Dynamic hysteresis in the rheology of complex fluids

Recently, rheological hysteresis has been studied systematically in a wide range of complex fluids combining global rheology and time-resolved velocimetry. In this paper we present an analysis of the roles of the three most fundamental mechanisms in simple-yield-stress fluids: structure dynamics, viscoelastic response, and spatial flow heterogeneities, i.e., time-dependent shear bands. Dynamical hysteresis simulations are done analogously to rheological ramp-up and -down experiments on a coupled model which incorporates viscoelasticity and time-dependent structure evolution. Based on experimental data, a coupling between hysteresis measured from the local velocity profiles and that measured from the global flow curve has been suggested. According to the present model, even if transient shear banding appears during the shear ramps, in typical narrow-gap devices, only a small part of the hysteretic response can be attributed to heterogeneous flow. This results in decoupling of the hysteresis measured from the local velocity profiles and the global flow curve, demonstrating that for an arbitrary time-dependent rheological response this proposed coupling can be very weak.Peer reviewe

Transient shear banding in viscoelastic Maxwell fluids

The fluidization of complex fluids is studied in the context of a Maxwell viscoelastic structural fluid model and compared to the purely viscous case. Solving iteratively the structural models together with the NavierStokes equation for the circular Couette flow gives spatially and temporally resolved velocity fields closely resembling those found experimentally for viscoelastic carbopol gels. Namely, transient shear banding is found during the initial fluidization phase. Although both structural models show transient shear bands, the viscoelastic one captures the experimental observations in greater detail, showing, for instance, the elastic backward flows during the transient shear band initialization stage

Transient shear banding in time-dependent fluids

We study the dynamics of shear-band formation and evolution using a simple rheological model. The description couples the local structure and viscosity to the applied shear stress. We consider in detail the Couette geometry, where the model is solved iteratively with the Navier-Stokes equation to obtain the time evolution of the local velocity and viscosity fields. It is found that the underlying reason for dynamic effects is the nonhomogeneous shear distribution, which is amplified due to a positive feedback between the flow field and the viscosity response of the shear thinning fluid. This offers a simple explanation for the recent observations of transient shear banding in time-dependent fluids. Extensions to more complicated rheological systems are considered

Modelling aerosol transport and virus exposure with numerical simulations in relation to SARS-CoV-2 transmission by inhalation indoors

We provide research findings on the physics of aerosol and droplet dispersion relevant to the hypothesized aerosol transmission of SARS-CoV-2 during the current pandemic. We utilize physics-based modeling at different levels of complexity, along with previous literature on coronaviruses, to investigate the possibility of airborne transmission. The previous literature, our 0D-3D simulations by various physics-based models, and theoretical calculations, indicate that the typical size range of speech and cough originated droplets (dPeer reviewe

Monitoring of ticks and tick-borne pathogens through a nationwide research station network in Finland

In 2015 a long-term, nationwide tick and tick-borne pathogen (TBP) monitoring project was started by the Finnish Tick Project and the Finnish Research Station network (RESTAT), with the goal of producing temporally and geographically extensive data regarding exophilic ticks in Finland. In the current study, we present results from the first four years of this collaboration. Ticks were collected by cloth dragging from 11 research stations across Finland in May September 2015-2018 (2012-2018 in Seili). Collected ticks were screened for twelve different pathogens by qPCR: Borrelia afzelii, Borrelia garinii, Borrelia valaisiana, Borrelia burgdorferi sensu stricto, Borrelia miyamotoi, Babesia spp., Anaplasma phagocytophilum, Rickettsia spp., Candidatus Neoehrlichia mikurensis, Francisella tularensis, Bartonella spp. and tick-borne encephalitis virus (TBEV). Altogether 15 067 Ixodes ricinus and 46 Ixodes persulcatus were collected during 68 km of dragging. Field collections revealed different seasonal activity patterns for the two species. The activity of I. persulcatus adults (only one nymph detected) was unimodal, with activity only in May July, whereas Ixodes ricinus was active from May to September, with activity peaks in September (nymphs) or July August (adults). Overall, tick densities were higher during the latter years of the study. Borrelia burgdorferi sensu lato were the most common pathogens detected, with 48.9 +/- 8.4% (95% Cl) of adults and 25.3 +/- 4.4% of nymphs carrying the bacteria. No samples positive for F. tularensis, Bartonella or TBEV were detected. This collaboration project involving the extensive Finnish Research Station network has ensured enduring and spatially extensive, long-term tick data collection to the foreseeable future.Peer reviewe

Monitoring of ticks and tick-borne pathogens through a nationwide research station network in Finland

