| 1. |
- Al-Najjar, Basim, 1954-
(author)
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Improved effectiveness of vibration monitoring of rolling bearings in paper mills
- 1998
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In: Journal of engineering tribology. - : SAGE Publications. ; 212:2, s. 111-120
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Journal article (peer-reviewed)abstract
- Rolling element bearing failures in paper mill machines are considered in relation to their critical role in the machine function. The paper discusses these failures according to what becomes damaged and how, and relates them to the vibration spectra and their development over the bearings’ lives. Interpretation of some variations in the vibration signature, i.e. relating vibration amplitude changes and frequency shifts to the deterioration processes involved, are proposed and discussed. The literature was found mainly to confirm this analysis. A new approach to envelope alarming is presented and shown theoretically (logically) to offer later renewal with fewer failures, and therefore lower cost and higher productivity. Deficiencies in data coverage and quality, and the feedback of case study results, are discussed. A model to improve maintenance experience is proposed and discussed. Using vibration to monitor component condition, the accurate prediction of remaining life requires (a) enough vibration measurements, (b) numerate records of operating conditions, (c) better discrimination between frequencies in the spectrum and (d) correlation of (b) and (c). This is because life prediction depends on the amplitudes of (and) the frequencies generated by the component damage. Much money could be saved because some present policies utilise as little as half of the bearing useful life.
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| 2. |
- Alemani, Mattia, et al.
(author)
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Scaling effects of measuring disc brake airborne particulate matter emissions – A comparison of a pin-on-disc tribometer and an inertia dynamometer bench under dragging conditions
- 2018
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In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - : Sage Publications. - 1350-6501 .- 2041-305X. ; 232:12, s. 1538-1547
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Journal article (peer-reviewed)abstract
- An important contributor to non-exhaust emissions in urban areas is airborne particulate matter originating from brake systems. A well-established way to test such systems in industry is to use inertia dynamometer benches; although they are quite expensive to run. Pin-on-disc tribometers, on the other hand, are relatively cheap to run, but simplify the real system. The literature indicates promising correlations between these two test stands with regard to measured airborne number distribution. Recent studies also show a strong dependency between the airborne number concentration and the disc temperature. However, a direct comparison that also takes into account temperature effects is missing. The aim of this paper is, therefore, to investigate how the transition temperature is affected by the different test scales, under dragging conditions, and the effects on total concentration and size distribution. New and used low-steel pins/pads were tested against cast iron discs/rotors on both the aforementioned test stands, appositely designed for particulate emission studies. A constant normal load and constant rotational velocity were imposed in both test stands. Results show that a transition temperature can always be identified. However, it is influenced by the test scale and the frictional pair status. Nevertheless, emissions are assessed similarly when an equivalent frictional pair status is analysed (e.g. run-in). Further investigations for fully run-in samples on the pin-on-disc should be performed in order to finally assess the possibility of using the tribometers for the initial assessment of different friction materials.
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| 3. |
- Almqvist, Andreas, et al.
(author)
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On lower-dimensional models in lubrication, Part A : Common misinterpretations and incorrect usage of the Reynolds equation
- 2021
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In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - : Sage Publications. - 1350-6501 .- 2041-305X. ; 235:8, s. 1692-1702
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Journal article (peer-reviewed)abstract
- Most of the problems in lubrication are studied within the context of Reynolds’ equation, which can be derived by writing the incompressible Navier-Stokes equation in a dimensionless form and neglecting terms which are small under the assumption that the lubricant film is very thin. Unfortunately, the Reynolds equation is often used even though the basic assumptions under which it is derived are not satisfied. One example is in the mathematical modelling of elastohydrodynamic lubrication (EHL). In the EHL regime, the pressure is so high that the viscosity changes by several orders of magnitude. This is taken into account by just replacing the constant viscosity in either the incompressible Navier-Stokes equation or the Reynolds equation by a viscosity-pressure relation. However, there are no available rigorous arguments which justify such an assumption. The main purpose of this two-part work is to investigate if such arguments exist or not. In Part A, we formulate a generalised form of the Navier-Stokes equation for piezo-viscous incompressible fluids. By dimensional analysis of this equation we, thereafter, show that it is not possible to obtain the Reynolds equation, where the constant viscosity is replaced with a viscosity-pressure relation, by just neglecting terms which are small under the assumption that the lubricant film is very thin. The reason is that the lone assumption that the fluid film is very thin is not enough to neglect the terms, in the generalised Navier-Stokes equation, which are related to the body forces and the inertia. However, we analysed the coefficients in front of these (remaining) terms and provided arguments for when they may be neglected. In Part B, we present an alternative method to derive a lower-dimensional model, which is based on asymptotic analysis of the generalised Navier-Stokes equation as the film thickness goes to zero.
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| 4. |
- Almqvist, Andreas, et al.
