Shaft System Research Articles

Evaluating the safety of the redesigned shafting system following the propeller redesign aimed at enhancing CII and EEXI

In July 2023, the International Maritime Organization (IMO) set a target to achieve net-zero greenhouse gas emissions by 2050, introducing key measures such as the Energy Efficiency Design Index (EEDI), the Energy Efficiency Existing Ship Index (EEXI), and the Carbon Intensity Indicator (CII). The maritime industry explored adaptations, including engine de-rating, energy-efficient technologies, and propeller modifications, and beyond. This study assessed the safety implication of a redesigned shafting system, resulting in a propeller redesign to enhance the CII and EEXI on a 6500 TEU container ship built in 2006. Through an analysis of annual output per TEU from 2000 to 2015, the study focused on container ships built from 2005 to 2007 with high-output engines (9.4–9.5 kW/TEU). After selecting a sample ship, the study determined engine power limits according to the EEXI regulations and assessed their impact on the CII. Subsequently, the study redesigned the shafting system, performing torsional vibration calculations and shaft alignment analyses to ensure the safety of the modified system. While an enhanced CII rating was predicted, the tightening CII regulations imply this benefit may be short-lived, lasting approximately two years. Thus, additional measures are essential to prolong the improved CII rating.

Multi-channel deterioration trend prediction of pumping storage unit based on temporal graph convolution network

Abstract The safe and stable operation of pumped storage units is related to the integrity of the power grid, and it is necessary to study the prediction of unit deterioration trends. Traditional degradation trend prediction methods are mostly for single channel, without considering the interaction between different channels of the shaft system. Therefore, a multi-channel degradation trend prediction model for pumped storage units shaft system is proposed. Firstly, the healthy model is obtained by constructing the mapping relationship between the working parameters and the swing of the shaft system through the fully connected network. Secondly, the deterioration trend sequence of each channel is calculated based on the historical monitoring data of each channel of the unit shaft system and the corresponding healthy model. Finally, the correlation coefficient analysis method is used to calculate the correlation between each channel, and the temporality of the degradation sequence of each channel and the correlation between channels are learned through the spatio-temporal graph convolutional network to realize the prediction of multi-channel degradation trends. The proposed model is verified by using the data of a pumped storage power station. The results show that the proposed model can accurately predict the multi-channel deterioration trend.

Study on the influence of vibration characteristics of ship’s stern structure

The stern structure of the ship, as the primary source of vibration and noise, has always been widely studied. Conducting an analysis of the vibration characteristics of the stern and determining the impact of local structures on the complex coupled vibration in the stern section are particularly important aspects of research. This paper employs the structural-acoustic coupling methodology to investigate the vibration features of the stern of a ship. The study explores the influence of variations in parameters such as the rudder, stern frame, and shaft system on the vibration response of the stern. The results provide valuable insights into controlling vibration and noise in the stern section of ships, as well as informing the design of related structures.

Study on the coupling vibration characteristics of vertical unit and plant of large underground pumping station for water transfer project

Abstract To investigate the coupled vibration characteristics of vertical pumping unit and plant structure of large underground pumping station for water transfer project, the coupled vibration differential equations are established. The structure nodes of are simplified from horizontal direction and vertical direction respectively by force. The structural parameters and load parameters of the model are analyzed and calculated, and the vibration response of each node are calculated by solving the vibration differential equations. A spectral analysis of white noise is applied to the coupled model, and the natural frequencies and vibration structures of dominant vibration modals are obtained. Research indicates that the vertical vibration modes of the system exhibit a relatively low coupling degree with the plant structure. The shaft system and the plant structure mainly display combined vertical vibrations, while the plant structure predominantly exhibits independent vertical vibrations. This implies that vertical vibrations are jointly influenced by shaft system stiffness and plant structure properties. In horizontal vibration modes, a strong coupling characteristic is observed between the upper structure of the pump station unit and the plant structure. This is primarily manifested as coupled vibrations between the support and the plant structure, which are collectively influenced by support constraints, shaft system stiffness, and plant structural properties.

