scholarly journals A general constitutive model for dense, fine-particle suspensions validated in many geometries

2019 ◽  
Vol 116 (42) ◽  
pp. 20828-20836 ◽  
Author(s):  
Aaron S. Baumgarten ◽  
Ken Kamrin
Keyword(s):  
Fine Particle ◽  
Mixture Theory ◽  
Shear Thickening ◽  
Time Dependent ◽  
Small Scale ◽  
Steady Flows ◽  
Particle Suspensions ◽  
Frictional Contacts ◽  
Continuous Shear ◽  
Flow Configurations

Fine-particle suspensions (such as cornstarch mixed with water) exhibit dramatic changes in viscosity when sheared, producing fascinating behaviors that captivate children and rheologists alike. Examination of these mixtures in simple flow geometries suggests intergranular repulsion and its influence on the frictional nature of granular contacts is central to this effect—for mixtures at rest or shearing slowly, repulsion prevents frictional contacts from forming between particles, whereas when sheared more forcefully, granular stresses overcome the repulsion allowing particles to interact frictionally and form microscopic structures that resist flow. Previous constitutive studies of these mixtures have focused on particular cases, typically limited to 2D, steady, simple shearing flows. In this work, we introduce a predictive and general, 3D continuum model for this material, using mixture theory to couple the fluid and particle phases. Playing a central role in the model, we introduce a microstructural state variable, whose evolution is deduced from small-scale physical arguments and checked with existing data. Our space- and time-dependent model is implemented numerically in a variety of unsteady, nonuniform flow configurations where it is shown to accurately capture a variety of key behaviors: 1) the continuous shear-thickening (CST) and discontinuous shear-thickening (DST) behavior observed in steady flows, 2) the time-dependent propagation of “shear jamming fronts,” 3) the time-dependent propagation of “impact-activated jamming fronts,” and 4) the non-Newtonian, “running on oobleck” effect, wherein fast locomotors stay afloat while slow ones sink.

Coherent structures in oscillatory boundary layers

2003 ◽  
Vol 474 ◽  
pp. 1-33 ◽  
Author(s):  
PAOLA COSTAMAGNA ◽  
GIOVANNA VITTORI ◽  
PAOLO BLONDEAUX
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Vortex Structures ◽  
Small Scale ◽  
Computational Domain ◽  
Steady Flows ◽  
Low Speed ◽  
Sequence Of Events ◽  
Low Speed Streaks ◽  
Oscillatory Boundary Layers

The dynamics of the vortex structures appearing in an oscillatory boundary layer (Stokes boundary layer), when the flow departs from the laminar regime, is investigated by means of flow visualizations and a quantitative analysis of the velocity and vorticity fields. The data are obtained by means of direct numerical simulations of the Navier–Stokes and continuity equations. The wall is flat but characterized by small imperfections. The analysis is aimed at identifying points in common and differences between wall turbulence in unsteady flows and the well-investigated turbulence structure in the steady case. As in Jimenez & Moin (1991), the goal is to isolate the basic flow unit and to study its morphology and dynamics. Therefore, the computational domain is kept as small as possible.The elementary process which maintains turbulence in oscillatory boundary layers is found to be similar to that of steady flows. Indeed, when turbulence is generated, a sequence of events similar to those observed in steady boundary layers is observed. However, these events do not occur randomly in time but with a repetition time scale which is about half the period of fluid oscillations. At the end of the accelerating phases of the cycle, low-speed streaks appear close to the wall. During the early part of the decelerating phases the strength of the low-speed streaks grows. Then the streaks twist, oscillate and eventually break, originating small-scale vortices. Far from the wall, the analysis of the vorticity field has revealed the existence of a sequence of streamwise vortices of alternating circulation pumping low-speed fluid far from the wall as suggested by Sendstad & Moin (1992) for steady flows. The vortex structures observed far from the wall disappear when too small a computational domain is used, even though turbulence is self-sustaining. The present results suggest that the streak instability mechanism is the dominant mechanism generating and maintaining turbulence; no evidence of the well-known parent vortex structures spawning offspring vortices is found. Although wall imperfections are necessary to trigger transition to turbulence, the characteristics of the coherent vortex structures, for example the spacing of the low-speed streaks, are found to be independent of wall imperfections.

scholarly journals Environmental Surveillance Can Dynamically Track Ecological Changes in Enteroviruses

