Chaotic Mixing in a Free Helix Extruder using a New Solution to the Biharmonic Equation

A recently published approach for modeling the cross flow in an extruder channel using a new solution to the biharmonic equation is utilized in a study of chaotic mixing in a free helix single screw extruder. This novel extruder was designed and constructed with the screw flight, also referred to as the helix, detached from the screw core. Each of the screw elements could be rotated independently to obtain chaotic motion in the screw channel. Using the new extruder, experimental evidence for the increased mixing of a dye, for both a Dirac and droplet input, with a chaotic flow field relative to the traditional residence time distribution is presented. These experimental results are compared using the new biharmonic equation-based model. Because of the ability to periodically rotate only the flight/helix, the chaotic mixing results are minimally confounded by the existence of Moffat eddies.

Numerical Investigation of Fluid Flow past Four Cylinders at Low Reynolds Numbers

A numerical investigation on the effects of separation ratios and Reynolds numbers on the flow around four square cylinders in diamond arrangement has been carried out using the lattice Boltzmann method. The separation ratios between the cylinders vary from g ∗ = 1 to 15. The Reynolds numbers based on the diameter of the square cylinder and the inlet uniform inflow velocity are selected from Re = 80 to 160. The computations show that a total of five different flow regimes are observed over the selected ranges: single bluff-body, quasi-unsteady, chaotic flow, in-phase synchronized vortex shedding, and antiphase synchronized vortex shedding flow regimes. It is found that the flow features significantly depend on both the separation ratio and Reynolds number, with the former’s influence being more than the latter’s. We found that the critical spacing for four square cylinders in diamond arrangement for selected Reynolds numbers (80 ≤ Re ≤ 160) is in the range of 2 ≤ g ∗ ≤ 5. The results reveal that the presence of secondary cylinder interaction frequencies indicates that, for chaotic flow regime, the wake pattern is not stable and there is a strong interaction of gap flows and continuous change in the direction of shed vortices behind the cylinders. The effects of the g ∗ and Re on fluid forces, vortex shedding frequency, and flow separation have been examined in detail.

Quantification of Measurement and Model Effects in Monopile Foundation Scour Protection Experiments

The present work introduces an analysis of the measurement and model effects that exist in monopile scour protection experiments with repeated small scale tests. The damage erosion is calculated using the three dimensional global damage number S3D and subarea damage number S3D,i. Results show that the standard deviation of the global damage number σ(S3D)=0.257 and is approximately 20% of the mean S3D, and the standard deviation of the subarea damage number σ(S3D,i)=0.42 which can be up to 33% of the mean S3D. The irreproducible maximum wave height, chaotic flow field and non-repeatable armour layer construction are regarded as the main reasons for the occurrence of strong model effects. The measurement effects are limited to σ(S3D)=0.039 and σ(S3D,i)=0.083, which are minor compared to the model effects.

Particle energization inside plasmoids: numerical and analytical investigations

<div> <div> <div> <p>In an idealized system where four magnetic islands interact in a two-dimensional periodic setting, we follow the detailed evolution of current sheets forming in between the islands, as a result of an enforced large-scale merging by magnetohydrodynamic (MHD) simulation. The large-scale island merging is triggered by a perturbation to the velocity field, which drives one pair of islands move towards each other while the other pair of islands are pushed away from one another. The "X"-point located in the midst of the four islands is locally unstable to the perturbation and collapses, producing a current sheet in between with enhanced current and mass density. Using grid-adaptive resistive magnetohydrodynamic (MHD) simulations, we establish that slow near-steady Sweet-Parker reconnection transits to a chaotic, multi-plasmoid fragmented state, when the Lundquist number exceeds about 3×10<sup>4</sup>, well in the range of previous studies on plasmoid instability. The extreme resolution employed in the MHD study shows significant magnetic island substructures. Turbulent and chaotic flow patters are also observed inside the islands. We set forth to explore how charged particles can be accelerated in embedded mini-islands within larger (monster)-islands on the sheet. We study the motion of the particles in a MHD snapshot at a fixed instant of time by the Test-Particle Module incorporated in AMRVAC (). The planar MHD setting artificially causes the largest acceleration in the ignored third direction, but does allow for full analytic study of all aspects leading to the acceleration and the in-plane, projected trapping of particles within embedded mini-islands. The analytic result uses a decomposition of the test particle velocity in slow and fast changing components, akin to the Reynolds decomposition in turbulence studies. The analytic results allow a complete fit to representative proton test particle simulations, which after initial non-relativistic motion throughout the monster island, show the potential of acceleration within a mini-island beyond (√2/2)c≈0.7c, at which speed the acceleration is at its highest efficiency. Acceleration to several hundreds of GeVs can happen within several tens of seconds, for upward traveling protons in counterclockwise mini-islands of sizes smaller than the proton gyroradius.</p> </div> </div> </div><div></div><div></div>

Push-pull flows reveal the scalar signature of chaos in porous media

<p>Recent works have shown that laminar flows through porous media generate Lagrangian chaos at pore scale, with strong implications for a range of transport, reactive, and biological processes in the subsurface. The characterization and understanding of mixing dynamics in these opaque environments remains an outstanding challenge. We present a novel experimental technique based upon high-resolution imaging of the scalar signature produced by push-pull flows through various porous materials (beads, gravels, sandstones) at high Péclet number. We show that this method provides a direct image (see below) of the invariant unstable manifold of the chaotic flow, while allowing a precise quantification of the incompleteness of mixing at pore scale. In the limit of large Péclet numbers, we demonstrate that the decay rate of the scalar variance is directly related to the Lyapunov exponent of the chaotic flow. Thus, this new push-pull method has the potential to provide a complete characterization of chaotic mixing dynamics in a large class of opaque porous materials.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.2deb367885ff54776299061/sdaolpUECMynit/12UGE&app=m&a=0&c=2dcb0848f87d632804dd684b486c506f&ct=x&pn=gepj.elif&d=1" alt=""></p><p> </p>

Fluid Media Artifacts: New Foundations for Symbolic Dominance

The significance of the paper is predefined by the qualitative shifts in the information environment of society, characterized by the fluidity of the media. Social and technological changes in the Internet have had a crucial impact on the media audience’s perception of cultural artefacts. A decisive and ongoing factor has been the change in the functions of the audience, which is increasingly being transformed into an actor of information relations in society. In particular, there is a radical rearrangement of the actors in the subject-object relationship in media propaganda. In the media environment, the linear flow of time gives way to a chaotic flow that violates possible cause-effect relations; the values of artefacts of the past and present “stop having a certain propaganda impact on the audience, rather they themselves are “irradiated” by the propaganda intensions of the audience. Thus, the practices of symbolic domination implemented in the media environment acquire new forms and new social content. The empirical basis of the research was the findings of focus groups comparing the socio-philosophical meaning of movies from different eras (1968, 2015) and different countries (the USSR, the USA), with the same events as the basis of the movies. The meaning of the current problem predetermined the reference to the works of philosophers, political scientists, sociologists, theorists of journalism (Z. Bauman, I. Hoffman, S. Dudnik, D. Dubrovsky, S. Ilchenko, T. Eriksen, etc.). Methodology of focus groups, supplemented by the highlighting of semantic counterpoints of the discussions, their grouping and further inclusion in the context of the discussion to record the respondents’ reflection on the generalizing conclusions was used; content analysis of the transcripts of focus groups was conducted. The materials of the paper may be of interest to culturologists, political scientists and theorists of journalism. Keywords: fluidity of media, mediatization, artefact, propaganda, symbolic dominance, reflection