Marine Propulsion System Research Articles

Qualitative and quantitative analysis of interaction between cavitation patterns and vortices of a pitching hydrofoil from Lagrangian viewpoint

The evolution of transient flow structures and mass transport in cavitating flow around a pitching hydrofoil is investigated qualitatively and quantitatively, and the interaction between cavitation patterns and vortices is elucidated from Lagrangian viewpoint. First, turbulence effects are estimated by the density-corrected k–ω model to account for the local compressibility of the multiphase flow at Reynolds number Re=6.4×105. Then, the formation and evolution of vorticity structures during the whole pitching cycle are analyzed using Lagrangian averaged vorticity deviation method. By comparing the flow structures and hydrodynamic properties at varying angles of attack, the cavitating flow is divided into two distinct stages, namely multi-scale cloud cavitation phase from α+=10° to α−=8°, and traveling sheet cavitation phase from α−=8° to α+=10°. Specifically in cloud cavitation, the formation of the cavitation pattern is closely related to the development of the main vortex. Furthermore, the quantitative analysis method based on Lagrangian flow network is developed to deeply analyze the transport and mixing processes. Importantly, the coherence ratio and the mixing parameter are proposed as transport indicators to precisely quantify the spatial connectivity behavior. Finally, the correlations between vapor fraction, codelength, global coherence ratio and global mixing parameter are evaluated. As the conclusion, it is shown that Lagrangian methods are powerful tool for both qualitative and quantitative analysis, and the results obtained could provide a key and important understanding of the flow structure and changing mechanism between cavitation and vortices in marine hydro and propulsion systems.

Performance Improvement of Permanent-Magnet-Synchronous Motors through Rotor Shape Optimization of Marine Blowing System with High-Speed Rotation

Currently, research is being carried out on the performance improvement of permanent-magnet-synchronous motors (PMSM) used in air conditioning and blowing systems for marine, as well as structural research, regarding their high-speed operation. Surface-mounted permanent magnet (SPM) motors used in marine propulsion and air-conditioning systems have the advantages of easy rotor manufacturing and a simple structure. However, owing to the structural characteristics associated with attaching a permanent magnet to the surface of the rotor, there is a risk of permanent magnet scattering when turning a rated load at high speed, and the rotor assembly is directly affected by the heat generated in the stator winding. Therefore, in this study, additional protrusions were proposed to prevent rotor scattering during high-speed operations. Additionally, optimization was performed to reduce the torque ripple at the rated load and the total harmonic distortion (THD) of the no-load-induced electromotive-force waveform generated by the protrusion. Consequently, the risk of scattering at high speeds was improved by securing the bonding force of the permanent magnet using the proposed structure, and the THD and torque ripple were reduced compared with those of the basic model through optimization. In addition, rotor structural stress analyses were conducted to solve the problem of scattering at high speeds and eigenmode analysis.

Healthy marine diesel engine threshold characterisation with probability density functions and ANNs

The condition-based maintenance of marine propulsion systems is attracting increasing interest in safety-related, financial, and environmental terms. Many researchers have studied different marine diesel engine models and fault identification techniques. However, the thresholds between a healthy and a faulty engine have not been thoroughly analysed. Thus, this study aims to determine healthy engine threshold values for multiple parameters of a marine diesel engine. To this end, an operative commercial fishing vessel was considered, and multiple engine performance variables were measured through 2020 and the first half of 2021, totalling 5181 operating hours of the main engine without any fault occurrence. Preliminary correlation and relative deviation studies suggested the analysis of some constant trend parameters with alternative modelling techniques. Hence, probability density functions (PDFs) were used to establish confidence intervals for such parameters with data from the entire year of 2020. The parameters with the highest correlation and deviation were alternatively modelled using artificial neural networks (ANNs). Four different ANNs were trained, validated, and tested with data from 2020, calculating the mean absolute percentage errors for all the predicted parameters. Finally, data from 2021 were used to validate both the PDF and ANN modelled parameter thresholds set in 2020. For the 2021 data, the confidence interval set with the PDF showed a maximum failure rate of 1.21%. Alternatively, the ANN model parameters exhibited maximum percentage errors of 1.1%, 1.22%, and 1.95% for the engine performance, cooling, and cylinder subsystems, respectively. Finally, all the obtained thresholds were summarised, providing a good source for establishing faulty engine threshold values in future fault detection studies.