(author)
-
On lower-dimensional models in lubrication, Part B : Derivation of a Reynolds type of equation for incompressible piezo-viscous fluids
- 2021
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In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - : Sage Publications. - 1350-6501 .- 2041-305X. ; 235:8, s. 1703-1718
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Journal article (peer-reviewed)abstract
- The Reynolds equation is a lower-dimensional model for the pressure in a fluid confined between two adjacent surfaces that move relative to each other. It was originally derived under the assumption that the fluid is incompressible and has constant viscosity. In the existing literature, the lower-dimensional Reynolds equation is often employed as a model for the thin films, which lubricates interfaces in various machine components. For example, in the modelling of elastohydrodynamic lubrication (EHL) in gears and bearings, the pressure dependence of the viscosity is often considered by just replacing the constant viscosity in the Reynolds equation with a given viscosity-pressure relation. The arguments to justify this are heuristic, and in many cases, it is taken for granted that you can do so. This motivated us to make an attempt to formulate and present a rigorous derivation of a lower-dimensional model for the pressure when the fluid has pressure-dependent viscosity. The results of our study are presented in two parts. In Part A, we showed that for incompressible and piezo-viscous fluids it is not possible to obtain a lower-dimensional model for the pressure by just assuming that the film thickness is thin, as it is for incompressible fluids with constant viscosity. Here, in Part B, we present a method for deriving lower-dimensional models of thin-film flow, where the fluid has a pressure-dependent viscosity. The main idea is to rescale the generalised Navier-Stokes equation, which we obtained in Part A based on theory for implicit constitutive relations, so that we can pass to the limit as the film thickness goes to zero. If the scaling is correct, then the limit problem can be used as the dimensionally reduced model for the flow and it is possible to derive a type of Reynolds equation for the pressure.
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| 5. |
- Almqvist, Andreas, et al.
(author)
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On lower-dimensional models of thin film flow, Part C: Derivation of a Reynolds type of equation for fluids with temperature and pressure dependent viscosity
- 2023
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In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - : Sage. - 1350-6501 .- 2041-305X. ; 237:3, s. 514-526
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Journal article (peer-reviewed)abstract
- This paper constitutes the third part of a series of works on lower-dimensional models in lubrication. In Part A, it was shown that implicit constitutive theory must be used in the modelling of incompressible fluids with pressure-dependent viscosity and that it is not possible to obtain a lower-dimensional model for the pressure just by letting the film thickness go to zero, as in the proof of the classical Reynolds equation. In Part B, a new method for deriving lower-dimensional models of thin-film flow of fluids with pressure-dependent viscosity was presented. Here, in Part C, we also incorporate the energy equation so as to include fluids with both temperature and pressure dependent viscosity. By asymptotic analysis of this system, as the film thickness goes to zero, we derive a simplified model of the flow. We also carry out an asymptotic analysis of the boundary condition, in the case where the normal stress is specified on one part of the boundary and the velocity on the remaining part.
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| 6. |
- Almqvist, Andreas
(author)
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Preface
- 2021
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In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - : Sage Publications. - 1350-6501 .- 2041-305X. ; 235:12, s. 2504-2505
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Journal article (other academic/artistic)
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| 7. |
- Almqvist, Andreas, et al.
(author)
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Reiterated homogenization applied in hydrodynamic lubrication
- 2008
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In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - 1350-6501 .- 2041-305X. ; 222:7, s. 827-841
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Journal article (peer-reviewed)abstract
- This work is devoted to studying the combined effect that arises due to surface texture and surface roughness in hydrodynamic lubrication. An effective approach in tackling this problem is by using the theory of reiterated homogenization with three scales. In the numerical analysis of such problems, a very fine mesh is needed, suggesting some type of averaging. To this end, a general class of problems is studied that, e.g. includes the incompressible Reynolds problem in both artesian and cylindrical coordinate forms. To demonstrate the effectiveness of the method several numerical results are presented that clearly show the convergence of the deterministic solutions towards the homogenized solution.Moreover, the convergence of the friction force and the load carrying capacity of the lubricant film is also addressed in this paper. In conclusion, reiterated homogenization is a feasible mathematical tool that facilitates the analysis of this type of problem.
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| 8. |
- Andersson, Martin, et al.
(author)
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Efficiency and temperature of spray lubricated superfinished spur gears
- 2022
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In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - : SAGE Publications. - 1350-6501 .- 2041-305X. ; 236:11, s. 2283-2291
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Journal article (peer-reviewed)abstract
- Gearboxes are one of the most power dense systems used today, and in certain instances their limiting factor is the ability to evacuate heat from the gear contact. This work analyses the efficiency (i.e. heat generation) and tooth temperature in the three lubricating conditions dip, into mesh spray and out of mesh spray for superfinished gears which are then compared to ground gears. A back-to-back gear test rig is employed to test maximum contact pressures at the pitch of 0.59 to 0.96 GPa and pitch velocities from 0.5 to 20 m/s at a controlled lubricant temperature of 90 °C. The results show superfinished gears have higher mesh efficiency and lower gear tooth and bulk temperatures, hence lower heat flux compared to ground gears in all lubricating conditions.
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| 9. |
- Andersson, Martin, et al.
(author)
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Efficiency and temperature of spur gears using spray lubrication compared to dip lubrication
- 2017
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In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - : SAGE PUBLICATIONS LTD. - 1350-6501 .- 2041-305X. ; 231:11, s. 1390-1396
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Journal article (peer-reviewed)abstract
- Increased machine efficiency is a requirement in today's world and geared transmissions are no exception. A back-to-back gear test rig was used to compare dip lubrication with spray lubrication regarding gearbox efficiency, mesh efficiency, gear temperature and surface roughness. Gears lubricated at the inlet of the mesh show a lower measured temperature when compared to spray lubrication at the outlet of the mesh. Spray lubrication, when compared to dip lubrication, yields the same efficiency for both rotating directions at the tested speeds of 0.5 to 20 m/s. Spray lubrication shows a significantly higher total gearbox efficiency at higher speeds, higher measured tooth temperature and no measurable change in surface roughness.
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| 10. |
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