A mixed contact model for an immersed collision between two solid surfaces

2008 ◽  
Vol 366 (1873) ◽  
pp. 2205-2218 ◽  
Author(s):  
Fu-Ling Yang ◽  
Melany L Hunt
Keyword(s):  
Surface Deformation ◽  
Elastohydrodynamic Lubrication ◽  
Solid Particles ◽  
Solid Surfaces ◽  
Additional Energy ◽  
Collision Model ◽  
Dry Granular Flow ◽  
Wide Range ◽  
The Impact ◽  
Surrounding Liquid

Experimental evidence shows that the presence of an ambient liquid can greatly modify the collision process between two solid surfaces. Interactions between the solid surfaces and the surrounding liquid result in energy dissipation at the particle level, which leads to solid–liquid mixture rheology deviating from dry granular flow behaviour. The present work investigates how the surrounding liquid modifies the impact and rebound of solid spheres. Existing collision models use elastohydrodynamic lubrication (EHL) theory to address the surface deformation under the developing lubrication pressure, thereby coupling the motion of the liquid and solid. With EHL theory, idealized smooth particles are made to rebound from a lubrication film. Modified EHL models, however, allow particles to rebound from mutual contacts of surface asperities, assuming negligible liquid effects. In this work, a new contact mechanism, ‘mixed contact’, is formulated, which considers the interplay between the asperities and the interstitial liquid as part of a hybrid rebound scheme. A recovery factor is further proposed to characterize the additional energy loss due to asperity–liquid interactions. The resulting collision model is evaluated through comparisons with experimental data, exhibiting a better performance than the existing models. In addition to the three non-dimensional numbers that result from the EHL analysis—the wet coefficient of restitution, the particle Stokes number and the elasticity parameter—a fourth parameter is introduced to correlate particle impact momentum to the EHL deformation impulse. This generalized collision model covers a wide range of impact conditions and could be employed in numerical codes to simulate the bulk motion of solid particles with non-negligible liquid effects.

Elastohydrodynamic Lubrication of Soft-Layered Solids at Elliptical Contacts: Part 1: Elasticity Analysis

1994 ◽  
Vol 208 (1) ◽  
pp. 31-41 ◽  
Author(s):  
J Q Yao ◽  
D Dowson
Keyword(s):  
Aspect Ratio ◽  
Surface Deformation ◽  
Applied Pressure ◽  
Numerical Procedure ◽  
Elastohydrodynamic Lubrication ◽  
Thin Layers ◽  
Elasticity Analysis ◽  
Synovial Joint ◽  
Wide Range ◽  
Non Linear System

In this two-part paper we consider the elastohydrodynamic lubrication (EHL) of soft-layered solids representing elliptical contacts. The problem has not previously attracted much attention, partly due to the lack of an effective numerical procedure to solve the coupled non-linear system of equations, but it is essential to the proper design of bearings with soft elastomeric liners and the full understanding of synovial joint lubrication. In Part 1, the elasticity analysis for the surface deformation of a low elastic modulus layer on a hard-backing half-space under various forms of normal loadings is considered, by means of both the rigorous Hankel transform method and various simplifications. For layers of compressible materials (v ≤ 0.4), a generalized foundation model described by a second-order differential equation is proposed to represent the relationship between the surface deformation and the applied pressure. The empirical equation developed in this study is valid for a very wide range of the aspect ratio of the contact and provides an alternative way of modelling the elastic deformation without recourse to the often tedious integration in the numerical analysis of the EHL problem. The simplest form (constrained column model) of the equation, where the surface deformation is directly proportional to the local applied pressure, was found to be reasonably accurate for compressible thin layers (the aspect ratio 2b/ht ≥ 5 and Poisson's ratio v ≤ 0.4).

Film Thickness and Asperity Load Formulas for Line-Contact Elastohydrodynamic Lubrication With Provision for Surface Roughness

2012 ◽  
Vol 134 (1) ◽  
Author(s):  
M. Masjedi ◽  
M. M. Khonsari
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Reynolds Equation ◽  
Surface Deformation ◽  
Elastohydrodynamic Lubrication ◽  
Load Ratio ◽  
Material Surface ◽  
Line Contact ◽  
Wide Range ◽  
Minimum Film Thickness

Three formulas are derived for predicting the central and the minimum film thickness as well as the asperity load ratio in line-contact EHL with provision for surface roughness. These expressions are based on the simultaneous solution to the modified Reynolds equation and surface deformation with consideration of elastic, plastic and elasto-plastic deformation of the surface asperities. The formulas cover a wide range of input and they are of the form f(W, U, G, σ¯, V), where the parameters represented are dimensionless load, speed, material, surface roughness and hardness, respectively.