Simultaneous and Global Optimizations of LNG-Fueled Hybrid Electric Ship for Substantial Fuel Cost, CO2, and Methane Emission Reduction

Natural gas (NG) is a promising low-carbon fuel to replace diesel for heavy-duty marine propulsion with prominent fuel cost and carbon dioxide equivalent (CDE) emissions reduction potential. However, using NG in compression ignition (CI) engines presents several inherent drawbacks. This research addresses the central issue of an NG-diesel CI engine with increased methane emissions, resulting in minor CDE emission reduction. The hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NOx) emissions are minimized in addition to fuel consumption and carbon dioxide emission reduction as in the current practice. The simultaneous optimizations of powertrain component sizes and the NG-engine hybrid electric propulsion control are introduced to minimize NG fuel consumption and CDE emissions globally. The top-level powertrain component sizing and bottom-level optimal power control and energy management are conducted simultaneously to achieve global optimization with balanced fuel cost and CDE emissions reductions. The new method reduced the fuel cost by about 75 percent and well-to-wake CDE emissions by about 40 percent over the traditional diesel-mechanical propulsion for the test ferry running under an actual operation profile. The research opened a new path to the global design and control optimization of the NG-diesel CI engine-powered hybrid electric marine propulsion system.

Пружинные демпферы крутильных колебаний в составе современных судовых дизелей: преимущества и недостатки

The article presents analysis of the advantages and disadvantages in assembling the spring dampers of torsional vibrations in modern marine diesel engines. There are considered the urgent problems of using spring dampers in the marine propulsion systems: lack of the systematized scientific data about the spring damper design, statistics of their prevalence in the marine diesel engines, analysis of breakdowns. It has been stated that today there is no methodology for assessing the technical condition of spring dampers, except for the methods recommended by the Russian Maritime Register of Shipping in relation to the silicone dampers. Disassembly diagnostics of the technical condition of spring dampers is extremely difficult and costly for a shipowner. Most of the vessels that are currently being operated in Russia are found obsolete, and there has started a gradual process of modernization and replacement 
 of morally and physically obsolete main engines G60,G70 (6CPH 36/45), SKL NVD, 6ChH18/22, 3D6 (6ChH 15/18) etc. by new foreign diesel engines manufactured by Wartsila (Finland), Caterpillar (USA), Volvo - Penta (Sweden), Scania (Sweden), Henan Diesel Engine Industry Co., Ltd (China) etc., which have new dampers of such companies as Geislinger (Germany), Hasse & Wrede (Germany), STE - Schwingungstechnik (Germany), Holset (England), Caterpillar (USA) etc. Diagnostics of dampers of modern diesel engines is a new direction for the domestic marine industry; it requires a revision of both the technological processes of working with such equipment and training the qualified specialists. The study of the structural and operational features of spring dampers of modern diesel engines will allow to accumulate the necessary amount of scientific and technical information to create in Russia the foundations of production of efficient structures and the development of engine building in general.

