Stern Tube Bearing Research Articles

Frictional Wear Behavior of Water-Lubrication Resin Matrix Composites under Low Speed and Heavy Load Conditions.

Resin matrix composites are commonly utilized in water-lubricated stern tube bearings for warship propulsion systems. Low-speed and high-load conditions are significant factors influencing the tribological properties of stern tube bearings. The wear characteristics of resin-based laminated composites (RLCs), resin-based winding composites (RWCs), and resin-based homogeneous polymer (RHP) blocks were investigated under simulated environmental conditions using a ring-on-block wear tester. Simulated seawater was prepared by combining sodium chloride with distilled water. The wetting angle, coefficient of friction (COF), and mass loss were measured and compared. Additionally, their surface morphologies were examined. The results indicate a significant increase in the COFs for the three materials with an increased speed or load under dry conditions. The COF of the RLCs is the lowest, indicating that it has superior self-lubricating properties. In wet conditions, the COFs of the three materials decrease with an increasing speed or load, exhibiting a pronounced hydrodynamic effect. The COF and mass loss of RWCs are the highest, while RLCs and RHP exhibit lower COFs and mass loss values. The reticulated texture and flocculent fibers on the surface of RLC enhance the heat diffusion and improve the material wettability and water storage capacity. The surface of RWC is dense, and the friction area under dry conditions is melted and brightened. The surface of RHP is smooth, while the worn material forms an agglomerate and exhibits susceptibility to burning and blackening under dry conditions. The laminated formation method demonstrates superior tribological performance throughout the wear evolution process.

Influence of Propeller–Ice Loads on the Wear Development in Stern Tube Bearings of Marine Propulsion Systems and Identification of Critical Operating Conditions

Abstract Increasing ship traffic in ice-covered waters leads to more frequent collisions between ship propellers and sea ice which causes extreme impulse loads on the propeller. These loads are transferred through the propeller shaft to the sliding bearings of the stern tube, especially, the aft stern tube bearings. Extreme bearing loads can lead to mixed friction regimes that cause wear in the bearings and eventually result in a failure of the entire propulsion system. The effect of ice-induced loads on the contact conditions in the sliding bearings is widely unknown. Thus, a study of the influence of these loads on the contact conditions and wear behavior in stern tube bearings resulting from observed sea ice conditions and operating conditions of the ship is necessary. This article aims to investigate the influence of ice collision loads on the contact conditions in the bearings of the stern tube of the research vessel SA Agulhas II. For this purpose, an elastohydrodynamic simulation and a multibody simulation based on field measurements were performed. As a result, this article identifies the operating condition thresholds (i.e., propeller torque and rotational speed) during propeller–ice collisions that cause mixed friction conditions in the bearings. On the basis of these conditions, a risk map is generated to assess the actual wear risk by including the frequency of occurrence of the corresponding mixed friction condition over the duration of a voyage.

Tribological evaluation of thermoplastic polyurethane-based bearing materials under water lubrication: Effect of load, sliding speed, and temperature

Polymers are widely used in bearing applications. In the case of water-lubricated stern tube bearings, thermoplastic polyurethane (TPU)-based composites are used due to their excellent wear resistance, corrosion resistance, and tunable mechanical properties. Their tribological performance, however, depends on operating conditions. In this work, TPU was blended with carbon fiber, graphene platelet, and ultra-high molecular weight polyethylene (UHMWPE). Friction tests of TPU based-composites against copper countersurface were carried out in water to mimic the actual operating conditions of the bearing. Most of the resulting contacts were in the boundary lubrication regime, in which friction was attributed to both contact mechanics of asperities as well as water lubrication. Our results show that the viscoelasticity of TPU has a considerable impact on its tribological performance. Water lubrication at 50 °C promotes the softening of polymer surface material during sliding, resulting in higher fluctuation in the coefficient of friction and wear loss. This is attributed to the reduced thermomechanical properties. In addition, Schallamach waviness is observed on worn surface. The tribological properties of TPU are significantly improved by the inclusion of carbon fiber, graphene platelet, and UHMWPE. The formation of graphene transfer-layers and UHMWPE transfer film reduces friction and wear loss, while the inclusion of carbon fiber enhances wear resistance due to improved mechanical properties and load bearing capacity.

