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Purpose: This paper aim to take the ship shaft stern bearing as the research object, and studies the influence of journal axial vibration on bearing dynamic characteristics under different misaligned angles and rotation speeds. Design/methodology/approach: Computational fluid dynamics (CFD) and harmonic excitation method were used to build bearing unstable lubrication model, and the dynamic mesh technology was used in calculation. Findings: The results indicate that journal axial vibration has a significant effect on bearing dynamic characteristics, like maximum oil film pressure, bearing stiffness and damping coefficients, and the effect is positively correlated with journal misaligned angle. The effect of shaft rotation speed and journal axial vibration on bearing dynamics characteristics are independent; they have no coupling. Bearing axial stiffness is mainly affected by the journal axial displacement, bearing axial damping is mainly affected by journal axial velocity and they are positively correlated with the misaligned angle. The influence of rotational speed on bearing axial stiffness and axial damping is not obvious. Originality/value: This paper establishes the bearing dynamic model by CFD and harmonic excitation method with consideration of cavitation effect and analyzing the influence of journal axial vibration on the dynamic characteristics. The results are benefit to the design of ship propulsion shaft and the selection of stern bearing. Also, they are of great significance to improve the operation stability of the shaft bearing system and the vitality of the ship. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2022-0337/ [ABSTRACT FROM AUTHOR]

Conventional numerical models struggle to accurately capture the whirling vibration characteristics of ship propulsion shafting due to the influence of multi-source uncertainties and gyroscopic effects. Hence, this study develops nonparametric modelling to incorporate multi-source uncertainties into the dynamic equations for shafting. Based on random matrix theory, these uncertainties are represented by random matrices for mass, damping, gyroscopic moment, and stiffness. The whirling frequency under different uncertainties is analysed, revealing that stiffness significantly influences on whirling frequency, followed by mass. Conversely, the gyroscopic moment has the most negligible impact. The range of the first four-order whirling frequencies is estimated accurately using confidence intervals. Additionally, the bearing vibration response is calculated by considering gravity, unbalanced force, and misalignment force. The findings suggest that the time-domain waveform fluctuates within a defined range when considering uncertainty, and unbalance and misalignment are exacerbated, leading to poor stability. Finally, a vibration signal acquisition experiment and modal testing are conducted using a test bench. The experimental results further confirm the effectiveness of nonparametric modelling that considers multi-source uncertainties and gyroscopic effects as more accurate. • The study investigates the whirling characteristics of ship propulsion shafting. • Describing multi-source uncertainty in numerical models using random matrix theory. • The effect of different matrix uncertainties on whirling characteristics is analysed. • The experiment verified that the nonparametric method can better reflect the actual. [ABSTRACT FROM AUTHOR]

Field inspection is a traditional way to detect the problem of shaft imbalance or abnormal vibration in a ship propulsion system; however, the ship cannot execute any tasks or activities during calibration. This study develops a human-machine monitoring interface (HMMI) to estimate vibration abnormalities and implement an intelligent active balance correction to the propulsion system online. In this study, Arduino IDE, InduSoft, and LabVIEW are used to create a function monitored by HMMI. By comparing the abnormal vibration amplification of the moment of inertia, HMMI calculates the correct mass to reduce the vibration. The experimental results show that, after HMMI carries out continuous active balance correction online, the correction rate achieves 105.37%. This indicates that HMMI can calculate the amount of imbalance and phase angles and drive a counterweight to the correct balance position while the device is still operating [ABSTRACT FROM AUTHOR]

Aiming at the problems existing in the method of using sensors to detect the rotor position of marine main propulsion motor at low speed, a sensorless rotor position identification method based on high-frequency pulse vibration signal is proposed. In this method, the low-pass filter is used to separate the high-frequency signal component, and the current component of d-axis to q-axis is demodulated. The control mode of PI action law is used to phase-locked processing of the demodulated signal, in which purpose is to obtain the rotor position signal. The design method is simulated and verified by MATLAB/Simulink software. The error between the estimated position and the actual position of the rotor in the simulation waveform is small, and the accuracy is high. The simulation results show that this method can achieve good results when applied to the ship electric propulsion system without position sensor, which provides a theoretical reference for the design of marine main propulsion motor control system. [ABSTRACT FROM AUTHOR]

The propulsion shafting is one of the main excitation sources of ship vibration and noise. Thus, shafting vibration and alignment are very important issues in the design of a propulsion system. In the present paper, the effects of shafting alignment on shafting whirling and bearing vibrations will be discussed. This study has been carried out experimentally on a test rig designed by the Wuhan University of Technology (WHUT). The results indicated that in design conditions, the effects of shafting alignment on both vibrations are mainly in the horizontal direction. It was found that both shafting whirling and bearing vibrations can be effectively reduced by adjusting the shafting alignment. However, compared to the vertical direction, the vibration in the horizontal direction can be more effectively reduced. Also, the minimum values of whirling vibration and bearing vibration are not in the same shafting alignment state. In addition, the effect of shafting whirling vibration on bearing vibration was little. Also, the bearing vibration changes little when the shafting rotation speed is between 90 and 300 r/min. Finally, it was found that at high rotation speeds, the bearing supporting performance is significantly affected by the shaft whirling effect. [ABSTRACT FROM AUTHOR]

