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.

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.

Experimental Investigation of Interstitial Fluid Effects on Particle Fluctuating Motion

2005 ◽  
Author(s):  
K. Hadinoto ◽  
J. Sinclair Curtis
Keyword(s):  
Interstitial Fluid ◽  
Stokes Number ◽  
Coefficient Of Restitution ◽  
Glass Beads ◽  
Viscous Force ◽  
Fluid Viscosity ◽  
Particle Collisions ◽  
Turbulence Modulation ◽  
Mass Flowrate ◽  
The Impact

The importance of interstitial fluid effects on particle fluctuating motion in gas-particle or liquid-particle flows with significant particle-particle collisions can be characterized by the ratio of the coefficient of restitution for inelastic particle-particle collisions in a fluid ef to the coefficient of restitution for collisions in a vacuum es. In previous research, the ratio ef/es has been found to depend on the impact Stokes number St, which relates the particle inertia to the viscous force. The value of the impact Stokes number is known to be a function of the particle velocity at impact, the size and density of the particle, and the fluid viscosity. In the present work, the effect of the interstitial fluid on particle fluctuating motion is investigated experimentally using LDV/PDPA in a vertical pipe flow configuration. The influence of the variation in the particle loading and Reynolds number, which affects the particle impact velocity and, hence, ef, is probed using particles of two different densities with comparable sizes. Specifically, the downward flow of 70 micron glass beads (density = 2500 kg/m3) and 60 micron hollow ceramic microspheres (density = 700 kg/m3) is investigated for solids loadings (ratio of solids mass flowrate to gas mass flowrate) from 0.4 to 7 and Reynolds numbers which vary from 6000 to 13,000. For this range of conditions, the values for ef range between 0.65 and 0.94 (0.94 is the value for es for glass beads colliding in a vacuum). Trends in the mean and fluctuating velocities for both the gas and particle phases, as well as the gas turbulence modulation in the presence of particles, are discussed in relation to the degree of influence of the interstitial fluid on the details of the particle motion.

scholarly journals Stokes' cradle: normal three-body collisions between wetted particles

2010 ◽  
Vol 650 ◽  
pp. 479-504 ◽  
Author(s):  
C. M. DONAHUE ◽  
C. M. HRENYA ◽  
R. H. DAVIS ◽  
K. J. NAKAGAWA ◽  
A. P. ZELINSKAYA ◽  
...  
Keyword(s):  
Stokes Number ◽  
Solid Particles ◽  
Particle Collisions ◽  
Particle Deformation ◽  
Additional Resistance ◽  
Newton’S Cradle ◽  
Target Particle ◽  
Three Body ◽  
Regime Map ◽  
The Impact

In this work, a combination of experiments and theory is used to investigate three-body normal collisions between solid particles with a liquid coating (i.e. ‘wetted’ particles). Experiments are carried out using a Stokes' cradle, an apparatus inspired by the Newton's cradle desktop toy except with wetted particles. Unlike previous work on two-body systems, which may either agglomerate or rebound upon collision, four outcomes are possible in three-body systems: fully agglomerated, Newton's cradle (striker and target particle it strikes agglomerate), reverse Newton's cradle (targets agglomerate while striker separates) and fully separated. Post-collisional velocities are measured over a range of parameters. For all experiments, as the impact velocity increases, the progression of outcomes observed is fully agglomerated, reverse Newton's cradle and fully separated. Notably, as the viscosity of the oil increases, experiments reveal a decrease in the critical Stokes number (the Stokes number that demarcates a transition from agglomeration to separation) for both sets of adjacent particles. A scaling theory is developed based on lubrication forces and particle deformation and elasticity. Unlike previous work for two-particle systems, two pieces of physics are found to be critical in the prediction of a regime map that is consistent with experiments: (i) an additional resistance upon rebound of the target particles due to the pre-existing liquid bridge between them (which has no counterpart in two-particle collisions), and (ii) the addition of a rebound criterion due to glass transition of the liquid layer at high pressure between colliding particles.

Flow-level performance and user mobility in wireless data networks

2008 ◽  
Vol 366 (1872) ◽  
pp. 2047-2058 ◽  
Author(s):  
Sem Borst
Keyword(s):  
Time Scale ◽  
Base Stations ◽  
Service Rate ◽  
User Mobility ◽  
Processor Sharing ◽  
Performance Bounds ◽  
Wide Range ◽  
Scheduling Strategies ◽  
The Impact ◽  
Level Performance

Channel conditions in wireless networks exhibit huge variations across space and time, giving rise to vast fluctuations in the transmission rates. Channel-aware scheduling strategies provide an effective mechanism for improving throughput performance by exploiting such rate variations, and these have been extensively examined at the packet level for a static user configuration. In this paper, we discuss the performance implications at the flow level for a dynamic user population, taking into account variations on a slower time scale and wide-range user mobility as well. First of all, we present simple necessary conditions for flow-level stability and prove that these are in fact (near) sufficient for a wide family of utility-based scheduling strategies. It is further shown how the flow-level performance of the proportional fair scheduling strategy may be evaluated by means of a processor-sharing model with a state-dependent service rate. In addition, we examine the impact of variations on a slower time scale, and establish that the so-called fluid and quasi-stationary regimes yield explicit, insensitive performance bounds. Finally, we turn our attention to a network of several base stations (BSs) with handoffs of active sessions governed by wide-range user mobility. It is demonstrated that mobility increases the capacity, not only in the case of globally optimal scheduling but also when each of the BSs adheres to a local fair-sharing discipline.

Vibration Response of Elastic Disks in Surrounding Fluid: Viscous Versus Acoustic Effects

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Anirban Jana ◽  
Arvind Raman
Keyword(s):  
Data Storage ◽  
Acoustic Radiation ◽  
Hard Disk Drives ◽  
Three Dimensional ◽  
Element Model ◽  
Ambient Conditions ◽  
Viscous Losses ◽  
Wide Range ◽  
Fluid Damping ◽  
Surrounding Fluid

The vibrations of thin, elastic, circular disks such as musical cymbals, hard disk drives, and microscale resonators are significantly influenced by the presence of a surrounding fluid. The energy of disk vibrations is known to dissipate into viscous losses and to radiate away as sound. However, the relative importance of these mechanisms is not well understood. In this paper, we present three-dimensional computations of the fluidic impedance of thin, elastic disks vibrating with small amplitudes under ambient conditions. These computations encompass both macroscale and microscale disks, a wide range of operating frequencies, and different fluidic environments. Viscous fluidic impedances are computed using a finite element model, whereas acoustic fluidic impedances are computed using a boundary element method. For a disk with a given clamping ratio vibrating in a specific mode, the nondimensional viscous impedance depends on the unsteady Reynolds number, while the nondimensional acoustic impedance depends on the ratio of structural to acoustic wavelengths. It is shown that viscous losses dominate the fluid damping of disks in data storage and circular saw applications and of conventional disk microresonators. However, for ultrahigh frequency resonators, acoustic radiation must be taken into account to correctly estimate the overall fluid damping. The computed fluidic impedances are expected to be an important aid in the design of a wide range of disk resonators up to the megahertz regime.

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

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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