Выбор методов постоянного мониторинга крутильных колебаний в судовых машинно-движительных комплексах

The article considers the problem of the continuing emergency damages to the elements of ship engine-propulsion systems with fatigue failures of shaft pipelines. The classification societies require to analyze and measure the dangerous torsional vibrations in ship power plants. There is given an overview and comparison of methods of measuring torsional vibrations in order to determine the most promising ones for constant monitoring and diagnostics of the technical condition of the elements of marine propulsion systems. In the course of analysis of scientific and technical literature there have been identified the main methods of measuring torsional vibrations, which formed the basis for developing the national and foreign measuring software and hardware complexes. The marine conditions surely require the appropriate design and operating principles from the monitoring systems, therefore, such methods as strain measurement, using laser and optical sensors with reflective tape, inductive sensors with gears are defined as promising. There is illustrated a diagram of the measuring bridge of four load cells, given an example of the design and positioning of the IVC Technologies strain gauge system on the shaft, considered the Geislinger systems with a spring damper and measuring gears. There are presented the illustrations of the OROS measuring system, the Konsberg system, the RT-660 radiotorsiograph, the SCAN optical torsiograph developed by JSC Central Research and Design Institute of the Marine Fleet (TsNIIMF), the TNK-1 sensor, the BAGS-4M measuring complex and others. The results of the study will be used to develop experimental samples of a monitoring system with the selected methods for measuring torsional vibrations and conducting tests in the laboratory and on board a ship.

A real-time shaft alignment monitoring method adapting to ship hull deformation for marine propulsion system

Shaft alignment states are strictly stipulated in the marine propulsion system. However, there are relatively limited studies on shaft alignment monitoring and control considering the effects of ship hull deformation (SHD). SHD can be caused by wave load, loading, depth, speed, etc., and leads to various relative displacements at different shaft supporting points between the ship foundation and the support bearings of the propulsion system. It leads to shaft misalignment, increases shaft vibration and noise, and even endangers the safety of shaft system during the operation stages. To overcome this problem, a real-time shaft alignment monitoring method based on laser displacement sensors (SAMM/LDS) is proposed. Firstly, the defects of a present shaft alignment monitoring method based on eddy current displacement sensors (SAMM/ECDS) are analyzed when considering the effects of SHD. The structure and working principle of a shaft alignment monitoring system adapted to SHD (SAMS/SHD) are proposed. It consists of three sub-systems: the shaft alignment monitoring sub-system adapting to SHD (SAMSS/SHD), the present shaft alignment monitoring sub-system (SAMSS/P), and the shaft alignment correcting sub-system (SACSS). Based on SHD data-driven, SAMS/SHD can not only take advantage of SAMSS/P for long-time operations but also reflect SHD by exploiting the advantages of SAMSS/SHD. Secondly, SAMM/LDS is deduced. Two laser displacement sensors (LDS) are placed on the driving shaft and the driven shaft to reflect the spatial relative displacement and attitude information affected by SHD. Therefore, two reference coordinate systems are fixed at the center of LDS, and the coordinate expressions of their imaging points are derived using a 4 × 4 homogeneous coordinate transformation matrix. For reducing computing complexity in engineering applications, a simplified monitoring model is proposed for very small rigid-body rotational angularities. Finally, the effectiveness and testing accuracy of the SAMM/LDS is verified on a five-DOF platform which can simulate the effects of SHD. The SAMM/LDS can be used to realize real-time and high-precision shaft alignment monitoring for marine propulsion system which can adapt to the effects of SHD and so on. Based on the foundation of this research, compensation control algorithms to solve the misalignment effects deduced by SHD will be studied for marine propulsion system with resilient mounts in the next few years.

Frictional vibration behaviors of a new piezo-damping composite under water-lubricated friction

Water-lubricated bearings have become an important component of marine propulsion systems due to the requirements of environmental friendliness and concealability. However, water-lubricated bearings are often subjected to bending stress, additional stress, frictional resistance and other multi-factor effects, resulting in boundary friction or even dry friction on the friction interfaces when encountering unique working conditions such as engine start-stop, steering, low-speed, and heavy-load. The severe frictional processes often induce vibration behaviors and generate frictional noise, which seriously weakens the sound concealment performance and service life of marine propulsion systems. Therefore, it is urgent to improve the vibration and sound pressure behaviors of the composite bearings under water-lubricated conditions. In this study, novel barium titanate/carbon black/polyurethane composites (BaTiO3/CB/PU) are fabricated and then explored the damping capacities and tribological properties of the new polymers. The results showed that the BaTiO3 concentrated on transforming the mechanical energy generated by frictional vibration into electrical energy which generates the thermal energy. The water cooled the frictional heat and the piezo-damping heat. This energy dissipation method increased the damping capacity to reduce the vibration and noise behaviors induced by friction. The composite with 3.0 wt% BaTiO3 performed the highest loss factor under the operating temperatures and presented the best frictional vibration reduction properties. The knowledge obtained in this study is useful not only to explore a new piezo-damping composite, but also to provide a theoretical basis for developing higher performance polymer-based water-lubricated bearing.