2019 ◽  
Vol 85 (24) ◽  
Author(s):  
Hiroki Ozawa ◽  
Hiromu Yoshida ◽  
Shuzo Usuku
Keyword(s):  
Multidimensional Scaling ◽  
Large Scale ◽  
Local Community ◽  
Amino Acid Sequences ◽  
Time Dependent ◽  
Small Scale ◽  
Dependent Manner ◽  
Environmental Surveillance ◽  
Ecological Changes ◽  
Over Time

ABSTRACT Environmental surveillance can be used to trace enteroviruses shed from human stool using a sewer network that is independent of symptomatic or asymptomatic infection. In this study, the local transmission of enteroviruses was analyzed using two wastewater treatment plants, which were relatively close to each other (15 km), designated as sentinels. Influent was collected at both sentinels once a month from 2013 to 2016, and viruses were isolated. Using neutralizing tests with type-specific polyclonal antisera and molecular typing, 933 isolates were identified as enteroviruses. Our results showed that the frequency of virus isolation varied for each serotype at the two sentinels in a time-dependent manner. Because echovirus 11 (Echo11) and coxsackievirus B5 isolates showed a high frequency and were difficult to distinguish, they were further grouped into various lineages based on the VP1 amino acid sequences. The prevalence of each lineage was visualized using multidimensional scaling. The results showed that Echo11 isolates of the same lineage were isolated continuously, similar to coxsackievirus B5 isolates of three lineages. Conversely, Echo1, Echo13, Echo18, Echo19, Echo20, Echo29, and Echo33 were isolated only once each. Our findings suggested that if an enterovirus is imported into the population, it may result in small-scale transmission, whereas if there are initially many infected individuals, it may be possible for the virus to spread to a wide area, beyond the local community, over time. In addition, our findings could provide insights into risk assessment of transmission for importation of poliovirus in polio-free countries and regions. IMPORTANCE In this study, we showed that environmental enterovirus surveillance can be used to monitor the propagation of nonpolio enteroviruses in addition to poliovirus detection. Since epidemiological studies of virus transmission based on the past were performed using specimens from humans, there were limitations to research design, such as specimen collection for implementation on a large-scale target population. However, environmental monitoring can dynamically track the ecological changes in enteroviruses in the region by monitoring viruses in chronological order and targeting the population within the area by monitoring viruses over time. We observed differences in the transmission of echovirus 11 and coxsackievirus B5 in the region according to lineage in a time-dependent manner and with a multidimensional scaling pattern.

scholarly journals Hydrodynamic and Contact Contributions to Continuous Shear Thickening in Colloidal Suspensions

2015 ◽  
Vol 115 (22) ◽  
Author(s):  
Neil Y. C. Lin ◽  
Ben M. Guy ◽  
Michiel Hermes ◽  
Chris Ness ◽  
Jin Sun ◽  
...  
Keyword(s):  
Shear Thickening ◽  
Colloidal Suspensions ◽  
Continuous Shear

scholarly journals A Numerical Modelling Approach for Time-Dependent Deformation of Hot Forming Tools under the Creep-Fatigue Regime

2016 ◽  
Vol 2016 ◽  
pp. 1-13
Author(s):  
B. Reggiani ◽  
L. Donati ◽  
L. Tomesani
Keyword(s):  
Plastic Deformation ◽  
Die Design ◽  
Time Dependent ◽  
Hot Forming ◽  
Small Scale ◽  
Regression Equations ◽  
Premature Failure ◽  
Extrusion Die ◽  
Temperature State ◽  
Creep Fatigue

The present study was aimed at predicting the time-dependent deformation of tools used in hot forming applications subjected to the creep-fatigue regime. An excessive accumulated plastic deformation is configured as one of the three main causes of premature failure of tools in these critical applications and it is accumulated cycle by cycle without evident marks leading to noncompliant products. With the aim of predicting this accumulated deformation, a novel procedure was developed, presented, and applied to the extrusion process as an example. A time-hardening primary creep law was used and novel regression equations for the law’s coefficients were developed to account not only for the induced stress-temperature state but also for the dwell-time value, which is determined by the selected set of process parameters and die design. The procedure was validated against experimental data both on a small-scale extrusion die at different stress, temperature, load states, and for different geometries and on an industrial extrusion die which was discarded due to the excessive plastic deformation after 64 cycles. A numerical-experimental good agreement was achieved.

