Search Results (66)

The lateral vibration of propulsion shafting is a critical factor affecting the acoustic stealth performance of underwater vehicles. As the main vibration isolation component in transmitting vibrational energy, the damping efficiency of the propulsion shafting support system (PSSS) holds particular significance. This study investigates the dynamic characteristics of the PSSS with the integral squeeze film damper (ISFD). A dynamic model of ISFD–PSSS is developed to systematically analyze the effects of shaft speed and external load on its dynamic behavior. Three test bearings (conventional, 1S, and 3S structure) are designed and manufactured to study the influence of damping structure layout scheme, damping fluid viscosity, unbalanced load, and shaft speed on the vibration reduction ability of ISFD–PSSS through axis orbit and vibration velocity. The results show that the damping effects of ISFD–PSSS are observed across all test conditions, presenting distinct nonlinear patterns. Suppression effectiveness is more pronounced in the vertical direction compared to the horizontal direction. The 3S structure bearing has better vibration reduction and structural stability than other schemes. The research results provide a reference for the vibration control method of rotating machinery. Full article

Naval ships are of paramount importance to national security, culture, and naval operations. A primary challenge for naval authorities is to balance the imperatives of maritime dominance with the operational demands of achieving sufficient, sustainable reliability. Shaft generators (SGs) are crucial to the energy conversion systems on naval ships, functioning as part of the main power systems on board and providing both propulsion and power for various operational loads. In this sense, the design of shaft generators is an engineering element that has a major impact on the overall ship performance. The design process will be conducted within the MATLAB/Simulink environment, a platform that facilitates the study of the dynamic behaviors of the system through simulation. The increasing demand for efficiency, reliability, and sustainability in the military, along with the impact of emerging technologies, will further underscore the significance of shaft generators. Analyses carried out in MATLAB/Simulink demonstrate that the selection of the most suitable power system for naval ships is dictated by the system requirements and operational demands. The main construction is such that this work is the first of its kind in the field of shaft generator research for naval ships. Full article

During the operation and service of a ship, its power system will affect the stability, reliability, and safety of the ship’s power system and the ship’s vitality if there are typical problems, such as unstable operation and vibration of the shaft system. If the tail bearing is not properly installed, it will lead to increased vibration at its support during operation, which will cause the propulsion system components to come loose and even produce destructive accidents. This paper combines the theory of multi-degree-of-freedom system dynamics to study the propulsion system vibration modeling technology based on the bearing–mounting error, analyze the mapping law between the bearing–mounting error and the shaft system vibration, construct a shaft system vibration model with the bearing–mounting error included, and analyze the influence of the bearing vertical mounting error and lateral mounting error on the vibration performance of the shaft system. This paper establishes the equations of motion of the shaft system with bearing–mounting errors and analyzes the relationship between the bearing vertical mounting errors and lateral mounting errors and the amplitude, speed, and acceleration of the paddle shaft system. The analyzed results show that the vibration response of the shaft system gradually increases with the increase in the bearing–mounting error. With the increase in the bearing vertical mounting error, the increase in vibration amplitude and the transient response of vibration acceleration in the vertical direction is larger than that in the horizontal direction, and the sensitivity of the transient response of vibration acceleration in the vertical direction to the bearing vertical mounting error is larger than that in the horizontal direction. With the increase in the bearing lateral mounting error, the increase in the vibration acceleration transient response value of the paddle shaft system in the horizontal direction is larger than that in the vertical direction, and the sensitivity of the vibration amplitude and vibration acceleration transient response to the bearing lateral mounting error in the horizontal direction is larger than that in the vertical direction. The bearing vertical installation error has a greater effect on the vibration of the paddle shaft system in the vertical direction than in the horizontal direction, and the bearing lateral installation error has a greater effect on the vibration of the paddle shaft system in the horizontal direction than in the vertical direction. The results of this paper can provide a theoretical basis and technical reference for the installation and calibration of ship propulsion system. Full article

