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Article
Publication date: 12 November 2020

Liangliang Li and Yonghui Xie

Owing to the development of the smaller-sized rotational machinery, the demand for the high-speed and low-resistance gas bearing increases rapidly. The research of micro gas…

Abstract

Purpose

Owing to the development of the smaller-sized rotational machinery, the demand for the high-speed and low-resistance gas bearing increases rapidly. The research of micro gas bearing in the condition of rarefied gas state is still not satisfied. Therefore, the purpose of this paper is to present a numerical investigation of the effect of misalignment and rarefaction effect on the comprehensive performance of micro-electrical-mechanical system (MEMS) gas bearing.

Design/methodology/approach

The Fukui and Kaneko model is expanded to 2D solution domain to describe the flow field parameters. The finite element method is used to discretize the equation. Newton–Raphson method is used to solve the nonlinear equations for the static performance of gas bearing, and partial deviation method is adopted for the solution of dynamic equations.

Findings

The static and dynamic characteristics of MEMS gas bearing are calculated, and the comparison is made to study the influence of rarefaction effect and misalignment. The results show that the rarefaction effect will decrease bearing load capacity compared with traditional solution of Reynolds equation, and the misalignment will reduce the stability of bearing. The influence of misalignment on gas film thickness is also analyzed in this paper.

Originality/value

The investigation of this paper emerges the change regularity of comprehensive performance of MEMS gas bearing considering rarefaction effect and misalignment, which provides a reference for the actual manufacturing of MEMS gas bearing and for the safety operation of micro dynamic machinery.

Peer review

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2020-0023/

Details

Industrial Lubrication and Tribology, vol. 73 no. 1
Type: Research Article
ISSN: 0036-8792

Keywords

Article
Publication date: 8 June 2015

Kai Feng and Xueyuan Zhao

The purpose of this paper is to investigate the effects of misalignment on the static and dynamics characteristics of bump-type foil bearings (BFBs). High-speed and…

Abstract

Purpose

The purpose of this paper is to investigate the effects of misalignment on the static and dynamics characteristics of bump-type foil bearings (BFBs). High-speed and high-temperature oil-free turbomachinery can be realized with the use of gas foil bearings (GFBs). GFBs have a flexible supporting structure; thus, they can tolerate a higher degree of misalignment compared with rolling element bearings.

Design/methodology/approach

A test rig for GFBs has been developed to measure the effects of misalignment on the structure characteristics of bump-type foil bearings. The link-spring model, which is the foil structure model presented previously by the authors, is used as a basis in the present study to predict the static and dynamic performances of the foil structure. In general, predictions of the dynamic characteristics exhibit good agreement with the measurements acquired from the dynamic load tests.

Findings

Results from the static tests show that GFBs develop high stiffness when the misalignment angle increases. Moreover, the dynamic characteristics of GFBs are identified by considering the test bearing supported by a non-rotating shaft as a one-degree-of-freedom system. The results indicate that the dynamic characteristics of GFBs strongly depend on excitation frequency and excitation amplitude because of the variation in the dynamic friction force within the foil structure. The structural stiffness and equivalent viscous damping increase with an increase in the misalignment angle.

Originality/value

The present study focuses on the misalignment of GFBs and investigates experimentally the effects of misalignment on the structure characteristics of GFBs.

Details

Industrial Lubrication and Tribology, vol. 67 no. 4
Type: Research Article
ISSN: 0036-8792

Keywords

Article
Publication date: 4 August 2021

Hao Li, Haipeng Geng and Hao Lin

The misalignment is generally inevitable in the process of machining and assembly of rotor systems with gas foil bearings, but the exploration on this phenomenon is relatively…

Abstract

Purpose

The misalignment is generally inevitable in the process of machining and assembly of rotor systems with gas foil bearings, but the exploration on this phenomenon is relatively less. Therefore, the purpose of this paper is to carry out the thermo-elastohydrodynamic analysis of the foil bearing with misalignment, especially the inhomogeneous foil bearing.

