resistance.

RESULTS: A comparison of protective properties showed that chalk enamel ensures better corrosion protection than talc enamel. The findings may be used to develop new paint and coating formulations and to improve corrosion protection technologies for ship structures.

CONCLUSION: The obtained data allowed to determine the following order of corrosion protection performance (steel structures): PF-167 marine enamel < talc coating < nanotalc coating < chalk coating ≈ nanochalk coating.

BACKGROUND: Additive manufacturing involves the creation of three-dimensional objects with layer-by-layer application of additive material. There are many additive manufacturing technologies, each differing in consumables, manufacturing speed, surface quality of the resulting sample, power source, etc. One of these is the arc-directed energy deposition technology. Arc-directed energy deposition is an additive manufacturing technology that uses electric arc energy as a heat source to melt additive material. It is widely used in contemporary mechanical engineering due to its high productivity and wide range of materials, especially in the manufacturing of special equipment and components of complex shapes, where conventional techniques are not effective enough.

AIM: This work aimed to design, manufacture, and test an arc torch Interface for an industrial robotic arm flange using arc-directed energy deposition.

METHODS: We used welding wire made of AlMg5 alloy and high-purity argon as a shielding gas. For manufacturing, we used a process system based on a Fanuc M-710iC robot arm and a Fronius TPS500i welding power source with a cold metal transfer capability. Experiments were conducted to select manufacturing conditions and strategies to ensure high quality of the test piece and minimize defects. The manufactured pieces underwent metallography and mechanical tests.

RESULTS: A range of standard manufacturing conditions has been selected. The chosen manufacturing strategy allowed to reduce anisotropy and avoid incomplete fusion. Mechanical tests showed that the properties of the deposited material exceed the requirements of GOST 17232-99. The study allowed to design, manufacture, and assemble an interface that meets the specified rigidity and dimensional criteria.

CONCLUSION: The study showed the effectiveness of manufacturing arc torch interfaces for robotic arm flanges using arc-directed energy deposition. The developed method allows to manufacture complex shape products with the required mechanical properties, which corroborates the potential of arc-directed energy deposition in mechanical engineering.

BACKGROUND: International and domestic standards require that technical equipment be resistant to electrostatic discharge. Testing experience shows that equipment designed without these requirements is disrupted by the discharge. The IEC 61000-4-2 standard provides a test method and includes discharges into the equipment enclosure and nearby metal sheets. However, electrostatic discharges can also occur in remote equipment located near cable routes connected to the equipment. It is important to be able to predict the effects of remote discharges through external cables of technical equipment.

AIM: The purpose of this work is to provide a mathematical model of induced voltages process in cables during remote electrostatic discharge, which will allow us to predict the effects of this type of discharge on various equipment.

METHODS: The results of the work are based on the requirements of the Russian Maritime Register of Shipping for electromagnetic compatibility, the IEC 61000-4-2 standard. It is used the mathematical description of the effect of a discharge through a capacitive connection between an object and a cable, which is considered as a distributed parameter circuit. The calculations are performed using a mathematical package and verified by comparing the results with those obtained from the SPICE program and experimental data.

RESULTS: Analytical expressions for calculating the induced voltage in cables caused by electrostatic discharge into an adjacent object are given, as well as the results of calculations with a wide variation of initial data. Graphs of voltage changes obtained by modeling and during field experiments are presented. Certified test generators are used as a source of discharges in experimental setup. The obtained dependencies are presented for determining the amplitude, front duration, and induced voltage duration on the cable, depending on the coupling capacitance and the voltage front duration on the object where the discharge occurred.

CONCLUSIONS: The given expressions for calculating the induced voltage on cables and the results of the calculations are recommended for use in predicting possible levels of interference on cables during indirect electrostatic discharge. The obtained dependences of the amplitude, the duration of the front, the duration of the induced voltage on the cable from the capacitance of the connection and the duration of the voltage front on the equipment are suitable for an operational assessment of the expected parameters of interference on cables during the implementation of electromagnetic compatibility work.

BACKGROUND: The paper presents the design of a shell-and-tube recirculation gas cooler for marine diesel engines and analyzes its performance. The study is necessitated by the ever-stricter regulations on monitoring and reducing marine engine emissions.

AIM: To improve the exhaust gas recirculation (EGR) system to reduce NOx emissions and increase the engine performance by improved cooler design.

METHODS: We used Ansys Fluent software to simulate the flow and temperature distribution in the cooler to increase cooling efficiency and improve the system design. Process simulation showed that coolant flow rate and heat exchanger tube structure adjustment significantly improves cooling efficiency and reduces energy consumption.

RESULTS: The study shows that at gas recirculation rates of 30% and 40%, the selected cooler design fully meets the recirculated gas cooling requirements and the minimum cooling temperature can be reduced to 133 ˚C. The analysis may be used in calculations to improve and increase the cooling efficiency of an existing cooler.

CONCLUSION: The method used in the study may be applied to other marine diesel engines to improve fuel efficiency and reduce environmental impact.