In 2015 a long-term, nationwide tick and tick-borne pathogen (TBP) monitoring project was started by the Finnish Tick Project and the Finnish Research Station network (RESTAT), with the goal of producing temporally and geographically extensive data regarding exophilic ticks in Finland. In the current study, we present results from the first four years of this collaboration. Ticks were collected by cloth dragging from 11 research stations across Finland in May–September 2015–2018 (2012–2018 in Seili). Collected ticks were screened for twelve different pathogens by qPCR: Borrelia afzelii, Borrelia garinii, Borrelia valaisiana, Borrelia burgdorferi sensu stricto, Borrelia miyamotoi, Babesia spp., Anaplasma phagocytophilum, Rickettsia spp., Candidatus Neoehrlichia mikurensis, Francisella tularensis, Bartonella spp. and tick-borne encephalitis virus (TBEV). Altogether 15 067 Ixodes ricinus and 46 Ixodes persulcatus were collected during 68 km of dragging. Field collections revealed different seasonal activity patterns for the two species. The activity of I. persulcatus adults (only one nymph detected) was unimodal, with activity only in May–July, whereas Ixodes ricinus was active from May to September, with activity peaks in September (nymphs) or July–August (adults). Overall, tick densities were higher during the latter years of the study. Borrelia burgdorferi sensu lato were the most common pathogens detected, with 48.9 ± 8.4% (95% Cl) of adults and 25.3 ± 4.4% of nymphs carrying the bacteria. No samples positive for F. tularensis, Bartonella or TBEV were detected. This collaboration project involving the extensive Finnish Research Station network has ensured enduring and spatially extensive, long-term tick data collection to the foreseeable future

STUDY AND DESIGN OF ENLARGED AUTOMATED TEST STATION FOR GRID AUTOMATION CONTROL CABINETS

The purpose of this thesis was to get acquainted with the routine testing of Control Cabinet which ABB manufactures as part of medium voltage product portfolio. The objective of the thesis was to study how product testing could be automatized due to increasing production volume. Due to the product family consisting of indoor and outdoor solutions the subject was limited to develop testing for GAO3 level outdoor control cabinets but keeping in mind that solutions need be modular for other cabinet models. In our thesis launch meeting the need of test specification came up and decision to create it as a part of this thesis set the start further than originally was planned. Partly from that reason time was left for only comparing the hardware and the implementation itself was left to a later time period. The theory part of this thesis presents how Control Cabinets are positioned in the distribution network and the construction of entire solution from primary device to control cabinet itself. ABBs manuals and brochures were used as sources for this. The test specifications broadly define which standard are met when the testing is done according the specifications. Tests which may vary depending on the model, different options are given in the test specifications. The test specifications are based on the product related IEC – standards. In the hardware comparison some of the devices were asked for test use and some were compared according to available manuals and brochures. Along with the creation of the test specification it became clear to which standard testing is related today and what changes are required if the testing is decided to be organized according to the “worst-case” situation. Also matters that need to be solved before the automatization were discovered during this thesis. The created test specifications and hardware comparison are as separate documents.Tässä työssä perehdyttiin ABB:n valmistamien keskijännitepuolen ohjainkaappien tuotannontestaukseen. Työn tavoitteena oli tutkia kuinka tuotannontestausta voitaisiin automatisoida kasvavan tuotantovolyymin vuoksi. Koska tuoteperheeseen kuuluu sekä ulko- että sisäkäyttöön tarkoitettuja eritasoisia ohjainkaappeja, päätettiin työtä rajata siten, että testauksen kannalta perehdyttiin ensisijaisesti ulkokäyttööntarkoitettujen GAO3 -tason ohjainkaappien testauksen kehittämiseen, ottaen kuitenkin huomioon modulaarisuuden tarve muiden mallien osalta. Aloituspalaverissa ilmennyt testispeksin tarve ja päätös sen tekemisestä osana tätä päättötyötä siirsi työn aloituspistettä kauemmaksi, kuin alun perin oli suunniteltu. Osaltaan tästä syystä aika riitti testispeksin lisäksi vain potentiaalisen laitteiston vertailuun itse toteutuksen jääden myöhemmälle ajankohdalle. Tämän työn teoriaosuudessa on esitelty laitteiston rakenne ja tuoteperheen asemoituminen osana sähkönjakeluverkkoa sekä sen rooli osana verkostoautomaatiota. Lähteinä näihin on käytetty ABB:n omia manuaaleja ja esitteitä. Pääpiirteiltään kuvattuna testispeksi määrittelee, mitkä standardit täyttyvät, kun tarkastukset ja testaus tehdään määrittelyjen mukaisesti. Testeihin, joiden toteuttaminen eri tuotteilla saattaa vaihdella, vaihtoehdot ovat kirjattuina testispeksiin. Testispesifikaatiot pohjautuvat tuotteelle relevantteihin IEC -standardeihin. Laitevertailuissa osaa laitteista pyydettiin saada kokeiltavaksi ja osaa vertailtiin saatavilla olleiden esitteiden ja manuaalien perusteella. Testispesifikaatioiden tekemisen myötä selvisi, mihin standardiin nykyinen testausprosessi pohjautuu ja minkälaisia muutoksia tulisi käytäntöihin tehdä, mikäli halutaan testata tuote vaativamman näkökulman kautta. Myös testausprosessia hidastavat ja ennen automatisointia tarvittavat toimenpiteet selvisivät työn aikana. Tehty testispesifikaatio ja laitteistovertailu jätettiin erillisiksi dokumenteiksi