The Impact of Slow Steaming on Fuel Consumption and CO2 Emissions of a Container Ship

Modern marine propulsion systems must be reliable, energy efficient, environmentally friendly, and economical. Efforts to reduce fuel costs and carbon dioxide (CO2) emissions per nautical mile have a significant impact on the choice of propulsion system. Considering that there is no alternative for maritime transport, various technical and technological solutions are being considered that aim to improve efficiency and reduce the negative impact on the environment. One of the ways to achieve this goal is slow steaming, which reduces fuel consumption and CO2 emissions. The designed speed of the vessel has a significant impact on the efficiency of slow steaming. Slow steaming is particularly suitable for large container ships with a design speed of more than 20 knots. In this paper, the effects of slow steaming are analyzed using the example of a container ship with diesel-engine propulsion. Propulsion systems with low-speed and medium-speed marine diesel engines with mechanical power transmission are investigated. Data on the required engine power and propeller speed were used for the study, obtained from calculations during testing of the ship’s hull model. The effects of speed reduction on specific fuel consumption and emission reduction were analyzed using numerical models of two-stroke and four-stroke diesel engines. The models were calibrated and validated using data provided by the engine manufacturers. The paper analyses four different cases where one or two low-speed diesel engines, or three or four medium-speed diesel engines, are used for propulsion. The analysis concludes that slow steaming can effectively reduce fuel consumption and CO2 emissions, but the choice of the optimal propulsion system is highly dependent on maritime market conditions in maritime transportation. The choice of propulsion system affects the potential of slow steaming.

Intelligent Adaptive PID Control for the Shaft Speed of a Marine Electric Propulsion System Based on the Evidential Reasoning Rule

To precisely and timely control the shaft speed for a marine electric propulsion system under normal sea conditions, a new shaft speed control technique combining the evidential reasoning rule with the traditional PID controller was proposed in this study. First, an intelligent adaptive PID controller based on the evidential reasoning rule was designed for a marine electric propulsion system to obtain the PID parameters KP, KI, and KD. Then, a local iterative optimization strategy for model parameters was proposed. Furthermore, the parameters of the adaptive PID controller model were optimized in real time by using the sequential linear programming algorithm, which enabled the adaptive adjustment of KP, KI, and KD. Finally, the performance of the adaptive PID controller regarding the shaft speed control was compared with that of other controllers. The results showed that the adaptive PID controller designed in this study had better control performance, and the shaft speed control method based on the adaptive PID controller could better control the shaft speed of the marine electric propulsion system.

Numerical assessment of the effect of length, angle of attack, and type of ducts on hydrodynamic parameters of a linear-jet propulsion system

