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1 – 10 of 345Arun Bangotra and Sanjay Sharma
This study aims to investigate the impact of surface waviness on the static performance parameters of hydrodynamic journal bearings operating with lubricants containing copper…
Abstract
Purpose
This study aims to investigate the impact of surface waviness on the static performance parameters of hydrodynamic journal bearings operating with lubricants containing copper oxide (CuO) and cerium oxide (CeO2) nanoparticles.
Design/methodology/approach
The static performance parameters of bearings with surface waviness and the addition of nanoparticles in lubricants were calculated using the nondimensional form of Reynolds equation and finite element method. Static performance parameters are calculated at different waviness numbers in the circumferential, axial and both directions at various wave amplitudes with variable viscosities of lubricants with nanoparticles using the viscosity equation forming a relationship between the relative viscosity, temperature and weight fraction of nanoparticles in lubricant developed from the experimental results.
Findings
The computed results indicate that the impact of waviness on the bearing surface enhances the load capacity, reduces friction coefficient, and is more effective in the circumferential direction than in the axial direction or in both directions. The addition of CuO and CeO2 to the lubricant enhanced its viscosity which further improved the steady-state parameters of the wave bearing.
Research limitations/implications
This study is based on a numerical technique, which has significant limitations, and the simulated results must be tested experimentally.
Practical implications
The current findings will be beneficial for designers to improve the performance of hydrodynamic journal bearings.
Originality/value
The calculated results demonstrate that the combined effect of the surface waviness on bearings and the addition of nanoparticles to lubricants can greatly increase the performance of hydrodynamic journal bearings.
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Haibin Geng, Jinglong Li, Jiangtao Xiong, Xin Lin, Dan Huang and Fusheng Zhang
As known, the wire and arc additive manufacture technique can achieve stable process control, which is represented with periodic surface waviness, when using empirical methods or…
Abstract
Purpose
As known, the wire and arc additive manufacture technique can achieve stable process control, which is represented with periodic surface waviness, when using empirical methods or feedback control system. But it is usually a tedious work to further reduce it using trial and error method. The purpose of this paper is to unveil the formation mechanism of surface waviness and develop a method to diminish it.
Design/methodology/approach
Two forming mechanisms, wetting and spreading and remelting, are unveiled by cross-section observation. A discriminant is established to differentiate which mechanism is valid to dominate the forming process under the given process parameters.
Findings
Finally, a theoretical method is developed to optimize surface waviness, even forming a smooth surface by establishing a matching relation between heat input (line energy) and materials input (the ratio of wire feed speed to travel speed).
Originality/value
Formation mechanisms are revealed by observing cross-section morphology. A discriminant is established to differentiate which mechanism is valid to dominate the forming process under the given process parameters. A mathematical model is developed to optimize surface waviness, even forming a smooth surface through establishing a matching relation between heat input (line energy) and materials input (the ratio of wire feed speed to travel speed).
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Prodip Kumar Das, Shohel Mahmud, Syeda Humaira Tasnim and A.K.M. Sadrul Islam
A numerical simulation has been carried out to investigate the buoyancy induced flow and heat transfer characteristics inside a wavy walled enclosure. The enclosure consists of…
Abstract
A numerical simulation has been carried out to investigate the buoyancy induced flow and heat transfer characteristics inside a wavy walled enclosure. The enclosure consists of two parallel wavy and two straight walls. The top and the bottom walls are wavy and kept isothermal. Two straight‐vertical sidewalls are considered adiabatic. Governing equations are discretized using the control volume based finite‐volume method with collocated variable arrangement. Simulation was carried out for a range of surface waviness ratios, λ=0.00‐0.25; aspect ratios, A=0.25‐0.5; and Rayleigh numbers Ra=100‐107 for a fluid having Prandtl number equal to 1.0. Results are presented in the form of local and global Nusselt number distributions, streamlines, and isothermal lines for different values of surface waviness and aspect ratios. For a special case of λ=0 and A=1.0, the average Nusselt number distribution is compared with available reference. The results suggest that natural convection heat transfer is changed considerably when surface waviness changes and also depends on the aspect ratio of the domain. In addition to the heat transfer results, the heat transfer irreversibility in terms of Bejan number (Be) was measured. For a set of selected values of the parameters (λ, A, and Ra), a contour of the Bejan number is presented at the end of this paper.
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Panagiota Polydoropoulou, Konstantinos Tserpes, Spiros Pantelakis and Christos Katsiropoulos
The purpose of this paper is the development of a multiscale model which simulates the effect of the dispersion, the waviness, the interphase geometry as well as the…
Abstract
Purpose
The purpose of this paper is the development of a multiscale model which simulates the effect of the dispersion, the waviness, the interphase geometry as well as the agglomerations of multi-walled carbon nanotubes (MWCNTs) on the Young’s modulus of a polymer filled with 0.4 Vol.% MWCNTs.