One of the challenges of our age is climate change and the ways in which it affects the Earth’s global ecosystem. To face the problems linked to such an issue, the international community has defined actions aimed at the reduction in greenhouse gas emissions in several sectors, including the aviation industry, which has been requested to mitigate its environmental impact. Conventional aircraft propulsion systems depend on fossil fuels, significantly contributing to global carbon emissions. For this reason, innovative propulsion technologies are needed to reduce aviation’s impact on the environment. Electric propulsion has emerged as a promising solution among the several innovative technologies introduced to face climate change challenges. It offers, in fact, a pathway to more sustainable air travel by eliminating direct greenhouse gas emissions, enhancing energy efficiency. Unfortunately, integrating electric motors into aircraft is currently a big challenge, primarily due to thermal management-related issues. Efficient heat dissipation is crucial to maintain optimal performance, reliability, and safety of the electric motor, but aeronautic applications are highly demanding in terms of power, so ad hoc Thermal Management Systems (TMSs) must be developed. The present paper explores the design and optimization of a TMS tailored for a megawatt electric motor in aviation, suitable for regional aircraft (~80 pax). The proposed system relies on coolant oil injected through a hollow shaft and radial tubes to directly reach hot spots and ensure effective heat distribution inside the permanent magnet cavity. The goal of this paper is to demonstrate how advanced TMS strategies can enhance operational efficiency and extend the lifespan of electric motors for aeronautic applications. The effectiveness of the radial tube configuration is assessed by means of advanced Computational Fluid Dynamics (CFD) analysis with the aim of verifying that the proposed design is able to maintain system thermal stability and prevent its overheating. Full article

This paper presents a comparative analysis of machine learning-based methods for predicting shaft power in ships, a key factor in optimizing ship performance. Accurate shaft power prediction facilitates efficient operations, reducing fuel consumption, emissions, and maintenance costs, aligning with environmental regulations and promoting sustainable maritime practices. The proposed approach evaluates three machine learning methods, analyzing 431 models to determine the most accurate and reliable option for VLCC tankers. XGBoost emerged as the top-performing model, delivering a 13% improvement in accuracy over traditional methods. Using the SHAP framework, key factors influencing shaft power predictions—such as GPS speed, draft, days from dry dock, and wave height—were identified, enhancing model transparency and decision-making clarity. This explainability fosters trust in the use of AI within marine engineering. The results demonstrate that machine learning can optimize maintenance scheduling by reducing unnecessary cleaning procedures, mitigating propulsion system wear, and improving reliability. By using predictive insights, ship operators can achieve better fuel efficiency, lower emissions, and cost savings. The study underscores the potential of explainable machine learning models as transformative tools for ship performance monitoring, supporting greener and more efficient maritime operations. Full article

This study investigates the environmental and operational performance of X-DF and ME-GI propulsion systems in large LNG carriers, focusing on key emission and transport efficiency metrics—CO₂, the EEOI, and the CII—and their relationship with operational factors such as shaft power, vessel speed, propeller slip, and specific fuel oil consumption. Statistical methods including correlation analysis, regression modeling, outlier detection, and clustering are employed to evaluate engine behavior across the ship’s fuel gas steaming envelope and to identify critical efficiency trends. The results show that ME-GI engines deliver lower CO₂ emissions and consistent efficiency under steady-load conditions, due to their higher thermal efficiency and precise control characteristics. In contrast, X-DF engines demonstrate greater adaptability, leveraging LNG combustion to achieve cleaner emissions and optimal performance in specific operational clusters. Clustering analysis highlights distinct patterns: ME-GI engines excel with optimized shaft power and RPM, while X-DF engines achieve peak efficiency through adaptive load and fuel management. These findings provide actionable insights for integrating performance indicators into SEEMP strategies, enabling targeted emission reductions and fuel optimization across diverse operating scenarios—thus supporting more sustainable maritime transport. Full article

The International Maritime Organization (IMO) mandates a reduction in carbon dioxide emissions from 2008 levels by at least 40% by 2030, prompting the widespread adoption of slow steaming and engine de-rating strategies. This study investigates the fatigue life of marine propulsion shafts under slow steaming conditions, focusing on the interplay between torsional and bending vibrations. A finite element (FE) model of a low-speed two-stroke propulsion system is developed, incorporating torsional and lateral excitation sources from both the engine and propeller. Vibrational stresses are computed for multiple operating conditions, and fatigue life is assessed using both the conventional Det Norske Veritas (DNV) methodology and a proposed biaxial stress approach. Results indicate that while torsional vibrations remain the primary fatigue driver, bending-induced stresses contribute marginally to the overall fatigue life. The proposed methodology refines high-cycle fatigue (HCF) assessment by incorporating a corrected S-N curve and equivalent von Mises stress criteria. Comparisons with classification society standards demonstrate that existing guidelines remain valid for most cases, though further studies on extreme alignment deviations and dynamic bending effects are recommended. This study enhances understanding of fatigue mechanisms in marine shafting and proposes a refined methodology for improved fatigue life prediction. Full article