Utjecaj ekscentrične porivne sile na odabir statvenog kliznog ležaja

Stern tube slide bearing of the shaft line of the ship's propulsion system causes losses during operation. Friction and material wear of the tribosystem occur. One of the reasons is the different navigating regimes of the ship, which have an influence on the formation of the velocity field on the ship's propeller. The variable velocity field defines the magnitude and the position of the thrust force. The methodology presented in this paper is based on the fact of the existence of the eccentricity of the thrust force, i.e. loads due to the action of the moment of the eccentric thrust force. Due to the changing position of the thrust force, the curvature of the elastic line of the sleeve inside the stern tube bearing, which is mostly spatial, changes. Spatial elastic line of the sleeve has an influence on the working area of the slide bearing. Therefore, the importance of a sufficient thickness of the lubricant layer for lubrication in relation to these changes was highlighted. In this paper, this is the initial criterion for the selection of materials and lubricants of the stern tube bearing. An equally important criterion would be to define the possible harmful impact of lubricant leakage with particles of bearing bush material on the ecosystem. In order to facilitate the whole process, the simplified analytical model is presented, which can be used in the initial stage of stern tube bearing selection. Such a model allows a simpler analysis of the influence of the elastic line on the condition of the stern tube bearing due to the loading by the weight of the ship's propeller and by the moment of the eccentric thrust force. The procedure for the initial selection of the stern tube bearing created by this methodological approach could have its practical application. For this reason, the paper analyzed different navigating regimes and their influence on the working area of the stern tube slide bearing. The obtained results can be useful in the selection of materials and lubricants for the stern tube bearing tribosystem.

Effect of Groove Structure on Lubrication Performance of Water-Lubricated Stern Tube Bearings

This study investigated the lubrication characteristics (i.e., the groove ratio and width) of water-lubricated stern tube bearings, based on the flexibility matrix method and lubrication theory. Considering the elastic deformation of the lining, a fluid structure interaction (FSI) model of the surface micro-groove texture of a water-lubricated stern tube bearing was established, and the correctness and rationality of the model were verified by experiments. Micro-grooved, surface-lubricated, water-lubricated stern tube bearings with three different cross-sectional shapes (rectangular, circular, and triangular) were designed. The influences of the groove area ratio and width on the bearing load-carrying capacity and friction coefficient were analyzed. At a groove area ratio of 0.31, the load-carrying capacity of the rectangular grooved stern tube bearing reached the maximum value and the friction coefficient reached the minimum value. It is recommended to design and use water-lubricated stern tube bearings, especially Thordon water-lubricated stern tube bearings, with rectangular micro-grooves, with a groove area ratio of 0.30–0.32, so that the best lubrication performance can be obtained. With the increase in the micro-groove width, the lubrication of water-lubricated stern tube bearings with partial rectangular micro-grooves is significantly better than that of others. Under the same conditions, the bearing load-carrying capacity and friction performance of local groove stern bearings is significantly better than that of global groove stern bearings.

Numerical Analysis of the Mixed-Lubrication Performance of Staved Stern Tube Bearings Lubricated with Water

The present study aims to establish a mixed lubrication model for staved stern tube bearings lubricated with water, in which the average Reynolds equation and a KE elastic–plastic contact model are introduced to calculate the hydrodynamic pressure and contact pressure, respectively. The difference in the mixed lubrication behaviors between circular- and flat-staved bearings is compared; moreover, the effects of the number of staves on the mixed-lubrication performance of these two kinds of staved bearing are investigated. The mechanism of action of the number of staves in staved bearings on the mixed-lubrication performance is revealed. The numerical results show that the number of staves has a significant effect on the mixed-lubrication performance in circular- and flat-staved bearings. Furthermore, there is an optimal value for the number of staves, shown to be 30 in the current simulation, for improving the mixed-lubrication performance of flat-staved stern tube bearings lubricated with water.

Comparative Wear Test of Journal Sliding Bearings with Sintered Bronze and Babbitt Alloy Bushes Lubricated by Environmentally Acceptable/Adapted Lubricants (EAL)

A growing awareness of the negative effects of mineral oils on the natural environment has resulted in the introduction of new regulations related to environmental protection. One of these regulations requires the use of environmentally acceptable/adapted lubricants (EAL) to lubricate marine main shaft bearings, in place of the mineral lubricating oils that have been used for decades. Classification Societies, which supervise the technical condition of ships, record a certain number of failures each year of heavy loaded stern tube bearings lubricated with modern, environmentally friendly lubricants. The reason often given for such failures is that the operating parameters of EAL lubricants are worse than those of mineral oils. The aim of the experimental research reported here was to compare the operating parameters and wear of EAL lubricated journal sliding bearings. For this purpose, two classic mineral lubricating oils and a group of four alternative lubricants from the EAL group were selected. The tests carried out for two types of bearing bushes—sintered bronze and Babbitt—did not show significant differences in terms of operating parameters or journal and bush wear for the entire group of tested lubricants.