Design/methodology/approach
For the determination of the homogenized elastic properties of the hybrid material representative unit cells (RUCs) have been used. The predicted homogenized elastic properties were used for the prediction of the Young’s modulus of the filled material by simulating a finite element (FE) model of a tensile specimen. Moreover, the model has been validated by comparing the predicted values of the numerical analysis with experimental tensile results.
Findings
As the MWCNT agglomerates increase, the results showed a remarkable decrease of the Young’s modulus regarding the polymer filled with aligned MWCNTs while only slight differences on the Young’s modulus have been found in the case of randomly oriented MWCNTs. This might be attributed to the low concentration of the MWCNTs (0.4 Vol.%) into the polymer. For low MWCNTs concentrations, the interphase seems to have negligible effect on the Young’s modulus. Furthermore, as the MWCNTs waviness increases, a remarkable decrease of the Young’s modulus of the polymer filled with aligned MWCNTs is observed. In the case that MWCNTs are randomly dispersed into the polymer, both numerical and experimental results have been found to be consistent regarding the Young’s modulus.
Practical implications
The methodology used can be adopted by any system containing nanofillers.
Originality/value
Although several studies on the effect of the MWCNTs distribution on the Young’s modulus have been conducted, limited results exist by using a more realistic RUC including a periodic geometry of more than 20 MWCNTs with random orientation and a more realistic waviness of MWCNTs with aspect ratio exceeding 150.
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Nishant Tiwari and Manoj Kumar Moharana
This paper aims to emphasize on studying various geometrical modification performed in wavy and raccoon microchannel by manipulating parameters, i.e. waviness (γ), expansion…
Abstract
Purpose
This paper aims to emphasize on studying various geometrical modification performed in wavy and raccoon microchannel by manipulating parameters, i.e. waviness (γ), expansion factor (α), wall to fluid thermal conductivity ratio (ksf), substrate thickness to channel height ratio (dsf) and Reynolds number (Re) for obtaining optimum parameter(s) that leads to higher heat dissipation rate.
Design/methodology/approach
A three-dimensional solid-fluid conjugate heat transfer numerical model is designed to capture flow characteristics and heat transfer in single-phase laminar flow microchannels. The governing equations are solved using finite volume method.
Findings
The results are presented in terms of average base temperature, average Nusselt number, pressure drop, dimensionless local heat flux, dimensionless wall and bulk fluid temperature, local Nusselt number and performance factor including axial conduction number. Heat dissipation rate with raccoon microchannel configuration is found to be higher compared to straight and wavy microchannel. With waviness of γ = 0.167, and 0.267 in wavy and raccoon microchannel, respectively, performance factor attains maximum value compared to other waviness for all values of Reynolds number. It is also found that the effect of axial wall conduction in wavy and raccoon microchannel is negligible. Additionally, thermal performance of wavy and raccoon microchannel is compared with straight microchannel.
Practical implications
In recent past years, much complex design of microchannel has been proposed for heat transfer enhancement, but the feasibility of available manufacturing techniques to fabricate complex geometries is still questionable. However, fabrication of wavy and raccoon microchannel is easy, and their heat dissipation capability is higher.
Originality/value
This makes the difference in wall and bulk fluid temperature smaller. Thus, present work highlighted the dominance of axial wall conduction on thermal and hydrodynamic performance of wavy and raccoon microchannel under conjugate heat transfer situation.
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Mohamed Taoufik Khabou, Taissir Hentati, Mohamed Slim Abbes, Fakher Chaari and Mohamed Haddar
The aim of this paper is to present a theoretical model to simulate the dynamic behavior of a spur gear, taking into account its ball bearings defects.
Abstract
Purpose
The aim of this paper is to present a theoretical model to simulate the dynamic behavior of a spur gear, taking into account its ball bearings defects.
Design/methodology/approach
The proposed model is based on the implicit Newmark‐β with Newton‐Raphson numerical integration technique in order to analyze the impact of the worn bearings on the non linear dynamic behavior of one stage spur gear transmission system.
Findings
The dynamic behavior of spur gear is studied taking into account ball bearings defects thanks to the proposed model.
Originality/value
A new numerical model is proposed to simulate the dynamic behavior of rotating spur gear system taking into account both waviness and backlash defects.
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Anastasios Zavos and Pantelis George Nikolakopoulos
The purpose of this paper is to review and to provide a dipper understanding of what happens to piston rings and cylinder surfaces when manufacturing errors depicted, such as…
Abstract
Purpose
The purpose of this paper is to review and to provide a dipper understanding of what happens to piston rings and cylinder surfaces when manufacturing errors depicted, such as waviness and straightness. The mechanism of friction and the piston ring structural integrity, due to the surface irregularities, are analyzed either for smooth ring surface or for artificial textured, while piston ring floats into the piston groove or not.
Design/methodology/approach
In this work two tribological models of a piston ring- cylinder package are presented using CFD analysis. Initially, the piston ring is considered as a secured ring in the groove of piston (secured ring) while in second model, the piston ring floats into the piston groove (free ring).