Analysis of oil film flow characteristics and lubrication performance of thrust bearing of 1000MW Hydraulic Turbine Unit

Abstract Hydro-generator unit is the core component of the hydropower station, and the stability of the shaft system directly determines the safety of the hydropower station. Thrust bearing is the only component to bear axial load, and working performance directly affects the stable operation and efficiency of the unit. In this study, a full 3D model of the shaft system of a 1000 MW hydro-generator unit is established, and the oil flow of thrust bearing oil film and oil in the oil tank considering the spray system and the overall model is analysed by means of the thermo-hydrodynamic method. The results show that the load increases with increasing inclination angle. Within certain limits, the pressure and temperature of the oil film increase with increasing inclination. And there are many vortices in the tank. Although the spray system reduces the oil churn, the lubricating oil flow between pads is chaotic. The loss is mainly caused by the chaotic flow between pads. Analyzing the effects of oil film thermal effects on bearing loads, lubricant flow, and bearing surface temperatures of tilting pads provides valuable insights for bearing design and maintenance guidance.

Modal analysis of tripod-ball type universal coupling composite transmission shaft system

Abstract In order to improve the dynamic performance of the tripod-ball type universal coupling composite transmission shaft system, ANSYS Workbench modal analysis is carried out. By modal analysis of the transmission shaft system, the vibration characteristics of the coupling have been obtained, which can avoid its natural frequency in practical situations. The figures for the first ten modes have been obtained. The results indicate that the areas with the greatest deformation are on the intermediate shaft, bell housing, and trident sleeve. This provides a theoretical basis for further research on the transmission shaft system.

Multivariate iterative nonlinear chirp mode decomposition: principles and applications

Abstract The rotor-bearing system (RBS) of a hydroelectric unit includes multiple components such as the rotor, rotor shaft, coupling, turbine, and main shaft. There is a strong coupling relationship between the vibration signals of multiple bearing sections. At the same time, the vibration signal of the RBS contains rich frequency components, which can effectively reflect the operating state of the shaft system of the unit. Therefore, synchronous signal analysis across multiple rotor bearing sections is required to completely grasp the operating status of the unit. In this study, the Multivariate Iterative Nonlinear Chirp Mode Decomposition (MINCMD) is proposed to analyze signals on multiple sections simultaneously. MINCMD follows the step-by-step extraction idea of Adaptive Multivariate Chirp Mode Decomposition (AMCMD), but it adopts a new algorithm framework by modifying the objective function. Furthermore, AMCMD does not converge well without a good initial instantaneous frequency (IF). Therefore, a method based on parameterized demodulation (PD) is introduced in MINCMD to solve the multi-channel frequency initialization problem. The effectiveness of the proposed algorithm is verified through a simulation test and real data from hydroelectric units.

Research on the excitation force and vortex dynamics characteristics of pump-jet propulsor induced by shafting whirling vibration: Non-uniform blade tip clearance

The propulsion shafting whirling vibration causes non-uniform dynamic changes in the rotor tip clearance, which directly have a significant influence on the excitation force and vortex dynamic characteristics of the pump-jet propulsor. In the current study, based on improved delay detached eddy simulation, the influence of non-uniform blade tip clearance on the excitation force and vortex dynamics characteristics of the pump-jet propulsor is studied under design conditions. The results show that the application of propulsion shafting whirling vibration induces significant changes in the excitation force of the pump-jet propulsor. The rotor blades modulate the excitation forces of the stator blades and duct. The transverse and vertical excitation forces are more significant than the longitudinal excitation force. The magnitude change in the circular orbit shows a linear relationship with the excitation force magnitude. The characteristic frequency of the transverse and vertical excitation forces of each component is the shaft rotation frequency. In contrast, the characteristic frequency of the longitudinal excitation force is twice the shaft rotation frequency. In the elliptical orbit, the excitation force of each component is compressed or stretched in the time domain, and the dominant frequency is shifted in the frequency domain; there is no longer a linear relationship between the vibration magnitude change and the excitation force magnitude. Furthermore, an energy generation mechanism in the wake field of the pump-jet propulsor induces vortex frequency due to the whirling vibration of the propulsion shafting system.