Ship's propulsion shafting is one of the main sources of ship vibration and noise. The shafting, whirling vibrations, and alignment are important factors that affect the comfort, stability, and reliability during a ship's navigation. However, the mechanism of the interacting of the both factors is not fully revealed. In this paper, the effect of shafting alignment on whirling vibration and the bearing temperature response is studied by experiment. The test scheme is designed reasonably according to the theoretical analysis. The results show that the horizontal component of the shafting whirling vibration can be effectively reduced by adjusting the shafting alignment state while the vertical component is not. The shafting axis balancing position (SABP) slightly moves upward in high speed, which should be considered in the dynamic alignment design of the shafting, especially for the high-speed shafting. Little ABSB (the angle between the shafting centre line and the No. 1 bearing centre line) is beneficial to the stable operation of shafting, while appropriately increasing the ABSB and bearing load is beneficial to reducing the shafting whirling vibration. By balancing the relationship between bearing load and ABSB, the performance of whirling vibration and bearing temperature response can be optimized. [ABSTRACT FROM AUTHOR]

In this paper, flexural vibration and power flow transmission of a ship propulsion shafting structure are analyzed via energy principle description in conjunction with Rayleigh–Ritz procedure, in which the shafting vibration displacement is constructed as a superposition of Fourier series and boundary-smoothing supplementary functions. Effect of the distributed bearing support and thrust loading of propulsion shafting system is considered in terms of potential energy of system Lagrangian. Numerical examples are presented to demonstrate the reliability and effectiveness of the established model by comparing results with those from finite element method. Results show that the current model can deal with the vibration analysis of ship propulsion shafting with thrust loading and distributed bearing very well. Influence of boundary restraints, stiffness of distributed bearings, and thrust loading on vibration characteristics of ship shafting system is studied and addressed. Numerical study on power flow analysis is also conducted to investigate the characteristics of vibrational energy transmission in such practical structure. Results show that the stiffness of spatial bearing support has significant influence on vibrational energy transmission and thrust force will greatly affect the total input power into such structure. [ABSTRACT FROM AUTHOR]

With the development of ship enlargement, the problems of coupling vibration between hull and propulsion system and vibration transmission via bearings are more and more prominent. Based on the theory of shaft vibration and the experimental system for dynamic characteristics of the shaft, an experiment plan about propulsion shaft vibration under dynamic excitations is designed in this paper. The performance of propulsion shaft vibration under hull deformation excitations applied on intermediate and stern bearings is studied. Hydraulic excitations in horizontal and vertical directions on the intermediate bearing and stern bearing of the experimental model of propulsion shaft are considered in this paper to simulate hull deformation on bearings of the ship. Vibration characteristics of the shaft under different excitations are gained and coupling effects are discussed. Moreover, the influences of amplitude and direction of excitations on bearings and the shaft rotation speed on the vibration of propulsion are studied. The results show that aiming at improving the safety and reliability of navigation, the hull deformation, especially the horizontal hull deformation excitation on the intermediate bearing, is not neglectable and should be considered during primary design. Also, rotation speed and resonant frequency are needed to be well designed with the frequencies of hull deformation excitations. [ABSTRACT FROM AUTHOR]

The propulsion system is one of the main sources of ship vibrations. A typical propulsion system consists of an engine, a shaft line and a propeller. In order to estimate the vibration levels of a ship propulsion system, analytical methods are still relevant in the preliminary ship design stage. In this paper, three analytical procedures for the vibration analysis of a ship shafting system are presented. The shafting system dynamic behaviour is simulated by reducing the problem to two-, three-, and multi-mass models. Propeller and engine damping is taken into account. Differential equations of motion for the two- and the three-mass models are solved analytically. In the case of the multi-mass model, Rayleigh's quotient and the Galerkin method are used for free and forced vibration analysis, respectively. Since the first natural mode of the shaft line is dominant, the problem can be reduced to a single d.o.f. in the modal space and solved analytically. For all three models, relatively simple formulae for the engine torque transfer factor to the intermediate shaft are derived. The presented procedures are validated by a comparison with measurements. The comparison indicates the high accuracy of the proposed procedures. [ABSTRACT FROM AUTHOR]

The article discusses a key problem of ship propulsion system vibration diagnostics, which concerns assessing this part of mechanical energy transmitted from the main engine to the ship propeller which is dissipated due to propeller shaft vibration. A simplified calculation model is proposed which allows the total energy of the generated torsional vibration to be assessed from the shaft deflection amplitude measured at the mind-span point between the supports. To verify the developed model, pilot tests were performed on the laboratory rotational mechanical system test rig. In those tests, cyclic bending moment was applied to a unified (cylindrical) material sample, which modelled, at an appropriate scale, structural and functional properties of a real propeller shaft. [ABSTRACT FROM AUTHOR]

