A framework for computing effective boundary conditions at the interface between free fluid and a porous medium

Interfacial boundary conditions determined from empirical or ad-hoc models remain the standard approach to model fluid flows over porous media, even in situations where the topology of the porous medium is known. We propose a non-empirical and accurate method to compute the effective boundary conditions at the interface between a porous surface and an overlying flow. Using multiscale expansion (homogenization) approach, we derive a tensorial generalized version of the empirical condition suggested by Beavers & Joseph (1967). The components of the tensors determining the effective slip velocity at the interface are obtained by solving a set of Stokes equations in a small computational domain near the interface containing both free flow and porous medium. Using the lid-driven cavity flow with a porous bed, we demonstrate that the derived boundary condition is accurate and robust by comparing an effective model to direct numerical simulations. Finally, we provide an open source code that solves the microscale problems and computes the velocity boundary condition without free parameters over any porous bed.Comment: 23 pages, 6 figures, 2 tables, under consideration for publication in Journal of Fluid Mechanic

A stable fluid-structure-interaction solver for low-density rigid bodies using the immersed boundary projection method

Dispersion of low-density rigid particles with complex geometries is ubiquitous in both natural and industrial environments. We show that while explicit methods for coupling the incompressible Navier-Stokes equations and Newton's equations of motion are often sufficient to solve for the motion of cylindrical particles with low density ratios, for more complex particles - such as a body with a protrusion - they become unstable. We present an implicit formulation of the coupling between rigid body dynamics and fluid dynamics within the framework of the immersed boundary projection method. Similarly to previous work on this method, the resulting matrix equation in the present approach is solved using a block-LU decomposition. Each step of the block-LU decomposition is modified to incorporate the rigid body dynamics. We show that our method achieves second-order accuracy in space and first-order in time (third-order for practical settings), only with a small additional computational cost to the original method. Our implicit coupling yields stable solution for density ratios as low as $10^{-4}$. We also consider the influence of fictitious fluid located inside the rigid bodies on the accuracy and stability of our method.Comment: Article has undergone final revision stage, minor adjustments in text, fixed citation

Passive control of a falling sphere by elliptic-shaped appendages

The majority of investigations characterizing the motion of single or multiple particles in fluid flows consider canonical body shapes, such as spheres, cylinders, discs, etc. However, protrusions on bodies -- being either as surface imperfections or appendages that serve a function -- are ubiquitous in both nature and applications. In this work, we characterize how the dynamics of a sphere with an axis-symmetric wake is modified in the presence of thin three-dimensional elliptic-shaped protrusions. By investigating a wide range of three-dimensional appendages with different aspect ratios and lengths, we clearly show that the sphere with an appendage may robustly undergo an inverted-pendulum-like (IPL) instability. This means that the position of the appendage placed behind the sphere and aligned with the free-stream direction is unstable, in a similar way that an inverted pendulum is unstable under gravity. Due to this instability, non-trivial forces are generated on the body, leading to turn and drift, if the body is free to fall under gravity. Moreover, we identify the aspect ratio and length of the appendage that induces the largest side force on the sphere, and therefore also the largest drift for a freely falling body. Finally, we explain the physical mechanisms behind these observations in the context of the IPL instability, i.e., the balance between surface area of the appendage exposed to reversed flow in the wake and the surface area of the appendage exposed to fast free-stream flow.Comment: 16 pages, 13 figures, 2 tables, under consideration for publication in Phys. Rev. Fluids; revisio

