Roll Flow Research Articles

Is vorticity-banding due to an elastic instability?

A possible mechanism for the vorticity-banding instability is proposed on the basis of experiments with colloidal rod-like particles that exhibit an isotropic-nematic phase transition. The proposed mechanism is similar to the well-known elastic instability for polymer systems that is due to nonuniform elastic deformation of polymer chains as a result of gradients in the local shear rate (the Weissenberg effect). However, the role of polymer chains is now played by inhomogeneities that exist in systems exhibiting vortic- ity banding. For the rod-like colloidal system investigated here, inhomogeneities are formed during the early stages of phase separation. Nonuniform deformation of these inho- mogeneities are thus proposed to lead to hoop stresses which give rise to banded structures where there is secondary, weakly rolling flow within each of the bands. Many of the features found experimentally for the rod-like colloidal system can be understood on the basis of this proposed mechanism. For different types of systems that also show vorticity banding, inhomogeneities can be identified, which might lead to vorticity banding for the same reasons as for the rod-like colloidal systems studied here.

Glycoprotein Ibα Forms Catch Bonds with von Willebrand Factor A1 Domain but Not with Mutant A1 Domains Exhibiting Properties of Type 2B von Willebrand Disease.

Interactions between glycoprotein Ibα (GPIbα) and von Willebrand factor (VWF) initiate platelet adhesion to injured vascular surfaces, which is enhanced by arterial blood flow. The flow requirement for adhesion is reduced (i.e., gain-of-function) by single-residue substitutions of the VWF-A1 domain, e.g., R543Q that occurs in some patients with type 2B von Willebrand disease (VWD) and R687E that was designed to exhibit type 2B VWD properties. Yet the mechanisms for flow-enhanced adhesion through GPIbα-VWF interactions are not understood. By probing single bonds with atomic force microscopy, we showed that lifetimes of GPIbα/VWF-A1 bonds first increased (catch) and then decreased (slip) with increasing force applied to the bond. Remarkably, the catch bond aspect of the GPIbα/VWF-A1 bonds was eliminated by the R543Q and R687E mutations, which exhibited slip bonds only with prolonged lifetimes at low forces. Flow chamber experiments showed that catch-slip transitional bonds governed flow-enhanced rolling of platelets and GPIbα-coated microspheres on wild-type A1, such that rolling velocities first decreased and then increased with increasing flow. By contrast, slip bonds governed rolling velocities on R543Q and R687E A1 mutants, which increased monotonically with increasing flow. We changed fluid viscosity by adding Ficoll to the medium, tether force by using microspheres of different radii, and platelet deformability by using a chemical fixative. The rolling velocity vs. flow curves aligned with tether force but not with transport parameters and were minimally affected by fixation, which respectively rule out transport-enhanced GPIbα/VWF-A1 bond formation and force-induced enlargement of platelet-surface contact area as the causes for flow-enhanced rolling. Flowing platelets agglutinated with microspheres bearing R543Q and R687E A1 mutants but not with those bearing wild-type A1, suggesting that GPIbα/VWF-A1 catch bonds prevent agglutination of circulating platelets via binding to VWF multimers and that platelet agglutination in patients with type 2B VWD may be explained by the prolonged lifetimes at low forces resulting from elimination of catch bonds in the interactions of GPIbα with VWF-A1 mutants.

Simulation of Material Flow, Microstructure and Properties Evolution in Bar and Wire Rolling

Simulation of Material Flow, Microstructure and Properties Evolution in Bar and Wire Rolling

Vorticity banding in rodlike virus suspensions

Vorticity banding under steady shear flow is observed in a suspension of semiflexible colloidal rods (fd virus particles) within a part of the paranematic-nematic biphasic region. Banding occurs uniformly throughout the cell gap within a shear-rate interval (.gamma-, .gamma+) , which depends on the fd concentration. For shear rates below the lower-border shear rate .gamma- only shear elongation of inhomogeneities, which are formed due to paranematic-nematic phase separation, is observed. Within a small region just above the upper-border shear rate .gamma+ , banding occurs heterogeneously. An essential difference in the kinetics of vorticity banding is observed, depending on the morphology of inhomogeneities formed during the initial stages of the paranematic-nematic phase separation. Particle tracking and polarization experiments indicate that the vorticity bands are in a weak rolling flow, superimposed on the applied shear flow. We propose a mechanism for the origin of the banding instability and the transient stability of the banded states. This mechanism is related to the normal stresses generated by inhomogeneities formed due to the underlying paranematic-nematic phase transition.

