R. Rashidi Meybodi, A. Rasoolizadeh Shooroki and M. Zare Mehrjardi
The purpose of this study is to examine the thermo-hydrodynamic performance of tilted non-circular journal bearings lubricated with a micropolar fluid. The investigated bearing…
Abstract
Purpose
The purpose of this study is to examine the thermo-hydrodynamic performance of tilted non-circular journal bearings lubricated with a micropolar fluid. The investigated bearing types are two- and three-lobe journal bearings with finite length.
Design/methodology/approach
For this purpose, modified Reynolds, energy and three-dimensional Laplace equations are solved numerically by using generalized differential quadrature method. The effects of micropolarity characteristics of lubricants, such as characteristic length and coupling number, as well as tilt angle as a design parameter, on the performance of non-circular two- and three-lobe journal bearings are studied.
Findings
The results show that the tilt angle can affect the temperature and pressure profiles causing variation in the performance of non-circular bearings. Increasing coupling number and decreasing characteristic length cause the load-carrying capacity to decrease because of the increase in maximum oil temperature of the fluid film of lubricant and decrease in the minimum oil base viscosity. So, it is possible to select suitable values of tilt angle for achieving optimum performance of these bearings.
Originality/value
The non-circular bearings suggest several design parameters such as tilt angle for designers. By considering thermal effects for micropolar lubricant, the requirements of a specific application can be fulfilled.
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R. Rashidi Meybodi, M. Zare Mehrjardi and A.D. Rahmatabadi
The purpose of this paper is to study tilt angle effects as design parameters of noncircular bearings, on the linear dynamic analyses of micropolar lubricated circular, two, three…
Abstract
Purpose
The purpose of this paper is to study tilt angle effects as design parameters of noncircular bearings, on the linear dynamic analyses of micropolar lubricated circular, two, three and four lobe journal bearings.
Design/methodology/approach
Reynolds equation in dynamic state is modified considering the micropolarity characteristics of lubricant, and it is solved using generalized differential quadrature method. The perturbed components of the dynamic pressure are extracted based on the linear dynamic model. To explain the transient state of the governing equation, through the linear dynamic approach, the whirling motion of rotor around the steady state position is assumed to be harmonic.
Findings
It is observed from the results that tilt angle has significant effects on the steady state and stability performance of lobed journal bearings. It may be selected suitably to improve the performance of rotor-bearing system, while all other lubricant properties and noncircular bearing design parameters are kept fixed. Results show that among the three types of bearings considered, the dynamic performance of two lobe bearings are more affected by the variation of tilt angle.
Originality/value
The present study is mainly concerned with the effects of tilt angle as a design parameter on the stability performance of a hydrodynamic noncircular journal bearing lubricated with micropolar fluid.
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Asieh Nazemi, Paria R. Zamanfashami, Pantea Foroudi, Manijeh Haghighinasab, Nader Seyyedamiri and Masoud Zare Mehrjardy
This study aims to address the following research questions: (1) What are the theoretical frameworks and areas of study that influence the development of service ecosystems? and…
Abstract
Purpose
This study aims to address the following research questions: (1) What are the theoretical frameworks and areas of study that influence the development of service ecosystems? and (2) To what extent does a service ecosystem align with the theoretical concepts presented in other research contexts within the study areas, thereby transforming the fundamental structure of the core concept?
Design/methodology/approach
We conducted a bibliometric systematic literature review, analyzing 280 papers from a sample of 52 journals listed in the Association of Business Schools (ABS). The review covered the period between 2004 and 2022, and we utilized co-citation analysis, multi-dimensional scaling analysis and hierarchical cluster analysis (HCA) on a total of 2,614 citations.
Findings
This study employs co-citation analysis to identify the conceptual structure of the service ecosystem based on highly cited papers. Additionally, we utilize multidimensional scaling (MDS) to uncover key approaches driving service ecosystem research. Through HCA and network analysis, we examine the research scope and its development, emphasizing theory-driven approaches. By combining quantitative and qualitative analysis, we explore the interrelationships between scope, domain and evolution. This comprehensive analysis allows us to delve deeply into the study of service ecosystems. To broaden the research scope, we propose a conceptual framework for comparing the main components of a service ecosystem. The current paper clarifies the service ecosystem's intellectual structure, including service performance, humanistic approach, sustainable innovations and service reflexivity and reformation and proposes a prospective research framework for specialists and researchers by introducing a metaverse service ecosystem.
Originality/value
For the first time, the findings of this study shed light on processes that facilitate the flow of technologies, business models and markets through social structures, ultimately contributing to social change. In service-based systems, the development and application of a more humanistic approach within and surrounding social service ecosystems are crucial as they evolve. Therefore, adopting a dynamic and multifaceted approach offers valuable insights into the drivers of value creation.