Achieving noble and more practical propulsion systems is still a major concern for engineers and researchers. Accordingly, many researchers have strived to opt for better and suitable system for the targeted vessels. One of the marine propulsion systems is linear-jet propulsion which includes rotor and stator. In this paper, the effects of geometrical shape of the duct in the form of different length and angle of attack for two types of the accelerating and decelerating ducts are comprehensively explored. Furthermore, section of rotor from Kaplan series are selected and the geometrical shape effects of the rotor on hydrodynamic performance of linear-jet propulsion system are also investigated. Therefore, to obtain the effects of the expressed parameters on the hydrodynamic characteristics of this propulsion system, Ansys-CFX software has been used. The governing equations of the studied problem are RANS equations and SST k-omega turbulent model is utilized. The obtained results are presented in the form of dimensionless coefficients of the forces applied on the propulsion system. The existing data for a ducted propeller are used to validate the numerical solution. Based on the results of the numerical solution, it is concluded that use of a decelerating duct increases the efficiency of the linear-jet system. On the other hand, the use of accelerating ducts reduces the hydrodynamic efficiency of the linear jet, so the performance is not desirable at high advance ratio. Therefore, the use of decelerating ducts in the linear-jet system is found to be the appropriate choice. Results further illustrate that, if the duct length increases, the generated thrust by the rotor increases. It is also concluded that, by increasing the angle of attack of the decelerating duct, the overall efficiency of the linear-jet propulsion system decreases.

Effects of unsymmetrical input power on the vibro-acoustic characteristics of the marine propulsion system: Theory and experiment

The propulsion system, as the crucial equipment to drive the ships, its stability is of great significance for the safe and reliable operation of the system. This study focuses on the propulsion system for large-scale ships with high- and low- integrated double-cylinder turbines, and carries out theoretical and experimental research on its dynamic characteristics and system stability. Firstly, based on comprehensively considering the key excitations and multi-state meshing of the system, a nonlinear dynamic model of the gear-rotor-bearing system including two power paths is established. Secondly, the influences of the load ratio between the unsymmetrical input power on the dynamic characteristics and motion stability are studied by global and local analysis methods. Finally, by establishing a comprehensive experimental platform for the parallel propulsion system, the in-depth experimental research on the vibration state, acoustic characteristics, and power loss of the system is carried out. The research results show that the increase of the load ratio has a positive effect on enhancing the system stability, reducing the vibration and noise, and improving the power efficiency. This research has the guiding significance for the power design and optimization of the marine propulsion system powered by double-cylinder turbines.

On the Prospects for the Development of Marine Propulsion Systems for Their Compliance with the Environmental Standards of the International Convention

Introduction. The shipping industry pays great attention to the safety of man-made and natural systems. At the same time, increased requirements are imposed not only on the quality of the fuel composition, but also on exhaust emissions. Currently, Annex VI of the MARPOL-73/78 Convention has been ratified by many of its signatories. The compliance with this document requires that engine emissions comply with the specified NOx level limits. Until recently, such rules were mainly applied in the Baltic and North Seas, but over time, the compliance with environmental standards will affect other areas of navigation.The work objective is to show through the study of modern technical solutions that we need an integrated approach to solve practical environmental problems, which will allow developing rational schemes of modern marine propulsion systems, taking into account their compliance with the safety requirements of technogenic and natural systems.Materials and Methods. The methods and recommendations given in open sources and corresponding to the requirements of the International Maritime Organization (IMO) were used in the work. The experience of leading foreign firms and domestic enterprises in terms of modern design solutions that will reduce ship emissions to acceptable limits is analyzed and summarized.Research Results. The issues related to the study of factors influencing the development of rational schemes of ship propulsion systems, taking into account their current level of development, pricing policy and the compliance with the environmental requirements, are considered. It is shown that one of the effective ways to reduce NOx emissions is the installation of a selective catalytic reducer (SCR) on the main engine, and the use of efficient and innovative power generation technologies to reduce technogenic emissions. In the medium term, the transition to gaseous fuels is predicted, and in the long term – to hydrogen technologies.Discussion and Conclusion. Possible technical solutions to reduce emissions of nitrogen oxides by installing selective catalytic reducers on the main marine engines are presented. It is established that one of the promising areas of development are diesel-electric propulsion systems. It is shown that in the medium term, due to stricter environmental requirements, there will be a transition to gaseous fuels, which will allow us with minor structural changes to increase the power of the existing main engines and to reduce emissions of nitrogen oxides and greenhouse gases. In the long term, the transition to hydrogen fuel cells with continuous improvement of the technological level of production, storage and development of the corresponding infrastructure can be considered as a real alternative to hydrocarbon fuels in marine transport.