CALL FOR CONTRIBUTIONS: Towards numerical benchmark solutions for 3D mixed convection flows in rectangular channels heated from below

The main purpose of this paper is to propose two three-dimensional Poiseuille–Rayleigh–Bénard flows (mixed convection flows in horizontal rectangular channels heated from below), covering two different flow ranges, as benchmark problems and to solicit numerical comparisons between various contributors in order to obtain two benchmark solutions for the validation of numerical codes. The second objective is to identify the less perturbing outflow boundary conditions for this flow type. The first test case is a steady longitudinal roll flow in a large aspect ratio channel ( A = L / H = 50 , B = l / H = 10 ) at moderate Reynolds number Re = 50 , Rayleigh number Ra = 5000 and Prandtl number Pr = 0.7 . The second one is a fully-established space and time periodic transversal roll flow in a small aspect ratio channel ( A = 25 , B = 4 ) at small Reynolds number Re = 0.1 , Ra = 2500 and Pr = 7 . The model equations are the incompressible Navier–Stokes equations under the Boussinesq approximation.

Unordered Roll Flow Patterns of Interfacial Turbulence and Its Influence on Mass Transfer

By utilizing the optical Schlieren method, Marangoni convection produced in different gas–liquid mass transfer processes was observed and recorded. Different liquid solvent mixtures were selected to investigate the flow patterns of the Marangoni convection as well as the driven mechanism of the surface tension gradient. Unordered flow patterns were observed frequently in experiments, and it is different from ordinary orderly Marangoni flow patterns such as regular roll and cellular flow patterns. Qualitative analysis of flow patterns in mass transfer was made through the Schlieren images observed, and in consequence a scaling analysis was made to discuss the relationship between the Marangoni effect and the unusual mass transfer performance. By combining the Marangoni hydraulic boundary condition with the penetration theory of mass transfer, the Marangoni number characterizing the intensity of Marangoni effect enters the conventional mass transfer correlation. The quantitative result successfully explains these different correlations between Sh and Ma obtained in mass transfer processes accompanied by the Marangoni effect.

Response of Elastomeric Blocks During Large Compression Strains

Abstract An experimental investigation has been conducted to evaluate the response of rubber blocks under large compressive loadings. Quantitative measurements of the nonlinear behavior of two rubber compounds were tested over compressive strains ranging from 17 to 74 percent. Three distinct phenomena were observed in the deformation behavior of both materials. The first was a dramatic increase in contact area (over 130 percent) between the rubber and the platens, beginning at strains above approximately 33 percent. This increased surface area is used to provide stress corrections in several quantitative models, and appears to physically represent a rolling flow phenomenon, similar to fountain flow in observed in polymer melts. The second and third phenomena are associated with a nonlinear normal stress distribution across the sample's surface. These two phenomena are stress maxima and minima associated with stress singularities predicted by nonlinear elastic models. Deviations in stresses across the specimen surface of up to a factor of four are reported. It is concluded that appropriate constitutive equations describing these phenomena are required before meaningful predictive models can be developed.

A Newly Developed Upper‐Bound Approach for Calculating the Width Flow in Hot Rolling

This paper presents an investigation of the 3D metal‐forming process during hot flat rolling by an upper‐bound approach. The general aspects of this limit analysis refer to the volume deformation taking into account a polynomial propagation of the free side surfaces. In this approach the deformation region is limited by the roll‐gap entrance and exit with parallel planes. It is characterized by a non‐linear velocity field. A mathematical model of an upper‐bound calculation for the symmetrical flat rolling is developed in order to examine the influence of the most relevant functions, namely the velocity field together with the boundary conditions. A comparison of reasonable onsets is proposed. Therefore, the study can offer useful knowledge for better prediction of lateral flow.

Effect of liquid steel flow pattern on slab quality and the need for dynamic electromagnetic control in the mould

This paper addresses surface/subsurface quality (slivers, pipe, pinholes, blowholes, inclusion content) and diversion rate (slab casting abnormality codes) of products cast on high or low throughput thick slab machines. Examples from LTV, NKK and TKS pertaining to curved mould and vertical/bending casters are reviewed, which make apparent the important effect of steel flow stability and steel flow pattern in the mold on defect occurrence. The first conclusion, which pertains mostly to slow speed or wide slab machines, is that creating or maintaining a stable double roll flow is key to eliminating slab defects. The second conclusion, relating mostly to high speed casters, is that the intensity of the double roll flow pattern must not be excessive. With this in mind, the efficiency of an existing versatile electromagnetic based technology that allows accelerating, slowing down, and stirring the liquid steel was examined. The analysis shows good response of the liquid steel to various imposed magnetic fields, presents corresponding slab/coil quality improvements, and demonstrates the relevance of the proposed hydrodynamic and metallurgical concepts.

