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Asymmetric rotating machinery supported by oil film bearings is relatively common in practical applications. The purpose of this study is to propose a method for estimating the oil film parameters of the bearings in an asymmetric rotor-bearing system.

The proposed method requires the finite element model and translational displacement responses at the center of mass and bearings locations to form a regression equation to estimate the unknown parameters. Due to the transverse stiffness of the asymmetric rotor is not symmetrical, the analysis and parameter estimation procedures are performed in a rotating coordinate. Numerical simulations were carried out to illustrate the vibration characteristics of the asymmetric rotor system. The proposed method is applied to the simulated responses to estimate the assumed oil film parameters. The influence of the estimated parameter deviations on the rotor dynamic characteristics is discussed.

The vibration characteristics of asymmetric rotors are different from those of symmetrical rotors. The bearing parameters estimated by the proposed method are close to the assumed values, within a maximum error of 9%. The deviations of the estimated parameters have little effect on the vibration characteristic of the rotor system.

The proposed method does not require changing the rotational speed or applying additional excitation force to the rotor, which is suitable for the field test.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-04-2023-0111/

The purpose of this paper is to bridge the gap between the existing theoretical and empirical studies by examining the asymmetric return–volume relationship. Indeed, the authors aim to shed light on the return–volume linkages for French-listed small and medium-sized enterprises (SMEs) compared to blue chips across different market regimes.

This study includes both large capitalizations included in the CAC 40 index and listed SMEs included in the Euronext Growth All Share index. The Markov-switching (MS) approach is applied to understand the asymmetric relationship between trading volume and stock returns. The study investigates also the causal impact between stock returns and trading volume using regime-dependent Granger causality tests.

Asymmetric contemporaneous and lagged relationships between stock returns and trading volume are found for both large capitalizations and listed SMEs. However, the causality investigation reveals some differences between large capitalizations and SMEs. Indeed, causal relationships depend on market conditions and the size of the market.

This paper explains the asymmetric return–volume relationship for both large capitalizations and listed SMEs by incorporating several psychological biases, such as the disposition effect, investor overconfidence and self-attribution bias. Future research needs to deepen the analysis especially for SMEs as most of the literature focuses on large capitalizations.

This empirical study has fundamental implications for portfolio management. The findings provide a deeper understanding of how trading activity impact current returns and vice versa. The authors’ results constitute an important input to build and control trading strategies.

This paper fills the literature gap on the asymmetric return–volume relationship across different regimes. To the best of the authors’ knowledge, the present study is the first empirical attempt to test the asymmetric return–volume relationship for listed SMEs by using an accurate MS framework.

The purpose of this paper is to propose a type of hybrid bearing lubricated with supercritical carbon dioxide (S-CO₂) and to investigate the stiffness and damping characteristics of the bearing under hydrostatic status.

Established a test rig for radial bearings lubricated with S-CO₂ and used it to measure the dynamic coefficients by recording the relative and absolute displacements of bearing. Test bearing is mounted on a nonrotating, stiff shaft. Using static loading experiments to obtain structural stiffness. The dynamic coefficient regularities of the test bearing under hydrostatic status were revealed through dynamic loading experiments.

Experiment results indicate that test bearing displayed increased stiffness when subjected to high excitation frequencies and low excitation forces, as well as elevated damping when exposed to low excitation frequencies and low excitation forces. Additionally, an increase in either environmental pressure or hydrostatic recess pressure can elevate the dynamic coefficient. The effect of temperature on the dynamic coefficient is more pronounced around the critical temperature of S-CO₂.

Designed a type of hybrid bearing for use in the Brayton cycle that is lubricated with S-CO₂ and uses hydrostatic lubrication during start-stop and hydrodynamic lubrication during high-speed operation. The hybrid bearing reduces the wear and friction power consumption of gas bearing. However, few experimental analyses have been conducted by researchers in this field.

The accuracy of the machining process is significantly impacted by the performance of hydrostatic bearings. This paper aims to analyze the influence of micro-textured on the performance of the hydrostatic bearing, and the performance of the bearing is improved by designing the arrangement of micro-textured.

Different designs have been used while creating micro-textured bearings. The finite element models of bearing with smooth and micro-textured were established and solved using the computational fluid dynamics method. The arrangement scheme of the micro-textured was evaluated by comparing the influence of the distribution position and arrangement of the micro-textured on the bearing performance.