Surface deformation and rebound for normal single-particle collisions in a surrounding fluid

2019 ◽  
Vol 871 ◽  
pp. 1044-1066 ◽  
Author(s):  
Angel Ruiz-Angulo ◽  
Shahrzad Roshankhah ◽  
Melany L. Hunt
Keyword(s):  
Time Scale ◽  
Surface Deformation ◽  
Stokes Number ◽  
Particle Collisions ◽  
Elastic Plastic ◽  
Viscous Losses ◽  
Wide Range ◽  
The Impact ◽  
Surrounding Fluid ◽  
Fluid Characteristics

This article presents experimental measurements involving immersed collisions between a rigid impactor and a deformable target for a wide range of Reynolds and Stokes numbers. Three aluminium alloys are used as solid targets submerged in seven different fluids covering a wide range of viscosity and density. The collision and rebound velocities as well as the depth and diameter of the crater produced by the collisions are measured with high resolution. Most of the experiments in this study occur at velocities for which the deformation is within the elastic–plastic regime. Results of the experiments in air are analysed by elastic, plastic and elastic–plastic theories, and demonstrate the complexities of modelling elastic–plastic collisions. For collisions in a liquid, the measurements show that the size of the crater is independent of the fluid characteristics if the Stokes number is beyond a critical value. The normal coefficient of restitution can be estimated by including both viscous losses and plasticity effects and assuming that the collision time scale is significantly shorter than the hydrodynamic time scale. The results of the crater dimensions are also used to develop an analytical expression for the volume of deformation of the material as a function of material properties and the impact and critical Stokes numbers.

Influences of transient impact and vibration on the lubrication performance of spur gears

2020 ◽  
pp. 135065012092597
Author(s):  
Xingbao Huang ◽  
Bintang Yang ◽  
Youqiang Wang
Keyword(s):  
Film Thickness ◽  
Thermal Effect ◽  
Surface Deformation ◽  
Load Condition ◽  
Elastohydrodynamic Lubrication ◽  
Minimum Thickness ◽  
Film Pressure ◽  
Lubrication Performance ◽  
The Coefficient Of Friction ◽  
The Impact

In this paper, the mathematical model of gear elastohydrodynamic lubrication is presented. The transient impact operating condition and underdamped load condition are considered. Taking thermal effect and squeeze effect into account, the full numerical solution of gear pairs is obtained. In this numerical calculation, multigrid method is applied to compute the film pressure; multigrid integration technique is used to calculate the solid surface deformation; column by column scanning technique is employed to calculate temperature. The simulation results show that an entrapped film dimple forms under transient impact condition; transient impact causes remarkable increases in film pressure and film temperature. Compared with the normal case the minimum thickness of the impact case is smaller, which is not beneficial to teeth lubrication. Thermal effect induces some decreases in film thickness because of the viscosity–temperature relationship. Vibrational load with high damped frequency causes greater increases in film thickness and greater decreases in the coefficient of friction than that of low damped frequency. However, the film temperature of high damped frequency is higher than that of low damped frequency.

THE IMPACT OF LEADERSHIP PRACTICES TO TEAM MEMBERS’ SATISFACTION

2009 ◽  
Vol 8 (1) ◽  
Author(s):  
Chalimah .
Keyword(s):  
Conflict Resolution ◽  
Leadership Practices ◽  
Hotel Industry ◽  
Leader Behavior ◽  
Team Leader ◽  
Shop Floor ◽  
Team Members ◽  
Top Executives ◽  
Wide Range ◽  
The Impact

eamwork is becoming increasingly important to wide range of operations. It applies to all levels of the company. It is just as important for top executives as it is to middle management, supervisors and shop floor workers. Poor teamwork at any level or between levels can seriously damage organizational effectiveness. The focus of this paper was therefore to examine whether leadership practices consist of team leader behavior, conflict resolution style and openness in communication significantly influenced the team member’s satisfaction in hotel industry. Result indicates that team leader behavior and the conflict resolution style significantly influenced team member satisfaction. It was surprising that openness in communication did not affect significantly to the team members’ satisfaction.