Kinematic roll dynamo computations at large magnetic Reynolds number

The behaviour of the magnetic field produced by spherical kinematic dynamos at large magnetic Reynolds number for two stationary axisymmetric roll flows is examined. Five numerical techniques to solve the large banded eigenvalue problems, which arise for the growth rate of the magnetic field, are compared, particularly their performance when eigenvalues are closely clustered. The five eigenvalue methods are inverse iteration, orthogonal iteration, lop-sided iteration, the implicitly restarted Arnoldi method and the non-symmetric Lanczos method. A shift and invert strategy was employed to obtain the growth rates of largest real part.

The atomic detail of a wetting/de-wetting flow

Atomistic simulation is used to study flow in the vicinity of the advancing (wetting) and receding (de-wetting) solid–liquid–vapor contact lines of a two-dimensional (in the mean) liquid drop in thermodynamic equilibrium with its own vapor and moving steadily on an atomically smooth solid surface under the influence of an applied body force. Wetting and de-wetting are found to be asymmetric, counter to some predictions based on linear theory. There is a rolling flow of the liquid in the drop and a dividing streamline extends from the wetting common line into the displaced vapor as observed macroscopically. At the de-wetting common line there is substantial evaporation, which alters the flow field behind the drop. Evaporation is also observed above the advancing contact line, but there is a net mass flux into the drop right at the contact line. There is evidence of slip flow just in advance of the wetting contact line, but not at the de-wetting line. Results are discussed in the context of phase-field models.

Prediction of Pressure Loss and Holdup in Two Phase Horizontal Co‐current Pipe Flow

AbstractA new method is presented for calculation of two‐phase parameters for horizontal stratified plus roll wave pipe flow. An iterative momentum balance calculation was performed based on the actual average phase velocities and the gas liquid interfacial shape. The liquid holdup and two phase pressure loss was predicted within ±2% of measured values for data obtained over a wide range of pipe diameters.

An experimental study of the flowing granular layer in a rotating tumbler

Granular flow in a rotating tumbler is of theoretical and industrial significance. However, in spite of its relative simplicity, little is known about the dynamics of the top flowing layer. Here we present an experimental study of the velocity field within the fluidized layer of monodisperse particles in a quasi-2D (two-dimensional) rotating tumbler in the rolling flow regime using particle tracking velocimetry. The granular flow is illuminated by a laser flash and recorded using a charge coupled device camera. Image processing is used to remove the experimental noise and to achieve sub-pixel accuracy in calculating the particle displacements. The ensemble-averaged streamwise and transverse velocity profiles are calculated based on the particle displacements for three angular velocities and three bead sizes. The normalized streamwise velocity profile is linear throughout the fluidized layer, but becomes logarithmic as it enters the “fixed” bed where slow particle rearrangements dominate. The rms velocities appear to be exponentially related to the depth in the layer. Nondimensionalizing the number density in the fluidized layer with a geometric factor based on the square packing results in collapse of the data over a range of bead sizes and angular velocities.

305 Simultaneous Consideration of Microstructural Evolution, and Phenomenological Metal Flow in Inverse Engineering Hot Rolling of Steel Bars

305 Simultaneous Consideration of Microstructural Evolution, and Phenomenological Metal Flow in Inverse Engineering Hot Rolling of Steel Bars

A parametric study of process parameters in external thread rolling

This paper summarizes the results of a numerical study conducted to analyze the effect of selected process parameters on material flow and thread profile in external thread rolling of large diameter blanks. Based on the previous work where a plane strain model was found to provide a reasonable approximation of the thread rolling process, the effect of varying thread form, friction factor, flow stress, and blank diameter on effective strain and thread height was analyzed using the finite element code DEFORM. The results of the study show that for the range of conditions considered, that blank diameter had little effect on the as-rolled thread while flow stress ( K and n), friction factor, and thread form all had significant impact on effective strain at the thread root and crest and the achievable thread height. While the rate of work hardening was found to have an effect on the crest profile, the results indicate that it is not the primary factor responsible for seam formation in rolled threads.