Design/methodology/approach

The rotor is allowed to misalign in two non-rotating directions. Then the static and dynamic performance of the inhomogeneous foil bearing is studied. The thermal-elastohydrodynamic analysis is realized by combining the Reynolds equation, foil deformation equation and energy equation. The small perturbation method is used to calculate the dynamic coefficients, then the critical whirl ratio is obtained.

Findings

The gas pressure, film thickness and temperature distribution distort when the misalignment appears. The rotor misalignment can improve the loading capacity but rise the gas temperature at the same time. Furthermore, the rotor misalignment can affect the critical whirl ratio which demonstrates that it is necessary to analyze the misalignment before the rotordynamic design.

Originality/value

The value of this paper is the exploration of the thermo-elastohydrodynamic performance of the inhomogeneous foil bearing with misalignment, the analysis procedure and the corresponding results are valuable for the design of turbo system with gas foil bearings.

Details

Industrial Lubrication and Tribology, vol. 73 no. 6
Type: Research Article
ISSN: 0036-8792

Keywords

Article
Publication date: 18 May 2010

Johan F. Lundin and Andreas Norrman

The purpose of this paper is to propose a framework for describing and analyzing misalignments in supply chain management related to changes in supply chain structures, processes…

1793

Abstract

Purpose

The purpose of this paper is to propose a framework for describing and analyzing misalignments in supply chain management related to changes in supply chain structures, processes and management components.

Design/methodology/approach

Based on the systems approach, a single‐case study including several embedded cases from the same supply chain was deployed. This was done according to the abductive research approach, which is favourable when extending existing and developing new theory. Data were collected through observations, interviews and workshops, and later analyzed through pattern matching. The case studied was the Swedish cash supply chain, which was appropriate since it has gone through several changes in its supply chain structure and management.

Findings

A framework to describe and analyze misalignments in the supply chain was developed. The framework consists of three steps: first, identify changes in the supply chain, second, Identify Misalignments, and third, identify symptoms. For each step, a specific and more detailed framework was developed in order to facilitate the identification processes.

Originality/value

Using the framework described in this paper a researcher or practitioner acquires a structured approach to mapping the management of a supply chain so that its current misalignments can be identified.

Details

International Journal of Physical Distribution & Logistics Management, vol. 40 no. 4
Type: Research Article
ISSN: 0960-0035

Keywords

Article
Publication date: 23 September 2020

Hongyang Hu, Ming Feng and Tianming Ren

The purpose of this paper is to study the characteristics of gas foil conical bearings (GFCBs) considering the misalignment, the static and dynamic performances with different…

Abstract

Purpose

The purpose of this paper is to study the characteristics of gas foil conical bearings (GFCBs) considering the misalignment, the static and dynamic performances with different misalignment cases were studied.

Design/methodology/approach

A test rig on the air compressor supported by GFCBs has been developed to measure the practicability. A nonlinear bump stiffness model and one-dimensional beam top foil stiffness model were used as a basis for the calculation of static and dynamic performance. The finite element method and finite difference method are adopted to solve the Reynolds equation and the film thickness equation coupled, in which different misalignment cases were considered by changing the film thickness.

Findings

The supporting performance of GFCB is excellent, and the film clearance plays a critical role. The misalignment effects depend on the assembled angle and the misalignment angle. The load capacity, friction torque, temperature of GFCB decrease when the misalignment assembled angle is between 120° and 240°, while the dynamic bearing stability is improved. The static and dynamic performances show the opposite law for the other assembled angles, and the misalignment effect is more dramatic when there is a larger misalignment angle. Moreover, the bearing and running parameters largely affect the bearing performance.

Originality/value

The present study focuses on the static and dynamic characteristics of GFCB and investigates the effects of misalignment on the bearing performance.