Asymptotic estimation of the fluid film pressure in non-metallic water-lubricated staved stern tube bearings

An analytical approach based on the asymptotic technique is applied to estimate hydrodynamic pressure in lubrication film of water-lubricated stave bearings with length/diameter ratio L/D> 1. Circular staves and flat staves with aligned and misaligned journals have been considered. Explicit small physical parameter (0.5D/L)2 < <1 is used for asymptotic series to solve the boundary value problem. Analytical results have been derived in the three first approaches on the small parameter and compared with the numerical results based on FEM calculations. Comparison of the results showed that difference in the results do not exceed 25 % for the maximum pressure, however at the same time value and variation of the pressure field strongly depend on the staves kind, eccentricity and misalignment of the journal.

Changes in Propeller Shaft Behavior by Fluctuating Propeller Forces during Ship Turning

It is known that a ship’s shafting system can be adversely affected by hull deformation, variations in the engine power, the propeller load, and eccentric propeller thrusts, thereby increasingly affecting the behavior of the shaft’s movement. A deformed shafting system may also lead to a potential risk of bearing damage by causing a change in the local load of the rear part of the after-stern tube bearing of the propeller shaft. With this concern, a series of previous studies were focused on optimizing the effects of hull deformation by securing a proper level of propulsion shaft stability and optimizing the relative inclination angle and oil film retention based on a quasi-static state, that is, Rules for the Classification of Steel Ships and experiences of shipyards. However, despite our efforts to resolve this issue, marine accidents involving stern tube bearing damage have continued to occur under relatively unattended ship motions in a transient state, that is, a quasi-static state that can possibly cause sudden stern flow field changes. Therefore, to improve the stability of the propulsion shaft, it is necessary to understand ship motions and the conditions of shafting systems in a dynamic state and a transient state when the system is designed. From this point of view, this study investigated the effect of changes in eccentric propeller forces on the motion of the propeller shaft in a representative transient state of a 50,000 deadweight tonnage tanker by means of the strain gauge method and a displacement sensor. The research findings demonstrate that propeller thrust fluctuations have a direct effect on the shaft stability by significant changes in the shaft motion that can lead to unbalanced supporting loads on the stern tube bearing. These results clearly reproduce the cause of damage to the ship in which the accident occurred at a reliable level and will be a reference for establishing pragmatic guidelines for preventing damage to similar ships in the future.

Technical and Ecological Aspects of Water-lubricated Stern Tube Bearings

A ship's propulsion system has a significant impact on the ship’s energy efficiency, environmental friendliness, reliability and safety. An indispensable part of a propulsion system with mechanical power transmission is a stern tube with bearings. During operation, the sliding bearings material is subjected to stresses caused by a force proportional to the total mass of the shaft and propeller. The reliability of stern tube bearings is particulary important for safety, and their durability has a significant impact on maintenance costs. Depending on the lubricant, there are bearings that are lubricated with oil or water. The permissible bearing load with hydrodynamic lubrication depends primarily on the material, the viscosity of the lubricant used and the shaft speed. Metals and their alloys with a low coefficient of friction are used for oil-lubricated bearings. Bearings lubricated with water are made of a special type of hardwood ("tree of life", lat. lignum vitae), rubber or various synthetic materials. The main advantages of oil-lubricated bearings are higher allowable load and durability than water-lubricated bearings. This paper analyses the technical and environmental aspects of the application of water-lubricated bearings whose main advantages are simplicity, better cooling and environmental protection.

Assessing the Potential Replacement of Mineral Oil with Environmentally Acceptable Lubricants in a Stern Tube Bearing: An Experimental Analysis of Bearing Performance

Abstract This study compares the performance of a plain bearing, with a similar structure to a tail shaft stern bearing, lubricated with either mineral oil or an environmentally acceptable lubricant (EAL). The main characteristic of the bearing is its length/diameter ratio of &lt;1. Measurements are carried out with the bearing operating under loads from 0.5 to 1 MPa and seven speeds ranging from 1 to 11 rev/s. The bearing lubricated with either mineral oil with a viscosity grade of 100 or an environmentally acceptable lubricant (EAL) with a viscosity grade of 100 or 150 is investigated according to the ISO standard. Bearing wear is simulated by increasing the clearance circle by 0.1 mm. According to the results obtained, the use of an EAL in place of mineral oil does not cause significant changes in the bearing performance, regardless of the value of the clearance radius. The pressure distribution in the oil film, bearing load carrying capacity, eccentricity and friction coefficient have similar values for the entire load and speed ranges considered, and the discrepancies in the results are within the range of the measurement errors. Only an increase in EAL viscosity causes significant changes in bearing performance and these changes comply with the general theory of lubrication.