Smectic–like order in the log–rolling flow of thermotropic random copolymers. A time–resolved wide–angle X–ray scattering study

Restricted accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Romo-Uribe Angel 2001Smectic–like order in the log–rolling flow of thermotropic random copolymers. A time–resolved wide–angle X–ray scattering studyProc. R. Soc. Lond. A.4571327–1342http://doi.org/10.1098/rspa.2000.0720SectionRestricted accessResearch articleSmectic–like order in the log–rolling flow of thermotropic random copolymers. A time–resolved wide–angle X–ray scattering study Angel Romo-Uribe Angel Romo-Uribe Ticona, Celanese AG, 86 Morris Avenue, Summit, NJ 07901, USA () Google Scholar Find this author on PubMed Search for more papers by this author Angel Romo-Uribe Angel Romo-Uribe Ticona, Celanese AG, 86 Morris Avenue, Summit, NJ 07901, USA () Google Scholar Find this author on PubMed Search for more papers by this author Published:08 June 2001https://doi.org/10.1098/rspa.2000.0720AbstractUnder a suitable combination of molecular weight, temperature and shear rate thermotropic random copolymers display macromolecular orientation orthogonal to the flow direction and along the vorticity axis; Romo–Uribe & Windle have called this a ‘log–rolling’ flow. Time–resolved wide–angle X–ray scattering has enabled the detection of a 002 meridional reflection as the orthogonal orientation develops from the non–oriented molten phase. Therefore, similar sequences of the random copolymer self–assemble during the log–rolling flow, giving rise to a smectic–like phase. After cessation of shear, neither the molecular sequence assemblage is lost nor is macromolecular orientation relaxation observed. Furthermore, applying shear to macromolecules that are already orthogonal to the velocity axis disrupts the chain register due to the macromolecular disorientation prior to the transition to the flow–aligning regime. Strikingly, after cessation of shear, the macromolecules recoil towards the orthogonal orientation and the molecular sequence assembly is re–established. The smectic–like order is therefore the mechanism that stabilizes the log–rolling flow. Previous ArticleNext Article VIEW FULL TEXT DOWNLOAD PDF FiguresRelatedReferencesDetailsCited by Romo-Uribe A (2022) Wide-angle X-ray diffraction and small-angle X-ray scattering studies of elastomer blends and composites Elastomer Blends and Composites, 10.1016/B978-0-323-85832-8.00010-9, (209-242), . Parisi D, Seo J, Schaake R, Rhoades A and Colby R (2021) Shear-induced nematic phase in entangled rod-like PEEK melts, Progress in Polymer Science, 10.1016/j.progpolymsci.2020.101323, 112, (101323), Online publication date: 1-Jan-2021. Romo-Uribe A (2021) Sequence segregation in the melt and viscoelasticity of thermotropic liquid crystalline polymer. A rheo-X-ray scattering study, Polymer, 10.1016/j.polymer.2020.123315, 213, (123315), Online publication date: 1-Jan-2021. Romo-Uribe A (2020) Scattering and Other Miscellanies Techniques for the Characterization of Shape Memory Polymers Shape Memory Polymers, Blends and Composites, 10.1007/978-981-13-8574-2_12, (269-309), . Reyes-Mayer A, Alvarado-Tenorio B, Romo-Uribe A, Benavente R, Jaffe M and Molina-Ocampo A (2015) Nanostructure reorganization in a thermotropic copolyester. A simultaneous WAXS and SAXS study, Polymers for Advanced Technologies, 10.1002/pat.3708, 27:6, (748-758), Online publication date: 1-Jun-2016. Romo-Uribe A (2007) Molecular orientation in sheared molten thermotropic random copolyester, Rheologica Acta, 10.1007/s00397-007-0192-9, 46:9, (1139-1152), Online publication date: 1-Dec-2007. Rendon S, Burghardt W and Bubeck R (2007) Orientation dynamics in commercial thermotropic liquid crystalline polymers in transient shear flows, Rheologica Acta, 10.1007/s00397-007-0177-8, 46:7, (945-956), Online publication date: 1-Aug-2007. This Issue08 June 2001Volume 457Issue 2010 Article InformationDOI:https://doi.org/10.1098/rspa.2000.0720Published by:Royal SocietyPrint ISSN:1364-5021Online ISSN:1471-2946History: Published online08/06/2001Published in print08/06/2001 License: Citations and impact Keywordstime–resolved X–ray scatteringthermotropic random copolymersnematic and smectic polymersmolecular sequence self–assemblymacromolecular orientation and relaxationlog–rolling and flow–aligning flow

