Numerical study of surface dimple phenomenon by starvation in simple sliding contact

2017 ◽  
Vol 69 (6) ◽  
pp. 980-989 ◽  
Author(s):  
Shun Cui ◽  
Hiroshi Nishikawa ◽  
Jing Wang ◽  
Qian Zou

Purpose This study aims to use a thermal elastohydrodynamic lubrication (EHL) algorithm incorporating an Eyring flow model to solve a steady-state contact in simple sliding motion. Design/methodology/approach A theoretical model was used to investigate the effect of starvation on the surface dimple phenomenon by gradually reducing the thickness of the inlet oil layer. Findings The increase in the starvation degree reduces the dimple depth, film thickness, the pressure peak and the temperature rise. Under the severe starvation condition, the dimple is eliminated so that the EHL contact becomes partly parched. In elliptical results, for the same starvation parameters, the oil replenishment is stronger than that in circular contact. Originality/value This paper fulfils an exploration to study how the oil starvation influences the surface dimple phenomenon.

2020 ◽  
Vol 72 (10) ◽  
pp. 1139-1145
Author(s):  
Mingyu Zhang ◽  
Jing Wang ◽  
Jinlei Cui ◽  
Peiran Yang

Purpose The purpose of this paper is to numerically study the variations of oil film pressure, thickness and temperature rise in the contact zone of plate-pin pair in silent chains. Design/methodology/approach A steady-state thermal elastohydrodynamic lubrication (EHL) model is built using a Ree–Eyring fluid. The contact between the plate and the pin is simplified as a narrow finite line contact, and the lubrication state is examined by varying the geometry and the plate speed. Findings With increase in the equivalent radius of curvature, the pressure peak and the central film thickness increase. Because the plate is very thin, the temperature rise can be neglected. Even when the influence of the rounded corner region is less, a proper design can beneficially increase the minimum film thickness at both edges of the plate. Under a low entraining speed, strong stress concentration results in close-zero film thickness at both edges of the plate. Originality/value This study reveals the EHL feature of the narrow finite line contact in plate-pin pairs for silent chains and will support the future works considering transient effect, surface features and wear.


2020 ◽  
Vol 72 (6) ◽  
pp. 713-722
Author(s):  
Hongwei Tang ◽  
Jing Wang ◽  
Nannan Sun ◽  
Jianrong Zhu

Purpose The influence of the cam angular speed on the pressure, film thickness and temperature profiles at some selected angular positions together with the oil characteristics are investigated. Design/methodology/approach A high-order polynomial cam is used, and thermal elastohydrodynamic lubrication (EHL) calculations are carried out by the multi-grid method and line-line scanning technique. Findings It is found that the film thickness decreases with a decrease in angular speed. The depth of the dimple that occurred in the reverse motion is also reduced because of the recession in the “temperature–viscosity wedge” effect. Originality/value It is revealed that the reduction in the cam angular speed makes the classical big surface dimple evolve into a small centralized dimple during the opposite sliding motion. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2019-0327


2020 ◽  
Vol 72 (5) ◽  
pp. 703-708 ◽  
Author(s):  
Jiaxing Pei ◽  
Xu Han ◽  
Yourui Tao

Purpose The purpose of this paper is to propose an simple and efficient stiffness model for line contact under elastohydrodynamic lubrication (EHL) and to investigate the gear meshing stiffness by the proposed model. Design/methodology/approach The method combines the surface contact stiffness and film stiffness as EHL contact stiffness. The EHL contact stiffness can be calculated by the external load and displacement of the load action point. The displacement is the sum of deformation of the film and contact surface and is equal to the distance of the mutual approach of two contact bodies. Findings The conclusion is drawn that the contact stiffness calculated by the proposed model is smaller than that by the minimum film model and larger than that by the mean film model. It is also concluded that the gear meshing stiffness under EHL is slightly smaller than that under dry contact. Originality/value The EHL contact stiffness can be obtained by the increment of external load and mutual approach directly. The calculation of oil film stiffness and surface contact stiffness separately is avoided. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2019-0465


2018 ◽  
Vol 70 (1) ◽  
pp. 23-32 ◽  
Author(s):  
Ye Zhou ◽  
Caichao Zhu ◽  
Huaiju Liu ◽  
Chaosheng Song ◽  
Zufeng Li

Purpose Coatings are widely used in gears to keep interface from wearing excessively. The purpose of this paper is to study the effect of coating properties and working conditions on the pressure, the shear traction, stresses as well as the fatigue life of spur gear. Design/methodology/approach A numerical contact fatigue life model of a coated spur gear pair under elastohydrodynamic lubrication (EHL) is developed based on the characteristics of gear geometry and kinematics, lubrication conditions and material properties. Frequency response functions and the discrete convolute and fast Fourier transform (DC-FFT) algorithm are applied to obtain elastic deformation and stress. Mutil-axial fatigue criteria are used to evaluate the contact fatigue life based upon the predicted time-varying stress fields of coated bodies. Findings The maximum Mises stress decreases while the fatigue life increases as the coating modulus decreases. A thinner coating leads to a longer life and a smaller maximum Mises stress for hard coatings. The load has more significant effect on the contact fatigue life of soft coatings. Originality/value The developed model can be used to evaluate the contact fatigue life of coated gear under EHL and help designers analyze the effect of coating elastic modulus and thickness on the contact pressure, film thickness and stress.


