The fluid inertia effect on the behavior of an elastic ring squeeze film damper (ERSFD) becomes significant at high whirl frequencies. However, the existing literature on the ERSFD lacks a comprehensive lubrication model concerning the fluid inertia. This study aims to establish a lubrication model for the ERSFD, taking into account the inertia effect by using the average velocity method. The temporal and convective inertia effects on the inner oil film force are analyzed under different operating conditions. The result shows that the temporal and convective inertias should be considered for the modeling of ERSFD, especially at large eccentricity ratios or high whirl frequencies; the oil film force of the ERSFD with the attitude angle exhibits a unique periodicity due to the action of bosses. This study is the first comprehensive investigation on how the temporal and convective inertias affect the ERSFD's behavior.

PurposeThe elastic ring squeeze film damper (ERSFD) is a key element of the high-speed rotor system in aero-engine. By far, the dynamic characteristics of ERSFD has not been investigated throughout. The purpose of this study is to investigate the dynamic behaviors of the ERSFD oil films considering the fluid inertia effect with using the perturbation method.Design/methodology/approachThe perturbation equations for the ERSFD, including the journal's acceleration perturbations, are derived by using the Taylor series expansion, and a comparative study of the oil film dynamic behaviors between the perturbation method and the parameter identification method is conducted.FindingsThe dynamic coefficients of ERSFD exhibit periodic change during an entire circle of whirling; the dynamic coefficient of the inner oil film is an order of magnitude larger than that of the outer oil film; the cross-coupled coefficients of the ERSFD's oil film cannot be disregarded; the fluid inertia effect can increase the direct stiffness and damping coefficients.Originality/valueThe perturbation method can be used to calculate the complete dynamic characteristics of the ERSFD with the attitude angle, including the direct and cross-coupled dynamic coefficients. This work contributes to existing knowledge of ERSFD by providing a detailed analysis of dynamic coefficients.

The hydrodynamic herringbone groove journal bearing (HGJB) performs exceptionallywell at high speeds but is limited by a low load-carrying capacity, largely due to the lubri-cation characteristics of water. To address this issue, a hybrid water-lubricated HGJB isproposed in this study. A lubrication model for the high-speed hybrid water-lubricatedHGJB is developed, taking into account turbulence, thermal effects, and tilt. A comparativeanalysis of the static characteristics is conducted between the hybrid HGJB and both thehydrodynamic HGJB and the hybrid plain journal bearing (PJB). The results show thatthe proposed hybrid water-lubricated HGJB offers significantly greater load-carryingcapacity than the conventional hydrodynamic HGJB, particularly during start-up or atlow speeds. For example, when the bearing operates at 1000 rpm with an eccentricityratio of 0.5, the load-carrying capacity of the water-lubricated hybrid HGJB under asupply pressure of 1.6 MPa reaches 650 N, compared to just 261 N for the water-lubricatedhydrodynamic HGJB. Additionally, the hybrid water-lubricated HGJB demonstrates ahigherflowrate and lower temperature rise than the traditional hybrid PJB, thanks to theimproved pumping effect of the herringbone grooves at high speeds.

Shear-thinning effect of pure oil and distribution of bubble size are essential factors affecting the viscosity of bubbly oil. This study aims to establish an improved equivalent viscosity model for bubbly oil by considering the shear-thinning effect and the bubble distribution effect. Based on the equivalence principle of frictional resistance, the viscosity of pure oil considering the shear thinning effect is derived; based on the energy conservation principle, the viscosity increment due to bubble deformation is derived. A series of experiments, including generation of bubbly oil, bubble observation, and measurement of bubble oil viscosity, are conducted to validate the model established. The simulated and experimental results indicate that the improved equivalent viscosity model of bubbly oil is more accurate than the traditional model. Notably, the effect of oil shear thinning on the equivalent viscosity is much more obvious than the effect on the distribution of bubble size.

Abstract Equivalent viscosity is a basic parameter of the bubbly oil, however, it is a controversy whether or not the bubble surface tension should be taken into account when modeling the equivalent viscosity of bubbly oil at high shear rate. In this technical brief, the effect of bubble surface tension on the equivalent viscosity of bubbly oil is examined experimentally using the proof by contradiction. The viscosity of bubbly oil is measured using test samples with clearances in series, and the bubble distributions of the bubbly oil before and after tests are observed. The test result shows that at a high shear rate, the equivalent viscosity of bubbly oil is not sensitive to the change in the sample clearance, whereas the bubble distribution after test is dependent on the clearance, suggesting that the effect of bubble surface tension can be disregarded for the equivalent viscosity of bubbly oil at high shear rate.