Findings
Increasing the number of waves across the piston ring thickness, the structural integrity of the ring is strongly influenced. Piston ring with surface texturing reduces the mean friction force, under the consideration of cylinder straightness. The gas leaks due to existence of the ring gap, affects significantly the maximum mechanical stresses.
Originality/value
The novelty of this paper is the analysis of manufacturing errors, such as waviness and straightness either for smooth or for artificial textured piston ring. In particular, the piston ring structural integrity investigated while chamber gas pressure leaks through the ring gap or not. The number of the waves, their amplitude and the fluid velocity are also taken into consideration.
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Zhen-Tao Li, Yangli Zhou, Xiaoli Yin, Muming Hao, Dechao Meng and Baojie Ren
The purpose of this paper is to investigate the effects of surface topography, including surface roughness, waviness and taper, on the cavitation of liquid film lubricated…
Abstract
Purpose
The purpose of this paper is to investigate the effects of surface topography, including surface roughness, waviness and taper, on the cavitation of liquid film lubricated mechanical seals (LFL-MS).
Design/methodology/approach
A universal governing equation considering cavitation is established, and an equivalent relative density is defined to characterize the cavitation degree. The equation is discretized by the finite volume method and solved by the Gauss–Seidel relaxation scheme.
Findings
Results indicate that both radial length and a circumferential width of the cavitation zone and cavitation degree are affected significantly by the waviness amplitude and taper, but the effect of surface roughness is limited.
Originality/value
Effect mechanism of surface topography on the cavitation of LFL-MS is investigated and cavitation degree is reflected by an equivalent relative density. The results further help to comprehensively explore the cavitation mechanism.
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Jing Liu, Zhifeng Shi and Yimin Shao
Combined defects in ball bearings may be caused during the use or manufacturing process, which can significantly affect their vibration characteristics. The previous defect models…
Abstract
Purpose
Combined defects in ball bearings may be caused during the use or manufacturing process, which can significantly affect their vibration characteristics. The previous defect models in the literature can only describe single defects such as the surface waviness and localized defect. This paper aims to propose an in-depth understanding of radial vibrations of a ball bearing with the combined defect.
Design/methodology/approach
A dynamic model for a ball bearing with the combined defect including the surface waviness and localized defect on its races is proposed. The effects of the combined defect sizes on the radial bearing vibrations are investigated. The results from the proposed model considering the combined defect are compared with the available results from the previous methods considering the single defects.
Findings
The acceleration amplitude is significantly affected by the surface waviness, localized defect and the combined defect on its races. The effect of the combined defect on the acceleration amplitude is larger than that of the single defect. The amplitude and peak frequency of the spectrum of acceleration for the combined defect increases with the defect sizes. The RMS value of the accelerations for the combined defect increases with the combined defect sizes.
Originality/value
Consequently, the proposed model can predict more accurate and in-depth understanding of the radial vibrations caused by the combined defect in the ball bearing.
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Keywords
Man Zhang and Abdelkader Frendi
The tubercles at the leading edge of Humpback Whale flippers have been shown to increase aerodynamic efficiency. The purpose of this paper is to compute the flow structures and…
Abstract
Purpose
The tubercles at the leading edge of Humpback Whale flippers have been shown to increase aerodynamic efficiency. The purpose of this paper is to compute the flow structures and noise signature of a NACA0012 airfoil with and without leading edge waviness, and located in the wake of a cylinder using the hybrid RANS-LES method.
Design/methodology/approach
The mean flow Mach number is 0.2 and the angle of attack used is 2°. After benchmarking the method using existing experimental results, unsteady computations were then carried-out on both airfoil geometries and for a 2° angle of attack.
Findings
Results from these computations confirmed the aerodynamic benefits of the leading edge waviness. Moreover, the wavy leading edge airfoil was found to be at least 4 dB quieter than its non-wavy counterpart. In-depth analysis of the computational results revealed that the wavy leading edge airfoil breaks up the large coherent structures which are then convected at higher speeds down the trough region of the waviness in agreement with previous experimental observations. This result is supported by both the two-point and space-time correlations of the wall pressure.
Research limitations/implications
The limitations of the current findings reside in the fact that both the Reynolds number and the flow Mach number are low, therefore not applicable to aircrafts. In order to extend the study to practical aircrafts one needs huge grids and large computational resources.
Practical implications
The results obtained here could have a huge implications on the design of future aircrafts and spacecrafts. More specifically, the biggest benefit from such redesign is the reduction of acoustic signature as well as increased efficiency in fuel consumption.
Social implications
Reducing acoustic signature from aircrafts has been a major research thrust for NASA and Federal Aviation Administration. The social impact of such reduction would be improved quality of life in airport communities. For military aircrafts, this could results in reduced detectability and hence saving lives.
Originality/value
Humpback Whales have been studied by various researchers to understand the effects of leading edge “tubercles” on flow structures. What is new in this study is the numerical confirmation of the effects of the tubercles on the flow structures and the resulting noise radiations. It is shown through the use of two-point correlations and space-time correlations that the flow structures in the trough area are indeed vortex tubes.
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