To improve the performance of the bearing, the bearing capacity was significantly increased, and the friction coefficient of the bearing was decreased when the micro-textured was distributed in the form of an obtuse angle arrangement in the maximum pressure area of the bearing. The experimental findings validate the analysis method.

In this paper, the effect of irregularly arranged micro-textured on bearing performance is investigated to improve the bearing capacity and lubrication status.

This study aims to improve the tribological properties of hydrodynamic journal bearing via surface texture, as well as the wear and antifriction mechanisms of textured bearing were represented. It provides a design direction for solving the tribological problem of rotor-bearing system.

In this paper, the variation of surface texture parameters (e.g. texture diameter, d; area density, sp; and depth, hp) were analyzed based on finite difference method. The optimal surface texture parameters were obtained by designing orthogonal experiments, and the relationship between friction and wear properties and microstructure was studied via combining electron probe microanalyzer, scanning electron microscope, X-ray diffractometer and friction and wear testing machine.

Dimensionless film pressure P increased as the d increased, whereas P first increased and then decreased as the sp and hp increased, and the maximum P was got as sp = 15% and hp = 25 µm, respectively. The friction coefficient of textured surface with suitable parameters was effectively reduced and the textured surface with the best antifriction effect was 5#. Orthogonal experimental design analysis showed that the influence order of factors on friction coefficient was as follows: sp > sp × d > d > d × hp > hp > sp × hp and the friction coefficient first decreased and then increased as the sp, d and hp increased. In addition, the friction and wear mechanism of textured bearing were three body friction and abrasive wear as the matrix structure and hard phase were a single β phase and Mn5Si3, respectively. While the antifriction mechanism of textured surface was able to store abrasive particles and secondary hydrodynamic lubrication was formed.

The sample with reasonable texture parameter design can effectively reduce friction and wear of hydrodynamic journal bearing without reducing the service life, which can provide a reference for improving the lubrication performance and mechanical efficiency of rotor-bearing system.

The purpose of this research is to study the dynamic behavior of hydrostatic squeeze film dampers made of four hydrostatic pads, fed through four capillary restrictors with micropolar lubricant.

The modified version of Reynolds equation is solved numerically by the finite differences and the Gauss–Seidel methods to determine the pressure field generated on the hydrostatic bearing flat pads. In the first step, the effects of the pad dimension ratios on the stiffness and damping coefficients are investigated. In the second step, the damping factor is evaluated with respect to the micropolar properties.

The analysis revealed that the hydrostatic squeeze film dampers lubricated with micropolar lubricants produces the maximum damping factor for characteristic length of micropolar lubricant less than 5, while the same bearing operating with Newtonian lubricants reaches its maximum damping factor at eccentricity ratios larger than 0.4.

The results obtained show that the effects of micropolar lubricants on the dynamic performances are predominantly affected by the pad geometry and eccentricity ratio.

The primary purpose is to investigate the dynamic relationships among urbanization, energy use and environmental pollution in the context of India from 1971 to 2018. The paper also examines the validity of Environmental Kuznets Curve (EKC) hypothesis in the present Indian context.

The study uses a nonlinear autoregressive distributed lag cointegration test (Shin et al., 2014) to investigate the dynamic relationship among the mentioned variables. The Wald test is also used to statistically check the presence of asymmetry. Additionally, the VECM test is applied to examine the causality among the variables.

This study documents that urbanization in India is good for environment in the long run, whereas energy consumption is bad for the environment. It also finds that positive and negative shocks of energy and urbanization exert asymmetric impacts on ecological footprint. Furthermore, the results could not validate the EKC hypothesis for India.

The outcome of the study suggests designing an environmental policy which considers the nonlinearity of the investigated relationships and bearing in mind the use of comprehensive indicator like ecological footprint is equally important to address the wide-ranging problem of the environment. Policy reorientation towards the production and consumption of green energy, investment in research and development, and use of efficient technology is very crucial to achieve sustainable outcomes in the long run.

In this study, the researchers use the ‘ecological footprint’ variable to obtain a more accurate and comprehensive assessment of environmental deterioration. The mentioned dynamic relationships are investigated using an improved methodology of the NARDL model, which assumes the asymmetric impact of the explanatory variables on the response variable. The novelty of this study lies in examining the non-linear impact of urbanization and energy on ecological footprint which is inadequately addressed in the context of Indian economy.

This study aims to investigate the effects of irregular groove textures on the friction and wear performance of sliding contact surfaces. These textures possess multiple depths and asymmetrical features. To optimize the irregular groove texture structure of the sliding contact surface, an adaptive genetic algorithm was used for research and optimization purposes.