Variational Principles for Vibrating Carbon Nanotubes Conveying Fluid, Based on the Nonlocal Beam Model

2015 ◽  
Vol 5 (3) ◽  
pp. 209-221 ◽  
Author(s):  
Sarp Adali
Keyword(s):  
Carbon Nanotubes ◽  
Variational Principles ◽  
Linear Time ◽  
Scale Effects ◽  
Time Dependent ◽  
Small Scale ◽  
Beam Model ◽  
Geometric Boundary ◽  
Double Walled Carbon Nanotubes ◽  
Walled Carbon Nanotubes

AbstractVariational principles are derived in order to facilitate the investigation of the vibrations and stability of single and double-walled carbon nanotubes conveying a fluid, from a linear time-dependent partial differential equation governing their displacements. The nonlocal elastic theory of Euler-Bernoulli beams takes small-scale effects into account. Hamilton’s principle is obtained for double-walled nano-tubes conveying a fluid. The natural and geometric boundary conditions identified are seen to be coupled and time-dependent due to nonlocal effects.

Effect of Inlet Flow Conditions on Flow Uniformity in a PEM Fuel Cell

2011 ◽  
Author(s):  
Lisa M. Grega ◽  
Steven Voinier
Keyword(s):  
Fuel Cell ◽  
Internal Combustion Engines ◽  
Plug Flow ◽  
Pem Fuel Cell ◽  
Small Scale ◽  
Inlet Flow ◽  
Velocity Statistics ◽  
Computational Data ◽  
Flow Configurations ◽  
Flow Maldistribution

The use of fuel cells as an alternative to traditional small scale power producing devices such as internal combustion engines or disposable batteries has continued to gain widespread acceptance. Flow maldistribution within cells in a stack continues to be an issue in fuel cell design and can adversely affect performance and longevity. Current research in this field has focused on effects of inlet configurations (plug flow versus circular inlet, for example) on the flow in a rectangular manifold and the resulting distribution into individual cells in the stack. In a typical small scale application, the piping which transports the reactant will contain bends in it. As these bends can introduce Dean vortices and flow asymmetries within the pipe flow, such conditions should be examined to determine whether they will affect the manifold flow and further impact cell maldistribution. A simplified scaled up model of a PEM fuel cell was fitted with different inlet flow configurations, including straight piping and piping containing a 90 degree bend prior to entering the manifold. Particle Image Velocimetry (PIV) was used to obtain mean and fluctuating velocity statistics within the manifold and in individual cells. These distributions will be compared with previous results obtained from this apparatus corresponding to a partially developed square inlet profile, as well as available experimental and computational data in the literature.

scholarly journals Time-Dependent Shear-Induced Nonlinear Viscosity Effects in Dilute CTAC/NaSal Solutions: Mechanism Analyses

2014 ◽  
Vol 6 ◽  
pp. 179394 ◽  
Author(s):  
Na Xu ◽  
Jinjia Wei
Keyword(s):  
Shear Rate ◽  
Apparent Viscosity ◽  
Shear Thickening ◽  
Stage Iv ◽  
Stage I ◽  
Time Dependent ◽  
Stage Ii ◽  
Stage Iii ◽  
Viscosity Effects ◽  
Nonlinear Viscosity

The time-dependent shear-induced nonlinear viscosity effects of dilute surfactant solutions (CTAC/NaSal) at constant shear rate were tested by using the rheometer Couette cell. The apparent viscosity evolution curve can be divided into five stages: weak shear-thickening (Stage I), weak shear-thinning and plateau (Stage II), sharp shear-thickening (Stage III), oscillating adjustment (Stage IV), and rough plateau (Stage V). In Stage I, the stretching effects of shear flow lead to the weak increase in apparent viscosity at the inception of shearing. The apparent viscosity curve firstly decreases in Stage II and then levels off. The apparent viscosity plateau is caused by the forming and slipping of micellar lumps at the inner cylinder wall surface. Once the volume of lump exceeds a certain degree, the nucleation process of forming SIS is triggered, which is the beginning of Stage III and then the apparent viscosity increases sharply. The variations of apparent viscosity in adjusting period are rather complicated in Stage IV, and the variations mainly depend on the situation of SISs network. In Stage V, coupled with obvious oscillations, the apparent viscosity maintains a basically constant plateau value, indicating that the SISs network is fully developed and saturated at the corresponding shear rate.