3-dimensional numerical modelling of rolling of superconducting Ag/BSCCO tape

Numerical simulation of the deformation process during flat rolling of multifilament HTS tapes has been investigated using a commercial FEM program, ELFEN. The numerical models were built up in 2D and 3D using a Drucker-Prager/Cap model for the powder. Three different roll diameters (o24 mm, o85 mm and o126 mm) have been investigated. It is found that it is possible to perform numerical simulation with 3D models of flat rolling of multifilament wire. Two 3D models have been used; 3D pressing with rolls and 3D rolling. 3D pressing with rolls have the advance that the simulation time is lower than in the 3D rolling. The 3D models have the advantage compared to 2D pressing that they can predict the 3 dimensional flow in the flat rolling, which has been showed to be very imported for the super conduction properties.

On the molecular orientation and viscoelastic behaviour of liquid crystalline polymers: the influence of macromolecular architecture

The influence of macromolecular architecture on the flow‐induced orientation of main‐chain thermotropic liquid crystalline polymers (LCPs) is investigated using in situ wide‐angle X‐ray scattering. In order to get more insight into the interrelationship between microscopic and rheological behaviour, the viscoelastic properties of the nematic melts were also studied. The LCPs studied are wholly aromatics , composed only of mesogenic units, and semiflexibles , which consist of mesogenic units separated by alkyl spacers. Rheo‐X‐ray scattering evidenced the detrimental influence of the flexible spacers on the orientation process. The wholly aromatic LCPs readily orient along the flow direction, even under modest shear flows ( γ = 0.1 s‐1). The semiflexible LCPs, however, display lower levels of orientation than the wholly aromatics, and the quality of the orientation worsens as the length of the flexible spacer increases. The rheological characterization shows that, like conventional flexible‐chain polymers, the thermotropic LCPs exhibit a linear viscoelastic (LVE) regime. Moreover, dynamic measurements, within the LVE regime, suggest a level of elasticity in the nematic melts. As the length of the alkyl spacer increases, the rheological behaviour is more akin to that displayed by common flexible molecular chains. The poor shear orientation exhibited by the semiflexible LCPs is then associated with a molecular network formed by the less‐than‐rigid molecular chains. Furthermore, the steady shear viscosity is always smaller than the dynamic viscosity, i.e. the Cox‐Merz rule does not hold. This is due to the fact that steady shear induces molecular orientation, whereas oscillatory shear does not. The relaxation of orientation after steady shear showed that the molecular orientation relaxes after hundreds of seconds. The shear stress, however, relaxes within only a few seconds. Strikingly, the rate of molecular orientation relaxation was slower for the semiflexible than for the wholly aromatic LCPs.

The influence of an immersive virtual environment on the segmental organization of postural stabilizing responses

We examined the effect of a 3-dimensional stereoscopic scene on segmental stabilization. Eight subjects participated in static sway and locomotion experiments with a visual scene that moved sinusoidally or at constant velocity about the pitch or roll axes. Segmental displacements, Fast Fourier Transforms, and Root Mean Square values were calculated. In both pitch and roll, subjects exhibited greater magnitudes of motion in head and trunk than ankle. Smaller amplitudes and frequent phase reversals suggested control of the ankle by segmental proprioceptive inputs and ground reaction forces rather than by the visual-vestibular signals. Postural controllers may set limits of motion at each body segment rather than be governed solely by a perception of the visual vertical. Two locomotor strategies were also exhibited, implying that some subjects could override the effect of the roll axis optic flow field. Our results demonstrate task dependent differences that argue against using static postural responses to moving visual fields when assessing more dynamic tasks.

Rayleigh-Bénard Convection: Structures and Dynamics

Part 1 Basic concepts. Part 2 Investigation tools: experiment theoretical approaches. Part 3 Main types of convective-flow structures: two-dimensional rolls and three-dimensional cells patterns of quasi-two-dimensional rolls convection textures roll-pattern defects. Part 4 Convection-regime sequences, selection of the wavenumbers of convection rolls: wavenumbers in experiments with random initial disturbances searches for universal selection criteria stability of two-dimensional roll flows Lyapunov function and selection selection mechanisms. Part 5 Peculiarities of stratification and vertical structure of convection.