Using adaptive genetic algorithm as an optimization tool, numerical simulations were conducted on surface textures by establishing a dimensionless form of the Reynolds equation and setting appropriate boundary conditions. An adaptive genetic algorithm program in MATLAB was established. Genetic iterative methods were used to calculate the optimal texture structure. Genetic individuals were selected through fitness comparison. The depth of the groove texture is gradually adjusted through genetic crossover, mutation, and mutation operations. The optimal groove structure was ultimately obtained by comparing the bearing capacity and pressure of different generations of micro-convex bodies.

After about 100 generations of iteration, the distribution of grooved textures became relatively stable, and after about 320 generations, the depth and distribution of groove textures reached their optimal structure. At this stage, irregular texture structures can support more loads by forming oil films. Compared with regular textures, the friction coefficient of irregular textures decreased by nearly 47.01%, while the carrying capacity of lubricating oil films increased by 54.57%. The research results show that irregular texture structures have better lubrication characteristics and can effectively improve the friction performance of component surfaces.

Surface textures can enhance the friction and lubrication performance of metal surfaces, improving the mechanical performance and lifespan of components. However, surface texture processing is challenging, as it often requires multiple experimental comparisons to determine the optimal texture structure, resulting in high trial-and-error costs. By using an adaptive genetic algorithm as an optimization tool, the optimal surface groove structure can be obtained through simulation and modeling, effectively saving costs in the process.

For a lightweight and accurate description of bearing temperature, this paper aims to present an efficient semi-empirical model with oil–air two-phase flow and gray-box model.

First, the role of lubricant/coolant in bearing temperature was discussed separately, and the gray-box models on the heat convection inside a bearing cavity were also created. Next, the bearing node setting scheme was optimized. Consequently, a novel semi-empirical two-phase flow thermal grid for high-speed angular contact ball bearings was planned. With this model, the thermal network for the selected motored spindle was built, and the numerical solutions for bearing temperature rise were obtained and contrasted with the experimental values for validation. The polynomial interpolation on test data, meanwhile, was also performed to help us observe the temperature change trend. Finally, the simulations based on the current models of bearings were implemented, whose corresponding results were also compared with our research work.

The validation result indicates that the thermal prediction is more accurate and efficient when the developed semi-empirical oil–air two-phase flow model is employed to assess the thermal change of bearings. Clearly, we provide a more proper model for the thermal assessment of bearing and even spindle heating.

To the best of the authors’ knowledge, this paper introduced the oil–air separation and gray-box model for the first time to describe the heat exchange inside bearing cavities and accordingly presents an efficient semi-empirical oil–air two-phase flow model to evaluate the bearing temperature variation by using thermal network method.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-06-2023-0180/

Several studies have examined the effect of formal economy (usually proxy by economic growth) on environmental quality; however, the symmetric and asymmetric impact of the informal economy on environmental quality has not been examined in Nigeria. Therefore, this study aims to explore the short- and long-run (a)symmetric effect of formal and informal economies and financial development on Nigeria’s environmental quality between 1984 and 2017.

The study uses ecological footprint to measure environmental quality. An increase in ecological footprint suggests a fall in environmental quality. Informal economy is calculated as a percentage of GDP using the currency demand approach. Autoregressive distributed lag (ARDL), nonlinear ARDL cointegration framework and vector error correction granger causality are used as estimation techniques.

The study’s outcomes establish the existence of asymmetric structure in the link between economic activities and the environment both in the short and long run. The asymmetric results reveal that positive and negative changes in the formal economy increase the ecological footprint in both periods. Hence, activities in the formal economy reduce environmental quality. On the other hand, positive and negative changes in the informal economy only positively influence the ecological footprint in the long run. In contrast, it negatively impacts the ecological footprint in the short run. This suggests that activities in the informal economy worsen the long-run environmental quality. Financial development has a positive influence on the ecological footprint, thus degrading the environmental quality. Furthermore, in the short run, a unidirectional relationship from the formal economy to the ecological footprint, while a bidirectional causality exists between informal and formal economies. Meanwhile, a unidirectional causality from the (in)formal economies and financial development to the ecological footprint was found in the long run.

The outcome of this study shows that both informal and formal economies contribute to ecological footprint; therefore, mainstreaming the informal economy into the formal economy will further increase the problem of environmental degradation and worsen environmental quality.

The study investigates the symmetric and asymmetric effect of formal and informal economies on environmental quality in Nigeria, which is largely missing in the empirical literature.