Longitudinal Vibration Transmission Control of Marine Propulsion Shafting with Friction Damper Integrated into the Thrust Bearing

Propeller-induced longitudinal vibration resonance in marine propulsion shafting systems causes great harm to the hull structure and is the primary source of shipboard noise. Integrating a friction damper with designed parameters into thrust bearings can prevent these issues. To investigate the performance of the damper-integrated thrust bearing in longitudinal vibration transmission control, an experimental and theoretical study is carried out in a laboratory-assembled test rig, which consists of components similar to the existing marine propulsion system. We developed a prototype of a thrust bearing designed with a friction-damping generation that allows switching from two supporting states, i.e., damper-connected and damper-disconnected states. Furthermore, a nonlinear analysis method for friction dampers is proposed. By this method, the way in which the friction damper changes the dynamic characteristics of the shafting system is analyzed. Based on the test rig, the acceleration frequency response function (AFRF) of the thrust bearing with and without a friction damper is measured. By comparison, the effectiveness of the friction damper is proved. The experimental results show that the friction damper suppresses the shafting longitudinal vibration response in a broadband frequency range and also confirms the stability of the damping effect, which does not change with the shafting rotational speed or static thrust from the propeller.

Experimental mild conversion of a lean burn natural gas engine with SCR to a hydrogen engine: NOx and GWP potential for marine applications

Emissions of nitrogen oxides (NOx) from marine propulsion systems have gained public interest resulting in emission limits as defined by the International Maritime Organization (IMO) with IMO Tier III, especially for vessels operating in Emission Control Areas (ECA). The reduction of greenhouse gas emissions is also increasingly important for marine propulsion. Minimizing NOx while reducing climate impact calls for technologies such as the gas engine with aftertreatment systems, preferably with the ability to run on alternative fuels. A proven technology for reducing NOx in marine engines is the Selective Catalytic Reduction (SCR) aftertreatment system. It is also possible to avoid engine raw emissions by shifting the combustion process to lower temperature levels. Hydrogen is an alternative fuel with combustion properties enabling premixed operation at significantly higher air-fuel ratio than natural gas (NG) and thus, reducing raw NOx emissions. The study uses a systematic approach to compare emissions and efficiency of a lean-burn gas engine with a natural gas and a mild conversion hydrogen setup, utilizing two different strategies: combustion of NG with the assumption of an SCR catalyst and high raw NOx emissions and combustion of pure hydrogen using the NOx reduction potential of higher excess air. The scope of the study makes it possible to illustrate engine concepts for future applications in the displacement class of 4.8 L per cylinder. The highest efficiency of 45.3% was achieved with the natural gas engine and SCR. The concept with the lowest Global Warming Potential (GWP) was the hydrogen fueled engine under the prerequisite of using green hydrogen, accompanied by a reduction in efficiency of 0.6% compared to the efficiency optimum of NG with SCR. Assuming the use of gray hydrogen, the GWP was 48% and 52% higher than with NG and NG with SCR, respectively, at the efficiency-optimal operating points.

The hydrodynamic analysis of multiple hydrofoils translating in tandem in presence of a free surface

Hydrofoils find its presence in various engineering applications including high speed marine crafts, blades of hydro-kinetic turbines etc. So, depending on the type of marine application, the foils are arranged in different complex arrangements (i.e. in line, or in tandem) that can alter flow dynamics of the working fluid flowing around them. In order to design efficient marine propulsion systems, it is important to study the effect of different arrangements of hydrofoil systems on its hydrodynamic characteristics (lift, drag, pressure coefficient, velocity contour, etc). In this study, the numerical simulation of fluid flow over a tandem hydrofoils is carried out in presence of a free surface. The present study is limited for a constant Reynolds number of 166,784.8, and at a Froude number of 0.57. The unsteady RANS equations are solved using the volume of fluid (VOF) method embedded in commercial software STAR-CCM+ incorporating [Formula: see text] turbulence model. The first part of the study focuses on varying spacing ratios ( l/ c) that range from 0.1 to 4. In the second part of the study, the angle of attack of the downstream hydrofoil was varied over zero degrees to stall keeping the upstream hydrofoil at a zero degree angle of attack. For both studies, pressure and velocity distributions, lift as well as drag coefficients were evaluated. It is concluded that the presence of a free surface in a close proximity to the foils, different spacing between the hydrofoils, and varying angle of attacks of the downstream hydrofoil have significant effects on the overall performance.