A time-dependent approach for calculating steady inverse boundary-layer flows with separation

1983 ◽  
Vol 389 (1796) ◽  
pp. 171-178 ◽  
Keyword(s):  
Boundary Layer ◽  
Streamwise Velocity ◽  
Time Dependent ◽  
Steady Flows ◽  
Boundary Layer Flows ◽  
Inverse Boundary ◽  
Iteration Parameter ◽  
Layer Method ◽  
Boundary Layer Method ◽  
Box Method

In this paper we describe an unsteady inverse boundary-layer method that can be used to compute steady flows with separation. The method uses Keller’s box method with Cebeci’s Mechul function formulation. De­pending on the complexity of the flow, two versions of the box method are used. In regions of positive streamwise velocity component u , the regular box is used; in regions where u becomes negative (t > 0), the zigzag box is used. When t = 0, and u becomes negative in some region across the layer, the regular box with the FLARE approximation is used. Calculations per­formed with this approach indicate that the use of a time dependent inverse boundary-layer method in which time is used as an iteration parameter provides a good approach in improving the accuracy of the solutions obtained from the FLARE approximation.

scholarly journals Roughness-dependent tribology effects on discontinuous shear thickening

2018 ◽  
Vol 115 (20) ◽  
pp. 5117-5122 ◽  
Author(s):  
Chiao-Peng Hsu ◽  
Shivaprakash N. Ramakrishna ◽  
Michele Zanini ◽  
Nicholas D. Spencer ◽  
Lucio Isa
Keyword(s):  
Surface Roughness ◽  
Shear Thickening ◽  
Lateral Force ◽  
Solid Loading ◽  
Nonspherical Particles ◽  
Stick Slip ◽  
Frictional Contacts ◽  
Force Microscopy ◽  
Direct Measurements ◽  
Capillary Interactions

Surface roughness affects many properties of colloids, from depletion and capillary interactions to their dispersibility and use as emulsion stabilizers. It also impacts particle–particle frictional contacts, which have recently emerged as being responsible for the discontinuous shear thickening (DST) of dense suspensions. Tribological properties of these contacts have been rarely experimentally accessed, especially for nonspherical particles. Here, we systematically tackle the effect of nanoscale surface roughness by producing a library of all-silica, raspberry-like colloids and linking their rheology to their tribology. Rougher surfaces lead to a significant anticipation of DST onset, in terms of both shear rate and solid loading. Strikingly, they also eliminate continuous thickening. DST is here due to the interlocking of asperities, which we have identified as “stick–slip” frictional contacts by measuring the sliding of the same particles via lateral force microscopy (LFM). Direct measurements of particle–particle friction therefore highlight the value of an engineering-tribology approach to tuning the thickening of suspensions.

scholarly journals Consititutive modeling of time-dependent flows in frictional suspensions

2021 ◽  
Vol 249 ◽  
pp. 01002
Author(s):  
Michael Cates
Keyword(s):  
Normal Force ◽  
Shear Thickening ◽  
Constitutive Modelling ◽  
Contact Forces ◽  
Time Dependent ◽  
Joint Work ◽  
Modelling Framework ◽  
New Concepts ◽  
Quantitative Accuracy ◽  
Granular Suspensions

This paper summarizes recent joint work towards a constitutive modelling framework for dense granular suspensions. The aim is to create a time-dependent, tensorial theory that can implement the physics described in steady state by the Wyart-Cates model. This model of shear thickening suspensions supposes that lubrication films break above a characteristic normal force so that frictional contact forces come into play: the resulting non-sliding constraints can be enough to rigidify a system that would flow freely at lower stresses [1]. Implementing this idea for time-dependent flows requires the introduction of new concepts including a configuration-dependent ‘jamming coordinate’, alongside a decomposition of the velocity gradient tensor into compressive and extensional components which then enter the evolution equation for particle contacts in distinct ways. The resulting approach [2, 3] is qualitatively successful in addressing (i) the collapse of stress during flow reversal in shear flow, and (ii) the ability of transverse oscillatory flows to unjam the system. However there is much work required to refine this approach towards quantitative accuracy, by incorporating more of the physics of contact evolution under flow as determined by close interrogation of particle-based simulations.

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