Longitudinal low-frequency vibration control of a propeller-shafting system using a hydraulic leveraged dynamic anti-resonance vibration isolator: A theoretical and experimental study

The longitudinal fluctuating forces of a propeller are a major cause of sound radiation of an underwater vehicle in the low frequency range. A hydraulic leveraged dynamic anti-resonance vibration isolator (HLVI) is proposed to attenuate the longitudinal vibration of a shaft system transmitted to the hull. The semi-analytical model of the shafting system with and without the isolator is set up by employing the frequency response synthesis method, in which the elasticity of the foundation is taken into consideration. Compared to the traditional isolation scheme and DVA, the proposed control scheme will not change the longitudinal effective stiffness and needs a small mass to attenuate the longitudinal vibration of the shafting system. A parametric study was conducted to investigate the key parameters of the isolator and their impact on its isolation performance. An experimental apparatus is set up to validate the isolation scheme. The acceleration frequency response results of the shafting system under axial excitation with both the frequency sweep method and discrete sinusoidal frequencies are presented and discussed. The results indicate that the proposed method is capable of attenuating the corresponding longitudinal vibration of the shafting system.

Influence of Unbalance and Differential Pressure on the Stability of Vertical Rotor-Seal System

Abstract The rotordynamic (RD) fluid force generated in fluid elements such as seals in turbomachinery affects the stability of turbomachinery and causes shaft vibrations. Various studies have been conducted to clarify the effects of seals on the stability of rotor systems. Many studies have investigated the rotor dynamics of horizontal rotating shaft systems, considering the RD fluid force generated in the seals, and in these studies, the stability of horizontal rotating shaft systems has been assessed via eigenvalue analysis using RD coefficients. However, few studies have analyzed vertical rotating shaft systems. The dynamic behavior of vertical rotating shafts differs significantly from that of horizontal rotating shafts because the weight of the rotor does not act on the seal in a vertical rotating shaft system. Vertical rotating shaft systems are generally prone to instability because of the fluid film whirl, and the amplitude of the shaft whirl tends to be large. When the amplitude is large, the RD fluid force cannot be linearized around the equilibrium point using RD coefficients. Therefore, destabilization and stabilization phenomena that appear in vertical rotating shaft systems cannot be predicted using eigenvalue analysis. Fluid–structure interaction (FSI) analysis that considers the interaction between the shaft vibration and the RD fluid force generated in seals is required to predict such phenomena. This study used FSI analysis to investigate the effects of unbalance and differential pressure on the stability of a vertical rotating shaft system subjected to RD fluid force generated in the seal.

Transient dynamic stress behavior analysis of the axial flow pump as turbine at part loads

To explore the structural dynamic characteristics of the impeller and shaft system of the axial flow pump as turbine, the variation law of impeller transient equivalent stress, deformation, and the impeller and shaft system mode are analyzed by the transient fluid-structure interaction method. Findings indicate that the equivalent stress is centralized at the blade root around the hub and tends to decrease as it moves towards the shroud. The maximum equivalent stress at 1.0Qbep and 1.1Qbep is 1.26 times and 2.0 times higher than that at 0.8Qbep. Blade deformation is significantly influenced by flow rate. The maximum deformation of the blade at 1.0Qbep and 1.1Qbep is 1.6 times and 3.6 times higher than that at 0.8Qbep. The impeller and shaft system with prestress in dry mode has an average natural frequency of the first 10 orders that is 16.7 Hz higher than without prestress. However, with the fluid adding mass and flow damping, the average natural frequency of the first 10 orders of the impeller and shaft system in wet mode is reduced by 278.08 Hz compared with dry mode. In fact, the impeller and shaft system of the axial flow pump as turbine is not prone to vibration.

Stress analysis under centrifugal load of the multiple corrugated diaphragm coupling based on rotating shell thin film model

Centrifugal force is one of the factors that cannot be ignored in high-speed shaft systems. The multiple corrugated diaphragm (MCD) Coupling is suitable for high-power and high-speed situations; hence, it is crucial to investigate the stress and deformation of the wave disc under centrifugal load. This paper first uses the rotating shell thin film model to derive the circumferential stress and deformation displacement of the MCD under centrifugal load. Then, the finite element method is used to verify the results obtained from the analytical solution. The results show the feasibility of using the rotating shell thin film model for centrifugal load analysis of the MCD, providing a new approach for the theoretical analysis of the MCD.