Effect of Temperature Change on Acoustic Emission Signal in IGBT Transistors of Marine Propulsion System Converters

The article presents the results of tests related to failure analysis and finding ways to diagnose used semiconductor elements, among others, in power electronics converter systems on vessels and offshore facilities (drilling and production rigs and wind turbines). Diagnostic relationships were found between the temperature change in the above systems and the signals generated in the form of elastic waves of acoustic emission. The authors confirmed the influence of the transistor’s working temperature on its amplitude-frequency spectrum of acoustic emission signals emitted. The range of ‘safe temperatures’ was considered which means temperatures that do not directly affect the damage of the component.

Modelling and predictive investigation on the vibration response of a propeller shaft based on a convolutional neural network

Abstract. It is crucial to detect the working state of a propeller shaft in real time, as its vibration affects the safety of the marine propulsion system directly. With the difficulty of obtaining an accurate signal due to the particularity of propeller shaft, a suitable method for estimating the vibration response of propeller shaft is proposed in this paper. The nonlinear relationship of vibration signals between the bearing and propeller shaft is obtained by fitting the existing data sets with various neural networks. The feasibility of the proposed method is demonstrated through a prediction of shaft vibration on the basis of a shaft experimental platform. Moreover, the optimal model of the neural network is obtained by comparing the influence of different hyper parameters and network models. The results indicate a prediction accuracy of over 95 % of the shaft vibration in the lower frequency band for a convolutional neural network. Therefore, the research provides an easier maintenance method for predicting the real-time monitoring for the vibration response of the propeller shaft.

An assessment of electric motors from the point of marine propulsion systems

The global environmental concern and the limited resources of fossil fuels warrant the use of alternative and renewable energy sources. The International Maritime Organisation aims to increase energy efficiency and reduce emissions from marine vessels. In this context, in addition to the conventional propulsion system, the application of hybrid propulsion system (HPS) and diesel-electric propulsion system (DEPS) comes to the fore. This study aims to analyse electric motors, one of the HPS and DEPS equipment, in detail. In this study, HPS gains are described by performing application load tests on electric motors and diesel engines in detail. Consequently, this article found that HPS and DEPS systems will be used more widely in the maritime industry in the future, especially on tugboats operated at low loads for most of their operating time. This paper will be a prominent source for researchers and maritime sector stakeholders whose studies are concerning HPS and DEPS, particularly on electric motors.
 
 Keywords: Efficiency, energy, electric motor, marine vessels, propulsion, system;

A Composite Method of Marine Shafting’s Fault Diagnosis by Ship Hull Vibrations Based on EEMD

The fault diagnosis is always a key issue in the security field of marine propulsion system. There are obvious problems like the unsteady working of sensors, distortion of original data, and ambivalent feature information from marine shafting’s vibration or motion. It is therefore critical to develop a more effective method to identify the fault information so that the safety of marine propulsion system can be pre-estimated. Hence, a composite method which is based on the ensemble empirical mode decomposition (EEMD) and coupled with the autocorrelation method (AM), the fast Fourier transform (FFT), is mixed and applied to identify the fault information of marine shafting during its operating by hull vibration. The contrastive analysis of the three methods and fault feature study are then conducted to assess the effectiveness of the proposed method thoroughly and validated by the author previously. The research indicates that the composite method is available to fault diagnosis of marine shafting by hull vibration which coupled the shafting vibration with fault feature.