중형 유조선의 프로펠러 추력변동이 축 거동에 미치는 영향 연구

The movement of the propeller shaft shows different changes in each condition, such as static, dynamic, and transient, mainly based on changes in propeller eccentricity due to changes in engine load. In general, this contributes to changing the bearing load of the shaft at the after stern tube bearing, and in severe cases causes damage to the stern tube bearing. To prevent this, various research regarding pragmatic designing on shafting system has been carried out focusing on optimize the relative inclination and retain the oil film thickness between the shaft and the stern tube bearing. However, in order to secure the integrity of the support bearing from damage, it is necessary to additionally consider dynamic conditions including transient conditions such as sudden alteration in the stern wake-field. In this context, this study cross validated the effect of propeller shaft movement during starboard turning of a medium range oil tanker at full laden draft using the strain gauge and displacement sensor. As a result of the analysis, it was confirmed that the propeller thrust fluctuation temporarily increased the load on the stern tube bearing.

A journal bearing performance prediction method utilizing a machine learning technique

A predictive analytics methodology is presented, utilizing machine learning algorithms to identify the performance state of marine journal bearings in terms of maximum pressure, minimum film thickness, Sommerfeld number, load and shaft speed. A dataset of different bearing operation states has been generated by solving numerically the Reynolds equation in the hydrodynamic lubrication regime, for steady-state loading conditions and assuming isothermal and isoviscous lubricant flow. The shaft has been modelled with four different values of misalignment angle, lying within the acceptable operating range, as defined in the existing regulatory framework. The journal bearing was modelled parametrically using generic geometric parameters of a marine stern tube bearing. The lift-off speed was estimated for each loading scenario to ensure operation in the hydrodynamic lubrication regime and the effect of shaft misalignment on lift-off speed has been evaluated. The generated dataset was utilised for training, testing and validation of several machine learning algorithms, as well as feature selection analysis, in order to solve several classification problems and identify the various bearing operational states.

Оценка эффективности методов прогнозирования технического состояния в системах судового валопровода

The article considers an approach to assessing the effectiveness of the most common methods of predicting the technical conditions and failure with reference to the ship shafting. There have been analyzed the main factors in operation of the ship shaft line, which cause the change in its technical state. It has been found that a special feature of some loads acting on the propeller shaft is their stochastic or changing nature over time, which hampers predicting the technical state of the shafting and its units. The features of stochastic and extrapolation forecasting methods have been analyzed. The possibility of using statistical methods in conditions of mass standard production of shafting units with a relatively short regulated service life is estimated. An extrapolation method is proposed for predicting the maximum permissible clearance of stern tube bearings. The case of accumulating samples of measuring results of the propeller shaft sagging in the given time intervals is considered, the approximating functions are constructed. The criteria for the reliability of the results of extrapolation methods for predicting the wear of stern tube bearings are determined. There have been developed the proposals for adapting the causal method as an alternative to the extrapolation method. A schematic diagram of a system for the ship shafting failure predicting has been developed using the registration and analysis of vibration parameters, which serves as the basis for constructing a regression model of damage accumulation. The proposed forecasting system allows studying the actual operating conditions of the shafting, defining the actual external loads and the regularities of their occurrence, measuring deformations and stresses, and determining quantitative indicators of the reliability of the shafting during normal operation and special operating modes, for example, with vibration resonance. The theoretical basis of the algorithm for calculating and registering loads affecting the service life of shafts is proposed.

A Study on Pressure Evaluation in the Stern Tube Bearing

A Study on Pressure Evaluation in the Stern Tube Bearing

Theoretical and experimental exploration on the micro asperity contact load ratios and lubrication regimes transition for water-lubricated stern tube bearing

The paper investigates the micro asperity contact load ratios and lubrication states of the water-lubricated bearing. New coupled models with consideration of micro-scale asperity contact effects are put forward. The relevance of load ratio with transition of lubrication regimes under multi coupled structural parameters and operating conditions are established. The three-dimensional relationships between typical parameters and contact ratio under typical working conditions have been further studied. Characteristic parameters of lubrication regimes transition under multi coupled factors are investigated. The mechanism of regimes transition is revealed at the micro level. Experimental measurements verify the correctness of the revised model. Researches are beneficial for the definition of micro asperity contact load ratio and lubrication regimes transition for such bearings.

