Water-lubricated Stern Bearing Research Articles

The Utilization of a Damping Structure in the Development of Self-Adaptive Water-Lubricated Stern Bearings

A novel water-lubricated stern bearing damping structure with self-adaptive performance is proposed to meet the load-balancing and vibration-damping requirements of water-lubricated bearings. This innovative damping structure comprises an elastic element and a damping alloy layer. The elastic element facilitates the static and dynamic load sharing of the stern bearing, mitigates the edge effects, ensures even distribution of the contact pressure along the axial direction, and enhances the overall bearing performance. Consequently, it prolongs the service life of the bearing and minimizes friction-induced stimulation. The damping alloy layer effectively attenuates the transmission of shafting vibrations to the foundation through the bearing, optimizing the vibration transmission characteristics. Leveraging the finite element model, an in-depth analysis of the compensation capability of the turning angle and damping performance of the adaptive stern bearing was conducted. The findings reveal that when the thickness of the elastic element is increased from 10 mm to 40 mm, the maximum contact pressure can be reduced by 12.53%. When the length ratio of the elastic element is reduced from 0.7 to 0.4, the maximum contact pressure is reduced by 12.42%. Therefore, increasing the thickness and decreasing the length of the elastic element in the adaptive damping device enhance the load performance, improve the compensation capabilities, and reduce the bearing wear, thereby promoting greater bearing uniformity. Furthermore, the adaptive vibration-damping device optimizes the vibration transmission characteristics from the propeller stimulation to the bearing node. The computational results demonstrate a noteworthy reduction in the speed, acceleration, and displacement responses at the first-order natural frequency, decreasing by 58.82%, 58.90%, and 58.86%, respectively. This substantial reduction in the vibration response at the first-order natural frequency signifies the effective mitigation of vibrations in the system.

Experimental research on lubrication and vibration characteristics of water-lubricated stern bearing for underwater vehicles under extreme working conditions

This paper aims at the demand of underwater vehicles for low noise, low vibration, high load capacity, and long service life water-lubricated stern bearing (WSB). A test bench was used to conduct a series of experiments to study lubrication and vibration characteristics for three test bearings with different bushing materials and structures. There are three main tests: specific pressure (0.55 MPa–0.95 MPa), environment temperature (26 °C–58 °C), flow rate (2 L/min ∼10 L/min). Friction torque, water temperature, load capacity, and vibration acceleration signal were acquired by a torque meter, a load sensor, two thermometers, and two acceleration sensors during the test for each bearing. The experimental results indicate that the modified polyurethane bearing has the best comprehensive performance under extreme working conditions. Specific pressure and environment temperature have a significant influence on bearing performance. Under the rotational speed is 60 r/min, the growth rate of friction coefficient of modified polyamide bearing is 366.63% during the increase from 26 °C to 58 °C. The effect of flow rate on both fully grooved and partially grooved bearings is limited. Moreover, the fully grooved bearings have the characteristic of “critical specific pressure” due to the poor capacity of water film, which needs to pay more attention to bearing performance. The experimental research results provide an important reference for the material and structure design and performance test scheme of WSB.

Experimental study on the distributed lubrication characteristics of full-size water-lubricated stern bearings under hull deformation

A full-size test rig of water-lubricated stern bearing (WSB) with an elevation adjustment device was built. High-precision wireless telemetry device obtained four film pressure signals. Six eddy current sensors were adopted to measure the axis orbit. The effect of bias load, rotational speed, and hull deformation on bearing lubrication characteristics are systematically studied. Experimental results showed the distribution lubrication characteristic of WSB at the axial direction. The WSB lubrication region can be divided into the three sub-regions in the middle and both ends of the bearing. Three lubrication sub-regions have different take-off speeds. Under the bias load, the negative pressure was found in the film pressure distribution. The hull deformation affects the position and area of each lubrication sub-region, changing the loads carried by the water film and asperity contact. Research results have a great contribution to WSB optimization structure design.

Analysis of the Tribological and Dynamic Performance of the Self-Adapting Water-Lubricated Stern Bearing

According to the design requirements of load equalization and vibration reduction for the stern bearing, a water-lubricated stern bearing with self-adaptation capacity is proposed. The bearing is mainly composed of three parts: the bearing bush, the elastic element, and the damping alloy. The elastic element is used to realize static and dynamic load sharing of the stern bearing, reduce the edge effect of the stern bearing, and make the contact pressure evenly distributed in the axial direction, thereby improving the service life of the bearing and reducing the frictional excitation of the bearing. Damping alloy is used to attenuate the shaft vibration transmission from the bearing to the foundation to optimize the vibration transmission characteristics. The revised lubrication models for such bearings are put forward. By analyzing the vibration characteristics of the stern bearing, the results show that the vibration transmission characteristics of the thruster excited to the bearing node are optimized, and the vibration response at the first-order fixed frequency is significantly reduced. A moderate increase in the support stiffness of the foundation can significantly reduce the vibration response of the bearing.