2021 ◽  
Vol 31 (5) ◽  
pp. 1373-1395
Author(s):  
Iman Mazinani ◽  
Mohammad Mohsen Sarafraz ◽  
Zubaidah Ismail ◽  
Ahmad Mustafa Hashim ◽  
Mohammad Reza Safaei ◽  
...  

Purpose Two disastrous Tsunamis, one on the west coast of Sumatra Island, Indonesia, in 2004 and another in North East Japan in 2011, had seriously destroyed a large number of bridges. Thus, experimental tests in a wave flume and a fluid structure interaction (FSI) analysis were constructed to gain insight into tsunami bore force on coastal bridges. Design/methodology/approach Various wave heights and shallow water were used in the experiments and computational process. A 1:40 scaled concrete bridge model was placed in mild beach profile similar to a 24 × 1.5 × 2 m wave flume for the experimental investigation. An Arbitrary Lagrange Euler formulation for the propagation of tsunami solitary and bore waves by an FSI package of LS-DYNA on high-performance computing system was used to evaluate the experimental results. Findings The excellent agreement between experiments and computational simulation is shown in results. The results showed that the fully coupled FSI models could capture the tsunami wave force accurately for all ranges of wave heights and shallow depths. The effects of the overturning moment, horizontal, uplift and impact forces on a pier and deck of the bridge were evaluated in this research. Originality/value Photos and videos captured during the Indian Ocean tsunami in 2004 and the 2011 Japan tsunami showed solitary tsunami waves breaking offshore, along with an extremely turbulent tsunami-induced bore propagating toward shore with significantly higher velocity. Consequently, the outcomes of this current experimental and numerical study are highly relevant to the evaluation of tsunami bore forces on the coastal, over sea or river bridges. These experiments assessed tsunami wave forces on deck pier showing the complete response of the coastal bridge over water.


Author(s):  
Mingfei Ma ◽  
Wen Wang ◽  
Wenxun Jiang

As a common phenomenon in elastohydrodynamic lubrication, cavitation has an effect on the completeness of the oil film in the contact area. Many studies have therefore been conducted on cavitation. Experimental researches on cavitation usually rely on optical interference observation, which offers a limited resolution and observation range. In this paper, an infrared thermal camera is used to observe the cavity bubbles on a ball-on-disc setup under sliding/rolling conditions. The results show that the cavity length increases with an increases of the entrainment speed and the viscosity of the lubricants. These observations are explained by a numerical model based on Elrod's algorithm. Effects of entrainment speed and lubricant viscosity on the breakup of cavitation bubbles and the cavitation states are investigated. Both the simulation and experimental results show that a negative pressure area is present behind the Hertzian contact area. The ambient pressure plays a role in maintaining cavitation state 1. The cavitation pressure is close to the vacuum pressure when the entrainment speed is low and to the ambient pressure instead when the entrainment speed is high.


2019 ◽  
Vol 10 (2) ◽  
pp. 138-154
Author(s):  
Farshid Masoumi ◽  
Ebrahim Farajpourbonab

Purpose The primary purpose of this research was to expand the knowledge base regarding the behavior of steel columns during exposure to fire. This paper presents the numerical study of the effect of heat on the performance of parking steel column in a seven-story steel building under cyclic loading. Design/methodology/approach In this research, the forces and deformations developed during a fire are estimated by using detailed 3D finite-element models. The analyses are in the form of a coupled thermo-mechanical analysis in two types of loading: concurrent loading (fire and cyclic loading) and non-concurrent loading (first fire and then cyclically), and the analyses have been conducted in both states of the fire loading with cooling and without cooling using the ABAQUS software. Further, it was investigated whether, during the fire loading, the specimen was protected by a 3-cm-thick concrete coating and how much it changes the seismic performance. After verification of the specimen with the experimental test results, the column model was investigated under different loading conditions. Findings The result of analyses indicates that the effect of thermal damage on the performance of steel columns, when cooling is happening late, is more than the state in which cooling occurs immediately after the fire. In this paper, thermal–seismic performance of parking steel columns has been specified and the effect of the fire damage has been investigated for the protected steel by concrete coating and to the non-protected steel, under both cooling and non-cooling states. Originality/value This study led to recommendations based on the findings and suggestions for additional work to support performance-based fire engineering. It is clear that predicting force and deformation on steel column during fire is complex and it is affected by many variables. Here in this paper, those variables are examined and proper results have been achieved.