Secret Signals from Another World: Walter Benjamin’s Concept of Innervation

Walter Benjamin refers to the “idea of revolution as an innervation of the technical organs of the collective” as one of the articles of his politics. The significance of this assertion has received relatively little attention in the philosophical reception of his political thought compared to the alternative model of revolution – made famous from the paralipomena to the late theses ‘On the Concept of History’ – as the emergency handbrake of history. Drawing on some of the debates and tensions generated by the work of Miriam Bratu Hansen, this discussion aims at an exegesis of some of the lesser known intellectual sources that influenced Benjamin’s theory of innervation. The purpose in doing so is not an attempt to reconcile or integrate these sources with dominant philosophical reconstructions of what is sometimes characterized as Benjamin’s “Western Marxism” and elaborated, in the more familiar context of Surrealist innervation, as a synthesis of Freud and Marx, but rather to reveal an alternative constellation of Soviet biomechanics and reactionary anti-capitalist Lebensphilosophie, united in their shared rejection of Freudian psychoanalysis

Recent Large-Scale Genotyping and Phenotyping of Plant Genetic Resources of Vegetatively Propagated Crops

Several recent national and international projects have focused on large-scale genotyping of plant genetic resources in vegetatively propagated crops like fruit and berries, potatoes and woody ornamentals. The primary goal is usually to identify true-to-type plant material, detect possible synonyms, and investigate genetic diversity and relatedness among accessions. A secondary goal may be to create sustainable databases that can be utilized in research and breeding for several years ahead. Commonly applied DNA markers (like microsatellite DNA and SNPs) and next-generation sequencing each have their pros and cons for these purposes. Methods for large-scale phenotyping have lagged behind, which is unfortunate since many commercially important traits (yield, growth habit, storability, and disease resistance) are difficult to score. Nevertheless, the analysis of gene action and development of robust DNA markers depends on environmentally controlled screening of very large sets of plant material. Although more time-consuming, co-operative projects with broad-scale data collection are likely to produce more reliable results. In this review, we will describe some of the approaches taken in genotyping and/or phenotyping projects concerning a wide variety of vegetatively propagated crops

Troksnis un vibrācija vidē - vides kvalitātes kritēriji

Vibrācija un troksnis ir vieni no visizplatītākajiem vides fizikālajiem piesārņotājiem, kas rada diskomfortu, īslaicīgus, pārejošus veselības traucējumus, kā arī var izraisīt vai veicināt dažāda veida saslimšanas, kuras atsevišķos gadījumos noved pie invaliditātes (vājdzirdība, kurlums, vibrācijas slimības IV stadija u.c.). Tiek pat uzskatīts, ka troksnis ir viena no vislielākajām mūsu gadsimta nelaimēm un viens no galvenajiem stresa izraisītājiem.Ar trokšņa un vibrācijas problēmām ir jāsastopas gan sadzīvē, gan arī darba vidē. Transporta kustība pilsētās un kokapstrādes rūpniecība, diskotēkas un tekstilrūpniecība, lidostas un ģimeniskas ķildas, dzērāju klaigāšana, skaļa mūzika daudzdzīvokļu namos - tas viss ir paaugstināta trokšņa un vibrāciju cēlonis. Ir zināms, ka apmēram 15% no visā pasaulē nodarbinātajiem ir pakļauti trokšņa kaitīgajai ietekmei. Latvijā no ik gadus pirmreizēji reģistrētajām arodslimībām aptuveni 15 līdz 30% ir dzirdes orgāna saslimšanas un apmēram tikpat daudz tiek diagnosticētas kā vibrācijas slimība. Patiesībā šo saslimšanu skaits ir lielāks, jo jāņem vērā, ka mūsu valstī vēl nav sakārtots arodekspertīzes reģistra darbs

Apoptosis, ANUP, Chromogranin A, PGP 9.5, Endothelins and VEGF in Acquired Heart Diseases : Review of Literature

According to the Centre for Disease Prevention and Control of Latvia data, in 2014 16076 latvians died from cardiovascular diseases and it is 57,03% of all deaths. Changes in myocardium of the diseased hearts are complex and pathogenesis is still not fully clear. Morphopathogenesis of cardiovascular diseases are complex molecular cell changes which include apoptosis, homeostasis regulating factors, and innervation and ischemia markers. In this article we wanted to provide an overview about apoptosis, atrial natriuretic peptide, chromogranin A, neuropeptide-containing innervation, endothelins and vascular endothelial growth factor in pathomorphology of acquired heart diseases and their clinical implications.publishersversionPeer reviewe