Film-Thickness Identification Method and Lubrication Characteristic Experiment of Full-Size Water-Lubricated Stern Bearing under Offset Load.

Water-lubricated stern bearing (WSB) is a vital part of the ship propulsion-shaft system, and it is of great significance to monitor and analyze its lubrication status through film thickness data to improve the equipment operational reliability. In this paper, a full-size, large length-to-diameter ratio WSB experiment is carried out, and multi-sectional journal displacement data are collected under offset load. Accordingly, a bearing film-thickness identification model is established, which can identify the dynamic film thickness data in the circumferential direction of bearing section by limited measurement points. On this basis, the film thickness distribution of the full bearing is obtained by combining finite element (FE) simulation and particle swarm optimization (PSO) algorithm. The effect of different speeds on the distributed lubrication characteristics of WSB under offset load was systematically analyzed based on film thickness data. Results show that the maximum identification error of the bearing film-thickness identification model is less than 7%. The bearing lubrication state changes dynamically as the speed increases, and the hydrodynamic lubrication effect in the middle of the bearing is enhanced. The area of each lubrication sub-region varies nonlinearly. Research results are instructive for further determine the service life of the shaft system.

Influences of bidirectional shaft inclination on lubrication and dynamic characteristics of the water-lubricated stern bearing

This paper investigates the lubrication and dynamic characteristics of water-lubricated stern bearing (WSB) under service conditions. A test scheme of bearing film pressure distribution and spatial shaft position is proposed. The experiment reveals the pressure bias and bidirectional shaft inclination phenomenon of full-size WSB, according to which the transient fluid–solid coupling dynamic model of the bearing is established, considering bidirectional shaft inclination and lining deformation. The calculation method of 16 dynamic coefficients is proposed. Influences of eccentricity ratio, shaft inclination angle, and bearing structure parameters on lubrication and dynamic characteristics are explored systematically. Results indicate that the rotating shaft produces apparent horizontal deflection during the working condition of low speed and heavy load. Under the existence of attitude angle, the horizontal and vertical shaft inclinations both affect the film thickness and pressure distribution, especially at low eccentricity ratio, the horizontal shaft inclination has a greater impact on the bearing. As the length to diameter ratio increases or as the clearance ratio decreases, the effect of vertical shaft inclination on lubrication and dynamic characteristics of the bearing decreases, and that of horizontal shaft inclination increases. Research results are instructive for further study on the effect of misalignment on the structural design and optimization for such bearings.

Study on Lubrication Performance of Composites Water-Lubricated Stern Bearing

Stern bearings are the main supporting part of ship stern shafts. Water-lubricated stern bearings have the advantages of compact structure, easy maintenance, no waste and no pollution, and. Water-lubricated stern bearing materials are generally non-metallic materials, which are easy to produce elastic deformation when working. Based on this, fiber resin matrix composite materials are selected as water-lubricated stern bearing materials, and the Fluid-Structure interaction numerical method is used to research the lubrication performance of water-lubricated stern bearings, which is verified by the test with water-lubricated stern bearing rig. The effect of rotating speed on the performance of water-lubricated stern bearing under different loads is studied in this paper. The results provide technical and theoretical basis for the study of water-lubricated stern bearings.

A Novel Hydrophilic PVA Fiber Reinforced Thermoplastic Polyurethane Materials for Water-lubricated Stern Bearing

As an important part of the marine propulsion system, the water-lubricated stern bearing has a major impact on ship safety. In order to improve the reliability of water-lubricated stern bearing under actual working conditions, hydrophilic PVA fibers were added to a typical water-lubricated bearing material, the thermoplastic polyurethane (TPU), to fabricate TPU/PVA fiber composites. The sliding friction-wear test, under water-lubricated conditions, of the TPU composites/QSn7-0.2 friction pairs were analyzed using a designed testing apparatus. The friction coefficients, worn surfaces and the wear losses from the test samples were examined. The results revealed that the addition of appropriate hydrophilic PVA fibers can effectively improve the tribological properties of TPU materials. The hydrophilic PVA fibers not only improved the affinity and the material surface storage ability to water medium but also absorbed water and formed swelling convex texture under water environment, thereby enhanced the hydrodynamic lubrication effect. When the mass fraction of PVA fiber reached 15 % or more, the debris gathered under the action of loading and fiber connection, formed solid lubrication film. Thus, it effectively improved the self-lubrication performance of the material. But that is not conducive to the tribological performances of the composites when the mass fraction of PVA fiber reached 30 %. Generally, the materials with 15 % to 20 % PVA fiber content showed better tribological properties under the experimental conditions. This work provides a new idea for the research of new water-lubricated bearing materials.