Peer review

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-04-2020-0117

Details

Industrial Lubrication and Tribology, vol. 73 no. 1
Type: Research Article
ISSN: 0036-8792

Keywords

Article
Publication date: 7 January 2019

Hock Tsen Wong

The purpose of this paper is to examine the impact of real exchange rate misalignment on economy and economic sectors, namely construction, manufacturing and mining and quarrying…

Abstract

Purpose

The purpose of this paper is to examine the impact of real exchange rate misalignment on economy and economic sectors, namely construction, manufacturing and mining and quarrying in Malaysia.

Design/methodology/approach

The equilibrium real exchange rate and economic models are estimated using the autoregressive distributed lag approach.

Findings

An increase in productivity differential or reserve differential will lead to an appreciation of real exchange rate in the long run. An increase in positive (negative) real exchange rate misalignment will lead to an increase (decrease) in economy. An increase in long-run real exchange rate misalignment will lead to a decrease in economy. Real exchange rate misalignment or long-run real exchange rate misalignment can influence the manufacturing sector in Malaysia. More specifically, undervaluation will promote whereas overvaluation will hurt the manufacturing sector.

Originality/value

Real exchange rate misalignment can be a policy to influence economy but may not be the best choice.

Details

Journal of Economic Studies, vol. 46 no. 1
Type: Research Article
ISSN: 0144-3585

Keywords

Article
Publication date: 20 October 2020

Abdulla Hil Mamun, Harun Bal and Shahanara Basher

The study mainly aims to examine the currency misalignment of Turkish lira and evaluate if it has an impact on economic growth of Turkey.

Abstract

Purpose

The study mainly aims to examine the currency misalignment of Turkish lira and evaluate if it has an impact on economic growth of Turkey.

Design/methodology/approach

It relies on Johansen cointegration technique for measuring currency misalignment relying on single-equation approach and the autoregressive distributed lag (ARDL) approach to evaluate how misalignment affects economic growth. The sample period covers from 1980 to 2016.

Findings

The study identifies that terms of trade, relative productivity differences, net foreign asset, investment and trade openness determine the equilibrium REER of Turkey, and the degree of currency misalignment is observed at a substantial level. The outcome of the ARDL approach suggests that higher currency misalignment reduces economic growth. Turning to the separate impacts of undervaluation and overvaluation, while the former falters economic growth, the later promotes it, a finding contrary to the conventional expectation. Therefore, the use of exchange rate as a policy variable is a critical concern to avoid misalignment for sustained economic growth.

Practical implications

The anti-growth effect of undervaluation and misalignment is an indication of redistribution of income which could be verified by examining the aggregate consumption behavior of the economy in response to RER movements.

Originality/value

The impacts of currency undervaluation and overvaluation on economic growth of Turkey have been studied in a number of time-series studies. But there is no documented study on the role of currency misalignment on Turkish economic growth. This study is the first that examines how the economic growth of Turkey is influenced by currency misalignment together with the impact of undervaluation and overvaluation.

Details

EuroMed Journal of Business, vol. 16 no. 4
Type: Research Article
ISSN: 1450-2194

Keywords

Article
Publication date: 16 November 2010

Siddiq M. Qidwai and V.G. DeGiorgi

The paper aims to highlight the computational implementation of a nonlinear piezoelectric constitutive model and its application in determining the impact of misalignment between…

Abstract

Purpose

The paper aims to highlight the computational implementation of a nonlinear piezoelectric constitutive model and its application in determining the impact of misalignment between initial poling direction and applied electrical field, and mechanical boundary conditions on actuator performance.

Design/methodology/approach

The numerical analysis is based on an existing three‐dimensional model, where the original rate‐independent evolution equations are replaced by their rate‐dependent counterparts to facilitate implementation, which is performed in a partial differential equation solver. The execution of the model is verified through several benchmark constitutive responses.