Stress, anxiety, depression and burnout in frontline health care workers during COVID-19 pandemic: a brief systematic review and new data from Russia

2021 ◽  
Author(s):  
Ekaterina Mosolova ◽  
Dmitry Sosin ◽  
Sergey Mosolov
Keyword(s):  
Risk Factors ◽  
Systematic Review ◽  
Female Gender ◽  
Assessment Tools ◽  
Care Workers ◽  
Younger Age ◽  
Wide Range ◽  
Associated Risk Factors ◽  
Anxiety Depression ◽  
The Impact

During the COVID-19 pandemic, healthcare workers (HCWs) have been subject to increased workload while also exposed to many psychosocial stressors. In a systematic review we analyze the impact that the pandemic has had on HCWs mental state and associated risk factors. Most studies reported high levels of depression and anxiety among HCWs worldwide, however, due to a wide range of assessment tools, cut-off scores, and number of frontline participants in the studies, results were difficult to compare. Our study is based on two online surveys of 2195 HCWs from different regions of Russia during spring and autumn epidemic outbreaks revealed the rates of anxiety, stress, depression, emotional exhaustion and depersonalization and perceived stress as 32.3%, 31.1%, 45.5%, 74.2%, 37.7% ,67.8%, respectively. Moreover, 2.4% of HCWs reported suicidal thoughts. The most common risk factors include: female gender, nurse as an occupation, younger age, working for over 6 months, chronic diseases, smoking, high working demands, lack of personal protective equipment, low salary, lack of social support, isolation from families, the fear of relatives getting infected. These results demonstrate the need for urgent supportive programs for HCWs fighting COVID-19 that fall into higher risk factors groups.

A MODELING SYSTEM FOR CLIMATE CHANGE RISK ASSESSMENT, MANAGEMENT AND HEDGING IN COASTAL AREAS

2017 ◽  
Author(s):  
Sergei Soldatenko ◽  
Sergei Soldatenko ◽  
Genrikh Alekseev ◽  
Genrikh Alekseev ◽  
Alexander Danilov ◽  
...  
Keyword(s):  
Climate Change ◽  
Risk Assessment ◽  
Coastal Areas ◽  
Mitigation Strategies ◽  
System Structure ◽  
The Arctic ◽  
Risk Modeling ◽  
Wide Range ◽  
Adverse Weather ◽  
The Impact

Every aspect of human operations faces a wide range of risks, some of which can cause serious consequences. By the start of 21st century, mankind has recognized a new class of risks posed by climate change. It is obvious, that the global climate is changing, and will continue to change, in ways that affect the planning and day to day operations of businesses, government agencies and other organizations and institutions. The manifestations of climate change include but not limited to rising sea levels, increasing temperature, flooding, melting polar sea ice, adverse weather events (e.g. heatwaves, drought, and storms) and a rise in related problems (e.g. health and environmental). Assessing and managing climate risks represent one of the most challenging issues of today and for the future. The purpose of the risk modeling system discussed in this paper is to provide a framework and methodology to quantify risks caused by climate change, to facilitate estimates of the impact of climate change on various spheres of human activities and to compare eventual adaptation and risk mitigation strategies. The system integrates both physical climate system and economic models together with knowledge-based subsystem, which can help support proactive risk management. System structure and its main components are considered. Special attention is paid to climate risk assessment, management and hedging in the Arctic coastal areas.

The Management of Post-Tonsillectomy Morbidity in Patients With Sleep Apnoea

2019 ◽  
Vol 70 (10) ◽  
pp. 3738-3740
Keyword(s):  
Day Surgery ◽  
Sleep Apnoea ◽  
Integrative Approach ◽  
Multicenter Studies ◽  
Therapeutic Modalities ◽  
Advantages And Disadvantages ◽  
Obstructive Sleep ◽  
Wide Range ◽  
The Impact ◽  
Surgery Center