Elastic ring squeeze film damper (ERSFD) is an effective damping element for the aero-engine, but the existing literature lacks comprehensive research about the fluid-structure interaction (FSI) and fluid inertia on the behavior of ERSFD. This study investigates the FSI and inertia effects on the static and dynamic characteristics of ERSFD. The Reynolds equation for the ERSFD considering the fluid inertia and the elastic deformation equation for the elastic ring are established to analyze the dynamic and static characteristics of the ERSFD. The result indicates that the influence of fluid inertia on the dynamic and static characteristics of the ERSFD is more significant than that of the FSI effect; the inner oil film pressure is an order of magnitude larger than the outer oil film pressure, suggesting that the damping capacity of the ERSFD comes from the inner oil film rather than the outer oil film.

In order to study the profile formation of photoresist microstructure (such as microlens) by the thermal reflow method, the viscoelastic dynamic model is developed based on motion equation, continuity equation, and thin film assumptions. The influence of viscoelastic properties, surface tension, as well as crosslinking effect on polymer melt profile evolution, are considered in this model, and the Oldroyd-B model is used to describe the viscoelastic constitutive relation of polymer melt. Since the viscoelastic dynamic model developed in this paper is a differential equation with regard to the height function of the polymer melt profile, the free surface profile of polymer melts can be obtained naturally during shape evolution by numerically coupling the solution of the film thickness equation and the Oldroyd-B constitutive equation. The computational efficiency of numerical simulation of the free-surface profile would be improved by using this equation as compared to solving the highly non-linear equations of viscoelastic hydrodynamics. The influence of key parameters such as baking time, baking temperature, and crosslinking effect on profile shape evolution is analyzed by this model, and the materials are compared by assigning them different Weissenberg number. In addition, the maximum relative error of verification experiments between the final profile predicted by the simulation and the experimental results is less than 10 %.

Water-lubricated hydrodynamic spiral-grooved bearings enable motorized spindles to achieve very high rotational speeds. Nevertheless, because water provides substantially lower viscous damping than oil, maintaining the dynamic stability of spindles supported by these bearings remains a critical challenge that demands immediate attention. A five-degree-of-freedom nonlinear rotor–bearing model was established for the proposed motorized spindle by coupling the rotor dynamic equations with the equivalent Reynolds equations of the hydrodynamic spiral-grooved bearings. The model was employed to evaluate spindle stability and cutting-force responses. A prototype spindle and a dedicated test rig were fabricated to characterize the system’s dynamic behavior experimentally. Finally, the dynamic stability of the new spindle was compared with that of a reference spindle with plain journal bearings (PJBs). Numerical simulations show that the logarithmic decrement of the proposed motorized spindle remains positive throughout the entire speed range up to 30 000 rpm, confirming dynamic stability. The calculated cutting-force response exhibits a strictly monotonic decay, indicative of a well-damped transient. Compared with the reference spindle with conventional plain journal bearings, the water-lubricated, hydrodynamic spiral-grooved bearing spindle demonstrates markedly superior stability. The results demonstrate that the motorized spindle with water-lubricated hydrodynamic spiral-grooved bearings exhibits outstanding dynamic stability and superior impact resistance.

Purpose The water-lubricated hydrodynamic herringbone groove journal bearing (HGJB) is capable of running at high speed. However, when running at a low speed, it suffers from a low load-carrying capacity due to the weak hydrodynamic effect. To overcome this problem, this study proposes a hybrid water-lubricated HGJB and aims to investigate its dynamic characteristics. Design/methodology/approach A hybrid lubrication model applicable to the hybrid water-lubricated HGJB is established based on the boundary fitted coordinate system, which considers the turbulent, thermal and tilting effects, and the finite difference method is used to calculate the dynamic characteristics of the hybrid water-lubricated HGJB. Findings The result shows that the hybrid HGJB has larger dynamic coefficients and better system stability compared with the hydrodynamic HGJB when running at low speed. Furthermore, the stiffness of hybrid HGJB are mainly governed by the hydrodynamic effect rather than the hydrostatic effect when running at high speed. Originality/value The proposed hybrid water-lubricated HGJB shows excellent dynamic characteristics at either low speed or high speed; and the hybrid water-lubricated HGJB has a large load-carrying capacity when running at low speed and has a good dynamic stability when running at high speed. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-06-2024-0233/