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M.M. Shahin, Mohammad Asaduzzaman Chowdhury, Md. Arefin Kowser, Uttam Kumar Debnath and M.H. Monir
The purposes of the present study are to ensure higher sustainability of journal bearings under different applied loads and to observe bearing performances such as elastic strain…
Abstract
Purpose
The purposes of the present study are to ensure higher sustainability of journal bearings under different applied loads and to observe bearing performances such as elastic strain, total deformation and stress formation.
Design/methodology/approach
A journal bearing test rig was used to determine the effect of the applied load on the bearing friction, film thickness, lubricant film pressure, etc. A steady-state analysis was performed to obtain the bearing performance.
Findings
An efficient aspect ratio (L/D) range was obtained to increase the durability or the stability of the bearing while the bearing is in the working condition by using SAE 5W-30 oil. The results from the study were compared with previous studies in which different types of oil and water, such as Newtonian fluid (NF), magnetorheological fluid (MRF) and nonmagnetorheological fluid (NMRF), were used as the lubricant. To ensure a preferable aspect ratio range (0.25-0.50), a computational fluid dynamics (CFD) analysis was conducted by ANSYS; the results show a lower elastic strain and deformation within the preferable aspect ratio (0.25-0.50) rather than a higher aspect ratio using the SAE 5W-30 oil.
Originality/value
It is expected that the findings of this study will contribute to the improvement of the bearing design and the bearing lubricating system.
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Sanyam Sharma, Chimata Murali Krishna and Rajesh Singh
This paper aims to evaluate the theoretical performance of elliptical dam bearing (EDB). The objective of this paper is to study the influence of eccentricity ratio, dam…
Abstract
Purpose
This paper aims to evaluate the theoretical performance of elliptical dam bearing (EDB). The objective of this paper is to study the influence of eccentricity ratio, dam parameters and micropolarity parameters on the stability of EDB with respect to micropolar lubrication.
Design/methodology/approach
In this study, the modified Reynolds’ equation for dynamic state is solved using the finite element method and Galerkin technique. A MATLAB code is written to compute pressure and stability and also to analyse the characteristics. The stability parameters of an EDB are computed for selected values of eccentricity ratios at four levels in the range of 0.20 to 0.35 and for length-diameter ratio of 2.0.
Findings
The results from stability analysis reveal that micropolar lubricated EDB provides better stability at smaller material length due to increased effective viscosity. Hence, it is better to select the smaller characteristic length and higher dam width to achieve optimum performance of these bearings.
Originality/value
Very few researchers investigated the effects of working eccentricity, bearing dam and micropolar fluid parameters on the EDB in the past. It is important to study these aspects for optimum performance of bearings.
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Hybrid journal bearing have long been used in machines requiring large load and high speed capacity operating under wide range of temperatures. Different compensating devices are…
Abstract
Purpose
Hybrid journal bearing have long been used in machines requiring large load and high speed capacity operating under wide range of temperatures. Different compensating devices are used in for efficient operation of bearings. This paper aims to help in selection of optimum compensating device by evaluating the comparative performance of constant flow valve, capillary compensated and slot entry hybrid journal bearing under the combined influence of thermal effects and micropolar nature of lubricant.
Design/methodology/approach
The variation in micropolar parameters and viscosity change due to temperature increase of lubricant are considered in present study. Finite element method is used for combined iterative solution of micropolar Reynolds, energy and conduction equations. Micropolar lubricant is assumed to be governed by two parameters, coupling number and characteristic length. The results in the study are presented for symmetric and asymmetric configurations of hole entry and slot entry non-recessed hybrid journal bearings
Findings
The results indicate that constant flow valve compensated hole entry hybrid journal bearing is the highest performing bearing for the given range of micropolar parameters of lubricant in terms of maximum fluid pressure and dynamic coefficients.
Originality/value
The performance variations of various configurations of hybrid journal bearing are presented in a single paper. The reader can get overview of combined effects of micropolar parameters and viscosity decrease due to temperature increase of the lubricant.
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This study aims to investigate the stability performance of partial journal bearings of 120° and 180° partial angles with micropolar lubricant.
Abstract
Purpose
This study aims to investigate the stability performance of partial journal bearings of 120° and 180° partial angles with micropolar lubricant.
Design/methodology/approach
To investigate the stability characteristics of partial journal bearing, a MATLAB source code is written. To solve the Reynolds’ equation, the finite element method is used. Stability performances of 120° and 180° partial journal bearings are computed for a wide range of non-dimensional micropolar fluid parameters and working eccentricities.
Findings
The presented results provide design data for stability parameters in terms of equivalent stiffness, whirl frequency ratio, critical mass and threshold speed of the rotor with respect to eccentricities and material size of the lubricant. The stability of 180° partial journal bearing is found to be higher than 120° partial journal bearing.
Originality/value
In open literature, it is rare to find the stability of a partial journal bearing lubricated with micropolar fluid. Very few researchers have studied the combined effect of eccentricities and micropolar lubricant parameters on the dynamic performance of such bearings. Hence, it is important to study the dynamic stability to explore the complete investigation of the performance of partial journal bearings with micropolar fluid.
