A finite‐element formulation is developed to analyze nonlinear electromagnetic devices in steady‐state conditions under specified alternating terminal voltages. The circuit…
Abstract
A finite‐element formulation is developed to analyze nonlinear electromagnetic devices in steady‐state conditions under specified alternating terminal voltages. The circuit equations are used to express current densities in terms of the unknown vector potential, so that only one nonlinear field equation must be solved. The mathematical formulation and the finite‐element and Fourier approximations are developed and the numerical algorithm used to solve the resulting block system is discussed. Finally, an application of the method to analyze an electromagnet with shading coils is presented.
Yangong Wu, Zheng Qiao, Jiadai Xue, Yutao Liu and Bo Wang
The purpose of this paper is to present a novel numerical approach to analyze the static performance of aerostatic thrust bearings by adopting a general finite element method…
Abstract
Purpose
The purpose of this paper is to present a novel numerical approach to analyze the static performance of aerostatic thrust bearings by adopting a general finite element method calculation program.
Design/methodology/approach
The characteristics of a gas film are described by the Reynolds equation and the pressure distribution is solved using the finite element method. A root iterative method is proposed to meet the requirement of the mass-conservation law because multiple pocketed orifice-type restrictors are treated as a series of special boundary conditions.
Findings
The static performance of a rotary table using aerostatic thrust bearings, including load carrying capacity and stiffness, can be predicted by the method; moreover, it can be further confirmed through experiments on the designed rotary table.
Originality/value
The method combining the finite element and root iterative methods is highly accurate and has a low time-cost for analyzing aerostatic thrust bearings with multiple pocketed orifice-type restrictors.
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A pneumatic‐fluidic system has been designed and built, with the purpose to recognize the side orientation of pieces.
Cheng‐Hsien Chen, Te‐Hui Tsai, Ding‐Wen Yang, Yuan Kang and Yeon‐Pun Chang
The purpose of this paper is to study the influences of both the number and locations of entry holes on the static and dynamic characteristics of a rigid rotor supported by two…
Abstract
Purpose
The purpose of this paper is to study the influences of both the number and locations of entry holes on the static and dynamic characteristics of a rigid rotor supported by two double‐rows, inherently compensated aerostatic bearings.
Design/methodology/approach
The air is assumed to be perfect gas undergoing the adiabatic process and passing through entry holes into the bearing clearance. Air film in the clearance is governed by Reynolds equation including the coupled effects of wedge due to rotor rotation and squeezed film due to rotor oscillation.
Findings
The method is used to analyze Reynolds equation, which is then solved by the finite difference method and numerical integration to yield static and dynamic characteristics of air film. The equation of motion of the rotor‐bearing system is obtained by using the perturbation method and the eigensolution method is used to determine the stability threshold and critical whirl ratio.
Originality/value
The paper considers the eccentricity, rotor speed, and restriction parameter in the analysis of the whirl instability of the rotor‐aerostatic bearing system for the comparisons between various designs in the number and locations of entry holes of aerostatic bearings.
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Victor Bloch, Avital Bechar and Amir Degani
The purpose of this paper is to describe a methodology for characterization of the robot environment to help solve such problem as designing an optimal agricultural robot for a…
Abstract
Purpose
The purpose of this paper is to describe a methodology for characterization of the robot environment to help solve such problem as designing an optimal agricultural robot for a specific agricultural task.
Design/methodology/approach
Defining and characterizing a task is a crucial step in the optimization of a task-specific robot. It is especially difficult in the agricultural domain because of the complexity and unstructured nature of the environment. In this research, trees are modeled from orchards and are used as the robot working environment, the geometrical features of an agricultural task are investigated and a method for designing an optimal agricultural robot is developed. Using this method, a simplified characteristic environment, representing the actual environment, is developed and used.