In this paper, a combined transport-defect evolution multiscale model describing the generation and the evolution of microstructure damage in silicon carbide (SiC) induced by focused helium ion beams is developed. In the proposed model, the transport of helium ions and displaced atoms in the SiC substrate and the generation of point defects are described by the Boltzmann transport equations, while the subsequent defect evolution is characterized by a set of rate equations with the contributions of the modeling of the bubble coalescence as well as the substrate swelling. The validity and superiority of the transport equations are verified by comparing the simulation results with the data from experimental measurements and available simulation methods. The subsurface amorphous profile, onsurface swelling profile, and the spatial and size distribution of helium bubbles in a SiC substrate irradiated by focused helium ion beams are simulated using the proposed multiscale model. The damage morphology simulated by the proposed model is in good agreement with the transmission electron microscopy images at different beam energies and doses. This work provides an effective tool for full-stage modeling of complex evolutionary mechanisms of microstructure damage induced by precise and high-throughput helium irradiation.

Bubbly oil lubrication is a type of lubrication method. However, the lubrication model of the bubbly oil has not been thoroughly considered. This paper aims to investigate the modelling for bubbly oil lubrication considering the interfacial effect and thermal effect, and a theoretical model is established based on the theory of multiphase mixtures. The interfacial and thermal effects on the static characteristics of a thrust bearing are analyzed. A test rig for the thrust bearing is developed to measure the static characteristics of the bearing under bubbly oil lubrication. The results show that the bearing static characteristics, i.e. bearing temperature rise, film thickness, friction torque, and volume flow, increase with consideration of three interfacial effects; the bearing temperature rise increases but the film thickness, friction torque, and volume flow rate decrease with consideration of the three thermal effects; the thermal effect on the bearing static characteristics is greater than the interfacial effect.

Cavitation is prone to occur in high-speed water-lubricated journal bearings. However, the effect of cavitation on the dynamic characteristics of high-speed water-lubricated journal bearings has not been studied thoroughly. This study focuses on this topic. A thermohydrodynamic (THD) cavitating lubrication model was established for the high-speed water-lubricated journal bearings, including the generalized Reynolds equation, the energy equation, and the force balance equation for bubbles. An equilibrium distribution was introduced to describe the cavitation effect, and parameters were obtained by fitting the measured volume distribution of bubbles. The dynamic characteristics of the water-lubricated journal bearings were calculated, considering the influence of thermal and cavitation effects. An experimental setup was developed to validate the proposed model. The simulated results show that two secondary temperature peaks appear in the divergence zone of the bearing due to the cavitation effect. The cavitation effect should be considered when establishing the model for high-speed water-lubricated journal bearings, especially if it is under a large eccentricity ratio.

The thermal evolution of defects introduced in silicon by line scanning with helium ion microscopy was investigated, confirming that the evolution of the defective structure after annealing at 650 degrees C for 1 h results in a central void channel and a sector ring of cavities surrounding it, located in the amorphous and transition regions of the unannealed pre-irradiated sample, respectively. The variation of defective structures with annealing temperature and ion dose indicates that high temperature is favorable for the formation of void channels and cavities, and the coarsening and recrystallization processes compete in the shaping of a void channel. The total volume of the defective structure is linearly related to the ion dose, while the zoning phenomenon is attributed to the differences in the vacancy amounts within their locations. These results provide direct experimental evidence for the thermal evolution of defects with zonal characteristics induced by precisely localized helium irradiation.