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M. Nekoeimehr, A.D. Rahmatabadi and R. Rashidi
The purpose of this paper is to analyse the static performance characteristics of lobe journal bearings lubricated with a micropolar fluid, considering effect of non‐circularity…
Abstract
Purpose
The purpose of this paper is to analyse the static performance characteristics of lobe journal bearings lubricated with a micropolar fluid, considering effect of non‐circularity. Number of lobes and their preload value are the non‐circularity parameters considered in the present study. The bearings undertaken for the investigation are two, three and four‐lobe symmetric journal bearings with finite width.
Design/methodology/approach
For this purpose, modified form of Reynolds equation is derived, based on Eringen's micropolar fluid theory and it is solved numerically using finite element method (FEM). The effect of the non‐circularity parameters of bearings on the steady‐state performance characteristics such as load carrying capacity, attitude angle, coefficient of friction and side leakage flow are presented and discussed.
Findings
The results show that the number of lobes and their preload value can influence the performance of lobe bearings. It is seen that, in order to provide certain improvement over simple cylindrical bearings, the non‐circularity parameters of lobe bearings must be chosen correctly. There is no single optimum profile for multi‐lobe bearing application.
Originality/value
Lobe bearings, compared with simple circular bearings, offer several geometric parameters to designers. These parameters must be chosen correctly, so that the requirements of a specific application can be fulfilled.
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Armin Mahmoodi, Leila Hashemi and Milad Jasemi
In this study, the central objective is to foresee stock market signals with the use of a proper structure to achieve the highest accuracy possible. For this purpose, three hybrid…
Abstract
Purpose
In this study, the central objective is to foresee stock market signals with the use of a proper structure to achieve the highest accuracy possible. For this purpose, three hybrid models have been developed for the stock markets which are a combination of support vector machine (SVM) with meta-heuristic algorithms of particle swarm optimization (PSO), imperialist competition algorithm (ICA) and genetic algorithm (GA).All the analyses are technical and are based on the Japanese candlestick model.
Design/methodology/approach
Further as per the results achieved, the most suitable algorithm is chosen to anticipate sell and buy signals. Moreover, the authors have compared the results of the designed model validations in this study with basic models in three articles conducted in the past years. Therefore, SVM is examined by PSO. It is used as a classification agent to search the problem-solving space precisely and at a faster pace. With regards to the second model, SVM and ICA are tested to stock market timing, in a way that ICA is used as an optimization agent for the SVM parameters. At last, in the third model, SVM and GA are studied, where GA acts as an optimizer and feature selection agent.
Findings
As per the results, it is observed that all new models can predict accurately for only 6 days; however, in comparison with the confusion matrix results, it is observed that the SVM-GA and SVM-ICA models have correctly predicted more sell signals, and the SCM-PSO model has correctly predicted more buy signals. However, SVM-ICA has shown better performance than other models considering executing the implemented models.
Research limitations/implications
In this study, the data for stock market of the years 2013–2021 were analyzed; the long length of timeframe makes the input data analysis challenging as they must be moderated with respect to the conditions where they have been changed.
Originality/value
In this study, two methods have been developed in a candlestick model; they are raw-based and signal-based approaches in which the hit rate is determined by the percentage of correct evaluations of the stock market for a 16-day period.
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Armin Mahmoodi, Leila Hashemi, Amin Mahmoodi, Benyamin Mahmoodi and Milad Jasemi
The proposed model has been aimed to predict stock market signals by designing an accurate model. In this sense, the stock market is analysed by the technical analysis of Japanese…
Abstract
Purpose
The proposed model has been aimed to predict stock market signals by designing an accurate model. In this sense, the stock market is analysed by the technical analysis of Japanese Candlestick, which is combined by the following meta heuristic algorithms: support vector machine (SVM), meta-heuristic algorithms, particle swarm optimization (PSO), imperialist competition algorithm (ICA) and genetic algorithm (GA).
Design/methodology/approach
In addition, among the developed algorithms, the most effective one is chosen to determine probable sell and buy signals. Moreover, the authors have proposed comparative results to validate the designed model in this study with the same basic models of three articles in the past. Hence, PSO is used as a classification method to search the solution space absolutelyand with the high speed of running. In terms of the second model, SVM and ICA are examined by the time. Where the ICA is an improver for the SVM parameters. Finally, in the third model, SVM and GA are studied, where GA acts as optimizer and feature selection agent.
Findings
Results have been indicated that, the prediction accuracy of all new models are high for only six days, however, with respect to the confusion matrixes results, it is understood that the SVM-GA and SVM-ICA models have correctly predicted more sell signals, and the SCM-PSO model has correctly predicted more buy signals. However, SVM-ICA has shown better performance than other models considering executing the implemented models.
Research limitations/implications
In this study, the authors to analyze the data the long length of time between the years 2013–2021, makes the input data analysis challenging. They must be changed with respect to the conditions.
Originality/value
In this study, two methods have been developed in a candlestick model, they are raw based and signal-based approaches which the hit rate is determined by the percentage of correct evaluations of the stock market for a 16-day period.