Shaft fatigue estimation based on characteristics of transient torsional vibration for propulsion shafting system according to variation of passing time in barred speed range

Shaft fatigue estimation based on characteristics of transient torsional vibration for propulsion shafting system according to variation of passing time in barred speed range

Experimental Research on Dynamic Characteristics of a Multi-Disc Rotor System Supported by Aerostatic Bearings

Gas bearings have the advantages of small friction loss, wide applicable speed range, no pollution, etc., and have important application prospects in micro and small high-speed rotating machinery. However, due to its compressibility and low viscosity, its dynamic stability in high-speed rotating machinery is the key to constraining its development. The experimental study of shaft system dynamics is the main means to explore the mechanism of rotor behavior. On the test platform of dynamic characteristics of multi-disc rotor system supported by aerostatic bearings, experimental research on the nonlinear dynamic characteristics of a rotor system was carried out, and nonlinear vibration test and analysis methods, such as axial orbits, bifurcation diagrams, and spectral characteristics, were adopted, and vibration phenomena, including the critical rotational speed accumulating energy and low-frequency accumulating energy, were presented and the vibration characteristics of bearing fracture faults were presented. The bearing supply pressure and rubber damping pad were introduced as a method to suppress the low-frequency vibration of the aerostatic bearing rotor system, and its vibration-reduction effect was verified by experiments. The above results can provide technical support for vibration control and fault diagnosis of rotor systems supported by aerostatic bearings.

System Identification and Dynamic Analysis of the Propulsion Shaft Systems Using Response Surface Optimization Technique

Marine vessels rely heavily on propeller shaft systems to adjust the engine torque and propeller thrust. However, these systems are subjected to various dynamic excitations during operation, such as transverse, longitudinal, and torsional excitations. These excitations can arise from factors like non-uniform stern flow fields, misaligned components, and the whirling motion of the shafts, which can affect the integrity and reliability of the vehicle. To analyze the dynamic response of the propulsion shaft system and ensure its reliability, numerical/analytical models are currently in practice. The finite element method (FEM) is a popular choice, but uncertainties in bearings and connectors stiffness lead to inaccuracies in the Finite Element model, resulting in significant differences between the experimental and theoretical models. This paper proposes the response surface optimization (RSO) technique to estimate unknown bearing stiffness in the propulsion shaft system. The experimental model of the propeller shaft system is constructed using steady-state response with step sine excitation. The RSO technique is then used to update the natural frequencies and vibration amplitude of the FE (Finite Element) model. The updated model shows less than a 10% difference in natural frequencies and vibration amplitude compared to the experimental model, demonstrating that the proposed technique is an efficient tool for marine shaft dynamic analysis.

Predicting propeller emergence severity in adverse sea conditions: An integrated approach using stacked machine learning models

In adverse sea conditions, variations in the propeller submergence depth can induce ventilation and out-of-water effects. These effects result in propeller-torque and thrust losses, impacting the shipboard power network's reliability and accelerate wear on propulsion shaft system. Ensuring the stability and safety of sailing ships necessitates predicting the occurrence and severity of ventilation and out-of-water effects. This, in turn, enables the implementation of a switching strategy with a fast response for propulsion control. Nonetheless, existing methods can only identify current propeller ventilation states, mainly categorised as ventilation and non-ventilation, or more elaborately, as full ventilation, partial ventilation and non-ventilation. These methods, however, face a critical limitation—they cannot predict the severity of ventilation or the out-of-water effect, leading to ineffective propulsion-control-strategy switching. This study proposes a method for predicting propeller emergence severity (that is, non-emergence, light emergence and severe emergence) under wave conditions. This method introduces a novel approach for establishing propeller emergence states and a sophisticated stacked model. The new method categorises different propeller emergence states for diverse classifications based on the maximum emergence severity that the propeller can develop. This to overcome the challenges in predicting the development of the ventilation severity and the out-of-water effect. The innovative stacked model helps improve the overall prediction performance of a single intelligent algorithm. Finally, using simulation experimental data, it is verified that the propeller emergence severity method has satisfactory effectiveness and accuracy. The proposed method provides crucial technical support for the efficient switching of propulsion control strategies in electric propulsion systems when ships are navigating under adverse sea conditions.