In order to investigate the natural vibration characteristics of ship propulsion shafting under uncertainties, the random matrixes of mass, damping, and stiffness are constructed based on a nonparametric approach. The effect of uncertainties on the natural vibration characteristics of ship propulsion shafting is discussed by the distribution characteristics of natural frequency. Meanwhile, the natural frequency identification experiment of ship propulsion shafting was used to illustrate the effectiveness of the nonparametric modelling method. The results show that different levels of uncertainties in stiffness, mass and damping matrixes could be obtained by controlling the divergence parameter. The natural frequency could fluctuate significantly under uncertainties. Furthermore, the uncertainties of stiffness and mass have significant impact on the natural frequency. However, the uncertainty in damping has little influence on it. Therefore, it is essential to consider the uncertainties in the analysis of natural vibration characteristics of the ship propulsion shafting. • The random matrixes of mass, damping and stiffness from the shafting are constructed based on the nonparametric approach. • The influence of uncertainty on the natural vibration characteristics of the ship propulsion shafting is discussed. • Different levels of uncertainty in the stiffness, mass and damping can be obtained by controlling the divergence parameter. • The natural frequency of ship propulsion shafting fluctuates significantly and presents a decreasing trend under uncertainty. [ABSTRACT FROM AUTHOR]

A correctly designed machine is characteristic of low vibration values. However wear processes occur during its operation. They are accompanied by a lack of balance of its rotating parts and elements, which results in non-coaxiality of shafts. For this reason energy and dynamic load resulting from machine vibrations grows. In this case cause and effect are mutually connected by feedback, that inevitably leads to occurrence of a failure. This paper presents results of investigations carried out on the basis of vibration analysis of propulsion systems installed on 207P minesweepers. In view of specific features of their operation it is very important to ensure high level of reliability for them. For this reason was done an attempt to develop a method intended for identifying non-coaxiality of shaft line systems of engines propelling the ships. 16 characteristic features of recorded vibration signals were selected. As any of them has not satisfied criteria assigned to features which unambiguously determine state of reliability of shaft line systems, the investigations have been continued and as a result a novel method for non-coaxiality identification was proposed. The method consists in determining unserviceability clusters and assumes that characteristic features are of a concentrated character. This way a non-coaxiality of main engine shaft lines of 207P minesweepers could be detected. This paper presents the proposed method and results of its application to the case in question. [ABSTRACT FROM AUTHOR]

Rotor-shaft-bearing system is an integral part of the engine and propulsion system of a ship. Ships are subject to water-waves which cause large rigid body motion of the ship hull involving all six degrees of freedom. This large time-varying ship-motion causes parametric excitation to the flexible rotor mounted on the ship, and may generate high vibratory response of the rotor, although fairly balanced. This paper proposes active control of lateral vibration in such rotors with a suitably placed electromagnetic actuator and compares simulated performance (response amplitude and control current) of different control laws, namely, (i) PD, (ii) PID and (iii) two novel control laws inspired by the mechanical models of a viscoelastic semi-solid. Realistic ship motion during sea-keeping conditions is generated by numerically solving the governing differential equations of motion of a ship under the action of water waves, using indigenously developed code. The equations of motion of the discretized rotor continuum subject to forces from conventional bearings, base motion and the actuator are obtained with respect to a non-inertial reference frame attached to the moving rotor base. Multi-objective optimization of control gains is carried out to obtain minimum rotor-disk response at the expense of the optimum control current. Numerical simulations reveal that the novel control law proposed in (iii) is the most efficient in terms of vibration response and control cost. [ABSTRACT FROM AUTHOR]

In the uneven flow field, the propeller excitation is transmitted to the hull along with the propulsion shaft system, which is the main exciting force that causes the structural vibration of the ship. A dynamic model to study the transverse vibration of the coupled system of the shaft and submerged conical-cylindrical shell was developed using an analytical method. Flügge equations of motion and beam theory were used to describe the motion of the shell and the shaft, respectively. The boundary conditions and continuous conditions of the shaft and the shell were given. Continuous conditions of the shaft and the shell were established at the bearing joint. The accuracy of the model was verified by FEM/BEM. The effects of fluid, excitations and bearing stiffness on the transverse vibration characteristics of the coupled system of the shaft and submerged conical-cylindrical shell were discussed. The results showed that bearing stiffness has a great impact on the transverse vibration of shaft and hull and make their vibration tend to be consistent when it increases. • An analytical method to study the vibration of the shaft-hull system was developed. • The vibration responses of the numerical model match well with the FEM/BEM. • Effects of the fluid, excitations and bearing stiffness were discussed. • Bearing stiffness has a great impact on the transverse vibration of shaft and hull. [ABSTRACT FROM AUTHOR]