Findings
Case studies showing that the optimal robot, which is designed based on the characteristic environment, is similar to the optimal robot, which is designed based on the actual environment (less than 4 per cent error), is presented, while the optimization run time is significantly shorter (up to 22 times) when using the characteristic environment.
Originality/value
This paper proposes a new concept for solving the robot task-based optimization by the analysis of the task environment and characterizing it by a simpler artificial task environment. The methodology decreases the time of the optimal robot design, allowing to take into account more details in an acceptable time.
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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/
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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.
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VDU Working Still Creates Health Problems There seems to be little agreement about the effects on health of working at Visual Display Units (VDUs). There has been a great deal of…
Abstract
VDU Working Still Creates Health Problems There seems to be little agreement about the effects on health of working at Visual Display Units (VDUs). There has been a great deal of discussion on the subject and a multitude of press reports about the dangers of the devices. In some instances litigation is pending. Recent reports from the United Kingdom note that office staff are losing thousands of working days a year through headaches and eye strain, which, it is claimed, are the results of working with VDUs. This has been confirmed by a group of opticians who advocate that firms make significant improvements in working conditions. The number of the units grew from four million in 1980 to 23 million in 1988 with users spending an estimated four hours in front of a screen being likely to suffer side effects.
Cheng‐Hsien Chen, Yuan Kang, Ding‐Wen Yang, Ren‐Ming Hwang and Shyh‐Shyong Shyr
The purpose of this paper is to study the influence of number of feeding holes on the performance of aerostatic bearings with spindle rotation. In traditional design of aerostatic…
Abstract
Purpose
The purpose of this paper is to study the influence of number of feeding holes on the performance of aerostatic bearings with spindle rotation. In traditional design of aerostatic bearings, the selection of hole numbers is dependent only on spindle size. However, when the hole numbers of air feeding are enough, the performance of the aerostatic bearing cannot be enhanced by increasing the hole numbers.
Design/methodology/approach
The Reynolds equation is utilized to model the air film within bearing clearance at constant temperature and the state equation of adiabatic process is for air feeding within bearing clearance. The finite difference method with relaxation algorithm is utilized to determine the pressure distributions from discretized and coupled equations of flow continuity. The eccentricity, spindle speed, and the number and arrangement of feeding holes are considered in the analyses to determine the load capacity, attitude angle, and flow rate for the comparisons between various designs of aerostatic bearings.
Findings
It is seen from the simulation results that the aerostatic bearing designed with a small number of feeding holes and without locating at bearing bottom is most suitable for the spindle operating at high speed, while the bearing designed with a large number of feeding holes is suitable for the spindle operating at low speed, and the load capacity is increased with the increasing number of feeding holes for low journal speed.
Originality/value
The paper proposes an extensive database as a critical requirement in the design for number and arrangement of feeding holes of aerostatic bearings for the spindle operating at low or high speed.
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Polina V. Khan, Dawit Zenebe Segu and Pyung Hwang
Aerostatic porous bearings are important for guide rails and spindles. It is well-known that flow restrictors made of porous materials offer major advantages over conventional…
Abstract
Purpose
Aerostatic porous bearings are important for guide rails and spindles. It is well-known that flow restrictors made of porous materials offer major advantages over conventional restrictors in such bearings, including design and manufacturing, load-carrying capacity, stiffness, damping and dynamic stability. Thus, this work numerically investigates the effect of the arc on a new combined annular-thrust aerostatic porous bearing.
Design/methodology/approach
The static characteristics of an annular-thrust aerostatic porous bearing were studied using a fast finite element scheme. The pressure distribution, radial load and thrust load were analyzed as functions of the arc, permeability and eccentricity.
Findings
The results reveal that the radial load achieves maximal values at an optimal arc value between 200 and 300, and the thrust load increases monotonically with increasing arc.
Originality/value
This work developed a new combined annular-thrust aerostatic porous bearing to investigate the effect of arc on the annular-thrust aerostatic porous bearings to increase the load-carrying capacity.