The electrification of ships and the use of electric propulsion systems are projects which have attracted increased research and industrial interest in recent years. Efforts are particularly focused on reducing pollutants for better environmental conditions and increasing efficiency. The main source of propulsion for such a ship’s shafts is related to the operation of electrical machines. In this case, several advantages are offered, related to both reduced fuel consumption and system functionality. Nowadays, two types of electric motors are used in propulsion applications: traditional induction motors (IMs) and permanent magnet synchronous motors (PMSMs). The evolution of magnetic materials and increased interest in high efficiency and power density have established PMSMs as the dominant technology in various industrial and maritime applications. This paper presents a comprehensive comparative analysis of PMSMs and both Squirrel-Cage and Wound-Rotor IMs for ship propulsion applications, focusing on design optimization. The study shows that PMSMs can be up to 3.11% more efficient than IMs. Additionally, the paper discusses critical operational and economic aspects of adopting PMSMs in large-scale ship propulsion systems, such as various load conditions, torque ripple, thermal behavior, material constraints, control complexity, and lifetime costs, contributing to decision making in the marine industry. Full article

The Hybrid Contra Rotating Propeller is a developing propulsion system that combines a conventional single-shaft propeller with a POD propeller to achieve high energy-saving performance through a Contra Rotating Propeller. In this paper, a new towing tank test method for the Hybrid Contra Rotating Propeller was suggested. By conducting seven patterns of propeller open-water tests and measuring the individual propeller performance and the interaction between the propeller and the POD, the propeller’s mutual interaction can be obtained. Towing tank tests for a study ship were conducted, and the analyzed results are shown. There exists the effect of the wake of the propeller open boat at an unusual (reversed) test layout, which simulates the Hybrid Contra Rotating Propeller, and this effect must be removed for the accurate estimation of the ship’s performance. In conventional towing tank test methods, this effect on the front propeller was obtained and used to correct the performance of the total unit of the Hybrid Contra Rotating Propeller. The presented method allows for the correct removal of the open boat effect on the performance of each propeller and the propeller mutual interaction, resulting in more accurate power estimation. Furthermore, by using the individual performance of two propellers and interaction terms, the presented method enables us to conduct a power estimation at an arbitrary revolution rate of two propellers. Full article

The design scheme of elastically supported submarine propulsion shafting can effectively realize the attenuation of the vibration energy and improve the stealth performance of the whole submarine. However, the elastic deformation generated by the system will affect the alignment state of shafting, thus affecting its safety and reliability. Aiming at this problem, taking a certain elastically supported submarine propulsion shafting as the study object of this paper, the alignment calculation model of the shafting was established and validated, and an equivalent line-surface method was proposed to measure the elastic bearing displacement. On this basis, the concept of the dynamic bearing load influence numbers (BLINs) was elicited, and a response surface method using Gaussian process regression (GPR) was designed to establish the mapping relationship between the elastic displacement and the dynamic BLINs. Taking the equivalent displacements of the bearings as variables, the alignment optimization of the shafting was achieved by combining the genetic algorithm and the response surfaces. After optimization, the load of the rear stern bearing was reduced by 16.67%, and the standard deviation of the bearing loads was reduced by 37.19%. Hence, the alignment state of the shafting was improved. The studied results can provide theoretical and technical support for the analysis and optimization of the alignment characteristics of elastically supported submarine propulsion shafting. Full article

This study aims to investigate the dynamic behavior of water-lubricated stern bearings during service. A transient rotor dynamics numerical model is developed to research the effects of operating conditions and critical structural parameters on the variation patterns of the dynamic characteristic coefficients and journal orbit of WLBs. The main stiffness and damping formulas for dimensionless bearings are fitted based on numerical results. Additionally, the accuracy of the model calculations is experimentally verified on a water-lubricated bearing test rig. The results demonstrate that the variation trends of the main stiffness and main damping coefficients in the horizontal and vertical directions of the bearings are proportional to the external load and inversely proportional to the rotational speed. Under eccentric excitation, the dynamic characteristic coefficients of the bearings change periodically with time as an approximately sinusoidal function. With the increase in the bearing length-to-diameter ratio or the decrease in the radial clearance-to-radius ratio, the main stiffness and the main damping coefficients in the horizontal direction increase, while the main stiffness coefficient in the vertical direction decreases. This study provides theoretical support for modeling the transient transverse vibration of a propulsion shaft system. Full article