Research on the Calculation Method for the Load Distribution of the Dual-Input Counter-Rotating Transmission System

In order to solve the problem of an uneven load distribution in a double-input and double-output gearbox, based on the small-displacement Jacobi spin theory and considering the manufacturing and assembly errors of the gearbox, a Jacobi spin analysis model of the gearbox was established. In order to improve the accuracy of the three-dimensional tolerance analysis of the gearbox, on the basis of the processing method of parallel chain of gears and shafts and box and shafts, the serialization method of parallel chain of meshing gear pairs is proposed, and the gearbox was established. For the three-dimensional tolerance analysis model, three-dimensional tolerance analysis was carried out on the side-clearance dimensions of double-input and double-output gearboxes, and the side clearance values under the extreme value method and Monte Carlo method were deduced and combined with the theoretical side clearance to obtain the range of the side clearance of the gearboxes. Elastic deflection analysis was carried out on the gearbox shaft system, and the compensation relationship between the elastic deflection and the side clearance was investigated, so as to calculate the range of the value of the gearbox uniform load coefficient from 1 to 1.259. The error between the theoretically calculated uniform load coefficient and the experimentally tested uniform load coefficient was 6.61%, which verifies the reasonableness of the load distribution method of double-input and double-output gearboxes calculated using three-dimensional tolerance analysis combined with the elastic deflection angle, and provides a theoretical basis for the optimal design of the uniform load of multi-branch input gearboxes.

Study on Torsional Vibration Response Characteristics of Marine Propulsion Shafting

_ The paper establishes the lumped parameter vibration mathematical model of shafting and uses the system matrix method to calculate and analyze steady-state frequency domain vibration characteristics of the shaft system in the range of diesel engine speed. Then in order to further study the transient torsional vibration of the shaft system under the resonance speed point, the state space method and finite element analysis method were used to compare and analyze the transient time domain response characteristic curve of the shaft system; finally, the test data of the real ship was compared with the theoretical calculation results, which verified the correctness of the mathematical model and the theoretical calculation method. This study has certain theoretical significance for carrying out the design of low-noise and vibration of shaft systems and improving the safety of ship navigation. Keywords shafting torsional vibration; transient time domain; finite element method; vibration test

Assessing health risks from cooking oil fume leaks in residential cooking exhaust shaft system

Kitchens in multi-floor and high-rise buildings utilize shared cooking exhaust shaft systems (CESS) to exhaust cooking oil fumes (COF) outside. On each floor shaft, a backdraft damper is installed to control the COF flow. However, residents may be exposed to particulate matter pollution when COF in the shaft leaks through the dampers and infiltrates non-cooking kitchens (NC Kitchens). Previous studies rarely considered the airtightness of dampers and their impact on the health of non-cooking residents. Therefore, a multizone network model was used to simulate PM2.5 concentrations in NC Kitchens with different airtightness dampers, and the health risks to people in NC Kitchens were assessed. Measures to reduce health risks were analyzed. Results indicate that, for 33- and 18-floor CESS under high diversity, utilizing good dampers led to inhalation cancer risks exceeding 1 × 10−6, signifying potential health hazards. Conversely, the 6-floor CESS demonstrated negligible health risks. For 33- and 18-floor CESS, dampers with air leakages of 100 and 140 m3/(h·m2) at 250 Pa static pressure, respectively, are advised. Additionally, expanding the shaft dimensions from 500 mm × 400 mm to 700 mm × 700mm and 400 mm × 300mm to 400 mm × 600mm respectively, ensures health in NC Kitchens. These findings hold importance in improving damper airtightness, optimizing CESS performance, and safeguarding non-cooking residents’ health.

Methodology for Evaluating a Distributed Variable-Camber Trailing-Edge System in Preliminary Aircraft Design

A controlled adjustment of the wing camber during cruise flight by an extension of each separate flap allows for wing shape optimization, depending on the current mission point including the prevailing conditions, contributing to an increase in efficiency. This is referred to as variable camber (VC). This paper aims to investigate a methodology for a retrofit application of VC technology with differential flap setting, especially for a segmented trailing-edge system at the overall aircraft level in the preliminary design phase. In addition, an assessment is conducted to clarify whether actuation on the basis of a central shaft system or a decentralized power-by-wire system is advantageous. The investigation is based on a commercial aircraft with a maximum takeoff mass of 270 t and compares the potential of a VC application with an aerostructural twist optimization of the wing. Different configurations of the trailing-edge flaps, ranging from a common two-flap configuration up to a configuration with six trailing-edge devices, are covered in order to give a holistic implementation recommendation, including actuation and flap segmentation. Depending on the reference aircraft, the study shows a considerable fuel-saving potential for VC applications, e.g., 3.5% for the pre-optimized reference on a long-range mission.