A new methodology for presenting hydrodynamics data from a large river confluence

Confluences are very complex fluvial networks where the combination of matter (water and sediment) and energy (flow strength) from two different channels take place.The confluence of Rio Negro, with is black waters, and the Rio Solimões, with its suspended white sediments, is one of the biggest confluences on the earth and attracts thousands of tourists every year near by the city of Manaus, Amazonas – Brazil. This paper presents the application of a new method to analyze the ADCP data which is using an in-house FORTRAN code in combination with the Tecplot and Surfer Softwares. The method was applied to ADCP transects collected on this confluence within the EU-funded Clim-Amazon Projectin two different periods of the hydrological cycle: low flow conditions on 30 and 31 October 2014, during the FS−CNS1 campaign, and relatively high flow conditions on 29 and 30 April 2015, during the FS−CNS2 campaign, both of them included 23 transects. These data were first extracted with WinRiver II software to produce ASCII files. The ASCII files were first processed using the code to derive input files containing the three velocity components, the average backscatter as well as the secondary currents from the Rozovskii method. These data were plotted in Tecplot to gain cross-sectional profiles. Furthermore, as past investigations were limited to the analysis of the depth-averaged quantities, the FORTRAN code was used even to extract the values of the velocity components as well as the backscatter along three layers in the channel: near the bed, at mid-depth and near the water surface. The data were then used to prepare Surfer maps, in a plane contour map format, of these quantities. The analysis of the data along these three layers can provide further findings into the complex three-dimensional structure of the flow at the Negro/Solimões confluence

Nonlinear Fluid Dynamics Description of non-Newtonian Fluids

Nonlinear hydrodynamic equations for visco-elastic media are discussed. We start from the recently derived fully hydrodynamic nonlinear description of permanent elasticity that utilizes the (Eulerian) strain tensor. The reversible quadratic nonlinearities in the strain tensor dynamics are of the 'lower convected' type, unambiguously. Replacing the (often neglected) strain diffusion by a relaxation of the strain as a minimal ingredient, a generalized hydrodynamic description of viscoelasticity is obtained. This can be used to get a nonlinear dynamic equation for the stress tensor (sometimes called constitutive equation) in terms of a power series in the variables. The form of this equation and in particular the form of the nonlinear convective term is not universal but depends on various material parameters. A comparison with existing phenomenological models is given. In particular we discuss how these ad-hoc models fit into the hydrodynamic description and where the various non-Newtonian contributions are coming from.Comment: Acta Rheologic

A modification of the convective constraint release mechanism in the molecular stress function model giving enhanced vortex growth

The molecular stress function model with convective constraint release (MSF with CCR) constitutive model [J. Rheol. 45 (2001), 1387] is capable of fitting all viscometric data for IUPAC LDPE, with only two adjustable parameters (with difference found only on reported ¿steady-state¿ elongational viscosities). The full MSF with CCR model is implemented in a backwards particle-tracking implementation, using an adaptive method for the computation of relative stretch that reduces simulation time many-fold, with insignificant loss of accuracy. The model is shown to give improved results over earlier versions of the MSF (without CCR) when compared to well-known experimental data from White and Kondo [J. non-Newt. Fluid Mech., 3 (1977), 41]; but still to under-predict contraction flow opening angles. The discrepancy is traced to the interaction between the rotational dissipative function and the large stretch levels caused by the contraction flow. A modified combination of dissipative functions in the constraint release mechanism is proposed, which aims to reduce this interaction to allow greater strain hardening in a mixed flow. The modified constraint release mechanism is shown to fit viscometric rheological data equally well, but to give opening angles in the complex contraction flow that are much closer to the experimental data from White and Kondo. It is shown (we believe for the first time) that a constitutive model demonstrates an accurate fit to all planar elongational, uniaxial elongational and shear viscometric data, with a simultaneous agreement with this well-known experimental opening angle data. The sensitivity of results to inaccuracies caused by representing the components of the deformation gradient tensor to finite precision is examined; results are found to be insensitive to even large reductions in the precision used for the representation of components. It is shown that two models that give identical response in elongational flow, and a very similar fit to available shear data, give significantly different results in flows containing a mix of deformation modes. The implication for constitutive models is that evaluation against mixed deformation mode flow data is desirable in addition to evaluation against viscometric measurements

Wall slip in primitive chain network simulations of shear startup of entangled polymers and its effect on the shear stress undershoot

In some recent experiments on entangled polymers of stress growth in startup of fast shear flows an undershoot in the shear stress is observed following the overshoot, i.e., before approaching the steady state. Whereas tumbling of the entangled chain was proposed to be at its origin, here we investigate another possible cause for the stress undershoot, i.e., slippage at the interface between polymer and solid wall. To this end, we extend the primitive chain network model to include slip at the interface between entangled polymeric liquids and solid walls with grafted polymers. We determine the slip velocity at the wall, and the shear rate in the bulk, by imposing that the shear stress in the bulk polymers is equal to that resulting from the polymers grafted at the wall. After confirming that the predicted results for the steady state are reasonable, we examine the transient behavior. The simulations confirm that slippage weakens the magnitude of the stress overshoot, as reported earlier. The undershoot is also weakened, or even disappears, because of a reduced coherence in molecular tumbling. In other words, the disentanglement between grafted and bulk chains, occurring throughout the stress overshoot region, does not contribute to the stress undershoot.Comment: 38 pages and 9 figure

Fluid dynamics, sediment transport and mixing about the confluence of Negro and Solimões rivers, Manaus, Brazil

As part of a project to investigate the hydrodynamic, sediment transport and mixing processes about the large confluences of the Amazon River, a field study was conducted about the confluence of the Negro and Solimões Rivers. This confluence ranks among the largest confluences on Earth the outcomes of this study may also provide some general insights into large confluence dynamics. A detailed series of ADCP, water quality and seismic profile measurements were collected to investigate key hydrodynamic and morphodynamic features about this confluence. Presented here are the key hydrodynamic features observed about this large confluence and how these relate to findings in previous studies conducted in flumes and small confluences. Finally some insights into how the differences in water characteristics and the hydrodynamics of these two rivers may influence the rate of mixing downstream are presented

Estimating the hydrodynamic and morphodynamic characteristics using Entropy theory at the confluence of Negro and Solimões Rivers

When two mega rivers merge the mixing of two flows results in a highly complex threedimensional flow structure in an area known as the confluence hydrodynamic zone

A study of the quadratic molecular stress function constitutive model in simulation

Constitutive models that conform to separable KBKZ specification have been shown to fit steady-state strain hardening rheological data in planar and uniaxial elongational flows, but with inaccuracy in the rate of strain hardening. The single parameter Molecular Stress Function model of Wagner [Rheol. Acta, 39 (2000), 97-109] has been shown to accurately fit the rise-rate in experimental data for a number of strain hardening and strain softening materials. We study this models accuracy against the well characterised IUPAC LDPE data, and present a method for full implementation of this model for flow solution which is suitable for incorporating into existing separable KBKZ software. A new method for particle tracking in arbitrarily aligned meshes, which is efficient and robust, is given. The Quadratic Molecular Stress Function (QMSF) model is compared to existing separable KBKZ based models, including one which is capable of giving planar strain hardening; the QMSF is shown to fit experimental rheological and contraction flow data more convincingly. The issue of `negative correction pressures¿ notable in some Doi-Edwards based models is addressed. The cause is identified, and leads to a logical method of calculation which does not give these anomalous results