Homeostasis Regulating Factors, Innervation, Ischemia and Inflammatory Markers in the Right Atrial Tissue from Patients with Degenerative Aortic Valve Stenosis and Coronary Heart Disease

Publisher Copyright: © 2021 Sciendo. All rights reserved.Both coronary heart disease (CHD) and degenerative aortic valve (AoV) stenosis have common risk factors, such as age, high blood cholesterol, diabetes, smoking, high blood pressure, inflammation, and metabolic syndrome. However, these diseases are not always observed together, confirming the existence of risk and pathogenesis factors specific to each disease. The aim of this study was to identify presence and distribution of common and different homeostasis regulating factors, innervation, ischemia and inflammatory markers in the right atrial tissue from patients with degenerative AoV stenosis and CHD. During elective cardiac surgery, right atrial tissue fragments were taken from 20 patients with CHD and from 9 patients with degenerative AoV stenosis. All tissue fragments were stained for immunohistochemical detection of protein-gene peptide 9.5 (PGP 9.5), atrial natriuretic peptide (ANUP), vascular endothelial growth factor (VEGF), chromogranin A, endothelin, interleukin 1 and 10 (Il-1 and Il-10) and defensins 2, and 3 (D2 and D3). For the quantification of structures, a semi-quantitative counting method was used. Mostly numerous Il-10 positive cardiomyocytes and epi-/endocardial endothelial cells were detected in all specimens taken from patients with CHD, and statistically more than in specimens taken from patients with degenerative AoV disease (p = 0.007 and p = 0.016). Also, the number of D3 positive cardiomyocytes was higher in the coronary heart disease group (p = 0.026). All other tested markers such as PGP 9.5, ANUP, VEGF, endothelin, chromogranin A, Il-1 and D2 showed similar expression in both groups. Increased production of ANUP in right atrial tissue characterises both CHD and degenerative AoV stenosis. Production of ChgA in right atrial endocardial endothelial cells might represent regulation of sympathetic activity as a compensatory homeostatic response. Increased PGP 9.5-containing innervation is characteristic in patients with degenerative AoV disease and secondary mitral insufficiency. A stable increase of VEGF and variations of endothelin without statistically significant difference suggest influence of ischemia on the local vascular blood supply. Decreased production of Il-1 together with moderate to rich production of Il-10, D2, and D3 indicates the dominance of the local immune system over inflammation.publishersversionPeer reviewe

Transfer of mass and momentum at rough and porous surfaces

The surface texture of materials plays a critical role in wettability, turbulence and transport phenomena. In order to design surfaces for these applications, it is desirable to characterise non-smooth and porous materials by their ability to exchange mass and momentum with flowing fluids. While the underlying physics of the tangential (slip) velocity at a fluid-solid interface is well understood, the importance and treatment of normal (transpiration) velocity and normal stress is unclear. We show that, when slip velocity varies at an interface above the texture, a non-zero transpiration velocity arises from mass conservation. The ability of a given surface texture to accommodate for a normal velocity of this kind is quantified by a transpiration length. We further demonstrate that normal momentum transfer gives rise to a pressure jump. For a porous material, the pressure jump can be characterised by so called resistance coefficients. By solving five Stokes problems, the introduced measures of slip, transpiration and resistance can be determined for any anisotropic non-smooth surface consisting of regularly repeating geometric patterns. The proposed conditions are a subset of effective boundary conditions derived from formal multi-scale expansion. We validate and demonstrate the physical significance of the effective conditions on two canonical problems -- a lid-driven cavity and a turbulent channel flow, both with non-smooth bottom surfaces.Comment: 31 page, 12 figures, 5 tables, under consideration for publication in Journal of Fluid Mechanic