Hybrid-electric aircraft (HEAs) represent a promising solution for reducing fuel consumption and emissions. However, the additional heat loads generated by the electrical propulsion systems in HEAs can diminish these benefits. To address this, an integrated power and thermal management system (IPTMS) is essential to mitigate these challenges by optimizing the interaction between thermal management and power management. This paper presents a preliminary IPTMS design for a parallel HEA operating under International Standard Atmosphere (ISA) conditions. The design includes an evaluation of active cooling, passive cooling, and active temperature control strategies. The IPTMS accounts for heat loads from the engine system, including the generators, shaft bearings, and power gearboxes, as well as from the electrical propulsion system, such as motors, batteries, converters, and the electric bus. This study investigates the impact of battery power (BP) contribution to cooling power on required coolant pump power and induced ram air drag. A comparison of IPTMS performance under 0% and 100% BP conditions revealed that the magnitude of battery power contribution to cooling power does not significantly impact the thermal management system (TMS) performance due to the large disparity between the total battery power (maximum 950 kW) and the required cooling power (maximum 443 W). Additionally, it was determined that the motor-inverter loop accounts for 95% of the pump power and 97% of the ram air drag. These findings suggest that IPTMS optimization should prioritize the thermal domain, particularly the motor-inverter loop. This study provides new insights into IPTMS design for HEAs, paving the way for further exploration of IPTMS performance under various operating conditions and refinement of cooling strategies. Full article

Retrofitting regional turboprop aircraft with hydrogen (H₂)-electric powertrains, using fuel cell systems (FCSs), has gained interest in the last decade. This type of powertrain eliminates CO₂, NOx, and fine particle emissions during flight, as FCSs only emit water. In this context, the “Hydrogen Aircraft Powertrain and Storage Systems” (HAPSS) project targets the development of a H₂-electric propulsion system for retrofitting Dash 8-300 series aircraft. The purpose of the study described in this paper is to analyze the performance of the retrofitted H₂-electric aircraft during critical operating conditions. Takeoff, as well as climb, cruise and go-around performances are addressed. The NLR in-house tool MASS (Mission, Aircraft and Systems Simulation) was used for the performance analyses. The results show that the retrofitted H₂-electric aircraft has a slightly increased takeoff distance compared to the Dash 8-300 and it requires a maximum rated shaft power of 1.9 MW per propeller. A total rated FCS output power of 3.1 MW is sufficient to satisfy the takeoff requirements, at the cost of lower cruise altitude and reduced cruise speed as compared to the Dash 8-300. Furthermore, a higher-rated FCS is required to achieve the climb performance required for the typical climb profile of the Dash 8-300. Full article

The vibration of a ship’s propulsion shaft system directly affects the ship’s lifespan, and many studies have designed vibration absorbers only for one of the natural frequencies of a ship’s propulsion shaft system without considering the influence of multiple low-order resonance frequencies. In this paper, a vibration absorber combined with a magnetorheological elastomer vibration absorber and a rubber vibration absorber in series is designed, and it can cover two torsional natural frequency band ranges to achieve better vibration reduction performances in multiple different torsional natural frequencies. The torsional natural frequency of the propulsion shafting of a 45 m fishing vessel is determined based on a multiple-degrees-of-freedom equivalent discretization model. Two natural frequencies, 22.4 Hz and 131.4 Hz, of a ship propulsion shaft system are selected as the design goal parameters of the combined vibration absorber. The magnetic field is simulated to ensure that the magnetic field generated by an energized coil can meet requirements. Then, a dynamic simulation of the ship propulsion shaft system with a combined vibration absorber is conducted via co-simulation. Afterward, the device is installed on the intermediate shaft of the ship propulsion shaft system for simulation, and the vibration reduction effect of the device is analyzed at different frequencies by controlling the current. When the device is controlled to operate at the optimal frequency point, the results show that the angular acceleration vibration amplitude reduction around the first and third torsional natural frequencies of the propulsion shaft system reaches 90% and 18%, respectively. This study provides new ideas for the intelligent and controllable vibration damping of ship propulsion shaft systems, especially for the development trend of intelligent ship equipment under complex working conditions. Full article

With the rapid growth of air travel, reducing carbon emissions in aviation is imperative. Electric aircraft play a key role in achieving sustainable aviation, especially for large civil aircraft, where reducing emissions, improving the fuel efficiency, and enabling flexible power regulation are essential. This study proposes a dual-shaft, separated-exhaust fuel cell hybrid aircraft propulsion system (HAPS), using a solid oxide fuel cell (SOFC) to replace the conventional turbine-driven compressor. The independent speed control of the high- and low-pressure spools is realized via a power distribution system. A thermodynamic model is developed, and performance evaluations, including parametric, exergy, and sensitivity analyses, are conducted. At the design point, the system delivers 36.304 kN thrust, 16.775 g/(kN·s) specific fuel consumption, 15.931 MW SOFC power, and 54.759% SOFC efficiency. The exergy analysis highlights the optimization of components like the heat exchanger and fan to reduce energy losses. The sensitivity analysis reveals that the spool speeds and fuel utilization significantly impact the performance. The findings provide valuable insights into optimizing control strategies and offer a novel, efficient, and low-carbon power solution for aviation, supporting the industry’s transition towards sustainability. Full article