Findings

The analysis shows that small angles of poling and loading axes misalignment such as may occur in fabrication (less than 5) have minor impact on piezoelectric performance regardless of the type of imposed mechanical boundary conditions. On the other hand, larger angles of misalignment can have a significant impact, the feasibility of which in actuator design remains to be seen. Furthermore, it is shown that the linear response range of these actuators can be expanded by increased levels of mechanical constraint at the cost of maximum actuation stroke regardless of the degree of misalignment.

Originality/value

The misalignment, which occurs accidentally, but can also be introduced purposefully during the fabrication process when poled material is cut into specimen form, may exhibit desirable performance features for actuator design when combined with appropriate mechanical constraints.

Details

Engineering Computations, vol. 27 no. 8
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 4 April 2020

Hao Li, Peng Hai Geng and Hao Lin

The normal operation of a rotor system is generally vulnerable to misalignment between gas foil bearing (GFB) and rotor. However, most theoretical and experimental researches…

Abstract

Purpose

The normal operation of a rotor system is generally vulnerable to misalignment between gas foil bearing (GFB) and rotor. However, most theoretical and experimental researches about the characteristics of GFBs have ignored this phenomenon. Therefore, the main purpose of this paper is to evaluate the static and dynamic performance of GFBs considering misalignment.

Design/methodology/approach

The shaft is allowed to misalign in two directions. Then the variations of bearing load, friction force, restoring moment, stiffness and damping coefficients are thoroughly explored. The hydrodynamic pressure on the gas film is modeled with compressible Reynolds equation, and the deformation of the flexible bearing is calculated with finite element method. Small perturbation method is used to obtain the displacement and moment dynamic coefficients.

Findings

The film thickness and pressure distribution distort when misalignments appear. The inclination of GFBs can enhance the restoring moment to withstand the imposed misalignment. Furthermore, the simulation phenomenon demonstrates the misalignment around load direction should be avoided as much as possible, while a small value misalignment around another direction is allowed.

Originality/value

The value of this paper is the exploration of the influence of misalignments on the static and dynamic performance of the Generation II journal GFB.

Peer review

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-10-2019-0418/

Details

Industrial Lubrication and Tribology, vol. 72 no. 7
Type: Research Article
ISSN: 0036-8792

Keywords

Article
Publication date: 28 August 2020

H. Girish and Raghuvir Pai

The purpose of this paper is to theoretically analyze an innovative form of variable bearing configuration having four pads with unique adjustability principle operated under…

Abstract

Purpose

The purpose of this paper is to theoretically analyze an innovative form of variable bearing configuration having four pads with unique adjustability principle operated under journal misaligned conditions. The parameters such as load positions, degrees of misalignment (DM) and pad adjustment configurations influencing the steady-state performance of the four-pad adjustable bearing are detailed in this paper.

Design/methodology/approach

The proposed adjustable pad geometry possesses the ability to undergo radial and tilt motions in both inward and outward directions. Analysis is carried out by considering journal misalignment in vertical and horizontal planes with bearing modelled for load-on-pad and load-between-pad configurations. The film thickness equation derived to incorporate the radial and tilt adjustment parameters is further modified to accommodate the different load orientations and misaligned journal conditions. The pressure field equation is solved by applying finite-difference technique combined with Gauss Siedel iterative method.

Findings

At higher DM, peak pressures generated in the minimum film thickness region near the pad ends highly influences the bearing load carrying capacity. Results indicated that the adjustable four-pad bearing geometry is highly efficient in withstanding the journal misalignment by radially displacing and tilting the four pads in negative directions.

Originality/value

For bearing designers, this research highlights the importance of considering the misalignment factor during the design stages of an adjustable journal bearing. The proposed adjustability concept is proven to be effective enough to improve the bearing performance and, in turn, withstand the journal misalignment.

Details

Engineering Computations, vol. 38 no. 4
Type: Research Article
ISSN: 0264-4401

Keywords

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