37K DWT 석유화학제품 운반선의 선미관 베어링 발열 사고 및 축계정렬에 대한 연구

Together with the emerging of the Eco-ship, the application of large-diameter and high-efficiency propeller required more careful attention than before in the design of the shafting system. After the adoption of Environmentally Acceptable Lubricants (EAL) to the stern tube lubrication oil, a number of aft stern tube bearing accidents have been reported, and a variety of institutions have actively conducted research on the cause relationship. This study attempted to find the cause of the accident by measuring the alignment of the shafting system of a medium-sized product/chemical tanker with aft stern tube bearing damage and analyzing the reaction force of each bearing. In addition, a reasonable solution to the correction of the shaft alignment was suggested and the feasibility was reviewed. Through various measured data and analysis, the actual installation of shafting system was slightly different from the design drawing condition, but it was found that each bearing load distribution was within the allowable range. Therefore, it was confirmed that the cause of this accident was due to the dissatisfaction the misalignment slope of aft stern tube bearing rather than the effect of the bearing overload. As a solution to this cause, countermeasures such as double slope were suggested in the aft stern tube bearing, and the characteristics of EAL also seem to have an indirect effect.

Stick-slip vibration in water-lubricated bearing-shaft system simulated in persistent homology-based machine learning model

Stick-slip vibration images of water-lubricated rubber stern bearing are collected by using machine vision technology. Then these images are analyzed by the methods of persistent homology-based machine learning (PHML). During this analysis, the corresponding barcode is obtained by calculating the homology of the simplicial complex of the vibration images, and the topological characteristics of the vibration images are obtained based on the barcode images, then the support vector machine (SVM) learning is used to study the topological features, and finally the classification and identification of the stick-slip vibration of water-lubricated rubber stern tube bearing are completed. The results have shown that the length of the longest 1D Betti number is closely related to vibration value. Based on these data, it is possible to use the warning beep effectively, create an intelligent description of the beep process, and provide a new idea for simulating stick-slip vibration in the stern bearing.

Study on shaft alignment of propulsion shafting system depending on single reaction force supporting position of aft stern tube bearing

Trends of large-scale ships have seen propulsion shaft and propeller sizes increase. This has enabled shafts to have greater stiffness, yet has caused flexibility to lessen and induce bearing failure at the aft stern tube bearing. In general, shaft alignment is calculated and evaluated in accordance with classification societies’ rule requirements. Especially, positioning reaction support and stiffness of aft stern tube bearing are based on the practical experience of shaft alignment. Therefore, in this study, to evaluate the feasibility of the reaction force supporting position and stiffness of the aft stern tube bearing as recommended by classification societies in shaft alignment, theoretical reaction force supporting positions for various ship propulsion shafting systems were examined and the differences were evaluated. The reaction force supporting position of the aft stern tube bearing provided by classification societies was evaluated and it was found that a propeller shaft diameter less than 600 mm is within the provided range. However, in the evaluated shafting system, a propeller shaft diameter of more than 600 mm tends to cause the ship to move to the forward side due to increased shaft stiffness.

MWCNTs filled high-density polyethylene composites to improve tribological performance

The water-lubricated stern tube bearings play a considerable role in the marine propulsion system. Due to poor mechanical properties and temperature resistance, polymer materials are prone to plastic deformation during friction under extreme conditions, which could induce frictional vibrations and noise. Reducing the coefficients of friction (COFs) and weakening the plastic deformation of the contact surface could significantly decrease its frictional vibrations and noise. A novel composite material composed of high-density polyethylene (HDPE) and multi-walled carbon nanotubes (MWCNTs) was prepared to investigate its tribological properties, which slid against ceramic balls under low velocity and heavy load. The influence of MWCNTs on wear behaviours was examined by comparing and analyzing the mechanical properties, scratch testing results, coefficients of friction (COFs), wear volumes, and wear morphologies. The results indicated that MWCNTs obviously enhanced the mechanical properties of HDPE and weakened the deformation behaviours on the friction interface, which resulted in reductions of COFs and wear volumes under dry and water-lubricated conditions. HDPE modified by 7.5 wt% MWCNTs presented the best COF reduction and wear resistance improvement, and the effect mechanism of the MWCNTs was revealed. The knowledge obtained in this research would be useful to develop polymer matrix composites with low COFs, and good deformation resistance and enhance the tribological properties and frictional vibration reduction ability of water-lubricated polymer bearings.