Simulation and experimental investigations on water-lubricated squeeze film damping stern bearing

In order to solve the contradiction between high load-carrying capacity and low natural frequency in designing ship water-lubricated stern bearing, an idea of independent design of load carrying and vibration reduction functions was proposed, and the squeeze film damper technology was innovatively introduced into a conventional water-lubricated stern bearing (CWSB) to form a water-lubricated damping stern bearing (WDSB). Harmonic responses of two bearings were calculated, and a dynamic characteristic experiment was carried out. The results show that the maximum displacement response (MDR) decreases with the increase in oil film clearance. With the increase in inner flange height, MDR increases first and then decreases. MDR decreases first and then increases with the increase in distribution angle. As rotation rate speeds, the difference between two bearings’ Root Mean Square (RMS) vibration amplitude remains unchanged. As load increases, relative reductions of two bearings’ maximum amplitude and RMS decrease. Amid a load of 0.2 MPa and a rotational speed of 200r/min, compared with CWSB, the maximum amplitude of WDSB in the vertical direction is reduced by about 71.8%, and the relative reduction in RMS is about 47.8%, which verifies the damping effect of WDSB is remarkable.

Water-Lubricated Stern Bearing Rubber Layer Construction and Material Parameters: Effects on Frictional Vibration Based on Computer Vision

The frictional vibration generated in water-lubricated rubber bearings operating under low speed, heavy load, startup and shutdown conditions can severely degrade the reliability and the sheltered performance of underwater vehicles. The rubber layer of the ship stern tube water-lubricated rubber bearings is easily elastically deformed under certain loads, which affects the damping performance of the bearing system. To explore the effects of thickness, hardness, and concavo-convexity on the damping property of water-lubricated rubber stern bearings, frictional force, vibration, noise, and displacement and deformation of the contact area were studied using a test rig with a transparent glass cylinder. An orthogonal L9(3)4 test design was applied accordingly to determine the optimum construction and material parameters of the rubber layer. Orthogonal test results indicate that among rubber layer hardness, thickness, and test block concavo-convexity, the former is most significant in terms of the frictional vibration, followed by the thickness and, finally, the radius of the surface. When the hardness is 65 A, the thickness is 12 mm, and the plate type is concave, the frictional vibration performance of the rubber layer is optimal. More important, based on the static deformation and the dynamic displacement of the rubber, the causes of the frictional vibration and the influence of different materials and structural parameters on frictional vibration were visually analyzed. The overall trends and the mechanism discussed in this research may be considered as a guideline for the design, optimization, and manufacture of water-lubricated bearings.

Research on the influence of the normal vibration on the friction-induced vibration of the water-lubricated stern bearing

During the slow voyage of ships, the friction-induced vibration noise often occurs in the contact region of the water-lubricated stern bearing and the tail shaft. The lateral vibration can impact the normal motion of the contact surface, then change the dynamic friction force, finally affect the behaviour of the friction-induced vibration. By adding the movement of the stern shaft journal into the normal load description of the dynamic friction, the equation of friction-induced vibration considering the effect of normal vibration was established. Then the effect law of normal vibration on friction-induced vibration was discussed by numerical simulation and test. The results show that the normal vibration would make the friction-induced vibration appear quasi-periodic, chaotic trend, and narrow the speed range in which the noise of friction-induced vibration appears.

Optimal Method of Selection of Water Lubricated Rubber Bearing Materials

Excellent material can improve the function of water lubricated stern bearing. According to the material properties and the theory of operational research, the mathematical model of the optimal selection material of water lubricated rubber bearing is established. The condition of selecting materials is discussed. The expression of the maximum value is obtained by using software. The influence of material properties on the objective function is discussed.

Influence of Stern Shaft Inclination on the Cooling Performance of Water-Lubricated Bearing

The water film model of the marine water-lubricated stern bearing was established by FLUENT. The influence law of water flow rate on the cooling performance of water-lubricated bearing was studied in consideration of the stern shaft inclination. It will be helpful to improve the performance of marine water-lubricated stern bearing and both security and reliability of propulsion system. The simulation results show that the increase of cooling water flow rate in a certain range can effectively reduce bearing temperature. The bearing temperature rises sharply with thinning of water film thickness which is caused by the increase of inclination angle. Larger inclination angle can deteriorate the operating reliability of bearing.

Numerical Calculation and Analysis of Water-Lubricated Stern Bearing Considering Elastic Hydrodynamic

The deformation of marine water-lubricated stern bearing which the lining materials are polymer materials is much bigger than the bearing built with metal materials. So, in order to improve the calculate accuracy of elastic hydrodynamic, it is necessary to consider the deformation of the lining. Both pressure and thickness distributions of water film which contrasts with the hydrodynamic lubrication are presented by the Reynolds equation, and combining with the elastic deformation of the stern bearing solved by using the finite element method theory. The result shows that the stern bearing water film pressure of elastic hydrodynamic lubrication is lower than that of hydrodynamic lubrication, while the water film thickness is larger.