A multiscale model describing the evolution of helium bubbles in the irradiated materials is established based on the rate equations and the population balance equation. The size distribution of the helium bub-bles and the evolution law of the statistical average size and number density of the bubbles with time changing predicted by the model are in good agreement with the experimental statistics. The influence of annealing temperature, annealing time, irradiation energy, irradiation flux, and coarsening mechanisms on the evolution of helium bubbles are numerically simulated and discussed, taking FeCrAl alloy as the irradiated material. The results show that the bubble evolution is dominated by the Ostwald ripening mechanism under high temperature annealing conditions ( >= 1073 K), and the time dependence of the average size and density of helium bubbles is consistent with the existing theoretical results. And the number of shrinking helium bubbles caused by Ostwald ripening is effectively reduced by the bubble co-alescence effect, leading to further growth of the proportion of large-sized helium bubbles. Consequently, a Gaussian bubble size distribution has been obtained modeling the coupling of the Ostwald ripening mechanism and the bubble coalescence mechanism. The generation rates of helium and vacancy in the material during irradiation, as well as their ratio, are significant factors that can affect the nucleation and evolution of helium bubbles. (c) 2022 Elsevier B.V. All rights reserved.

For China’s welding vocational training equipment backward, research and development of multi-functional stir friction welding equipment for teaching and research. Through experimental research found that, under the premise of ensuring constant axial pressure（0.5 kN）,in the case of a small n/v value（n/v=6, n/v=4）, the weld core area, the shoulder zone and heat-affected zone at the junction of the three easy to appear hole-type defects, when the n/v increased to 8 and above, no visible defects inside the weld, the reason is mainly due to the n/v value is small resulting in heat Input is too low resulting in poor mobility of thermoplastic aluminum alloy in the junction area; also found that compared to the constant displacement control method, the use of constant pressure control method of welding the weld surface is smooth and flat, the amount of flying edge and the absence of surface defects, research and development of teaching and research equipment to meet the practical training of vocational education in welding, and successfully applied to teaching and research work.

Bubble evolution and shear thinning effect are main factors affecting lubrication behavior of bubbly oil. In this study, a thermohydrodynamic lubrication model for the bubbly oil considering the bubble evolution and the shear thinning effect was established based on the multiphase mixtures theory. The influence of bubble evolution and shear thinning effect on the static behavior of bubbly oil lubricated bearing was analyzed, and an experimental study was conducted to verify the model. The result shows that the bubble radius is mainly dependent on the liquid pressure; the bearing static behavior is affected by the bubble evolution through the interface effect; the shear thinning effect of the pure oil can be enhanced with regarding the bubble evolution effect.

This paper aims to investigate the lubricating performance of the bubbly oil. Due to space limitation, the work is divided into two parts. Part 1 concluded that the bubbly oil under high shear rate has a lower viscosity than the non-aerated oil, and the air volume fraction can be adjusted conveniently to reach a high value. Based on this, in Part 2, we intend to explore the feasibility of using the bubbly oil in lubricating high-speed bearings. Here, we select a step thrust bearing as object and analyze its static characteristics under the bubbly oil lubrication. A test rig for the high-speed step thrust bearing was developed to measure the static characteristics of the bearing under the bubbly oil lubrication. The lubrication models for the hydrodynamic step thrust bearing were established to predict the bearing static characteristics. The results show that the static characteristics parameters of the bearing under the bubbly oil lubrication are less than those under the non-aerated oil lubrication, and the differences of static characteristics parameters of the bearing between the non-aerated oil lubrication and the bubbly oil one become larger with the increase of air volume fraction and the external load, especially at a higher speed.

A bubbly oil lubrication model is established in this paper. Interface effect is included in this new model. Two single-component coupled nonlinear generalized Reynolds-type equations are derived based on the theory of multiphase-mixture flow and the second law of thermodynamics. The static characteristics of the finite journal bearings with bubbly oil lubrication are predicted using this theoretical model. The results show that the friction torque is significantly reduced compared to pure oil lubrication at a higher initial bubble volume fraction, and the sidle leakage are significantly increased compared to pure oil lubrication.

The water-lubricated bearings tend to be turbulent and cavitating when running at a high speed. However, the modeling of the water-lubricated bearing considering the turbulence and cavitation effects has not been studied thoroughly. For high-speed water-lubricated journal bearings, a turbulent flow model considering cavitation effect was proposed on the basis of two-phase flow theory. The simulation was conducted to show the influence of turbulence and cavitation effects on the static characteristics of the water-lubricated journal bearing. The proposed model was validated with the test by using a self-developed experimental setup. The result shows that the turbulence effect has a great impact on static characteristics of bearing, and cavitation effect significantly affects the minimum film thickness and leakage flowrate, while the friction torque is hardly affected by the cavitation effect.