The Tonsillectomy in children or adults is an intervention commonly encountered in the ENT (Ear Nose and Throat) and Head and Neck surgeon practice. The current tendency is to perform this type of surgery in major ambulatory surgery centers. Two objectives are thus pursued: first of all, the increase of the patient quality of life through the reintegration into the family as quickly as possible and secondly, the expenses associated with continuous hospitalization are reduced. Any tertiary (multidisciplinary) sleep center must ensure the complete diagnosis and treatment (including surgery) of sleep respiratory disorders. Under these conditions the selection of patients and especially the implementation of the specific protocols in order to control the postoperative complications it becomes essential. The present paper describes our experience of tonsillectomy as treatment for selected patients with chronic rhonchopathy (snoring) and mild to moderate obstructive sleep apnoea. It was presented the impact of antibiotics protocols in reducing the main morbid outcomes following tonsillectomy, in our day surgery center. The obtained results can also be a prerequisite for the integrative approach of the patients with sleep apnoea who were recommended surgical treatment. Considering the wide range of therapeutic modalities used in sleep apnoea, each with its specific advantages and disadvantages, more extensive and multicenter studies are needed. Keywords: post-tonsillectomy morbidity, day surgery center, sleep disorders

Multiple interactions in riverine biofilms - surfactant adsorption, bacterial attachment and biodegradation

1995 ◽  
Vol 31 (1) ◽  
pp. 61-70 ◽  
Author(s):  
Graham F. White
Keyword(s):  
Organic Pollutants ◽  
Bacterial Attachment ◽  
Solid Surfaces ◽  
Sediment Surface ◽  
Liquid Interfaces ◽  
Polluted Soils ◽  
Biofilm Bacteria ◽  
The Impact ◽  
Multiple Interactions

Many organic pollutants, especially synthetic surfactants, adsorb onto solid surfaces in natural and engineered aquatic environments. Biofilm bacteria on such surfaces make major contributions to microbial heterotrophic activity and biodegradation of organic pollutants. This paper reviews evidence for multiple interactions between surfactants, biodegradative bacteria, and sediment-liquid interfaces. Biodegradable surfactants e.g. SDS, added to a river-water microcosm were rapidly adsorb to sediment surface and stimulated the indigenous bacteria to attach to the sediment particles. Recalcitrant surfactants and non-surfactant organic nutrients did not stimulate attachment Attachment of bacteria was maximal when biodegradation was fastest, and was reversed when biodegradation was complete. Dodecanol, the primary product of SDS-biodegradation, markedly stimulated attachment. When SDS was added to suspensions containing sediment and either known degraders or known non-degraders, only the degraders became attached, and attachment accelerated surfactant biodegradation to dodecanol. These cyclical cooperative interactions have implications for the design of biodegradability-tests, the impact of surfactant adjuvants on biodegradability of herbicides/pesticides formulated with surfactants, and the role of surfactants used to accelerate bioremediation of hydrocarbon-polluted soils.

Cognitive Impact of Cerebellar Damage: Is There a Future for Cognitive Rehabilitation?

2018 ◽  
Vol 17 (3) ◽  
pp. 199-206 ◽  
Author(s):  
Kim van Dun ◽  
Frank V. Overwalle ◽  
Mario Manto ◽  
Peter Marien
Keyword(s):  
Affective Disorders ◽  
Cognitive Rehabilitation ◽  
Therapeutic Interventions ◽  
Posterior Fossa Surgery ◽  
Daily Life Activities ◽  
Wide Range ◽  
Affective Deficits ◽  
Cerebellar Injury ◽  
Cognitive Therapies ◽  
The Impact

Background & Objective: During the past 3 decades, numerous neurophysiological, neuroimaging, experimental and clinical studies have evidenced a crucial role for the cerebellum in cognitive, affective and behavioral functions. As a result of the acknowledged modulatory role of the cerebellum upon remote structures such as the cerebral cortex, cerebellar injury may give rise to a constellation of behavioral, affective and cognitive symptoms (Schmahmann's Syndrome). In sharp contrast to the wide range of therapeutic interventions to treat cognitive and affective disorders following cerebral cortical lesions and despite the consequences of Schmahmann’s syndrome upon daily life activities, the literature is surprisingly only scantly documented with studies investigating the impact of cognitive therapies on cerebellar induced cognitive and affective disorders. This survey aims to present an overview of the therapeutic interventions available in the literature as a possible treatment for Schmahmann’s Syndrome after cerebellar injury, after posterior fossa surgery in children, and in children with neurodevelopmental disorders. Although systematical studies are clearly warranted, available evidence suggests that cerebellar-induced cognitive and affective disorders should be treated in a specific way. Approaches where the patients are explicitly made aware of their deficits and are considered to act as an “external cerebellum” are the most promising. Conclusion: The study of the anatomical connectivity of the cerebellar microcomplexes involved in cognitive/affective deficits is likely to play a major-role in the future.

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