UNSTEADY FLOW OF A NON-LINEAR VISCOELASTIC FLUID IN PIPES

ABSTRACT Flow of a viscoelastic fluid in round pipes is analyzed for the case where the pressure gradient is oscillatory with varying amplitude. The fluid is modelled according to Phan-ThienTanner´s constitutive equation. The analysis is carried out by using the perturbation method in which a material parameter is considered small. Velocity field and other kinematic and dynamic variables are evaluated for a range of relevant parameters. The results are compared with the base Newtonian and linear Maxwell flows. The effect of the PTT model in these type of flows is highlighted. INTRODUCTION The non-linear viscoelastic characteristics of some fluids induce many interesting phenomena in pipe flow, which have been recently investigated. Some of those phenomena are steady secondary flows [5], unsteady secondary flows [2] and heat transfer enhancemen

FEDSM2008-55058 AN INVERSE APPROACH TO MAGNETORHEOLOGICAL DAMPER DESIGN: HERSHEL-BULKLEY MODEL

ABSTRACT Magnetorheological fluids (MRF) are increasingly used for the design of dampers in many cases when a given response is critical for desired performance. Some recent examples are self-powered magnetorheological dampers, cable vibration control and wheeled vehicle dampers. Loads of this type can be very big, especially in the case of seismic-dampers as well as in heavy vehicles and aircraft landing gear. This problem can be more efficiently dealt with by using an inverse-problem strategy, where the required performance is specified a priori, and the fluid parameters are changed accordingly by means of a variable magnetic field. The effect on the flow of the time-variation of the parameters of the Herschel-Bulkley constitutive model is analyzed in this paper. In this way, the influence of a varying magnetic field on the unsteady flow of a magnetic fluid is explored. Yield stress, viscosity and power index are assumed time-dependent. In particular, linear variations in time of these parameters are considered, and the case where the yield stress and viscosity oscillate in time is explored in detail. The characteristics of the velocity field are analyzed for different values of the constants that determine the time structure of the constitutive parameters

STEADY SECONDARY FLOWS OF PHAN-THIEN-TANNER FLUIDS IN THE VICINITY OF A CORNER

ABSTRACT Secondary flows of Phan-Thien-Tanner fluids in channels formed by two intersecting walls, and driven by a pressure gradient parallel to the intersection line, are studied by means of perturbation analysis, where the perturbing parameter is the relaxation time. The velocity field is analysed in relation to the opening angle and distance from the comer within the fluid region

Spatial and temporal variations of coastal fish larvae, ectoparasites and oceanographic conditions off central Chile

The objective of this study is to determine the temporal variation of oceanographic conditions, ichthyoplankton and their ectoparasites in nearshore marine waters. From October 11th 2012 to June 5th 2014, 30 ichthyoplankton surveys were carried out along a cross-shelf transect from 0.25 km of the coastline to 4.50 km offshore off Montemar, Bahía Valparaíso, central Chile. We identified a total of 5,553 fish larvae, belonging to 37 taxa. The most abundant fish larvae with pelagic spawning were the common sardine Strangomera bentincki (relative abundance= 26.39%), the anchoveta Engraulis ringens (8.94%), and the lanternfish Hygophum bruuni (7.72%); whereas the most abundant species with benthic brooding were the blennies Scartichthys viridis (15.77%), Hypsoblennius sordidus (8.27%) and the clingfish Gobiesox marmoratus (7.06%). The most parasitized fish larvae were from benthic brooding origin, namely the clingfishes G. marmoratus (prevalence= 9.63%) and Sicyases sanguineus (0.54%), the kelpfish Auchenionchus variolosus (1.72%), and triplefin blenny Helcogrammoides cunninghami (3.28%). Only one species from pelagic spawning origin, the sandperch Prolatilus jugularis (0.57%), had ectoparasites. The abundance of some larval fish species with ectoparasite decreased with distance to the shore; S. bentincki, H. bruuni (pelagic spawning) or S. viridis (benthic brooding) were found to be more abundant at 2.0 km offshore. The ectoparasites were identified as Trifur spp. (Copepoda: Pennellidae) and Caligus spp. (Copepoda: Caligidae), with pennellids being the most frequent (1 to 3 parasites per larva). Ninety-four and 88% of pennellids and caligids, respectively, were collected in the nearshore station. During periods of high ectoparasite prevalence on fish larvae, seawater was vertically stratified with a cross-shelf deepening (late autumn) or shoaling (summer) of the pycnocline from offshore to nearshore. The results suggest that fish larvae with BB were more frequently parasitized and that physical conditions of the water column may contribute both to coastal retention of fish larvae as well as ectoparasite infestation in nearshore waters.El objetivo de este estudio fue determinar la variación temporal de las condiciones oceanográficas, ictioplancton y sus ectoparásitos en aguas costeras marinas. Se realizaron 30 muestreos de ictioplancton entre el 11 de octubre 2012 y el 5 de junio 2014 a lo largo de una transecta desde 0,25 km hasta 4,5 km de la costa frente a Montemar, Bahía Valparaíso, Chile central. Se identificó un total de 5.553 larvas de peces, pertenecientes a 37 taxa. Las larvas de peces más abundantes originadas de desove pelágico fueron la sardina común Strangomera bentincki (abundancia relativa= 26,39%), anchoveta Engraulis ringens (8,94%), y el mictófido Hygophum bruuni (7,72%); las especies más abundantes originadas de posturas bentónicas fueron la borrachilla Scartichthys viridis (15,77%), el cachudito Hypsoblennius sordidus (8,27%) y el pejesapo Gobiesox marmoratus (7,06%). Las larvas de peces más parasitadas provinieron de posturas bentónicas, los pejesapos G. marmoratus (prevalencia= 9,63%) y Sicyases sanguineus (0,54%), el tomollo Auchenionchus variolosus (1,72%), y el trombollito de tres aletas Helcogrammoides cunninghami (3,28%). La única especie con desove pelágico que presentó ectoparásitos fue el blanquillo Prolatilus jugularis (0,57%). Las larvas de peces con ectoparásitos mostraron una disminución en abundancia con la distancia a la costa; S. bentincki, H. bruuni (desove pelágico) o S. viridis (postura bentónica) fueron más abundantes a 2,0 km de la costa. Los ectoparásitos fueron identificados como Trifur spp. (Copepoda: Pennellidae) y Caligus spp. (Copepoda: Caligidae), siendo los penélidos los más frecuentes (1 a 3 parásitos por larva). El 94 y 88% de los penélidos y calígidos, respectivamente, fue recolectado en la estación más costera. Durante los periodos de mayor prevalencia de ectoparásitos en las larvas de peces, el agua de mar estuvo verticalmente estratificada con una profundización a fines de otoño y un ascenso en verano de la picnoclina desde mar afuera hacia la costa. Por lo tanto, los resultados sugieren que las larvas de peces originadas de posturas bentónicas son parasitadas más frecuentemente y que las condiciones físicas de la columna de agua pueden favorecer tanto la retención costera como la infestación por ectoparásitos en las aguas más cercanas a la costa