Author(s):  
Ahmada Omar Ali ◽  
Oluwole Daniel Makinde ◽  
Yaw Nkansah-Gyekye

Purpose – The purpose of this paper is to investigate numerically the unsteady MHD Couette flow and heat transfer of viscous, incompressible and electrically conducting nanofluids between two parallel plates in a rotating channel. Design/methodology/approach – The nanofluid is set in motion by the combined action of moving upper plate, Coriolis force and the constant pressure gradient. The channel rotates in unison about an axis normal to the plates. The nonlinear governing equations for velocity and heat transfer are obtained and solved numerically using semi-discretization, shooting and collocation (bvp4c) techniques together with Runge-Kutta Fehlberg integration scheme. Findings – Results show that both magnetic field and rotation rate demonstrate significant effect on velocity and heat transfer profiles in the system with Cu-water nanofluid demonstrating the highest velocity and heat transfer efficiency. These numerical results are in excellent agreements with the results obtained by other methods. Practical implications – This paper provides a very useful source of information for researchers on the subject of hydromagnetic nanofluid flow in rotating systems. Originality/value – Couette flow of nanofluid in the presence of applied magnetic field in a rotating channel is investigated.


2019 ◽  
Vol 91 (3) ◽  
pp. 428-436 ◽  
Author(s):  
Agnieszka Kwiek

Purpose The purpose of this research is a study into a mathematical approach of a tailless aircraft dynamic stability analysis. This research is focused on investigation of influence of elevons (elevator) on stability derivatives and consequently on the aircraft longitudinal dynamic stability. The main research question is to determine whether this impact should be taken into account on the conceptual and preliminary stage of the analysis of the longitudinal dynamic stability. Design/methodology/approach Aerodynamic coefficients and longitudinal stability derivatives were computed by Panukl (panel methods). The analysis of the dynamic stability of the tailless aircraft was made by the Matlab code and SDSA package. Findings The main result of the research is a comparison of the dynamic stability of the tailless aircraft for different approaches, with and without the impact of elevator deflection on the trim drag and stability derivatives. Research limitations/implications This paper presents research that mostly should be considered on the preliminary stage of aircraft design and dynamic stability analysis. The impact of elevons deflection on the aircraft moment of inertia has been omitted. Practical implications The results of this research will be useful for the further design of small tailless unmanned aerial vehicles (UAVs). Originality/value This research reveals that in case of the analysis of small tailless UAVs, the impact of elevons deflection on stability derivatives is bigger than the impact of a Mach number. This impact should be taken into consideration, especially for a phugoid mode.


2018 ◽  
Vol 46 (5) ◽  
pp. 17-25
Author(s):  
Timothy Galpin

Purpose Mergers and acquisitions (M&As) have become the preferred growth strategy for many executives. However, simply “doing deals” is not enough to create a competitive advantage for their companies. Only focusing on M&A as a financial transaction is too narrow of an approach, which is easily duplicated across firms. Using Woodward, Inc. as a case example, this article shows how using an actionable, end-to-end process model, and embedding integrated capabilities within the organization, across the entire process, managers can make M&A a core competence to provide a valuable, rare, and inimitable advantage for their firms. Design/methodology/approach A mixed-methods approach, combining action research with a narrative synthesis of empirical and practice literature was used to develop a comprehensive M&A process model - the Deal Flow Model - consisting of ten stages across three phases. The resource-based view, core competencies, and the VRIO framework provide a theoretical foundation for the model. An application of the Deal Flow Model using Woodward Inc. as a case example is also presented. Findings Only focusing on M&A as a financial transaction is too narrow of an approach, which is easily duplicated across firms. Instead, using an actionable, end-to-end process model, and embedding integrated capabilities within the organization across the entire M&A process provides a valuable, rare, and inimitable advantage for firms. Research limitations/implications Researchers will find the Deal Flow Model useful as a structure to examine the M&A process as a whole or to frame single-stage, single-discipline research in the broader context of the overall M&A process. Practical implications A practice-oriented Deal Flow Model, providing a cross-disciplinary, end-to-end view of the M&A process is presented. The model is designed to be actionable by managers, who can apply the process to build the M&A competence of their organization. Originality/value The Deal Flow Model is unique as it is designed to be actionable by managers, who can apply the process to build the M&A competence of their organization. Likewise, researchers will find the model useful as a structure to examine the M&A process as a whole or to frame single-stage, single-discipline research in the broader context of the overall M&A process.


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